Hardwood neutral sulfite pulping

Neutral Sulfite Pulping Neutral sulfite pulping is mainly used for the production of high-yield pulps from hardwoods. The process is often named the "NSSC" (Neutral Sulfite Semi-Chemical) process. The wood is delignified only partially and mechanical fiberization is thus required. The prod-... 

Fig. 8-24. Response of various pulp types to peroxide bleaching. 1, Semichemical (cold alkali) hardwood 2, acid sulfite softwood 3, mechanical spruce 4, semichemical (neutral sulfite) hardwood pulps (Rydholm, 1965).

Figure 2D compares a number of sulfite pulps. Two of them, an unbleached spruce sulfite, USS, and an unbleached mixed hardwood sulfite, HS, have remarkably similar degradation curves but show different final residues. A bleached neutral sulfite semichemical pulp, FB, and an unbleached semichemical birch sulfite, SBS, have similar and much steeper initial degradation curves than the other two pulps. The semichemical birch sulfite pulp, SBS, has a degradation curve which crosses over those of the other three pulps shown in Figure 2D. 

Wood is converted into pulp by mechanical, chemical, or semichemical processes. Sulfite and kraft (sulfate) are the common chemical processes, and neutral sulfite is the principal semichemical process (NSSC). Coniferous wood species (softwoods) are the most desirable, but the deciduous, broad-leaved species (hardwoods) have gained rapidly in their usage and constitute about 25 percent of pulp-wood. Table 28.2 summarizes the conditions utilized with the various pulping processes,... 

Wood resin is the water-insoluble material that is soluble in neutral, non-polar organic solvents. Large amounts of it pass through mill systems that utilize softwoods and some of the hardwoods. This resin can cause pitch problems, particularly with sulfite pulping and the manufacture of unbleached sulfite pulps and to a lesser extent with mechanical and chemi-mechanical pulping. Problems are less frequently encountered with kraft pulping and usually they are less severe and of a different type. 

The dominant process of semiwith sodium or ammonium sulfite as the digestion chemicals. The pulp yield is in the range 70-80% depending on the wood species, most commonly hardwood species like birch, beech, maple, oak and eucalyptus. This pulp is used for fluting production - often as the sole component in furnish. 

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