The influence of carboxymethylation on the fiber flocculation process

This study deals with the effect of charged groups on the rheology and stat e of dispersion of papermaking fibers. The charged groups were introduced o nto a softwood kraft pulp through carboxymethylation. The rheology of the f iber network was studied using a jar with a rotor equipped with a force gau ge so that the yield stress of the fiber network could be determined. The state of flocculation was characterized by studying the characteristic flee size in a flowing suspension using a digital camera interfaced with a dedicated image analysis system. The results showed that the yield stress a nd flee size decreased when the degree of carboxymethylation (Na-form) incr eased. 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 su rface molecules at the fiber-water interface was increased through the intr oduction of charged carboxymethyl groups.