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

The effect of water hydrolysis on the mechanical properties of PHBV/PLLA blends was investigated. The results were interpreted with models able to predict the Young's modulus of multiphase systems. On the basis of the experimental results relative to the pure components, the models were used to calculate the expected values of the blends; these data were therefore compared with the experimental results in order to verify 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 degradation kinetics of the PLLA phase when PHBV is added to the polymer and forms a partially miscible system. The strength, which depends on both molecular weight and surface erosion that determine crack initiation, decreases faster than the modulus for those systems whose degradation is accompanied with remarkable surface modifications.