(655d) Optimization of Chitin Nanowhisker Deacetylation for Utilization in Renewable Oxygen Barrier Films and Coatings

The low oxygen permeabilities (OP) of cellulose and chitin nanocrystals have generated considerable interest in their application in food and beverage packaging as renewable substitutes for petroleum-based plastics. One approach is to apply aqueous suspensions of chitin and cellulose nanomaterials as coatings on a substrate film to improve its oxygen barrier property. Because chitin is cationic in acidic solution while sulfate-modified cellulose is anionic, the electrostatic attraction of the opposite charges may allow the fabrication of their nanomaterials into multilayered coatings. When such coatings dry very slowly, over several days, the nanofibers or nanocrystals pack densely and create low OP structures. However, when coating and drying are accelerated to realistic manufacturing throughputs, the OP of the resulting films increases and barrier performance is lost. This work demonstrates how the OP of high-throughput coated chitin and chitin-cellulose films can be improved considerably through optimization of the degree of acetylation (DA) of the chitin nanowhisker (ChNW). The DA is the percentage of acetamino groups to the sum of amino and acetamino groups, and indicates the charge density on the surface of ChNW.

In this work, ChNW and cellulose nanocrystals (CNC) were spray-coated on cellulose acetate (CA) film in an alternating sequence. The deacetylation of chitin extracted from crab shells was optimized to improve the oxygen barrier property of the coated film. Three factors influencing the deacetylation reaction were adjusted: concentration of sodium hydroxide (NaOH), reaction temperature and reaction time. The Taguchi method was applied for the design of experiments, the determination of the optimal deacetylation conditions and the relative effect of each factor.

The optimal conditions in the specified region of study were determined as 35 wt%, 140℃ and 140 min, and the order of the contribution of each factor was temperature (68.0%) > NaOH concentration (21.7%) > time (10.3%). The ChNW prepared under more aggressive conditions resulted in better oxygen barrier properties (lower OP). In layered coatings containing ChNW and CNC on CA, the OP decreased from 1550 cm³âˆ™Î¼m/m²/day/kPa for uncoated CA, to 44.0 cm³âˆ™Î¼m/m²/day/kPa for coating without ChNW optimization, to a minimum of 16.7 cm³âˆ™Î¼m/m²/day/kPa for the optimal coating. This result is comparable to the OP of oriented poly(ethylene terephthalate). In addition, the coating led to ~20% improvement in water vapor transmission rate and similar mechanical properties to those of the neat CA film.

Furthermore, we present the preliminary results of improving the oxygen barrier property with the addition of chitosan to ChNW. Chitosan is highly deacetylated chitin, the DA of which is <10% in this work. When the mass ratio of chitosan to ChNW prepared under more aggressive conditions was 1:1, the OP of the coated CA film with ChNW+chitosan and CNC decreased to 8.9 cm³âˆ™Î¼m/m²/day/kPa. This improvement showed the possibility of increasing the charge density to improve the oxygen barrier property.