High strength films with gas-barrier fabricated from chitin solution dissolved at low temperature

The fabrication of pure chitin materials remains a challenge due to the difficult dissolution and regeneration of chitin. It has been a stumbling block for chitin research and utilization. In this work, chitin was dissolved completely in 11 wt% NaOH–4 wt% urea aqueous solution via the freezing/thawing method without derivatization, as supported by 13C NMR spectra. The pure regenerated chitin films with high strength were successfully prepared from the transparent chitin solution by coagulating with ethanol or 45 wt% dimethylacetamide (DMAc) aqueous solution. The influences of the interactions between the chitin solution and coagulants on the structure and properties of the chitin films were investigated by UV, FT-IR spectra, scanning electron microscopy, X-ray diffraction, nitrogen adsorption isotherms, thermo-gravimetric analysis and tensile testing, indicating the good coagulating condition. The dissolution and regeneration of chitin was confirmed to be an entirely physical processes. The chitin films possessed homogeneous structure, high optical transmittance (87% at 800 nm), moderate thermal stability, as well as excellent tensile strength (up to 111 MPa). Moreover, these chitin films had good gas barrier properties (0.003 barrer for oxygen permeability), indicating great potentials in the materials field. This work would open up a completely new avenue with green technology to investigate the most intransigent chitin.