technology of manufacturing the machine parts from anionic

technology of manufacturing the machine parts from anionic

KOMISJA BUDOWY MASZYN PAN – ODDZIAŁ W POZNANIU
Vol. 28 nr 1
Archiwum Technologii Maszyn i Automatyzacji
2008
KRYSTYNA KELAR∗
TECHNOLOGY OF MANUFACTURING THE MACHINE
PARTS FROM ANIONIC POLYAMIDE 6 MODIFIED
WITH MONTMORILLONITE
The paper presents the results of investigations of structure and properties of polyamide 6
(PA6) nonmodified and modified with montmorillonite. The polyamide/clay hybrid (PACH) was
prepared by in situ anionic polymerization of ε-caprolactam in the presence of organic modified
montmorillonite (OMMT). The polymerization product was granulated and, then injection molded
into standard specimens. In this work thermal behavior (DMTA, TGA), X-ray diffraction, mechanical properties (tensile strength, Charpy's notched impact strength) of both PA6 and PA6/MMT
nanocomosite were studied. DMTA results showed that the magnitudes of storage modulus are
higher for the nanocomposite than for the unmodified PA6 throughout the temperature range
between –100 and 200oC. Nanocomposite PA6/MMT exhibited higher yield strength and moduli,
lower elongation at break and lower impact strength. The heat stability of the PA6/MMT nanocomosite was higher than that for neat PA6.
Key words: anionic polyamide 6, montmorillonite, nanocomposites, structure, physical properties
1. INTR0DUCTION
One of the most important features of polymers is the possibility of controlling macroscopic physical properties by tailored manipulation of their structures
at a micro- and nanoscopic scale. In recent years, organic-inorganic nanoscale
composites have attracted great interest since they frequently exhibit unexpected
hybrid properties synergistically derived from two components [2, 9, 16]. Since
the pioneering work of Toyota group on polyamide/clay nanocomposites, in the
late 1980s [12, 17, 18], intensive study of nanocomposites is going in many laboratories and research facilities. Clay minerals such as montmorillonite
(MMT), have received a great attention as reinforcing materials for polymers
owing to their potentially high aspect ratio and unique intercalation/exfoliation
characteristics [2]. In the pristine state, MMT is hydrophilic in nature, which
hinders the formation of homogeneous dispersions in organic polymers and is
∗
Dr hab. – Insitute of Material Technology, Poznan University of Technology.
154
K. Kelar
immiscible with the hydrophobic polymer. To make the MMT compatible with
the polymer, the clay is modified with an organic ammonium salt, such as aminododecanoic acid, octadecylammonium etc., by cation exchange [10, 19].
In this paper, a method in situ anionic bulk polymerization of ε-caprolactam
(CL), in the presence (1.0 wt%) of organic modified montmorillonite (OMMT),
was used for the preparation of PA6/clay hybrid (PACH).
2. EXPERIMENTAL
2.1. Materials and sample preparation
All materials used in this work are commercial products.
– crystalline ε-caprolactam (quality I), (melting point ≈ 70oC/760 mmHg;
boiling point ≈ 137oC/10 mmHg, made by Nitrogen Chemistry Plant in Tarnow
(Poland), was used without additional purification,
– sodium bis[(2-methoxyethoxy)caprolactam]-aluminate (initiator), made by
Chemopetrol Spolana Neratovice, Czech Republic was used without additional
purification,
– 2.4-toluene diisocyanate (activator), having a density of 1.2175 g/cm3,
made by Nitrogen Chemistry Plant ZACHEM in Bydgoszcz (Poland),
– montmorillonite untreated (MMT) was purchased from Fluka.
The precise preparation procedure of the organophilic montmorillonite
(OMMT) have been reported in a paper [11].
