Abstract: In nature, chitin generally exists in the form of ordered crystalline nanocrystalline fibers, which gives organisms excellent mechanical properties. In this study, chitin was extracted from discarded crab shells by two methods of ‘mild condition’ and ‘high temperature condition’, respectively. Then the room temperature α-chitin nanofiber films (mild condition film) and the high temperature α-chitin nanofiber films (high temperature condition film) were prepared by vacuum filtration through mechanical grinding and other processing methods. To further discuss the influence of the nanofiber morphology and uniformity on the film mechanics, optical transparency, the microstructural morphology, mechanical tensile properties, crystal structure, surface characteristics, optical properties and thermal performance of the prepared chitin nanofiber films were characterized. The results show that, compared with the extraction of ‘high temperature condition’, the α-chitin nanofibers extracted under the ‘mild condition’ have higher aspect ratio and uniform size distribution, and retain the excellent original natural structure of chitin. Among them, the mild condition films have good flexibility, whose tensile strength can reach (152±2.56) MPa, and the elongation at break is nearly 10.0%, which is about 2.50 times than that of the high temperature condition films. At the same time, the mild condition films also have excellent optical and thermal stability, with the light transmittance as high as 91.0% and the haze as low as 3.19%, and it can still maintain stable properties at 200 ℃. Thus, chitin nanofiber extracted under the “mild condition” retains its natural structural advantages, which contribute to the film excellent mechanical strength and light transmittance. The research results in this work provide theoretical basis and technical support for the preparation of all-biomass flexible transparent film materials with high strength and low haze, and are expected to be used as flexible transparent substrates in the research fields of flexible electronics components, electronic skin, smart tags and flexible sensors, etc.
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