The properties of cellulose microcrystals and their colloidal suspensions obtained by acid treatments of nativecellulose have been investigated. Bleached softwood kraft pulp was treated with 65% (w/w) sulfuric acid or 4 Nhydrochloric 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 hydrolysatethan in the case of H2SO4 treatment. The H2SO4-treated and HCl-treated samples had similar particle sizes andshapes when observed by electron microscopy. Conductometric titration of suspensions revealed that theH2SO4-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 inviscosity, 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 HCltreatedsuspensions were 135 and 1380, respectively. The former value, when used in Simha’s equation for rod-likeparticle suspension, roughly corresponds to an axis ratio of 50 estimated from the micrographs. © 1998 ElsevierScience B.V. All rights reserved.
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