Toughening poly(lactic acid) with novel polyolefin-graft-poly(lactic acid) copolymers maintaining high transparency and stiffness

The combination of well-balanced mechanical performance, high transparency and appealing eco-friendly attributes endows poly(lactic acid) (PLA) with significantly potential for wide-ranging applications in high-value packaging sectors. However, effectively toughening PLA without compromising its transparency and stiffness remains a formidable challenge. In this study, we synthesized a series of graft copolymers by incorporating hydroxyl-functionalized linear low density polyethylene (LLDPE_OH) and copolymers of cycloolefin (COC_OH) as the main chain and PLA as the side chain, which were subsequently employed as novel toughening agents for commercial PLA. The achievement of high-performance PLA blends with a balanced combination of toughness, strength, and transparency can be realized through meticulous tuning of the structure and mass fraction of the blended graft copolymers. The maximum elongation at break for the PLA blends increased by about 50 times that of neat PLA, reaching up to 300 %. Furthermore, these materials retained their high strength (54 MPa) and excellent transparency (light transmittance up to 90 %). The excellent properties of PLA blends could be ascribed to the well-designed chain structure of the graft copolymer which leaded to and excellent compatibility with the PLA matrix and unique phase morphology. This work is significant in guiding the design and synthesis of graft copolymers as toughening agents for PLA, thereby expanding its application range in areas where high transparency and toughness are required.