High Yield Pulping of Hardwoods

Pulp yield is the weight of fiber obtained (dry basis) when wood is cooked to extract water soluble materials (lignin and pentosans) and free fiber suitable for paper or chemical use. Some of the various methods of pulping—groundwood, semichemical, chemigroundwood, and full chemical–are more suitable to some species of woods than others. Generally the very high yields are obtained with combinations of mechanical and chemical treatments, and lower yields are obtained by full chemical and mild mechanical treatment. This report deals with yields above 55 percent by the sulfate and sulfite methods and above 65 percent by other methods. The principal species of hardwood used for pulping can be converted to high yield pulps by either the NSSC, cold soda, or kraft cooking processes, and either continuous or batch pulping can be used. Improvement of liquor penetration to improve product uniformity is becoming increasingly important. Recent tests on the use of hardwood for the production of high yield packaging boards confirm prior conclusions that the use of high yield hardwood pulps can be successfully extended into the field of packaging papers and paperboards.

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