Toughening modification of PLLA by combination of copolymerization and in situ reactive blending

Abstract

The inherent brittleness and low melt strength of poly(L-lactide) (PLLA) are major bottlenecks for its large scale commercial applications. In this work, high toughness and high melt strength PLLA blends were prepared by reactive blending of PLLA, PLLA-b-poly(butylene adipate-co-terephthalate)-b-PLLA (PLLA-b-PBAT-b-PLLA) in the presence of (PLLA-block-poly(glycidyl methacrylates))₃ (PLLA-b-PGMA)₃. Among them, PLLA-b-PBAT-b-PLLA was synthesized by the combination of melt condensation and ring-opening polymerization (ROP), and (PLLA-b-PGMA)₃ was synthesized by the combination of ROP and atom transfer radical polymerization (ATRP). The structure was confirmed by NMR spectra, FTIR spectra and GPC. Mechanical testing demonstrated that the blends containing PLLA, PLLA-b-PBAT-b-PLLA, and (PLLA-b-PGMA)₃ exhibited higher elongation at break compared to the neat PLLA, and did not significantly lose tensile strength. The higher viscosity and storage modulus of PLLA blends indicated the production of the longer chains or even long chains branching. The strain hardening behaviour was observed obviously with increased elongational viscosity. The imperfect crystallization of PLLA/PLLA-b-PBAT-b-PLLA/(PLLA-b-PGMA)₃ blends was demonstrated by the lowered melt point of PLLA. Scanning electron micrographs showed that the PLLA-b-PBAT-b-PLLA was dispersed well in the PLLA, and the interface adhesion was further increased after addition of (PLLA-b-PGMA)₃. Moreover, optimization of parameters such as the PLLA-b-PBAT-b-PLLA concentration, and (PLLA-b-PGMA)₃ content revealed that blends containing 30 wt% PLLA-b-PBAT-b-PLLA and 2 wt% (PLLA-b-PGMA)₃ were optimal in terms of comprehensive properties.