GB460812A - Improvement in methods of producing paper pulp from fibrous materials - Google Patents

Abstract

Paper pulp is produced from decorticated bast fibre, e.g. flax or hemp, by submitting the fibre to the action of water, washing the same, cooking the fibres in a digester under a pressure of over 30 lbs./sq. inch and in the presence of an alkaline substance and a soluble sulphite, treating the product with chlorine in the presence of water, washing the conglomerate obtained and then treating the latter with an alkaline hypochlorite. The mechanically decorticated material, e.g. flax should contain approximately 90 per cent crude bast fibre. It is steeped, if desired together with a crushing action (e.g. in a beater or rod mill) in hot or cold water for 15--30 minutes, then thoroughly washed, and cooked in a rotary digester for approximately 2 hours under a pressure of 30--75 lbs./sq. inch with a mixture of approximately 95 per cent of alkali, e.g. calcium hydroxide, sodium carbonate or sodium hydroxide or a mixture thereof and about 5 per cent sodium sulphite. The proportion of alkali should be 5--15 per cent of the dry weight of the fibre. The digester is then blown and the fibre thoroughly washed, and then treated for 15--30 minutes with chlorine water, hypochlorous acid, or gaseous chlorine in the approximate proportion of 2--3 grams of chlorine for each 100 grams of conglomerate. After washing, if desired with dilute sodium hydroxide or sodium carbonate, the material is treated with sodium or calcium hypochlorite for about 7 hours. The equivalent of 2--4 lbs. of ordinary bleaching powder is used per 100 lbs. of conglomerate. The pulp is then finally washed and is ready for making high grade paper.