Due to its effects on marine species and human health, plastic pollution has become one of the largest environmental concerns of the last decade. While poly(lactic acid) (PLA) and other biodegradable and/or sustainably-sourced polymers have the potential to offset our dependency on oil-based plastics, it is necessary to have simple methods to study their enzymatic stability. To evaluate the stability of PLA, we use a diffraction-based method that has been demonstrated previously in our group for other biopolymers. In this method, a biopolymer film is patterned with regular lines that act as an optical grating, and degradation is observed by monitoring the change in the intensity of the first order diffraction spot as material is removed from the surface. PLA thin films were cast on a polydimethylsiloxane mold to obtain PLA surfaces patterned with line structures (1.6 µm periodicity and 400 nm height, total film thickness of less than 10 µm). These films were immersed in a solution of the PLA-degrading enzyme proteinase K at various concentrations, pHs, and temperatures. During enzymatic degradation, a laser (20 mW power, 532 nm) irradiated the surface of the PLA films, such that the grating diffracted the beam. The diffracted laser beam was measured with a photodetector, and as the grating degraded, the decrease in diffracted intensity was tracked. Various intensity profiles were recorded, and optimized conditions were identified. AFM images were also collected from samples at various stages in the degradation process to determine how the diffracted intensity responds to surface degradation. These images provided information about the relationship between the state of the PLA surface and the diffracted intensity, leading toward a calculation of mass-loss rate throughout the degradation process. This work presents a diffraction based-method to evaluate the stability of polymer films in different degradation environments.

Diffraction-based method to evaluate enzymatic degradation of poly(lactic acid) films

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.