pobierz - Drewno

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pobierz - Drewno

INSTYTUT TECHNOLOGII DREWNA
WOOD TECHNOLOGY INSTITUTE
DREWNO
PRACE NAUKOWE ● DONIESIENIA
KOMUNIKATY
WOOD
RESEARCH PAPERS ● RESEARCH REPORTS
ANNOUNCEMENTS
Vol. 55
POZNAŃ 2012
Nr 188
Wydanie publikacji dofinansowane przez Ministerstwo Nauki i Szkolnictwa Wyższego
w ramach programu „Index Plus”.
The journal is financially supported by Polish Ministry of Science and Higher Educations
under the „Index Plus” programme.
Recenzenci vol. 55 (Reviewers) prof. Ing. Pavlo Bekhta, Dr. Sc.; dr Ricco Emmler; prof.
RNDr. František Kačík, PhD.; prof. Ing. Jozef Kúdela, CSc.; prof. mgr Jurai Ladomersky,
CSc.; prof. Robert Lanouette; prof. Wojciech Lis; dr inż. Andrzej Mazur; prof. dr. Peter
Niemz; dr inż. Adam Niesłochowski; prof. Pekka Ollonqvist; prof. dr hab. Stanisław Proszyk;
prof. Roger M. Rowell; dr. hab. Jerzy Świgoń, prof. UP; Ing. Marek Trenciansky, PhD.
Publikacje indeksowane są w bazach danych (Publications are indexed in the databases): Agro – http://agro.icm.edu.pl/agro, Science Citation Index Expanded –
http://thomsonreuters.com, BazTech – http://baztech.icm.edu.pl, SCOPUS –
http://www.scopus.com, DREWINF – http://www.itd.poznan.pl, The Central European
Journal of Social Sciences and Humanities – http://cejsh.icm.edu.pl
W 2010 roku czasopismo znalazło się na tzw. liście filadelfijskiej (ISI Master Journal List)
z obliczonym Impact Factorem (IF).
W 2010 roku czasopismo zostało uhonorowane Medalem im. Michała Oczapowskiego.
Artykuły polskojęzyczne zawierają streszczenia w języku angielskim, a obcojęzyczne –
w języku polskim. Spisy treści, streszczenia i pełne teksty artykułów są dostępne na stronie www.itd.poznan.pl/pl/drewno.
Wersja pierwotna – papierowa.
In 2010 the journal was indexed on ISI Master Journal List with calculated Impact Factor (IF).
In 2010 the journal was honored with Michał Oczapowski Medal.
Polish language articles have summaries in English language, and foreign language articles have summaries in Polish language. Tables of contents, summaries, and full versions
of the articles are available at www.itd.poznan.pl/en/wood.
The original version – paper.
Wydawca (Publisher): Instytut Technologii Drewna
ul. Winiarska 1, 60-654 Poznań, Polska (Poland)
Adres Redakcji (Editor’s address): Instytut Technologii Drewna
ul. Winiarska 1, 60-654 Poznań
tel.: +48 61 849 24 01, +48 61 849 24 61, fax: +48 61 822 43 72,
e-mail: [email protected]
© Copyright by Instytut Technologii Drewna w Poznaniu
Poznań 2012
ISSN 1644-3985
Projekt okładki (Cover design): Piotr Gołębniak
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Nakład (Edition): 520 egz.
SPIS TREŚCI – CONTENTS
Prace naukowe – Research papers
Adam Krajewski, Piotr Witomski, Piotr Bobiński, Aleksandra Wójcik,
Magdalena Nowakowska: An attempt to detect fully-grown house Longhorn Beetle larvae in coniferous wood based on electroacoustic signals
(Próba wykrywania wyrośniętych larw Spuszczela Pospolitego w drewnie
iglastym na podstawie sygnałów elektroakustycznych) ..............................
5
Jan Bocianowski, Krzysztof Joachimiak, Adam Wójciak: The influence of process variables on the strength properties of NSSC birch pulp. Towards the
limits of optimization: part one – the effect of liquor ratio (Wpływ zmiennych czynników procesowych na właściwości wytrzymałościowe brzozowych mas półchemicznych (NSSC). W kierunku granic optymalizacji: część
pierwsza – wpływ modułu cieczy warzelnej) .................................................
17
Iwona Frąckowiak, Karolina Mytko, Ryszarda Bendowska:: Content of
formaldehyde in lignocellulosic raw materials for particleboard production
(Zawartość formaldehydu w surowcach lignocelulozowych do produkcji
płyt wiórowych) ............................................................................................
33
Maciej Wilczyński, Krzysztof Warmbier: Elastic moduli of veneers in pine
and beech plywood (Moduły sprężystości fornirów w sklejce sosnowej
i bukowej) .....................................................................................................
47
Zbigniew Czech, Magdalena Witczak, Agnieszka Kowalczyk, Jagoda
Kowalska: The influence of residue monomers on selected properties
of acrylic pressure-sensitive adhesives (Wpływ nieprzereagowanych
monomerów na wybrane właściwości poliakrylanowych klejów samoprzylepnych) ........................................................................................................
59
Monika Zajemska: Analiza teoretyczno-eksperymentalna wpływu współspalania odpadów drzewnych w formie paliw reburningowych z gazem ziemnym na skład chemiczny spalin (Theoretical and experimental analysis of
the impact of wood co-combustion, as a reburning fuel, with natural gas on
the chemical composition of flue gases) ......................................................
71
Elżbieta Mikołajczak: The profitability of converting sawmill by-products
into energy (Opłacalność przerobu tartacznych produktów ubocznych na
energię) .........................................................................................................
87
Doniesienia naukowe – Research reports
Kinga Szentner, Izabela Ratajczak, Bartłomiej Mazela: Improvement of water-based wood coating performance – MTMOS reactivity with wood (Poprawa
parametrów wodorozcieńczalnej powłoki do drewna – reaktywność MTMOS
z drewnem) .................................................................................................... 103
Jakub Gawron, Magdalena Szczęsna, Tomasz Zielenkiewicz, Tomasz
Gołofit: Cellulose crystallinity index examination in oak wood originated
from antique woodwork (Badanie indeksu krystaliczności drewna dębowego pochodzącego z zabytkowej stolarki budowlanej) ................................... 109
Csilla Vanya: Damage problems in glued laminated timber (Problemy uszkodzeń w tarcicy klejonej warstwowo) ............................................................. 115
Drewno. Pr. Nauk. Donies. Komunik. 2012, vol. 55, nr 188
PRACE NAUKOWE – RESEARCH PAPERS
Adam Krajewski, Piotr Witomski, Piotr Bobiński,
Aleksandra Wójcik, Magdalena Nowakowska1
AN ATTEMPT TO DETECT FULLY-GROWN HOUSE
LONGHORN BEETLE LARVAE IN CONIFEROUS WOOD
BASED ON ELECTROACOUSTIC SIGNALS
Initial comparative tests of a method for the detection of house longhorn beetle
larvae (Hylotrupes bajulus L.) were carried out by means of recording the acoustic
effects caused by these insects, as well as another instrumental method based on the
use of X-ray pictures. Insofar as the X-ray method brings completely reliable results
as regards the detection of the presence of fully-grown house longhorn beetle larvae
in wood, the accuracy of situation assessment based on the electro-acoustic method
is estimated to be approximately 70-80%, based on the results of the research presented herein. In this research the accuracy of situation assessment is understood
as the correct determination of an estimated number of larvae and their condition.
The differences in situation assessment accuracies using both methods were statistically verified by means of the Czebyszew method. Since the tests were initial in
nature without the use of standard patterns, as these have not been developed yet,
the obtained results are considered highly satisfactory.
Keywords: woodworm, wood, longhorn beetle, electroacoustic, instrumental detection, detection of insects, Hylotrupes bajulus L.
Adam Krajewski, Warsaw University of Life Sciences – SGGW, Poland
Piotr Witomski, Warsaw University of Life Sciences – SGGW, Poland
Piotr Bobiński, Warsaw Technical University, Poland
Aleksandra Wójcik, Warsaw University of Life Sciences – SGGW, Poland
Magdalena Nowakowska, Warsaw Academy of Computer Science, Management and
Administration, Poland
6
Adam Krajewski, Piotr Witomski, Piotr Bobiński, Aleksandra Wójcik, Magdalena Nowakowska
Introduction
The answer to the question whether wood contains the living larvae of xylophagous insects which are destroying it, or only abandoned insect galleries, is a basic
issue when it comes to taking action concerning the protection of wooden structures and objects. Most often the traditional method for situation assessment is
used. Decisions are made based on a series of symptoms, which are often subjectively formulated by the person assessing. According to all handbook publications,
amongst these symptoms are the following:
–– occurrence of new outlets on the wood surface,
–– so-called wood meal spilling out from the outlets, making little mounds or
trickles on the wood surface,
–– the presence in buildings or at storage yards of living or dead adult forms of
a given pest species or its parasites and predators,
–– in the case of some insect species the sounds of wood boring by larvae, which
is audible to the naked ear.
These symptoms would often be unreliable, therefore attempts to apply instrumental methods to the assessment of wood infestation by insects have been made.
The instrumental methods for the detection of xylophagous insects in wood have
aroused great interest for many years. However, not all the instrumental methods
may be used in practice, especially in field conditions. X-ray photography and
CAT scanning, which are examples of effective methods, cannot be classified as
field test methods. Video-endoscopy does not enable an insight into the wood
inside, but offers only an image of inaccessible structural parts, which must be
examined during a traditional examination.
Previous laboratory attempts to apply electro-acoustics to the detection of feeding house longhorn beetle larvae were made in Europe, i.e. in Germany [Kerner
et al. 1980; Plinke 1991; Esser et al. 1999] and Poland [Bobiński et al. 2006;
Krajewski et al. 2011].
Even in the case of such an unquestionable symptom as the sounds of wood
boring by house longhorn beetle larvae, there are some classification issues nonetheless – the insects do not make a sound when the evaluator assessing the
feeding grounds would like them to. This may be a result of thermal conditions
or periodic inactivity of the larvae due to other reasons. One should also take into
consideration that so-called background may overlap with the electro-acoustic record of the vital activity of the larvae. If the house longhorn beetle larvae are large
and make a lot of “noise”, sometimes they may create effects that may be misinterpreted if heard by the naked ear. The development and perfecting of a method
which would enable the recording of some of the vital activities of xylophagous
and under-the-bark insects and the interpretation of the number or behaviour of
these animals based on the obtained results, would also (besides being of practical
use) enable basic research on some aspects of the biology of some species. Based
An attempt to detect fully-grown house longhorn beetle larvae in coniferous wood based on ...
7
on the promising results of the recording of the electro-acoustic signals of the
house longhorn beetle [Bobiński et al. 2006], an assessment of the possibilities of
detecting the larvae of this species, using a simplified simulation of conditions in
a large-dimensional wooden structure, was carried out at SGGW in Warsaw in the
Faculty of Wood Technology in the Wood Protection Department.
Materials and methods
The effects of the movements of house longhorn beetle larvae’s maxillae and bodies in the feeding ground were recorded electro-acoustically. Based on the recordings, an attempt to determine the activity of these insects in wood was made
together with an attempt to define the presence and approximate number of individual organisms based on the activity determination. The research was carried out
in the form of laboratory tests simulating field conditions, taking into account constraints resulting from the lack of developed standards and thus the lack of objectivity showed by the people classifying the presence of the larvae in the galleries.
The house longhorn beetle larvae (Hylotrupes bajulus L.) used in the research
were fully-grown individual organisms of a mass ranging from 30 to 190 mg.
A simplified simulation of conditions found within a large-dimensional structure
was used. The insects were placed in 200 mm blocks (sections) of structural wood
with a cross-section of 60×120 mm. The experiment was carried out on Scots
pine (Pinus sylvestris L.) and silver fir (Abies alba Mill.). A larvae-free Norway
spruce (Picea abies (L.) Karst.) was also used as the equivalent of a placebo used
in medical science. All the blocks were randomly marked with letters from A to L.
The larvae were placed in pine and fir wood, 10 individual organisms per
block. All the blocks, including the larvae-free ones, had holes bored to place the
larvae, holes which were plugged with compacted wood meal left by feeding insects. In the case of larvae-free blocks, wood meal was artificially put in the holes
and compacted. The aim of simulating the places seemingly bored by the larvae
was to avoid a situation, where evaluators are influenced by the initial number
of the test material. The larvae were placed in the holes bored in the blocks’ fronts.
The holes were twice as deep as a larva’s body length, and a diameter approximately 0.5 mm larger than that of a larva’s body-width at the widest point. The larvae
placed in the wood were left there for 4 weeks in an incubator at a temperature
of 28°C, which gave the insects time to bore into the wood.
The research aimed at an objective evaluation of the effectiveness of house longhorn beetle larvae detection in wood. The lack of knowledge about the
blocks’ contents, which was characteristic of evaluators assessing the recording
of electro-acoustic activity of the larvae, was achieved in the following way. Individual blocks with the larvae were subjected to an asphyxiating atmosphere
of nitrogen for various periods with a view to causing a different death rate of
these insects. The time needed to ensure mortal effects from a low-oxygen at-
8
mosphere was determined in separate research devoted to the effectiveness
of combating xylophagous insects with nitrogen and argon, the results of which
will be published in the future. Due to these actions, the number of living larvae
in particular blocks was not known to any of the observers interpreting the results
of the experiment. The adopted method for misinforming the observers interpreting the record of the blocks’ contents, enabled a reduction in the possibility
of them being influenced (while evaluating the larvae’s activity) by the knowledge
of the number of the larvae placed, as indicated by the number of holes bored in
the front of each sample. After gas treatment, the block containing the larvae were
mixed with the larvae-free blocks, which also had 10 bored holes in their fronts
plugged with wood meal.
The presence of larvae in wood was recorded using a prototype apparatus built
at Warsaw University of Technology at the Faculty of Electronics and Information
Technology in the Electro-Acoustic Institute. The apparatus was previously used
to identify the acoustic characteristics of a single feeding larva of xylophagous
insects [Bobiński et al. 2006]. This apparatus processes all and any acoustic waves
carried by wood into electric signals. The apparatus is equipped with, among other
things, an acceleration sensor, the signal of which was strengthened by a charge
preamplifier. Signals were recorded by a sound card and presented in the form
of a graphical record on a computer monitor. The signals were recorded as a level
of signal amplitude in relation to the maximum amplitude that can be registered
by the sound card, i.e. an amplitude, which may be achieved by the maximum
regulation of an analogue-digital converter.
The average density of the pine blocks was 440 kg/m3 and their average ring
width was 4.2 mm. The average density of the fir blocks was 448 kg/m3 and their
average ring width was 5.0 mm. To record the electro-acoustic activity of the
larvae, the sensor was placed in the middle of a block’s front 60×120 mm (situation α), therefore at its cross-section. For comparative reasons, in the case of most
blocks a recording of the electro-acoustic effects transversely to the grain was
carried out as well, i.e. the sensor was placed in the middle of a sample’s surface
120×200 mm (situation β).
The air (ambient) temperature during the recording of the acoustic signals
ranged from 20°C to 24°C: for samples A-D approximately 21°C on average and
for samples H-L approximately 20°C on average. The acoustic signals were recorded for 24 hours.
The obtained results were classified independently by three evaluators. The
evaluators were marked with numbers from 1 to 3. The following recording times
were analysed: 24 hours, 2 hours and 20 minutes of recording time. In order to
present multi-hour records graphically, the recording effects were compressed by
computer. To assess the activity and contents of the feeding grounds, the records
of electro-acoustic activity of the larvae, recorded when the sensor was placed
in the middle of a block’s front 60×120 mm (situation α), were used. The re-
9
cords taken when the sensor was placed in the middle of a sample 120×200 mm
(situation β) did not substantially differ from the first variant. The assessments
of particular evaluators are given in table 1. It was assumed that the recording
of electro-acoustic activity of the “entomological contents” of the feeding grounds
characterised the presence and number of the larvae in the wood. The following
scale of the electro-acoustic assessment of the feeding grounds’ activity, which
should stem from the following number of living larvae in a block, was applied:
–– no record of activity – lack of larvae in the wood or all larvae are dead,
–– low activity recorded – the equivalent of the presence of a small number
of living larvae in the wood (1–4 individual organisms),
–– high activity recorded – the equivalent of the presence of a large number
of living larvae in the wood (5–10 individual organisms).
Table 1. Evaluation of electroacoustic signals as a result of the presence, activity and
abundance of old house borer larvae (marked in bold are accurate assessment)
Tabela 1. Ocena elektroakustycznej aktywności, będącej wynikiem obecności, czynności
i liczebności żywych larw spuszczela pospolitego w drewnie iglastym (pogrubionym drukiem
zaznaczono trafne oceny)
Oznaczenie
Liczba żywych
klocka, gatunek
larw
drewna
w momencie
i teoretycznie
prowadzenia
zakładana aknasłuchu
tywność larw (na The number of live
larvae at the time
podstawie zaof listening
wartości klocka)
Aktywność larw
w drewnie
według
obserwatora nr 1
Aktywność larw
w drewnie
według
obserwatora nr 2
Aktywność larw
w drewnie
według
obserwatora nr 3
Activity of larvae
in the wood
according to
observer 1
Activity of larvae
in the wood
according to
observer 2
Activity of larvae
in the wood
according to
observer 3
Determination
of sample, wood
species and theoretically expected
activity of the
larvae (based on
the content of the
sample)
1
2
3
4
5
A, sosna,
aktywność mała
2 żywe larwy
brak
mała
mała
B, sosna,
aktywność duża
10 żywych larw
10 live larvae
substantial
substantial
substantial
C, jodła,
aktywność mała
1 żywa larwa
brak
brak
brak
A, pine, little
activity
B, pine, substantial activity
C, fir, little
activity
2 live larvae
1 live larva
no
duża
no
little
duża
no
little
duża
no
10
Table 1. Continued
Tabela 1. Ciąg dalszy
1
2
D, jodła,
aktywność duża
10 żywych larw
D, fir, substantial
activity
E, świerk,
brak aktywności
E, spruce,
no activity
3
duża
4
duża
5
duża
10 live larvae
substantial
substantial
substantial
nie obsadzono
larw
brak
brak
brak
larvae not inserted
no
no
no
F, jodła,
aktywność duża
8 żywych larw
8 live larvae
substantial
G, sosna,
aktywność duża
6 żywych larw
mała
little
substantial
substantial
nie obsadzono
larw
brak
brak
brak
nie obsadzono
larw
brak
brak
brak
2 żywe larwy
brak
brak
brak
brak
brak
brak
nie obsadzono
larw
brak
brak
brak
→
67%
83%
83%
F, fir, substantial
activity
G, pine, substantial activity
H, świerk,
brak aktywności
H, spruce,
no activity
I, świerk,
brak aktywności
I, spruce,
no activity
J, sosna,
aktywność mała
J, pine, little
activity
K, jodła,
brak aktywności
K, fir,
no activity
L, świerk,
brak aktywności
L, spruce,
no activity
Udział
prawidłowych
ocen sytuacji
The share of the
correct assessment of the situation
6 live larvae
larvae ot inserted
larvae not inserted
2 live larvae
brak żywych larw
w wyniku duszącego działania
azotu
no live larvae as a
result of choking
action of nitrogen
larvae not inserted
duża
no
no
no
no
no
duża
substantial
duża
no
no
no
no
no
duża
substantial
duża
no
no
no
no
no
11
Following this, X-ray photographs of the samples were taken in order to see
the positions of the larvae, and then the wood was chipped. The X-ray photographs
were verified by the assessment of the larvae’s condition by means of direct observation after the blocks were split into very small pieces of wood in which no larva
could hide. The movement was considered an attribute of a living larva – the insects brought out from the wood were regarded as alive if they showed liveliness,
either spontaneously or when mechanically irritated.
The results of the actual “entomological contents” of the 12 blocks, accurately
imaged in the X-ray photographs, were compared with the assessments carried out
by each of the 3 evaluators drawing conclusions based on the recorded electro-acoustic signals. If the evaluator’s assessment of the feeding ground conditions
(the presence of living larvae and their number within the assumed limits), carried
out separately for each block based on the electro-acoustic signals, was correct,
then it was marked with the number 1, if the assessment was wrong, then it was
marked with the number 0. In the case of the X-ray photographs, all 12 results of
the interpretations were correct and their assessment number was 1. Hence, these
results became an element of the verification of the accuracy of the assessment
carried out by means of classifying the electro-acoustic recordings as particular
categories. For the 12 cases of assessment carried out by each evaluator separately, an arithmetic mean was calculated. Using Czebyszew inequality, the significance of the difference between an average from a given evaluator’s assessments
of the blocks’ contents, carried out by means of recording the electro-acoustic
activity of the larvae, and the average from classifications made based on the
X-ray photographs, which corresponded with the visual assessment of the blocks’
contents carried out after they were split, was determined.
Using this method, the absolute difference between the arithmetic mean from
the assessments carried out separately by each evaluator and the mean from classifications based on the X-ray photographs were compared, with a triple standard
error in the difference of these arithmetic means:
(1)
while:
(2)
where:
– an average assessment based on the X-ray photographs,
xR – classification of the “contents” of block no. “i” based on the X-ray
photograph,
– an average assessment based on the interpretation of the electroacoustic effects carried out by evaluator N,
xNi – classification of the assessment of evaluator N concerning block no. “i”,
n – number of compared assessments (corresponding with the number
of blocks).
12
In the case that the first inequality (or equation) is satisfied, the difference
between the means is significant, otherwise the difference may be incidental.
In order for the method to hold promise for practical use, the difference between
the average assessment carried out by each evaluator and the average assessment
resulting from the X-ray photographs (which corresponds with the actual situation
evaluated after the blocks are split) should be insignificant.
Results and discussion
The levels of amplitudes of the recorded electro-acoustic impulse range from
approximately -20 to 0 dB on average in relation to a maximum amplitude, which
may be recorded by the sound card. These are levels recordable by the sound card.
The 20-minute recordings, cut from a multi-hour recording, proved to be the most
useful for an assessment of the presence of the larvae in the wood and determination of their number. The examples of the recordings of the electro-acoustic
activity of the numerous larvae in the wood and of the lack of larvae, but with
background interference, are presented in fig. 1.
The results of the assessment of the presence and number of the larvae in the
wood are given in table 1.
Comparing the absolute difference between the arithmetic means obtained
from the assessment carried out using the recording of electro-acoustic effects
and X-ray photographs with a triple value of the standard error between them, it
was observed that there was no statistically significant difference between the assessment of the condition of the blocks’ “contents” carried out using the recording
of the electro-acoustic activity of the larvae and the actual condition.
In the case of evaluator no. 1 it was 0.33 < 0.43, and in the cases of evaluators
no. 2 and no. 3 it was 0.17 < 0.34.
Previously only the recordings of the electro-acoustic activity of a single house longhorn beetle larva were published, without any classification concerning
the effectiveness of the determination of the larvae number in wood [Kerner et al.
1980; Plinke 1991; Bobiński et al. 2006; Krajewski et al. 2011]. It was observed
that the sound signals emitted by house longhorn beetle larvae during feeding
encompass the frequency range hovering at 10 kHz, while in the case of house
furniture beetle larvae (Anobium punctatum De Geer) this range hovers at approximately 20 kHz [Esser et al. 1999].
Despite the lack of a previously developed reference scale, in the case of the
test results described herein, in most cases the three evaluators correctly classified
the approximate number of larvae in the wood. However, none of the evaluators
achieved 100% classification accuracy, although the “eavesdropped” larvae quite
often may be audible to the naked ear. Difficulties in the interpretation of the records might have been caused by the very limited activity of some larvae in the
13
blocks, larvae which beforehand were subjected to the asphyxiating atmosphere
of nitrogen for a longer time. The insects probably needed a relatively long time
to get over the modified atmosphere with the reduced content of oxygen in favour
of nitrogen. In such cases, the presence of a living larva might not be revealed
as a recording of electro-acoustic activity corresponding with a healthy insect.
Fig. 1. Varying examples of electroacoustic activity of old borer house larvae in wood:
F – large, G – small and E – zero, when 24-hour recordings are compressed and
2-hour and 20-minute fragments are isolated from them
Rys. 1. Przykład zapisu różnej intensywności elektroakustycznej aktywności larw spuszczela
pospolitego w drewnie: F – dużej, G – małej i E – zerowej przy skompresowaniu wyników
odsłuchiwania w czasie 24 h oraz wyjęciu z nich okresów 2 h i 20 min
14
Research on the electro-acoustic method for the detection of insects in wood
are continuing in the Wood Protection Institute in co-operation with the Electro-Acoustic Institute, with a view to applying it in practice and in discovering some
aspects of the biology and behaviours of both xylophagous and under-bark species.
It should be added that research on the use of this method for the detection
of the presence of the larvae of a dangerous species of Asian longhorn beetle
(Anaplophora glabripennis) (carried to Europe) in the wood of living and dying
trees [Becker 2000] and also in the wood of pallets and crates [Fleming et al.
2005], as well as for the detection of various species of earth termites, arouses
great interest all over the world. Hitherto the research on termites was carried out
as laboratory [Lemaster et al. 1997] and field tests [Fujii et al. 1999; Mankin et. al.
2002; Dunegan 2005; Mankin, Benshemesh 2006].
Conclusions
Although the tests were relatively little advanced, the results obtained using the
method of electro-acoustic recording of the activity of the grown larvae of the
house longhorn beetle, were satisfying in terms of the assessment of the contents
of the feeding grounds of this insect. It can be assumed that this method holds
great promise of success, provided it is further improved, and may probably be
applied to the detection of wood pests and to the entomology used in wood science and forestry when some aspects of the biology of xylophagous (and probably
also cambium-feeding) insects are researched. The average accuracy of the assessments of 3 observers evaluating the activity of the house longhorn beetle larvae hovered at approximately 70-80%, and the average results of the assessment
of the feeding ground contents, obtained by this method, were not statistically
different from the actual contents of the tested wood samples determined by examination of the X-ray photographs and by evaluation.
Acknowledgements
Research financed from the funds for science in the years 2008-2011 granted in the form
of a research project no. N N309 297834.
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Becker H. [2000]: Asian Longhorned Beetles, Agricultural Research, June 2000, www.ars.
usda.gov. 18–21
Bobiński P., Krajewski A., Witomski P. [2006]: Acoustic properties of xylophagic insect
activity. Annals of Warsaw Agricultural University [58]: 66–69
Dunegan H. L. [2005]: Detection of movement of termites in wood by acoustic emission
techniques, www.patenstorm.us
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Esser P., van Staalduinen P., Tas A. [1999]: The Woodcare project: Development of detection methods for Death watch beetle larvae and fungal decay, prepared for the 30th Annual
Meeting, Rosenheim
Fleming M. R., Bhardwaj M. C., Jankowiak J. J., Shield J. E., Roy R., Agrawal D. K.,
Bauer L. S., Miler D. L., Hoover K. [2005]: Noncontact ultrasound detection of exotic
insects in wood packing materials, Forest Product Journal [6]: 33–37
Fujii Y., Yanase Y., Yoshimura T., Imamura Y., Okumura S., Kozaki M. [1999]: Detection
of Acoustic emission (AE) Generated by Termite Attack in Wooden House, prepared for
30th Annual Meeting, Rosenheim
Kerner G., Thile H., Unger W. [1980]: Gesicherte und Zerstörungsfreie Ortung der Larven
holzzerstörender Insekten im Holz, Holztechnologie, [21]: 131–137
Krajewski A., Kozyra K., Wójcik A., Witowski P., Bogusław A., Bobiński P. [2011]: The
use of electro-acoustics in the evaluation of the effectiveness of old house borer in wood
with p-dichlorobenzene. Lisowe Gospodarstwo, Lisowa, Papierowa i Dieriewoobrobna
Promisłowist [37.1]: 114–116
Lemaster R. L., Beall F. C., Lewis V. R. [1997]: Detection of termites with Acoustic Emission, Forest Product Journal [2]: 75–79
Mankin R. W., Osbrink W. L., Oi F. M., Anderson J. B. [2012]: Acoustic detection of termite infestations in urban trees, Journal of Economic Entomology [5/95]: 981–988
Mankin R. W., Benshemesh J. [2006]: Geophone Detection of Subterranean Termite and Ant
Activity, Journal of Economic Entomology, [1/99]: 244–250
Plinke B. [1991]: Akustische Erkennung von Insektenbefall in Fachwerk. Holz als Roh und
Werkstoff [10]: 4
PRÓBA WYKRYWANIA WYROŚNIĘTYCH LARW SPUSZCZELA
POSPOLITEGO W DREWNIE IGLASTYM NA PODSTAWIE
SYGNAŁÓW ELEKTROAKUSTYCZNYCH
Streszczenie
Przeprowadzono wstępne badania porównawcze metody wykrywania larw spuszczela
pospolitego (Hylotrupes bajulus L.) za pomocą rejestracji efektów akustycznych powodowanych przez te owady z inną metodą instrumentalną, opartą o wykorzystanie zdjęć
rentgenowskich. O ile metoda rentgenowska daje całkowicie pewne wyniki w stosunku do
wykrywania obecności wyrośniętych larw spuszczela pospolitego w drewnie, to poziom
trafności oceny sytuacji przy użyciu metody elektroakustycznej szacuje się na podstawie
rezultatów niniejszych badań na ok. 70-80%. Jako trafność oceny sytuacji rozumiano tu
prawidłowe określenie szacunkowej liczby larw i ich stanu. Różnice w trafności oceny sytuacji za pomocą obu metod poddano weryfikacji statystycznej przy użyciu metody Czebyszewa. Ponieważ były to wstępne badania bez użycia standardowych wzorców, które
nie zostały jeszcze wypracowane, uznaje się uzyskane wyniki za bardzo zadowalające.
Słowa kluczowe: drewno, spuszczel pospolity, owady, elektroakustyka, metody instrumentalne,
wykrywanie owadów, Hylotrupes bajulus L.
Jan Bocianowski, Krzysztof Joachimiak, Adam Wójciak1
THE INFLUENCE OF PROCESS VARIABLES ON THE
STRENGTH PROPERTIES OF NSSC BIRCH PULP.
