Kraft pulping penetration

A high yield chemical pulp, eg, 52—53% bleached yield from softwoods, can be obtained, but strength properties ate inferior to those obtained from the kraft process. If a protector, eg, potassium iodide, is added, an additional 2—3% yield is obtained, as is an improvement in all strength properties. The gas penetration problem can be minimized if ftbetization is accompHshed before treatment with oxygen. Oxygen treatment of virtually all types of semichemical and mechanical pulps has been explored (55). Caustic, sodium bicarbonate, and sodium carbonate have been used as the source of base (56,57). In all cases, the replacement of the kraft by these other processes has not been justified over the alternative of pollution abatement procedures. 

Chemical wood pulping is an important industrial process, with a relatively low yield. However, this process is attractive, because of the low requirements of wood quality and wood species. Moreover, it includes very short cooking times due to the easy penetration of alkaline solutions into wood. A well established processing of the spent liquor, generation of process heat, recovery of the pulping chemicals and production of valuable by-products such as turpentine and tall oil are also advantages of the kraft cooking. Major drawbacks are however, the odour and the dark colour of the unbleached pulp. 

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