Much effort is being expended on modifying nanocellulose materials to enhance their suitability as reinforcing agents in polymer composites. We think that unmodified cellulose nanocrystals (CNC) are best suited to reinforce water-soluble polymers and aqueous gels. As illustration, we have shown that cellulose nanocrystals may be uniformly incorporated in the physical gels formed by subjecting aqueous poly(vinyl alcohol) (PVA) to freeze-thaw cycles. The nanocrystals induce order in the gels at concentrations as low as 0.75 wt.%. An increase in gel modulus was measured by a method that applied pressure on a sample of radially-constrained gel between an impermeable and a porous plate. [Reinforcement with cellulose nanocrystals of poly(vinyl alcohol) hydrogels prepared by cyclic freezing and thawing, Tiffany Abitbol, Timothy Johnstone, Thomas M. Quinn and Derek G. Gray, Soft Matter, 7(6), 2373-2379 (2011)]
A piece of poly(vinyl alcohol)/cellulose nanocrystal gel.
Polarized optical micrographs of physical gels of PVA prepared by freeze-thaw cycling. Incorporation of cellulose nanocrystals generates order in the otherwise isotropic gel structure.