US2026068A - Process for the improvement of cellulose - Google Patents

Description

Patented PATENT OFFICE raocass roa THE IDIPROVEMIEN'I OF CELLULOSE Emil Scheller, Ilorsbach-in-the-Taunus, Germany,

assignor, by mesne assignments, to E. I.

du Pont de Nemours and Company, a corporation of Delaware No Drawing. Application August 22, 1930, Serial No..477,191. In Germany September 11, 1929 8 Claims.

disadvantageous, however, in that it will not produce a cellulose of the desired low ash content, low copper number and with an adjustable contentof the particularly desirable alpha cellulose. In addition, this process of the prior art results in disintegrations and damages to the cellulose which, when the same is later incorporated into'solutions, confer an undesired low viscosity to the solutions.

One object of this invention is to produce a continuous, effective and non-damaging treatment to cellulose fibers. Another object of the invention is to produce cellulose with an adjustable content of undecomposed alpha cellulose. A further object is to produce a cellulose of low ash content and low copper number. And finally, the invention has also for its object the production of treated viscose, with all the desirable properties previously mentioned, in such undamaged form that solutions resulting therefrom have a high viscosity and are particularly suitable for the spinning of artificial silk.

In general, the invention comprises a four stage treatment of cellulosic materials; active chlorine is first employed, this is followedby an alkali treatment preferably while air is excluded, the cellulose is next treated with active oxygen in alkaline solutions,-and finally the goods are acidified or soured. By this ccmbination treatment, it has been found that the cellulose is effectively bleached, has a low ash content, remains undamaged, and can be produced with an adaptable quantity of desirable alpha cellulose.

The invention will now be more particularly 7 described in terms cf'its application to the preparation of cellulose suitable for making viscose solutions of the type used in spinning artificial silk. The process here given is broad in its applicatfon, however, and the particular descriptive means here employed will be understoodnot to limit the scope of the invention. The cellulose is bleached in the usual manner with chlorine. The quantity of chlorine here employed can advantageously be less than that which is".

usual in the art. This results in obtaining an article which is bleached from /2 to white.

The material is then thoroughly washed, and afterward .is subjected to a treatment with an alkaline solution at ordinary or increased pressures and at high temperatures. Air should be excluded during this treatment, for example, the process may be carried out in anautoclave. In general, the highest content of alpha cellulose is obtained by the use of sodium hydroxide. One can, however, use sodium carbonate, lime, or a mixture of the two. The quantity of alkali employed will depend upon the quality of the celluloseand is preferably so limited that immediately after the boiling process the liquor still 1 gives alkaline reaction. Ordinarily, 5 to 10% of caustic alkali, based on the dry weight "of the cellulose will prove satisfactory. Boiling for longer periods and at increased pressure increases the quantity of alpha cellulose. In case 20 the pre-treatment with chlorine has been longer than is recommended, i. e. if the goods are bleached more than to A white it is necessary to'carry out a more energetic alkali treatment in order to produce a high content of alpha cellu- 25 I ticularly the viscosity of solutions of this product which are made, for. example, by dissolving 5 the product after treatment in carbon bisulphide plus sodium hydroxide or in ammoniacal cop'- per solutions, may be varied to a considerable extent by regulating the amount of molecular or elemental oxygen present during. the bleach 4o ing process. This regulation of the oxygen pres k ent is especially important during the bleaching with the alkalimetal peroxides. If the elementary oxygen is entirely absent during this treating stage, a product giving-solutions of very 45- high viscosity is produced. On the other hand, to-obtain solutions of varying viscosity, as is sometimes desired, measured amounts of oxygen may be intentionally introduced.

-Particular care should be exercised during 5 this alkali peroxide bleach, and three cases are distinguished. e 1

1. Materials which have not been disinte grated. These should be treated in a pressure cooker. I

In working with these materials, it is advantageous to employ stabilizers. Sodium silicate solutions in quantities up to 1% of the weight of the goods have given very satisfactory results.

It is also preferable to carry out the bleaching process in this case slowly and at lower temperatures, for example, temperatures of up to 60 C.

2. Partwise disintegrated materials. These are also advantageously treated in a pressure cooker.

3. Disintegrated materials. These may be bleached in an ordinary bleaching hollander.

With materials f this class, it is not in general necessary employ stabilizers, since the water employed will ordinarily carry a suillcient amount of stabilizing materials. The sodium peroxide solution can be strengthened by the addition of further alkali if necessary. Open apparatus, such as bleaching hollanders, may be used for carrying out operations on these materials, and it is preferable to agitate the Alkaline solutions of hydrogen peroxide, obtained from sodium peroxide,-are the most advantageous sources of active oxygen. The

. amount of sodium peroxide employed will in general range from 1 to 2% of the weight of the oods.

