US1749003A - Mercerized wood-fiber tissue and process of preparing same - Google Patents

Description

Patented 4, 1930 This invention relates to the preparation 4 of material adapted for conversion 1nto pure or high grade cellulose derivatives, andv is more especially concerned with the prepara-" 5 tion ofcellulosic fiberadapted for conversion into the lower nitrocelluloses, such as those customarily employed for the manufacture of artificial silk, films, lacquers, and kindred products.

Although the process herein to be described may be practised with cellulosic fiber of various kinds, it is applicable most expediently to paper or-tissue prepared from wood pulp, particularly one containing a high percentage of alpha or resistant cellulose. 1 Such high alpha cellulose fiber, which for convenience of designation will herein- 'aftei' be termed alpha fiber, may be con- 1 verted into cellulose derivatives having '20 physical and chemical properties compara- 'ble to derivatives prepared fromv cotton fiber or cotton linters, in contrast to the relative- Lly impure derivatives having inferior. prop erties, prepared from chemical wood fiber of lower alpha cellulose content. Such alpha fiber may beproduced as described inv application for patent, Serial No. 72,522, filed December 1, 1925, by George A. Richter and Milton 0. Schur, by treating a pulp, e. g.,

the usual-commercial sulphite pulp conta1ning, say, about 85% to 8 7% alpha cellulose, in a solutionof caustic soda or equivalent alkaline compounds under the appropriate conditions of time, temperature, and'chem -'35 real concentratlon.

lulose contentofithe fiber, viz, beta and gamma celluloses, ligneous and other coloring material, is dissolved, so that there is 40, produced a fiber containing upward of 93% a1 ha cellulose and which requires only a rel ativel small amount of bleach for conversion into /fiber of high whiteness, and is usable as anew rag or cotton fiber substitute in the manufacture of high gradev writing papers and in the preparation of cellulose derivatives of high commercial value and purity. Sometimes it is desirable to treat the pulp, prior to the alkaline treatment, with a By such treatment, a I considerable portion bf-the non-alpha cel- PATENT OFFICE 0P BERLIN, NEW HAMPSHIRE, Assrenons HAMPSHIRE, A CORPORATION or MAINE AND PROCESS or PREPARING SAME v 5, 1927. Serial No. 159,235.

When alpha fiber of very high alpha cellulose content, about 95% to 98%, is desired, the initial alkaline treatment, is succeededby a secondfalkaline treatment, as described in application for patent, Serial No. 75,888, filed December 16, 1925, by George A. Richter. Such double alkaline treatment not only further reduces the quantity of bleach required to whiten the fiber, but produces fiber which constitutes an excellent raw material for the preparation of high grade cellulose derivatives. t 1

In application, Serial N o.-140,676, filed October 9, 1926, by George A.-Richter, Milton 0. Schur,-and Royal I-L Rasch, the advantages of mercerizing cellulose fiber, and more particularly alpha fiber, prior to conversion into cellulose derivatives, especially the lower nitrocelluloses, are disclosed, and, in our application, Serial No. 140,675, filed October 9, 1926, the advantages of'mercerizing paper or tissue formed from such fiber preferably beaten, and a subsequent treatment with hot alkaline water, are disclosed. I

We have now discovered that the addition of a relatively small amount of an oxidizing or bleaching agent, e. g.., hypochlorite 'or permanganate, to the 'mercerizing solution ita nt additional removal of undesirable color ing matter and yields a fiber which is convertible into cellulose derivatives or cellulose products, such as rayon, films, lacquers, etc., of colorlessness or freedom from color practically equal to like derivatives or cellulose products prepared from good cotton fiber.

and/or to the hot water, efl:'ects an imporfin The use of a small amount of oxidant t0 remove coloringmaterial from the alpha fiber" while such fiber isbeing treated with a strongly alkaline solution is believedito be distinctly advantageous, for thetremendous OH ion concentration in solution, we believe,

represses substantially entirely a tendency toward the oxidation of the alpha or resistant 0 1 halogenizmg or. an oxidizing solution, e. g., \cellulose content of the fiber, while permitting 100 cellulose products.

