Reduction of molar mass loss and enhancement of thermal and rheological properties of recycled poly(lactic acid) by using chain extenders obtained from RAFT chemistry

The synthesis of block copolymers of glycidyl methacrylate (G), styrene (S) and acrylonitrile (AN) (represented as GS-SAN) by reversible addition-fragmentation chain transfer (RAFT) polymerization, with well-defined average molar masses and epoxy functionalities, and evaluation of their performance as macromolecular chain extenders for recycled poly(lactic acid) (rPLA), is reported. The introduction of the GS-SAN chain extenders during the extrusion processing of rPLA leads to recovery of molar mass as well improvement of thermal stability and rheological properties, compared to recycled unmodified PLA. Differential scanning calorimetry (DSC) results revealed a reduction in cold crystallization temperature and an increase in the degree of crystallinity of chain extended rPLA. Increasing epoxide content in the synthesized block copolymers leads to increased degrees of crystallinity. The rheological study revealed that the GS-SAN copolymers allowed significant increases in modulus, strength and complex viscosity of chain extended rPLA, indicating that better mechanical performance and processability were obtained. These increases become more pronounced as the concentration of reactive epoxy functional group is increased.