Determination of the wettability of European lime wood

Determination of the wettability of European lime wood

Annals of Warsaw University of Life Sciences – SGGW
Forestry and Wood Technology № 93, 2016: 99-104
(Ann. WULS - SGGW, For. and Wood Technol. 93, 2016)
Determination of the wettability of European lime wood (Tilia
cordata Mill.) as sculptures and painting supports material
AGNIESZKA KUROWSKA, PAWEŁ KOZAKIEWICZ
Department of Wood Science and Wood Preservation, Faculty of Wood Technology, Warsaw University of Life
Sciences - SGGW, 159 Nowoursynowska St., 02-776 Warsaw
Abstract: Determination of the wettability of European lime wood (Tilia cordata Mill.) as sculptures
and painting supports material. European lime wood, which is the subject of the research, is used in Europe
principally for making sculptures, frames and painting supports. In this paper, the wettability of European lime
wood has been determined by measuring the contact angle of wood wetted with water and diiodomethane, using
the sessile drop method. Surface tension, wetting energy and work of adhesion for the wood - water
and wood - diiodomethane structures have been marked. Surface free energy of the tested wood species
was determined in accordance with the Owens - Wendt method. The course of wetting the wood with polar
liquid, i.e. water, showed considerable dynamics. After 60 s from placing a water drop on the lime wood surface
the contact angle decreased by 70%. When the wood was wetted with diiodomethane, however, the contact angle
decreased by 30%. The dominant component, which was also more variable in time, was the energy which
originated from the polar liquid (water).
Key words:
European lime, wettability, contact angle, surface free energy, wetting energy, work of adhesion,
surface tension
INTRODUCTION
Lime (Tilia cordata Mill.) is a common tree species in Poland; it grows in the entire
plain and in sub - mountainous areas. It is a relatively slow - growing species, but it does not
have high habitat requirements (Gałczyński 1928, Strojny 1981). It is also a longeval tree.
An 18th century author, Fr Krzysztof Kluk, wrote (1778) "it stands unspoilt for more than
a thousand years". Moreover, it grows to considerable size, reaching ca. 40 m in height
and ca. 800 cm in trunk circumference (Strojny 1981).
Lime wood belongs to diffuse - porous wood species without heartwood. Because of its
low density, 350 - 600 kg/m3 in air drying condition (Kollmann and Cöte 1968, Krzysik
1978), and straight fibre composition, lime wood is an easy material for planing, turning
and sculpting (Warywoda 1957, Galewski and Korzeniowski 1958). Many valuable historic
objects (sculptures and painting supports) made of lime wood are found at the present time
in museum collections and churches. These objects are in different states of preservation
(e.g. Popescu et al. 2005, Trochimowicz and Swaczyna 2005, Trochimowicz 2010, Wiłkojć
2012), as this type of wood has low natural durability (only class 5 according
to EN 350-2:1994) and is often attacked by insects and microorganisms (Galewski
and Korzeniowski 1958, Strzelczyk 2004, Kozakiewicz et al. 2011).
In preserving and restoring objects made of lime wood it is often necessary to insert
plug patches made of modern wood. Glued patches are covered and saturated with various
substances. The crucial role in such treatment is played by the characteristics of wettability
as well as the physicochemical properties of lime wood surface, such as the contact angle,
surface tension, wetting energy, work of adhesion, and surface free energy. Quantification
of the above has been the purpose of this paper.
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MATERIAL AND METHODS
European lime wood (Tilia cordata Mill.) was used for the tests. Samples
of 135×135×15 mm were cut in accordance with the principal anatomical section lines of the
wood in such a manner as to obtain tangential section (dominant in lime wood products)
on the broad surfaces (planes). The surfaces of wood samples were planed. The samples
having been brought to air drying condition, wood moisture content was determined
in accordance with ISO 13061-1:2014, and wood density in accordance with the requirements
of ISO 13061-2:2014.
Table 1. Data of surface tension and components of the test liquids
Liquid
Property
Surface tension
Dispersion
[mN/m]
[mJ/m2]
water (H2O)
72.80
21.90
diiodomethane (CH2I2)
50.80
50.80
Polar
[mJ/m2]
51.00
0.00
Acid
[mJ/m2]
25.50
0.00
Base
[mJ/m2]
25.50
0.00
The contact angles in wetting the wood with reference liquids were measured according
to the sessile drop method in Phoenix 300 goniometer manufactured by Surface Electro
Optics. The reference liquids were polar, i.e. water, and nonpolar, i.e. diiodomethane (tab.1).
Surface tension, wetting energy and work of adhesion were determined for the wood - water
and wood - diiodomethane structure. Surface free energy of the wood was determined on the
basis of tests using the Owens - Wendt method (Owens and Wendt 1969). The parameters
characterizing wood wettability were measured after 1, 2, 3, 10, 20, 30, 40, 50 and 60 seconds
from placing the liquid drop on the wood surface. Trend lines illustrating the changes in time
in individual parameters were drawn, parameters of curve equation (yD) were stated, as well
as determination coefficients R2. The statistical study of the tests results was carried out
at a significance level of 0.050.
