New Approach for the Fabrication of Carboxymethyl Cellulose Nanofibrils and the Reinforcement Effect in Water-Borne Polyurethane

Nanocellulose has attracted significant attention due to its fascinating properties and great potential in the preparation of high-performance functional materials for specific end-use applications. Most cellulose nanocrystals and cellulose nanofibrils are in the cellulose I crystal structure; however, attempts to fabricate cellulose nanofibrils with the cellulose II crystal structure by self-assembly from cellulose solutions are rarely reported. Here, we demonstrate a new approach to the fabrication of carboxymethylated cellulose nanofibrils (CMCNFs) by homogeneous carboxymethylation and the self-assembly of cellulose chains from cellulose solutions using sequential “top-down” and “bottom-up” strategies. Furthermore, CMCNFs were used as reinforcing nanofillers to enhance the properties of water-borne polyurethane (WPU) and were evenly distributed in the WPU matrix. Dynamic thermomechanical analysis on the WPU/CMCNF nanocomposites demonstrated a significant reinforcement effect based on the tensile storage modulus above the glass transition temperature of the soft segments of the WPU, and the results were well-fit by the percolation model. The sequential top-down and bottom-up strategies developed here produce CMCNFs and should contribute to the reinforcement of polymer matrices, improving the practical exploitation of CMCNFs.