A Simple and Versatile Strategy To Improve the Mechanical Properties of Polymer Nanocomposites with Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are widely studied as reinforcing fillers for polymers. In many cases the mechanical properties of polymer/CNC nanocomposites do not match the theoretical predictions, arguably on account of CNC aggregation. This problem can be mitigated through the addition of a small amount of a judiciously selected polymeric dispersant that also serves as a binder among the CNCs. We show that the addition of 1–5% w/w poly­(vinyl alcohol) (PVA) has a very significant impact on the mechanical properties of poly­(ethylene oxide-co-epichlorohydrin)/CNC nanocomposites. Remarkable improvements of the stiffness and strength were observed at a PVA content as low as 1% w/w, and the extent of reinforcement increased up to a PVA content of 5% w/w, where Young’s modulus, storage modulus, and strength increased by up to 5-fold vis-à-vis the PVA-free nanocomposites. Similar effects were observed for CNC nanocomposites made with polyurethane or poly­(methyl acrylate) matrices, demonstrating that the approach is broadly exploitable. Laser scanning microscopy based resonance energy transfer experiments that involved nanocomposites made with CNCs and PVA that had been labeled with rhodamine and fluorescein, respectively, confirmed that the enhanced mechanical properties of the three-component nanocomposites are indeed related to an improved dispersion of the CNCs.