(629f) When and Where Do Bio-Plastics Make Sense?

Bioplastics are often touted as a solution to plastic waste, however when life cycle assessment is carried out this is often not the case and detailed analysis is needed to decide when and where bioplastics might make sense.

The term bioplastic can refer to plastics that are bio-based (i.e. made from a bio source) and/or biodegradable. A more helpful end-of-life term is compostable, but that can refer to both at home composting or industrial composting, which occurs at higher temperatures. Here we analyse pairs of plastics that can be used for the same purpose - PET & bio PET, LDPE & PBAT, polystyrene & PLA - and compare their life cycle carbon footprints.

Producing plastic from a bio source requires a complex series of steps with associated energy input. As such, with current UK grid electricity and gas, the fossil based plastics assessed have lower carbon footprints than their bio alternatives. As grid electricity decarbonises over time, a break-even point can be reached and the bioplastic has a lower carbon footprint that the fossil plastic. We also analysis the impact of moving to hydrogen from natural gas as a source of heat.

It is not only carbon footprint that is important - the impact of the plastic if it becomes litter is also important. We will discuss metrics developed to measure the impact of littering.

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.

[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