Largely improved tensile extensibility of poly(L‐lactic acid) by adding poly(ε‐caprolactone)

Poly(L ‐lactic acid) (PLLA) has good biocompatibility, biodegradability and physical properties. However, one of the drawbacks of PLLA is its brittleness due to the stiff backbone chain. In this work, a largely improved tensile toughness (extensibility) of PLLA was achieved by blending it with poly(ε‐caprolactone) (PCL). To obtain a good dispersion of PCL in the PLLA matrix, blends were prepared via a solution‐coagulation method. An increase in extensibility of PLLA of more than 20 times was observed on adding only 10 wt% of PCL, accompanied by a slight decrease in tensile strength. However, annealing of the samples led to a sharp decrease of extensibility due to phase separation and a change of crystalline structure. To conserve the good mechanical properties of PLLA/PCL blends, the blends were crosslinked via addition of dicumyl peroxide during the preparation process. For the crosslinked blend films, the extensibility was maintained nearly at the original high value even after annealing. Morphological analysis of cryo‐fractured and etched‐smoothed surfaces of the PLLA/PCL blends was carried out using scanning electron microscopy. Differential scanning calorimetry and polarized light microscopy experiments were used to check the possible change of crystallinity, melting point and crystal morphology for both PLLA and PCL after annealing. The results indicated that the combination of solution‐coagulation and crosslinking resulted in a good and stable dispersion of PCL in the PLLA matrix, which is considered as the main reason for the observed improvement of tensile toughness. Copyright © 2010 Society of Chemical Industry