Mechanical recycling of poly(lactic acid): Evaluation of a chain extender and a peroxide as additives for upgrading the recycled plastic

Abstract

Mechanical recycling of poly(lactic acid) (PLA) could improve the social, economic and environmental impacts of the use of this bioplastic. However, the degradation of the polymer during its service life and during mechanical reprocessing reduces the performance of the recycled material, so it would be of great interest to develop cost-effective methods to improve the properties of this material. In this work, the effects of two additives, a chain extender and an organic peroxide, on the structure and properties of mechanically recycled PLA have been investigated. Two PLA residues, a simulated post-consumer one and a severely degraded material, have been considered. The study of the mechanisms of action has revealed that the two additives react with the PLA residues giving rise to cross-linking, branching and chain extension reactions, but also to degradation processes, thus explaining that the overall effect of the additives depends on the amount used and the previous degradation of the polymer. Significant improvements in viscosity, thermal stability and microhardness have been obtained, indicating that the use of these additives could be suitable for improving the recyclability of PLA and reducing the consumption of raw materials.