Biomimetic Reversible Heat-Stiffening Polymer Nanocomposites.

Inspired by the ability of the sea cucumber to (reversibly) increase the stiffness of its dermis upon exposure to a stimulus, we herein report a stimuli-responsive nanocomposite that can reversibly increase its stiffness upon exposure to warm water. Nanocomposites composed of cellulose nanocrystals (CNCs) that are grafted with a lower critical solution temperature (LCST) polymer embedded within a poly(vinyl acetate) (PVAc) matrix show a dramatic increase in modulus, for example, from 1 to 350 MPa upon exposure to warm water, the hypothesis being that grafting the polymers from the CNCs disrupts the interactions between the nanofibers and minimizes the mechanical reinforcement of the film. However, exposure to water above the LCST leads to the collapse of the polymer chains and subsequent stiffening of the nanocomposite as a result of the enhanced CNC interactions.

Miscanthus Giganteus: A commercially viable sustainable source of cellulose nanocrystals.

With a goal of identifying a new scalable source for cellulose nanocrystals (CNCs), we successfully isolated CNCs from a sustainable, non-invasive grass, Miscanthus x. Giganteus (MxG). Subjecting MxG stalks to base hydrolysis, bleaching and acid hydrolysis allowed access to cellulose nanocrystals (MxG-CNC) in high yields.

pH-Responsive Cellulose Nanocrystal Gels and Nanocomposites.

We show that functionalization of the surface of cellulose nanocrystals (CNCs) with either carboxylic acid (CNC-COH) or amine (CNC-NH) moieties renders the CNCs pH-responsive. At low pH, where the amine groups are protonated, CNC-NH forms aqueous dispersions in water on account of electrostatic repulsions of the ammonium moieties inhibiting aggregation. However, a transition to hydrogels is observed at higher pH where the CNC-NH are neutral and the attractive forces based on hydrogen bonding dominate.