High wet-strength, thermally stable and transparent TEMPO-oxidized cellulose nanofibril film via cross-linking with poly-amide epichlorohydrin resin

One of the major challenges towards the practical application of nanocellulose films is to maintain their high mechanical properties under humid environment. Herein, the physicochemical properties of TEMPOoxidized cellulose nanofibril (TOCNs) films cross-linked with different dosages of polyamide epichlorohydrin resin (PAE) were investigated. The PAE/TOCNs film containing 0.5 wt% PAE was treated via an impregnation method in a 0.9 wt% PAE solution. The resulting film exhibited a high transparency of 79.5% at a wavelength of 600 nm with high tensile strength and Young's modulus of approximately 135 MPa and 11 GPa, respectively. A high wet strength of 95 MPa was also obtained due to the compact cross-linking net structure. FTIR spectra indicated that the surface carboxyl groups of the TOCNs were converted into an ester bond with the active groups of PAE, which effectively improved the thermostability of the TOCN/PAE hybrid films.