US2138014A - Preparation of viscose sirup - Google Patents

Description

Patented Nov. 29, 1938 UNITED STATES PATENT OFFICE PREPARATION OF VISC'OSE SIRUP George A. Richter, Berlin, N. H., assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application May 1, 1937, Serial No. 140,222

4 Claims. (01. 260-100) This invention relates to the preparation of kraft base pulp. The filterability test employed viscose and has for its general objective the .ecoherein is performed under standard conditions nomical preparation of viscose sirup such as is with a filter pad of standard structure and area; suitable for the manufacture of artificial silk, and the volume of viscose sirup filtrate delivered 5 films, and regenerated cellulose products. by the pad before it becomes plugged with fiber 5 In accordance with the present invention, visfragments or gelatinized particles present in the cose sirup is prepared by the Xanthation of alkali r p s taken s the filterebility 0f the pcellulose comprising a blend of acid-preliberated When viscose sirup was prepared pursuant to the cellulose pulp of the nature of sulphite pulp and invention hereof from a blend consisting of about alkali-preliberated cellulose pulp of the nature equal proportions of the same sulphite pulp and 10 of kraft and soda pulps, although krait or simthe same kraft pulp productive of the viscose ilar alkali-preliberated pulps do not by themsirups whose filterabilities have just been given, selves yieldv viscose sirups satisfactory for the it was found that the viscose sirup had a filtermanufactureof artificial silk, films, and similar ability of about 1400 to 1600, that is, partook in ultimate products, the blending therewith of upsurprisingly large measure of the quality of fil- Wards of about 25% sulphite or similar acidterability possessed by the viscose sirup prepared preliberated pulp, based on the weight of the from the sulphite pulp alone, despite the fact blend, preparatory to Xanthation makes possible that the sulphite pulp and the kraft base pulp the obtainment of viscose sirups quite satisfachad app ox t y the Same Solution Viscosity tory for manufacture into such ultimate prodas measured by the usual cuprammom'um cel- 20 ucts. lulose solution test.

The advantages to be realized from the prac- While it is difficult to account for the results tice hereof may perhaps be best appreciated by e d y the practice hereof, y y y considering the results realized when acid-prelibp ps be explai y What pp s whe Grated Wood pulp, such as sulphite, and lkalialkali-cellulose crumbs are prepared from sulpreliberated wood pulp, such as kraft, separately phite p p alone and from kiaft p p aloneundergo the usual Viscose-making 0perati0ns Thus, alkali-cellulose crumbs prepared from sul- These operations involve dipping sheets of the phite pulp are Characterized y a fiuffy p pulp in strong caustic soda solution, pressing the Structure Permitting Teddy and Substantially sheets to form alkali cellulose of appropriate form access of Carbon bisulphide Vapor g 30 solution content, grinding t sheets t crumbs out such structure. Per contra, alkali-cellulose or shreds, aging the crumbs, and xanthating the Crumbs Prepared from Kraft p p are of crumbs by tumbling them in a slowly revolving atively dense, Course, and stringy texture drum in the presence of carbon bisulphide vapor. because of non-uniform access of carbon bi- When xanthate crumbs are thus prepared from p e Vapor to their interiors, y d dense, O5 sulphite pulp, it is found that they dissolve reado y X n hate r m Wh i tanc ow rd ily and substantially completely in dilute caustic sumciently complete dissolution in dilute caustic soda solution to yield a cellulose xanthate solu- Soda Solution has already been mentioned. It s tion or viscose sirup suitable for the manufacture evidently the case that n the alkali-cellulose of artificial silk. When, on the other hand, Xanproduct of sulphite p p and the u ose thate crumbs are similarly prepared from kraft product of Kraft p are ground Simultaneously pulp, it is found that they are resistant to subinto s, the resulting ass or blend of stantially complete dissolution in dilute caustic Crumbs is rendered sufficiently o inous or soda solution and that the resulting viscose distended 50 that h the s iS l to a sirup contains a substantial residue of fiber low y ro at d a d Xehthated y exposure fragments or gelatim'zed particles bespeaking into carbon bisulphide vapor, the vapor can pencomplete Xanthation of the pulp and inutility of etrate into and throughout the distended or volthe viscose sirup for the manufacture of artificial uminous mass With sufficient rapidity and unisilk. The fact is that in terms of filterability or formity to yield Xanthate crumbs of the desired capacity for filtration the iscose sirup prepared substantially 001111016178 solubility in dilute caustic 50 from sulphite pulp generally displays a filtrasoda solution to conduce to viscose sirup suitable bility of about 1500 to 1800 cubic centimeters as for manufacture into artificial silk. compared with a filterability of only about 100 A typical example of procedure in conformity to 200 cubic centimeters in the case of viscose with the invention hereof may involve the use of 55 sirup prepared under similar conditions from a bleached sulphite pulp and bleached kraft pulp whose compositions, other than pentosan content, may be substantially similar. Thus, the compositions of the two bleached pulps may be those appearing in the table below:

