Chitin Nanofiber-Reinforced Waterborne Polyurethane Nanocomposite Films with Enhanced Thermal and Mechanical Performance.

To attain eco-friendly polyurethane composites with enhanced thermal and mechanical properties, in this study, a series of cationic waterborne polyurethane (cWPU) nanocomposite films reinforced with 1-50 wt% chitin nanofiber (ChNF) loadings was fabricated by a facile aqueous dispersion casting. The microstructure, thermal and mechanical properties of the nanocomposite films were investigated by considering the loading content and the interfacial interaction of ChNF in the cWPU matrix. For the purpose, a hard/soft segmented cWPU with an average particle size of ∼151 nm in aqueous dispersion was synthesized by using poly(tetramethylene glycol), isophorone diisocyanate, N-methyldiethanolamine, and 1,4-butanediol. The FT-IR spectra confirmed the existence of specific hydrogen-bonding interactions between hydroxyl/acetyl amine/ammonium groups of ChNFs and urethane/protonated amine groups of cWPU hard segments. Accordingly, the thermal decomposition temperatures of cWPU/ChNF nanocomposite films increased with increasing the ChNF content. In addition, the storage moduli of cWPU/ChNF nanocomposite films increased significantly with the increment of ChNF content up to ∼7 wt%, which stems from the restricted chain mobility of cWPU backbones composed of semicrystalline soft segments and hard segments interacting with ChNFs via multiple hydrogen-bonding interactions.