Susana M. Meza Huaman, Jake H. Nicholson, and Alex P. S. Brogan, King’s College London, UK, have developed a chemical recycling process that uses enzymes typically found in organic detergents to break down deposited bioplastics. The team solubilized and stabilized the commercially available lipase B from Candida antarctica (CaLB) in ionic liquids. The enzyme hydrolytically depolymerizes post-consumer polylactic acid (PLA) plastic, demonstrating complete degradation within 24 hours and complete conversion to monomers within 40 hours at 90°C. Until now, an industrial composting process that takes 12 weeks has been used to recycle bioplastics.

The researchers modified the surface of CaLB to enable stability and activity in the readily available ionic liquid [emim][OAc], selected for its ability to solubilize PLA, using a three-step synthesis process. This involved cationization of the acidic residues to produce a cationized enzyme (C-CaLB), which was then complexed with a surfactant (S) to form [C-CaLB][S]. Dehydration and annealing of [C-CaLB][S] resulted in a dark brown solvent-free liquid with enhanced solubility in various ionic liquids.

The team says that this simple and scalable modification method provides a blueprint for improving the efficacy of any hydrolytic enzyme for plastics recycling. After conversion to monomers, the material can be converted to plastics of comparable quality. According to the researchers, their study represents a significant advancement in the recyclability of single-use biodegradable plastics, advancing the potential for a sustainable circular economy. The scientists are now working to expand their research to improve the recycling of other commonly used and mass-produced plastics, such as polyethylene terephthalate (PET).

• A general route to retooling hydrolytic enzymes toward plastic degradation,
  Susana M. Meza Huaman, Jake H. Nicholson, Alex P. S. Brogan,
  Cell Reports Physical Sciences 2024.
  https://doi.org/10.1016/j.xcrp.2024.101783