Chain Extension Effects of para-Phenylene Diisocyanate on Crystallization Behavior and Biodegradability of Poly(lactic acid)/Poly(butylene terephthalate) Blends

The blends of poly(lactic acid) (PLA) and poly(butylene terephthalate) (PBT) were prepared with paraphenylene diisocyanate (PPDI) through reaction extrusion. The crystallization behavior of the PLA/PBT blends was investigated by using a differential scanning calorimeter (DSC), a wide angle X-ray diffractometer (WAXD) and a contact angle goniometer. The biodegradability was evaluated with a buffer solution containing esterase. The addition of PBT into a PLA polymer matrix induced the cold crystallization of the PLA phase. The crystallization rate of the PLA phase was accelerated significantly when both PBT and PPDI reacted with PLA simultaneously. But the chain extension caused by PPDI decreased the crystallinity of PLA and PBT phases. The phase separation between PLA and PBT in PLA/PBT blends increased the interfacial area exposed to hydrolysis, resulting in the improved degradability of the PLA phase. In contrast, the improved interfacial adhesion between PLA and PBT caused by the reaction with PPDI reduced the area that was exposed to enzyme and the degradation rate of the PLA phase.