The polymerization process was carried out in a thermostatic chamber (bath
with silicone oil), electrically heated to the constant temperature 170 ± 2oC, and
equipped with a stirrer, under normal conditions in the presence of air. No
process stabilizer was used. The concentration of initiator was kept constant at
0.4 mol%, and the amount of activator was kept at 0.2 mol% based on the total
monomer feed. The polymerization of ε-caprolactam was carried out following
the procedure: in the vessel, ε-caprolactam and 1.0 wt% of OMMT were placed
and the mixture was heated at 100 ± 2oC in an oil bath and held at this temperature for about 15 min. After homogenization of the molten monomer and
OMMT by using homogenizer, the initiator was introduced. The mixture was
heated at 135 ± 2oC and the activator was added with vigorous stirring, and then
the mixture was immediately poured in the glass test tube molds (length 160
mm, φ12 mm, wall thickness 0.5 mm), and were placed into the thermostatic
chamber.
The polymerization product was mechanically crushed, and the particles were
extracted three times with fresh portions of boiling water for 20 min (to extract
the unreacted monomer and the oligomers) and dried in vacuum at 80oC to constant weight. The neat PA6 was identically processed to ensure the same ther-
Technology of manufacturing the machine parts from anionic polyamide 6 …
155
momechanical history. The pellets of PA6 and PACH were molded using an
Engel injection molding machine. The test specimens for various measurements
were formed using a barrel temperature of 270oC, mold temperature of 65oC,
injection pressure of 11 MPa and holding pressure of 3 MPa.
2.2. Characterization and test
Because the equivalent weight of the quaternary ammonium salts and the actual loading levels are different, the mineral content of the final PACH is different. The concentration of MMT was determined by the weighing of the specimens before and after heating and burning at 600oC for 2 h [7]. The actual mineral content is 0.6 wt%.
Wide-angle X-ray diffraction (WAXS) measurements were carried out using
a TUR M52 diffractometer at room temperature. The Cu Kα radiation source
(λ = 1.5418 Å) was operated at 30 kV and 25 mA. The XRD patterns were recorded with a step size of 0.04 from 2θ = 2 to 30o.
The analyzer STA 409C (Netzsch, Germany) was used to investigate the
thermal stability of the PA6 and PACH composites. The specimens (about 10
mg) were heated under nitrogen atmosphere from ambient temperature to 600oC,
at the heating rate of 10oC/min in all cases. The thermal degradation temperature
was taken as the onset temperature at which 5 wt% of weight loss occurs [21].
The dynamic mechanical tests were done using the MK III DMTA Polymer
Laboratories instrument operating in the bending mode. Measurements were
taken at a frequency of 1 Hz. The temperature was raised from –100˚C to 240˚C,
at a scanning rate of 4oC/min, under nitrogen atmosphere.
The tensile tests were carried out using an Instron tensile machine (Model
1115, UK). All tests being done at a crosshead speed of 5 cm/min and a temperature of 20 ±3oC. Charpy impact strength was measured at room temperature
using an Instron pendulum tester, type PW-5.
For measurements of mechanical properties ten specimens of each polymer
were tested and average values were taken as experimental data for further analysis.
3. RESULTS AND DISCUSSION
The clay modification and dispersion within PA6 matrix has been characterized by X-ray diffraction (Fig. 1 and Fig. 2).
156
K. Kelar
Intensity (a. u.)
b
a
2
3
4
5
6
7
2 Theta (o)
8
9
10
Fig. 1. XRD patterns: (a) pristine sodium montmorillonite (MMT), (b) modified montmorillonite
(OMMT)
Rys. 1. Dyfraktogramy rentgenowskie: (a) montmorylonit (MMT), (b) modyfikowany montmorylonit
(OMMT)
The X-ray diffraction curve of pristine MMT (Fig. 1a) shows a diffraction
peak at 2θ = 7.28o, resulted from the diffraction of the (001) crystal surface of
layered silicates with a corresponding d spacing of 1.21 nm. Surface modification of the pristine clay by the organic ammonium salts (Fig. 1b) increases the
interlayer spacing of the clay galleries and subsequently shifts the basal peak
position of XRD to the smaller of 2θ = 3.48o with d-spacing of 2.54 nm, indicating that a swollen and intercalated structure is formed in organoclay [8].
Figure 2 shows the X-ray diffraction intensity curves, in the range of 2θ = 2–30o,
of the injection molded PA6 (curve a) and PACH (curve b) specimen. The absence of the characteristic clay d001 peak suggesting that during the polymerization and after injection molded the layered structure MMT was destroyed by the
growing of the PA6 chains and voluminous exfoliated in the PA6 matrix
[16, 19].
