US3010781A - Process of producing viscose rayon - Google Patents

Description

United States Patent 3,010,781 PROCESS OF PRODUCING VISCOSE RAYON Marion Lytton, West Chester, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., 21 corporation of Delaware No Drawing. Original application Dec. 30, 1954, Ser. No. 478,939. Divided and this application Nov. 25, 1958, Ser. No. 776,172

15 Claims. (Cl. 1854) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose,a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the-like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and aLiali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequntly subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The crossflsection of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent ditferences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relativelyhigh tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiff.

It has now been discovered that the presence of small amounts of alkali-soluble alkylene oxide adducts of mono fatty alkyl hydrazines in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the adduct is maintained with certain limits and the composition of the spinning bath is maintained with certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of alkylene oxide lution in the viscose.

adducts of mono fatty alkyl hydrazines having from at least about 10 to about 50 or more alkylene oxide groups per molecule, preferably from about 14 to about 30 alkylene oxide units per molecule of the mono fatty alkyl hydrazine. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water, in alkali solutions and in acid solutions, the ethylene oxide adducts are preferred. Although the invention is described by specific reference to ethylene oxide adducts, it is to be understood that other alkylene oxide adducts such as propylene oxide adducts are also satisfactory.

The fatty alkyl group or radical is a straight hydrocarbon or fatty alkyl chain containing from 6 to 24 carbon atoms and may be saturated or unsaturated. The radical or radicals may be obtained from the fatty acids derived from animal and vegetable fats and oils such as coconut oil, cottonseed oil, corn oil, soya bean oil, palm oils, peanut oil, tallow and the like and the hydrogenated fats and oils. The mono fatty alkyl hydrazine as utilized for the preparation of the adducts may be pure compounds such as lauryl hydrazine or the mono fatty alkyl hydrazine may consist of a mixture of compounds wherein the fatty alkyl radicals are obtained or derived from a mixture of the fatty acids of a particular fat or oil such as coconut oil. The adducts may be prepared by reacting the amino hydrogens of a mono fatty alkyl hydrazine or a mixture of mono fatty alkyl hydrazines with an alkylene oxide or a polyoxyalkylene glycol. Adducts which are satisfac tory may be denived from capric, lauric, myristic, oleic, stean'c and like acids or from mixtures of fatty acids such as obtained from coconut oil or other fat or oil, for example, from the commercially marketed Lorol acid which is a mixture of the fatty acids of coconut oil.

The production of all skin products requires that certain minimum amounts of the alkylene oxide adduct be in so- Therefore, the alkylene oxide adduct must have suflicient solubility to permit the minimum amount of the adduct to be dissolved in the viscose. The adduct may be conveniently added to the viscose in the form of a solution in alkali or in water.

The amount of the adduct which is incorporated in the viscose must be at least about 0.25% by weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from 0.5% to 2% for low denier filaments and from about 0.25% to about 1% for high denier filaments. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the prefenred range are The adduct is preferably added after thecel-lulose xanthate has been dissolved in the caustic solution and prior to filtration. I a

The viscose may contain from about 6% to about 8% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfidecontent may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of adduct, may have a salt test above about 8 and preferably above about 10 at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinnirig bath be maintained within a well defined range. The presence of the alkylene oxide adducts in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath and contains from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15 to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the Zinc-sulfate. The temperature of the spinning bat-h may vary from about 25 C. to about 80 0., preferably between about 45 C. and about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, 'as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufficiently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufiiciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing the adducts ofmono fatty alkyl hydrazines lies between about and about 8%. The acid concentration may be increased asthe' amount of adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the adduct is increased beyond about 4% while other conditions are maintained constant. .i-Increasing the caustic soda content of the viscose beyond about 8% is uneconomical for commercial production methods. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 41% (based on the weight of cellulose) carbon disulfide, 1% (based on the weight of cellulose) of an ethylene oxide adduct of lauryl hydrazine containing about 19 ethylene oxide units per molecule and having a salttest of about 11.5 when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than-about 7.9%, results in the production of all skin filaments. 1

