Gelation of Methylcellulose Chains Versus Methylcellulose Fibers

Upon heating in aqueous solutions, MC reversibly self-assembles into ~ 7–10 nm fibrils that percolate, resulting in physical gelation. We have chemically crosslinked both MC solutions at room temperature, and MC physical fibril gels at 80 °C, and compare the swelling and shear modulus properties. Hydroxyl moieties on MC were substituted with allyl groups, with a degree of substitution of about one pendant double bond per nine anhydroglucose repeat units. The allyl groups undergo crosslinking in the presence of a photo-initiator and UV light. Chemically crosslinking MC fibril gels at 80 °C results in opaque solid materials, and locks in the fibril structure, which persists even on cooling to room temperature. The shear modulus G' increases modestly with temperature, and the volume fraction scaling is consistent with previous results for fibril gels. On the other hand, chemically crosslinking MC solutions at room temperature leads to clear, solid hydrogels which no longer form fibrils. Instead, swelling measurements show that the MC gels shrink by an order of magnitude when the temperature is increased from 25 °C to 80 °C. The equilibrium polymer volume fraction and G¢ are consistent with established theories for crosslinked polymer chains.