Pulp and Paper 3133 



25-7 CHEMICAL PULPING" 



The kraft chemical pulping process accounts for most hardwood pulped for 

 paper and paperboard in the South. Schroeder (1976), in his survey of pulp mills 

 in the southern United States, found that 79 percent of total hardwood admitted 

 to pulp mills was for bleached kraft pulp (36 mills), 7 percent for unbleached 

 kraft linerboard (21 mills), and 14 percent for NSSC pulp (17 mills) mostly for 

 corrugating medium. About one-quarter of all the kraft pulp produced in the 

 South was from hardwoods. 



Schroeder's (1976) survey further showed that one southern mill pulps by the 

 cold soda process producing 220 tons daily at approximately 79 percent yield; 

 the pulp is bleached to 58 GE brightness and used in newsprint as 15 percent of 

 the furnish. One mill pulped by the hot soda process producing 270 tons daily at 

 an approximate yield of 47 percent; after bleaching to 85 GE brightness the pulp 

 is used in fine papers as 63 percent of the furnish. The hot soda process, like the 

 kraft process, is an alkaline delignification process. The Owens-Illinois non- 

 sulfur process is currently used by two northern mills to produce pulp for 

 corrugating medium; one produces about 550 tons per day at a yield of 78 

 percent, and the other about 1,000 tons daily. 



Since hardwoods are easier to delignify than softwoods some newer develop- 

 ments in pulping are more readily adaptable to hardwoods providing wood 

 density is not a limiting factor. Alkaline oxygen pulping of hardwoods should be 

 feasible without encountering the same difficulties presented by southern pines 

 (Nicholls et al. 1975; Fugii and Hannah 1977; McKelvey et al. 1978). Acid 

 sulfite pulping of most southern hardwoods is technically not feasible because of 

 their high phenolic extractive content. Two-stage sulfite pulping, in which the 

 first stage of relatively high pH (Stora process), or alkaline sulfite pulping of 

 hardwoods to obtain a full chemical pulp is possible but perhaps not commercial- 

 ly viable. There would be no advantage over kraft pulping. 



The discovery that additions of small amounts of anthraquinone increases the 

 rate of delignification during alkaline pulping (Holton'-, Holton and Chapman''') 

 holds promise of increasing pulp yields, and reducing cooking time and tem- 

 perature. Anthraquinone has been used in a sulfur- free process to pulp birch 

 (Lachenal et al. 1979), and in kraft pulping of Canadian hardwoods (Goel et al. 

 1980). 



' 'Text under this heading is, with minor changes, taken from Schroeder (1976), by permission of 

 H. A. Schroeder and the Forest Products Research Society. 



'^Holton, H. H. Paper presented at 63rd CPPA-TS Annual Meeting, Montreal, 1977. 

 "Holton, H. H., and F. L. Chapman. Paper presented at TAPPI Alkaline Pulping Secondary 

 Fibers Conference, Washington, D. C, 1977. 



