Degradation of Dirt Particles by Kraft Pulp Bleaching Reagents, 1996 International Pulp Bleaching Conference Proceedings

R.C. Francis

SUNY College of Environmental Science and Forestry

J. Devenyns

Solvay Interox Research

Six kraft pulp bleaching reagents were investigated to see how effective they were at removing dirt particles. The dirt particles were obtained from kraft pulping rejects and were added to a partially bleached, commercial softwood kraft pulp with kappa number 2.0 and brightness 61.4% Elrepho. The rejects, primarily shives and knots, were disk-refined at low plate clearance to decrease the average size of the fiber bundles. After refining. the reject had a Canadian Standard Freeness of 650 mL and a kappa number of 83. Dirt bleaching was monitored by quantifying residual particles using an image analysis method standardized against Tappi Method T 213 om-89, and by measuring the decrease in bleached brightness or increase in light absorption coefficient when the reject content was increased from 1.0% to 3.0% on pulp. The six reagents were chlorine dioxide (D), oxygen (0), hydrogen peroxide (P), ozone (Z), Caro’s acid (K) and peracetic acid (PAA). The ranking was PAA=D>K>P>O=Z. The two most effective oxidants (PAA and D) were effective delignifiers and brighteners. Also, unlike ozone, they were not rapidly consumed. Caro’s acid was a less effective brightener, while hydrogen peroxide was a less effective delignifier. The poor ranking for oxygen was due to its inability to completely delignify the 83 kappa number particles that were used. Ozone was ineffective because of its high reactivity. It was consumed before it had time to diffuse into some dirt particles with low porosity.