Microstructure and viscoelastic behavior of waterborne polyurethane/cellulose nanofiber nanocomposite

Cellulose nanofiber (CNF) has been widely used to reinforce the mechanical properties of waterborne polyurethane (WPU). There are, however, few works that focus on structure, rheological behavior, and creep resistance of WPU/CNF composites. To fill this research gap, in this work, the m-CNF was obtained by γ-aminopropyltriethoxysilane modification to improve the interfacial strength of CNF and WPU, and then it was introduced into the polyurethane matrix. Structure characterization of WPU/m-CNF nanocomposites is performed using Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The obtained results show that with the increase of m-CNF, the hydrogen bonding index (HBI) increased, which meant a significant improvement in the mechanical properties. The tensile strength improved by 480%. Moreover, with the increase of m-CNF content, the viscosity, storage modulus, and loss modulus of the dispersions increased and showed more obvious shear-thinning behavior. In addition, m-CNF improved the thermal stability and creep resistance of WPU. The creep strain of WPU decreased from 3% to 0.2%. This work offers a simply feasible way to prepare environmental friendly green nanocomposites.