Highly alkynyl-functionalization of cellulose nanocrystals and advanced nanocomposites thereof via click chemistry

A series of reactive GAP (glycidyl azide polymer)/PTPB (propargyl-terminated polybutadiene) nanocomposites reinforced by alkynylated cellulose nanocrystals (ACNC) were synthesized by Huisgen click chemistry. High-efficiency substitution (more than 80%) of the hydroxyl groups by alkynyl groups on the surface of CNC was realized through the esterification reaction between the alkynylated anhydride compound and the cellulose nanocrystals. The covalent bonding from the alkynyl groups of ACNC and the azide groups of GAP was proved by Fourier transform infrared spectroscopy, which indicated the possible participation of the click reactions among the ACNC, GAP, and PTPB components in the composites. The nanoreinforcing effect of the rigid ACNC on the GAP/PTPB matrix and the strong interfacial interaction through the covalent grafting between nanoparticles and the matrix significantly improved the mechanical properties of the prepared nanocomposites. In comparison with the neat GAP/PTPB (GP2) material, the tensile strength, Young's modulus, and the elongation at break of the GP2/ACNC-1.0 nanocomposite (containing only 1.0 wt% ACNC) were increased by 103.3%, 100.0% and 12.4%, respectively. This study is a promising attempt to develop advanced polymeric composites reinforced with biomass-based nanoparticles with the simultaneous improvement of strength, modulus and toughness.