Polymer Induced Gelation of Aqueous Suspensions of Cellulose Nanocrystals

We investigated the gelation of cellulose nanocrystals (CNCs) in polyelectrolyte and neutral polymer solutions. Cellulose nanocrystals (CNCs) with half-ester sulfate groups produced by acid hydrolysis of wood pulp were used in this study. The microstructure of CNCs/polymer suspensions was investigated in semidilute concentration regimes by selecting carboxymethyl cellulose (CMC700) as an anionic polymer and poly(ethylene oxide) (PEO600) as a neutral polymer solution. Together with quartz crystal microbalance with dissipation monitoring (QCM-D), theology, scanning electron microscopy (SEM), and cryotransmission electron microscopy (cryo-TEM), we characterized CNCs-polymer interactions, the suspension microstructure, and the macroscopic gel flow. Significant viscosity increases at low shear rates coupled with high shear-thinning behaviors were observed in CNC colloid-CMC700 polymer mixtures, but not those CNCs in PEO600 solutions. The apparent differences between CNCs-CMC700 and CNCs-PEO600 mixtures were due to their chain confirmations. On the basis of the evaluations from STEM, cryo-TEM, and polarized optical microscopy, we proposed that the excess CMC700 molecules in solutions result in the depletion of CNCs and the formation of anisotropic domains.

Automated summary

The study revealed that CNCs-CMC700 polymer mixtures exhibited significant viscosity increases at low shear rates and high shear-thinning behaviors, which were not observed in CNCs in PEO600 solutions. The apparent differences were attributed to the different chain conformations of CNCs-CMC700 and CNCs-PEO600 mixtures. Evaluations from STEM, cryo-TEM, and polarized optical microscopy suggested that the excess CMC700 molecules in solutions led to the depletion of CNCs and the formation of anisotropic domains.