Synthesis and characterization of poly(ether/ester) based thermoplastic elastomer nanocomposites

Ezeroğlu, Fadile
In this thesis, there are three goals; to synthesize Poly(ether/ester)s (PEEs) based on Poly(butylene terephthalate) (PBT) and Poly(ethylene glycol) (PEG) by changing the soft segment / hard segment compositions and investigate the influence of hard segment length on the structure, to synthesize PEE nanocomposites by in-situ polymerization and observe the effects of introduction of modified organoclay at different ratios to the polymer matrix, and thirdly, to prepare PEE nanocomposites by melt intercalation, and to compare in situ polymerization and melt intercalation methods in terms of mechanical, and thermal properties and morphology. First the optimum reaction conditions were determined based on the temperature and duration of transesterification. PEEs with different PBT weight ratios varying from 37 wt% to 75 wt% were synthesized according to two different reaction procedures, namely, constant transesterification time and constant volume ratio of methanol collected. The procedure with constant volume ratio gave higher mechanical properties and molecular weight, and it was also applied for in-situ polymerization of nanocomposites. The synthesized polymers were characterized by FTIR-ATR analysis. PEEs with 57 wt % PBT and 75 wt % PBT showed better tensile strength and elongation at fracture, thus, nanocomposites of these polymers containing 0.1%, 0.3% and 0.5% modified organoclay were prepared by both in-situ polymerization and melt intercalation methods whereas the PEE nanocomposites of 37 wt% PBT and 49 wt% PBT were obtained only by melt intercalation. The structure-properties relationships were examined by mechanical, thermal and morphological analyses. Specimens for analysis were prepared by injection molding. For neat PEEs, the increase in weight content of PBT resulted in better mechanical properties. Melting point of PBT increased with increasing PBT as observed in DSC curves, while the glass transition temperature of PEG was not significantly affected. For PEE nanocomposites with 37 wt % PBT, mechanical properties were not improved considering tensile strength and elongation at fracture. In the case of 49 wt % PBT nanocomposites, addition of modified organoclay resulted in lower mechanical properties. Considering PEE nanocomposites with 57 wt % PBT in both two methods, the addition of modified organoclay improved the mechanical properties such as tensile strength and elongation at fracture with the increase of organoclay wt%, and the best results were obtained with 0.5 wt % organoclay loading. 75 wt % PBT PEE nanocomposites with 0.1 wt % modified organoclay loading which were synthesized by in-situ polymerization gave better result than the neat polymer in terms of tensile strength. Among the nanocomposites which were prepared by melt intercalation, the highest tensile strength was obtained in PEE with 0.3 wt % organoclay loading. DSC analysis of PEE nanocomposites with 37, 49 and 57 wt % PBT showed that with the addition of organoclay, melting point of PBT decreases due to restricted crystallinity of PBT. However, it was observed that for PEE nanocomposites of 75 wt % PBT, addition of organoclay does not have a significant effect on the melting point of PBT. In order to discuss the dispersion of clay particles in the polymers, X-Ray Diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy were used. The results of these analysis indicated that in-situ polymerization method is better than melt intercalation method in terms of dispersion of silicate layers in PEEs with both 57 wt % PBT and 75 wt % PBT.