TOWARDS THE LIMITS OF OPTIMIZATION: PART ONE –
THE EFFECT OF LIQUOR RATIO
The aim of this work was to establish the best mechanical and strength properties
of NSSC pulp using operating conditions at which the lowest (optimal) spent
liquors, cooking temperature and time of treatment can be obtained. Minimal and
maximum limits of independent variables were proposed using real mill conditions
as starting points. The analyzed variables were: cooking time (13 to 15.5 min), cooking temperature (172 to 179°C), liquor- to- wood ratio (from 1.2 to 2.2). In spite
of the extremely narrow ranges of controlled cooking variables, a large database
and combined statistical methods (analysis of variance, parallel coordinates, principal component analysis) allowed the distinction of the optimal range limits of studied technological factors determining the tested pulp’s properties. The mechanical
and strength testing of the pulp’s sheets showed that the analyzed time, temperature
and liquor- to- wood ratio influenced the CMT, SCT, Tear strength and to some
extent Burst strength.
Keywords: NSSC, pulp, liquor ratio, statistical methods
Introduction
Neutral sulfite semi chemical (NSSC) pulp accounts for approximately 5-7%
of the overall production of paper pulp. The main advantage of this type of pulp
are that it provides fibers of a very high quality for special types of paper, especially the so-called microwave for multilayer cartons (corrugated medium). NSSC
pulp may be used as such or it may also partially replace other pulp from wood,
Jan Bocianowski, Poznan University of Life Sciences, Poland
Krzysztof Joachimiak, Poznan University of Life Sciences, Poland
Adam Wójciak, Poznan University of Life Sciences, Poland
18
Jan Bocianowski, Krzysztof Joachimiak, Adam Wójciak
lignocellulosic residues or old paper during the manufacture of various products
such as printing and writing paper, tissue paper, cardboard, bag grades and other
products [Farrington, Hickey 1989; Odom 1991; Myers et al. 1996; Area et al.
1997; Ahmadi et al. 2010].
Although the relatively traditional process of neutral sulfite pulping maintains
its industrial importance, the question of the recovery of spent liquor chemicals
still needs to be resolved. Most producers use the cross recovery system with
Kraft spent liquors, while others have fluidized bed combustion systems. In every
case, the problem is the relatively high inorganic to organic ratio in spent liquors
and that is why the liquor- to- wood ratio is (among others) such an important
technological factor [Area et al. 2001a, 2001b].
The pulping process of various wood and non-wood plants has been analyzed
with the use of many mathematical models and statistical methods allowing the
estimation of pulp quality in terms of process variables and determining optimal
operating conditions. Most of these models were based on delignification kinetics
and only a few took into consideration the influence of process variables on pulp
quality [Jimenez et al. 1999, 2000, 2004]. Moreover, most of these models were
established by applying the results of laboratory scale experiments only and with
arbitrary admitted ranges of variables.
The aim of this work was to examine the influence of extremely low changes in industrial operating variables (liquid/solid relation, temperature, pulping
time) on the mechanical and strength properties of the NSSC pulp paper sheets
(CMT, SCT, Burst and Tear strength) obtained, using mathematical and statistical
methods.
Industrial chips obtained from birch trees growing in Poland (Betula verrucosa) were used as the raw material. The chips included the following fractions:
>O45 – 1.1%, >II8 – 5.7%, >O7 – 91.0%, >O3 – 2.1%, the rest – 0.1% (O and
II mark holes and slots, diameter in mm according to Brecht-Holl classification)
[SCAN–CM–40:01]). The birch wood contained 82.4% holocellulose, 27.31%
α-cellulose, 31.44% lignin by dry matter weight.
All cooking experiments were carried out on a real industrial NSSC production
line with a controlled capacity and with an 82% average process yield. Pulping:
continuous cooking, a vapour-gas phase technique, pulp kappa no 120±10.
The most important units composing the pulp line were: an atmospheric chip bin,
a plug screw feeder, a pressurized impregnator, a continual digester and a cooked
chip disintegration refiner. After the release of air at the chip bin, the wood was
squeezed by the screw feeder and then pushed to the pressurized impregnator. The
impregnator was connected directly with the digester and that construction had the
The influence of process variables on the strength properties of NSSC birch pulp. Towards the ...
19
same operational pressure 9.2 bar. The initial cooking liquor concentration was
the same during all the experiments (165g/dm3 Na2SO3; 50g/dm3 Na2CO3). After
processing at different conditions of liquor-to-wood ratio, at a fixed temperature
of 178/179°C and cooking time of 14.5 min, the chips were defibred by a double-disc disintegration refiner with a concentration of 36% (Andritz Sprout Bauer,
2.5 MW, optimal energy consumption 130 kWh/Mg). The retention time of the
line was calculated for approx. 1 hour.
For each studied technological parameter (liquor-to-wood ratio, time and
temperature of cooking), the obtained pulp samples were refined in a PFI laboratory mill to reach four Schopper-Riegler degrees: 20 ºSR, 25 ºSR, 30 ºSR,
35 ºSR. After Schopper-Riegler freeness tests from all pulp samples, hand sheets
were made. From the dried and conditioned paper sample, four strength properties were examined: SCT – short crush test [EN/ISO 9895], CMT – Concora
medium test [EN/ISO 7263], Tear strength [EN 21974] and Burst strength
[EN/ISO 2758].
Liquor-to-wood ratio
Pulp samples were collected after cooking with 1.4, 1.5, 1.7, 1.8 and 2.2 liquid-to-wood ratios (l/w). The other technological variables (temperature and cooking
time) were determined with l/w ratio 1.8 and 1.55. The total number of observations used for l/w ratio analysis: CMT (373), SCT (642), Burst strength (442), Tear
strength (150). The number of observations resulted from the different number
of paper sheets qualified as convenient for strength analysis. In particular, the compression strength of paper (CMT, SCT) is measured at high grammage 130 g/m2
and all the paper sheets which did not have an appropriate weight per unit area and
caused the risk of bad readings were not analyzed.
Statistical analysis
Firstly, the normality of the distribution of the CMT, SCT, Tear and Burst strength
was tested using Shapiro-Wilk’s normality test [Shapiro, Wilk 1965]. A two-way
analysis of variance (ANOVA) was carried out to determine the effects of liquid-to-wood ratio, Schopper-Riegler numbers and interaction of liquid-to-wood ratio × Schopper-Riegler numbers on the variability of CMT, SCT, Tear and Burst
strength development. The least significant differences (LSDs) for each variable were calculated and, on this basis, homogeneous groups for the analyzed variables were determined. The relationship between CMT, SCT, Tear and Burst
strength were estimated on the basis of correlation coefficients. The relationship
between the analyzed properties was presented in the form of scatter-plot [Kozak
et al. 2010]. The application of principal components analysis (PCA) made it possible to find on the plane the graphic dispersion of pairs of liquid-to-wood ratio
20
and Schopper-Riegler degrees characterized with regard to all properties treated
together.
The parallel coordinate plot is proposed as an efficient tool for liquid-to-wood ratio × Schopper-Riegler freeness interaction visualization [Kozak 2010].
Analysis of the data was performed using the statistical package GenStat v. 10.1
[GenStat 2007].
Because of the variety of effects of chemical and mechanical treatment on final
product properties, it becomes especially important for the papermaking process
to understand how the different technological factors affect the technological practice of NSSC pulping.
Little differences among the controlled operating conditions on the industrial-scale production line (liquor-to-wood ratios, temperature, cooking time)
make the choice of both appropriate statistical tools and the possession of a sufficient database very important. As the most appropriate indices for the evaluation of the technological efficiency, first of all CMT [N] and SCT [kN/m]were
admitted, then Burst [kPa] and Tear [mN]. Literature in this area is very limited
but it is generally accepted that the most important property of fluting papers is
the compression strength: CMT and SCT. CMT is a measure of opposition to the
crushing of the flute after it is developed by the corrugator. The use of the SCT
strength index has been found to be an accurate indicator of refining effect and
is widely used because of the simplicity of testing. Burst strength is the result
of a combination of many factors, depending amongst others on the amount and
preparation of the fiber present. It is a useful indicator of strength property regardless of paper grade. The tearing resistance, which is a way of evaluating the
crack sensitivity of the paper, is a strength dimension of central importance for
all paper [Ek et al. 2009].
Initially, the significant differences were analysed between all the results
of the strength properties measured, which were obtained for different l/w
ratios and different Schopper-Riegler (SR) freeness numbers. The essential
point for further studies is that the analysis of variance (table 1) showed that
when all the studied strength properties (CMT, SCT, Burst and Tear) were
tested together, they also differed significantly with regard to l/w ratio and SR
freeness. The same statistics allowed an evaluation of the possible interaction
between the studied technological parameters and analytical data e.g. l/w and
SR freeness. Although, in relation to SCT values, the interaction was weaker
than in the case of CMT, Burst and Tear, the analysis of variance proved that
l/w and PFI refining (SR tests) together influenced the pulp’s strength properties (table 1).
21
Table 1. Mean squares from the analysis of variance for CMT, SCT, Tear and Burst
strength
Tabela 1. Średnie kwadraty z analizy wariancji dla oznaczeń CMT, SCT, oporu przedarcia
i przepuklenia
CMT
Source of
variation
CMT
Źródło
zmienności
ms
śk
df
4
962.4***
4
4.804***
4
9053***
4
88027***
3
12497.1***
3
5.731***
3
167741***
3
144625***
12
1247.4***
12
0.342**
12
7315***
12
13670***
196
120.6
352
0.123
274
1164
79
2752
SR
SR
Residual
Błąd
Tear
Przedarcie
ms
df
ss
śk
ss
moduł
moduł × SR
Burst
Przepuklenie
ms
df
ss
śk
df
l/w
l/w × SR
SCT
SCT
ms
śk
ss
l/w – liquid-to-wood ratio
moduł – moduł cieczy warzelnej
SR – freeness in °SR (Schopper Riegler)
SR – smarność w stopniach °SR (Schopper Riegler)
df – degrees of freedom
ss – stopnie swobody
ms – mean squares
śk – średnie kwadraty
** – significant at 0.01 level
** – istotne na poziomie 0,01
*** – significant at 0.001 level
*** – istotne na poziomie 0,001
Table 2. The correlation matrix for CMT, SCT, Tear and Burst strength
Tabela 2. Macierz współczynników korelacji dla oznaczeń CMT, SCT, oporu przedarcia
i przepuklenia
Correlation
Korelacje
CMT
CMT
SCT
SCT
Burst
Przepuklenie
Tear
Przedarcie
CMT
CMT
SCT
SCT
Burst
Przepuklenie
Tear
Przedarcie
1
0.538*
1
0.839***
0.665**
1
-0.479*
-0.210
-0.549*
1
*,** or ***show increasing significance of correlation between analysed strength properties.
Minus before value indicates reverse correlation.
*,** lub *** oznaczają wzrastającą istotność korelacji pomiędzy analizowanymi właściwościami
wytrzymałościowymi. Znak ujemny przed wartościami wskazuje korelację odwrotną.
22
Fig. 1. Scatter plot matrix for CMT, SCT, Tear and Burst strength
Rys. 1. Wykresy rozproszenia dla oznaczeń CMT, SCT, oporu przedarcia i przepuklenia
In order to recognize more closely the mutual tendencies and interactions
of the studied technological factors and pulp properties, correlations between the
pairs of tested strength features (table 2, fig. 1) were analyzed. As seen in table 2
and on the scatter plot (fig. 1) the strongest correlation appeared between the CMT
and Burst (r = 0.839). A weaker correlation showed SCT and Burst (r = 0.665).
The less significant (P < 0.05) correlations were observed for SCT and CMT
(r = 0.538), then Burst and Tear (r = -0.549) and at the end for SCT and Tear (the
two last pairs showed negative correlations). The most important point is that in
spite of the scattering data, a positive correlation between the increasing CMT,
SCT and Burst values (fig. 1) is confirmed. The correlations were independent
of the refining energy applied during sample preparation.
The pulp freeness is directly related to several processes that occur during
refining such as external fibrillation, fiber shortening and fines creation. The other
known result of refining is the internal fibrillation reflecting the increase in fiber
swelling, which is caused by the delamination of cell walls and the general growth
23
of the capacity of pulp to retain water [El-Sharkawy et al. 2008]. During the next
step significant differences were observed between the separate results of strength
properties gained for the whole range of studied l/w ratios, and with regard to the
increasing SR freeness numbers (table 3). The repeating letters (capital – for mean
values) inserted according to the results of the pulp strength analysis prove the
lack of significant differences. As could be expected, the CMT and SCT values
generally increased with the higher SR numbers [Kim, Jo 2000]. Thus, refining
in a PFI mill increased the tested paper sheet strength by influencing the surface
area of the fibers allowing their optimum papermaking properties to develop. The
mean values (calculated for all SR freeness range) of CMT showed significant
differences between the 1.4 and 1.5 l/w ratios used.
Table 3. Mean values and coefficients of variation for CMT, SCT, Tear and Burst
strength
Tabela 3. Wartości średnie i współczynniki zmienności dla CMT, SCT, oporu przedarcia
i przepuklenia
CMT [N]
CMT
SRº
l/w
moduł
20
mean
25
cv
śr
wz
mean
śr
30
mean
cv
wz
śr
mean
35
cv
wz
mean
cv
śr
śr
wz
1.4
227.9gh 3.85 249.3abcdef 5.63 250.9abcdef 2.58 252.7abcde 3.09 245.4B
1.5 247.2bcdef 6.45 253.2abcd 6.88
261.3abc 2.97 252.3abcde 2.15 253.8A
1.7 240.6defg 4.55
226.7gh
3.60 247.8abcdef 4.19 263.2ab
1.91 244.4B
1.8
223.3h
5.66 236.6efgh 3.58 253.9abcd 4.14 262.2ab
3.80 243.7B
2.2
235.4fgh 3.21 249.8abcdef 7.13
245cdef 5.09
264a
5.46 248.6AB
mean
231T
242.8S
251.7R
258.8P
śr
SCT [kN/m]
SCT
SRº
l/w
moduł
20
mean
śr
cv
wz
1.4
4.426efg 6.42
1.5
4.336fg
8.21
1.7
4.22g
8.95
1.8
4.427efg 7.42
2.2 4.857cdef 8.83
mean
4.452S
śr
25
mean
cv
śr
wz
4.691defg
4.435efg
4.413efg
4.636defg
5.551a
8.71
5.94
8.24
7.27
6.41
30
mean
śr
4.96bcd
4.774cdef
4.677defg
5.033abcd
5.245abc
4.737R
4.965P
Burst [kPa]
Przepuklenie
mean
35
cv
wz
mean
śr
7.55 4.795cdef
6.30 4.715defg
6.14 4.89cde
8.61 5.078abcd
7.32
5.42ab
4.981P
cv
śr
8.28
5.05
4.55
5.46
6.85
4.72B
4.575B
4.542B
4.787B
5.26A
wz
24
Table 3. Continued
SRº
l/w
moduł
20
mean
cv
śr
1.4
1.5
1.7
1.8
2.2
mean
śr
wz
399h
424.9fg
478bcde
400.6g
445.6efg
25
mean
śr
5.36
467cdef
8.95
458.7def
6.32
427.2fg
11.81 452.6def
6.45 490.4abcde
422.4T
30
mean
cv
wz
śr
wz
mean
497.7R
śr
cv
śr
wz
6.78 489.5abcde 6.10 515.8abc
4.67 490.7abcde 7.05 501.4abcd
4.41 499.4abcd 7.19
529.6a
7.35 498.3abcd 7.82 519.6ab
5.97
515abc
8.86 523.4ab
459.8S
mean
35
cv
6.17
468B
4.36 470.4AB
6.94 483.2AB
7.36 466.8B
8.14
493A
518.2P
Tear [mN]
Przedarcie
SRº
l/w
moduł
20
mean
śr
cv
wz
1.4
859.6a
4.25
1.5 788.2abcd 5.24
1.7
720.8def 1.27
1.8
801.1abc 9.79
2.2
836.7ab
1.86
mean
809.3P
śr
25
mean
cv
śr
wz
802.7abc
682.7ef
711.2def
712.8def
694ef
9.79
2.38
3.75
7.56
4.93
732.4R
30
mean
śr
749.7cdef
694.2ef
715.8def
712.2def
737.5cdef
725.2R
mean
35
cv
wz
mean
śr
cv
śr
wz
8.13 758.6bcde 7.77 792.4A
7.10
676.2f
10.21 708.2C
3.19 700.2ef
5.10 712.1C
8.23 757bcde
4.50 745.7BC
7.84 736.7cdef 4.49 753.4B
736.2R
l/w – liquid-to-wood ratio
l/w – moduł cieczy warzelnej
SR – freeness in °SR (Schopper Riegler)
SR – smarność w stopniach °SR (Schopper Riegler)
abc… – repeated small letters show no significant difference between variables
abc… – powtarzające się małe litery wskazują na brak istotnych różnic pomiędzy zmiennymi
ABC… – repeated capitals show no significant difference between mean values of variables
ABC… – powtarzające się duże litery wskazują na brak istotnych różnic pomiędzy średnimi
wartościami zmiennych
mean – mean value
śr – wartość średnia
cv – coefficient of variation
wz – współczynnik zmienności
In opposition to this, the average SCT values differed significantly at higher
l/w ratios – between 1.8 and 2.2. Taking into consideration the preferences for
aiming at high CMT pulp indices as seen in industrial practice, the results seem
to show the possibility of pulping with a low l/w ratio. However, when plotting
the analyzed data as a function of l/w ratio the same tendencies for these proper-
25
ties were not obtained (fig. 2). The SCT behaves in the same way, according to
the increasing l/w. The other properties, only to some extent reflect this tendency
(table 3). The plot of CMT is the worst (fig. 2). It is unknown which of many factors caused the fluctuations of the data, although it is supposed that cooking is the
reason. It should be noticed that cooking in the vapour-gas phase at l/w ratio 1.6
does not assure the covering of the chips by the liquor. Different l/w ratios (from
1.4 up to 1.8) were used, and for that reason the results of analysis may fluctuate.
Fig. 2. CMT and SCT values as a function of l/w ratio
Rys.2. Wartości CMT i SCT w odniesieniu do zmian modułu cieczy warzelnej
The Burst results, increasing with higher SR freeness, showed similar tendencies as the SCT indices – significant differences were observed between 1.8 and
2.2 l/w ratios. Tear, in contrast, decreased when higher SR degrees were obtained.
In this case, the LSD values of the mean results appeared for extreme l/w ratios:
26
1.4 versus 1.5 and 1.7 versus 2.2. The lowering of the Tear strength confirms
well-known papermaking relations [Smook 1992]. Tear strength is a function of
both the quantity of long fibers and inter-fiber bonding – when more fibers are cut
a lower Tear strength is produced [El-Sharkawy et al. 2008].
The results of the statistical analysis of separate data inserted in table 3 (averages marked with small letters) showed a relatively small number of significantly
differing results. Apart from the SCT values, more differences were observed for
lower SR freeness – from 20°SR up to 25°SR. This can be explained by the known
papermaking phenomena: on the one hand the increase of 5º SR freeness more at
the beginning brings more fiber strength than at the end of refining. On the other
hand, Burst, CMT and SCT indices generally grow with higher SR freeness, but at
some specified point of refining they start to weaken [Markstrom 2005].
The tabular observation of pulp strength development tendencies (table 3)
was difficult, thus in the next step, Principal Component Analysis (PCA) was
carried out as a method facilitating the visual inspection of the obtained data sets.
The PCA analysis made it possible to reduce the set of observations (all analyzed
strength properties for 1.4, 1.5, 1.7, 1.8 and 2.2 l/w ratios and for all SR freeness)
and to answer the question regarding which l/w and SR freeness values formed
a similar data collection. The PCA was performed with the use of the mean values
because we had at our disposal the different number of readings for all studied
properties (CMT, SCT, Burst and Tear). Fig. 3 represents the visualization of the
researched coordinates in a two-dimensional data space. The most important features that influenced this arrangement of points are CMT, SCT, Burst and Tear
strength. Only 0.92% of the primary data (100% - 78.17% - 20.91%) was lost after
a transformation from the four-dimensional space to the two-dimensional plane,
therefore the observed arrangement of data may be treated as almost original.
As seen in fig. 3 five similar groups of points representing different l/w and SR
freeness can be distinguished. The visualization shows that the results (combination of l/w and SR freeness) group together according to higher l/w ratios and
in this case the SR freeness does not significantly differentiate the pulp as regards
strength properties. When lower l/w ratios were used (e.g. 1.4), the SR degrees,
in contrast, differentiated strongly the strength properties and that is why the combination of l/w and SR freeness appears separately. However, we can already distinguish two similar groups of l/w and SR freeness: 1.5/35°, 1.5/30° and 1.5/20°,
1.5/25° for l/w 1.5. It should be mentioned that similarities between the analyzed
data pairs (l/w and freeness) along the OX axis (first principal component) are
weaker than along the OY axis (second principal component). Taking that into
consideration, as seen in fig. 3, l/w ratios 1.4 and 1.5 – the lowest ones used during the experiment – differentiated the most importantly pulp strength properties,
independently of the SR freeness values. The results of the PCA analysis suggest
that pulp produced at the lower l/w ratios would need special care during refining
assuring optimal papermaking properties.
27
Fig. 3. Confirmation of combinations of liquid-to-wood ratio stages and SR freeness
in the space of two principal components for CMT, SCT, Tear and Burst strength
Rys.3. Potwierdzenie kombinacji modułów cieczy warzelnej i smarności masy w przestrzeni
dwóch głównych składowych dla oznaczeń CMT, SCT, oporu przedarcia i przepuklenia
Parallel coordinate plots (PCPs) are an efficient tool for visualizing multivariate data [Inselberg 1985; Wegman 1990]. PCPs can be a very useful tool for the
selection of interesting (the best) combinations of liquid-to-wood ratios and SR
degrees in the case of many attributes of interest.
The most important application of the tested NSSC pulp is the production of
the corrugated medium, and that is why there was a focus on the analysis of CMT
and SCT indices. CMT = SCTmd × 60(N), approaching the correlation between
CMT and SCT measured along paper machine direction (md) [Markstrom 2005]
is a well-known formula. Generally, pulp’s CMT and SCT indices should increase
simultaneously with higher SR numbers. The PCPs analysis made it possible to
observe the tendency of the CMT and SCT development caused by the l/w changes. Fig. 4 shows PCP for 20 objects (combinations of l/w and SR freeness) and
four properties (CMT, SCT, Burst and Tear). The reciprocal orientation of breaking lines confirms or excludes the correlation between the neighboring variables.
The orientation close to parallel and with a similar angle of inclination, representing the position of CMT on the plot higher than SCT, indicates a correlation
that was marked as “positive”. The crossing lines show a “negative” correlation
among the variables. As seen in fig. 4, 13 positive correlations between CMT and
SCT can be distinguished, concerning nearly the whole range of l/w and SR fre-
28
eness combinations used for analysis. Apart from one combination of l/w and SR
freeness (2.2/35° respectively), negative correlations appeared rather for the lower
SR freeness numbers (between 20°SR and 25°SR) and/or for the highest value
of liquor-to-wood ratio used during cooking i.e. 2.2 (table 4).
Table 4. Positive and negative correlations between CMT and SCT values – Parallel
coordinate plot analysis
Tabela 4. Pozytywne i negatywne korelacje pomiędzy wartościami oznaczeń CMT i SCT wykres współrzędnych równoległych
Positive correlations
Negative correlations
Korelacje pozytywne
Korelacje negatywne
Liquor to solid ratio/SR° freenes
Moduł/smarność SR°
2.2/35°, 1.7/35°, 1.8/35°, 1.5/30°, 1.8/30°,
1.5/25°, 1.4/35°, 1.5/35°, 1.4/30°, 1.4/25°,
1.7/30°, 1.5/20°, 1.7/20°
2.2/25°, 2.2/30°, 1.8/25°, 2.2/20°, 1.4/20°,
1.7/25°, 1.8/20°
Fig. 4. Parallel coordinate plot for 20 objects (combinations of liquid-to-wood ratio
stages and SR freeness) and four traits (CMT, SCT, Burst and Tear strength)
Rys.4. Wykresy współrzędnych równoległych dla 20 analizowanych obiektów (kombinacje modułów cieczy warzelnej i smarności masy) i czterech cech (CMT, SCT, przepuklenie i opór przedarcia)
29
The visualization shows that the best pulp strength properties (CMT, SCT and
Burst) were gained for the combination of l/w and SR freeness – 2.2/35°. However, the rest of the results obtained at the highest l/w (2.2) indicating a negative
correlation with the combination mentioned above, (2.2/35°), suggests that pulps
obtained at such cooking conditions may present unpredictable strength properties.
Besides the highly refined pulps (1.7/35°SR and 1.8/35°SR) that will be discussed
below, the next combination representing high CMT values is 1.5/30°SR and then
1.8/30°SR. Although the pulp obtained after cooking at 1.8 l/w showed better SCT
and B values as compared to those processed at 1.5 l/w (all refined to 30°SR),
the latter ones showed better correlations between the neighboring variables. As
opposed to 1.8 l/w, PCPs analysis for 1.5 l/w shows that all lines were relatively
parallel and with a similar angle of inclination. Thus, cooking at such a low liquorto- wood ratio makes it possible to produce the pulp not only with good but also
predictable strength properties and may be implemented in industrial practice.
The other question, relating to the results of statistical analysis presented above, is the choice of appropriate l/w values and the evaluation of the SR number
influence for further studies (time, temperature). Birch pulp refined above the
30º SR brings a less dynamic strength property increase. To reach better tensile
stiffness, it is necessary to involve too much refining energy [Lumiainen 2000].
Applied to high specific energy consumption (SEC) the refining process makes
paper less competitive from the cost point of view [Lumiainen 2000]. Higher
energy consumption is not proportionally transferred into gains in SCT, CMT or
Burst strength. Although high SR freeness (for example, 35°SR) positively influences fiber swelling, it also causes worse dewatering on the wet end of the paper
machine and consequently worse paper web dryness after the wire and press section [Smook 1992; Lumiainen 2000]. Although, for further studies the same range
of SR freeness (pulp samples refined up to 35°SR) was chosen, at the same time at
30°SR the best CMT, SCT and Burst strength developments were obtained for pulp
processing at 1.5 and 1.8 l/w ratio respectively (fig. 4), and these liquor-to-solid
ratios were used during further research concerning the influence of time and cooking temperature on papermaking NSSC pulp properties.
Conclusions
1. Using a set of three statistical methods (analysis of variance, parallel coordinates, principal components analysis) it was shown that by having a sufficiently large database it is possible to evaluate industrial scale technological
factors varying in extremely narrow ranges of values.
2. When applying statistical methods it has been proved that when the liquor-to-wood ratio 1.5 is used during cooking, it is possible to obtain NSSC pulp with
strength properties comparable to those processed at higher liquor volumes.
30
Saving the liquor, and consequently limiting inorganic to organic ratio in spent
liquors, may be beneficial for its further treatment and/or recovery.
Acknowledgement
The research paper was financed by The European Social Fund within the framework of
The Integrated Program of the Regional Development Process.
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Markstrom. H. [2005]: Testing methods and instruments for corrugated board, Lorentzen &
Wettre, Kista, 35 pp.
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List of standards
EN/ISO 9895:2002 Paper and board – Compressive strength – Short span test
EN 21974:2002 Paper – Determination of tearing resistance (Elmendorf method)
EN/ISO 2758:2005 Paper – Determination of bursting strength
EN/ISO 7263:2008 Corrugating medium – Determination of the flat crush resistance after
laboratory fluting
SCAN–CM–40:01:2001 Wood chips for pulp production – Size distribution. Scandinavian
Pulp, Paper and Board Testing Committee
WPŁYW ZMIENNYCH CZYNNIKÓW PROCESOWYCH NA
WŁAŚCIWOŚCI WYTRZYMAŁOŚCIOWE BRZOZOWYCH
MAS PÓŁCHEMICZNYCH (NSSC). W KIERUNKU GRANIC
OPTYMALIZACJI: CZĘŚĆ PIERWSZA – WPŁYW MODUŁU
CIECZY WARZELNEJ
Streszczenie
Celem pracy było ustalenie warunków obojętnosiarczynowego roztwarzania drewna brzozowego i otrzymywania mas półchemicznych (NSSC) o możliwie najwyższych właściwościach wytrzymałościowych, przy wykorzystaniu możliwie najniższych wartości czynników procesowych: modułu cieczy warzelnej, temperatury i czasu warzenia. Badania
oparto na granicznych (minimalnych i maksymalnych) wartościach zmiennych niezależnych procesu roztwarzania drewna prowadzonego w warunkach przemysłowych. Analizowano następujące zmienne: czas warzenia (od 13 do 15,5 min), temperaturę warzenia
(od 172 do 179°C) i moduł cieczy warzelnej (od 1,2 do 2,2). Pomimo bardzo wąskich
zakresów kontroli zmiennych procesu roztwarzania, połączenie obszernej bazy danych
i zestawu metod analizy statystycznej (analiza wariancji, analiza współrzędnych równoległych, analiza składowych głównych) pozwoliło na wyznaczenie optymalnych zakre-
32
sów badanych czynników technologicznych determinujących testowane właściwości wytrzymałościowe mas włóknistych. Analizy statystyczne wykazały, że zmienne niezależne
wpływały na poziom wartości badanych wskaźników wytrzymałościowych: CMT, SCT,
oporu przedarcia i do pewnego stopnia również przepuklenia. Obniżając moduł cieczy
warzelnej do 1,5, uzyskano masy włókniste o porównywalnych właściwościach wytrzymałościowych do mas warzonych przy wyższych modułach. Ograniczenie ilości dozowanego ługu warzelnego, a zatem możliwość zmniejszenia udziału substancji nieorganicznych do organicznych w ługu powarzelnym, może być korzystne z ekonomicznego
punktu widzenia oraz dalszego przerobu ługu powarzelnego.
