Environmental degradation of biodegradable polyesters 2. Poly( ε-caprolactone), poly[(R)-3-hydroxybutyrate], and poly(L-lactide) films in natural dynamic seawater

Abstract

The (bio)degradation of aliphatic polyesters, poly( ε-caprolactone) (PCL), poly[(R)-3-hydroxybutyrate] (R-PHB), and poly(L-lactide) (PLLA) films in natural dynamic seawater was investigated using polarizing optical microscopy, gravimetry, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and tensile testing. The results were compared with those reported for the polyester films biodegraded in the controlled static seawater to reveal the physical effects in the natural dynamic seawater on the degradation of the aliphatic polyesters. The gravimetry and tensile testing showed that the mechanical stresses and strains in the natural dynamic seawater caused mechanical destruction or degradation of the films, resulting in seemingly accelerated (bio)degradation of all the films compared with that in the controlled static seawater. Such mechanical acceleration effects in the natural dynamic seawater were higher for the R-PHB and PLLA films with relatively high T g than for the PCL films with relatively low T g, when their (bio)degradation was monitored by gravimetry. The polarizing microscopy showed that the R-PHB films were (bio)degraded predominantly at the centers of and between the spherulites. The tensile strength and Young's modulus were lower for the initially crystallized PLLA films than for the initially amorphous PLLA films when compared at the same degradation time.