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

Abstract

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).

Roll-to-Roll, Dual-Layer Slot Die Coating of Chitin and Cellulose Oxygen Barrier Films for Renewable Packaging

“…This OP is also lower than that of a spray-coated PLA-ChNF-CNC film from a previous study (∼20 cm 3 ·μm/m 2 /day/kPa with a 1-μm-thick coating layer), which is probably because of the much thicker coating layer in this work (i.e., 31 and 39 μm). Another possibility is that the ChNFs used in the aforementioned work were significantly longer than those in our work, i.e., several microns versus 118 ± 55 nm, and it has been found that shorter ChNFs may result in a lower OP because they pack more densely …”

“…This was repeated 10 times and averaged. The degree of acetylation (DA) of ChNF was determined by potentiometric titration using a pH meter (Seven Excellence S400, Mettler Toledo) . The ζ potential values of 0.025 wt % ChNF and 0.025 wt % CNC, which were diluted with pH = 3 HOAc solution and 5 mM NaCl solution at pH = 7, respectively, were measured by a Zetasizer Nano ZS (Malvern Panalytical, U.K.).…”

“…However, the mixing could be due to the higher viscosity ratio in our work (i.e., the viscosity of the top layer is higher than that of the bottom layer), leading to mixing along the lip of the middle die plate. 39 Schmitt et al 16 investigated dual-layer slot coating of relatively high-viscosity liquids. They found that up to a critical point, high wet thickness ratio (the top coating is thicker than the bottom coating), the coating would be stable due to the pressure gradient.…”

“…CNC film fabrication from suspension has utilized batch techniques such as spin coating and continuous processes such as slot die and gravure coating. Methods such as spray coating, regeneration from the gel, and layer-by-layer deposition have been used for coating ChNF suspensions (or chitin nanowhiskers) for biomedical, optical, and barrier applications. ,− Gravure and spray coatings often require multiple applications to achieve a desired, uniform thickness and can be challenging for suspensions with relatively high viscosity . Spin coating is not suitable to produce films continuously with a large area .…”

Optimization of spray-coated nanochitin/nanocellulose films as renewable oxygen barrier layers via thermal treatment

“…A 0.5 wt% ChNW suspension was obtained by deacetylating commercial chitin (Tidal Vision, USA) sourced from crustacean shells under the optimized conditions as previously reported, i.e., in a 40% sodium hydroxide (NaOH) solution heated with an oil bath at 155 1C for 140 min with a liquid-solid ratio of 25 : 1 (mL g À1 ), followed by high-pressure homogenization. 22 A 0.5 wt% CNC suspension was obtained by diluting a 10 wt% CNC slurry extracted from pulp provided by USDA Forest Products Laboratory, USA. The properties for CA, ChNW, and CNC are available in Tables S1, S2 and S3 (ESI †) respectively, and details about their characterizations are available in the ESI.…”