Solvent-Free One-Pot Recycling of Polylactide to Usable Polymers and Their Closed-Loop Recyclability

Abstract

Due to concerns of environmental pollution and resource shortage related to the fossil fuel-based nondegradable plastics, biomass/biobased degradable polymer materials, especially polylactide (PLA), have received increasing attention in recent years. Although PLA can be depolymerized back to the cyclic monomer lactide, achieving a closed-loop cycle of “polymer-monomer-polymer”, it is very attractive but still a great challenge for recycling PLA to a high-performance polymer through a simple and green strategy suitable for industrialization. Herein, a facile solvent-free one-pot recycling strategy is developed to efficiently convert PLA and end-of-life PLA disposable products into an upgraded PLA-based polymer with enhanced performance. The recycling strategy involves a controlled fast catalytic alcoholysis to prepare a dihydroxyl-terminated PLA oligomer, i.e., PLA-diol, and subsequently a chain extension reaction to obtain PLA-based polyurethane, i.e., PLA–PU. The resulted PLA-diol and PLA–PU with well-defined structures were clearly characterized by ¹H NMR, MALDI-TOF MS, etc. Significantly, the PLA–PU exhibits enhanced mechanical properties that are preferable to those of PLA and can be processed through injection molding, melt spinning, and 3D printing. Besides, PLA–PUs can be directly depolymerized into monomer l-lactide with a high yield under vacuum, revealing its excellent recyclability, which demonstrates a proof of concept for closed-loop recycling from PLA to PLA–PUs and back to PLA. This work opens a potentially new industrial avenue of recycling PLA and other aliphatic polyester plastics.