Minimizing Oxygen Permeability in Chitin/Cellulose Nanomaterial Coatings by Tuning Chitin Deacetylation

The demand for packaging materials with low gas permeabilities is increasing, but commonly used petroleum-derived single-use plastics are not renewable, biodegradable, or easy to recycle. Nanomaterials composed of chitin and cellulose, which are abundant in nature, have high crystallinities and low oxygen permeabilities (OPs), providing a viable alternative. In this work, we explore how deacetylation conditions of crab shell chitin can be used to tune the charge and size of the resulting chitin nanowhiskers (ChNWs) and the resulting OP of layered film structures. Three deacetylation factors, the concentration of sodium hydroxide (% NaOH), temperature (T), and reaction time, were explored using a three-factor three-level Taguchi design with an orthogonal array. The resulting ChNW suspensions were sequentially spray-coated with suspensions of cellulose nanocrystals (CNCs) onto cellulose acetate (CA) films to form a multilayer structure. We show that ChNWs prepared under more aggressive deacetylation conditions inside the original orthogonal array (higher % NaOH, T, and time) had shorter lengths but the surface charge was significantly influenced only by more aggressive deacetylation outside of the original design conditions. With only ∼10% decrease in the ultimate tensile strength and no significant loss in failure strain, the ChNW-CNC coating resulted in ∼20% decrease in the water vapor transmission rate in comparison to uncoated CA films. The optimization of process conditions resulted in CA-ChNW-CNC films with a 91-99% decrease in OP (132-16.7 cm3·μm/m2/day/kPa vs 1553 cm3·μm/m2/day/kPa for uncoated CA).