Enzymatic Recycling of Polyurethanes

New recycling methods are needed to deal with the ever-increasing generation of plastic waste. Conventional recycling processes are limited by cost and the gradual degradation of material with each cycle. Although chemical recycling allows the production of virgin-quality plastic, it generally requires high energy consumption. Enzymatic recycling is emerging as a green alternative because it enables the use of mild processing conditions to regenerate the polymer’s building blocks. In this technique, enzymes are utilized to catalyze the hydrolysis of chemical bonds in polymers. Ideally, enzymatic repolymerization is then applied to these monomers to complete the green cycle. While current research efforts in the field mostly focus on polyethylene terephthalate (PET), the enzymatic recycling of polyurethanes (PU) is gaining momentum. As the sixth most produced type of plastic, PU is an exciting candidate for enzymatic depolymerization, which is enabled by its hydrolyzable backbone. In this chapter, the state of the art of enzymatic recycling is provided from the patent perspective and the scientific literature. Patents related to the enzymatic depolymerization of polyesters, polyamides, and polyurethanes will be discussed. This will be followed by a brief overview on recent progress in the enzymatic degradation and recycling of PU. Finally, this chapter will paint a picture of the future of this field by discussing current limitations and solutions.