Blends of aliphatic polyesters.: Part 7.: Effects of poly(L-lactide-co-ε-caprolactone) on morphology, structure, crystallization, and physical properties of blends of poly(L-lactide) and poly(ε-caprolactone)

Blended films of poly((L)-lactide) [ie poly((L)-lactic acid)] (PLLA) and poly(epsilon-caprolactone) (PCL) without or mixed with 10wt% poly((L)-lactide-co-epsilon-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. (C) 2003 Society of Chemical Industry.