Changes in zeta potentials of amorphous cellulose particles with aluminum sulfate.

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Microcrystalline cellulose powder, linter cellulose, softwood bleached kraft pulp (SBKP), and hardwood bleached kraft pulp (HBKP) were converted to amorphous particles, and ζ-potentials of suspended samples were measured with the addition of aluminium sulfate (alum). ζ-Potentials of these samples without alum were related to their carboxyl content, and the sample with higher carboxyl content has the more negative ζ-potential. In the presence of alum in suspensions, ζ-potentials are influenced not only by carboxyl content but also swelling degrees of samples. When amorphous samples with different swelling degrees were prepared from microcrystalline cellulose powder, the amorphous sample with higher swelling degree had the more negative ζ-potential. ζ-Potentials of amorphous particles prepared from linter cellulose, SBKP, and HBKP were shifted to positive direction by the addition of alum to suspensions, but never turned to positive over the wide range of alum addition. ζ-Potentials of amorphous particles prepared from linter cellulose, SBKP, and HBKP were almost unchanged at least for one day, during standing of suspensions at room temperature after the addition of alum. In contrast, ζ-potentials of microcrystalline cellulose powder and those of amorphous particles prepared from microcrystalline cellulose powder were shifted to negative direction by standing of suspensions. These relaxation phenomena of ζ-potentials in the presence of alum may depend on structural changes of alum in suspensions during the standing.