Life cycle assessment of manufacturing cellulose nanofibril-reinforced chitosan composite films for packaging applications.

Purpose: Increased accumulation of fossil-based polymer packaging films on land and ocean surfaces poses major environmental challenges to our ecosystem. Developing alternative packaging films with no or minimal environmental burdens is critically important. Cellulose nanofibril (CNF)-reinforced chitosan biopolymer composites are the most promising bio-based alternatives for packaging applications due to their biodegradable, biocompatible, and antimicrobial properties. This study evaluates the life cycle environmental impacts of chitosan-CNF composite films to identify the environmental hotspots that can be eliminated during large-scale production. Methods: A cradle-to-gate life cycle assessment is conducted to evaluate the environmental impacts of citric acid crosslinked chitosan-CNF composite films that can be used for packaging applications. The main manufacturing operations include (i) production of chitosan from shrimp shell waste, (ii) CNF production from forest biomass, and (iii) production of citric acid crosslinked composite films by the solvent-casting method. Life cycle inventory data are obtained from published literature and laboratory experiments. The environmental impacts are evaluated by US EPA's TRACI 2.1 impact assessment method. The effects of key process parameters on the environmental impacts of composite films are also evaluated. Results and discussion: The global warming potential (GWP) of manufacturing chitosan-CNF composite films is about 3.91 kg CO₂ eq./kg of the film, which is marginally lower than that of the fossil-based low-density polyethylene (LDPE) and bio-based poly(lactic acid) (PLA) films. The film casting sub-process in the composite film production contributes up to 90% of the total CO₂ emissions. The amount of sodium hydroxide used in the deproteination of shrimp shells is the most sensitive factor in all impact categories. The scenario analysis shows the increase in the CNF loading rate to improve the mechanical and barrier properties does not substantially increase the global warming potential (GWP) and other environmental impacts. Conclusion: A cradle-to-gate life cycle assessment of the chitosan-CNF composite film has demonstrated that the overall environmental impacts are comparable or lower than that of fossil-based polymers and other biopolymers considered in the flexible packaging applications. The development of renewable energy-based film dryers and environmentally benign methods to extract chitosan from shrimp shell waste can further reduce the GWP of composite films. When the end of life of fossil-based polymers is considered, the biodegradable nature of chitosan-CNF composite can be an environmentally attractive film for packaging applications. [ABSTRACT FROM AUTHOR]