Study of dynamic vulcanized PLA/ENR TPV filled with various organic modified MMT (OMMT)

บทคัดย่อ

In this research, we investigated the crystallization behavior of PLA and properties of PLA/ENR thermoplastic vulcanizates (TPVs). ENR was compounded with phenolic resin and with PLA at the blend ratio of 40/60 by using an internal mixer at 170°C and rotor speed of 70 rpm. Three types of organic modified montmorillonite (OMMT) which are Cloisite^® 15A, Cloisite^® 20 A and Cloisite^® 30B were also added at various contents during mixing. The TPVs were pressed to form thin film in a compression molding machine and cooled down under pressure for 10 minutes. Crystallization behavior, thermal properties and morphology of TPVs were investigated using DSC, TGA and SEM, respectively. On the first heating, cold crystallization temperature (T_cc) of PLA, in the TPVs both with and without OMMT, was clearly occurred at lower temperature than that of the neat PLA. The melting temperature (T_m) of neat PLA exhibits 2 melting temperatures, i.e. T_m1 and T_m2, as well as those in the TPVs. The crystallinity of PLA was found to be increased with the present of ENR. This confirmed the crystallization of PLA having ENR as nucleating agent. In this case crystallization of PLA during cooling could also be observed. On the second heating scan, the well defined T_g, T_m1 and T_m2 could be observed. The crystallinity of PLA of all TPVs was also considerably increased accept for TPV without OMMT where T_g and T_ms are slightly lowered by the degradation during heat experience, clarified by onset of degradation temperature (T_d). The addition of OMMT was found to enhance both crystallization behavior and thermal stability. The research shows that types and content of OMMT did not much affect T_g and melting behavior of PLA but they affected crystallization behavior of PLA through sharpening cold crystallization peak and reducing cold crystallization temperature. In addition, there was a small exothermic peak during cooling. All types of organoclay could improve thermal stabilities of TPVs similarly. Especially, the presence of 3 and 5 phr of organoclay could compensate for lost thermal stabilities of TPVs satisfactorily.