Blended films of poly(L-lactide) [ie poly(L-lactic acid)] (PLLA) and poly(ε ε ε ε ε ε-caprolactone) (PCL) without or mixed with 10 wt% poly(L-lactide-co-ε ε ε ε ε ε-caprolactone) (PLLA-CL) were prepared by solution-casting. The effects of PLLA-CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA-CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross-section of the PLLA/PCL blend film. The melting temperatures (T m ) of PLLA and PCL in the films remained unchanged upon addition of PLLA-CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4-0.7 and at most of the X PLLA values, respectively. The addition of PLLA-CL improved the tensile strength and the Young modulus of the films at X PLLA of 0.5-0.8 and of 0-0.1 and 0.5-0.8, respectively, and the elongation at break of the films at all the X PLLA values. These findings strongly suggest that PLLA-CL was miscible with PLLA and PCL, and that the dissolved PLLA-CL in PLLA-rich and PCL-rich phases increased the compatibility between these two phases.

Poly(l-lactide), that is, poly(l-lactic acid) (PLLA), poly(-caprolactone) (PCL), and their blend (50/50) films containing different amounts of poly(l-lactide-co--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 proteinase 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 proteinase K-catalyzed hydrolyzabilities of the PLLA-based blend films.