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(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐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. © 2003 Society of Chemical Industry