Solvent-free infrared polymerization of lactic acid: toward greener PLA production

Abstract

Polylactic acid (PLA) is a biodegradable polymer derived from renewable feedstocks, offering significant environmental advantages for applications in packaging, biomedical devices, and textiles. Despite its many advantages, PLA synthesis often involves energy-intensive processes that limit its sustainability. Here, we present a rapid, solvent-free method for PLA synthesis employing infrared (IR) irradiation as an alternative energy source, combined with Brønsted or Lewis acid catalysts to achieve direct, stereo-controlled polymerization of lactic acid (water solution 85%) under atmospheric pressure. Through systematic evaluation of organic, inorganic, and organometallic catalysts, we identify Sc(OTf)₃ and PTSA as optimal catalysts, yielding PLA with molecular weights (M_n) up to 8 kDa, within six hours under atmospheric pressure. Scaling the reaction from 2, 4, 5 to 50 g demonstrated process robustness. The whole synthesis requires only 1.5 kW of energy in 6 h, generates no chemical waste, and minimizes environmental impact, highlighting a sustainable, scalable approach for PLA production. This work establishes an effective balance between catalytic efficiency, polymer quality, and sustainability, offering a promising route towards greener biopolymer manufacturing aligned with global environmental goals.