Biodegradability of polyhydroxyalkanoate (PHA) biopolyesters in nature: a review

In the search for sustainable alternatives and substitutes to overcome plastic pollution, polyhydroxyalkanoates (PHA) stand out as the gold standard. The very fact that PHA are microbially produced from renewable carbon sources, biodegraded by microbial action, and possess the beneficial properties of over 50% of the world's plastics has caught the attention of a wide range of producers, converters, brand owners, and policy makers with a view to replace conventional fossil-based plastics with these natural materials. PHA are readily biodegraded by the enzymatic toolbox of living organisms, aligning with the principle of natural circularity. Over 150 different monomeric building blocks of PHA have been identified, leading to a wide variety of naturally accessible PHA biopolyesters with diverse properties that include thermoplastic and crosslinkable polymers for single use and durable uses for packaging and personal care and as paints, coatings and adhesives, and as fibers for fabrics and textiles. The type of monomer and microstructure, as well as the environment, play important roles in their production and biodegradation. This comprehensive paper reviews the degradability of commercially available and other PHA types with varying microstructures in fresh water, sea water, soil, as well as in home and industrial composting and anaerobic conditions. Unlike previous reviews the authors integrate information from diverse biodegradation studies and provide a holistic view and understanding of the biodegradability of the PHA biopolymer family in nature and in industrial environments.