Sulphite Kraft Alpha cellulose 88 to 89% 88 to 89% 2 to 4 2 to 4 Pentosans 2.5 to 4% 5 to 9% Both the sulphite and kraft pulp may be derived from spruce or other coniferous wood and may be used in the form of drier sheets or pulpboards as ordinarily. Equal portions of such pulps may be steeped in strong caustic soda solution to form alkali cellulose, as by stacking sheets of the sulphite pulp alternately with sheets of the kraft pulp and submersing the stack in the solution with the sheets in upstanding position. The stack may thus be put into the usual steeping press wherein the sheets may be thoroughly soaked or saturated with caustic soda solution of about 18% strength at about 20 C. for about 3 hours. Excess soaking solution may be drained from the press and the stack of soaked sheets then pressed to a solution to pulp ratio of about 3 to 1, based on the original weight of the sheets. The pressed sheets may then be taken from the stack and disintegrated into soda cellulose crumbs in the usual grinders, wherein the grinding of a mass of, say, 200 pounds cellulose content may be effected for a period of about 3 hours at a temperature of about 20 to 24 C. The resulting soda-cellulose crumbs, which are of fluffy open structure, may then be aged at about 20 C. for about 70 hours, whereupon they may be charged into the usual rotary Xanthating drum into which carbon bisulphide in the form of vapor may be progressively delivered in the amount of, say, about 35%, based on the dry weight of original cellulose, for a period of about 3 hours while the mass in the drum is kept at a temperature of about 25 C. At the end of such period, the resulting porous mass of orange-colored Xanthate crumbs may be sluiced from the xanthating drum into a dissolving tank wherein the xanthate crumbs may be mixed with dilute caustic soda solution predetermined as to volume and causticity to yield viscose sirup of about 7.5% cellulose content and about 6.5% causticity based on the weight of the sirup. The desired substantially complete dissolution of the xanthate crumbs may be had after mixing intimately with the dilute caustic soda solution at about 15 to 20 C. for about 3 to 4 hours. The resulting viscose sirup is a thick clear liquid practically free from unxanthated or incompletely xanthated residues and hence of good filterability. Upon being deaerated, as usual, such viscose sirup is spinnable into artificial silk of strength and color qualities comparing favorably with artificial silks as heretofore manufactured by the viscose process from sulphite pulp or cotton linters.

It is possible to depart in various respects from the particular example hereinbefore given. Thus, rather than mixing sheets of the sulphite and kraft pulp while they are being dipped or soaked in the strong caustic soda solution, it is possible to dip or soak sheets consisting of a blend of the two pulps; and it is also possible to dip or soak the sulphite pulp sheets in strong caustic soda solution independently of the kraft pulp sheets, provided that the resulting sheets of soda cellulose are ground together at the same time so that crumbs or alkali cellulose produced from the sulphite pulp sheets are substantially uniformly blended with the crumbs of alkali cellulose produced from the kraft pulp sheets, thereby providing an alkali-cellulose blend or mass of the appropriate fiuffiness or voluminous structure for the xanthating reaction. When sheets of sulphite pulp and sheets of kraft pulp are dipped or soaked in separate caustic soda'solutions, it is possible to operate under dipping conditions, i. e., time and temperature of dipping and causticity of dipping solution, different for each of the two types of sheet and designed to promote the formation of the best kind of alkali cellulose from each type of sheet. Thus, it may be desirable to furnish for the kraft pulp sheets a dipping or soaking solution of much greater causticity, namely, of much greater than 18% strength, and/or to maintain such sheets in a solution at lower temperature and/or for a longer period of time than in the case of the sulphite pulp sheets. In this latter connection, it should be understood that the stronger the dipping solution, the lower the temperature at which it is used, and the longer the dipping period, the greater is the reactivity of the resulting soda cellulose in the subsequent xanthating reaction.

