METHOD FOR THE PRODUCTION OF FIBER PULP

摘要

METHOD FOR THE PRODUCTION OF FIBER PULP This invention relates to a method for the production of fiber pulp from lignocellulosic material containing at least 70% spruce or spruce-like material. The method comprises the steps of lignin softening and defibration/refining, the step of lignin softening being performed prior to the step of defibration/refining and comprising impregnating the starting material with a dilute aqueous solution of a lignin softening agent, namely a solution of sulfurous acid, metal bisulfite salts and/or metal sulfite sales in an amount sufficient to provide a defibrated/refined pulp containing an absorbed and bonded amount of sulfonate groups within the range of from 0.06 to 0.75 wt.-%, calculated as Na2SO3 and based on the dry pulp weight. The absorbed and bonded amount of sulfonate groups is balanced to the composition of the starting material and the temperature-pressure conditions in the defibration step to provide a pulp of maximum tensile strength such as to represent a point within the polygon ABGH in Fig. 1. The invention makes it possible to utilize favorable effects, not earlier known, resulting from very low concentrations of the lignin softening agent, and to produce a pulp with high yield and optimum strength and optical properties at a comparatively low energy input in the defibrator/refiner.