Crazing mechanism in Poly (3-Hydroxybutyrate-co-3-Hydro-Xyvalerate) (P3HB-co-3HV) Thin Film - How Semi-Crystalline Polymers in Rubbery State Were Deformed

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB-co-3HV) is a promising semi-crystalline biodegradable polymer that may be used for a wide range of medical applications. Prior investigations were focused on the effect of hydrolysis and enzyme degradation, but few studies focused on the deformation mechanism of thin films. In this study we aim to reveal how the spherulites were deformed and to investigate the effect of hydrolysis and enzyme degradation on the micro-mechanical properties. It was found that even above Tg P3HB-CO-3HV films still produce intercrystalline crazes under external load. Impurities from biological origin were seen as defects to result in stress concentration under an external stress. "Egg-shell structures" emerged not only in the P3HB-CO-3HV films, which were hydrolyzed for 24 hours and 36 hours, but also in the films degraded by lipase for 3 days, indicating enzyme and nonenzyme hydrolysis destroy the crystal structure of P3HB-CO-3HV and lead to the degradation of the mechanical properties. The "Islands" structure observed in the crazes indicates that craze could not propagate as freely as in amorphous films due to interactions between crazes tips and the high crystallinity regions in the films.