RESULTS AND DISCUSSION
Lime wood was characterized by 497 kg/m3 density (±11 kg/m3) and 6.41% (±0.6%)
moisture content. The density was typical for this wood species (Galewski and Korzeniowski
1958, Wagenführ 2007), as well as its variation. For example, according to the tests of Sekhar
and Negi (1960) involving 250 logs of 50 different wood species, the variation coefficient
within a single wood species in air drying condition amounts on the average to ca. 6%. The
results of the wettability measurements are presented in figures 1 and 2.
a).
b).
Figure 1. Contact angle (a) and surface tension (b) of the structure lime wood - water (yW), lime wood diiodomethane (yD)
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Lime wood parameters changed significantly within the analysed time span,
i.e. 60 seconds. The changes had exponential function character; they were most rapid in the
first seconds of the tests. The process of wetting the wood with polar liquid, i.e. water,
showed greater dynamics than with nonpolar liquid, i.e. diiodomethane; this is significant
dependence for gluing lime wood and finishing its surface. After 60 s from placing the water
drop on the lime wood surface the contact angle changed from 56o to 16o (i.e. by 71%). In the
case of nonpolar liquid, i.e. diiodomethane, the decrease in contact angle was from 23o to 16o
(by 30%) (fig. 1a). Other effects of wood wetting included changes in liquid surface tension;
they were largest in the drop of water (fig. 1b). The surface tension doubled in 60 s from
placing the water drop on the surface of lime wood. In the case of diiodomethane, however,
the increase in surface tension observed 60 s after placing the drop on wood surface was
by 20%.
a).
b).
Figure 2. Wetting energy (a) and work of adhesion (b) of the structure lime wood - water (yW), lime wood diiodomethane (yD)
Moreover, significant changes in wetting energy (fig. 2a) and the work of adhesion
(fig. 2) were observed in the lime wood – water structure. After 60 seconds from placing
the water drop on the tangential surface of lime wood the wetting energy increased by
ca. 70%. In the case of the lime wood – diiodomethane structure, however, 5% increase
in wetting energy was observed 60 s after depositing the drop on the surface of wood.
Furthermore, in the case of wetting the wood with water, an increase in the work of adhesion
by ca. 26% was observed after 60 seconds from placing the drop on the surface of wood.
For the structure lime wood – diiodomethane, however, the increase in the work of adhesion
was at the level of 2%, i.e. statistically insignificant.
Figure 3. Surface free energy (SFE), dispersion and polar components
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Figure 3 presents the curves which illustrate the changes in time in surface energy
and its components (polar and dispersive). Obtained results indicate that the dominant
component, which is also more variable in time, is the energy which originates from the polar
liquid (water). The results are typical for species without heartwood with open wood structure
and low extractives content, e.g. beech or poplar wood (Santoni and Pizzo 2011).
CONCLUSIONS
The research into the surface wettability of lime wood (Tilia cordata Mill.) enabled
the following conclusions to be drawn:
1. The course of the wetting process, in particular with polar liquid (water), shows
considerable dynamics. After 60 s from placing a water drop on lime wood surface
the contact angle decreased by 70%. However, when the wood was wetted with
diiodomethane, the contact angle decreased by 30%.
2. When the wood was wetted with water, 60 seconds after the drop was deposited on wood
surface the wetting energy was observed to increase by ca. 70%. In the case of lime wood
– diiodomethane structure, the increase in wetting energy was at the level of 5%.
3. The dominant component, which was also more variable in time, was the energy which
originated from the polar liquid (water).
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Streszczenie: Oznaczenie zwilżalności drewna lipy drobnolistnej (Tilia cordata Mill.)
jako materiału używanego w rzeźbiarstwie i na podobrazia drewniane. Drewno lipy
stosowane jest w krajach europejskich głównie do wytwarzania rzeźb, ram i podobrazi.
Przy konserwacji i restauracji obiektów z drewna lipowego często istnieje potrzeba
stosowania uzupełnień ze współczesnego drewna. Wklejane wstawki są pokrywane
i przesycane różnymi substancjami. Przy tego typu zabiegach decydujące znaczenie mają
właściwości charakteryzujące zwilżalność i fizykochemiczne właściwości powierzchni.
W pracy określono zwilżalność drewna lipy metodą ”osadzonej„ kropli dla układu drewno woda oraz drewno - dijodometan. Przebieg procesu zwilżania, w szczególności cieczą polarną
(wodą), wykazuje znaczną dynamikę. W przypadku zwilżania drewna wodą stwierdzono
wzrost wartości energii zwilżania o ok. 70% po 60 sekundach od naniesienia kropli
na powierzchnię drewna. Natomiast dla układu drewno lipy - dijodometan wzrost wartości
energii zwilżania był na poziomie 5%. Dominującą składową swobodnej energii
powierzchniowej drewna lipy jest energia pochodząca od cieczy polarnej (wody).
Corresponding authors:
Agnieszka Kurowska
Department of Wood Sciences and Wood Preservation
Faculty of Wood Technology
Warsaw University of Life Sciences – SGGW
159 Nowoursynowska St.
02-776 Warsaw, Poland
email: [email protected]
phone: +48 22 59 38 661
Paweł Kozakiewicz
Department of Wood Sciences and Wood Preservation
Faculty of Wood Technology
Warsaw University of Life Sciences – SGGW
159 Nowoursynowska St.
02-776 Warsaw, Poland
email: [email protected]
http://pawel_kozakiewicz.users.sggw.pl
phone: +48 22 59 38 647
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