Advancing circular additive manufacturing: Life cycle sustainability assessment of gears made from recycled polylactic acid

This study evaluates the mechanical performance and life cycle sustainability of post-consumer recycled polylactic acid (rPLA) for use in the fused filament fabrication of 3D-printed gear components. Five material compositions ranging from 0 % to 100 % rPLA blended with virgin PLA (vPLA) were assessed through tensile testing and gear function trials. To balance the technical evaluation, a comprehensive life-cycle sustainability assessment was conducted, incorporating environmental (ELCA), economic (LCC), and social (SLCA) indicators using a triple bottom line sustainability framework. Mechanical testing showed a slight reduction in tensile strength with increased rPLA content, with the 50:50 blend (V50:R50) achieving 52.83 MPa compared to 61.12 MPa for 100 % vPLA. All the blends maintained functional gear performance with no slippage. Environmentally, rPLA-rich blends significantly lowered global warming potential, cumulative energy demand, and abiotic resource depletion. Economically, although rPLA reduces raw material and energy costs, filament quality variability introduces preprocessing challenges, slightly increasing the overall production costs. Socially, rPLA-inclusive systems have demonstrated strong potential for improving local employment, training, and worker safety, particularly within decentralised recycling networks. The V50:R50 blend achieved the highest overall sustainability score (−1.35), offering the most balanced trade-off between mechanical performance and triple bottom line sustainability, outperforming both pure vPLA (−1.96) and pure rPLA (−1.75). These findings support the viability of rPLA in noncritical gear applications and underscore the importance of future research on quality assurance systems and cost-effective preprocessing technologies.