Blends of aliphatic polyesters.: VIII.: effects of Poly(L-lactide-CO-E-caprolactone) on enzymatic hydrolysis of poly(L-lactide), poly(E-caprolactone), and their blend films

Poly(L-lactide), that is, poly(L-lactic acid) (PLLA), poly(e-caprolactone) (PCL), and their blend (50/50) films containing different amounts of poly(L-lactide-co-epsilon-caprolactone) (PLLA-CL), were prepared by solution casting. The effects of added PLLA-CL on the enzymatic hydrolysis of the films were investigated in the presence of proteinase K and Rhizopus arrhizus lipase by use of gravimetry. The addition of PLLA-CL decreased the proteinase K-catalyzed hydrolyzabilities of the PLLA and PLLA/PCL (50/50) films as well as the Rhizopus arrhizus lipase-catalyzed hydrolyzability of the PCL and PLLA/PCL (50/50) films. The decreased enzymatic hydrolyzabilities of the PLLA and PCL films upon addition of PLLA-CL are attributable to the fact that the PLLA-CL is miscible with PLLA and PCL and the dissolved PLLA-CL must disturb the adsorption and/or scission processes of the enzymes. In addition to this effect, the decreased enzymatic hydrolyzabilities of the PLLA/PCL (50/50) films upon addition of PLLA-CL can be explained by the enhanced compatibility between the PLLA-rich and PCL-rich phases arising from the dissolved PLLA-CL. These effects result in decreased hydrolyzable interfacial area for PLLA/PCL films. The decrement in protemase K-catalyzed hydrolyzability of the PLLA film upon addition of PLLA-CL, which is miscible with PLLA, was in marked contrast with the enhanced proteinase K-catalyzed hydrolyzability of the PLLA film upon addition of PCL, which is immiscible with PLLA. This confirms that the miscibility of the second polymer is crucial to determine the protemase K-catalyzed hydrolyzabilities of the PLLA-based blend films. (C) 2002 Wiley Periodicals, Inc.