Increasing concern over plastic waste has led to the development of more degradable plastics, such as the bioplastic polylactic acid (PLA), which are widely used in applications such as 3D printing and packaging. However, even plastics not derived from crude oil products have limitations in their degradability, often requiring industrial composting conditions of high temperatures and humidities to be fully broken down. Researchers from the University of Bath’s Centre for Sustainable and Circular Technologies (CSCT) have now developed a new plastic based on PLA that degrades more easily under UV light, produced by incorporating sugar units into the polymer chains of the plastic.
Adding sugars into the polymer chains of PLA causes the material to be linked together by bonds that are easily broken using UV light, explained Antoine Buchard, Royal Society University Research Fellow and Reader in Polymer Chemistry from CSCT, who led the research. The plastic is thus weakened and can be broken into smaller polymer chains that are more sensitive to hydrolysis than the longer polymer chains typically present in PLA. More specifically, the PLA was copolymerized with a cyclic xanthate monomer synthesized from tri-O-acetyl-D-glucal, a derivative of d-glucose.
The resulting plastic, called poly(lactide-co-xanthate), was found to lose 40% of its mass within six hours of UV exposure, while incorporating only 3% of sulfur-containing linkages. The team found they could also tweak the degradability of the plastic by incorporating different amounts of sugar molecules into the polymer. The copolymerization method could be used to increase the degradability of the PLA without significantly changing its materials properties, the authors concluded. The improved degradability could allow the plastic to break down more easily in natural environments such as the ocean or a compost heap, without needing to use an industrial waste composter to effectively break down, Buchard said. This research was published in Chemical Communications.
“Previously scientists have looked at enhancing the degradability of PLA to water – hydrolysis – but this is the first time anyone has looked at using light,” said Buchard. “This strategy remains to be translated to real-life plastics objects and tested with sunlight, but we hope our technology could be used in the future to make plastics that are strong when you’re using them, but can break down easily when reuse and recycling are not possible anymore.”
The technology used to produce the UV-degradable plastic is compatible with existing plastic manufacturing processes, meaning it could potentially be tested and adopted quickly by the plastics industry; the researchers hope their findings will be used by the industry to help make plastic waste more sustainable in the future.