Toughening modification of PLLA with PCL in the presence of PCL-b-PLLA diblock copolymers as compatibilizer

To obtain an effective compatibilizer for the blends of poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL), the diblock copolymers PCL-b-PLLA with different ratios of PCL/PLLA (CL/LA) and different molecular weights (M-n) were synthesized by ring-opening polymerization (ROP) of L-lactide with monohydric poly(epsilon-caprolactone) (PCL-OH) as a macro-initiator. These copolymers were melt blended with PLLA/PCL (80/20) blend at contents between 3.0 and 20 phr (parts per hundred resin), and the effects of added PCL-b-PLLA on the mechanical, morphological, rheological, and thermodynamic properties of the PLLA/PCL/PCL-b-PLLA blends were investigated. The compatibility between PLLA matrix and PCL phase was enhanced with decreasing in CL/LA ratios or increasing in M-n for the added PCL-b-PLLA. Moreover, the crystallinity of PLLA matrix increased because of the added compatibilizers. The PCL-b-PLLA with the ratio of CL/LA (50/50) and M-n >= 39.0 kg/mol were effective compatibilizers for PLLA/PCL blends. When the content of PCL-b-PLLA is greater than or equal to 5 phr, the elongations at break of the PLLA/PCL/PCL-b-PLLA blends all reached approximately 180%, about 25 times more than the pristine PLLA/PCL(80/20) blend.