Biodegradable and conventional plastic packaging: Comparison of life cycle environmental impacts of poly(mandelic acid) and polystyrene

Abstract

Most of plastic packaging waste does not degrade over time, which can lead to harmful effects on aquatic life and humans, highlighting the need for packaging materials that are easily degradable. Poly(mandelic acid) (PMA) is a biodegradable polymer that has been proposed as an alternative to polystyrene for use in packaging. However, its potential to replace the existing packaging materials also depends, among other factors, on the environmental sustainability of its production. This study aims to estimate and compare the life cycle environmental impacts of the production of PMA via polymerisation of 5-phenyl-1,3-dioxolane-4-one (Ph-DOX) and o-carboxyanhydride (OCA) monomers. For each route, the impacts are evaluated for 18 ReCiPe categories for reported laboratory scales and potential scaled-up commercial production. The results suggest that most of the impacts of PMA production via the Ph-DOX route are significantly lower (≥20%) than that of the OCA route for both the laboratory and large scales. However, compared to polystyrene, the impacts of large-scale PMA production via the (better of the two) Ph-DOX route are more than five times higher. This is largely due to the use of benzaldehyde, enzymes, hydrocyanic acid and sodium phosphate in the production of mandelic acid and the solvents utilised in monomer synthesis. A sensitivity analysis shows that the bio-transformation of bio-glycerol to produce mandelic acid would reduce 16 out of 18 life cycle impacts of PMA by 6–77%. The impacts are also sensitive to the assumptions used in the scaling-up of laboratory data for solvents. However, the results indicate clearly that, despite all the uncertainties in the scaling-up method, the proposed production routes for PMA would still have several times higher environmental impacts than polystyrene. Therefore, further research would be needed to improve significantly the production process for (bio-)mandelic acid, synthesis of monomers and their polymerisation before PMA can be considered an environmentally sustainable option for packaging applications.