Thermoresponsive Nanocellulose Hydrogels with Tunable Mechanical Properties

Abstract

Cellulose microfibrils physically bound together by soft hemicellulose chains form the scaffolding that makes plant cell walls strong. Inspired by this architecture, we designed biomimetic thermoreversible hydrogel networks based on reinforcing cellulose nanocrystals (CNC) and thermoresponsive methylcellulose (MC). Upon dissolving MC powder in CNC aqueous dispersions, viscoelastic dispersions were formed at 20 °C, where the storage modulus (<i>G</i>') is tunable from 1.0 to 75 Pa upon increasing the CNC concentration from 0 to 3.5 wt % with 1.0 wt % MC. By contrast, at 60 °C a distinct gel state is obtained with <i>G</i>' ≫ <i>G</i>″, <i>G</i>' ∼ ω⁰, with an order of magnitude larger <i>G</i>' values from 110 to 900 Pa upon increasing the CNC concentration from 0 to 3.5 wt % with constant 1.0 wt % MC, due to the physical cross-links between MC and CNCs. Therefore, simply mixing two sustainable components leads to the first all-cellulose thermoreversible and tunable nanocellulose-based hydrogels.