Manufacturing process significantly impacts the rate of degradation of polylactic acid (PLA) under controlled composting conditions

Abstract

Bioplastic usage is increasing steadily to combat the negative environmental impacts associated with traditional, petrochemical-based plastics. Global bioplastics production is set to increase from 2.18 million tonnes in 2023 to 7.43 million tonnes by 2028. Polylactic acid (PLA) is the leading bioplastic on the market, with 31% of the global market share in 2023. With an increase in the use of PLA forecast for the near future, it is imperative to understand the real-world end-of-life options for this polymer. In this work, the effect of 3D printing versus injection moulding on the disintegration rates of PLA labware components was investigated. Commercially available PLA granules were 3D-printed using fused deposition modelling or injection moulded. 3D-printed PLA specimens showed an increased rate of disintegration (>90% after 12 weeks) under industrial composting conditions compared to the injection moulded specimens (∼54% disintegration after 12 weeks). The effect of mechanical recycling of neat PLA on disintegration rate was also investigated. PLA that had undergone mechanical recycling three times showed a slight increase in the rate of disintegration. The impact of surface topography and manufacturing method on the rate of disintegration of PLA is comprehensively studied through various analytical techniques (GPC, DSC, FTIR, SEM, and profilometry). This study provides insights into the effect of processing and postprocessing techniques on the real-life applications and end-of-life options of PLA components. The importance of component design and production method when developing ‘biodegradable’ alternative plastics is highlighted.