. the use of which mercerizlng strength and stretch a deep brown color,

borne out by the fact that the treatment has substantially no effect upon the excellent nitrating yield, low acid retention, and high 'of filaments and films prepared from the mercerized fiber. The nitrated fiber may yield solutions pf slightly lower viscosity than usual, but this is advantageous for the preparation of many nitro- In carrying out one mode of procedure, the alpha fiber, preferably in tissue form and beaten more or less, is treated by steeping it in a caustic soda solution of mer'cerizing strength and containing the oxidizin agent, until the desired mercerization of the 'ber has or treated with water, preferably hot water,

latter effects a further purification of the fiber. The hot water preserves the tissue in a firm, integral condition, whereas cold water is likely to cause the disintegration ofrthe tissue into a pulpy mass which is diflicult to handle Theme of hot water after the mercerizing treatment, as indicated, is therefore a step of paramount importance, as'it makes possible the practice of a continuous and economical process. Should'the solution contain no oxidizing agent, as heretofore, the hot water assumes the depth of color depending upon the purity or alpha cellulose content of the alpha fiber. When the mercerizing solution contains anoxidizing agent as in accordance with the present invention, however, the hot water is of much lighter color and frequently is colorless, as the tissue retains suflicient oxidant after the mercerizing treatment to oxidize or to bleach coloring matter extracted from or generated in the fiber by the hot, dilute caustic soda solution formed with the hot water. water treatment, the tissueis neutralized of residual caustic soda by a steeping in an acid or souring solutionwhich-preferably contains an acid reducing agent, which, in addition to neutralizing the free caustic soda, neutralizes or reduces the last traces of freeoxidant. If'desired, of a mixture ofaan acid and a reducing compound ma expedient to use a single compound to effect both the neutralizing and reducing actions. Thus, for example, sodium h-y ochlorite may be used as the oxidant in t e mercerizing solution, and sulphurous acid may be used in the souring. solution as the acid reducing agent. After the souring, the tissue is washed free from neutralized products with cold water, and finally is dried. The tissue tends to crinkle, upondrying, so that if the tension usually applied during drying when the material is in continuous sheet form is reduced drowned mercerizing solution.

After the hot course, a solution containing. dergo crinkling, be used, but 1t 1s usually more or removed, there results a crinkled tissue. Such crinkled tissue may be cut up into small pieces, which when nitrated have but little tendency to stick together'in the nitrating bath or in the centrifuge.

A specific example of procedure which may be practised and which has been found to give excellent results, may be substantially as follows. The alpha fiber is sheet or nitrating tissue, preferably below 20 preferably treated in the form of a continuous thin waterleaf" pounds in basis welght (480-2 LX36), or

equivalent to a thickness of approximately .003 inches. The fiber is preferably beaten prior to formation into the tissue, as a beaten fiber has proven to give better results upon nitration than an unbeaten fiber. The tissue is passed through or immersed in a caustic soda solution containing about 19% NaOH and about 0.3% available chlorine (based on solution), at about 68 F., the time of immersion being from about two to ten seconds. Under these conditions, we not only realize more effective removal and color-generating substances, i. e., substances causing coloration in nitrocellulose products such as lacquers, films, etc., but we retain all the advantages accruing from mercerization. The tissue is then preferably passed between squeeze rolls, which serve to express therefrom excess solution for reuse in mercerfization. The tissue 5 s then treated with water, preferably by passing it through a countercurrent flowing stream of hot water at or near the boiling point. The concentrated caustic soda solution retained by the tissue forms with the hot water a dilute caustic soda solution which effects a further removal or extraction of those impurities unaflected by the relativel cold, concentrated ince suflicient oxi dant is retained by the tissue to bleach any coloring material extracted from or generated in-the fiber, the hot alkaline water is light colored and frequently colorless. The tissue is then passed through a 0.15% to 0.25% sulphurous acid solution at room temperature, and then washed with sufiicient cold water to remove the reaction products. 7 The neutral tissue is then dried, either under ten sion or under conditions permitting it to unwhich may be preferable, as the crinkled tissue when out up into small pieces and nitrated has but little tendency to stick together in the nitrating bath or in the centrifuge. v

By our process, two ver important ends are simultaneously attaine as in our application hereinbefore identified, .viz, the apha fiber is mercerized or chemically hydrated, and it is simultaneously purified or refined.

