Due to low molecular weight and wide molecular weight distribution, polyethylene terephthalate (PET) shows weak melt strength properties. In this study, the synergistic effect of using different types of chain extenders and catalyst on rheological behavior of PET has been investigated. Long-chain branching is known as a suitable method for developing the structure of PET during reactive melt processing. Thus, pyromellitic dianhydride (PMDA) and pentaerythritol (PENTA) were added to the fiber grade PET. The best formulation was determined based on rheological results, which revealed an improvement in both storage modulus and complex viscosity of PMDA-modified samples. Samples containing 1.5% PMDA and 0.5% PENTA exhibited the best rheological properties. Also, dibutyltin dilaurate (DBTDL) acted as an accelerator for chain extension reaction during reactive melt blending. Subsequently, the rheological properties were improved by increasing the chain extending rate. Moreover, thermal properties such as crystallization and melting temperatures and the degree of crystallinity for modified PET were investigated by differential scanning calorimetry.

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Thermal degradation of polyethylene terephthalate (PET)/carbon nanotube (CNT) nanocomposites is a serious issue in the manufacturing process of this nanocomposite that can limit the applications of the nanocomposite. In this study, the effects of two kinds of chain extenders, pyromellitic dianhydride (PMDA) and pentaerythritol (PENTA), on the rheological behavior, thermal characteristics, and crystallinity of the PET were investigated. The results of shear rheology revealed improvement of the storage modulus and complex viscosity, which indicated the recoupling of broken chains, increasing the chain length, and the generation of long branches was the reason for chain extension. Also, differential scanning calorimetry (DSC) results clarified an increase in PET crystallization rate in the presence of CNT and chain extenders. Furthermore, SEM was performed to detect CNT dispersion in the nanocomposite, and four-probe technique test was utilized to determine the influence of CNT on the electrical properties of PET.

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