Scientists at King’s College London have developed a new method to chemically recycle polylactic acid (PLA) at much faster rates than the standard 12-week-long industrial composting process.
PLA accounts for 27% of bioplastics production worldwide, out of a total of 1.79 million tonnes in 2023. It is the most popular biopolymer for commercial applications and its mostly used in single-use packaging applications. However, PLA recycling is severely limited at present and its biodegradation in industrial composting settings is very slow, taking up to 84 days at 60 C.
To address this problem, the researchers developed a PLA depolymerisation technology using ionic liquids. Ionic liquids are organic salts with melting temperatures below 100 C. They have been shown to have the ability to solubilise polymers used in common plastics such as PET and PLA. However, the enzymes needed to depolymerise plastics are known to have low tolerance to ionic liquids and are often insoluble in them.
The academics solved this issue by solubilising and stabilising an enzyme commonly found in biological laundry detergent, the enzyme lipase B from Candida antarctica, in ionic liquids. In doing so, they unlocked the ability of the enzyme to hydrolytically depolymerise post-consumer PLA.
Results show full PLA degradation within 24 hours and full conversion to monomer within 40 h at 90 C.
“This facile and scalable modification strategy allows for elevated operation temperatures in combination with the superior solvent capabilities of ionic liquids, providing a blueprint for enhancing the capability of any hydrolytic enzyme for plastic recycling,” the academics wrote.
The scientists are now extending their research into improving the recycling of other commonly used and mass-produced plastics, including PET.
“The inspiration for this project came from a problem with bioplastics used in medical and surgical products degrading in the body,” explained Dr Alex Brogan, Lecturer in Chemistry at King’s. “We’ve turned this problem around and applied it to the issue of recycling the single-use bioplastics we use in our everyday lives using a common enzyme found in biological laundry detergent. Being able to harness biology to deliver sustainable solutions through chemistry, allows us to start thinking of waste as a resource so that we can move away from oil and other non-renewable sources to create the materials we need for modern life.”
The team shared their findings in “A general route to retooling hydrolytic enzymes toward plastic degradation,” recently published in Cell Reports Physical Science.