Reduced Chlorine Usage in the Production of Sulfite Dissolving Pulp, 1994 Pulping Conference Proceedings

P. C. Leithem, Y. Huang, E. M. Wallace, R. L. Casebier

The production of high purity chemical cellulose dissolving pulps for ester (acetate), ether, nitrate and viscose rayon industries differs markedly from that of pulps produced for fibrous end-use markets. Pulping and bleaching processes must promote the separation and removal of the non-cellulosic components of the wood structure while controlling the chemical and physical properties of the resulting cellulose.

Bleaching in dissolving pulp production is not synonymous with brightening but is instead a continuation and completion of the purification process which was started in the digesters. The current movement away from chlorine in pulp bleaching presents a particular challenge for dissolving pulp manufacturers. Sulfite processes in general are noted for the ease of brightening of relatively well-delignified pulp. This relative ease of brightening is apparent in traditional chlorine based bleaching as well as in total chlorine free bleaching response. Since dissolving pulp bleaching results in cellulose purification by design, the ease of brightening alone is not a predictor of the effectiveness of non-chlorine bleaching. Examples of non-chlorine and totally chlorine compound free bleaching of acid sulfite pulps are given. The utility of the resulting pulps is dependent both on the analytical characteristics and end-use evaluations.