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(ε‐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(ε‐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.