Tailoring softwood kraft pulp properties by fractionation and refining

摘要

Fractionation of softwood pulp offers potential for different products with different strength properties.In this study,fractionation was done in two stages:coarse screening with a 1.6mm-diameter hole screen,followed by a 0.15mm slot screen.The rejects of first-stage coarse screening,which have the highest average fiber length and coarseness,were tested with low and high SEL refining.Refining with a low specific edge load was beneficial for preserving the fiber length and tear index of the rejects.The refining energy input was higher,however,than in refining with a high specific edge load,when compared at a certain tensile index.The rejects from the two screens were mixed to test optimum filling and refining conditions.Conical filling with low bar-edge cutting speed resulted in gentle treatment with less fiber cutting and better tear index,but required more refining energy for a certain tensile index level.Narrow-bar disc filling with high cutting speed was more energy efficient and low SEL refining produced less fiber cutting.The accept fraction had a low average fiber length and contained more short and thin fibers and fines.The accepts were used to modify once-dried kraft pulp before refining by replacing a certain percentage of the pulp.The modified pulp consumed less energy when refined to the same tensile index and increased the internal Scott bond strength of the original pulp.Fractionation shows good potential for tailoring softwood pulp for different products with different strength properties and can serve as a flexible tool in getting the most out of available raw materials.