Influences of cellulose nanofibril on microstructures and physical properties of waterborne polyurethane-based nanocomposite films.

We herein report the effects of carboxymethylated cellulose nanofibril (c-CNF) on the microstructure, thermal and mechanical properties of waterborne polyurethane (WPU)-based nanocomposite films. For the purpose, an aqueous dispersion of hard/soft segmented WPU with a mean particle size of ∼169 nm was manufactured by using poly(propylene glycol), isophorone diisocyanate, 2,2-dimethylolpropionic acid and 1,4-butanediol. WPU nanocomposite films with 1-50 wt% c-CNF loadings were then manufactured via an efficient casting method. The FT-IR spectra revealed the presence of hydrogen-bonding interactions between the urethane/urea groups of WPU hard segments and the carboxymethyl/hydroxyl groups of c-CNF. Accordingly, the thermal and thermo-oxidative stability of the nanocomposite films was noticeably enhanced by the introduction of c-CNF. In addition, the storage moduli of the nanocomposite films as well as the glass transition temperatures of WPU hard segments increased significantly with increasing the c-CNF content by ∼7 wt% owing to the specific interactions between c-CNF and WPU hard segments.