Słowa kluczowe: NSSC, masa obojętnosiarczynowa, moduł cieczy warzelnej, metody statystyczne
Iwona Frąckowiak, Karolina Mytko, Ryszarda Bendowska1
CONTENT OF FORMALDEHYDE
IN LIGNOCELLULOSIC RAW MATERIALS FOR
PARTICLEBOARD PRODUCTION
The article contains the results of tests for formaldehyde content in selected wood
species, alternative raw materials from experimental and agricultural plantations,
particles dried under industrial conditions, recycled chips, and in boards made
of elements of furniture, at the end of its life cycle. An unexpectedly high content
of formaldehyde was determined in particleboards produced a few dozen years ago.
It was observed that the amount of formaldehyde in particles dried under industrial
conditions may have a bearing on the content of this compound in finished products
and/or its emission into the environment. Control tests of raw materials may be
performed using the flask method.
Keywords: formaldehyde content, wood raw material, conventional, alternative,
recycled
Introduction
In 2006 the International Agency for Research on Cancer (IARC), which belongs
to the World Health Organization (WHO), tightened up the assessment of the
incidence of cancer caused by formaldehyde through recognizing this compound
as a 1. group substance, i.e. a substance that is considered carcinogenic to humans [Christianson 2004; Kupczewska-Dobecka 2007]. Before that date, the
IARC considered formaldehyde a compound that was “probably carcinogenic to
humans” [International Agency for Research on Cancer 2004]. The recommendation of the IARC has no legal efficacy, nevertheless it brought about an intensification of research aimed at the reduction of formaldehyde emissions, as well
Iwona Frąckowiak, Wood Technology Institute, Poznan, Poland
Ryszarda Bendowska, Wood Technology Institute, Poznan, Poland
Karolina Mytko, Wood Technology Institute, Poznan, Poland
34
Iwona Frąckowiak, Karolina Mytko, Ryszarda Bendowska
as a discussion on the sources of formaldehyde emissions and the permissible
level as regards production processes and products. In 2011, the US government
added “formaldehyde used, among others, for the production of synthetic resins”
to a list of carcinogenic factors, which resulted in the tightening of regulations
concerning formaldehyde content in and emission from wood-based materials
[In the USA formaldehyde …]. In Europe the IARC assessment resulted in the
classification of formaldehyde as a category 3. substance, i.e. a substance that
may be carcinogenic to humans [Kupczewska-Dobecka 2007, Reduction of formaldehyde 2010]. Discussions concerning the harmful effect of formaldehyde
often raise the argument that formaldehyde is ubiquitous in nature, i.e. in most
living organisms such as people, animals, trees, plants etc. [Reduction of formaldehyde 2010, Timber Trades Journal]. The research on formaldehyde content in
and emission from natural wood has been conducted for years. Within this field,
the formaldehyde emission from wood and the changes of this emission due to
thermal technological processes were tested [Marutzky, Roffael 1977; Sachsse,
Roffael 1993; Roffael 2000], the emission of formaldehyde from birch, aspen and
pine was determined [Ellbert 1995], as well as the effect of the storage period of
pine and spruce wood on formaldehyde release [Schäfer 1996]. Schäfer, Roffael
[2000], Roffael [2006] conducted broad research on the role of major components
(lignin, cellulose, hemicelluloses, and wood extracts) as potential sources of formaldehyde.
One of the most recent publications [Weigl et al. 2009] presents the results
of tests of formaldehyde content in various European wood species: Scots pine,
Norway spruce, birch, poplar, and oak. Different classes of wood and samples
of early and late wood were tested. The content of formaldehyde was determined
by the extraction method based on tests of particles obtained, dried and stored
in constant conditions. The principle of the perforator method, according to EN
120:1992 standard, was adopted with only some of its parameters modified.
The formaldehyde content was within the range of 0.15-0.71 mg/100 g oven dry
wood. Coniferous wood was characterised by a higher content although wood
species seemed irrelevant. Clear differences between juvenile and mature wood
were observed. The lowest formaldehyde content was observed in juvenile red
beech wood (0.15 mg/100 g), and the highest in mature pine wood, where it was
approximately 0.70 (mg/100 g). The tests of formaldehyde content in natural
wood, conducted by Meyer and Boehme [1997], resulted in similar values, from
within the above range. Within the framework of prefatory research conducted
in the Wood Technology Institute in 2005, it was observed that the formaldehyde
content in so-called “dry particles”, which had been sampled randomly in one
particleboard plant, was 1.8-2.1 mg/100g of oven dry particles, approximately
25% of the permissible formaldehyde content in E1 class particleboards. The approximate value of the perforator, i.e. 1.6 mg/100 g of oven dry particles after
conversion to a moisture content of 6.5%, was determined based on the tests of
Content of formaldehyde in lignocellulosic raw materials for particleboard production
35
particle samples after drying in industrial conditions in 2009 [Danecki 2009].
More and more diverse raw wood material has been used in the production of
wood-based panels, especially particleboards. The situation on the wood market
and an attempt to minimise waste, essential for sustainable development, are the
reasons for the drive to use production waste and post-consumer wood, including recycled furniture, as a source of material. This article presents the results
of tests for formaldehyde content in and emission from: natural wood of selected
domestic species, alternative lignocellulosic raw materials for wood-based panel
production, so-called post-consumer wood”, and particles used in the production
of boards in various plants.
The test were performed on selected domestic wood species most often used in
wood-based panel production, as well as on alternative raw materials, which were
proved useful for the production of composite panels for the furniture industry
and construction, based on the results of statutory research carried out in the
Wood Technology Institute in the period 2007-2009 [Frąckowiak 2007, 2010].
Post-consumer wood, mainly from particleboards originating from elements
of furniture, which after a long period of use was at the end of its life cycle, was
tested as well. The test samples were cut out in the Institute. The samples of
recycled chips, intended for tests for formaldehyde content and emission, were
randomly taken from a chip bunker at one of the domestic panel producers. The
tests also took into account particles industrially-dried in diaphragm and non-diaphragm dryers, and sampled at various particleboard producers in Poland and
Germany.
The characteristics of the tested materials are given in tables 1-4.
The particles were tested according to the methods described in the following
standards:
–– PN EN 120:1994 Wood-based panels – Determination of formaldehyde content – Extraction method called the perforator method,
–– PN EN 322:1999 Wood-based panels – Determination of moisture content,
–– PN EN 717-3:1999 Wood-based panels – Determination of formaldehyde release – Part 3: Formaldehyde release by the flask method (modified by the
authors with particle testing in mind).
The particles for emission testing were put into a receptacle made of thick,
thin and transparent polyamide fabric. The mass of a particle sample, due to
the relatively large volume, was reduced to 15±1 g. The amount of water was
in accordance with the assumptions of the standard method. Formaldehyde release was calculated taking into consideration the mass and moisture content
of the particles.
36
Table 1 presents the results of the tests for formaldehyde content in and emission
from pine, alder, birch and alternative lignocellulosic raw materials for the production of particleboards. Pine sapwood was characterised by the highest content
and emission of formaldehyde amongst the tested wood species. A relatively high
formaldehyde content in birch bark and yellow rape straw, i.e. fresh and, tested before storage, also draws attention. The lowest formaldehyde content was found in the
wood from two-year-old root offshoots of the locust tree (Robinia pseudoacacia).
Table 1. Average values of formaldehyde content in and emission from various raw material assortments – wood from forest plantations and plantations, agricultural waste
Tabela 1. Średnie wartości zawartości i emisji formaldehydu z różnych sortymentów surowca
– drewno z upraw leśnych i plantacji, odpady rolnicze
Characteristics of the
tested material [%]
Charakterystyka badanego
materiału [%]
[mg/100 g]
[%]
[mg/kg]
3
4
5
16.4
0.41
-
-
77.9
1.42
15.4
0.52
19.0
0.83
10.8
0.62
26.7
0.51
-
-
44.0
0.35
44.0
0.12
wood from the
middle part of
trunk/
57.0
0.38
57.0
0.00
bark/kora
38.6
1.11
-
-
12.3
0.26
12.3
0.21
13.0
0.15
13.0
0.19
twardziel
bark/kora
lat
Birch/Brzoza
Betula
verrucosa
Ehrh
37 years old/
lat
Emisja
formaldehydu
Wilgotność w formaldehydu
Wilgotność
po przeliczeniu
chwili badania po przeliczeniu
w chwili
na suchą masę badania emisji na suchą masę
zawartości
drewna
drewna
formaldehydu
formaldehydu
2
Pine/Sosna
bark/kora
Pinus
sapwood/biel
sylvestris L)
52 years old/ heartwood/
Alder/Olcha
Alnus
glutinosa (L.)
Gaertn
66 years old/
Formaldehyde
emission converted into dry
mass of wood
[%]
1
lata
Moisture
Moisture
Formaldehyde
content when content con- content when
formaldehyde verted into dry formaldehyde
content was mass of wood emission was
Zawartość
tested
tested
peripheral wood/
drewno obwodowe
drewno ze środkowej części pnia
peripheral wood/
drewno obwodowe
wood from the
middle part of
trunk/
drewno ze środkowej części pnia
37
Table 1. Continued
1
Miscanthus straw
Słoma z miskanta olbrzymiego
Miscanthus sinesis giganteus
Two-year-old shoots of fastgrowing willow/Pręty dwuletnie
szybko rosnącej wierzby
2
3
4
5
13.3
0.34
13.3
0.1
7.3
0.21
7.4
0.3
13.5
0.11
13.0
0.6
14.9
1.9
-
-
8.9
0.9
-
-
Salix Viminalis L.
Two-year-old root offshoots of
locust tree/Odrośle korzeniowe
dwuletnie robiniii akacjowej
Robinia pseudacacia L.
Yellow rape straw/
Słoma rzepakowa zółta
Brasica napus L.
Grey rape straw/
Słoma rzepakowa szara
Brasica napus L.
Unexpected test results were obtained for particleboards from the elements
of furniture, at the end of its lifecycle. The highest (27.0 mg/100 g of oven dry
board), but also the lowest formaldehyde content was determined in the case of
panels produced in the 1970s. The samples of the panels came from furniture
used in conditions familiar to the authors and from materials sent to the Institute
for testing. Therefore, the influence of the conditions in which the tested furniture panels and materials were used or stored on the content of formaldehyde in
the panels may be excluded. The level of formaldehyde content seems connected
rather with the technology than with the time that had passed since the panels
were produced. Laminating or veneering of the panels’ surface, which hindered formaldehyde release from the material, could have some influence on the
high formaldehyde content. The panel samples were tested after removing the
coatings.
The content of formaldehyde in the tested recycled chips ranged from 1.6 to
4.1 mg/100 g of chips.
Fig. 1 illustrates the interrelation between the formaldehyde content in the
panels and the emission from them tested by the flask method. Data presented in
Fig. 1 indicates a strong correlation between the test results obtained using these
methods, thus it confirms the conclusions from previous research [Frąckowiak
2003], i.e. that the flask method is useful (and at the same time inexpensive and
environmentally-friendly) for the testing of particleboards stored in different periods, produced using various technologies and raw materials.
38
Table 2. The results of the tests for formaldehyde content in and emission from post-consumer wood
Tabela 2. Wyniki badań zawartości i emisji formaldehydu z drewna poużytkowego
Formaldehyde content
Zawartość formaldehydu
Characteristics of the tested
material
Charakterystyka badanego
materiału
Double-side laminated particleboard (liquor cabinet from
1970s)
Płyta wiórowa dwustronnie
laminowana (barek z lat 70.)
Double-side laminated particleboard – thickness 18 mm
(1990s)
Płyta wiórowa laminowana
dwustronnie – grubość 18 mm
(lata 90.)
Double-side laminated board
– thickness 18 mm (particles
with an addition of ground
laminate); 1970s
Płyta dwustronnie laminowana – grubość 18 mm (wióry
z dodatkiem rozdrobnionego
laminatu); (lata 70.)
(cabinet from 1970s)
laminowana – grubość 17 mm
(szafka z lat 70.)
(cabinet from 1970s); made
from debarked particles
Płyta wiórowa dwustronnie laminowana – grubość 16 mm (szafka
z lat 70.) z wiórów bez kory
Emisja
formaldehydu
Moisture
at moisture at moisture content of
content content of the the samples after con- test
Wilgotność samples when version into moisture results average
value
wyniki
tested
content of 6.5%
wartość
badaprzy wilgotności
przy wilgotności
średnia
próbek w chwili próbek po przeliczeniu nia
badania
na wilgotność 6,5%
[%]
1
Formaldehyde
emission
2
[mg/100 g z.s.p.]
3
4
[mg/kg]
5
6
37.7
8.1
34.5
27.0
32.0
40.1
42.5
5.5
6.2
7.0
7.4
6.9
5.9
4.5
21.9
25.3
8.6
22.3
16.0
23.9
24.5
10.9
10.0
6.9
12.2
11.5
11.1
12.3
17.0
14.0
7.4
16.4
14.4
16.0
12.0
39
Table 2. Continued
1
Particle-flax board – thickness
21 mm (80% particles, 20%
harl of flax); from 1970s
Płyta wiórowo-paździerzowa
– grubość 21 mm (80% wióry;
20% paździerze); (lata 70.)
Double-side veneered particleboard – thickness 22 mm;
1980s
oklejana – grubość 22 mm;
(lata 80.)
Particleboard (wardrobe from
the end of 1950s) – thickness
19 mm
Płyta wiórowa (szafa – koniec
lat 50.) – grubość 19 mm
2
3
4
5
6
5.0
5.6
7.7
7.3
6.1
5.3
4.2
14.6
8.3
17.4
13.2
10.9
15.7
16.7
13.1
10.4
11.2
-
8.5
11.8
10.4
Chips from post-consumer
wood, from a bunker in a particleboard plant – batch 1
9.9
2.3
-
wood, from production line in
a particleboard plant – batch 2
11.7
4.1
-
-
wood, from production line in
a particleboard plant – batch 2
7.5
1.6
-
-
Zrębki z drewna poużytkowego,
z zasobnika w zakładzie płyt
wiórowych – partia 1
z linii produkcyjnej w zakładzie
płyt wiórowych – partia 2
z linii produkcyjnej w zakładzie
płyt wiórowych – partia 2
-
-
40
Fig. 1. The interrelation between the formaldehyde content determined by the perforator method and its emission tested by the flask method – based on post-consumer
wood in the form of particleboards from furniture elements
Rys. 1. Zależność między zawartością formaldehydu oznaczoną metodą perforatora i jego
emisją badaną metodą butelkową – na podstawie drewna poużytkowego w postaci płyt wiórowych z elementów mebli
Table 3 contains the results of the tests for formaldehyde content in the particles randomly sampled in various production plants and prepared in the Institute’s
laboratory.
The particles sampled at the panel producers (table 3) were tested after various storage periods at the Institute. Hence the formaldehyde content might have
changed over a period, i.e. decreased, in relation to the value characteristic of particles directly after drying. This especially concerns the particles from sample 3
and 5, the moisture content of which was much higher than that characteristic of
so-called “dry” industrial particles. The content of formaldehyde in the tested particles was within a range of 0.7-2.7 mg/100 g of oven dry particles. Based on the
obtained results, one cannot draw conclusions as to the influence of the drying
method on formaldehyde content in particles. The suggestions that particles dried
in a diaphragm dryer will not contain formaldehyde at all or will contain only trace
amounts of it were not confirmed. After a thorough organoleptic assessment of the
particles dried in a diaphragm dryer (samples 5 and 6), parts of ground panels were
detected in the particles, which explains a relatively high content of formaldehyde.
Table 3 also contains the results of the tests for formaldehyde content in particles
dried to a constant mass under laboratory conditions. As a result of additional drying, the content of formaldehyde decreased many times. The results of the tests for
formaldehyde emission from the particles are given in table 4. The decrease in the
formaldehyde emission resulting from additional drying is illustrated in fig. 2.
41
Table 3. Formaldehyde content in particles
Tabela 3. Zawartość formaldehydu w wiórach
Formaldehyde content
Zawartość formaldehydu
Sample of
particles
Particle origin/
/dryer type
Moisture
content of at moisture at moisture content
particles content when after conversion
into oven
tested
Wilgotność
przy
wilgotdry
particles
wiórów
at moisture content after drying
to constant mass
Próba
wiórów
Pochodzenie wiórów/
/typ suszarki
1
Polska/Poland A/1
2.1
1.8
1.8
-
2
Polska/Poland A/1
2.6
2.6
2.7
-
3
Polska/Poland B/1
7.4
0.7
0.8
-
4
Polska/Poland B/1
3.3
0.9
0.9
0.3
5
Niemcy/Germany A/2
5.1
2.2
2.3
0.4
6
Niemcy/Germany A/2
2.7
2.0
2.0
-
7
Polska/Poland A/1
2.7
1.5
1.5
0.6
8
Polska/Poland A/1
2.9
1.2
1.2
0.6
Polska/Poland A/1
3.9
1.6
1.7
0.2
5.3
0.8
0.8
0.2
przy wilgotności
ności w chwili przy wilgotności po po wysuszeniu do
badania przeliczeniu na z.s.w.
stałej masy
%
9
10
Pine wood particles
cut and dried in ITD/3
Skrawane i suszone
z drewna sosny w ITD/3
mg/100 g z.s.w./of oven dry particles
1 – non-diaghragm/bezprzeponowa
2 – diaghragm/przeponowa
3 – chamber, eletrically heated/komorowa ogrzewana elektrycznie
Table 4. Formaldehyde emission from particles
Tabela 4. Emisja formaldehydu z wiórów
Formaldehyde emission
Moisture
Emisja formaldehydu
content of
at moisture content
Sample marking acc. particles
Number of
after drying to constant mass
when tested
to Table 3
Wilgotność analysis
po wysuszeniu do stałej masy
przy wilgotności
Oznakowanie próby
wg tabeli 3
wiórów
Nr analizy
x
w chwili badania
x
xs
%
1
6
2
7.4
x
xs
mg/kg
3
4
6a
3.4
6b
3.0
6c
3.7
5
6
7
0.6
3.4
0.3
0.3
0.4
42
Table 4. Continued
1
7
8
9
10
2
3.4
5.1
5.3
12.6
3
4
7a
2.0
7b
2.6
7c
2.6
0.3
8a
1.5
0.1
8b
1.4
8c
1.5
9a
2.9
9b
2.4
9c
2.5
10a
0.1
5
6
7
0.5
2.4
1.5
0.4
0.1
0.4
0.1
0.2
0.8
2.6
0.6
0.7
0.4
0.0
0.0
0.0
Fig. 2. The influence of the additional drying of particles on the formaldehyde emission
Rys. 2. Wpływ dodatkowego suszenia wiórów przemysłowych na emisję formaldehydu
The interrelation between formaldehyde content in and emission from the particles (fig. 3) was calculated based only on the results of the tests of the particles,
which were not additionally dried in the Institute. It should be stressed, that although the method of emission testing, modified for the needs of this research,
was used, the obtained correlation of the tested interrelation was very good. The
coefficient of determination indicates that the formaldehyde emission was 99%
connected with the content of formaldehyde in the particles.
43
Fig. 3. The interrelation between the formaldehyde content determined by the perforator method and its emission tested by the flask method – based on the particles
from industrial plants and obtained in laboratory conditions
Rys. 3. Zależność między zawartością formaldehydu oznaczoną metodą perforatora i jego
emisją badaną metodą butelkową – na podstawie wiórów z zakładów przemysłowych i pozyskanych w warunkach laboratoryjnych
Conclusions
The research carried out proved that the amount of formaldehyde contained in
natural wood of domestic species, which are commonly used in the production of
wood-based panels, reaches a maximum of approximately 1 mg/100g of panel.
The range defined, based on, tests of natural wood, also encompasses alternative
raw materials (fast-growing willow, locust tree, miscanthus giganteus straw, and
grey rape straw, i.e. straw tested after storage). The content of formaldehyde in
yellow rape straw was relatively high – 1.9 mg/100g of oven dry particles. The
panels from elements of furniture manufactured a few dozen years ago contained
a large amount of formaldehyde – even 27 mg/100g of oven dry panels (after
conversion to moisture content 6.5%). The particles randomly sampled at various
producers were characterised by different formaldehyde content, but higher than
in the case of natural wood. Therefore, it seems purposeful to broaden the research
on the phenomena connected with the recycling of materials containing formaldehyde in the panel industry. The results of the tests confirmed the usefulness of
the flask method for the control of formaldehyde content in particleboards and the
possibility of its adaptation for control tests of raw material.
44
Acknowledgements
This research was carried out within the framework of a project no. NN 309 078 338 financed by the National Science Centre (NCN) (and previously by the Ministry of Science
and Higher Education).
References
Christianson R. [2004]: Formaldehyde under fire. Wood a. Wood Products, vol. 109 nr 9, s. 13
Danecki L. [2009]: Formaldehyd na stanowiskach pracy. Biuletyn Informacyjny OBRPPD [3–4]
Elbert A. A. [1995]: Influence of hardener systems and wood on the formaldehyde emission
from urea-formaldehyde resin and particleboards. Holzforschung [49]: 358–362
Frąckowiak I. [2003]: Badanie przydatności butelkowej metody oznaczania emisji formaldehydu w przemysłowej kontroli zawartości formaldehydu w płytach wiórowych. Drewno,
46 [170]: 27–41
Frąckowiak I. [2007]: Czy można ograniczyć skutki deficytu drewna? Gazeta Przemysłu
Drzewnego 5[103]
Frąckowiak I. [2010]: Alternatywne surowce do produkcji płyt. ��
Gazeta Przemysłu Drzewnego 5[1160]
International Agency for Research on Cancer press release N°153, 15 June 2004
Kupczewska-Dobecka M. [2007]: Ocena działania rakotwórczego formaldehydu w świetle
najnowszych danych literaturowych. Medycyna Pracy [586]: 1–13
Marutzky R., Roffael E. [1977]: Über die Abspaltung von Formaldehyd bei der thermischen
Behandlung von Holzspänen: Holzforschung [31]: 8–12
Meyer B., Boehme C. [1997]: Formaldehyde Emission From solid wood. Forest Products
Journal 47[5]: 45–48
Reduction of formaldehyde exposure in the woodworking industries [2010]: Projekt
partnerów społecznych zrealizowany przez Europejską Federację Producentów Płyt
(EPF), Konfederację Przemysłu Drzewnego (CEI-Bois) oraz Europejską Federację
Pracowników Budownictwa i Przemysłu Drzewnego (EFBWW) przy wsparciu UE,
www.cei-bois.org/.../REDUCTION_OF_FORMALDEHYDE
Roffael E. [2006]: Volatile organic compounds and formaldehyde in nature, wood and wood
based panels. Holz als Roh- und Werkstoff [64]: 114–149
Sachsse H., Roffael E. [1993]: Untersuchung der Schälfurnier-Eignung von in Deutschland
erwacgsenem Douglasienholz. Holz Roh-Werkstoff [51]: 167–176
Schäfer M., Roffael E. [2000]: On the formaldehyde release of wood. Holz als Roh-und
Werkstoff [58]: 259–264
Schäfer M. [1996]: Einfluß der Lagerung von Fichten- und Kifern-Industrierestholz aus der
Profilzerspanung auf die Eigenschaften von Spanplatten und mitteldichten Faserplatten
(MDF). Dissertation am Forstwissenscgftlichen Fachbereich der Georg-August-Uniwesität, Göttingen
Weigl M., Wimmer R., Sykacek E., Steinwender M. [2009]: Wood-borne formaldehyde
varying with species, wood grade, and cambial age. Forest Products Journal, 59[1/2]
More formaldehyde in a tomato than OSB floor [1995]: Timber Trades Journal [6164]: 4
W USA formaldehyd wpisany na listę karcynogenów
http://www.naukawpolsce.pap.pl/aktualnosci/news,382743,w-usa-formaldehyd-wpisany--na-liste-karcynogenow.html
45
ZAWARTOŚĆ FORMALDEHYDU W SUROWCACH
LIGNOCELULOZOWYCH DO PRODUKCJI PŁYT
WIÓROWYCH
Streszczenie
Do produkcji płyt drewnopochodnych, szczególnie wiórowych, stosuje się coraz
bardziej zróżnicowany surowiec drzewny. Sytuacja na rynku drewna oraz niezbędna
dla zrównoważonego rozwoju minimalizacja odpadów wymuszają materiałowe
wykorzystywanie odpadów produkcyjnych i drewna poużytkowego, w tym mebli
z recyklingu. Decyzja IARC o zakwalifikowaniu formaldehydu do substancji
o rakotwórczym działaniu na ludzi spowodowała intensyfikację badań zmierzających m.in.
do poszerzenia wiedzy o źródłach emisji formaldehydu w procesach technologicznych oraz
z gotowych produktów. W niniejszym artykule przedstawiono wyniki badań zawartości
i emisji formaldehydu z:
–– drewna naturalnego – sosny zwyczajnej (Pinus sylvestris L.), olszy czarnej (Alnus glutinosa Gaertn.), brzozy (Betula verrucosa Ehrh.) - powszechnie stosowanego do produkcji płyt wiórowych,
–– lignocelulozowych surowców alternatywnych, których przydatność do wytwarzania
płyt kompozytowych dla meblarstwa i budownictwa wykazały wyniki wcześniejszych
badań wykonanych w Instytucie Technologii Drewna, tj. dwuletnich odrośli robinii
akacjowej – Robinia pseudacacia L., dwuletnich prętów wierzby szybko rosnącej (Salix viminals L.), słomy miskanta olbrzymiego (Miscanthus sinesis), słomy rzepakowej
(Brasica napus L.),
–– drewna poużytkowego w postaci elementów mebli z płyt wiórowych i zrębków recyklingowych,
–– wiórów stosowanych do produkcji płyt w różnych zakładach - w Polsce i w Niemczech.
Zawartość formaldehydu badano metodą perforatora, według PN-EN 120:1994. Emisję
formaldehydu oznaczano metodą butelkową według PN-EN 717-3:1999. Metodę butelkową zmodyfikowano w celu jej adaptacji do badania wiórów. Spośród badanych gatunków
drewna największą zawartością i emisją formaldehydu charakteryzowało się drewno sosny z części bielastej. Uwagę zwraca również stosunkowo duża zawartość formaldehydu
w korze brzozy i w słomie rzepakowej żółtej, tj. świeżej, badanej przed składowaniem.
Najwyższą (27 mg/100 g z.s.p.), ale i najniższą (6,1 mg/100 g z.s.p.) zawartość formaldehydu oznaczono w płytach wyprodukowanych w latach siedemdziesiątych ubiegłego
wieku. Próbki płyt pochodziły z mebli, których warunki użytkowania były znane, oraz
z materiałów przesłanych do badań w Instytucie Można więc wykluczyć wpływ warunków użytkowania czy przechowywania na zawartość formaldehydu w płytach. Poziom
zawartości formaldehydu wydaje się związany raczej z technologią niż okresem jaki
upłynął od wyprodukowania płyt. Różną, od 0,7 – 2,7 mg/100 g. z. s., zawartością formaldehydu charakteryzowały się wióry pobrane losowo u różnych producentów. Wartość perforatora nie była związana z typem suszarki (przeponowa i bezprzeponowa). Wpływ na
nią miały przypuszczalnie cząstki rozdrobnionych płyt zawarte w wiórach. Wióry pobrane
u producentów płyt badane były po różnym czasie przechowywania. Zawartość formalde-
46
hydu mogła więc w tym okresie ulec zmianie – tzn. zmniejszeniu, w stosunku do wartości
charakteryzującej wióry bezpośrednio po suszeniu.
Celowe wydaje się, w związku z powyższym, poszerzenie badań zjawisk związanych
z recyklingiem materiałów zawierających formaldehyd w przemyśle płytowym poprzez
okresową kontrolę zawartości formaldehydu w stosowanych surowcach. Badania wykazały możliwość adaptacji do tych celów butelkowej metody oznaczania emisji.
Słowa kluczowe: zawartość formaldehydu, surowiec drzewny: konwencjonalny, alternatywny,
z recyklingu
Maciej Wilczyński, Krzysztof Warmbier1
ELASTIC MODULI OF VENEERS IN PINE AND BEECH
PLYWOOD
The paper presents the results of a study concerning the elastic moduli of veneers
assembled in pine and beech plywood panels. The elastic modulus of veneers in the
direction of the grain and the elastic modulus of veneers in the direction perpendicular to the grain were determined by bending plywood strips with their longitudinal axis parallel and perpendicular to the grain of the face plies. The effects
of a resin type and the number of veneer plies in the plywood were evaluated. Threeand five-ply plywood bonded with urea and phenol resins were tested. The effect
of glue lines in the plywood on the veneer elastic moduli was also evaluated.
Keywords: veneer, plywood, elastic modulus, pine wood, beech wood
Introduction
Plywood is regularly used for many applications. It is a wood-based material with
good performance and important strucural parts are made of it. The elastic properties of entire plywood are fairly well known, whereas those of veneer in plywood
are poorly understood. It is worth noting that the properties of veneers assembled
in plywood panels differ from the properties of veneers before pressing. The veneers in plywood have a greater density as a result of their compaction and adhesive diffusion into the wood [Mansouri et al. 2006].
The elastic moduli of veneer in plywood have rarely been the subject of study.
Curry and Hearmon [1967] determined the elastic moduli of veneers in three-ply plywood made of gaboon (Aucoumea klaineana) and other wood species from Commonwealth countries. They calculated these moduli basing on elastic moduli in the bending of the plywood strips with the longitudinal axis parallel and perpendicular to the
grain of the face plies. Okuma [1976] calculated the elastic moduli of veneer in Hoop
pine (Araucaria cunninghamii) plywood. He used the method of comparing theoretical and empirical equations for elastic moduli in the bending of the plywood strips.