It should be understood that our process is its more compact condition, g ves a higher unbeaten. With tissue, however, certain practical advantages are to benoted, to wit:

r tively (a) Uniformity of treatment is easier to attain, as all the fibersIare more easily accessible to the reagents applied.

(b) The apparatus necessary is comparasimple and inexpensive.

(0 Continuous operation is more easily realized. e i (d) The dried, processed tissue, because of yield of nitrocellulose, and has a lower acid retention.

Again, while inthe example given certain definite-conditions of processing have been specified which have yielded excellent results, nevertheless, we desire to have it understood that the temperature and composition of mercerizing solution, and the time of treatment with'such solution,'may be varied within rather wide limits.

The tissue may be steeped in the mercerizing solution immediately after sheeting and partial or comple'tejdrying, or after sheeting on the wet end ofa Fourdrinier or cylinder paper-ma king machine and passing through press. rolls but without drying. A partial or complete conservation of the steam usually expended in drying the tissue may thus be realized, when desired, bythe latter ,method. When a damp or wet tissue is to be mercerized, it is advantageous to employ astronger solution than otherwise, so as to attain the necessary rate of diffusion into and through .50, before the bleaching zone-in the countercur:

rent streannaoiji hot water is reached. The

the tissue to produce the 'desired merceri zation, but withoilt causing a disintegration or falling apart of thetissue into fragments or into pulp.

If desired, we may also add a very small amount of oxidant to the countercurrent flowing stream of hot water at any suitable point, 1 preferably midway between its influent and efiluent ends. Of course, should we so desire,

we might omit the addition of oxidant to the mercerizing solution, and add the appropriate amount of oxidant to the countercurrent stream of hot water only. Less oxidant need be added here than to the mercerizing solution, because some of the coloring matter, is independently removed by thehot water eflectivenessbf removing coloring material is not lessened, even though the tissue first contacts with eflluent colored hot water, because any residual coloring matter in the tissue after mercerization, and/orcoloring materialo'ador absorbed thereby from the eflluent hot water, are gradually removed as the tissue proceeds through the bleaching zone in-the countercurrent flowing stream. Suchremoval of coloring is evidenced by a gradual lightening of the color of the water stream;

. toward the influent end of the countercurrent dant, washing the web aration of nitrocellulose and other cellulose derivatives substantially free from coloring matter and from which colorless-filaments,

films, and congeneric products .may be produced. Inasmuch as the absence of coloring matter in nitrocelluloses andother cellulose derivatives prepared from good cotton fiber has in the past been one of the outstanding advantages of cotton'as a raw material, and, again, inasmuch as the product of the present inventionmay be manufactured at a unit cost below that ofcotton and its characteristics closely controlled or definitely varied, it is preeminently satisfactory as a pure cellulose raw material.

While the advantages of the present invention have been described in detail in connection with the prepars'ztionof nitrocelluloses, and more especially the lower nitrocelluloses,

v it is to be noted, as previously adverted, that advantages are gained in the preparation of other cellulose derivatives. Thus, in the preparation of cellulose acetate, smoothness of acetylation and quality of cellulose acetate are improved, particularly with regard to the elimination of undesirable color.

We claim:

1. A process which comprises treating a high alpha cellulose fiber with a caustic soda solution of mercerizing strength containing a small amount of an oxidizing agent, substantially completely removing the treating chemicals from the fiber, and converting the fiber into a cellulose derivative.

2. A process which comprises treating. a

,high alpha cellulose wood fiber with a caustic soda solution of mercerizing strength containing. an oxidant, washing the treating fiber, neutralizing'the lasttraces of caustic soda and oxidant, and washing the fiber free from reaction products. r

3. A process which comprises treating a high-alpha-cellulose-containing -wood fiber witha caustic soda solution of mercerizing strength containin'ga small amount of an oxidant, washing the treated fiber, neutralizing the last traces of caustic soda and oxidant, washing the fiber free from reaction products, and nitrating the fiber.

