Chemical Pulp Hardwoods Native to the South – Review of Techniques, Properties, and Markets

The various factors effecting the kraft pulping of hardwoods growing in the south was compared with that of the southern pines. The density of the wood being pulped has a multifacet effect. Denser woods, such as the oaks tend to have advantages in procurement, transportation and storage of pulpwood in addition to greater digester capacity and a lower liquor to wood ratio, but a disadvantage in chipping. Other disadvantages to the use of hardwood pulpwood include a slower growth rate, difficulty in debarking, poorer pulping chemical regeneration and by-product recovery. Hardwoods, however, are easier to chemically pulp, resulting in milder pulping conditions and a pulp of higher yield with a lower residual lignin content. The pulp is easier to beat and bleach. Hardwood pulps have poor strength properties, but high bulk, opacity, absorbancy and degree of softness. These pulps also possess good surface texture and bonding characteristics. Primary uses of hardwood pulps tend to take advantages of the desirable properties and include tissue, towelling, fine papers, and bleached board products. In a survey of pulp mills in southern and border states conducted in conjunction with the review it was shown that unbleached kraft linerboard usually contains some hardwood pulp, averaging 9 percent of the total fiber content. Except for a small amount of hardwood pulped by other means, most is pulped by either the neutral sulfite semichemical process, which actually amounts to only 14 percent of the total, or the kraft process. Approximately one-quarter of all the kraft pulp produced in the south is hardwood pulp. The preferred hardwood species for pulping are oaks followed by the gums collectively.

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