Patent GB-345208-A (GB)
Title: Improvements in or relating to the manufacture of cellulose pulp for use in the chemical industry
Filed: 1929-12-12
Abstract: Pulp, preparation of; viscose.-Cellulose pulp is broken down at any desired stage by chemical reactions which give rise to depolymerization of the cellulose molecule to a "copper viscosity" (as described below) of less than 6 units, and immediately after such breaking-down treatment the pulp is freed from hemicellulose by reagents having an alkaline reaction, until the alphacellulose content is at least 90 per cent, and preferably more than 93 per cent.  A product is thus obtained which is suitable for conversion into cellulose compounds and the production of solutions therefrom, or for direct solution in cellulose solvents to yield thin fluid solutions, for example it may be worked up into viscose without the usual preliminary ripening.  The breaking-down treatment may take place during the process of manufacture of the pulp, or in a separate subsequent treatment, or in a preliminary treatment of the wood, or by a combination of such methods.  Thus the cellulose material may be subjected to an intensified boiling treatment by increasing the temperature, pressure, concentration of liquors or time of boiling, or by adding agents such as hydrochloric, nitric and sulphuric acid or peroxides.  Or an intensified bleaching treatment may be employed wherein the concentration of bleaching liquor, the temperature or time of action may be increased or substances such as peroxides added.  Or the bleached or unbleached pulp may be treated with dilute acid, such as sulphuric or hydrochloric acid in a submerged condition, or with alkalies in the presence of oxidizing substances. Or the wood may be subjected, prior to boiling, to the action of reagents such as dilute acids.  The pulp obtained by such treatments is freed from hemicelluloses by extraction with dilute alkalies or boiling with alkaline earths, further oxidation preferably being prevented by excluding air or by adding a reducing agent such as sodium sulphite.  In examples (1) pine wood chips are boiled with sulphite liquor under pressure and at a final temperature of 130 DEG C. until the material shows a viscosity of 4 units.  The material is then bleached, and treated with soda solution, washed and dried: (2) finished bleached artificial silk pulp is treated with 30 per cent sulphuric acid at 60 DEG  C. for 24 hours, washed and purified with soda solution: (3) boiled and bleached sulphite pulp is treated with soda solution at 0 DEG  C., a current of air being circulated through the solution; the product is then purified with soda solution as above.  The Specification as open to inspection under Sect. 91 (3) (a) claims breaking-down treatments to produce a product which can be converted directly into cellulose compounds and solutions, followed by treatment with alkaline reagents, and claims in such process the breaking down of the cellulose to a "copper viscosity" of less than 10 units, but this subject-matter does not appear in the Specification as accepted.  Determination of viscosity.-About 60 c.cs. of a cuprammonium solution containing 0,5 grams. of the pulp are contained in a 100 c.c. bottle.  This is fitted with a bored rubber stopper carrying the viscosimeter and a tube for forcing the solution into the latter.  The viscosimeter comprises a tube 15 mm. diameter carrying two marks enclosing a volume of 10 c.cs.  A bored rubber stopper at either end carries 2 mm. capillary tubing; the lower capillary tube is 15 cms. long and its end 1,5 cms. away from the lower mark.  The time required for the passage of 10 c.cs. of the solution through the capillary divided by the water value gives the "copper viscosity" of the pulp.