Date of Award

4-1996

Degree Name

Bachelor of Science

Department

Paper Science and Engineering

Abstract

In recent years, the paper industry has received increased pressure from environmental groups to reduce both air-borne & water-borne discharges. During element-chlorine bleaching processes, absorbable organic halides are formed , some of which are considered harmful to aquatic life. To reduce absorbable organic halides, many mills are moving towards chlorine-free bleaching stages. A potential chlorine-free bleaching agent is dimethyldioxirane. Dimethyldioxirane is an intermediate produced in-situ from acetone and peroxymonosulfate. Due to the bond strain of the oxygen-oxygen bond in this cyclic peroxide, it behaves as a strong oxidizing agent.

The goal of this thesis was to determine the optimum levels of pH, dimethyldioxirane charge, and bleaching time for a thermomechanical pulp. It was determined that the optimum brightness of 40% could be reached at a pH of 8, charge level of 9%, and by bleaching for 30 minutes. This same brightness could be obtained by using two 2.5% (5%-split) dimethyldioxirane bleaching stages in-lieu of one 9% stage. When a 4% hydrogen peroxide stage is added to the optimized 5%-split run, a maximum brightness of 58.3% could be obtained.

A linear correlation between pulp yield and brightness was found until the pulp yield dropped below 82%. At this point, as the yield decreased, the brightness remained constant. There appeared to be no decrease in zero-span tensile index as the charge addition level was increased.

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