Free volume can control biodegradation rate of polylactic acid

We evaluated whether the enzymatic degradation rate of biodegradable plastics is related to the amorphous structure of the polymer. The "free-volume," meaning the cavity between the polymer chains in the amorphous part, is known to influence various physical properties. In this study, enzymatic degradation tests were performed on polylactic acid (PLA) films with free-volume hole sizes estimated by positron annihilation lifetime spectroscopy (PALS). Films with different free-volume hole sizes near the surface region degraded in different modes, and a positive correlation, with a correlation coefficient of 0.713, was observed between the degradation rate in the initial 30 min and the free volume size near the surface. These results suggest the possibility of controlling the degradation rate of the amorphous region by controlling the free volume size, which is important for future applications of biodegradable plastics in a wide range of fields.