Crystallization, mechanical, rheological and degradation behavior of polytrimethylene terephthalate, polybutylene terephthalate and polycarbonate blend.

Blends of polycarbonate (PC), polytrimethylene terephthalate (PTT) and poly butylene terephthalate (PBT) are an important class of commercial blends with numerous applications providing good chemical resistance and impact resistance even at low temperatures. Polycarbonate/polyester blends are known to react during thermal processing causing the formation of copolymers to have new mechanical and thermal properties. The aim of this project was to study the crystallization, mechanical, rheological and degradation behavior of blends of PC, PTT and PBT and explain these behaviors in terms of transesterification and other plausible mechanisms. PC, PTT and PBT (50:25:25 wt/wt ratio) were melt-blended in a single screw extruder and the extruded blends were pelletized. Non isothermal crystallization kinetics of the blend and neat polymers were investigated using a Perkin Elmer diamond DSC instrument having a fast response time. This thermoplastic blend was able to crystallize rapidly from the melt. Non isothermal crystallization kinetic parameters were analyzed using different numerical methods. Those parameters of the blend fell between those of PTT and PBT. The cause of this behavior could be due to the nature of PC as an amorphous polymer. Rheological properties of the blends were also studied at different temperatures. Rheological measurements were conducted to study the storage modulus, loss modulus, and viscosity values vis a vis the neat materials. Changes in complex viscosity (η*) and shear viscosity (η) were attributed to transesterification. The study presented in this work showed two fundamental issues that have never been addressed in the literature: one is the synthesis of a novel tricomponent system and other is how transesterification during polymer processing might affect the degradation and rheological properties of the tricomponent blend. Effect of blending on mechanical properties was carried out using tensile tests revealing a higher yield strength and elastic modulus of the blend. The morphology of the blend and neat polymers was studied using Scanning electron microscope (SEM), showing immiscibility of the blend components. X ray analysis was carried out to determine the crystalline nature of the blend vis a vis neat polymers. Existence of PTT and PBT peaks proved the immiscible nature of the system. Polymer blends can undergo, during processing, degradation because of the presence of both temperature and mechanical stresses. Compared to neat polymers, degradation of polymer blends shows distinct features because of the interaction between the different chemical species. These interactions can give rise to degradation or to the formation of copolymers which act as stabilizing agents. The non isothermal degradation kinetics of the blend and neat polymers were studied using dynamic thermogravimetry. The thermal stability of the polymers in air was studied and compared to that in nitrogen. The kinetic parameters were analyzed using different numerical methods. Polymers normally transesterify, above their melting points and interchange reactions commonly occur between polyester moieties or among polyester and polycarbonate entities. The transesterification occurring in the blend was analyzed with the help of Fourier Transform Infra- Red (FTIR) using spectral features based on changes of infra red bands