Surface-Vinylated Cellulose Nanocrystals as Cross-Linkers for Hydrogel Composites.

Cellulose nanocrystal (CNC) fillers have been shown to significantly improve the performance of polymer composites and hydrogels, elevating both strength and toughness. Polymer grafting from the surface of the nanocrystals has been employed to enhance matrix-filler interactions and keep the fillers dispersed within the matrix. However, such approaches often rely on multistep syntheses and diligent process control. Here, we propose modifying the nanocrystal surface to carry vinyl moieties, turning the particles into cross-linking comonomers. Using allyl glycidyl ether in an aqueous modification route, we were able to decorate the CNCs with varying amounts of vinyl moieties. Subsequent dispersion in 2-hydroxy methacrylate and thermally initiated free radical polymerization yielded composite materials that showed superior mechanical performance compared to those obtained from monomeric cross-linkers and unmodified CNCs. The large discrepancies in the observed glass transition temperatures of the obtained materials suggest, however, that the impact of the fillers on the polymerization kinetics is significant and less easily explained.