Effect of epoxy chain extenders on molecular structure and properties of polylactic acid

In this work, a novel functional polylactic acid (PLA) was prepared by melt blending using epoxy Joncryl ADR 4468 (ADR) as chain extender. The effects of the epoxy chain expander ADR on the molecular structure, crystallization properties, rheological properties, and mechanical properties of PLA were studied. Furthermore, the chain expansion mechanism was analyzed. It was found that the epoxy group of the epoxy chain extender reacted with the terminal hydroxyl and terminal carboxyl groups of PLA in the molten state, thus significantly increasing the molecular weight of PLA. Meanwhile, the weight average molecular weight of PLA increased by 42.51% when the maximum additional amount of epoxy chain extender was 1.2 wt%. The dynamic rheological experiments also confirmed that ADR can effectively improve the storage modulus, loss modulus and complex viscosity of PLA systems and the Cole-Cole diagram reveals the branched structure of PLA chain expansion systems. The formation of this branched structure will destroy the regularity of the PLA chain, reduce the crystallization capacity of PLA, and increase the cold crystallization temperature of the PLA system. Through SEM and mechanical property tests, it is found that the addition of ADR makes the molecular chain form a micro-crosslinked structure, thereby improving the tensile strength of PLA. Therefore, the molecular structure of PLA was effectively regulated and exhibited a promising performance, which greatly expands the potential applications of PLA.