Elucidation of the microscopic mechanism of enzymatic degradation of poly(L-lactic acid) films

To eliminate plastic waste, biopolymers are preferred, one of which is polylactic acid (PLA). However, PLA degrades extremely slowly under normal environmental conditions because there are no microorganisms that break down PLA in nature. To remedy this situation, Proteinase K enzyme has been used to accelerate the hydrolysis of PLA. The hydrolytic degradation is expected to proceed by two different mechanisms: (i) surface erosion (heterogeneous degradation) or (ii) bulk erosion (homogeneous degradation). It is also suggested that chain scission reactions in the hydrolytic degradation of PLA occur preferentially in the amorphous region. However, there are few studies on the degradation process of PLA at the microscopic scale. In this talk, we focus on the surface morphology changes during degradation using PLA thin films prepared on silicon substrates. The PLA thin films were degraded in Proteinase K enzyme in TRIS-HCl buffer at 37°C and pH=8.5. The PLA thin films were then removed from the solution and dried with air at different degradation times (every 12 hours). The surface morphology and crystal structures studied by atomic force microscopy and grazing incidence wide-angle X-ray scattering will be discussed and further compared as a function of initial thickness.