Life Cycle Assessment of Automobile Parts Made of Cellulose Nanofiber-Reinforced Bio-Polyethylene Using the Pulp Direct Kneading Method

Abstract

The development of cellulose nanofiber-reinforced plastics (CNFRPs) is a possible option for reducing the environmental impact of plastic products, such as automotive components. This study conducted a life cycle assessment (LCA) of CNF-reinforced bio-polyethylene (CNF-BioPE) as an alternative to conventional talc-reinforced polypropylene (Talc-PP). The CNF-BioPE was produced using the pulp direct kneading method, which simultaneously disintegrates pulp and disperses CNF into the polymer matrix, enabling industrial-scale feasibility. An LCA was conducted to compare the environmental performance of CNF-BioPE and Talc-PP. The study analyzed process inventories from raw material extraction to molding, including energy consumption during kneading and injection molding. The results indicated that scaling up CNF-BioPE production significantly reduces life cycle greenhouse gas (LC-GHG) emissions because of improved process efficiency and energy savings. While laboratory-scale production showed higher emissions than Talc-PP, industrial-scale production reduced emissions to nearly half of those for Talc-PP. Additionally, incorporating low-carbon electricity further reduced LC-GHG emissions by up to 43%. The study also examined the effects of land use change (LUC) associated with biomass cultivation, revealing that variations in LUC scenarios significantly influenced overall emissions. Furthermore, optimizing cooling time during injection molding resulted in energy reduction of 24% at the process level, with a reduction of 4% across the product life cycle. These findings suggest that CNF-BioPE has the potential to outperform Talc-PP in environmental performance when process improvements and renewable energy are applied. However, successful large-scale implementation requires advancements in acetylation process efficiency, stable demand for CNF-BioPE parts, and improvements in recycling infrastructure. Overcoming these challenges will be crucial for the widespread adoption of CNFRPs in the transition toward a decarbonized and resource-efficient society.