An efficient and scalable melt fiber spinning system to improve enzyme-based PET recycling

Abstract

Chemical recycling technologies based on hydrolase enzymes that can depolymerize PET thermoplastic are emerging, yet these approaches require the polymer to be low crystallinity to achieve high conversion. To prepare the polymer for enzymatic depolymerization, current processes rely on melting and cryomilling PET at depressed temperatures to reduce crystallinity and prevent annealing during micronization; however, these approaches require large capital investment in costly equipment, and are not easily incorporated into intermediate-scale, distributed systems. Here, we describe a melt fiber spinning system that achieves significant reduction in crystallinity for real-world PET feedstocks without the need for any active cooling, and can easily be scaled up or down as needed. Single-use water bottles and drinking cups are tested, where they are extruded, drawn and spooled as thin fibers that cool by passive heat dissipation rapidly enough to quench the polymer to low crystallinity (<10%). Additionally, we estimate the fiber spinning also increases the feedstock surface-area-to-volume ratio by up to 15-fold, which further benefits heterogenous enzyme biocatalysis. In small scale PET hydrolase enzyme incubation tests, fiber spinning increased monomer released from PET by 4-fold for drinking cups and 10-fold for water bottles compared to shredded-only controls. Finally, we also show that this system can scale to >300 gs, with the potential for much larger scales, and allows for >95% depolymerization in a larger 20 liter bioreactor run.