Patent GB-683385-A (GB)
Title: Improvements in or relating to the treatment of cellulose and its conversion into cellulose derivatives
Inventor: DOWNING JOHN
IPC: C08B1/00
Filed: 1949-02-14
Abstract: Fibrous cellulose is treated to render it easily flaked or powdered by subjecting it to the action of heat and mechanical pressure accompanied by a shearing action such that in appearance it becomes partly sintered, but not charred, the greater part or all of the heat required being generated within the cellulose by the mechanical deformation to which it is subjected.  Actual sintering may take place during the treatment which may be carried out by passing the cellulose through the nip of one or more pairs of closely set hard-surfaced rolls until it has lost its fibrous form and is in the form of a brittle sheet.  The rolls may be cooled or heated (e.g. to about 50-100 DEG  C., especially to about 60-80 DEG  C.) and may be provided with means for varying the width of the nip.  The rolls may be run at peripheral speed ratios of between about 1.0 to 1.0 and 1.5 or 2.0 to 1.0 and especially at about 1.25 to 1.0.  The clearance at the nip is preferably below 0.05 inch and especially 0.01-0.025 inch. The cellulose may be in the form of sheets of purified wood pulp (rayon pulp) or of cotton linters.  It may be in a normal air-dry condition or conditioned by steaming or water spraying to a moisture content of over 8 per cent before treatment.  A small proportion of an anti-oxidant, e.g. hydroquinone may be applied to the cellulose, e.g. dissolved in the water spray.  The cellulose, when dry or of low moisture content may be broken down all the way to a fine powder in the rolls, but when of higher moisture content is flaked or powdered by separate treatment.  In an example, an air-dry sheet of a purified wood pulp is passed a number of times through the nip of a pair of steel rolls heated to about 60 DEG  C., set to a clearance of 0.015 in, and running at the same peripheral speed until a brittle, semi-transparent sheet is obtained.  This sheet is then broken up in a hammer mill to form a mixture of small flakes and fine powder which is screened on 15- and 40-mesh sieves.  Flakes and powder produced from the treated cellulose have a high packing density and may be converted into alkali cellulose by mixing it with concentrated aqueous caustic soda solution as for example described in Specifications 637,133 and 637,134 or with solid caustic alkali, or by mixing it with aqueous caustic soda solution of 18-65 per cent concentration, only so much solution being employed as corresponds with the required caustic alkali-anhydro-glucose unit ratio.  The alkali cellulose thus produced has itself a high packing density. Examples are given of the preparation of alkali cellulose from cellulose treated according to the invention and of sodium carboxymethyl cellulose, using chloro-acetic acid, sulphoethyl cellulose, using sodium 2-chloroethane sulphonate, ethyl cellulose, using ethyl chloride, and methyl cellulose, using methyl chloride, from the alkali cellulose, also of the preparation of cellulose acetate from cotton linters treated according to the invention. Alkali cellulose prepared from cellulose treated according to the invention may also be used for viscose production.  Powder or flake cellulose of high packing density prepared from cellulose treated according to the invention requires less caustic alkali than usual for conversion into alkali cellulose and in the manufacture of cellulose derivatives from the latter less vigorous and less prolonged mixing is required and in the preparation of cellulose ethers using liquid alkyl chlorides the proportions of the latter may be reduced.