EFFECT OF DEGRADATION ON THE MECHANICAL-PROPERTIES OF MULTIPHASE POLYMER BLENDS - PHBV PLLA/

The effect of water hydrolysis on the mechanical properties of PHBV/PL LA blends was investigated. The results were interpreted with models a ble to predict the Young's modulus of multiphase systems. On the basis of the experimental results relative to the pure components, the mode ls were used to calculate the expected values of the blends; these dat a were therefore compared with the experimental results in order to ve rify the theoretical predictions. The results show that the modulus of the degraded blends containing a low amount of PLLA is included in a range individuated from the upper and lower bound models and is close to the Halpin-Tsai prediction. This behavior is not present when PLLA is the continuous phase, and this can be due to the reduction of the d egradation kinetics of the PLLA phase when PHBV is added to the polyme r and forms a partially miscible system. The strength, which depends o n both molecular weight and surface erosion that determine crack initi ation, decreases faster than the modulus for those systems whose degra dation is accompanied with remarkable surface modifications.