Spray-Coated Multilayer Cellulose NanocrystalChitin Nanofiber Films for Barrier Applications

Chitin is an abundant biopolymer whose natural production is second only to cellulose. Similar to cellulose nanocrystals (CNCs) or nanofibers (CNFs), chitin nanofibers (ChNFs) can be isolated and used as sustainable O₂ barrier materials for food, electronics, and pharmaceutical packaging. These bioavailable nanomaterials are readily dispersed in water enabling spray-coated films to be deposited at high rates onto uneven or delicate surfaces. In the present study, we demonstrate the successful layer-by-layer spray coating of cationic ChNF and anionic CNC suspensions onto poly­(lactic acid) (PLA) films. ChNF/CNC multilayers were found to lead to a reduction in the O₂ permeability of the final composite film by as much as 73% with the largest effects seen in composites with three alternating layers (ChNF-CNC-ChNF). Multilayer ChNF/CNC coatings were found to have lower O₂ permeability and lower haze than those coated with ChNF or CNCs alone (72% and 86% lower haze, respectively), pointing to a synergistic effect. The composites had a water vapor transmission rate similar to the PLA substrate