| Summary: | The main focus of this research project was to understand the effect of clay particles
incorporation on the thermal and thermomechanical behaviour of biodegradable polymers.
Clay minerals, due to their unique layered structure, rich intercalation chemistry and
availability at low cost, are promising nano-particles reinforcement for polymers to
manufacture low cost, light weight, and high performance nanocomposites. Up to this date
very few attention has been given to using nano-dimentional clay particles as a means of
increasing the crystallinity and improving the thermal and mechanical properties.
Understanding the structure-property relationship in polymer-clay layered silicate
nanocomposites is of fundamental importance in designing materials with desired properties.
To understand the relations, in the case of poly(ethylene succinate) (PES), poly(butylene
succinate) (PBS) and the organically modified layered silicates: montmorillonite (MMT) and
synthetic fluorine mica (SFM), wide-angle x-ray diffraction (WAXRD), small-angle x-ray
scattering (SAXS) and transmission electron microscopy (TEM) analyses were conducted for
the structural and morphological analysis.
The PES/OMMT nanocomposite was prepared by a solution-intercalation-film-casting
technique. SAXS and TEM observations show the homogeneous dispersion of silicate layers
in the PES matrix. The crystallization and melting behaviour of the PES matrix in the
presence of the dispersed silicate layers were studied by differential scanning calorimetry
(DSC), polarized optical microscopy (POM), and WAXRD. The results show that the
incorporation of OMMT stops the super-cooling effect and significantly accelerates the
mechanism of nucleation and crystal growth of the PES matrix. The incorporation of OMMT
also significantly improves the thermal stability of the PES.
The effect of the change of variables like temperature, time, and heating rate on the
crystallization behaviour was studied. It was observed that the double melting behaviour of
the PBS matrix is a function of these variables. Various models namely the Avrami method,
the Ozawa method, and the combined Avrami-Ozawa method, were applied to describe the
kinetics of the pure PBS and its nanocomposite samples during non-isothermal crystallization.
The Ozawa equation did not provide an adequate description of the non-isothermal
crystallization kinetics of PBS and its nanocomposite. In contrast, the Avrami analysis modified by Jeziorny and the method developed by Liu et al. were successful in describing
the non-isothermal crystallization kinetics of pure PBS and its nanocomposite. The results
show that the crystal growth of the PBS matrix retards in the presence of dispersed
intercalated organoclays and supports the reduced crystallization of the PBS matrix in the
presence of Cloisite® 30B nanoclay.
The structure and morphology of the PBS nanocomposites, with three different weight ratios
of organically modified synthetic fluorine mica (OMSFM) were also characterized. We
observed the homogeneous dispersion of the intercalated silicate layers into the PBS matrix.
The thermal properties of pure PBS and the nanocomposite samples were studied by both
conventional and temperature modulated differential scanning calorimetry (DSC) analysis,
which shows multiple melting behaviour of the PBS matrix. The investigation of the
thermomechanical properties was performed by dynamic mechanical analysis (DMA). The
results reveal a significant improvement in the storage modulus of the PBS in the presence of
OMSFM. The tensile modulus of the PBS is also significantly increased in the presence of
OMSFM. However, the yield strength and the elongation at break of the PBS systematically
decrease with the loading of OMSFM. The thermal stability of the nanocomposites compared
to that of the pure polymer sample was examined under both pyrolytic and thermo-oxidative
environments. The thermal stability of PBS increased moderately in the presence of 3 wt% of
OMSFM, but there is no significant effect on further silicate loading in the oxidative
environment. In the nitrogen environment, however, the thermal stability systematically
decreased with increasing clay loading.
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