This is a sample of textual material. We deal with complex technologies, therefore no matter how many graphics we make - there is a need to present some textual theory as well. Students can print this material for their use - especially to review before a job interview. Generally we do not require students to purchase any textbooks.

Effect of Bleaching on Cellulose

Excessive reaction between chemicals and cellulose is undesirable because if it causes damage to the cellulose, which results in a decrease in the strength of the pulp sheet. This damage can be measured by the I.V. Test. A low I.V. indicates severe degradation of the cellulose.

The most important aspect in the treatment of the pulp with chemicals is the relative rate of the cellulose degradation compared to the rate of delignification or brightening.

Pulp comes out of the digesters at a particular K-number. This K-number allows the pulp to progress through the bleach sequence and become brighter without too severe of a drop in I.V.

Effect of Bleaching on Hemicellulose

Hemicellulose is the second highest fraction of pulp. Both cellulose and hemicellulose are carbohydrates (a group of chemical compounds including sugars, starches, and cellulose containing carbon, hydrogen, and oxygen only). Hemicellulose is similar to cellulose in many ways, and what we’ve said about cellulose is true also for hemicellulose, except that its degree of polymerization is much lower. This means that during the cooking process much of the hemicellulose is oxidized, or dissolved, into the cooking liquor.