Biodegradation of polyurethane: a review

Lack of degradability and the closing of landfill sites as well as growing water and land pollution problems have led to concern about plastics. Increasingly, raw materials such as crude oil are in short supply for the synthesis of plastics, and the recycling of waste plastics is becoming more important. As the importance of recycling increases, so do studies on elucidation of the biodegradability of polyurethanes. Polyurethanes are an important and versatile class of man-made polymers used in a wide variety of products in the medical, automotive and industrial fields. Polyurethane is a general term used for a class of polymers derived from the condensation of polyisocyanates and polyalcohols. Despite its xenobiotic origins, polyurethane has been found to be susceptible to biodegradation by naturally occurring microorganisms. Microbial degradation of polyurethanes is dependent on the many properties of the polymer such as molecular orientation, crystallinity, cross-linking and chemical groups present in the molecular chains which determine the accessibility to degrading-enzyme systems. Esterase activity (both membrane-bound and extracellular) has been noted in microbes which allow them to utilize polyurethane. Microbial degradation of polyester polyurethane is hypothosized to be mainly due to the hydrolysis of ester bonds by these esterase enzymes.