Effect of solid-state polymerization on the structure and properties of mechanically recycled poly(lactic acid)

Abstract

Poly(lactic acid) (PLA) is one of the most important alternatives to fossil-fuel based polymers due to its biodegradability and good properties. However, the growing production along with the increasing resistance to degradation of the newer grades could lead to waste management problem. The application of mechanical recycling, which could be the best valorization method for biodegradation-resistant PLA residues, is limited by the degradation of the polymer, which decreases its performance, so it is interesting to develop simple and acceptable methods to improve the recycled plastic. The aim of this work is to study the effect of thermal treatments of PLA residues (with two levels of degradation) on the structure and properties of recycled PLA. During thermal treatments, both polycondensation and degradation reactions take place, and the net result depends on the degradation level of the residue and the time and temperature of the treatment. In adequate conditions, polycondensation reactions increase the molecular weight of the residue and lead to significant improvements of the mechanical and thermal properties of the recycled plastic. These results suggest that thermal treatments represent a simple, cost-effective and environmentally friendly method to improve the recyclability of PLA and, hence, the environmental impact of this plastic.