| 摘要 |
In a semi-chemical pulping process, wood chips ar cooked up to 155 DEG C. at a pH of 3-5 with a solution of sodium, potassium or ammonium bisulphite having no free sulphur dioxide, and then mechanically refining to separate the fibres. By "free sulphur dioxide" is meant sulphur dioxide other than that present as bisulphite. In an example, a digester was charged with 1 part by weight of spruce chips and 5 parts of a solution of sodium metabisulphite to give a total sulphur dioxide content of 2.5 per cent. The temperature was raised to 110 DEG C. during 2 hours, to 155 DEG C. during 2 1/2 hours and maintained at 155 DEG C. for a further 1 1/2 hours. The initial pH value was 4.7 and the final pH, 3.5. The yield was 74 per cent. The cork was blown, the softened chips washed and passed through a disc refiner. Alternatively, the cooking liquor could be prepared from a solution of soda ash and sulphur dioxide gas.
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