Maciej Wilczyński, Kazimierz Wielki University, Bydgoszcz, Poland
Krzysztof Warmbier, Kazimierz Wielki University, Bydgoszcz, Poland
48
Maciej Wilczyński, Krzysztof Warmbier
Wilczyński [2007] determined the elastic moduli of veneers in beech plywood basing their analysis like Curry and Hearmon [1967] on elastic moduli in
the bending of two plywood strips with different longitudinal axes, and taking
into account the glue lines that bonded the veneers. The method required the assumption of anisotropy of veneer elasticity expressed as a ratio of veneer elastic
modulus in the grain direction to that modulus in the direction perpendicular to
the grain. This method was also used for evaluating the effect of the thicknesses
of glue lines on the elastic moduli of veneer in beech plywood [Wilczyński et
al. 2008]. Moreover, the effect of veneer anisotropy on the elastic moduli of veneers in plywood determined by this method was examined [Wilczyński, Warmbier 2009]. In the previous study [Wilczyński 2011], the author used a simplified
method for determining the veneer elastic moduli, neglecting the effect of the glue
lines bonding veneers.
The elastic properties of the veneer before making up plywood, under free
conditions, were studied by Lang et al. [2003]. They determined Young’s modulus for different directions in the veneer plane, using an ultrasound stress-wave
method. The veneers of five hardwood species were the subject of the study but
these species did not contain beech wood.
Veneer elastic moduli data can be useful for an analysis of stresses in the
construction parts made of plywood, and also for application of the theory of the
layered systems. These moduli are affected by many factors. The objective of this
study was to evaluate the effects of wood species, a resin type and the number of
veneer plies in plywood on the veneer elastic moduli.
The plywood panels for this study were fabricated in a laboratory using selected
pine (Pinus silvestris L.) and beech (Fagus silvatica L.) veneers 50 cm by 50 cm,
without defects, of 1.5 mm thickness. The moisture content of the veneers
(according to EN 322) was approx. 7%, and the average density (according to EN
323) of the pine and beech veneers were 0.48 and 0.63 g/cm3, respectively.
Two types of adhesive, a phenol and an urea resin, were used to bond the veneers. Their physical properties are given in table 1. The formulation of the phenol
adhesive was:
–– phenol-formaldehyde resin … 100 parts by weight,
–– water … 10.5 parts by weight,
–– rye flour with tannin … 14 parts by weight,
and that of the urea adhesive was:
–– urea-formaldehyde resin … 100 parts by weight,
–– water … 20 parts by weight,
–– rye flour … 10 parts by weight,
–– hardener MZ … 10 parts by weight.
49
Elastic moduli of veneers in pine and beech plywood
Table 1. Properties of resins and adhesive masses
Tabela 1. Właściwości żywic i mas klejowych
Property
Właściwość
dynamic viscosity
lepkość dynamiczna
dry mass content
zawartość suchej
masy
gelation time
czas żelowania
Standard
Norma
Phenol-formaldehyde
Urea-formaldehyde
Unit Fenolowo-formaldehydowa Mocznikowo-formaldehydowa
Jednostka
PN-92/C-89402 mPa·s
resin
adhesive mass
masa klejowa
żywica
resin
adhesive mass
340
1450
1630
2100
żywica
masa klejowa
EN 827
%
48.4
-
68.1
-
BN-67/6317-01
BN-75/6327-01
s
-
235
-
75
Three- and five-ply panels were made, using standardized procedures that
simulated industrial production. The adhesive spread was 160 g per 1 m2. The panels were pressed with 1.6 MPa for 4 and 6 min for the three- and five-ply panels,
respectively. The press temperature was 135 and 100°C for the plywood bonded
with phenol and urea resins, respectively. Prior to testing, all the panels were
stored in controlled conditions (50% relative humidity and 20°C) for two weeks.
The compression ratio of plywood was calculated as:
(1)
where:
tp
= total thickness of the veneers before pressing,
= thickness of plywood panel after pressing and conditioning.
Two kinds of specimens were cut from the plywood panels, one with the longitudinal axis parallel and the other with that axis perpendicular to the grain of
face veneers. These specimens were 50 mm wide, and 170 and 210 mm long for
the three- and five-ply panels, respectively. Fifteen specimens for each species,
adhesive type, number of plies, and specimen axis direction were prepared.
Plywood is the layered system which consists of compressed veneers and glue
lines. The flexural rigidity of plywood is the sum of the rigidities of its layers:
EI =
(2)
where: E = modulus of elasticity of plywood,
I = moment of inertia of the full cross section about its neutral axis,
Ei = modulus of elasticity of the ith layer (veneer or glue line),
Ii = moment of inertia of the cross section of the ith layer about the neutral
axis of the full cross section.
50
Consider the plywood strips subjected to bending, in which the grain direction
of the face plies runs parallel or perpendicular to the longitudinal axis of the strip
(fig.1): when glue lines are neglected, the flexural rigidity of the strip is the sum of
the rigidities of the plies with the longitudinal axis parallel to their grain and the
plies with that axis perpendicular to their grain:
E1I2 = ExI2x + EyI2y
(3)
E2I1 = EyI1y + ExI1x
(4)
where: E1 and E2 = modulus of elasticity in the bending of the plywood strip with
the longitudinal axis parallel and perpendicular to the grain
direction of the face plies, respectively,
I2 and I1 = moment of inertia of the cross section of the plywood strip
with the longitudinal axis parallel and perpendicular to the
grain direction of the face plies about the neutral axis 2 and
1, respectively,
Ex and Ey = Young’s modulus of the veneer in the grain and perpendicular
to grain directions, respectively,
I2x and I1x = moment of inertia of all the veneer plies with the longitudinal
axis parallel to the grain about the neutral axis 2 and 1, respectively,
I2y and I1y = moment of inertia of all the veneer plies with the longitudinal
axis perpendicular to the grain about the neutral axis 2 and 1,
respectively.
Assuming that all compressed veneers are of the same thickness, one obtains:
I1 = I2 ,
I1y = I2x ,
I1x = I2y
(5)
Using the following factors:
,
(6)
and combining eqs (3) – (6) gives the relations:
E1 = AEx + BEy
(7)
E2 = AEy + BEx
(8)
which can be rearranged to expressions for the Young’s moduli of the veneer:
(9)
51
(10)
Eqs (9) and (10) permit the calculation of Young’s moduli Ex and Ey of the veneer
through the experimental determination of elastic moduli E1 and E2 of plywood
strips.
The tested plywoods were multilayered structures consisting of veneers (plies) and glue lines. When Young’s moduli Ex and Ey were determined the glue lines
were neglected as too thin when compared to the veneers. If the glue lines are
considered, eqs (3) and (4) take the following form:
E1I2 = Ex* I2x* + Ey* I2y* + EgIg
(11)
E2I1=Ey*I1y*+Ex*I1x*+EgIg
(12)
where: Ex* and Ey* = Young’s modulus of the veneer in the grain and perpendicular
to grain direction, respectively,
I2x* and I2y*= moment of inertia of all the veneer plies with the longitudinal
axis parallel and perpendicular to the grain about the neutral
axis 2, respectively,
I1x* and I1y*= moment of inertia of all the veneer plies with the longitudinal
axis parallel and perpendicular to the grain about the neutral
axis 1, respectively,
Eg
= Young’s modulus of the glue line,
Ig
= moment of inertia of all the glue lines about the neutral axis.
Using the following factors:
,
,
(13)
and rearranging eqs (11) and (12), one obtains the expressions for Young’s moduli
of the veneer:
(14)
(15)
The factors A*, B* and C* depend on the thicknesses of the veneers and the
glue lines in the plywood. For the five-ply beech plywood bonded with the phenol
52
adhesive, the average veneer and glue line thicknesses determined by microscopic
measurements were 1.33 and 0.07 mm, respectively [Wilczyński 2011]. The factors A*, B* and C* calculated by eqs (13) on the basis of these thicknesses were
equal to 0.773, 0.202 and 0.025, respectively.
The moduli E1 and E2 were determined in the bending test, as shown in
fig. 2, using an Instron 3367 machine and a deflectometer measuring the deflection
with an accuracy of 0.001 mm. The span l was equal to 24 times the thickness tp of
plywood, the distance l1 for measuring the specimen deflection was 5/6 of the distance between the loading heads. The bending speed was 2 mm/min. The values
of the moduli E1 and E2 were calculated using the formulas:
,
(16)
where: ΔF = increment of load on the straight line portion of the load-deflection
curve,
Δw = increment of deflection corresponding to ΔF.
The obtained data were statistically analyzed using the Statistica version 10.
A two-way analysis of the variance (ANOVA) was conducted to determine the significance of the effects of wood species and adhesive type on the moduli E1 and E2.
Tukey’s test was also applied to evaluate the statistical significance between the mean
values of the moduli of plywood made from the different wood species and resin types.
Results
The results of the bending tests, the mean values and the standard deviations of
the elastic moduli of the examined plywood, are given in table 2. The results of
the ANOVA analysis showed that both moduli E1 and E2 only depend significantly
on veneer wood species (table 3). Tukey’s test results are shown in table 1. The
values with different letters for given modulus are significantly different at the 5%
significance level.
Considering the results of the statistical analysis, the specimens with phenol
and urea adhesives were included in one group. The mean values of the moduli
E1 and E2 for these groups were the basis for calculating Young’s moduli of the
veneer, in the grain direction, Ex, and in the direction perpendicular to grain, Ey, in
plywood expressed by eqs (9) and (10) (table 4). The factors A and B, expressed
by eqs (6), were equal to 0.963 and 0.037, respectively, for the three-ply plywood,
and 0.792 and 0.208, respectively, for the five-ply plywood.
The moduli Ex and Ey of the veneer in the 5-ply plywood are about 4% and 5%
greater than those in the three-ply plywood, for the pine and beech plywood, respectively. This is the result of a greater compression of five-ply plywood (table 4).
53
Table 2. Elastic moduli of tested plywood
Tabela 2. Moduły sprężystości testowanych sklejek
Three-ply plywood
Sklejka trzywarstwowa
Wood species
Resin type
Gatunek
drewna
modulus E1
(MPa)
Rodzaj żywicy
modulus E2
(MPa)
moduł E1
(MPa)
moduł E2
(MPa)
Five-ply plywood
Sklejka pięciowarstwowa
modulus E1
(MPa)
modulus E2
(MPa)
moduł E1
(MPa)
moduł E2
(MPa)
urea-formaldehyde
pine
sosna
mocznikowo-formal- 13790 (1260)a
dehydowa
phenol-formaldehyde
13940 (920)ab
fenolowo-formaldehydowa
beech
1050 (110)a 11730 (1030)a 3520 (320)a
1070 (100)a
11910 (910)a
3540 (290)a
urea-formaldehyde
buk
mocznikowo-formal- 14580 (850)ab
dehydowa
phenol-formaldehyde
14970 (1290)b
fenolowo-formaldehydowa
1450 (130)b 12560 (740)ab 4050 (290)b
1510 (150)b 12880 (960)b 4140 (220)b
Numbers in parentheses are standard deviations
W nawiasach odchylenia standardowe
Values within the same line column followed by different letters are significantly different
at P<0.05
Wartości w tej samej kolumnie oznaczone różnymi literami różnią się istotnie przy P<0.05
Table 3. Two-way ANOVA test on the effects of wood species and resin type on plywood elastic moduli (p-values)
Tabela 3. Dwuczynnikowy test ANOVA wpływu gatunku drewna i rodzaju żywicy na moduły
sprężystości sklejki
Three-ply plywood
Variable
Zmienna
Sklejka trzywarstwowa
modulus E1
modulus E2
modulus E1
modulus E2
0.0018*
<0.0001*
0.0004*
<0.0001*
0.3323ns
0.1001ns
0.2901ns
0.4479ns
0.6692ns
0.2261ns
0.7634ns
0.5864ns
moduł E1
wood species
gatunek drewna
resin type
rodzaj żywicy
wood species x resin type
gatunek drewna x rodzaj żywicy
Five-ply plywood
Sklejka pięciowarstwowa
moduł E2
*Denotes significance at 0.01; ns - not significant at 0.05
*Oznacza istotność przy 0.01; ns - nieistotny przy 0.05
moduł E1
moduł E2
54
Table 4. Elastic moduli of veneers in plywood
Tabela 4.Moduły sprężystości fornirów w sklejce
Wood
species
Gatunek
drewna
pine
sosna
beech
buk
Number of
plies
Modulus Ex (MPa) Modulus Ey (MPa)
Liczba warstw
Moduł Ex (MPa)
Moduł Ey (MPa)
3
5
3
5
14380
14780
15310
15790
550
580
950
1020
Ex/Ey
26.2
25.5
16.1
15.5
Compression
ratio of plywood (%)
Stopień sprasowania
sklejki (%)
5.5
9.2
4.3
7.0
The moduli of the beech veneer are greater than those of the pine veneer.
The modulus Ex of the beech veneer is slightly, approx. 7% greater, whereas the
modulus Ey is considerably greater, about 74%. This disproportion is related to
the anisotropy of the elastic properties of the veneer in the plywood, which can
be expressed by the Ex/Ey ratio. This ratio amounts to about 26 for the pine veneer
and to about 16 for the beech veneer (table 4). The Ex/Ey ratio for the veneer in
the plywood can be compared with the EL/ET ratio for wood. For softwood in general the EL/ET ratio range is from 20 to 24 [Bodig, Goodman 1973; Bodig, Jayne
1993]. For hardwood, the anisotropy of elasticity in the plane LT is smaller than
for softwood, therefore the EL/ET ratio is smaller. According to Hearmon [1948],
for the beech wood with the density of 0.75 g/cm3, moisture content of 11%, and
modulus EL of 13700 MPa, the EL/ET ratio is equal to 12. The greater Ex/Ey ratio
for the veneer compared to the EL/ET ratio for the wood is probably due to peeler
checks caused by the rotary-cut processing.
In comparing the determined moduli Ex and Ey of the veneer in tested plywood with the moduli EL and ET of beech and pine wood, it is found that the average values of the moduli Ex and Ey of the veneer in beech plywood are 15550
and 985 MPa, respectively, whereas the values of the moduli EL and ET of beech
wood with a density of 0.75 g/cm3 and a moisture content of 11% are 13700 and
1140 MPa [Hearmon 1948], respectively. Thus, the value of Ex is greater than the
value of EL, and the value of Ey is smaller than the value of ET. The average values
of the moduli Ex and Ey of the veneer in pine plywood are 14580 and 565 MPa,
respectively. The values of the moduli EL and ET of beech wood are 16300 and
570 MPa, respectively for wood with a density of 0.55 g/cm3 and a moisture
content of 10% [Hearmon 1948], and 12100 and 480 MPa for wood with a density of 0.49 g/cm3 and a moisture content of 12% (Leontiev 1952). Therefore,
the values of the moduli Ex and Ey of the veneer in pine plywood are smaller than
the values of the moduli EL and ET of pine wood with a density of 0.55 g/cm3
and greater than those of pine wood with a density of 0.49 g/cm3. It should be
noticed that the above comparisons have a limited importance. As it has been
pointed out in this paper, the properties of veneers assembled in plywood dif-
55
fer from those of the wood from which the veneers were made. Moreover, the
elastic moduli of a given wood species are affected by many factors, particularly
by its density
In order to calculate the veneer moduli Ex* and Ey*,the modulus Eg of a glue
line should be known. As there are no data about Eg in literature it was assumed
that the value of this modulus can range from 1000 to 10000 MPa. The values
of the veneer moduli Ex* and Ey* for the five-ply beech plywood bonded with the
phenol adhesive calculated by eqs (14) and (15) are given in table 5 and compared
with the veneer moduli Ex and Ey obtained when the glue lines were neglected.
The values of the Ex* are greater than those of the Ex but the relative difference
between these values is very small and ranges from 0.9 to 2.3%. The relative difference between the veneer moduli Ey* and Ey is greater and ranges from 1.9 to
(-19.4%). For other tested plywood these differences are similar. In general,
it can be concluded that the effect of the glue lines on the results of the determination of Young’s moduli of veneer in plywood is negligible.
Table 5. Comparison of Young’s moduli of veneer in plywood calculated by considering and neglecting the glue lines; Eg = Young’s assumed modulus of glue line
Tabela 5. Porównanie modułów Younga forniru w sklejce obliczonych przy uwzględnieniu
i pominięciu spoin klejowych; Eg = założony moduł Younga spoiny klejowej
Eg (MPa)
Ex (MPa)
Ex* (MPa)
1000
5000
10000
15990
16360
16250
16130
(%)
2.3
1.6
0.9
Ey (MPa)
Ey* (MPa)
1030
1050
950
830
(%)
1.9
-7.8
-19.4
Conclusions
The elastic moduli in the bending of plywood strips, the modulus of the strip with
the longitudinal axis parallel and the modulus of the strip with the longitudinal
axis perpendicular to the grain direction of the face plies, are influenced by the
wood species and are not influenced by the resin type.
The elastic moduli of the veneers in five-ply plywood, the modulus in the
grain direction and the modulus in the direction perpendicular to the grain, are
slightly greater than those in three-ply plywood. The moduli of the beech veneer
are greater than those of the pine veneer. The anisotropy of the elastic properties of
the veneer in the veneer plane, expressed by the ratio of the modulus in the grain
direction to the modulus in the direction perpendicular to the grain, is greater for
pine than for beech veneer. The effect of the glue lines that bond the veneers on
their elastic moduli is negligible.
56
References
Bodig J., Goodman J.R. [1973]: Prediction of elastic parameters for wood. Wood Science
5 [4]: 249–264
Bodig J., Jayne B. A. [1993]: Mechanics of wood and wood composites. Krieger Publishing
Co., Malabar, Florida
Curry W. T., Hearmon R. F. S. [1967]: The strength properties of plywood. Part 2. The effect
of the geometry of construction. Forest Products Research, London, Bulletin No. 33
Hearmon R. F. S. [1948]: The elasticity of wood and plywood. Forest Products Research,
London, Special Report No. 7
Lang E. M., Bejo L., Divos F., Kovacs Z., Anderson R. B. [2003]: Orthotropic strength and
elasticity of hardwoods in relation to composite manufacture. Part III: Orthotropic elasticity of structural veneers. Wood and Fiber Science 35 [2]: 308–320
Leontiev N. L. [1952]: Elastic deformation of wood (in Russian). Goslesbumizdat, Moscow
Mansouri H. M., Pizzi A., Leban J.-M. [2006]: Improved water resistance of UF adhesives for
plywood by small pMDI additions. Holz als Roh-und Werkstoff [64]: 218–220
Okuma M. [1976]: Plywood properties influenced by the glue line. Wood Science and Technology 10 [1]: 57–68
Wilczyński M. [2007]: Modulus of elasticity of veneers in beech plywood (in Polish). Przemysł Drzewny [7–8]: 48–50
Wilczyński M. [2011]: Elastic constants of veneer in beech plywood. Folia Forestalia Polonica
Ser. B [42]: 37–47
Wilczyński M., Starecki A., Warmbier K. [2008]: Effect of the thickness of glue layers on
the elastic moduli of veneers in plywood. Annals of Warsaw University of Life Science
SGGW, Forestry and Wood Technology 6 [6]: 225–230
Wilczyński M., Warmbier K. [2009]: Determination of elastic moduli of veneers in plywood.
Effect of the veneer anisotropy. Annals of Warsaw University of Life Sciences-SGGW,
Forestry and Wood Technology [69]: 429–432
List of standards
PN-92/C-89402 [1992]: Plastics. Resins in the liquid state or as emulsions or dispersions.
Determination of apparent viscosity by the Brookfield’s method (in Polish)
BN-67/6317-01 [1967]: Phenol-formaldehyde resins for hot gluing (in Polish)
BN-75/6327-01 [1975]: Liquid amino resins (in Polish)
EN 322:1999 Wood-based panels. Determination of moisture content
EN 323:1999 Wood-based panels. Determination of density
EN 827:2006 Adhesives. Determination of conventional solid content and constant mass solid
57
MODUŁY SPRĘŻYSTOŚCI FORNIRÓW W SKLEJCE
SOSNOWEJ I BUKOWEJ
Streszczenie
Właściwości fornirów w arkuszu sklejki różnią się od ich właściwości w stanie początkowym,
przed prasowaniem arkusza. Forniry w sklejce mają większą gęstość, co jest wynikiem ich
sprasowania i przesycenia klejem. Znajomość właściwości sprężystych tych fornirów umożliwi analizę naprężeń i odkształceń w elementach konstrukcyjnych wykonanych ze sklejki,
w tym stosowanie teorii układów warstwowych. W pracy przedstawiono wyniki badań dotyczących modułów sprężystości fornirów zawartych w sklejce sosnowej i bukowej. Obiektem
badań były sklejki trzy- i pięciowarstwowe sklejone klejem mocznikowo- i fenolowo-formaldehydowym. W pierwszej części badań wyznaczono moduły sprężystości przy zginaniu pasm
sklejek o osi podłużnej równoległej i prostopadłej do kierunku włókien w obłogach sklejki
(rys. 1 i 2). Ich wartości przedstawiono w tabeli 2. Analiza wariancji wykazała, że moduły
sprężystości przy zginaniu sklejki zależą od gatunku drewna sklejki, nie zależą natomiast od
rodzaju użytego kleju (tabela 3). Na podstawie uśrednionych, dla sklejek z żywicą mocznikowo- i fenolowo-formaldehydową, wartości modułów sprężystości pasm sklejki, obliczono
moduły sprężystości fornirów w sklejce: moduł w kierunku włókien i moduł w kierunku prostopadłym do włókien (tabela 4). Pominięto przy tym spoiny klejowe. Dla fornirów w sklejce
pięciowarstwowej uzyskano nieco większe, o około 5%, moduły niż dla fornirów w sklejce
trzywarstwowej. Moduły fornirów bukowych, zwłaszcza moduł w kierunku prostopadłym do
włókien, są większe niż moduły fornirów sosnowych. Stopień anizotropii właściwości sprężystych forniru w jego płaszczyźnie, wyrażony jako stosunek modułu w kierunku włókien do
modułu w kierunku prostopadłym do włókien, jest znacznie większy dla forniru sosnowego
(około 26) niż dla forniru bukowego (około 16). Oszacowano błąd wynikający z pominięcia
spoin klejowych przy wyprowadzeniu wzorów na moduły sprężystości forniru (tabela 5).
Okazał się on mały.
Słowa kluczowe: fornir, sklejka, moduł sprężystości, drewno sosnowe, drewno bukowe
Zbigniew Czech, Magdalena Witczak, Agnieszka Kowalczyk,
Jagoda Kowalska 1
THE INFLUENCE OF RESIDUE MONOMERS ON
SELECTED PROPERTIES OF ACRYLIC PRESSURE–
–SENSITIVE ADHESIVES
Self-adhesive materials manufactured from acrylic polymers, especially acrylic pressure-sensitive adhesives (PSA) are widely used in different industrial applications. The
wide ranges of self-adhesive products comprise self-adhesive tapes which are used for
the mounting of composite plates in the furniture industry. The goal of the investigations
was the synthesis of solvent-based acrylic PSA used as furniture tape and the testing of
the influence of free residue monomers on their properties (tack, peel adhesion, shear
strength, shrinkage). The best performance for self-adhesive tapes in the form of polymeric films with 30 g/m² and 60 g/m² coating weights and containing less than 0.3 wt.%
residue monomers was observed.
Keywords: adhesives, PSA, acrylics, polymer, monomers, tack, peel adhesion,
shear strength, shrinkage
Introduction
Since its introduction half a century ago, pressure-sensitive acrylic adhesive has
been successfully applied in many fields. ��
PSA applications cover the mounting of decorative trims made of PCV, MDF, wood, aluminium, glass and also
in buildings used for roof bow attachment and glass glazing. They are used in
self-adhesive tapes, labels, sign and marking films and protective films as well as
in dermal dosage systems for pharmaceutical applications and in biomedical elecZbigniew Czech, West Pomeranian University of Technology, Szczecin, Poland
Magdalena Witczak, Wood Technology Institute, Poznań, Poland
Agnieszka Kowalczyk, West Pomeranian University of Technology, Szczecin, Poland
Jagoda Kowalska, West Pomeranian University of Technology, Szczecin, Poland
60
Zbigniew Czech, Magdalena Witczak, Agnieszka Kowalczyk, Jagoda Kowalska
trodes. Pressure-sensitive adhesives based on acrylics are available on the market
as solvent-based, water-borne and solvent-free systems. The difference between
pressure-sensitive adhesives and other adhesives, such as contact adhesives,
is in the permanent surface stickiness of the pressure-sensitive adhesives before,
or after, application [Bendek 2006; Gnanou, Fontanille 2002].
The properties useful in characterizing the nature of pressure-sensitive adhesives are: tack, peel adhesion, shear strength and shrinkage. Solvent-based acrylic
PSAs offer several advantages, such as: excellent aging characteristics, resistance
to elevated temperatures and plasticizers, exceptional optical clarity due to the
polymer compatibility, non-yellowing and excellent water resistance. Lower adhesion to non-polar substrates such as PP, PE, EPDM is caused by the polar chemistry of acrylics [Czech 2001].
Nowadays, pressure-sensitive adhesive acrylic solutions are predominantly
manufactured by polymerization from a wide selection of acrylic monomers in a
refluxing organic solvent in the presence of an initiator, such as organic peroxides
or azo compounds. For the manufacture of acrylic pressure-sensitive adhesives,
tackifying common acrylic acid esters are primarily preferred, with C4 – C8 carbon atoms in the alkyl moiety together with other comonomers. The composition
of acrylic polymers that are inherently pressure-sensitive, is a combination of soft
(low Tg – glass transition temperature), hard (high Tg) and functional monomers
[Czech, Wesołowska 2007].
The tack and the peel properties are impacted by the soft or low glass transition temperature monomers such as 2-ethylhexyl acrylate, isooctyl acrylate or
n-butyl acrylate. The harder monomers, e.g. methyl acrylate or ethyl acrylate are
included to provide internal strength. The functional groups containing monomers
such as acrylic acid or 2-hydroxyethyl acrylate are incorporated into the balanced
monomers for specific adhesion to desired substrates and to provide sites in the
form of active centres for cross-linking after coating.
After the synthesis of acrylic pressure-sensitive adhesives, the final acrylic
PSA contains free residue monomers which characteristically smell and worsen
the properties of coated materials such as carrier and carrier-free self-adhesive
mounting tapes [Wicks et al. 2007]. Due to the very high reactivity, acrylic acid
is not present, as a free monomer, in the synthesized pressure-sensitive adhesives.
Residue monomers in synthesized acrylic PSA can be reduced with the addition of
further radical thermal reactive polymerization starter or with post-reaction time
(for medical grade of acrylic PSA often 8 h).
Self-adhesive tapes are manufactured for packing, masking, marking, construction, decoration, protection, mounting and within the field of medicine.
According to their carrier material, double-sided mounting tape may be divided into nonwoven, polymeric films or foam, especially PE foam. These kinds
of mounting-tapes and carrier-free tapes are used in the furniture industry for the
bonding of different furniture components [Mahdavi, Taghizadeh 2005].
The influence of residue monomers on selected properties of acrylic pressure-sensitive adhesives
61
A variety of tapes are used in the furniture industry in the assembly of composite wood panels with veneered surfaces [Skeist, Miron 1981; Bolitsky, Hartman 2001; Spratling 2002; Pederson 2003]. Complex versions of these composite
wood panels are known as “fancy face” veneered surface panels. The current
practice in the furniture industry is to assemble furniture with thin wooden veneers covering a dimensionally stable but cheaper core board, such as particle
board. The decorative wood species desired by consumers, such as oak, maple,
cherry, and others, are expensive and thus are most commonly used in the form
of thin veneers about 0.8 mm. These veneer pieces are often arranged in a sideby-side relationship and fastened together to form a composite panel or veneer
surface.
The aim of the experiments carried out was to study the influence of residue
monomers concentration in acrylic PSA and self-adhesives on the main properties
of acrylic pressure-sensitive adhesives, such as tack, peel adhesion, shear strength
and shrinkage.
Synthesis of a solvent-borne acrylic pressure-sensitive adhesive
The solvent-borne acrylic pressure-sensitive adhesive was synthesized with
50 wt.% polymer content in ethyl acetate at a temperature of approx. 78°C (boiling point of polymerization medium) in the presence of a radical polymerization
starter 0.1 wt.% 2,2’-azo-bis-diisobutyronitrile (AIBN) according to the amount
of monomers by the use of the following mixture of monomers: 30 wt.% isooctyl
acrylate (IOA), 25 wt.% 2-ethylhexyl acrylate (2-EHA), 17 wt.% butyl acrylate
(BA), 10 wt.% ethyl acrylate (EA), 10 wt.% methyl acrylate (MA), 5 wt.% 2-hydroxyethyl acrylate (2-HEA) and 3 wt.% acrylic acid (AA). The polymerization
was conducted in a 1 l four-necked round-bottom flask equipped with a thermometer, condenser, dropping funnel and mechanical stirrer. The polymerization reactor was charged initially with 20 wt.% of ethyl acetate/monomers mixture, and
then polymerization was started at 78°C. The rest of the ethyl acetate/monomers
mixture was added slowly over 2 h and the polymerization reactor was kept at
80°C for 3 h in order to pursue the polymerization in a more uniform manner.
All the monomers used, the polymerization medium, ethyl acetate, and the thermal radical starter AIBN were provided by POLY-CHEM (Germany).
Evaluation of viscosity and molecular weight
The viscosity of the synthesized solvent-borne acrylic pressure-sensitive adhesive
was determined with a Rheomat RM 189 from Rheometric Scientific with spindle
No 3 at 23°C.
62
The molecular weight studies were performed in tetrahydrofurane with
a liquid chromatography system LaChrom: RI Detector L-7490 and LaChrom UV
Detector L-7400 from Merck-Hitachi, equipped with a PLgel 106Å column from
Hewlett-Packard.
Evaluation of residue monomer concentration
The residual monomers in the acrylic PSA synthesized in ethyl acetate and in
dry coated self-adhesive layers were measured with a gas chromatograph Unicam
610, J&W DB-1 column, FID detector and integrator Unicam 4815. The same
method for evaluation of residue monomers in acrylic PSA was used after different post-reaction times following polymerization.
