High brightness pulps from lignin rich waste papers

摘要

This present invention relates to methods for preparing premium or near-premium brightness pulps for towel and tissue applications from fiber sources comprising substantial amounts of lignin-containing pulp and chemical pulp while controlling fines, scale and anionic trash. These methods use alkaline hydroxide in combination with peroxide and oxygen for initial bleaching stages followed by treatment with a peroxide activating agent to convert residual peroxide in the pulp into peracetic acid followed by a final reductive bleaching stage.

主权项

1. Multi-stage process for bleaching of a recycle pulp comprising the steps of:
a) contacting a cellulosic admixture of recycle containing fiber with a magnesium hydroxide generating species chosen from one or more of MgO and Mg(OH)2 in an amount of from about 0.1 to about 2.0% based on the OD weight of the pulp; b) contacting the admixture of pulp and Mg(OH)2 with H2O2 in an amount of from about 0.1 to about 5.0% based on the OD weight of the pulp, while retaining a residual level of H2O2 in the admixture of at least about 0.1% to about 3%, maintaining said H2O2 containing mixture at a pH from about 8 to about 9.5 to generate perhydroxyl anions; c) thereafter contacting the H2O2 containing mixture with a peroxide activating agent chosen from one or more of tetraacetylethylenediamine, and acetic anhydride, and thereby generating peracetic acid in-situ; or adding an amount of a perhydroxyl generating agent sufficient to convert substantially all of the residual hydrogen peroxide in the admixture in-situ to perhydroxyl ions; said perhydroxyl generating agent being chosen from one or more of sodium hydroxide, NA2CO3; and calcium hydroxide; d) thereafter treating the brightened pulp with a reductive bleaching composition.