A comparative life cycle assessment of kraft lignin and hemp straw fillers to improve ductility of polylactide (PLA) 3D printed parts

Abstract

This research is motivated by the increasing demand for bio-based materials, the recent growth of the U.S. hemp industry, and the broader trend of using sustainable filaments in additive manufacturing. This study presents a comparative life cycle assessment (LCA) of untreated hemp straw and kraft lignin as fillers for polylactic acid (PLA) 3D-printed tensile specimens to evaluate their environmental impacts. Both materials, being low-cost renewable bio-based fillers, can enhance elongation of PLA while reducing the environmental footprint of 3D-printed components. The environmental impacts of hemp straw-PLA and kraft lignin-PLA were assessed using several life cycle impact assessment (LCIA) methods, including ReCiPe 2016 Endpoint (H), Cumulative Energy Demand (CED), and IPCC GWP100. Hemp straw showed lower environmental impacts than kraft lignin across most categories, making it a more favorable option for eco-conscious prosumers. The ReCiPe 2016 results indicated that major impact categories for kraft lignin-PLA were fine particulate matter formation, global warming potential, and human toxicity, with filament production being the major contributor. For hemp straw-PLA, hemp straw pre-processing was the major contributor. The CED method revealed that nonrenewable fossil resources had the highest impact on both materials. IPCC GWP100 results aligned with CED, showing higher greenhouse gas emissions for kraft lignin-PLA, mainly due to fossil fuel use. Sensitivity analysis of transportation distances showed no significant differences in impact results, while alternative LCIA methods (TRACI and IMPACT World+) confirmed the consistency of the findings. To build upon this study, future work will explore the environmental performance of treated hemp materials as alternative fillers for 3D-printed components.