Preparation of self-adhesive layers in the form of carrier-free acrylic films
For the measurement of tack, peel adhesion, shear strength and shrinkage, the
synthesized PSA was cross-linked with 0.3 wt.% (according to polymer content)
cross-linking agent AlACA and, after that, were coated with 30, 60, 90, 120 and
150 g/m² coat weight on a corona-treated 36 µm thick polyester film from Kalle
Chemie (Germany) and dried in an oven for 10 min at 105°C. The dried acrylic
films were protected with thick silicon paper (75 g/m²) from Laufenberg (Germany). Before the tests, the films were stored for 3 days at room temperature and
65% relative humidity.
Measurement of tack, peel adhesion, shear strength and shrinkage
The influence of residue acrylate monomers on pressure-sensitive adhesiveproperties, such as tack, peel adhesion, shear strength and shrinkage is determined by
the AFERA (European Association for the Self Adhesive Tape Industry) standard.
Tack (acc. AFERA 4015). A sample of PSA-coated material 25 mm wide and
178 mm long is bonded to a vertical of clean steel test plate with at least 100 lineal
mm in film contact. The vertical steel test plate is clamped in the jaws of a tensile
testing machine. The scale reading in Newtons is recorded as the tape is peeled
from the steel surface with a constant rate of 100 mm per minute. Loop tack has
the advantage of allowing for the use of wood substrates from Roholl (Germany).
Peel adhesion (acc. AFERA 4001). A sample of PSA-coated material 25 mm
wide and 178 mm long is bonded to a horizontal target substrate surface of a clean
steel test plate with at least 127 mm in firm contact. A 2 kg hard rubber roller is
used to apply the strip. The free end of the coated strip is doubled back nearly touching itself so the angle of removal will be 180°. The free end is attached to the
adhesion tester scale. The steel test plate is clamped in the jaws of a tensile testing
machine, which is capable of moving the plate away from the scale at a constant
rate of 300 mm per minute.
63
Shear strength (acc. AFERA 4012) is a measure at 20°C and at 70°C. Each
test is conducted on an adhesive-coated strip applied to a standard stainless
steel panel in such a manner that a 25 mm × 25 mm portion of the strip is in
fixed contact with the panel, with one end of the strip free at a standard load
of 10 N.
Shrinkage presents the percentage or millimetre change of dimensions of the
PVC foil covered with PSA after PSA cross-linking, and attached to the glass
after keeping it for 3 weeks at a temperature of 60°C. For acceptable application,
shrinkage under 0.5% or 0.5 mm is necessary. Self-adhesive products with shrinkage greater than 0.3% or 0.3 mm are considered unacceptable or only partially
acceptable in the adhesive industry.
Evaluation of viscosity and molecular weight
The apparent viscosity, molecular weights (
– average molecular weight,
– average molecular weight number) and polydispersity (PD) of acrylic PSA were
respectively 11.3 Pa∙s, and
614 000 D,
150 000, PD, 4.1. The synthesized
acrylic PSA is relatively high molecular and shows a relatively small distribution
of molecular weight.
Evaluation of residue monomer concentration
The residue monomer concentrations in synthesized acrylic PSA directly after
polymerization are presented in table 1.
Table 1. Residue monomer concentration in synthesized acrylic PSA
Tabela 1. Stężenie nieprzereagowanych monomerów w otrzymanym poliakrylanowym kleju
samoprzylepnym
Monomer
Monomer
Concentration
Percentage
Stężenie
Udział procentowy
[wt.%]
[%]
IOA
2.9
27.4
2-EHA
2.5
23.6
BA
2.0
18.9
EA
1.6
15.1
MA
1.0
9.4
2-HEA
0.6
5.7
AA
0
0
10.6
100
Total
Suma
64
The concentration of all residue monomers in the synthesized solvent-based
acrylic PSA was relatively high (10.6 wt.%) and the exact concentration values
of used acrylate monomers corresponded to their reactivity. Acrylic acid with an
extremely high reactivity was not present in the synthesized PSA. To reduce the
concentration of residue monomers after polymerization, post-reaction time was
applied. The concentration of residue monomers over a 6 h post-reaction time is
illustrated by fig. 1.
Fig. 1. Concentration of residue monomers as a function of post-reaction time
Rys. 1. Zależność stężenia nieprzereagowanych monomerów od czasu doreagowania
The post-reaction time after polymerization allows the reduction of residue
monomers and improves the quality of self-adhesive products. After 1h of post-reaction time, the total measurement of residue monomers concentration attained
7.7 wt.%, after 3, 5 and 6h – 3.1, 0.8, and 0.6 wt.%, respectively. The decrease in
total residue monomers concentration is dependent on the reactivity of the monomers. For example 2-hydroxyethyl-, methyl- and ethyl acrylates are more reactive
than long chain butyl- 2-ethylhexyl- and isooctylacrylates.
It was very interesting to investigate the influence of the drying time of solvent-based acrylic PSA, in the form of carrier-free self-adhesive, on the concentration of residue monomers as a function of drying time at a constant temperature
and various coating weights of 30, 60, 90, 120 and 150 g/m² of the acrylic polymer
films. This dependence is illustrated by fig. 2.
65
Fig. 2. Concentration of residue monomers as a function of drying time at 105°C for
PSA layers with different coating weights
Rys. 2. Zależność stężenia nieprzereagowanych monomerów od czasu suszenia w temperaturze 105°C dla powłok samoprzylepnych o różnej gramaturze
The obtained results of the tested solvent-based acrylic PSA show that, at the
same drying time, with an increase in the coating weight of PSA layers, the concentration of free acrylate monomers decreases. It is easier to dry thin PSA layers
containing more polymerization medium and free monomers. An extension of the
drying time to 10 min allows the reduction of free monomers at a relatively low
level, between 0.9 wt.% for thick PSA layers with 30 g/m² and 2.3 wt.% for layers
with 150 g/m² coat weight.
Influence of residue monomers on tack, peel adhesion, shear strength and shrinkage
The goal of this part of the experiment was to find the influence of free monomers
concentration in acrylic pressure-sensitive layers on their main performance,
such as tack, peel adhesion, shear strength and shrinkage and to find the most
suitable solvent-based acrylic PSA systems, without the loss of their important
properties.
The details of the investigations carried out for the tested PSA layers are presented in fig. 3–6 (the influence of free monomers on tack – fig. 3, peel adhesion
– fig. 4, shear strength – fig. 5 and shrinkage – fig. 6).
66
Fig. 3. Tack of self-adhesive tapes as a function of free monomers concentration
Rys. 3. Zależność adhezji początkowej samoprzylepnych taśm od stężenia wolnych monomerów
Fig. 4. Peel adhesion of self-adhesive tapes as a function of free monomers concentration
Rys. 4. Zależność adhezji przy oddzieraniu taśm samoklejących od stężenia wolnych monomerów
67
The best tack and peel adhesion values, dependent on the PSA layer coat
weight, were observed when a 150 g/m² thick polymer layer was used. As figs.
4-5 show, the negative influence of free monomers on the tack and peel adhesion
of self-adhesive tapes as a function of their thickness is more visible for tapes
with a higher coat weight such as 150, 120 and 90 g/m², although in the area up to
3 wt.%, the decrease in tack is ignored and the reduction in the peel adhesion level
is considered unacceptable for industrial application.
Typical shear strength resistance testing is performed with a controlled area
of adhesive tape applied to a standard test surface. Because shear failure is the
inability of the pressure-sensitive adhesive to resist continuous stress, any task
that is a measure of stress relaxation within the adhesive gives meaningful data.
A high shear resistant adhesive will maintain the stress, while a poor shear resistant
adhesive will relieve the stress quite rapidly. Fig. 5 presents the shear strength of
acrylic self-adhesive layers dependent on the free monomers concentration in the
polymer layers.
Fig. 5. Shear strength of self-adhesive tapes as a function of free monomers concentration
Rys. 5. Zależność wytrzymałości na ścinanie taśm samoprzylepnych od stężenia wolnych
monomerów
As can be seen in fig. 5, the shear strength of 30 g/m² and 60 g/m² thick PSA
layers tested at 20°C and 70°C stay at the same level until 2 wt.% of free monomers. Firstly, if the concentration of free monomers increases, the cohesion values are significantly reduced. Secondly, the free monomers concentration above
1 wt.% negatively influences other investigated PSA layers with 90, 120 and
68
150 g/m² coat weights. Among the tested PSA layers, the best shear strength level
was observed for acrylic layers with a low coating weight.
Fig. 6. Shrinkage of self-adhesive tapes as a function of free monomers concentration
Rys. 6. Zależność skurczu taśm samoprzylepnych od stężenia wolnych monomerów
Although acrylic polymers have been used successfully as pressure-sensitive
adhesives in a variety of industries, a property inherent to all acrylic PSAs, which
negatively impacts adhesion performance is shrinkage on different surfaces,
for example wood, upon cross-linking. The shrinkage profiles of solvent-borne
acrylic PSA dependent on free monomers content are shown in fig. 10. The best
shrinkage results under 0.3–0.5% were achieved for self adhesive layers between
30 and 120 g/m² containing not more than approx. 2–3 wt.% of free monomers.
The shrinkage run for a 150 g/m² coat weight self-adhesive layer containing more
than 2 wt.% free monomers was completely unacceptable.
Conclusions
The investigations conducted concerning the synthesis of solvent-based acrylic PSA with a determination of the concentration of residue monomers (after
the polymerization process, and after post-reaction time, and in prepared self-adhesive layers with different coating weights) have shown the following
results:
1.The concentration of all residue monomers in synthesized acrylic PSA was
relatively high, about 10.6 wt.%, and corresponded with their reactivity.
69
2.There is an influence of free monomers contents of solvent-based acrylic
pressure-sensitive adhesives on a decrease in the mechanical properties
of coated self-adhesive films such as: tack, peel adhesion, shear strength and
shrinkage.
3.The use of acrylic PSA with a percentage of free monomers higher than
2-3 wt.% negatively influences all the evaluated properties of solvent-based
acrylic PSA, especially the shear strength tested at 20°C and 70°C.
4.The synthesis of acrylic PSA containing less than 1 wt.% of free monomers,
allows excellent tack, peel adhesion, shear strength and shrinkage performance
to be reached.
5.The best results regarding the investigated properties were obtained for carrierfree films characterized by coat weights of 30 g/m² and 60 g/m² containing not
more than 3 wt.% of residue monomers.
6.The unacceptable results with respect to the important evaluated properties are
observed for thick PSA layers with 120 g/m² and 150 g/m² coating weights.
References
Benedek I. [2006]: Developments in Pressure-Sensitive Products, Edited by Taylor & Francis
a CRC Press Book, New York, p. 126-167
Bolitsky R. E., Hartman R. B. [2001]: Veneer tape and method of use. Patent US 6,187,127 B1
Czech Z. [2001]: Solvent-based pressure-sensitive adhesives for PVC sign and marking films,
Journal of Applied Polymer Science, 81[13]: 3212-3219
Czech Z., Wesołowska M. [2007]: Development of solvent-free acrylic pressure-sensitive adhesives, European Polymer Journal, 43 [8]: 3604-3612
Gnanou Y., Fontanille M. [2002]: Organic and Physical Chemistry of Polymers, Wiley-Interscience, New Jersey
Mahdavi H., Taghizadeh S.M. [2005]: The Effect of Alpha Hydroxy Acids on the Tack of
Pressure-sensitive Adhesive. Iranian Polymer Journal 14 [4]: 379-385
Pederson J. C. [2003]: Adhesive measuring tape. Patent US 6,637,124 B2
Skeist I., Miron J. [1981]: History of Adhesives, Journal of Macromolecular Science: Part
A – Chemistry, 15[6]:1151-1163
Spratling M. [2002]: Adhesive materials for flooring and methods of using same. Patent US
2002/0127374 A1
Wicks Z. W., Jones F. N., Pappas S. P., Wicks D. A. [2007]: Organic Coatings, Wiley-Interscience, New Jersey
List of standards:
AFERA 4015 Quick stick
AFERA 4001 Self Adhesive Tape. Peel adhesion of adhesive tape on stainless steel.
AFERA 4012 Self-Adhesive Tapes. Measurement of static shear adhesion
70
WPŁYW NIEPRZEREAGOWANYCH MONOMERÓW NA
WYBRANE WŁAŚCIWOŚCI POLIAKRYLANOWYCH KLEJÓW
SAMOPRZYLEPNYCH
Streszczenie
Materiały samoprzylepne wytworzone na bazie polimerów akrylanowych, w tym poliakrylanowekleje samoprzylepne (PSA) mają powszechne zastosowanie w przemyśle. Do
szerokiej gamy materiałów samoprzylepnych zaliczamy taśmy samoprzylepne, stosowane
przy montażu płyt kompozytowych w przemyśle meblarskim. Celem przedstawionych
badań była synteza używanych w taśmach meblarskich rozpuszczalnikowych klejów samoprzylepnych na bazie poliakrylanów oraz zbadanie wpływu nieprzereagowanych monomerów na ich właściwości (kleistość, adhezja, wytrzymałość na ścinanie, skurcz). Najlepszymi właściwościami charakteryzowały się taśmy samoprzylepne w postaci filmów
klejowych grubości 30g/m2 oraz 60g/m2, zawierających nie więcej niż 0.3% wagowych
nieprzereagowanych monomerów.
Słowa kluczowe: kleje, PSA, poliakrylany, polimery, kleistość, adhezja przy oddzieraniu, wytrzymałość na ścinanie, skurcz
Monika Zajemska1
ANALIZA TEORETYCZNO-EKSPERYMENTALNA
WPŁYWU WSPÓŁSPALANIA ODPADÓW DRZEWNYCH
W FORMIE PALIW REBURNINGOWYCH Z GAZEM
ZIEMNYM NA SKŁAD CHEMICZNY SPALIN
W artykule podjęto problematykę wykorzystania stałych odpadów drzewnych jako
paliw reburningowych, w procesie współspalania z gazem ziemnym. Zaproponowana forma spalania stwarza możliwość nie tylko zagospodarowania odpadów
przemysłu drzewnego, ale również redukcji zanieczyszczeń, a w szczególności tlenków azotu, ze względu na specyfikę metody reburningu. Ze względu na ograniczone
możliwości pomiarowe eksperyment laboratoryjny poszerzono o symulacje numeryczne.
Słowa kluczowe: współspalanie, reburning, odpady drzewne, emisja zanieczyszczeń, numeryczne modelowanie
Wprowadzenie
Ze względu na ograniczone zasoby paliw kopalnych oraz postępujące zanieczyszczenie środowiska, a w szczególności zmiany klimatyczne, będące wynikiem spalania, obserwuje się od pewnego czasu wzrost zainteresowania biomasą,
w tym drewnem odpadowym. Wykorzystanie biomasy do produkcji energii cieplnej oraz elektrycznej w postaci produktów ubocznych z przemysłu drzewnego
pozwala ograniczyć zużycie węgla oraz obniżyć emisję niektórych zanieczyszczeń do atmosfery np. CO2, ze względu na tzw. zerowy bilans dwutlenku węgla.
Dodatkowym efektem ekologicznym jest stosunkowo niska emisja dwutlenku
siarki oraz tlenków azotu. Najprostszym sposobem zagospodarowania odpadów drzewnych jest ich spalanie lub współspalanie z węglem, które na szeroką skalę jest stosowane w energetyce. Głównym źródłem odpadów drzewnych
są tartaki oraz zakłady przerabiające drewno i dostarczające odpady w postaci
pyłu, trocin, wiór, zrzyn i klocków. Dużą grupę stanowi też drewno pochodzące ze starych mebli, opakowań, drewno ogrodowe, rozbiórkowe, jak również
Monika Zajemska, Politechnika Częstochowska, Polska
72
Monika Zajemska
drewno z zabiegów pielęgnacyjnych [Nawrot 2007; Panek – Gondek 2007;
Karwasz 2007].
Energetyczne zagospodarowanie paliw odpadowych pochodzenia roślinnego
jest korzystne nie tylko ze względów ekonomicznych, ale przede wszystkim ekologicznych, o czym świadczą liczne wyniki badań [Cichy i in. 2010; Poskart i in.
2008; Szecówka i in. 2008].
W niniejszym artykule omówiono jeden ze sposobów energetycznego
wykorzystania biomasy w procesie pośredniego jej współspalania z paliwem
konwencjonalnym, którym był gaz ziemny, a mianowicie proces reburningu.
W procesie tym odpady pochodzenia roślinnego stosuje się jako paliwa redukcyjne,
a ich udział w całkowitej ilości ciepła doprowadzanego do procesu nie powinien
przekraczać 20% [Szecówka 2009]. Metoda reburningu oprócz korzyści ekonomicznych, polegających na oszczędności paliw kopalnych cechuje się wysokim
stopniem redukcji zanieczyszczeń. Należy ona bowiem do grupy pierwotnych
metod redukcji emisji szkodliwych produktów spalania, a w szczególności NOx,
które należą do jednych z najbardziej uciążliwych zanieczyszczeń gazowych formowanych podczas spalania.
Istota procesu reburningu polega na wprowadzaniu do komory spalania
w strefę popłomienną dodatkowego paliwa, którym jest paliwo węglowodorowe,
a powstające z jego rozpadu rodniki CHi, reagując z tlenkami azotu, redukują
je do azotu molekularnego. Istotnymi parametrami wpływającymi na skuteczność reburningu są m.in.: stosunek nadmiaru powietrza, stechiometria w strefie
reburningu i czas przebywania reagentów. Proces ten charakteryzuje się dużą skutecznością przy swej prostocie i stosunkowo niskich nakładach inwestycyjnych.
Obok gazu ziemnego, pyłu węglowego czy lekkich olejów opałowych jednym z
paliw węglowodorowych jest również biomasa drzewna w postaci trocin, zrębków, pyłu oraz biogaz. Biomasa stanowi idealne paliwo redukcyjne w procesie
reburningu ze względu na swoje właściwości fizyko-chemiczne, m.in. wysoką
zawartość części lotnych [Golec 2004; Borycka 2009; Ściążko i in. 2006; Kruczek
i in. 2003; Kordylewski 2000].
Ze względu na złożony mechanizm chemiczny procesu współspalania paliw
konwencjonalnych z biomasą, w analizie eksperymentalnej zjawisk towarzyszących procesom spalania wykorzystuje się coraz częściej metody numeryczne
[Williams 2012; Lee i in. 2007; Venturini i in. 2010; Ouimette i in. 2009]. Przykładem jest opisana w niniejszym artykule numeryczna analiza procesu formowania
zanieczyszczeń podczas spalania gazu ziemnego z odpadami drzewnymi.
Cel badań
Zasadniczym celem badań była analiza wpływu współspalania gazu ziemnego
z paliwami w postaci odpadów drzewnych w procesie tzw. reburningu na kon-
Analiza teoretyczno-eksperymentalna wpływu współspalania odpadów drzewnych w formie ...
73
centrację wybranych produktów spalania, a mianowicie tlenków azotu (NOx)
w spalinach.
Zakres badań
Zakres pracy obejmował:
–– przygotowanie próbek: suszenie, rozdrabnianie,
–– analizę składu ziarnowego wytypowanych materiałów,
–– wyznaczenie własności cieplno-fizycznych: oznaczenie zawartości wilgoci
i popiołu, oznaczenie zawartości części lotnych, oznaczenie ciepła spalania
i obliczenie wartości opałowej,
–– wstępny eksperyment „na gorąco” w komorze grzewczej: ustalenie parametrów przepływowych, pomiar stężenia NOx w spalinach wylotowych, pomiar
temperatury na długości komory,
–– zasadniczy eksperyment laboratoryjny z paliwem reburningowym: pomiar
stężenia NOx na wyjściu z komory, pomiar temperatury spalin,
–– symulacje komputerowe.
Metodyka badań
Zaprezentowane w artykule badania obejmowały zarówno eksperyment laboratoryjny, jak i symulacje numeryczne z użyciem profesjonalnego oprogramowania CHEMKIN – PRO. Pierwsze, miały na celu zbadanie wpływu wybranych
materiałów pochodzenia roślinnego współspalanych z gazem ziemnym na skład
chemiczny spalin, a w szczególności stężenie NOx. Ze względu na ograniczone
możliwości pomiarowe, o których wspomniano w dalszej części artykułu, przeprowadzono symulacje komputerowe, który dały pełen obraz formowanych zanieczyszczeń, a także umożliwiły dokonanie obliczeń w szerszym niż eksperyment zakresie.
Zasadnicze badania eksperymentalne wymagały przeprowadzenia szeregu działań wstępnych, mających na celu przygotowanie próbek do badań
„na gorąco”, analizę składu ziarnowego analizowanych materiałów, czy też
określenie własności cieplno-fizycznych. Końcowym etapem przygotowań
do zasadniczych prób było przeprowadzenie wstępnych pomiarów na wygrzanej komorze o ustabilizowanej temperaturze. Określono parametry przepływowe, tj. strumienie powietrza i gazu ziemnego dla spalania ze stosunkiem nadmiaru powietrza =1,07. Ponadto, wyznaczono profil temperatury na
długości komory oraz zmierzono stężenia wybranych produktów spalania,
a następnie przeprowadzono eksperyment zasadniczy z zastosowaniem paliw
reburningowych.
74
Monika Zajemska
Surowce do badań
Analizie poddano dwa rodzaje odpadów drzewnych o różnym stopniu granulacji,
a mianowicie:
–– pył drzewny z zakładu stolarskiego,
–– odpady z tartaku.
Przygotowanie próbek do badań
Przed przystąpieniem do badań wszystkie materiały poddano suszeniu, a następnie
rozdrobnieniu w laboratoryjnym młynku nożowym do frakcji 1 mm. Rozdrobniony materiał przesiewano dodatkowo na sitach o oczkach 1 mm, a pozostałe na sicie
ziarna o rozmiarach powyżej 1 mm zawracano do ponownego rozdrobnienia. Dodatkowo próbki poddano analizie składu ziarnowego za pomocą analizatora IPS U,
służącego do pomiaru wielkości cząstek niesklejających się od 2 do 2000 µm.
Wyznaczanie własności cieplno-fizycznych analizowanych materiałów
Przed przystąpieniem do badań „na gorąco” wytypowane materiały poddano
analizie, mającej na celu wyznaczenie własności cieplno-fizycznych. Zgodnie
z polskimi normami oznaczono:
–– zawartość wilgoci (PN-80/04511),
–– zawartość części lotnych (PN-G-04516),
–– zawartość popiołu (PN-80/G-04512),
–– ciepło spalania i wartość opałową (PN-81/G-04513).
W tabeli 1 zestawiono wybrane własności cieplno-fizyczne analizowanych
materiałów.
Tabela 1. Wybrane własności cieplno-fizyczne analizowanych materiałów
Table 1. Selected thermo-physical properties of analyzed material
Lp.
Paliwo
Fuel
Wartość
opałowa
Ciepło spalania
MJ/kg
MJ/kg
Calorific value
Heat of
combustion
Zawartość
popiołu
Ash contents
%
Zawartość
części lotnych
Contents of
volatile matter
%
Zawartość
wilgoci
Moisture
%
Odpady z przemysłu drzewnego
Waste from wood industry
1
2
Pył
Drzewny
Wood dust
Odpady
z tartaku
Sawmill
waste
17,172
18,502
0,36
76,015
12,2
16,255
17,506
1,32
79,053
6,2
75
Z przeprowadzonej analizy wybranych własności badanych materiałów wynika, że zarówno odpady z zakładu stolarskiego, jak i z tartaku nadają się do
energetycznego wykorzystania, ze względu na dość wysoką wartość opałową
(tabela 1).
Sposób wprowadzania próbek do komory grzewczej
Wprowadzanie do komory eksperymentalnej wytypowanych do badań próbek wymagało odpowiedniego podajnika, który zapewniłby równomierne
podawanie materiału. W tym celu wytypowano dwa urządzenia, a mianowicie
podajnik fluidyzacyjny i podajnik ślimakowy. Pierwszy z wymienionych charakteryzował się wysoką skutecznością rozpylania, w wyniku wytworzenia mieszanki paliwowo-powietrznej, co z kolei wymagało doprowadzenia odpowiedniego
strumienia objętościowego powietrza fluidyzacyjnego. Stwarzało to jednak problemy związane z uzyskaniem atmosfery redukcyjnej (λ < 1), warunku koniecznego dla strefy reburningowej. Zmniejszenie strumienia powietrza powodowało
nierównomierności w doprowadzaniu materiałów, polegające na występowaniu
okresów wytwarzania mieszanki o mniejszej oraz większej koncentracji cząstek stałych, co uniemożliwiało prowadzenie eksperymentów. Ponadto, niektóre próbki ulegały zbrylaniu, co dodatkowo zakłócało pracę podajnika. Drugim
z wytypowanych podajników, był podajnik ślimakowy o stałym wydatku objętościowym próbek. Wprowadzane na wylocie powietrze nadawało odpowiednią dynamikę mieszance pneumatycznej biomasy, co umożliwiało dobre przemieszanie
materiałów ze spalinami pierwotnymi oraz osiągnięcie odpowiedniej atmosfery
(λ < 1) w strefie reakcji.
Stanowisko badawcze
Do przeprowadzenia badań wykorzystano cylindryczną komorę doświadczalną
(rys. 1 i 2) zbudowaną z 12 kręgów betonowych (BOS 145-II) o średnicy wewnętrznej 0,34 m i sumarycznej długości 3,12 m.
Komorę zaizolowano 0,05 m warstwą wełny mineralnej i osłonięto pancerzem z blachy aluminiowej. W początkowym segmencie komory umiejscowiono przemysłowy palnik wirowy o mocy 90 kW, w którym spalano gaz ziemny
o składzie: CH4 = 96,7%, C2H6 = 0,7%, N2 = 2,5%, CO2 = 0,1%. Na końcu komory znajdowało się okno wziernikowe, umożliwiające obserwację procesów
zachodzących w komorze. Na długości komory wykonano otwory pomiarowe
(tabela 2), umożliwiające pomiar temperatury oraz stężeń wybranych produktów spalania, a w szczególności NOx. Paliwa reburningowe w postaci odpadów
drzewnych wprowadzano do komory za pomocą podajnika ślimakowego w odległości ok. 1/3 jej długości od palnika głównego, co podyktowane było warunkami spalania.
76
Monika Zajemska
Rys. 1. Schemat stanowiska eksperymentalnego z komorą ceramiczną: 1 – komora,
2 – palnik wirowy, 3 – otwory pomiarowe, 4 – sonda, 5 – analizator spalin TESTO
360, 6 – komputer, 7 – termoelement PtRh-Pt, 8 – karta pomiarowa, 9 – okno wziernikowe
Fig. 1. The scheme of experimental stand: 1 – chamber, 2 – turbulent burner, 3 – measurement holes, 4 – probe, 5 – flue gas analyzer TESTO 360, 6 – computer, 7 – PtRh-Pt
thermocouple, 8 – measuring card, 9 – eyehole window
Rys. 2. Widok ogólny stanowiska eksperymentalnego od strony wirowego palnika
głównego
Fig. 2. View of the chamber from the side of the burner
Skład spalin mierzono za pomocą analizatora TESTO 350 połączonego
z komputerem, natomiast temperaturę za pomocą termoelementu aspiracyjnego
77
PtRh-Pt. Ilość doprowadzanych mediów gazowych tj. gazu ziemnego i powietrza
mierzono za pomocą rotametrów przepływowych. Strumień paliwa reburningowego wyznaczano z zależności (1):
(1)
gdzie:
– strumień paliwa reburningowego, kg/s,
m – masa wprowadzanej próbki, kg,
τ – czas podawania, s.
Tabela 2. Rozmieszczenie punktów pomiarowych wzdłuż komory eksperymentalnej
Table 2. Distribution of measurement points along the experimental chamber
Numer punktu pomiarowego
Odległość od wlotu palnika
Number of measuring point
Distance from the inlet burner
[m]
1
0.100
2
3
4
5
6
7
8
9
0.370
0.640
0.910
1.180
1.450
1.720
1.990
2.260
10
2.530
11
2.900
Warunki i przebieg prowadzenia eksperymentu
Po wykonaniu prac przygotowawczych przeprowadzono badania na gorąco. Paliwem zasadniczym był gaz ziemny doprowadzany do palnika głównego. W wyniku przeprowadzenia szeregu prób ustalono ostatecznie następujące parametry
pracy komory ceramicznej, a mianowicie:
–– dla głównej strefy spalania:
–– strumień gazu
= 2,835 m3n /h,
–– strumień powietrza
= 29 m3n /h,
–– nadmiar powietrza λ = 1,07,
–– dla strefy reburningu:
–– strumień paliwa reburningowego (tabela 3),
–– nadmiar powietrza λ = 0,95–0,78.
Udział ciepła wnoszonego przez paliwo reburningowe w całkowitej ilości ciepła doprowadzanego do komory obliczano na podstawie zależności:
78
Monika Zajemska
udział w cieple
Qw(paliwo reburningowe)
Qw(gaz ziemny)
(2)
Qw(paliwo reburningowe)
gdzie: Qw(paliwo reburningowe) – strumień paliwa reburningowego, kg/s,
Qw(gaz ziemny)
– masa wprowadzanej próbki, kg,
– czas podawania, s.
W tabeli 3 zestawiono parametry charakterystyczne dla paliwa reburningowego, tj. strumień masowy oraz udział w cieple dla analizowanych materiałów.
Tabela 3. Zestawienie wybranych parametrów charakteryzujących paliwa reburningowe
Table 3. Summary of parameters characterizing the reburning fuel
Lp.
Ordinal
number
1
2
Paliwo reburningowe
Reburning fuel
Pył drzewny
Wood dust
Odpady z tartaku
Sawmill waste
Strumień masy
Udział w cieple
kg/h
%
Mass flux
Heat fraction
0.475
7.683
0.480
7.372
Otrzymane wyniki stężeń tlenków azotu przeliczono na emisję wyrażoną
w mg/s, a następnie określono stopień redukcji emisji NOx w oparciu o zależność
(3):
(3)
gdzie: emisja 1 – emisja NOx na wylocie z komory bez reburningu,
emisja 2 – emisja NOx na wylocie z komory z zastosowaniem reburningu.
