Crystallization and mechanical properties of PET nanocomposites

The critical issue for preparing a true polymer nanocomposite is to obtain proper dispersion and exfoliation of inorganic materials in polymer matrix. The first objective of this study is to investigate the best conditions for dispersing and exfoliating clay platelets in polyethylene terephthalate (PET). Previous members of our research group had already carried out the synthesis and preparation of montmorillonite (MMT), hectorite (HCT), Ethoquad-modified MMT (eMMT) and phenyl-modified HCT (phHCT), as well as in situ polymerization of PET-platelet nanocomposites.;In order to characterize the effect of the clays on the properties of PET, these PET-platelet nanocomposites were extruded into strands via melt flow indexer (MFI). Both quenched and annealed strands of each sample were characterized by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) to investigate the mechanical properties and crystallization, respectively. DMA data showed that the measurements were repeatable and allowed us to make fair comparisons. With increasing eMMT weight loading, the storage modulii of quenched eMMT nanocomposite strands were significantly increased because of the favorable interaction between PET and eMMT. DSC indicated that the crystallization of PET was inhibited due to the presence of eMMT. There is no clear trend in the variation of the glass transition temperature (T g) with eMMT loading. However, HCT and phHCT nucleated PET crystallization, and their nanocomposites showed greater decreases in storage modulus (E') above Tg, compared to control PET (CPET), due to the cold crystallization effect. We observed a significant increase in Tg for both HCT and phHCT nanocomposites with increasing platelet weight loading.;Annealed strands of PET-platelet nanocomposites were further characterized to investigate the effect of thermal annealing. The sharp drop in E' just above Tg was not observed in annealed HCT and phHCT nanocomposites due to the presence of reinforcing crystallites. We observed that all nanocomposite samples showed improvement of E' due to the presence of crystallites formed during annealing. In addition, HCT and phHCT platelets had a significant effect on increasing Tg of the corresponding nanocomposites. The eMMT nanocomposites did not show an obvious trend for variation of Tg with eMMT loading.;We also used the solution blending route to prepare PET-platelet nanocomposites. Partially sulphonated PET (AQ55) was employed to deliver exfoliated MMT into PET in an attempt to obtain exfoliation of MMT (AQ55-MMT) in the PET matrix. The extruded film produced via micro-compounder was characterized by DMA to investigate the mechanical properties. The DMA results showed that the values of E' did not show any enhancement, probably due to the agglomeration of AQ55-MMT in PET matrix and the unfavorable surface interaction between platelet and polymer. We observe that the values of Tg and loss tangent peak show no clear trend with increasing AQ55-MMT weight loading.