Effect of processing variables on efficiency of eucalyptus pulps for internal curing

This study evaluates the effect of fiber composition and morphology, as altered by various papermaking processes, on internal curing performance of hardwood eucalyptus pulp fibers. The autogenous deformations of cement pastes containing each of five different eucalyptus pulps—unbleached soda pulp, bleached soda pulp, unbleached kraft pulp, bleached kraft pulp, and semi-chemical pulp—were examined and analyzed in the context of the known relevant chemical composition and morphology, e.g., cellulose-to-hemicellulose ratio, cell wall thickness, and “hard to remove” (HR) water content. The results revealed that the internal curing efficiency of these pulps is related more strongly to their physical morphology than chemical composition, as measured by cellulose-to-hemicellulose ratio. The partial defiberization during mechanical treatment associated with semi-chemical pulping resulted in fiber fracture and also produced materials which were poorly dispersible; together, these factors limit internal curing capability of semi-chemical pulp. The soda fibers, both unbleached and bleached, with their thicker cell wall and higher HR water content were more effective for internal curing than kraft fibers. It is proposed that for hardwood pulp fibers a slower rate of entrained water release is beneficial for internal curing.