Comparative characterization of aqueous dispersions and cast films of different chitin nanowhiskers/nanofibers

Water dispersions of TEMPO-oxidized α-chitin nanowhisker (TOChN), partially deacetylated α-chitin nanowhisker/nanofiber mixture (DEChN), HCl-hydrolyzed chitin nanowhisker (HHChN) and squid-pen β-chitin nanofiber (SQChN) were prepared, and the properties of nano-dispersions and their cast films were characterized between the four chitin nano-samples. Because SQChN has the highest aspect ratio, its 0.1% dispersion had the highest shear stress and viscosity at the same shear rate in the four chitin nano-samples, and showed gel-like behavior in the whole shear rate range from 10−3 to 103 s−1. AFM images of the self-standing films showed that film surfaces consisted of characteristic chitin nano-elements with different morphologies and degrees of orientation between the four chitin samples, whereas all chitin nanowhisker/nanofiber films had similar thermal degradation points at ∼200 °C. The DEChN film had the highest tensile strength of ∼140 MPa, elongation at break of ∼10% and light-transmittance of 87% at 400 nm. In contrast, the SQChN film had the lowest tensile strength, Young's modulus and light-transmittance. All chitin nanowhisker/nanofiber films had similar oxygen permeabilities of ∼1 mL μm m−2 day−1 kPa−1, which was clearly lower than that (184 mL μm m−2 day−1 kPa−1) of a poly(lactic acid) film.