GB462871A - Improvements in or relating to the refining of wood pulp - Google Patents

Abstract

A method of refining wood pulp, for use in the manufacture of rayon or as filler for moulded articles, comprises treating the pulp in aqueous suspension with chlorine in the presence of an alkali metal chloride, and washing the pulp with soft water. The chlorination may be an essential step in a bleaching operation, e.g. when operating on unbleached sulphite pulp. The treatment has the effect of reducing the alkaline earth content of the pulp which after treatment contains less than 0,025 per cent CaO and less than 0,005 per cent MgO. The reaction is preferably carried out at high density, e.g. 5 per cent. The temperature need not exceed 40 DEG C. and the reaction is normally not longer than 30--90 minutes. In an example, unbleached pulp containing 0,15 per cent CaO is treated for one hour at 20 DEG C. and a density of 3,5 per cent with 2 per cent gaseous chlorine and 2,5 per cent sodium chloride calculated on the fibre weight. The pulp is then washed with water substantially free from lime and contains not more than 0,01 per cent CaO. In a second example, a bleached pulp containing 0,08 per cent CaO and 0,02 per cent MgO is treated at 5 per cent density for \ba1/2\be hour with 0,75 per cent C12 and 1,5 per cent potassium chloride calculated on the fibre weight. The chlorine is added as chlorine water containing 4 grams C12/litre. The pulp is then washed with water free from calcium or magnesium and contains 0,01 per cent CaO and is practically free from magnesium.