Prospective Life Cycle Assessment of Cellulose Nanofiber-Reinforced Plastics Produced by the Reactive Processing Method, Considering Continuous Production and Scale-up for Industrialization

Cellulose nanofiber-reinforced plastics (CNFRPs), composites of nanofibrillated plant-derived pulp, have become possible substitutes for conventional structural materials because of their advantageous properties of lightness, stiffness, and recyclability. The reactive processing (RP) method is one of the emerging technologies for producing CNFRPs, promoting the nanofibrillation of cellulose during kneading and simultaneously dispersing it into the base polymer, and is therefore expected to reduce life cycle greenhouse gas (LC-GHG) emissions from structural materials such as automotive parts. Their environmental impacts should be assessed in advance. However, at this stage, the composites are usually produced by small-scale or inefficient processes, making proper evaluation challenging. In this study, we performed a prospective life cycle assessment for CNF-reinforced bio-polyethylene (CNF/bioPE) and CNF-reinforced fossil-derived polyethylene polypropylene (CNF/PP) in comparison with talc-reinforced polypropylene (talc/PP), commonly used in automotive parts. The estimates are based on actual measurement data from laboratory-scale equipment, considering the influence of technological development and scale-up by industrial implementation. The results show that only CNF/bioPE has lower LC-GHG emissions than talc/PP. This remains true regardless of the scenarios, whether including or excluding the effects of bagasse power generation and high or low direct land use changes (dLUC) associated with sugarcane cultivation in the production of bioPE. The LCA based on LIME impact categories shows that there are some categories in which CNF/bioPE has a higher impact than talc/PP. However, in the integration category, the impact of CNF/bioPE is lower than that of talc/PP. This suggests that substituting talc/PP with CNF/bioPE could reduce overall environmental impacts. Contributing to this result is the CO2 absorption effect during bioPE production. The key advantage of this method for producing CNFRPs lies in their ability to strengthen biomaterials to a practical level with low environmental impacts.