Procedura modelowania
Symulacje numeryczne przeprowadzono z użyciem najnowszej wersji profesjonalnego oprogramowania CHEMKIN–PRO, opracowanym w Sandia National
Laboratories. Do obliczeń przyjęto model rozpatrujący procesy spalania zachodzące w tzw. „reaktorze idealnego wymieszania” – Perfectly Stirred Reaktor. Dla
spalania samego gazu ziemnego zastosowano model chemiczny spalania metanu Millera–Bowmana obejmujący 132 reakcje chemiczne oraz 35 pierwiastków
i związków chemicznych, a mianowicie: H2, H, O, O2, OH, HO2, H2O2, H2O, N,
N2, NO, NH, NH2, NH3, HNO, NO2, N2O, CH4, CO2, CO, CH3, CH2, CH, HCO,
C, C2H4, C2H3, C2H5, C2H6, CN, HCNO, HCN, HOCN, HNCO, NCO. Do modelowania procesu reburningu przyjęto model poszerzony o reakcje z udziałem
siarki i jej związków, a mianowicie SO, SO2, SO3, SN, SH, COS, H2S, HSO, HSO,
79
H2SO, HOS, HOSHO. Ostatecznie mechanizm chemiczny obejmował 163 reakcji
chemicznych i 47 pierwiastków i związków chemicznych. Schemat procedury
modelowania przedstawiono na rys. 3.
Rys. 3. Schemat procedury modelowania
Fig. 3. Scheme of numerical modelling procedure
Symulacje numeryczne przeprowadzono dla jednego paliwa reburningowego, a mianowicie dla wiór sosnowych. Analiza techniczna i elementarna ww.
odpadów drzewnych została zaczerpnięta z literatury (C = 52,0%, S = 0,08%,
H = 6,2%, N = 0,12%, O = 41,59%, Cl = 0,01%, W = 4%, A = 0,1%, Qw = 20,23 MJ/kg)
[Williams 2012].
W obliczeniach numerycznych przyjęto pewne uproszczenia, a mianowicie
nie uwzględniono zawartości chloru w paliwie, co, ze względu na mniejszą ilość
reakcji chemicznych w mechaniźmie, znacznie skróciło czas obliczeń.
W pierwszym etapie badań przeprowadzono symulacje numeryczne spalania
samego gazu ziemnego, natomiast w drugim współspalania z odpadami drzewnymi w postaci tzw. paliwa reburningowego. Plik wejściowy obejmował następujące dane:
–– dla spalania gazu ziemnego:
–– skład chemiczny mieszanki gaz ziemny + powietrze wyrażony w udziałach molowych: CH4 = 0,0861; C2H6 = 0,0016; CO2 = 0,0003; N2 = 0,721;
O2 = 0,191,
–– strumień masowy mieszanki gaz ziemny+ powietrze – 0,011 kg/s,
–– ciśnienie 1 atm,
–– czas przebywania – 0,01 s,
–– profil temperatur uzyskany w ramach eksperymentu (rys. 4);
–– dla spalania gazu ziemnego i odpadów drzewnych:
–– skład chemiczny odpadów,
–– strumień masowy odpadów: 0,00011 kg/s; 0,00024 kg/s,
–– udział w cieple – 8%; 15%,
–– ciśnienie – 1 atm,
–– czas przebywania – 1 s,
–– profil temperatur uzyskany w ramach eksperymentu (rys. 4).
80
Monika Zajemska
Rys. 4. Rozkład temperatur wzdłuż komory eksperymentalnej dla spalania samego
gazu i współspalania gazu ziemnego z pyłem drzewnym
Fig. 4. Temperature distribution along the experimental chamber for natural gas combustion and natural gas and wood dust co-combustion
Wyniki i dyskusja
Na rys. 5 przedstawiono stężenie tlenków azotu w spalinach wylotowych dla spalania samego gazu i jego współspalania z odpadami drzewnymi.
Rys. 5. Stężenie tlenków azotu w spalinach wylotowych
Fig. 5. The concentration of nitric oxides in outlet flue gas
81
Na podstawie uzyskanych wyników można stwierdzić, że zarówno pył drzewny z zakładu stolarskiego (21%), jak i odpady drzewne z tartaku (24%) wykazują dobrą skuteczność redukcji emisji NOx, przy niespełna 8% udziale w cieple. Niewiele wyższą skuteczność redukcji tlenków azotu uzyskano dla odpadów
z tartaku, pomimo mniejszego udziału w cieple aniżeli odpady z zakładu stolarskiego. Podyktowane to było wysoką zawartością części lotnych, wyższą niż dla
pyłu drzewnego.
Na rys. 6, 7 i 8 zobrazowano wyniki obliczeń numerycznych składu chemicznego spalin dla różnych warunków prowadzenia procesu. Na rys. 6 przedstawiono
zrzut ekranu pliku wynikowego dla spalania samego gazu.
Rys. 6. Zrzut ekranu pliku wynikowego składu chemicznego spalin na wylocie z komory dla spalania gazu ziemnego
Fig. 6. Screenshot of the output file of the flue gaschemical composition from the outlet
of the chamber for natural gas combustion
Z uzyskanych drogą obliczeń numerycznych wyników badań dla spalania samego gazu ziemnego wynika, że przyjęty do obliczeń model i mechanizm spalania były poprawne, ze względu na dużą zgodność wyników. Nie jest jednak
możliwa szczegółowa analiza wyników numerycznych i eksperymentalnych
pod względem ilościowym, ze względu na ograniczone możliwości pomiarowe.
Analizę porównawczą można przeprowadzić dla wybranych produktów spalania,
wskazywanych przez analizator TESTO, a mianowicie NOx, CO2, O2 i CO. Dla
przykładu, porównując zmierzone wartości tlenków azotu na wyjściu z komory
i te uzyskane drogą obliczeń można zauważyć niewielką różnicę, wynikającą
z przyjętego do obliczeń założenia warunku idealnego mieszania. Stężenie tlenków azotu w spalinach w ramach eksperymentu wyniosło 125 ppm, natomiast
obliczone 114 ppm, przy czym należy podkreślić, że jest to udział NO. Koncentracje pozostałych związków azotu, a mianowicie NO2 i N2O pominięto w rozważaniach, ze względu na śladowy udział w spalinach (rys. 6).
Na rys. 7 i 8 przedstawiono wyniki symulacji współspalania gazu ziemnego
z odpadami drzewnymi dla dwóch różnych udziałów w całkowitym cieple wnoszonym do procesu.
Jak wynika z rys. 7 podczas, współspalania gazu ziemnego z odpadami
drzewnymi obserwuje się niższe wartości stężenia NOx aniżeli dla spalania gazu
ziemnego, na skutek zachodzącej w strefie reburningu redukcji tlenków azotu.
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Monika Zajemska
Rys. 7. Zrzut ekranu pliku wynikowego składu chemicznego spalin na wylocie z komory dla spalania gazu ziemnego i odpadów drzewnych (8-proc. udział w cieple)
Fig. 7. Screenshot of the output file of the flue gas chemical composition from the outlet of
the chamber for natural gas combustion and wood waste (heat fraction – 8%)
W ramach obliczeń otrzymano porównywalną skuteczność redukcji do tej
uzyskanej w eksperymencie, a mianowicie 25%. Duża zgodność wyników świadczy o poprawności przyjętych do obliczeń założeń. Otrzymany w wyniku obliczeń numerycznych skład chemiczny spalin umożliwił szczegółową analizę formowanych w procesie współspalania związków chemicznych, których pomiar
w warunkach eksperymentu jest często niemożliwy lub trudny do realizacji.
Należy wspomnieć, że stosowanie metody reburningu obok zmniejszenia emisji tlenków azotu może prowadzić do wzrostu emisji CO, szczególnie
w przypadku, gdy jego dopalanie jest prowadzone niewłaściwie. Dlatego też, przy
stosowaniu redukcji emisji NOx metodą reburningu, należy koniecznie kontrolować emisje CO, aby nie uzyskać końcowego negatywnego efektu ekologicznego.
Zwiększanie udziału paliwa reburningowego skutkuje bowiem wyższymi wartościami stężenia tlenku węgla (rys. 8). Zwiększa się również udział tlenków siarki
w spalinach.
Rys. 8. Zrzut ekranu pliku wynikowego składu chemicznego spalin na wylocie z komory dla spalania gazu ziemnego i odpadów drzewnych (15-proc. udział w cieple)
Fig. 8. Screenshot of the output file of the flue gas chemical composition from the outlet of
the chamber for natural gas combustion and wood waste (heat fraction – 15%)
83
Niekorzystny efekt wzrastającego stężenia CO można ograniczyć, a nawet
wyeliminować poprzez doprowadzenie dodatkowego powietrza dopalającego.
Podsumowanie
Energetyczne zagospodarowanie paliw odpadowych pochodzenia roślinnego,
a w szczególności analizowanych w niniejszej pracy odpadów drzewnych, jest
korzystne nie tylko ze względów ekonomicznych, ale przede wszystkim ekologicznych, o czym świadczą przeprowadzone wyniki badań. Jednym ze sposobów
wykorzystania odpadów drzewnych do celów energetycznych jest ich współspalanie z innymi paliwami np. z gazem ziemnym (lub węglem) w procesie reburningu, co prowadzi do redukcji zanieczyszczeń, a w szczególności do obniżenia
stężenia tlenków azotu, o czym świadczą przedstawione w pracy wyniki badań.
Metoda reburningu może być stosowana w wielu urządzeniach energetycznych,
zarówno w energetyce zawodowej, jak i przemysłowej. Jako paliwa reburningowe używane są głównie paliwa konwencjonalne, jednak istnieje wiele przesłanek
do zastosowania również biopaliw, ze względu na ich właściwości redukcyjne.
Przeprowadzone badania modelowe potwierdziły dodatkowo, że współspalanie gazu ziemnego z odpadami drzewnymi w procesie reburningu jest skuteczną
metodą obniżania stężenia tlenków azotu. Wyniki tych badań były bardzo zbliżone do wyników badań eksperymentalnych, co świadczy o poprawności przyjętych
założeń. Niewiele niższa wartość stężenia NOx otrzymana w badaniach modelowych wynika z warunku idealnego mieszania reagentów, tj. głównego założenia
w przyjętym do obliczeń modelu.
Ponadto, symulacje numeryczne dostarczyły danych, których uzyskanie
drogą eksperymentów byłoby niemożliwe. Dane te odzwierciedlają szczegółowy
skład spalin dla różnych udziałów paliwa reburningowego. Ze względu na wysokie
stężenie CO jego rzeczywisty pomiar w warunkach eksperymentu nie był możliwy.
Zadawalające wyniki przedstawionych badań wymuszają potrzebę dalszych
eksperymentów z zastosowaniem pulsacji ciśnieniowych, w celu zwiększenia intensyfikacji mieszania, a co za tym idzie uzyskania większej skuteczności obniżenia stężenia tlenków azotu. Należałoby jednak rozpatrzyć bardziej uproszczony model, obejmujący mniejszą liczbę reakcji i związków chemicznych, których
udział w spalinach był śladowy.
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THEORETICAL AND EXPERIMENTAL ANALYSIS OF THE
IMPACT OF WOOD CO-COMBUSTION, AS A REBURNING
FUEL, WITH NATURAL GAS ON THE CHEMICAL
COMPOSITION OF FLUE GASES
Summary
The energy utilization of waste fuels of vegetable origin, in particular wood waste, is beneficial not only for economic reasons, but primarily ecological reasons, as demonstrated
by the research results obtained. One way of utilizing wood waste for energy purposes is
its co- combustion with other fuels, such as natural gas (or coal), in the reburning process,
85
which leads to a reduction in pollution, in particular a reduction in the concentration of
nitrogen oxides.
A reburning method can be used in much power equipment, both in the power industry,
and industry as a whole. Although in the reburning of fuel conventional fuels are mainly
used, there are many reasons to use biofuel, because of its reductive properties. The results
of this research were very close to experimental, proving the accuracy of the assumptions
adopted in the model. The slightly lower NOx concentration value obtained in the model
research is the result of the condition of a perfect stirring of the reactants, ie, the main
assumptions adopted in the calculation model. Furthermore, numerical simulations provided data that would be impossible in the experiments, namely, the detailed composition
of flue gases for different reburning fuel shares. Due to the high concentration of CO,
actual measurement in experimental conditions was not possible. The satisfactory research
results presented in this article create the need for further experiments using a pressure
pulse to increase the intensification of stirring, and thus receive a more effective reduction
in nitrogen oxide concentration . However, a more simplified chemical model should also
be considered, containing a smaller number of reactions and chemical compounds, whose
share in the flue gases is not as large.
Keywords: co–combustion, reburning, wood wastes, pollution emission, numerical modelling
Elżbieta Mikołajczak1
THE PROFITABILITY OF CONVERTING SAWMILL
BY-PRODUCTS INTO ENERGY
An analysis of the profitability of generating energy from sawmill by-products
was carried out by applying a method embracing a number of indicators to facilitate the evaluation.. The research accounted for both those sawmills generating
energy for their own internal usage, setting the profitability threshold of substituting
a given source of energy for post-production wood, as well as those generating
energy from biomass with the intention of further sales. It has been proven that wood
waste is the ideal type of sawmill by-product in relation to all kinds of fuels being
replaced, while energy production from pulp chips with 25% moisture content is the
least profitable, hence they should be sold unprocessed. An entrepreneur generating
energy from biomass purchased outside his plant reaches the highest margin level of
15% when burning wet defibered chips with 50% moisture content and wood waste.
Keywords: wood by-products, generating energy from wood biomass, profitability
of processing.
Introduction
In order to fulfill EU obligations concerning the share of renewable energy in the
overall national energy balance, there has been a rapid growth in the utilization of
biomass, the most easily accessible source of renewable energy in Poland. According to expert estimations [Polityka ekologiczna 2010] if this trend continues,
this will lead by 2020 to a five-fold (20 mln tonnes) increase in energy plant demand for biomass.
The most easily accessible type of biomass is wood biomass. As an energy-generating fuel it can be obtained from eucalyptus, willow, poplar or Pennsylvania mallow plants, forest waste not used by the paper or board industry, post-production waste from sawmills and carpentry houses, as well as waste from
other industry sectors, such as from mines, the building sector or railways.
Currently the most frequently used types of biomass embrace: forest biomass
namely fuel wood and wood of irregular shape - wigs, trimmings, brushwood, and
Elżbieta Mikołajczak, Poznan University of Life Sciences, Poland
88
Elżbieta Mikołajczak
post-production waste from the wood sector in the form of bark, wood particles,
sawdust, wood chips and other wood waste.
According to estimates from the State Forests General Board of Directors,
the technical potential of forestry wood which can be used for energy amounts
to approximately 41.6 PJ (6.1 mln m3). While the technical potential of wood
waste from the wood sector and other sources has been estimated by the Institute
of Wood Technology to have reached 58.1 PJ (8.3 mln m3), the total share of this
type of biomass in the overall technical potential of biomass in Poland (755 PJ)
accounts for 13.2% [Krajowy Plan Działania... 2010].
The basic volume of wood biomass is generated by the wood industry in numerous forms of post-production residues (wood waste). It is estimated that from
100 m3 of forest wood, waste accounts for 64%, including 10 m3 of bark, 15 m3
of wigs, 20 m3 fuel bole (wigs and stumps), and 19 m3 of sawdust and chips. The
main product,lumber, constitutes 36 m3, out of which only 20-25 m3 will, following the conversion process, become part of finished products [Janowicz 2006].
Basic groups of wood by-products, their brief characteristics and areas of usage
are shown in table 1.
Table 1. Characteristics of various groups of wood by-products
Tabela 1. Charakterystyka różnych grup pozostałości drzewnych z przerobu litego drewna
Group
Grupa
1
Origin/characteristics
Źródło pochodzenia/charakterystyka
2
Usage
Zastosowanie
3
––pieces of trunks, wigs and roots between 15 and 30
cm long
kawałki pni, gałęzi i korzeni o długości 15-30 cm
Wastewood
––the leftovers following conversion of logs in
a sawmill: wings and edgings
pozostałości po przecieraniu kłód w tartaku: opoły,
zrzyny
Odpady
kawałko- ––the remains of construction lumber cut to pre-ordered size
we
resztki drewna konstrukcyjnego, przycinanego na wymiar
––remains from the production of half-finished
products (for example strips) cut to particular size
––direct burning
bezpośrednie spalanie
––converting into chips for
cellulose and chipboard
industry and energy sector
przerób na zrębki dla przemysłu
celulozowego i płytowego oraz
energetyki
odpad z produkcji półproduktów (np. fryzów)
przycinanych na wymiar
––by-products of converting wood in sawmills and
carpenter’s workshops
produkt uboczny z przecierania drewna w tartakach
i stolarniach
Sawdust ––difficult for storing
Trociny
trudne w magazynowaniu
––prone to scalding ( beech sawdust)
skłonne do zaparzania (trociny bukowe)
––prone to damp
podatne na zawilgocenia
––direct burning (mainly wet)
bezpośrednie spalanie (głównie
mokre)
––conversion into pellets and
wood briquettes
przerób na granulat drzewny
i brykiety
The profitability of converting sawmill by-products into energy
89
Table 1. Continued
Wood
particles
Wióry
––by-product of converting dry wood in furniture
factories and carpenter’s workshops
produkt uboczny obróbki suchego drewna (skrawanie,
frezowanie) w fabrykach mebli i stolarniach
––small amount of mineral pollutants
niewielka ilość zanieczyszczeń mineralnych
––wooden pieces irregular in shape between 5 and
50mm long
ścinki drzewne o nieregularnych kształtach, długości
5-50 mm.
Wood
chips
Zrębki
drzewne
––product of grinding sawmill residue and secondary
conversion as well as that from the first clearing
and other post-cutting residue
wrażliwe na zmiany wilgotności powietrza
––prone to fungus-related illnesses
podatne na choroby grzybowe
Pył
drzewny
––conversion into pellets and
briquettes
i brykiety
––direct burning in boilers
bezpośrednie spalanie w kotłach
––production of chipboard (defibered chips- with bark) and
paper (pulp chips- debarked)
produkcja płyt wiórowych
(zrębki defibracyjne- z korą)
i papieru (zrębki papiernicze-pozbawione kory)
produkt rozdrobnienia odpadów z przemysłu
tartacznego i przerobu pogłębionego oraz z pierwszego ––used in metallurgy
topnik w hutnictwie
trzebienia drzewostanów, wierzchołków i innych
pozostałości po wyrębach
––converted into pellets and
––sensitive to changes in humidity
Wood
dust
––by-product of converting dry wood in furniture
factories and carpenter’s workshops
odpad z obróbki suchego drewna w fabrykach mebli
i stolarniach
briquettes following previous
grinding (less often)
i brykiety po uprzednim
rozdrobnieniu (rzadziej)
––accessory in the production
of briquettes
dodatek do produkcji brykietów
Bark
Kora
––by-product from converting logs in sawmills and
pulp mills
odpad z korowania kłód w tartakach i celulozowniach
––high content of mineral pollutants
duża zawartość zanieczyszczeń mineralnych
––raw material for briquettes
production (mixed with other
types of wood residue)
surowiec do produkcji brykietów
drzewnych zmieszany z innymi
rodzajami odpadów drzewnych
Source: own elaboration
Źródło: opracowanie własne
Research carried out by the Institute of Wood Technology [Szostak, Ratajczak, Bidzińska, Gałecka 2004] into the Polish industrial wood waste market showed that the majority of post-production waste is generated by the sawmill sector
together with the laminated board sector –approximately 60%. The source of 14%
of this is the furniture sector and 10.4% is generated by the wood panel sector.
In the structure of wood waste the domineering part is taken by solid waste, namely 46.4%. Most of it is generated by the sawmill industry (70.1%), which, due
to its character, is also the leader in the production of sawdust and chips (74.4%).
90
One of the options concerning the use of sawmill post-production wood waste
is its direct conversion into energy. Such a decision concerning the processing of
this type of by-product requires a profitability analysis, which would also take into
account other options as regards its usage. Such an evaluation is made possible by
the formula described by Mikołajczak [2008], that is, the formula of pricing post-production wood waste into energy:
[PLN/m3]
where: Wei –
i
–
cje –
g –
wo –
mj –
p –
kpi –
kti –
(1)
value of a certain type of wood waste of “i” number when processed into energy [PLN/m3],
number of type of wood waste product being processed,
i ϵ <1, n>,
unit sales price of energy obtained from burning by-products
[PLN/GJ],
bulk density of the type of by-product being burnt [t/m3],
absolute moisture of the type of by-product being burnt.
assumed net profit margin level, satisfactory for the producer,
mj: {0,01; 0,05; ... 0,15},
income tax (CIT), for 2011 = 0,19,
unit cost of processing into energy a given type of by-product
of “i” number along with the remaining unit operating costs
[PLN/m3],
unit cost of transporting a given type of by-product of “i” number
to the place of its processing into energy [PLN/m3].
Methodology
The use of sawmill by-products in the direct generation of energy for own purposes
In the case of a sawmill determining the value of wood by-products converted into
energy in accordance with the formula (1), this most frequently means determining
the profitability of substituting a given type of energy source with post-production
wood. Energy obtained from wood waste burning is then used for own use, most
often lumber drying and social needs. It is not aimed at further sales, thus the calculations account for a zero margin level (mj). Then the value of by-products burnt
at the place where they have been generated can be shown as follows:
[PLN/m3]
(2)
91
Because sawmill by-products may substitute any fuel used for energy purposes, their value when processed into energy was determined individually for
each of 7 groups (sawdust: wo = 10% and 50%, defibered chips and pulp chips:
wo = 25% and 50%, wood waste wo = 25%) subsequently replacing them for
various other forms of energy sources. For example, in order to determine in
this type of processing the value of sawdust, which substitutes natural gas, the
assumption was made that cje is a unit price of energy generated from natural gas,
which should be interpreted as sales of energy from wood biomass at the price
level of natural gas.
The use of sawmill by-products in the direct processing into energy with the intention of selling.
In the case of an entrepreneur generating energy from wood biomass with the
intention of further sales, determining the value of the individual types being
processed and comparing this with the price of purchased material being burnt
enables an estimation of the possibility of obtaining an expected net profit margin
level. A producer of wood and wood feedstock selling to the network only the
excess amount of energy not used by himself, should consider the alternative of
selling by-products being assigned for energy usage when evaluating the profitability .
In the calculations here both types of producers have been accounted for, that
is, the producer who uses the energy surplus generated by the by-products for
his own purposes, and sells to the network (excluding costs of transport), as well
as the producer of energy generated from biomass, buying the raw material on
the market (including costs of transport). In both cases, three levels of expected margin have been assumed (mj = 5%, 10%, 15%). The price of the energy
unit (cje), was assumed as the price of electric energy generated from renewable
energy sources. Its level is determined on the basis of the provisions of the Act
on Energy Law [Ustawa 1997] published annually by 31st March in the bulletin
of the President of the Energy Regulatory Office, and equals the average sales
price of electric energy on a competitive market in the previous calendar year. In
2010, this price binding transactions between distributors purchasing energy from
renewable resources from its producers amounted to 197.21 PLN/kWh (for 2011
– 195.34 PLN/kWh),
The profitability of processing sawmill by-products into energy generated as a by-product (excluding cost of transport) and basic (including cost of transport)
A profitability analysis of converting sawmill by-products was carried out based
on the ratios defined by Mikołajczak (2011):
92
–– maximum margin:
(3)
where: megr – maximum margin – the highest margin level to be obtained conditioned by the remaining variables,
cpub – unit sales/purchase price of a given type of by-product [PLN/m3],
–– maximum costs of conversion:
[PLN/m3]
(4)
[PLN/m3]
(5)
–– maximum unit cost of transport:
–– maximum distance for obtaining raw material:
[km]
where: v
skm
(6)
– capacity of by-products being transported by cartage over the distance l [m3],
– unit cost of transport services of by-products to the place of conversion [PLN/km],
–– maximum purchase price of raw material to be processed:
[PLN/m3]
(7)
–– the lowest sales price of generated energy, deemed satisfactory by the producer:
[PLN/GJ]
(7)
where: cemin – minimum sales price of energy.
Results and analysis
The use of sawmill post-production by-products in direct conversion into energy for
own use.
The results of the calculations carried out are shown in table 2. Their analysis
allows us to make the following statements:
93
1. Burning sawdust with a moisture content of 10% may be an economical alternative for all but firewood and coal energy sources. At the same time the
increase in the cost of generating heat units due to the cost of cartage makes
the energy generated from dry sawdust financially unattractive even in comparison with pellets.
2. Using sawdust of 50% moisture content for heat production, due to its lower
price, is more profitable than using each of the fuels under analysis.
3. Heating using wet defibered chips is competitive compared with all the fuels
under analysis even if the chips have to be transported.
4. Using defibered chips of 25% of moisture instead of coal is unprofitable in the
case of their usage in the same place as they have been generated. Transported chips are also uncompetitive in comparison with eco-coal and fireplace
wood.
5. The least profitable fuel among the wood by-products are pulp chips of 25%
moisture content. Those burnt where they have been generated are less profitable than both types of coal and firewood. The need to transport them also
lowers their economic attractiveness in relation to pellets and wooden briquettes.
6. Matchless in comparison with all substituted kinds of fuels is solid wood waste, regardless of the place of further processing.
Table 2. Profitability of generating energy from 10% moisture sawdust (bulk density 0.150 t/m3) and 50% moisture (bulk density 0.250 t/m3), defibered chips of 25%
moisture (bulk density 0.200 t/m3) and 50% moisture (bulk density 0.300 t/m3), pulp
chips of 25% moisture (bulk density 0.200 t/m3) and 50% moisture (bulk density
0.300 t/m3), waste wood of 25% moisture (bulk density 0.200 t/m3), substituted by
various energy carriers
Burnt material
Spalany materiał
Tabela 2. Opłacalność przerobu na energię trocin o wilgotności 10% (gęstość usypowa
0,150 t/m3) i 50% (gęstość usypowa 0,250 t/m3), zrębków defibracyjnych o wilgotności 25%
(gęstość usypowa 0,200 t/m3) i 50% (gęstość usypowa 0,300 t/m3), zrębków papierniczych
o wilgotności 25% (gęstość usypowa 0,200 t/m3) i 50% (gęstość usypowa 0,300 t/m3), odpadów kawałkowych o wilgotności 25% (gęstość usypowa 0,200 t/m3), zastępowanych różnymi
nośnikami
1
Price of
burnt
material
Cena
spalanego
materiału
Type of substituted
energy carrier
Rodzaj zastępowanego
nośnika energii
[PLN/m3]
2
3
Unit price of
substituted
energy carrier
Cena jednostki
energii zastępowanego
nośnika
Value converted into energy
excluding cost
of transport
Value converted into energy
including cost
of transport
[PLN/m3]
[PLN/m3]
[PLN/GJ]
Wartość
w przerobie
na energię
bez kosztów
transportu
4
5
Wartość
w przerobie
na energię
z kosztami
transportu
6
94
Table 2. Continued
1
2
120.00
120.00
trociny, wo = 10%
sawdust, MSTR = 10%
120.00
120.00
120.00
120.00
120.00
120.00
120.00
120.00
103.00
103.00
trociny, wo = 50%
sawdust, MSTR = 50%
103.00
103.00
103.00
103.00
103.00
103.00
103.00
103.00
3
firewood
drewno kominkowe
briquettes
brykiety drzewne
pellets
granulat drzewny
coal bricks
węgiel kostka
węgiel ekogroszek
coal
natural gas
gaz ziemny
fuel oil
olej opałowy
liquified petroleum gas
gaz płynny LPG
electric energy G12
energia elektryczna G12
electric energy G11
firewood
drewno kominkowe
briquettes
brykiety drzewne
pellets
granulat drzewny
coal bricks
węgiel kostka
coal
węgiel ekogroszek
natural gas
gaz ziemny
fuel oil
olej opałowy
gaz płynny LPG
electric energy G12
electric energy G11
4
5
6
45.29
109.32
97.72
54.17
132.63
121.03
53.62
131.19
119.59
42.86
102.94
91.34
45.71
110.44
98.84
66.84
165.91
154.31
96.90
244.80
233.20
108.90
276.31
264.71
119.44
303.98
292.38
138.89
355.02
343.42
45.29
126.71
116.71
54.17
153.73
143.73
53.62
152.06
142.06
42.86
119.32
109.32
45.71
128.02
118.02
66.84
192.31
182.31
96.90
283.75
273.75
108.90
320.26
310.26
119.44
352.34
342.34
138.89
411.50
401.50
95
Table 2. Continued
1
2
120.00
120.00
zrębki defibracyjne, wo = 25%
defibered chips, MSTR = 25%
120.00
120.00
120.00
120.00
120.00
120.00
120.00
120.00
120.00
120.00
zrębki defibracyjne, wo = 50%
defibered chips, MSTR = 50%
120.00
120.00
120.00
120.00
120.00
120.00
120.00
120.00
3
firewood
drewno kominkowe
briquettes
brykiety drzewne
pellets
granulat drzewny
coal bricks
węgiel kostka
coal
węgiel ekogroszek
natural gas
gaz ziemny
fuel oil
olej opałowy
gaz płynny LPG
electric energy G12
electric energy G11
firewood
drewno kominkowe
briquettes
brykiety drzewne
pellets
granulat drzewny
coal bricks
węgiel kostka
coal
węgiel ekogroszek
natural gas
gaz ziemny
fuel oil
olej opałowy
gaz płynny LPG
electric energy G12
electric energy G11
4
5
6
45.29
125.77
117.87
54.17
152.59
144.69
53.62
150.94
143.04
42.86
118.44
110.54
45.71
127.07
119.17
66.84
190.88
182.98
96.90
281.65
273.75
108.90
317.89
309.99
119.44
349.73
341.83
138.89
408.45
400.55
45.29
152.05
145.45
54.17
184.47
177.87
53.62
182.47
175.87
42.86
143.18
136.58
45.71
153.61
147.01
66.84
230.76
224.16
96.90
340.49
333.89
108.90
384.31
377.71
119.44
422.80
416.20
138.89
493.79
487.19
96
Table 2. Continued
1
2
151.00
151.00
pulp chips, MSTR = 25%
zrębki papiernicze, wo = 25%
151.00
151.00
151.00
151.00
151.00
151.00
151.00
151.00
151.00
151.00
pulp chips, MSTR = 50%
zrębki papiernicze, wo = 50%
151.00
151.00
151.00
151.00
151.00
151.00
151.00
151.00
3
firewood drewno
kominkowe
briquettes
brykiety drzewne
pellest
granulat drzewny
coal bricks
węgiel kostka
coal
węgiel ekogroszek
natural gas
gaz ziemny
fuel oil
olej opałowy
gaz płynny LPG
electric energy G12
electric energy G11
firewood
drewno kominkowe
briquettes
brykiety drzewne
pellets
granulat drzewny
coal bricks
węgiel kostka
coal
węgiel ekogroszek
natural gas
gaz ziemny
fuel oil
olej opałowy
gaz płynny LPG
electric energy G12
electric energy G11
4
5
6
45.29
125.77
117.87
54.17
152.59
144.69
53.62
150.94
143.04
42.86
118.44
110.54
45.71
127.07
119.17
66.84
190.88
182.98
96.90
281.65
273.75
108.90
317.89
309.99
119.44
349.73
341.83
138.89
408.45
400.55
45.29
152.05
145.45
54.17
184.47
177.87
53.62
182.47
175.87
42.86
143.18
136.58
45.71
153.61
147.01
66.84
230.76
224.16
96.90
340.49
333.89
108.90
384.31
377.71
119.44
422.80
416.20
138.89
493.79
487.19
97
Table 2. Continued
1
2
105.00
105.00
waste wood, MSTR = 25%
odpady kawałkowe, wo = 25%
105.00
105.00
105.00
105.00
105.00
105.00
105.00
105.00
3
firewood
drewno kominkowe
briquettes
brykiety drzewne
pellets
granulat drzewny
coal bricks
węgiel kostka
coal
węgiel ekogroszek
natural gas
gaz ziemny
fuel oil
olej opałowy
gaz płynny LPG
electric energy G12
electric energy G11
4
5
6
45.29
125.77
117.87
54.17
152.59
144.69
53.62
150.94
143.04
42.86
118.44
110.54
45.71
127.07
119.17
66.84
190.88
182.98
96.90
281.65
273.75
108.90
317.89
309.99
119.44
349.73
341.83
138.89
408.45
400.55
Calculations on the basis of data provided by an entrepreneur utilizing wood by-products for energy
purposes with the following assumptions:
––depreciation in accordance with annual depreciation rate – 7% position 3 symbol KŚT:”Boilers
and energy machines” and rate 2.5%, position 01, symbol KST 10: “Non-residential housing”
[Ustawa 1992],
––investment value including the boiler house – 2 000 000 PLN (boiler 2 326 kW). 1 744 500 PLN,
––remaining operating costs 28 466 PLN per year,
––annual conversion – 2000m3 of by-products,
cje = 54.52 PLN/GJ – average sales price for energy at which distributors are obliged to buy electric
energy from producers generating it from RES, (article. 23 part 2 point 18 letter b) [Ustawa 1997];
average for two years has been accepted: 2010 (197.21 PLN/kWh) and 2011 (195.32 PLN/MWh)
calculated in GJ.
