Alcohol induced gelation of TEMPO-oxidized cellulose nanofibrils

Cellulose nanofibrils (CNFs) are colloidal sized fibrils obtained mostly from plant based materials. CNFs present a versatile material from which dispersions or films may be formed. The surface of fibrils may be chemically modified to modulate properties. TEMPO mediated oxidation produces negatively charged fibrils. Oxidized CNFs (OCNFs) can be easily dispersed in water, and
caused to gel by of addition of co-solutes; including surfactants, salts, or co-solvents. OCNF alcohol/water dispersions form shear thinning fluids with low yield stress (weak physical gels). These dispersions are quick drying and film forming suggesting that, with adequate rheological profiles, these would allow for a system that can be a physical gel at rest, a shear-thinning sprayable fluid
and a quick drying filming forming mixture. In this work, we focus on CNF gelation induced by addition of low M w alcohol cosolvents. Rheological data showed that all the alcohols studied are capable of inducing OCNF gelation. The addition of alcohol leads to an increase of viscosity, producing shear-thinning fluids, up to a certain critical alcohol concentration at which the gel forms. This
critical concentration, and the shear modulus of the gel, depends on the type of alcohol: the more hydrophobic alcohols lead to onset of gelation at lower concentration but exhibiting lower shear modulus. Small-angle X-ray scattering (SAXS) shows that the OCNF behave as rigid rods and, upon gelation, an increase of OCNF cross-section is observed, signalling aggregation. The random phase
approximation model [5] was used to extract an interaction parameter that suggests an increase in attractive interactions between OCNFs in presence of alcohols.