Many researchers have reported that montmorillonite can stabilize polymer
matrix [6, 14, 20]. The curve of thermal degradation of PA6 and the PACH are
shown in Fig. 3.
Technology of manufacturing the machine parts from anionic polyamide 6 …
157
Intensity (a. u.)
γ
α
α
b
a
2
6
10
14
18
22
26
30
2 Theta (o)
Fig. 2. XRD patterns: (a) PA6, (b) PACH sample
Rys. 2. Dyfraktogramy rentgenowskie próbek: (a) PA6, (b) PACH
Weight remained (%wt)
100
80
1
2
60
40
20
0
0
100
200
300
400
500
600
o
Temperature ( C)
Fig. 3. TGA curves of: the neat PA6 (1) and PACH specimens (2)
Rys. 3. Krzywe termograwimetryczne próbek: (1) PA6 oraz (2) PACH
Table 1 provides details of the degradation temperature, based on the thermogravimetric analysis (TGA curves) of the PA6 and PACH. The decomposition temperature T5% [21] of PACH increases of 45oC as compared to that for
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K. Kelar
neat PA6, as given in Table 1. The improvement in the degradation temperature
was mainly due to the homogeneous dispersion of the silicate nanoplatelets in
the PA6 matrix [3, 14]. The origin of the noticeable increase in the degradation
temperature mainly resulted from the dispersed nanoscale silicate layers to hinder the permeability of the volatile degradation products out of the material. Pramoda et al. [15] suggests that only exfoliated polymer nanocomposites exhibit
improved thermal stability. Agglomerated clay particles do not significantly
affect the thermal stability of the polymer matrix.
Table 1
Thermal degradation data of PA6 and PACH
Degradacja termiczna PA6 i PACH
Degradation temperature (oC) at different loss weight, wt%
Specimen
PA6
PACH
5
10
15
30
50
322
367
376
388
396
399
417
416
431
430
Dynamic mechanical thermal analysis (DMTA) was performed on PA6 and
PACH specimens in the temperature range between –100 and 240oC. The loss
tangent temperature and storage modulus dependencies for PA6 and PACH specimens are shown in Figs. 4 and 5, respectively.
1,2
α relaxation
tan δ
1,0
0,8
2
0,6
0,4
1
β relaxation
0,2
0,0
-100
-50
0
50
100
150
200
o
Temperature [ C]
Fig. 4. Temperature dependence of damping factor tan δ for: the neat PA6 (1) and PACH specimens (2)
Rys. 4. Zależność kąta stratności mechanicznej tgδ od temperatury dla próbek: (1) PA6 oraz (2) PACH
The results of DMTA experiments are summarized in Table 2. The PA6 and
PACH shows two loss angle tangent (tan δ) peaks in the above temperature
range, which have been labeled α- and β-relaxation transitions occurring for
PA6 at 73oC (and 66oC for PACH specimen) and –37oC (–40oC for PACH specimen), respectively.
Technology of manufacturing the machine parts from anionic polyamide 6 …
159
1200
Module E' [MPa]
1000
800
2
1
600
400
200
0
-100
-50
0
50
100
150
200
250
o
Temperature [ C]
Fig. 5. Temperature dependence of storage modulus E’ for: the neat PA6 (1) and PACH (2) samples
Rys. 5. Zależność modułu zachowawczego E’ od temperatury dla próbek: (1) PA6 oraz (2) PACH
Table 2
A list of values determined by the DMTA for PA6 and PACH
Wartości wyznaczone na podstawie badań DMTA dla PA6 oraz PACH
Beta peak
location
Storage
modulus
at 23 ± 2oC
(MPa)
Alpha peak
location
( C)
Alpha peak
magnitude
PA6
840
73
1.1
–37
0.25
PACH
950
66
0.82
–40
0.21
Specimen
o
o
( C)
Beta peak
magnitude
The α-relaxation is assigned to the glass transition temperature (Tg) of the
PA6, which involves the motion within the amorphous region and depends on
the polymer crystallinity [1]. The magnitude of the tanδ attributed to PA6 Tg
decreases with the addition of OMMT (Table 2). This is due to exfoliated structure and strong interactions between OMMT and polymer chains in PACH [5].