Obliczenia na podstawie danych udostępnionych przez przedsiębiorcę wykorzystującego drzewne produkty uboczne na cele energetyczne, przy następujących założeniach:
––amortyzacja - zgodnie z wykazem rocznych stawek amortyzacyjnych – stawka 7%, pozycja 03, symbol
KŚT 3: „Kotły i maszyny energetyczne” oraz stawka 2,5%, pozycja 01, symbol KŚT 10: „Budynki niemieszkalne” [Ustawa 1992],
––wartość inwestycji łącznie z budynkiem kotłowni – 2 000 000 PLN (kocioł 2 326 kW). 1 744 500 PLN,
––pozostałe koszty operacyjne 28 466 PLN/rok,
––przerób roczny – 2 000 m3 produktów ubocznych,
cje = 54,52 PLN/GJ – średnia cena sprzedaży energii elektrycznej na rynku konkurencyjnym, po której spółki
dystrybucyjne mają obowiązek kupować energię elektryczną od wytwórców z OZE, (art. 23 ust. 2 pkt 18 lit.
98
b) [Ustawa 1997]; przyjęto średnią z dwóch lat: 2010 (197,21 PLN/kWh) i 2011 (195,32 PLN/MWh)
w przeliczeniu na GJ.
The use of sawmill post-production by-products in direct energy generation with
the intention of further sales
The results of calculations presented in table 3 show that for the owner of sawmill
by-products it is more profitable to sell:
–– pulp chips of moisture content of 25% - for all assumed margin levels,
–– dry sawdust, when the producer estimates reaching a 10% and 15% margin level,
–– pulp chips of 50% moisture content – for 15% margin level
–– than to generate energy from them.
An entrepreneur generating energy based on purchased wood biomass wanting to obtain a 5% or 10% margin should not burn pulp chips of 25% moisture
content and dry sawdust. Reaching a 15% margin will only be possible when
using defibered chips with a moisture content of 50% and wood waste.
Table 3. Value of sawmill by-products converted into energy including and excluding
cost of transport
Tabela 3. Wartość tartacznych produktów ubocznych w przerobie na energię z kosztami i bez
kosztów transportu
By-product
price
Type of by-product
Rodzaj produktów ubocznych
Defibered chips
Pulp chips
Wartość odpadów w przerobie na energię
with margin
Cena produktu
ubocznego
with margin
z marżą
5%
[PLN/m3]
w0 = 10%
Value of by-products in conversion divided
into energy
10%
z marżą
15%
5%
10%
15%
without transport cost
including transport cost
[PLN/m3]
[PLN/m3]
bez kosztów transportu
z kosztami transportu
120.00
124.72 115.89 107.05 113.12 104.29
w0 = 50%
103.00
144.57 134.33 124.09 134.57 124.33 114.09
w0 = 25%
120.00
143.50 133.33 123.17 135.60 125.43 115.27
Zrębki defibracyjne w = 50%
0
120.00
173.48 161.19 148.90 166.98 154.69 142.40
w0 = 25%
151.00
143.50 133.33 123.17 135.60 125.43 115.27
151.00
173.48 161.19 148.90 166.98 154.69 142.40
105.00
143.50 133.33 123.17 135.60 125.43 115.27
Sawdust
Trociny
Zrębki papiernicze w = 50%
0
Waste wood w0 = 25%
Odpady kawałkowe
95.45
99
The profitability of processing sawmill by-products into energy generated as
a by-product (excluding costs of transport) and basic (including cost of transport)
Defibered chips of 50% moisture content (mgr = 26,8%) as well as sawdust of
the same moisture content (mgr = 25,3%) produce the highest profitability when
processed into energy (table 4) if burnt in the place where they were produced.
When an energy producer purchases the raw material, the border margin decreases by 4.9% and 2.7% respectively. The owner of pulp chips of 25% moisture
content (mgr = 1,3%) will operate on the limits of profitability. Adding the cost
of transport will make the conversion of that material into energy unprofitable
(mgr = –2,6%).
Subsequent ratios confirm regularities proven earlier in the analysis of border
margin, that is the highest profitability is characteristic of converting defibered
chips of 50% moisture content into energy and the lowest of pulp chips of 25%
moisture content. Hence:
1. The maximum cost of processing including the cost of transport ranges from
13.65 PLN/m3 (pulp chips of 25% moisture content) up to 79.05 PLN/m3 (defibered chips of 50% moisture content).
2. The maximum distance from which the raw material is obtained, resulting
directly from determining the maximum cost of transport ranges from 7 km
(in the case of pulp chips of 25% moisture content) up to 181 km (in the case
of defibered chips of 50% moisture content).
3. The maximum price of purchasing raw material for further processing should not exceed: in the case of dry sawdust: 121.96 PLN/m3, wet sawdust:
144.81 PLN/m3, defibered chips of 50% moisture content: 179.26 PLN/m3,
pulp chips of 25% moisture content: 145.79 PLN/m3 at current (December 2011) prices of unprocessed by-products, respectively: 120 PLN/m3,
103 PLN/m3, 120 PLN/m3, 151 PLN/m3.
4. The lowest sales price of energy generated from pulp chips of 25% moisture content to be accepted by the producer, is higher (56.25 PLN/GJ) than
the price at which the distributors are obliged to purchase electric energy
from the producers of energy generated from renewable energy sources
(54.52 PLN/GJ).
5. The maximum prices of purchasing wood by-products indicate some possibilities of accepting change in this area. The break-even point is the decrease
in prices of pulp chips of 25% moisture content – of 3.5%,an increase in the
price of defibered chips of 50% moisture content – of 49% as well as a price
increase on average of 24% for the remaining by-products, keeping the rest
of the parameters stable.
Type of by-products
151.00
Pulp chips
w0 = 25%
105.00
23.94
14.15
1.31
26.76
16.56
25.30
7.67
20.05
11.50
-2.58
24.12
12.67
20.41
1.11
59.65
48.05
13.65
79.05
44.65
62.88
23.12
48.66
34.76
2.66
65.76
33.66
51.81
13.56
133.98
95.71
7.33
181.07
92.68
142.64
37.32
Maksymalna
odległość
pozyskiwania
surowca*
l
[km]
145.76
179.26
145.76
179.26
145.76
144.81
121.96
* transport 25 m3, stawka 4,54 PLN/km
udział różnego typu opakowań w produkcji i sprzedaży granulatu drzewnego oraz brykietów drzewnych: big bag – 1/3, small bag – 1/3, luz – 1/3.
41.02
46.78
56.25
38.29
45.99
40.78
53.78
Minimalna
Maksymalna cena
cena zbytu
zakupu surowca
energii
do przerobu
cmin
codp
[PLN/GJ]
3
[PLN/m ]
* transport 25 m3, rate 4.54 PLN/km,
share of various types of packaging in production and sales of pellets and briquettes: big bag1/3, small bag – 1/3, in bulk – 1/3.
Odpady kawałkowe
Waste wood
151.00
120.00
Zrębki defibracyjne w =50%
0
w0 =25%
Defibered chips
w0 =50%
120.00
Zrębki papiernicze
103.00
w0 =25%
120.00
w0 =50%
w0 =10%
jednostkowe
koszty
transportu
kt
[ [PLN/m3]
Maximum
Maximum unit
Maximum cost
distance from
Maximum
costs of conversion
Minimum
of transport per
which raw
purchase price of
including transport
selling price
unit
materials can be raw materials for
Maksymalne
of energy
Maksymalne
transported*
conversion
Cena produktu
jednostkowe koszty
basic
ubocznego
przerobu łącznie
byproduction
cpub
z kosztami
production
produkcja
[PLN / m3]
transportu
produkcja
podstawokp + kt
uboczna
wa
[PLN/m3]
Trociny
Sawdust
Rodzaj produktów ubocznych
By-product
price
Marża graniczna
mgr
[%]
Break-even margin
Tabela 4. Opłacalność przerobu drzewnych produktów ubocznych na energię, wytwarzaną jako produkt uboczny (bez kosztów transportu)
oraz podstawowy (z kosztami transportu)
Table 4. Profitability of processing wood by-products into pellets, briquettes and energy generated as by-product (excluding cost
of transport) and basic (including cost of transport)
100
101
Summary
The described method of pricing sawmill by-products when processed into energy
allows for a multilateral analysis of the profitability of this form of their usage.
It is a useful tool for an entrepreneur enabling an economically- sound decision
to be reached concerning how post-production waste from mechanical wood conversion is used. The formula enables a comparison of the profitability of using
generated energy for one’s own purposes with the profitability of selling it to other
buyers and accounting for different margin levels.
References
Janowicz L. [2006]: Biomasa w Polsce. Energetyka 8
Krajowy Plan Działania w zakresie energii ze źródeł odnawialnych [2010]: Ministerstwo
Gospodarki, Warszawa
Mikołajczak E. [2008]: Wood waste value as a function of energy production profitability
criteria. Journal of Agribusiness and Rural Development 3[9]: 111-118
Mikołajczak E. [2011]: Ekonomiczne aspekty przerobu odpadów drzewnych na paliwa ekologiczne. Wydawnictwo Uniwersytetu Przyrodniczego. Poznań, s. 261
Monitor Polski [2010]: Polityka energetyczna państwa do 2030 r. nr 2, poz. 11
Szostak A. Ratajczak E., Bidzińska G., Gałecka A. [2004]: Rynek przemysłowych odpadów
drzewnych w Polsce. Drewno. Prace naukowe. Doniesienia. Komunikaty 47[172]
Ustawa [1992] o podatku dochodowym od osób prawnych z 15 lutego 1992 r. Dz. U. 1992 r.
Nr 21, poz. 86 z późn. zm.
Ustawa [1997] Prawo energetyczne z dnia 10 kwietnia 1997 r. Dz. U. 1997 r. Nr 54 poz. 348
OPŁACALNOŚĆ PRZEROBU TARTACZNYCH PRODUKTÓW
UBOCZNYCH NA ENERGIĘ
Streszczenie
Wykorzystaniu drzewnych produktów ubocznych do produkcji energii sprzyja nie tylko konieczność spełnienia unijnych zobowiązań w zakresie udziału energii odnawialnej
w bilansie energetycznym kraju, ale również zmieniające się relacje cen na rynku nośników energii. Zakłady mechanicznego przerobu drewna, dysponując określonym zasobem
odpadów, dążą do jak najbardziej efektywnego ich zagospodarowania. Jedną z możliwości jest produkcja energii: na cele własne i z zamiarem sprzedaży. W pracy przeprowadzono analizę opłacalności takiego przedsięwzięcia. Zastosowano przy tym metodę
wyceny tartacznych produktów ubocznych w przerobie na energię, która obejmuje szereg
wskaźników umożliwiających przeprowadzenie oceny. Należą do nich: marża graniczna, maksymalne koszty przerobu, maksymalna cena zakupu produktów ubocznych, prze-
102
znaczonych do przerobu, maksymalna odległość pozyskiwania surowca oraz minimalna, możliwa do zaakceptowania przez wytwórcę, cena zbytu wytworzonego produktu.
W badaniach uwzględniono zarówno przedsiębiorstwa tartaczne, wytwarzające energię na
własne cele, oceniając opłacalność zastąpienia określonego rodzaju nośnika energii drewnem poprodukcyjnym, jak i zakłady wytwarzającego energię z biomasy drzewnej z zamiarem sprzedaży. W drugim przypadku, wyznaczoną wartość poszczególnych sortymentów
w przerobie na energię, porównano z ceną zakupu spalanego materiału, ustalając możliwość zrealizowania oczekiwanej marży zysku netto. W przeprowadzonych obliczeniach
rozpatrzono przypadek przedsiębiorcy, który do sieci sprzedaje jedynie nadmiar energii,
wytworzonej z produktów ubocznych na własne cele (bez kosztów transportu), jak i producenta energii wytwarzanej z zakupionego surowca (z kosztami transportu).
Słowa kluczowe: drzewne produkty uboczne, wytwarzanie energii z biomasy drzewnej, opłacalność przerobu.
DONIESIENIA NAUKOWE – RESEARCH REPORTS
Kinga Szentner, Izabela Ratajczak, Bartłomiej Mazela1
IMPROVEMENT OF WATER-BASED WOOD COATING
PERFORMANCE – MTMOS REACTIVITY WITH WOOD
The study analyzed the reactivity of wood with water-based systems containing
methyltrimethoxysilane (MTMOS) and an acrylic binder. A structural analysis
of wood treated with organosilanes and then extracted with water, was performed
using (Fourier transform infrared spectroscopy (FTIR). In the FTIR spectra, the analyzed bands included 1250 cm-1which are responsible for vibrations of SiC and/or
SiO groups. These bands are characteristic for silicon bonds with atoms of carbon
and oxygen originating from the methoxy groups found in organosilanes. The presence of these bands in the spectra proves the occurrence of a reaction between
wood and MTMOS. The concentration of silicon was determined by Atomic absorption spectroscopy (AAS) in treated wood and then extracted with water.
Keywords: wood coatings, organosilanes, acrylic resin, MTMOS, FTIR, AAS
Introduction
Wood coatings based on acrylic resin modified with silicon compounds considerably diminish the water uptake of this material. A structural analysis of the bonds
between the basic chemical compounds and silicone compounds of wood can determine the developed structures and explain the chemical reactions. This explains
the effectiveness of silicone compounds as agents increasing the resistance of
wood to water, and thus to biotic degradation. Donath et al. [2007] treated wood
with alkoxysilanes and other organofunctional silanes. The method relies on the
Kinga Szentner, Poznan University of Life Sciences, Poland
Izabela Ratajczak, Poznan University of Life Sciences, Poland
Bartłomiej Mazela, Poznan University of Life Sciences, Poland
104
Kinga Szentner, Izabela Ratajczak, Bartłomiej Mazela
hydrolysis of alkoxysilanes and the subsequent condensation of the silanol groups
formed within the porous wood surface. This was shown to be an effective method
of reducing the water uptake of wood after cyclic water immersion and drying
exposure [Tingaut et al. 2006]. The enhanced dimensional stability observed after
these treatments is due to the replacement of hydrophilic hydroxyl groups with
hydrophobic substances.
The aim of this study was to investigate the reactivity of the wood with an
aqueous coating system based on acrylic resin, containing MTMOS.
Material and methods
The reaction of a water-based system containing organosilane (methyltrimethoxysilane (MTMOS, CH3Si(OCH3)3) and acrylic resin (Findisp A10) was run through deionized water solutions at room temperature at different volumetric ratios.
The homogenous wood material - Scots pine sapwood (Pinussylvestris L.), in the
form of powder, was treated with silane systems (1/25 w/v) at room temperature with simultaneous stirring with a magnetic bar stirrer for 2 hours. The wood
samples were left in working solutions at room temperature for another 2 hours,
then filtered and dried in air flow at room temperature. The obtained materials
were leached using continuous extraction with deionized water, at a constant ratio
(1/100 w/v) for 2 hours. Homogeneous samples of the wood material, of 5 g each,
were collected from the test material just after treatment, as well as after being
subjected to leaching.
Infrared Spectroscopy
The wood powder samples were mixed with Potassium bromide KBr at
a 1/200 mg ratio. The spectra were registered using an Infinity Series Fouriertransform spectrophotometer (ATI Mattson) at a range of 500–4000 cm-1 and
at a resolution of 2cm-1,registering 64 scans.
Atomic Absorption Spectrometry
The samples were mineralized in a Marsxpress CEM International semi-closed
microwave mineralization system. The solutions obtained by the digestion were
analysed for silicon contents by flame atomic absorption spectrometry (FAAS)
using the Spectra 200 AA spectrometer Varian. The final results were median values of three simultaneous measurements. Analytical curves were prepared on the
basis of a series of freshly prepared standard solutions with a silicon concentration
of 1000 mg/dm3.
Improvement of water-based wood coating performance – MTMOS reactivity ...
105
Fig. 1a and 1c present the FTIR spectra of wood following a reaction with MTMOS and acrylic resin (i.e. after wood treatment), while fig. 1b and 1d – those of
wood after reaction and elution (i.e. after water leaching of treated wood).
It should be emphasized here that a new band of 1750 cm-1 was found in all
spectra after the reaction of homogenous wood with the tested system. The new
band is responsible for the stretching vibrations of the C=O group. The presence
of this band indicates the conversion of wood treated with acrylic resin. This band
is visible also on IR spectra after extraction, which indicates a permanent bond
between the acrylic resin and the wood components.
Fig. 1. Spectra of wood after reaction with MTMOS 1%/acrylic resin 20% (A), wood
after extraction with water (MTMOS 1%/acrylic resin 20%) (B), wood after reaction
with MTMOS 2.5%/acrylic resin 20% (C), wood after extraction with water (MTMOS 2.5%/acrylic resin 20%) (D)
Rys. 1. Widma drewna po reakcji z MTMOS 1%/żywica akrylowa 20% (A), drewna po
ekstrakcji wodą (MTMOS 1%/żywica akrylowa 20%) (B), drewna po reakcji z MTMOS
2,5%/żywica akrylowa 20% (C), drewna po ekstrakcji wodą (MTMOS 2,5%/żywica
akrylowa 20%) (D)
Following the reaction with the systems of acrylic resin/MTMOS, a band of
1250 cm-1 characteristic for Si-C and/or Si-O bonds was recorded in the wood
spectra. This band is also found in the wood spectra after extraction. This is characteristic for a silicon bond with carbon and oxygen atoms originating from the
methoxy group present in organosilanes [Ghosh et al. 2009; Sèbe et al. 2004;
Tjeerdsma, Millitz 2005]. The results of the AAS analysis (silicone concentration)
confirm a high reactivity of wood components with the tested system. The highest
values of the silicon concentration in the wood, amounting to 320 mg/kg, were
recorded for the wood samples treated with 20% acrylic resin and 5% MTMOS.
106
Kinga Szentner, Izabela Ratajczak, Bartłomiej Mazela
Fig. 2. Silicon concentrations in wood after reaction with MTMOS/acrylic resin and
in wood after extraction with water
Rys. 2. Stężenie krzemu w drewnie po reakcji z MTMOS/żywica akrylowa oraz w drewnie po
ekstrakcji wodą
A very low percentage of silicon elution from wood, at its simultaneous high
reactivity, is particularly evident in the case of the system of 20% acrylic resin/
5% MTMOS. This shows a permanent chemical bond between organosilane and
wood, which was not broken in the process of hydrolysis.
Conclusions
The presence of bands at 1250 cm-1(from thebSiC and SiO groups) characteristic
for vibrations of silicon-carbon and silicon-oxygen bonds, shows a chemical reaction between wood and MTMOS. There are bands responsible for vibrations
of SiOCH3 on IR spectra of wood treated with a system and then subjected to
leaching. The presence of these bands proves the permanent character of bonds
between the hydroxyl and methoxy groups of organosilanes. These Si-O-C bonds
are susceptible to hydrolysis. The high concentration of silicon in treated wood
after extraction was compared to the silicon concentration in wood after reaction
with MTMOS. The results confirm the permanent character of the bond between
wood and treatment system.
Acknowledgement
This project (NN 309071736) was financed by the Ministry of Scientific Research and
Information Technology.
Improvement of water-based wood coating performance – MTMOS reactivity ...
107
References
Donath S., Militz H., Mai C. [2007]: Weathering of silane treated wood. Holz a. Roh. u.
Werkst. [65]: 35–42
Ghosh S.C., Militz H., Mai C. [2009]: The efficacy of commercial silicones against blue stain
and mould fungi in wood. Eur. J. Wood Prod. [67]: 159–167
Sèbe G., Tingaut P., Safou-Tchiama R., Petraud M., Grelier S., De Jeso B. [2004]: Chemical reaction of maritime pine sapwood (PinuspinasterSoland) with alkoxysilane molecules: A study of chemical pathways. Holzforschung[58]: 511–518
Tingaut P., Wiegenand O., Militz H., Sèbe G. [2006]: Chemical reaction of alkoxysilane
molecules in wood modified with silanol groups. Holzforschung[60]: 271–277
Tjeerdsma B.F., Millitz H. [2005]: Chemical changes in hydrothermal treated wood: FTIR
analysis of combined hydrothermal and dry heat-treated wood, Holz a. Roh. u. Werkst.
[63]: 102–111
POPRAWA PARAMETRÓW WODOROZCIEŃCZALNEJ
POWŁOKI DO DREWNA – REAKTYWNOŚĆ MTMOS
Z DREWNEM
Streszczenie
Celem pracy było zbadanie reaktywności drewna sosny zwyczajnej (Pinus sylvestris L.)
z wodnym systemem powłokowym na bazie żywicy akrylowej, zawierającym MTMOS
(metylotrimtoksysilan). Analizę strukturalną drewna po reakcji z MTMOSi żywicą akrylową oraz po ekstrakcji wodą, wykonano metodą spektroskopii w podczerwieni (FTIR).
Przedstawione wyniki analizy strukturalnej drewna z MTMOS wskazują na wysoką reaktywność badanego organosilanu z substancją drzewną. Zarejestrowane pasma absorpcji
na widmach IR drewna po reakcji z MTMOS, jak i po ekstrakcji wodą (1250 cm-1) są
odpowiedzialne za drgania grupy SiC i/lub SiO. Pasma te zarejestrowane na widmach
IR drewna z MTMOS są charakterystyczne dla wiązania krzemu z atomem węgla i tlenu
pochodzącym od grupy metoksylowejobecnej w organosilanie. Obecność tych pasm na
widmie świadczy o zajściu reakcji między pyłem drzewnym a organosilanem. Potwierdzeniem jest wysokie stężenie krzemu wykazane w analizie AAS. Bardzo niski procent
wymycia krzemu z pyłu drzewnego, przy wysokiej jego reaktywności, jest szczególnie
widoczny w przypadku mieszaniny: 20% żywicy akrylowej z udziałem MTMOS o stężeniu 5%, jak również MTMOS o stężeniu 2,5%.
Słowa kluczowe: powłoki do drewna, organosilany, żywica akrylowa, MTMOS, FTIR, AAS
Jakub Gawron, Magdalena Szczęsna, Tomasz Zielenkiewicz,
Tomasz Gołofit1
CELLULOSE CRYSTALLINITY INDEX EXAMINATION IN
OAK WOOD ORIGINATED FROM ANTIQUE WOODWORK
The influence of oak wood age on the crystallinity index of cellulose was determined. Antique wood originating from Warsaw woodwork from the middle of the
18th century, the turn of XIXth and 20th century and the middle of the 20th century
was analysed. It was reported, using FTIR spectrometry, that the crystallinity index
increases with wood age. It is consistent with previous examinations in other papers
and shows that the chosen method of crystallinity index analysis is correct.
Keywords: crystallinity degree, cellulose crystallinity, antique wood, Quercus sp.
Introduction
The process of natural wood ageing is a very complicated issue. Specialized literature presents unspecified, often contradictory, opinions about it. The negative influence of UV radiation, temperature and humidity variations or changes in
static and dynamic stresses on wood ageing in residential areas is a commonly
known fact. Seifert [1972] states that the degradation of wood structure is the
effect of natural wood ageing in a closed space. First of all, the destruction of the
polysaccharide chains takes place, as well as in the cellulose, both in ordered and
disordered areas.
Kohara and Okamoto [1955], based on chemical analyses carried out on
wood originating from old Japanese sanctuaries (300–1300 years old), reported that the degree of crystallinity in the cellulose (calculated using the Battist
Jakub Gawron, Warsaw University of Life Sciences, Poland
Magdalena Szczęsna, Warsaw University of Life Sciences, Poland
Tomasz Zielenkiewicz, Warsaw University of Life Sciences, Poland
Tomasz Gołofit, Warsaw University of Technology, Poland
e-mail:[email protected]
110
Jakub Gawron, Magdalena Szczęsna, Tomasz Zielenkiewicz, Tomasz Gołofit
method) increases with the age of the wood. This was explained by the creation
of new cross-bonds between cellulose chains which leads to an increase incrystalline areas.
A knowledge of the degree of crystallinity, meaning the ratio of ordered
(crystalline) and disordered (amorphous) cellulose configuration, is very useful
to the evaluation of wood properties. An increase in cellulose crystallinity causes a lower value of swelling and water sorption, and higher values of density,
hardness and compression strength. The determination of the degree of cellulose
crystallinity may be important for the proper usage of wooden components in
woodwork.
The Crystallinity Index measures the degree of crystallinity. It is easier to
determine with such a common instrumental technique as FTIR. It has been widely used in different papers to define the influence of cellulose crystallinity on
a series of wood and cellulose properties [Mansfield, Meder 2003; Park et al. 2010;
Kataoka, Kondo 1998].
The aim of this paper is to determine the influence of natural wood ageing on
cellulose crystallinity. The results obtained will extend previous knowledge about
the changes in wood during ageing. This will enable a prediction of the behaviour
of wood nowadays and the effective protection of wood, especially antique woodwork.
Oak wood (Quercus sp.) was examined. It was chosen because of the fact that oak
wood together with pine wood (Pinus sp.) were the main materials available for
wooden constructions in previous centuries. Samples were gained from renovated
or pulled down antique buildings built in Warsaw in the middle of the 18th century,
at the turn of 19th and 20th century and in the middle half of 20th century. This is a
unique collection of wood in the shape of furnishing components (floor boards,
paneling, stairs and balustrade components).
Samples were prepared in several stages. In the first stage, the samples were
cut from antique wood fragments. Their dimensions were compatible with standards concerning the determination of basic wood parameters (moisture content
– PN-77/D-4100, density – PN-77/D-04101). The samples were divided into three
groups:
–– group 1: wood from the 20th century (1960),
–– group 2: wood from the turn of 19th and 20th century (1895),
–– group 3: wood from the 18th century (1750).
Then samples of recent wood (group 0 – control samples, 2005 year) with
a similar density and annual increment width were matched to selected samples
from group 1, 2 and 3 (table 1). The next stage consisted of sample disintegra-
Cellulose crystallinity index examination in oak wood originated from antique woodwork
111
tion and fractioning. Afraction of air-dry sawdust, passing through a 0.6 mm and
remaining on a 0.5 mm mesh sieve was taken for analysis. The cellulose which
was used for crystallinity index examination was isolated according to the Seifert
method (PN-92/P-50092).
The crystallinity index was determined with the FTIR method (Thermo Fisher
Scientific Inc. Nicolet 6700). The cellulose samples were dried in a vacuum dryer
before FTIR analysis. 0.6 g KBr was added to 0.003 g of cellulose (1:200 ratio)
and the mixture was homogenized in a Retsch MM400 ball grinder (120 s, 30 Hz).
