Chemical Recycling of Polyethylene Terephthalate (PET) Driven by the Use of Protic Ionic Liquids: A Strategy to Mitigate Microplastic Pollution

Abstract

Microplastic pollution is a growing environmental concern, requiring the development of efficient recycling processes to mitigate its impact and ensure proper waste disposal. Chemical recycling has emerged as a promising strategy; however, conventional techniques often rely on hazardous solvents, long reaction times, and extreme operating conditions, like high temperatures and pressures. In this context, protic ionic liquids (PILs) have gained attention as sustainable alternatives due to their thermal stability, reusability, and ability to optimize reaction conditions. This study investigates the hydrolysis of polyethylene terephthalate (PET) microplastics using low-toxicity PILs as solvents. The depolymerization efficiency was evaluated using four PILs: choline formate ([ChFor]), triethanolammonium acetate ([TEAA]), 1,5-diazabicyclo [4.3.0] non-5-ene acetate ([DBNH][OAc]), and tetramethylammonium formate ([TeMA][For]). These PILs were synthesized and characterized by FTIR and ¹H NMR spectroscopy to confirm their structures. Cytotoxicity assays using Artemia salina classified these compounds as low or nontoxic (LC₅₀ > 250 μg/mL). The results demonstrated that all studied PILs were capable of depolymerizing PET. Among them, [DBNH][OAc] exhibited the highest efficiency, achieving 99.67% PET conversion and 92.52% terephthalic acid (TPA) yield at 110 °C within 30 min. Structural characterization confirmed the production of TPA, supporting its potential reintegration into industrial applications and preventing recontamination by microplastics.