The β damping peak is attributed to the carbonyl group of the polyamide forming hydrogen bonds, and depends on the moisture content [4].
The E’ curves (Fig. 5) indicates at low temperatures a high material stiffness,
which decreases considerably with the appearance of certain relaxation
processes. The first decrease of E’ corresponds to the β-relaxation transitions.
With increasing temperature, another significant decrease in E’ is observed at
the glass transition of the amorphous region of the PA6. As shown in Fig. 5, the
magnitudes of storage modulus are higher for the nanocomposites than for the
unmodified PA6 throughout the temperature range between –100 and 200oC.
160
K. Kelar
This increase in the storage modulus agrees with the results of the tensile experiments discussed below.
The effect of clay content on the mechanical properties has been studied by
tensile testing and Charpy impact properties as reported in Table 3.
Table 3
Tensile properties and Charpy impact strength of PA6 and PACH
Właściwości wytrzymałościowe w próbie rozciągania i udarność według Charpy’ego PA6 oraz PACH
Specimen
Tensile strength
(MPa)
Young’s modulus
(MPa)
Elongation at
break
(%)
Charpy impact
strength
(kJ/m2)
PA6
40.1 ± 4.5
1100 ± 26
25.8 ± 2.0
29.2 ± 2.1
PACH
51.4 ± 3.2
1280 ± 21
24.3 ± 1.8
27.9 ± 2.5
The tensile strength and Young’s modulus of the PACH nanocomposite are
higher compared to the neat PA6, as result of the intercalated/exfoliated structure. For instance, the Young’s modulus increased from 1100 MPa for neat PA6
to 1280 MPa for the PACH. The elongation at break and Charpy impact strength
of the PACH revealed no noticeable change.
4. CONCLUSIONS
The results showed that the heat stability of the PACH specimen was higher
than that for neat PA6. DMTA results showed that the magnitudes of storage
modulus are higher for the nanocomposite than for the unmodified PA6 throughout the temperature range between –100 and 200oC. The results showed that the
tensile strength and Young’s modulus of the PACH nanocomposite are higher
compared to the neat PA6. The elongation at break and Charpy impact strength of
the PACH revealed no noticeable change. Possibility to use these new materials
for the production of machine parts is a practical aspect of this work.
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ACKNOWLEDGEMENTS
The author thank the Poznan University of Technology (grant TB-25-198/07/DS) for financial
support.
Praca wpłynęła do Redakcji 5.03.2008
Recenzent: prof. dr hab. inż. Danuta Żuchowska
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K. Kelar
TECHNOLOGIA WYTWARZANIA CZĘŚCI MASZYN
Z ANIONOWEGO POLIAMIDU 6
MODYFIKOWANEGO MONTMORYLONITEM
W artykule przedstawiono badania struktury i właściwości poliamidu 6 (PA6) niemodyfikowanego i modyfikowanego montmorylonitem (MMT). Metodą anionowej polimeryzacji ε-kaprolaktamu, w obecności modyfikowanego jonami organicznymi montmorylonitu (OMMT),
otrzymano hybrydę poliamidowo-montmorylonitową (PACH). Produkt polimeryzacji granulowano i wtryskiwano znormalizowane próbki do badań. Badania właściwości PA6 i PA6/MMT obejmowały: właściwości cieplne (TGA, DMTA), badania rentgenowskie i właściwości mechaniczne
(wytrzymałość na rozciąganie, udarność metodą Charpy’ego). Na podstawie badań DMTA stwierdzono, że w zakresie temperatury od –100oC do +240oC moduł zachowawczy E’ nanokompozytu
jest większy niż niemodyfikowanego PA6. Nanokompozyt PA6/MMT ma większą wytrzymałość
na rozciąganie i większy moduł, ale mniejsze wydłużenie i mniejszą udarność niż niemodyfikowany PA6. Stabilność termiczna nanokompozytu PA6/MMT jest wyższa niż niemodyfikowanego
PA6.
Słowa kluczowe: anionowy poliamid 6, montmorylonit, nanokompozyt, struktura, właściwości fizykochemiczne