Influence of surface charge on viscosity behavior of cellulose microcrystal suspension

Microcrystalline cellulose with minimal surface charge was prepared from so ftwood kraft pulp via hydrolysis by 4N hydrochloric acid instead of sulfuri c acid. To this material, sulfate ester groups as surface charge were intro duced by treating with 55 % (w/w) sulfuric acid. A treatment at 60 degrees C for 2h gave nearly the same level of surface charge as that of the H2SO4- hydrolyzed microcrystal. The number of sulfate groups were controlled by ch anging the H2SO4 treatment conditions. Although the microscopic size and sh ape of the microcrystalline particles were the same irrespective of the pre paration method, the introduction of surface charge drastically reduced the viscosity and removed its time dependence. These changes in viscosity beha vior are considered to result from charge-induced dispersion of loose aggre gates existing in the initial charge-free microcrystals prepared by HCl hyd rolysis.