Effect of the ratio of softwood kraft pulp to recycled pulp on formation and strength efficiency in twin-wire roll forming

Paper furnishes often contain a mixture of a weak pulp with relatively short fibers and a strong pulp with relatively long fibers. Whereas increased proportion of the long-fiber pulp can be expected to impair formation, it has been unclear to what extent a change in formation through the pulp ratio affects the strength efficiency. (Strength efficiency is a measure of how well the strength potential of the furnish, as reflected by the handsheet strength, is utilized in the machine-made paper.) This pilot machine investigation examined the effect on strength efficiency in twin-wire roll forming when changing formation through the ratio between softwood kraft pulp (long fibers) and recycled pulp (short fibers) in the furnish. For comparison, the effect of formation, as changed by headbox consistency, was evaluated. Tensile strength efficiency and Z-strength efficiency both decreased when the formation was deteriorated by increased softwood kraft content. The effect of a change in formation through the kraft content was similar to the effect of a corresponding change in formation through headbox consistency (headbox flow rate). ADDRESSES OF THE AUTHORS: Bengt Nordström ([email protected]), SCA R&D Centre, P.O. Box 716, SE-851 21 Sundsvall, Sweden; Lennart Hermansson ([email protected]), RISE Bioeconomy, P.O. Box 5604, SE-114 86 Stockholm, Sweden. Corresponding author: Bengt Nordström