Impact of Carboxymethylation Pretreatment on the Rheology of Cellulose Nanofiber from Bleached Rice Hull

Abstract

Rice is widely produced; however, large quantities of non-edible biomass are also generated during its production, mainly straw and hulls. These lignocellulosic materials have great value potential but are less used than other biomass resources. We produced cellulose nanofiber (CNF) from rice husks through delignification (as chlorine dioxide bleaching), pretreatment (as carboxymethylation substitution reaction), and nanofiber-making processes (as supermass-collider grinding and high-pressure homogenization). The rheological properties of rice-hull cellulose nanofiber were investigated to determine the relationship between carboxyl content, number of grinding, and high-pressure homogenization to rheological properties of rice-husk CNF gels. Increased carboxymethylation and mechanical treatments lead to higher viscosity, better hydrogel strength, and water retention value (WRV). Further mechanical processes decreased the viscosity and hydrogel strength after attaining the maximum value. For high-quality hydrogel production, optimum pretreatment and mechanical processes are required as pretreatment to DS 0.3 for carboxymethylation and optimum grinding and high-pressure homogenization combination.