Fabrication of self-reinforced chitin composites by double crystalline blend approach

In this study, all-chitin composite films, named self-rein orced chitin composite (SR-ChC) films, were fabricated from aqueous acetic acid dispersions of highly-crystalline scaled-down chitin nanofibers (SD-ChNFs, crystalline index (CI) = 90.5 %) and scaled-down low-crystalline chitin (SD-LC-Ch, CI =57.4 %) powder. A SD-ChNF dispersion with aqueous acetic acid was obtained by regeneration from a chitin ion gel and subsequent disintegration of the resulting ChNFs. Separately, the SD-LC-Ch powder was prepared by treating chitin powder under alkaline conditions and subsequent additional deacetylation, which showed well-dispersibility in aqueous acetic acid. The two dispersions were mixed, followed by suction filtration and drying, to obtain the SR-ChC films. The composite films were characterized by scanning electron microscopic, powder X-ray diffraction, and tensile testing measurements. As weight ratios of the SD-LC-Chs increased, the components gradually embedded the SD-ChNFs, allowing reduction of the crystallinity of the SR-ChC films (CIs = ∼ 63.4 %). The tensile testing revealed that the SR-ChC film with the SD-LC-Ch/SD-ChNF weight ratio of 6.6/1 exhibited superior mechanical properties, including tensile strength of 64.0 MPa, elongation of 22.4 % at break, Young's modulus of 0.924 GPa, and toughness of 1109 J m^-3. The mechanism for the improvement of properties was also discussed.