Canadian International Paper Company

William R Saxton

William H Lawford

An improved, three-stage process for producing high yield chemimechanical pulps from wood or other lignocellulosic materials, such as chips, whereby, in the first stage, the wood or other lignocellulosic material is treated with sulfur dioxide gas or aqueous solution of sulfur dioxide, whereby sufficient sulfur dioxide is present to provide an amount of at least about 1 percent by weight based on weight of wood or other lignocellulosic material; in the second stage, said wood is sulfonated in an aqueous solution of sodium sulfite at a temperature of between about 100.degree. C. and 150.degree. C. for between about 10 and 90 minutes, said aqueous solution having a pH of between about 6 and 8.5 at the end of said sulfonating, without reducing the pulp yield to below about 90 percent; and, in the third stage, subjecting the resulting sulfonated wood to mechanical defibration.

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l'Orignal, Canada

William R Saxton