(361c) Bio-Based and Biodegradable Plastics - When and Where Do They Make Sense?

Bio-based and biodegradable plastics offer interesting alternatives to traditional fossil based plastics, however it is not as simple as just substituting one for the other. Producing bio-based plastics uses a lot of energy, with associated environmental impacts, and biodegradable plastics must degrade in the environments they find themselves and not contaminate recycling streams.

Here we discuss some of the challenges associated with life cycle assessment of bio-based and biodegradable plastics, then we use life cycle assessment to compare pairs of similar polymers, for example bio-based and fossil based PET, and Polystyrene and PLA. The assessment takes into account the predicted decarbonisation of the electricity grid and the use of alternative heating sources to replace natural gas. The comparisons allow a ‘cross-over’ to be evaluated - the year in which the bio-based polymer has a lower global warming potential than the fossil-based polymer.

The bio sources used to make bioplastics take in carbon dioxide during growth. When the bioplastic reaches end of life this carbon is most often released to the atmosphere, either through composting, incineration or landfill. If instead bioplastics were made to be durable, they would effectively lock in carbon for a long period of time and become a route for carbon sequestration. Over 1 gigatonne of carbon could be sequestered in plastics every year1. The sequestration potential of plastics will be discussed, highlighting the opportunities and challenges.

[1] Ryan, A.J., Rothman, R.H. Engineering chemistry to meet COP26 targets. Nat Rev Chem 6, 1–3 (2022). https://doi.org/10.1038/s41570-021-00346-6