Synthesis and chemical recycling of polyesters promoted by Zn complexes

Polylactide (PLA) is an aliphatic polyester obtained from renewable sources, it is biocompatible, biodegradable and thanks to its good mechanical properties it can be used to replace common petroleum-based polymers in many sectors. Although these features design a green profile for PLA, its current production and waste management strategies show some weaknesses in terms of sustainability. PLA is obtained industrially by Ring-Opening Polymerization (ROP) of lactide (LA) promoted by toxic Sn-based catalysts, and its end-of-life management is still aligned to a linear economic model. A desirable fate for PLA is chemical recycling that enables the production of monomers and/or value-added materials to create a circular economic model for PLA that supports the growing use of this plastic.1 Currently, hydrolysis and alcoholysis are the two most effective methods for treating PLA waste. Hydrolysis produces lactic acid, thus closing the life cycle of PLA (path a). Alcoholysis, an efficient upcycling strategy, converts PLA waste into alkyl lactate, which is widely used as an environmentally friendly solvent (path b). In addition, the use of diols such as ethylene glycol and 1,4-butanediol enables the production of polyols (path c), which are valuable for the preparation of polyurethanes.