Valorization of Poly(lactic acid) to Lactate Esters Using Task-Specific Ionic Liquids

Abstract

This work proposes a methodology based on the use of acidic task-specific ionic liquids (TSILs) to obtain lactate esters from poly(lactic acid) (PLA). TSILs differing for both the cation and the anion were synthesized, featuring imidazolium, ammonium, piperidinium, and morpholinium cations, bearing a solfobutyl chain. For anions, besides chloride, HSO4–was also used. TSILs were prepared under microwave irradiation and applied considering the sustainability guidelines to minimize the environmental impact of the upcycling process. After optimizing experimental conditions for reaction time and temperature, catalyst loading, nucleophile amount, catalyst reuse and scale-up of the process were performed, processing a 5-fold higher polymer amount. Considering the industrial applications of lactate esters, we tested the general applicability of our methodology using different alcohols as nucleophiles. Results evidence the promising performance of aliphatic TSILs that at 100 °C, under autogenous pressure, allowed the obtainment of different lactate esters from PLA, with quantitative conversion and yield from 47 to 88%. The process can be easily scaled up, and the best catalyst can be reused for at least three cycles without significant performance loss. Results collected were evaluated by the holistic approach to Green Chemistry and compared with IL-catalyzed processes reported in the literature.