Cationic and anionic cellulose nanocrystalline (CNC) hydrogels: A rheological study

Although the rheology of cellulose nanocrystalline (CNC) suspensions has been widely studied, less attention has been paid to the modified cellulose nanocrystals such as cationic and anionic cellulose hydrogels. In this work, the rheological behavior of cellulose nanocrystals (CNCs), anionic CNCs (pCNCs), and cationic CNCs (nCNCs), was comparatively studied. The rheological behavior demonstrated that the nCNC and pCNC form hydrogen bonding, which significantly contributes to the increase in the gel strengths in the sonicated state. The formation of such structures between individual fibers prevents flocculation due to the increased suspension stability. In addition, the extensive formation of hydrogen bonding in the case of nCNC compared to that of pCNC explains its enhanced rheological properties. The effect of pre-shear has been studied in detail for these systems by considering a combination of pre-shear and startup of steady shear in different shearing directions with certain rest/recovery time in between to eliminate strain history and thus eliminate the possible bias of pre-shearing on structure formation.

Automated summary

The rheological behavior of cationic and anionic cellulose nanocrystals was studied, showing that the formation of hydrogen bonding significantly enhanced the gel strengths and prevented flocculation. The presence of more hydrogen bonding in cationic CNCs compared to anionic CNCs explained the enhanced rheological properties. Through a detailed study of the effect of pre-shear on these systems, bias on structure formation was minimized by considering a combination of shear directions and pre-shearing.