4. That. step which comprises treating a wood fiber web with a caustic soda solution ofmercerizing strength containing anoxi- 7 substantially free from treating chemicals, and converting into a cellulose derivative.

5. A process which comprises treating a high alpha cellulose wood-fiber tissue with a caustic soda solution of mercerizing strength containing an oxidizing agent, and treating the tissue with hot water.

6. A process which comprises treating a high alpha cellulose wood-fiber tissue with a caustic soda solution of mercerizing strength containing an oxidizing agent, squeezing excess solution from the tissue, and passing the treated tissue through a'countercurrnt flowing stream of hot water.

7. A process which comprises treating a high alpha cellulose wood-fiber tissue with a caustic soda solution of mercerizing strength containing an oxidizing agent, passing the treated tissue through a'countercurrent flowing stream of hot water,- and adding an oxidizing agent to the stream of water.

8. A continuous process which comprises successively passing a continuous sheet of high alpha cellulose fiber through a caustic soda solution of mercerizing "strength and through a countercurrent flowing stream of hot water containing an oxidizing agent;

9. A process which comprises treating a high alpha cellulose wood-fiber tissue with a caustic soda solution of passingthe treated tissue through a countercurrent flowing stream ofhotwater, and adding an oxidizing agent to the stream of water.

10. A process which comprises treating a high alpha cellulose wood-fiber tissue with a caustic soda solution ofmercerizing strength containing an oxidant, treating the tissue with hot water, neutralizing caustic soda and oxidant remaining in the tissue, and washing the tissue free from reaction prod ucts.

, 11. A continuous process which comprises successively passing a continuous. sheet of high alpha cellulose fiber through a caustic soda solution of mercerizing strength containing an oxidant, through a countercurrent flowing stream of tralizing solution, and through wash water.

12. A process which comprises treating a high alpha cellulose wood-fiber tissue with a containing an oxidant, treating the tissue mercerizing strength,

hot water, through a neusignatures. caustic soda solution of mercerizing strength I 14. A process which comprises treatin a.

high alpha cellulose wood-fiber tissue wit a caustic soda solution of mercerizing strength containing an oxidant, treating the tissue with hot water, neutralizing caustic soda and oxidant remaining in the tissue, washing the tissue free from reaction products, drying the tissue under conditions permitting it tocrinkle, and nitrating the crinkled tissue.

15. A process which comprises treating a high alpha cellulose wood-fiber tissue in a caustic soda solution of mercerizing strength containing an oxidant, substantially completely removing the treating chemicals from the tissue, and converting the tissue into a cellulose derivative.

16. A mercerized, high alpha cellulose wood-fiber tissue suificiently free from non-. alpha' cellulose ,components including beta and gamma cellulose, ligneous, and other coloring material to be convertible into lower nitrocelluloses of colorlessness or freedom prepared from good cotton fiber.

17. A process which comprises treating cellulose fiber with a mercerizing solution containing an oxidant, washing the treated fiber substantially free from chemicals, and converting the washed fiber into a cellulose derivative. a

18. A process which comprises treating a from color practically equal to nitrocelluloses cellulose fiber tissue with a mercerizing solution containing an oxidant, and washing the tissue substantially free from chemicals in hot water. i f

19. A process which comprises treating cellulose fiber tissue with amercerizing solution containing an oxidant, washing the tissue substantially free from chemicals inhot water, and converting the washed tissue into a cellulose derivative.

20. A cellulose fiber tissue with a mercerizing solution containing an oxidant, treating the tissue with hot water, drying the tissue under conditions permitting it to crinkle, and conyerting the crinkled tissue into a cellulose derivative.

In testimony whereof we have afiixed our MILTON 0. serum. ROYAL H. RAYSCH.

with hot water, neutralizing caustic soda and V oxidant remaining in the tissue, washing the 55 tissue free from reaction products, and drying the tissue.

13. A process which-comprises treating a high alpha cellulose wood-fiber tissue with a caustic soda solution of mercerizing strength contalning an oxidant, treating the tissue process which comprises treating a llO