Hydrolytic stability of polycarbonate/poly(lactic acid) blends and its evaluation via poly(lactic) acid median melting point depression

The hydrolytic degradation of polycarbonate (PC)/poly(lactic) acid (PLA) blends in deionized water media first time was studied in this research. Effects of degradation on mechanical properties and elasticity of the blends was presented and evaluated. Median PLA melting point depression approach is proposed for determination of degree of degradation. The proposed technique allowed true degree of degradation estimation not subjected to numerous phenomena affecting mechanical properties like moisture absorption and crystallization. The use of median melting point of PLA allowed accounting for numerous effects of PLA degradation resulting in its asymmetric melting curve. The presence of the acrylic impact modifier in blend significantly decreased the rate of moisture absorption rate and properties deterioration at later stages of degradation. This phenomenon was attributed to limited propagation of degradation areas due to the presence of acrylic modifier droplets having hydrophobic nature. It was found that degradation of PC/PLA blends due to hydrolysis may proceed in two distinctive stages: a) water diffusion and pit formation and b) hydrolytic degradation in PLA phase where degradation was supported by water transport via pits. The second stage is accompanied by accelerated water absorption due to the hydrolysis reaction and rapid properties deterioration. It was also found that PC phase also subjected to degradation due to pH decrease caused by PLA degradation. The PC degradation by-products like bisphenol A were not detected in degraded polymer samples which was attributed to their continuous removal into surrounding water media.