The invention hereof affords the important advantage that it makes available for satisfactory use in the viscose-rayon process the various alkali-preliberated wood pulps heretofore found unsuitable for viscose-rayon manufacture, including alkali-preliberated .pulps derived from various resinous or deciduous woods which, although lending themselves nicely to low-cost pulping by the soda, kraft, and other alkaline fiber-liberating processes, do not respond to pulping in acid sulphite or similar acid fiber-liberating liquors. The expressions alkali-preliberated cellulose pulp or alkali-preliberated wood pulp used herein are meant to include wood pulps derived from both coniferous and deciduous woods by kraft, so, or equivalent alkaline pulping liquors and to include such pulps in unbleached, semi-bleached, bleached, unrefined, or refined conditions, as all such pulps may advantageously undergo the process hereof. Insofar as concerns unbleached or semi-bleached alkali-preliberated pulps, it will, of course, be appreciated that their utility herein extends to the making of artificial silk or other regenerated cellulose products' wherein the color factor is of no particular materiality but wherein the factor of strength is of importance. So far as concerns the factor of strength, regenerated cellulose products resulting from the process hereof, when the alkali-cellulose blends contain alkali-cellulose produced from unbleached or semi-bleached alkali-preliberated cellulose pulps, exhibit a strength superior to that of the usual regenerated cellulose products. The utility of the instant invention resides more especially in the making of viscose sirups of a cellulose content and causticity each ranging from about 6% to 10%, since it is the making of viscose sirup of such composition from alkalipreliberated cellulose pulp that has presented the problem solved in such a simple and satisfactory way by the instant invention.

I claim:

1. A process of making viscose, which comprises producing an alkali-cellulose blend from acid-sulphite-preliberated cellulose pulp and alkali-preliberated cellulose pulp in approximately equal proportions to not less than about 25% of said first-named pulp relative to the total cellulose content of said alkali-cellulose, xanthating the alkali-cellulose blend, and dissolving the resulting cellulose xanthate to form viscose.

2. A process of making viscose, which comprises grinding into crumbs sheets of alkali-cellulose whose cellulose includes both acid-sulphitepreliberated cellulose pulp and alkali-preliberated cellulose pulp in approximately equal proportions to not less than about of said firstnamed pulp relative to the total cellulose content of said alkalicel1ulose, xanthating the crumbs, and dissolving the xanthated crumbs to form viscose sirup.

3. A process of making viscose, which comprises grinding into crumbs sheets of alkali-cellulose comprising at least two different cellulose components, one of said components being acidsulphite-preliberated wood pulp and the other of said components being alkali-preliberated wood pulp of the nature of kraft and soda pulp in such proportions as to yield a blend of alkalicellulose crumbs whose cellulose content is furnished to the extent of about 25% to by said first-named pulp, xanthating the blend, and dissolving the resulting cellulose xanthate to form viscose.

4. A process of making viscose, which comprises forming alkali-cellulose from sheets of acid-sulphite-preliberated cellulose pulp and from sheets of alkali-preliberated cellulose pulp, simultaneously grinding into crumbs the sheets of alkali-cellulose produced from both types of pulp in such proportions as to yield a blend of alkali-cellulose crumbs whose cellulose content is furnished to the extent of about 25% to 50% by said first-named pulp, xanthating the blend of alkali-cellulose crumbs, and dissolving the xanthated crumbs to form viscose sirup.

GEORGE A. RICHTER.