Solid-State Enzymatic Hydrolysis of Mixed PET/Cotton Textiles

Waste polyester textiles are not recycled due to separation challenges and partial structural degradation during use and recycling. Chemical recycling of polyethylene terephthalate (PET) textiles through depolymerization can provide a feedstock of recycled monomers to make "as-new" polymers. While enzymatic PET recycling is a more selective and more sustainable approach, methods in development, however, have thus far been limited to clean, high-quality PET feedstocks, and require an energy-intensive melt-amorphization step ahead of enzymatic treatment. Here, high-crystallinity PET in mixed PET/cotton textiles could be directly and selectively depolymerized to terephthalic acid (TPA) by using a commercial cutinase from Humicola insolens under moist-solid reaction conditions, affording up to 30±2 % yield of TPA. The process was readily combined with cotton depolymerization through simultaneous or sequential application of the cellulase enzymes CTec2®, providing up to 83±4 % yield of glucose without any negative influence on the TPA yield.