After bleaching, the goods are washed and acidified. This acidification is preferably carried to'a point wherethe solution is weakly acid, as indicated by the Congo red acid reaction. This has a favorable effect in decreasing the ash content, provided the. goods are subjected to a careful and thorough washing out afterwards. The latter part of this washing out is generally conducted in the presence of small quantities of alkali or ammonia. It will be understood that the matter of regulating the time of bleaching, the temperature and, the alkalinity will vary considerably according to the quality of the material with which one starts, and also according to the qualities which one desires to impart to the final product, and I, therefore, do not desire to be limited to the specific disclosures of this kind which have been given here largely by way of example. It must be understood that in art of this kind one necessarily must determine experimentally certain features of the process which are inherently subject to variation.

Having now particularly described. my invention, what I desire to claim is:

1. Process for treating cellulose materials comprising subjecting the materials to the treatment with active chlorine to the extent of about to =54 bleach, washing, treating the material with an alkali boil in the absence of oxygen at high temperatures, washing, subsequently completing the bleaching by subjecting the materials to treatment with solutions containing alkali peroxides, washing, souring the product with a faintly acid solution, and finally washingwith water which is slightly alkaline during the last stage in washing.

2. Process for treating cellulose materials comprising incomplete bleaching with active chlorine containing solutions, washing, subjecting the cellulose to an alkali boil in the absence of air, washing, subsequently completing the bleaching by treating the cellulose with solution containing alkali metal peroxides and adding quantities of a stabilizer, washing, souring 5 the product with faintly acid solution, and removing the said acid by a final washing process wherein the wash water is faintly alkaline in the last stage of washing.

3. Process for treating cellulose comprising treating the cellulose to a V to bleach with solutions containing active chlorine, washing, bucking the solution. under increased pressure with caustic alkali in the absence of oxygen, washing, subsequently completing the bleaching by subjecting the cellulose to treatment with solutions containing an amount of sodium peroxide equivalent to 1 to 2% of the weight of the goods, washing, souring the product with faintly acid solution until acid to Congo red, and finally washing thoroughly with water which during the last stageof the operation is iraade faintly alkaline with ammonium hydrox 4. Process for treating cellulose comprising subjecting the material to a V2 to bleach with active chlorine, washing, bucking the material at increased temperatures and pressure with solutions containing 5 to 10% of caustic alkali based on the weight of the goods, washing, subsequently completing the bleaching by treating the cellulose with an alkaline solution containing alkali metal peroxides and simultaneously introducing measured quantities of oxygen thereinto, washing, souring the product 6 with faintly acid solution, and finally thoroughly washing the material, the wash water at this stage of the process being made faintly alkaline during the last stage of the washing operation.

- 5. A process for treating cellulose which com- 40 prises subjecting said material toa one-half to three-quarters bleach with active chlorine, washing, bucking the material at an increased temperature and pressure with a solution containing 5 to 10% of caustic alkali based on the weight of the cellulose, washing, subsequently completing the bleaching by treating the cellulose with an alkaline solution containing an alkali metal peroxide, elemental oxygen being excluded, washing, souring the product with a faintly. acid solution and finally washing the cellulose, the wash water at this stage of the. process being made faintly alkaline during the last stage of the washing operation.

6. A process for improving and bleaching cellulose which comprises treating said cellulose with chlorine to effect a partial bleach, treating said cellulose with. an aqueous alkaline solution at an elevated temperature in the substantial absence of elemental oxygen, subsequently completing the bleaching with an active oxygen containing substance in alkaline solution and capable of yielding hydrogen peroxide under the conditions of the process and then acidifying said material. 6

7. A process for bleaching and improving cellulose, which comprises partially bleaching said cellulose with chlorine, treating said cellulose with an .aqueous alkaline solution at an elevated temperature, subsequently completing the bleaching with an active oxygen containingmaterial in .alkaline solution and capable of yielding hydrogen peroxide under the conditions of the process, elemental oxygen being active oxygen containing substance in alkaline solution and capable of yielding hydrogen peroxide under the conditions or the process while regulating the quantity of elemental oxygen present, and then acidifying said cellulose 5 material.

EMIL SCHELLER.