Rapid Depolymerization of Polyester Fibers: Dimethyl Carbonate-Aided Methanolysis Combined with the Ball-Milling Approach

Abstract

Although polyethylene terephthalate (PET) bottles are conventionally reused using a material recycling process, the high content of impurities, such as dyes, pigments, and/or other fibers in the PET fibers, complicates the process. Chemical recycling is a promising method for PET fibers, but the depolymerization of PET fibers under mild conditions is still challenging due to their high crystallinity from the yarn-making process. Herein, we developed a rapid and efficient depolymerization process for PET fibers at room temperature by combining dimethyl carbonate (DMC)-aided methanolysis (DCAM) with a ball-milling (BM) approach. Compared with DCAM of PET fibers in a flask, the BM approach reduced not only the reaction time but also the amount of DMC required, which are key advantages toward practical application. To clarify the acceleration effect of BM on the depolymerization, PET fiber residues after the reaction were analyzed by gel permeation chromatography, differential scanning calorimetry, X-ray scattering, and solid-state NMR. The findings suggested that BM promotes the phase transformation of PET from its crystalline phase to its amorphous phase. In addition, BM induces efficient contact of the surface of the polymer with the catalyst/reagent, even in heterogeneous reaction media.