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The influence of carboxymethylation on the fiber flocculation process

This study deals with the effect of charged groups on the rheology and state of dispersion of papermaking fibers. The charged groups were introduced onto a softwood kraft pulp through carboxymethylation. The rheology of the fiber network was studied using a jar with a rotor equipped with a force gauge so that the yield stress of the fiber network could be determined. The state of flocculation was characterized by studying the characteristic floc size in a flowing suspension using a digital camera interfaced with a dedicated image analysis system. The results showed that the yield stress and tloc size decreased when the degree of carboxymethylation (Na-form) increased. These results were interpreted in terms of a lower fiber-fiber friction due to the creation of gelatinous surface layers when the solubility of the surface molecules at the fiber-water interface was increased through the introduction of charged carboxymethyl groups.