(159b) Thermal, Mechanical, and Barrier Properties of PET-Platelet Nanocomposites

This study investigates the conditions for dispersing and exfoliating clay platelets in polyethylene terephthalate (PET) by in situ polymerization. Target clay materials included montmorillonite (MMT), hectorite (HCT), Ethoquad-modified MMT (eMMT) and phenyl-modified HCT (phHCT) at weight loadings of up to 4%. Both thermally-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. Water uptake measurements were used to assess barrier performance. The storage modulii of quenched eMMT nanocomposite strands increased with eMMT weight loading because of the favorable interaction between PET and eMMT. DSC indicated that eMMT inhibited the crystallization of PET. Both 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 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. Barrier to water uptake correlated with the ability of the platelets to induce PET crystallization.