Essentials of pulping and papermaking: By Christopher J. Biermann. Academic Press, Inc. San Diego, CA, 1993, 488 pp. ISBN 0-12-097360-X. price $49.95

Abstract

Pulp consists of wood or other lignocellulosic materials that have been broken down physically and/or chemically such that discrete fibers are liberated and can be dispersed in water and reformed into a web. There are four broad categories of pulping processes: chemical, semichemical, chemimechanical, and mechanical pulping. These are in order of increasing mechanical energy required to separate fibers (fiberation) and decreasing reliance on chemical action. Chemical pulping methods rely on the effect of chemicals to separate fibers, whereas mechanical pulping methods rely completely on physical action. The more the chemicals are involved, lower is the yield and lignin content because chemical action degrades and solubilizes components of the wood, especially lignin and hemicelluloses. Chemical pulping yields individual fibers that are not cut and give strong papers because the lignin, which interferes with hydrogen bonding of fibers, is largely removed. Semichemical pulping processes involve two steps with pulp yields of 60%–80%. In the first step a mild chemical treatment is used, which is followed by moderate mechanical refining. The chemimechanical pulping process yields 85%–95% pulp. A particularly mild chemical treatment is followed by a drastic mechanical action. The most common chemimechanical process is chemithermomechanical pulp.