Disperger Bleaching With Hydrogen Peroxide: A Tool for Brightening Recycled Fiber, 1993 Pulping Conference Proceedings

Given the increasing use of recycled fibers in a wide variety of paper applications, cleanliness and brightness are both very important properties for a deinked pulp. To reduce the size of remaining visible ink specks, a hot dispersion system (= disperger) is often included in the wastepaper reprocessing line. Although the positive effect of this practice on cleanliness is very clear, ink dispersion has a negative effect on the brightness. This brightness loss can be avoided by using the hot dispersion system for bleaching at the same time as for ink dispersion.

Since a dispersion unit is operated at high consistency and high temperature it is a suitable place to add hydrogen peroxide.

Different parameters which could influence the efficiency of disperger bleaching with hydrogen peroxide were studied in the laboratory and at the pilot plant of the Research and Development Centre of LAMORT.

It was shown that the brightness loss due to ink dispersion depends highly on the efficiency of the deinking operation prior to dispersion. Nevertheless, the brightness gain obtained by hydrogen peroxide bleaching in the hot dispersion system is independent of the deinking effectiveness. The final brightness is increased by +/- 8°IS0 with 1% hydrogen peroxide applied in the disperger.