Samples of 0.3 g mixture were pelletized with a bench press (10000 kG, 5 minutes). The pellets obtained (with 13 mm diameter) were analysed within the range
of wave length between 400 and 4000 cm-1 (64 scans, 2 cm-1 resolution, every
60 minutes background measurement). Each pellet was measured five times at
different points. OMNIC 8.1 software was used for spectral analysis. 2900, 1429,
1370, 895, 670 cm-1 absorption bands were taken for crystallinity index calculations. The following ratios of values were applied:
CI = H1429 cm-1/H895 cm-1
CI = H1370 cm-1/H2900 cm-1
CI = A1370 cm-1/A670 cm-1
where: CI – crystallinity index, A – peak area, H – peak height.
Table 1. Characteristics of analyzed wood
Tabela 1. Charakterystyka analizowanego drewna
Group
Grupa
Density (ρ) [kg·m-3]
Gęstość (ρ) [kg·m-3]
ρ av
sd
0
671
18
1
675
2
680
3
677
Width of annual increments (S) [mm]
Szerokość przyrostów rocznych [mm]
S av
sd
2.2
0.4
20
2.1
0.3
25
2.1
0.3
12
1.9
0.4
Results and Discussion
A comparison of exemplary FTIR spectra of samples from each group is presented in fig. 1. There are no visible differences between them but the values of CI
calculated based on particular ratios (presented in the table 2) indicatethat distinctions might be noted. There are visible tendencies for H1429cm-1/H895cm-1
and A1370cm-1/A670cm-1. The standard deviation for this second ratio is so
high that changes in character may be aberrant. The CI value increases with the
age of the analysed wood. There is no unequivocal dependence for the third ratio (H1370cm-1/H2900cm-1). However, all three ratio values indicate a gradual
increase of CI with wood age which is clearly visible in fig. 2.
112
Fig. 1. Comparison of exemplary FTIR spectra of samples from each group (roman
numbers means the century of sample origin)
Rys. 1. Porównanie przykładowych widm FTIR otrzymanych dla próbek z wszystkich grup
(cyframi rzymskimi zaznaczono wiek pochodzenia drewna)
Fig. 2. Dependence of calculated ratios of FTIR peaks height and area on the wood
age
Rys. 2. Zależność obliczonych stosunków liczbowych wysokości i powierzchni pików FTIR
od wieku drzewa
A higher CI value also means ahigher degree of crystallinity [Drożdżek 2011]
which is equivalent to higher crystalline area volume in cellulose. The observed
phenomenon may be caused by the effect described in the above mentioned paper of Kohara and Okamoto [1955]. Faster decomposition of the amorphous part
of the cellulose which is more susceptible to degrading factors than crystalline
cellulose could be another reason. This has been reported, for example by Gehlen [2010]. Formerly decomposed chains of cellulose are easily removed during cellulose isolation. It cannot be excluded that both of these explanations are
correct.
Cellulose crystallinity index examination in oak wood originated from antique woodwork
113
Conclusion
The crystallinity index changes with the age of the wood. Its values are higher
in antique wood in relation to recent wood. The highest CI value was obtained
for the woodwork from 18th century, the lowest difference compared with recent
wood was denoted for components from the middle of 20th century.
Data from literature cited above confirm such a dependence indicating that
the presented method of determining the crystallinity index is the correct one.
The possibility of wood age determination using the crystallinity index cannot be
excluded but the further experiments should be performed.
References
Drożdżek M. [2011]: Study of cellulose separated by selected laboratory methods from pinewood (Pinus sylvestris L.) and poplar wood (Populus sp.). Doctoral dissertation, WULSSGGW Press, Warsaw
Gehlen M. K. [2010]: Kinetics of autocatalytic acid hydrolysis of cellulose with crystalline
and amorphous fractions. Cellulose [17]: 245–252
Kohara J, Okamoto H. [1955]: Studies on the permanence of wood. XI: The crystallized
region of cellulose in old timbers. Journal of Applied Physics [19, 11]: 491–506
Kataoka Y., Kondo T. [1998]: FT-IR Microscopic analysis of changing cellulose crystalline
structure during wood cell wall formation. Macromolecules [31]: 760–764
Mansfield S. D., Meder R. [2003]: Cellulose hydrolysis – the role of monocomponent cellulases in crystalline cellulose degradation. Cellulose [10]: 159–169
Park S., O’Baker J., Himmel M. E., Parilla P. A., Johnson D. K. [2010]: Cellulose crystallinity index: measurement techniques and their impact on interpreting cellulase performance. Biotechnology for Biofuels [3]: 10–19
Seifert J. [1972]: Zur Sorption und Quellung von Holz und Holzwerkstoffen. II. Mitteilung:
Das Quellungsverhalten von Holz und Holzwerkstoffen. Holz als Roh- und Werkstoff
[30]: 294–303
List of standards:
PN-77/D-04101 Drewno. Oznaczanie gęstości
PN-77/D-4100 Drewno. Oznaczanie wilgotności
PN-92/P-50092 Surowce dla przemysłu papierniczego. Drewno. Analiza chemiczna
114
BADANIE INDEKSU KRYSTALICZNOŚCI DREWNA
DĘBOWEGO POCHODZĄCEGO Z ZABYTKOWEJ STOLARKI
BUDOWLANEJ
Streszczenie
Wraz z upływem czasu stare drewniane okna, drzwi, podłogi podobnie jak i inne elementy stolarki budowlanej nabierają wartości muzealnej i dlatego, jako świadectwo kultury materialnej minionych stuleci powinno zostać zachowane dla przyszłych pokoleń. Za
pozostawieniem tych elementów, poza argumentami dotyczącymi wartości zabytkowych
i estetycznych, przemawiają właściwości samego drewna, które pomimo upływu czasu
często nie ulegają istotnym zmianom, a materiał ten zachowuje pełne funkcje użytkowe.
Wobec panujących obecnie niejednoznacznych poglądów na temat skutków długotrwałego starzenia się drewna, istnieje potrzeba podejmowania możliwie wielostronnych badań
zmierzających do określenia właściwości zabytkowego drewna.
Celem niniejszych badań było określenie indeksu krystaliczności celulozy w drewnie
pochodzącym z zabytkowej warszawskiej stolarki budowlanej z połowy 18, przełomu
19 i 20 wieku, a także z połowy 20 wieku w porównaniu do drewna pozyskanego współcześnie. Analizę stopnia krystaliczności celulozy przeprowadzono metodą spektrometrii
w podczerwieni FTIR przy użyciu modelu Nicolet 6700, Thermo Fisher Scientific Inc.
Wyniki przeprowadzonych badań pozwalają stwierdzić, że w zabytkowym drewnie,
w porównaniu do drewna pozyskanego współcześnie, następuje zmiana indeksu krystaliczności celulozy. Wielkość zmian uzależniona jest od wieku drewna. Największym
indeksem krystaliczności celulozy charakteryzuje się drewno elementów stolarki budowlanej z 18 wieku, a najmniejszą różnicę wykazało drewno pochodzące z zabytkowych elementów z połowy 20 wieku. Obserwacje te potwierdzają z fachowej literatury,
co świadczy także na korzyść wybranej metody określania indeksu krystaliczności.
Słowa kluczowe: stopień krystaliczności, krystaliczność celulozy, zabytkowe drewno, Quercus sp.
Csilla Vanya
1
DAMAGE PROBLEMS IN GLUED LAMINATED TIMBER
On a number of occasions glued laminated timber breaks apart before the end of
their service life. Examples in Germany (Frese M., Blaß H. J. [2011]) and Denmark (Hansson, Larsen [2005] ) show that this problem is real. In order to find
the causes of the problem, extensive tests were conducted: 16 buildings with glued
laminated timber were examined on the spot, calculations and laboratory work
were carried out. These examinations told us that not only did the properties of the
wooden material cause the damage, but the problems were also due to the wood
used and the method of construction. In the calculations, the external load and
residual stresses occurring in the glued laminated timber were included. Residual tensions in this timber were generated by climatic stresses and also due to the
method of construction. These stresses also accumulated along with the stresses of
the external load. Laboratory work was carried out to measure the delamination.
We examined whether these analyses and calculations prove or disprove the results
of the on- the- spot examinations.
Keywords: stresses in glued laminated timber, internal stresses, manufacturing
stresses, climatic stresses, damage of glued laminated timber, reasons
for damage
Introduction
The first step to finding the reasons for damage in arched glulam timber is deciding on what constitutes an external load and how to calculate the stresses caused by this load. The calculation of the external stresses in glulam arches has
been carried by a number of researchers. Many scientists have published their
solutions: Heimeshoff [1973], Routh and Epple [1981a, 1981b], Schelling [1981],
Möhler [1976a, 1976b], Möhler and Hemmer [1980]. They calculated the stresses
and examined the relationships between the shape of the construction, the statical
model, the cross section and the load distribution types. Most of these calculations
applied isotropic material models.
Noack and Roth [1972] published a calculation method for arched glulam beams loaded with normal forces, shear forces and bending moment. Their work is
Csilla Vanya, University of Pécs, Hungary
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Csilla Vanya
one of the most ambitious research projects ever carried out because they applied
an anisotropic material model. They proved that we can use an ideal elastic and
isotropic model if the radius of the curvature and the height of the beam correspond to some determined conditions. A smaller radius and changing height (nonprismatic beam) caused inaccurate results, therefore we have to use the accurate
anisotropic model in special cases.
In arched glulam beams, internal stresses can be born near the stresses caused by the external load. This situation was studied in Szalai [1985, 1984, 1985,
2001], Garab, Tóth, Szalai, Bejó, Dívós [2010]. He separatelythe stresses caused
by the gluing process and those caused by the climatic changes.
Several authors have examined the correlation between climatic and residual stresses from different points of view. For example Niemz, Bärtschi, Howald
[2005], Angst, Malo [2012], Häglunk [2009], Gustafsson, Hoffmeyer, Valentin
[1998], Olejniczak, Gustafsson [1994], D’Amico, Hrabalova, Müller, Berghofer
[2012].
These three types of stresses are the most important if we want to create
a complete picture of the reasons for damage in glulam beams. To summarise,
three stresses in glulam beams can help us uncover and understand most of the
problems of damage in Hungarian glulam constructions.
Test methodology
Background of the research.
Due to general practical knowledge and the report from our research [Bartal, Rabb
2010], we can say that the reasons for cracking in glulam beams can be the following:
–– change in air humidity,
–– cyclic changing in climatic conditions,
–– hindered shrinking and bulking (mainly at connections),
–– outrunning grain,
–– endgrain lamellas without surface protection,
–– different moisture content in the lamellas,
–– different thickness of the lamellas,
–– perpendicular normal stresses,
–– incorrect gluing (pressure, adhesive application etc.),
–– low quality adhesive,
–– other kinds of technological problems.
Small cracks are not rare in glulam beams. One reason for this is changes
in humidity. Wood is an orthogonal anisotropic material, thus the absorption of
water – as its other physical properties – depends on the grain direction. The absorbed volume of water is higher in the direction of the grain than perpendicular to
Damage problems in glued laminated timber
117
it. The absorbed water builds between the fibers and causes bulking. For the same
reason, loss of water causes shrinking. When air humidity changes too quickly,
this bulking and shrinking cannot follow this process, and the developing internal
stresses cause deformations and cracking in the wood.
Cyclic climatic changes decrease the strength of the wood. After 25 full periods of change, this weakening can be confirmed through measuring, therefore
cyclic climatic changes have the fatigue effect. (A full period is when the moisture
content of wood changes from 30% to 0% and back. This full period cannot occur
in real life, just in part).
Metal connectors such as steel-plates and bolts do not change size due to climatic changes, thus this constructional hardware hinders the bulking and shrinking of the wood elements. This effect is called hindered deformation.
When the height of the beam changes along the length, it is unavoidable that
the grains will run out from the beam. These outrunning grains are more intensive
in the absorption and desorption of water than any other part of the beam surface.
Lamellas with higher moisture content want to bulk, while others with lower moisture content want to shrink. This difference causes relevant inner stresses. Those
beams which have a triangular shape (because of the sloping of the roof) have
outrunning lamellas on the top side and full lamellas on the bottom side. This means that the upper side of the beam is much more hygroscopic than the lower side.
Unprotected end grains are the next problem to be mentioned. A crack can
easily develop when the end of the beam is not closed, because the opened fibers
swallow the humidity very quickly. The adhesive layers have a moisture barrier
effect, but this effect does not protect the outside lamellas.
When there is a difference between the moisture content of the single lamellas, delamination can develop even if D4 adhesive is used during the gluing process. This can be explained by the fact that inner stresses caused by shrinking are
sometimes larger than the strength of any adhered connection.
Stresses which are perpendicular to the length axis of the beam can be a basic
reason for damage of the construction. Some types of external load can cause
these kinds of stresses, and these are added to the inner stresses caused by the
changing moisture content.
General technological rules in Hungary dictate that the moisture content
of the lamellas must be 12 ± 2%. This means that the difference can be almost
4%, and this difference is not even considered a quality fault. However, it can
be proved through calculations that a 4% difference can cause delamination
itself, without any external load. In our opinion, this ± 2% tolerance must be
decreased.
Different lamella thickness is not recommended because the inner stresses
are smaller in thinner lamellas than in thicker ones. Therefore, different lamellas
are not able to deform together, and delamination of the adhesive layer between
a thick and a thin lamella is predicted.
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If we focus on some aspects of the calculation results, we can say that internal stresses are always smaller in glulam beams made of thin lamellas than
the beams made of thick lamellas. Thick lamellas cause further bending stresses in arched glulam beams. This thesis was proved in our earlier research
[Kánnár 2012].
Other parameters, not only the moisture content and the thickness, must also
be the same in the single lamellas. Every kind of inhomogeneity decreases the
strength of the beam. Lamellas with pith can cause general damage of the construction, because part of the wood around the pith has various hygroscopic or
bulking-shrinking properties. This part of wood is called juvenile-wood and it is
recommended that it is excluded from any kind of timber construction.
16 buildings with glued laminated timbers were examined on the spot. The damage noticed during these examinations was partially proved by our calculations
and laboratory work.
List of the observed buildings in Hungary:
1. Harkány Medical Bath Centre pool Nr. III.,
2. Eger Swimming Pool,
3. Hajdúszoboszló City Swimming Pool,
4. Hajdúszoboszló City Training Swimming Pool,
5. Harkány High School,
6. Eger Water Adventure Park,
7. Mohács City Swimming Pool,
8. Kisharsány Church,
9. Bennet Business Centre, Comacchio Italy,
10.Harkány Medical Bath Centre Water Adventure Pool,
11.Hajdúszoboszló Water Adventure Pool,
12.Tapolca Event Hall,
13.Harkány Medical Bath Centre pool ‘B’,
14.Pécs Market Hall,
15.Sopron City Swimming Pool,
16.Sopron City Sport Arena.
Our “on site” experiments were the following: We examined 16 buildings
altogether, and we found manufacturing or building faults in 4 cases. The lamellas in the beams of pool Nr. III. in Harkány (1) were screwed together, because
maintenance personnelfound delamination problems during building control. The
beams of the swimming pool in Eger (2) were strengthened with bolts, perhaps
to repairfaults in manufacturing. The bolts were sinked and covered with the outside lamellas. The beams of the swimming pool in Hajdúszoboszló (3) had been
standing in the rain for years, before the building was ready, and this outdoor
climate caused delamination in the adhesive layers. The builders made steel bandage elements to strengthen the construction (fig. 1). The oak glulam beams of the
yacht-club were seriously damaged, which can be explained by the use there of
119
an unusual and quite unknown hardwood material, non-structural purpose PUR
adhesive and the unregulated manufacturing process.
Fig. 1. Steel bandage element on the frame column in the pool at Hajdúszoboszló
Rys. 1. Stalowa opaska na kolumnie szkieletu konstrukcji – basen w Hajdúszoboszló
Typical problems were cracks on the ends of the beams, and delamination at
the metal connectors. The bolted connections were hindering the shrinking and
bulking, and the beam showed splits between the bolts. The effect of the hindered
deformation was also examined at the University of West Hungary Testlab.
It also became clear during the on- site inspections that thin lamellas are favorable for glulam beams. For example, the 3 beams of the High School in Harkány
(5) – which were made from thick lamellas – were all damaged, whilst the only
one made of thin lamellas was in good condition.
Thin lamellas are ideal for glulam beams but this may not be enough in every
case to prevent damage. The water-adventure-park in Eger (6) had a special valley
beam between two spherical domes made of thin lamellas. These beams were also
cracked because the two different roofs caused a large load on the beams.
The glulam columns of the city pool Mohács (7) were oversized but these
elements were in good condition. The glulam purlins had quite large shear forces
at the ends, and the steel bolts hindered the deformation, therefore cracks and
delamination developed.
Concentrated forces raise the inclination of the cracks. The beams of the roof
construction of the church in Kisharsány (8) were delaminated at the connection
point of the tie rod. The Comacchio Bennet business house (9) had a special construction, the beams were hanged up at the points which divide the span into three
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equal parts, and the connection could cause cracking. The bearing plate spread the
concentrated force and the damage was avoided.
We also took climate changes into consideration. Where the climate properties were uniform, the beams were generally in a better condition. The adventure pool in Harkány (10) had a retractable roof, and the delamination incidents
were significant. In Eger (6) and Hajdúszoboszló (11), the air conditioning was
continuous, and the climatic properties were uniform, therefore the beams were
in a good condition. The sportshall in Tapolca (12) had no air conditioning
or airing equipment, the building was just heated during the winter. The climate
properties changed with the seasons of the year. The climate properties were more
favorable with continuous air conditioning than in a seasonly heated building.
End grains and outrunning lamellas caused delamination hazards in glulam
beams. The beams over pool Nr. III. in Harkány (1) also had outrunning lamellas,
and this part of the beams cracked. The newly built pool “B” (13) had a glulam
frame construction with outrunning lamellas at the corner, which were also delaminated. The beams in the roof construction of the market hall in Pécs (14) were
cracked at the end grains, but the outrunning lamellas did not cause any damage.
The columns and beams of the city pool in Mohács (7) were both oversized, and
the risk of delamination was very low.
Inhomogeneity of the beams can also cause problems. Wood is an inhomogeneous anisotropic material, but gluing lamination decreases this inhomogeneity,
because the glulam beam is made of thin lamellas. Ultrasound measuring on the
controlled buildings was carried out, and large inhomogeneity in the beams was
found. The theory of the relatively high homogeneity of glulam beams cannot
be proved. For example, beam Nr. 3. in the roof of pool “B” (13) was measured,
and the difference in the values is shown in table 1.
Table 1. Harkány, pool ”B”, beam no. 3 – strength classification of the lamellas
Lamella no.
Lamella nr
Tabela 1. Harkány, basen “B”, belka nr 3 – wytrzymałościowa klasyfikacja lamelli
1
1
MI-04.183Strength
Strength
Strength
-81
class
class of
TechnoMSZ class MSZ
Homo15025
the static
logical
15025
geneous
design
directive
(left end) (right end)
beam
Klasa wyKlasa
Klasa
3.1.1.
Belka
wytrzywytrzyma- trzymałości
Dyrektywa
homogemałości
łości MSZ 15025
technoloniczna
statycznej giczna MIMSZ 15025 (prawy
koniec)
konstrukcji -04.183-81,
(lewy
koniec)
3.1.1.
2
III
3
I
4
5
I
6
I
Valuation
Ocena
7
does not meet the requirements
nie spełnia wymogów
121
Table 1. Continued
1
2
3
2
III
I
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
II
II
II
II
III
II
I
II
III
III
III
II
I
I
II
I
II
II
III
II
I
4
II
I
I
I
II
I
II
I
I
I
II
I
III
I
II
I
II
I
II
I
II
I
II
III
II
II
I
I
II
III
I
I
I
I
6
I
I
I
5
I
X
I
I
I
I
I
I
I
I
II
II
II
II
II
II
II
II
II
II
II
II
II
II
I
I
I
I
I
7
meets the requirements
spełnia wymogi
spełnia wymogi
spełnia wymogi
spełnia wymogi
spełnia wymogi
spełnia wymogi
spełnia wymogi
spełnia wymogi
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The difference was significant, and certain parts of the beam did not meet
either the new norms, or the old ones. The orthotropic behaviour of the wood was
increased by the different MOE of the lamellas. This inhomogeneity had significant influence upon the timber service life of the whole construction. The lamellas
with different MOE behaved unpredictably during climatic changes, and inner
stresses developed. These inner stresses were sometimes as large as the stresses
caused by the external load. These two kinds of stresses combined, and delamination or complete damage occured.
The width of the lamellas was also problematic. The beams were made
of 20 cm wide lamellas for the roof construction of the Comacchio Bennet (9)
building. This uncustomary width could cause delamination even when the utilization rate was low. Delamination of inhomogeneic lamellas was predictable.
The wood species also has an effect on the end product. It is our general experience that the gluing process of hardwoods is always more complicated than the
gluing of softwoods. The beams of the yacht club were made of oak and the gluing
was imperfect, therefore delamination was observable.
Table 2. Calculated cases glulam beams
Tabela 2. Obliczone przypadki belek typu glulam
Lamella
thickness
Grubość
lamelli
Glulam type
Typ elementów
klejonych warstwowo (glulam)
Climatic load (moisture content of the lamellas)
Obciążenie klimatyczne (wilgotność lamelli)
1
2
3
Whole beam u = 12% (no climatic load)
Cała belka u = 12% (brak obciążenia klimatycznego)
10 mm
Top side lamella: u = 16%
All other lamellas: u = 12%
Lamella na górnej stronie: u = 16%
Wszystkie inne lamelle: u = 12%
Homogeneous
glulam beam
(GL28h)
Homogeniczna
belka glulam
(GL28h)
30 mm
10 mm
30 mm
Lamella no. 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.: u = 13%
all other lamellas: u = 12%
Lamella nr 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.: u = 13%
wszystkie inne lamelle: u = 12%
10 mm
Lamella no. 1., 5., 7., 9.: u = 13%
Lamella nr 1., 5., 7., 9.: u = 13%
30 mm
Starting moisture content in lamella no. 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.:
u = 13% all other lamellas: u = 12%,
ending moisture content of the whole beam u = 12%
Początkowa wilgotność lamelli nr 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.: u = 13%
wszystkie inne lamelle: u = 12%,
końcowa wilgotność całej belki u = 12%
10 mm
Starting moisture content in lamella no. 1., 5., 7., 9.: u = 13%
Początkowa wilgotność lamelli nr 1., 5., 7., 9.: u = 13%
30 mm
123
Table 2. Continued
2
3
Whole beam u = 12% (no climatic load)
Cała belka u = 12% (brak obciążenia klimatycznego)
10 mm
1
Top side lamella: u = 16%
All other lamellas: u = 12%
Lamella na górnej stronie: u = 16%
Wszystkie inne lamelle: u = 12%
Combined
glulam beam
(GL28c)
Łączona belka
glulam (GL28c)
30 mm
10 mm
30 mm
Lamella no. 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.: u = 13%
Lamella nr 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.: u = 13%
10 mm
Lamella no. 1., 5., 7., 9.: u = 13%
Lamella nr 1., 5., 7., 9.: u = 13%
30 mm
Starting moisture content in lamella no. 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.:
u = 13% all other lamellas: u=12%,
Początkowa wilgotność lamelli nr 1, 3., 7., 9., 13., 15., 18., 21., 22., 24., 27.,30.: u = 13%
wszystkie inne lamelle: u = 12%,
10 mm
Starting moisture content in lamella no. 1., 5., 7., 9.: u = 13%
Początkowa wilgotność lamelli nr 1., 5., 7., 9.: u = 13%
30 mm
Control examination with calculation
A detailed calculation was made to determine the residual (inner) stresses of different kinds of glulam beams. Moreover, the calculation determined the external
load and a summary of the two kinds of stresses.
To model the real climatic properties, various cases were calculated.
For the examined cases see table 2.
Control examination with laboratory work
The laboratory work was carried out at the University of West Hungary. The first and
most important result is that climatic loads reduced the shear strength and the module
of shear elasticity by about 15%. The reduction could be observed after just 20 days
of cyclic changing. The effect of longer-lasting changes could be much larger.
The examinations proved our calculated theory that thin lamella beams have better
resistance against delamination. It is important to mention that the MSZ EN 391 Norm
describes the method but does not stipulate a limit value, therefore we had to decide if
the results met our expectations or not. In our opinion, this is a serious deficiency, and
we will initiate the introduction of a classification value, at least in Hungary.
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Csilla Vanya
Following our research, theoretical analysis and our skilled experience,
we propose a 5% delamination limit on the whole glulam beam and a 15% limit
on one adhesive layer.
If delamination stays within this limit, the load-bearing capacity of the glulam
beams will meet the expectations, meaning that the adhesive quality, the pressure
and the whole production process is correct.
To compare, we carried out a delamination test on the oak glulam terrace elements at the yacht club. The lamella thickness was 20 mm, and the adhesive was
PUR (for joinery application, not for load-bearing constructions). The testing process was the same as previously (fig. 2). After the test, delamination was almost
100%, and the glulam elements could be separated by hand.
In addition, railway sleepers made of oak were examined. The test specimens
were made by Lignum Európa Ltd. with the Swedish Cascomin 1247 adhesive.
Delamination was more extensive than our proposed limit. Therefore, we can conclude that glulam blocks are not applicable for railway sleepers, even if they are
made of oak.
The results and industrial experience indicate 3 basic rules:
1. Only qualified constructional adhesives are permitted for fabrication of glulam beams.
2. The chemical industry develops adhesives for fir and spruce, because 90–95%
of glulam constructions are made of these 2 wood species. Gluing other species of wood can cause various problems. Fabrication of hardwood glulams
with common adhesives is not recommended.
3. Outdoor climatic conditions can damage even the most resistant adhesives,
therefore unprotected beams or beam parts shall be avoided [Kánnár 2012].
Fig. 2. Delamination on oak test specimens
Rys. 2. Rozwarstwienie na próbkach dębu
125
Test results
Conclusion of the calculations
Normal stresses can be superposed on any kind of inner stresses. It does not matter
which kind of climatic stress or which kind of lamella arrangement we calculate, the
summarized stresses are larger than the stresses caused only by the external load.
In beams glued using thick lamellas, the summed stresses can be many times
larger than the external stresses. In beams glued using thin lamellas, this effect is
not so significant, because the inner stresses are smaller in thin lamellas. The stresses are larger in beams which are made of wood from different strength categories
(so-called combined glulam) than in the homogeneous ones, but the difference is
not significant.
In arched glulam beams, inner stresses perpendicular to the grain can only
develop during manufacture and due to climatic parameters. These stresses can be
called residual stresses, because they are there in the beam after manufacture, without any external loading. Combined lamella quality beams show results approx.
10% worse than the homogeneous ones. The worst situation is when the upper
lamella is wet (u = 16%) but the beam is dry (u = 12%). This situation can occur
in real life: when there is no airing equipment in the building, air humidity can
condense on the bottom side of the roofing, and the condensed liquid water can
soak through the upper side of the beam. Beams made of thick lamellas are more
unfavorable in this case than thin lamella beams.
Greater parts of shear stresses develop from residual stresses. Dependence on
climatic properties is not so significant as in the case of the other kinds of stresses.
The shear-stress distribution is varied and unusual. Combined and homogeneous
glulam beams are more or less the same, but the effect of lamella thickness is important. Lamellas which are three-times thicker cause shear stresses three times as
large. Thin lamella beams are favorable.
If the moisture content of the glulam beam is homogenous, there are no inner
stresses. This phenomenon is irrespective of the value of the moisture content. In
new built glued laminated wooden construction, there is no homogeneity in the
moisture content of the lamellas, at least not before a certain time elapses. Wood
endeavors to be equal in humidity, but this takes time, and during this equalization
process, the superposition of the inner and external stresses can cause damage.
The new EN Norms decrease the strength of wood (safety factor 1.25, environmental damage factor 0.5–0.6 for permanent loads). If we calculate the design
value of strength, and compare with the summarized inner and external stresses,
we can see that the beams are not safe or in some cases the beams do not meet the
requirements of the Norms. It is no wonder that glulam beam constructions become damaged or collapse before the service life of the timber, if manufacturing
regulations or climatic changes are disregarded.
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As a summary, it can be said that engineers do not make correct static calculations, if they do not calculate the residual stresses. If the manufacturer uses
lamellas which are as thin as possible, the effect of the climatic or manufacturing
stresses can be reduced significantly.
Conclusion of the laboratory work
It is prohibited to use non-certified adhesives for gluing load-bearing construction.
Manufacturing of hardwood glulams using common adhesives, which were
developed for fir or spruce wood, is not recommended.
Outdoor climatic properties can damage even the most resistant adhesives,
therefore unprotected beams or beam parts should be avoided [Kánnár 2012].
Acknowledgement
The author is grateful to the Baross Gábor program of the National Office for Research and Technology for financial support for the project (REG ND KFI 09). Further
thanks to Péter RABB and to the employees of Bartal & Rabb Inc. for their help and
teamwork.
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List of standards
EN 386:2001 Glued laminated timber. Performance requirements and minimum production
requirements
ISO 554:1976 Standard atmospheres for conditioning and/or testing. Specifications
MSZ EN 386:2002 Rétegelt-ragasztott fa. Teljesítménykövetelményének és a gyártás
alapkövetelményei
MSZ 2370:2003 Vizsgálati normák légterek
128
Csilla Vanya
PROBLEMY USZKODZEŃ W TARCICY KLEJONEJ
WARSTWOWO
Streszczenie
Wyniki obliczeń potwierdzają obserwacje dokonane w warunkach naturalnych. Naprężenia wewnętrzne spowodowane właściwościami klimatycznymi muszą być uwzględniane
przy projektowaniu, w procesie produkcyjnym oraz użytkowaniu. Badania laboratoryjne
potwierdzają zjawiska widoczne w rzeczywistej konstrukcji budowlanej.
Badania powinny być kontynuowane w celu uzyskania większej ilości informacji na
temat rozwarstwiania oraz opracowania rozwiązań dla projektantów, producentów drewna
typu glulam lub właścicieli budynków.
Słowa kluczowe: naprężenia w tarcicy klejonej warstwowo, naprężenia wewnętrzne, naprężenia
podczas procesu produkcyjnego, naprężenia klimatyczne, uszkodzenia tarcicy
klejonej warstwowo, przyczyny uszkodzeń

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