Flow properties of microcrystalline cellulose suspension prepared by acid treatment of native cellulose

The properties of cellulose microcrystals and their colloidal suspensions obtained by acid treatments of native cellulose have been investigated. Bleached softwood kraft pulp was treated with 65% (w/w) sulfuric acid or 4 N hydrochloric acid and the resulting particle morphology and flow properties of the aqueous suspensions were studied. Colloidal dispersion of the HCl-treated sample was obtained by more thorough removal of acid from the hydrolysate than in the case of H2SO4 treatment. The H2SO4-treated and HCl-treated samples had similar particle sizes and shapes when observed by electron microscopy. Conductometric titration of suspensions revealed that the H2SO4-treated sample had a surface charge of 84 m-equiv kg−1 dry material due to the introduction of sulfate groups, while that of the HCl-treated sample was undetectable. The H2SO4-treated suspension showed no time dependence in viscosity, while the HCl-treated suspension was thixotropic at concentrations >0.5% (w/v) and anti-thixotropic <0.3%. The inclination of the relative viscosity–concentration plot (Einstein coefficient) for the H2SO4- and HCl-treated suspensions were 135 and 1380, respectively. The former value, when used in Simha's equation for rod-like particle suspension, roughly corresponds to an axis ratio of 50 estimated from the micrographs.