Novel aspects of the degradation process of PLA based bulky samples under conditions of high partial pressure of water vapour

This work describes differences between the degradation of poly(l-lactic acid) bulky samples in high partial pressure of a water vapour environment versus a buffered liquid medium. Analytical techniques (optical and electron microscopy, size exclusion chromatography, differential scanning calorimetry) were used to evaluate the material's morphology, molecular weight, crystallinity and thermal properties. In particular, the extent of degradation was studied separately in the core and surface of the testing specimens. The results reveal significant differences in the bulk degradation profiles and morphological changes for both environments. Degradation in the liquid medium leads to multiphase core-cortex morphology formation, while the environment with high partial pressure of water vapour provides homogeneous-like bulk degradation of the samples due to significantly different diffusion conditions on the liquid-polymer and water vapour saturated air-polymer interface.