Chemical method for producing wood pulp using caustic soda and sodium sulfide as the liquor in which the pulpwood is cooked to loosen the fibres.
The process (from German kraft , "strong") produces particularly strong and durable paper ; another advantage is its capability of digesting pine chips; resin s dissolve in the alkaline liquor and are recovered as tall oil, a valuable by-product. Recovery of sodium compounds is important in the economy of the process. In modern kraft mills, operations are completely contained; waste streams are recycled and reused, eliminating water pollution.