Lesser 'amounts of sulfuric acid may be employed. Greater amountsofsulfuric acid result in the production of products having skin and core. A lowering of the amount of adduct, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skimfilaments. It has been determined that the maximum concentration of acid which is permissible for the production of all skin products is about 8% Y The presence of the adducts of mono fatty alkyl hydrazines in the viscose retards the coagulation and, therefore, the amountof adduct employed must be reduced at high spinning speeds and for higher denier filaments'or thicker bodies. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts within the lower portion of the range, for example, about 0.25%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of. simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period suflicient to eflect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 120%, preferably between and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. If desired, the filaments may be stretched in air. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a, finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the alkali-soluble alkylene oxide adducts of mono fatty alkyl hydrazines and spun in the spinning baths of limited acid content have a smooth or non-crenula'ted surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments pre pared from viscose containing the alkylene oxide adducts of mono fatty alkyl hydrazines have a high tensile strength as compared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforce ment of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7% cellulose, about 6% caustic soda, and having a total carbon disulfide content of about 41% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. An additional 5% carbon disulfide was then added to the mixer and the mass mixed for about one hour. The desired amount of an ethylene oxide adduct of a mono fatty alkyl hydrazine was added to the solution and mixed for about /2 hour. The viscose was then allowed to ripen for about 30 hours at 18 C.

Example I Approximately 0.5% (based on the weight of the cellulose) of an ethylene oxide adduct of lauryl hydrazine containing about 14 ethylene oxide units per molecule was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 11.2. The viscose was extruded through a spinneret to form a 210 denier, 120 filament yarn at a rate of about 43 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 7.5% sulfuric acid, 7.8% zinc sulfate and 18% sodium sulfate. The yarn was stretched about 75% While passing through a hot water bath at 95 C. The yarn was collected in a spinning box, washed free of acids and salts and dried.

. The individual filaments had a smooth, non-crenulated exterior surface and consisted entirely of skin, no core being detectable at high magnification (e.g. l500 The filaments of a control yarn spun with the same viscose but without the addition of the modified agent and spun under the same conditions, exhibited a very irregular and serrated surface and are composed of about 90% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 A viscose solution of the same composition and salt test but, containing 1% of an ethylene oxide adduct of lauryl hydrazine containing about 14 ethylene oxide units per molecule was spun into the spinning bath of Example 1v to form a 320 denier, 40 filament yarn at a spinning speed of about 25 meters per minute. The filaments were stretched about 57% in the hot water bath. The individual filaments had a smooth, non-crenulated exterior surface and consisted entirely of core. The filaments' of. a control 'yarn exhibited very irregular and ser rated surface and are composed of about 80% skin and the balance core with a sharp line of demarkation between the skin and core.

Example 3 To a viscose as described above, there was added 0.5% of an ethylene oxide adduct of lauryl hydrazine containing about 19 ethylene oxide units per molecule. The viscose had a salt test of 11.6 and was spun into a 205 denier, 120 filament yarn by extrusion into a spinning bath containing 7.9% sulfuric acid, 8% zinc sulfate and 19% sodium sulfate. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 95 C. and stretched about 82%. The

Example 4 The viscose solution of Example 3 was spun at the same salt test and under the same conditions as set forth in Example 3 except that the extrusion rate was 44 meters per minute and the yarn was stretched 74%.

The individual filaments, like those of Example 3, had smooth, non-crenulated surfaces and consisted entirely of skin. They differed from those of Example 3 in having lower tenacity and elongation values.

Example 5 Example 3 was repeated except that the viscose contained 1%, based on the weight of the cellulose, of the ethylene oxide adduct of lauryl hydrazine and the viscose had a salt test of 11.4.

The individual filaments, like those of Example 3, had smooth, non-crenulated surfaces and consisted entirely of skin. The other physical properties were closely the same as those of the filaments of Example 3.

Example 6 As a control for the foregoing examples, a viscose solution, prepared as described above, having a salt test of 11.2 was spun into a 210 denier, 120 filament yarn by extrusion into a bath containing 7.5% sulfuric acid, 7.8% zinc sulfate and 18% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at a temperature of about 95 C. and the filaments were stretched 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments have a very irregular and serrated surface and consist of about skin and the balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows:

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit appreciable improvements in tenacity and elongation and in some instances show a decrease in the values of these properties, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when 7 wet withwater, this Swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

If desired, small amounts of the alkylene oxide adducts may be added to the spinning bath. Since the materials are also water-soluble, some of the adduct will be leached from the filaments andwill be present in the bath.

The alkylene oxide adducts may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above being merely for illustrative purposes. The adduct may be added at any desired stage in the production of the viscose and may be present in the'cellulosic raw material although it maybe necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at thetime of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is'placed in successive baths of 60% and 30% alcohol fora few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS cone. (General Dyestuffs Corp.) for 1 to 2 hours. At'this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and 90% dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

This application is a division of my copending application Serial No. 478,939, filed December 30, 1954, entitled Process of Producing Viscose Rayon.

, While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

l. A viscose spinning solution containing a small amount of a modifier selected from the group consisting of allcylene oxide adducts of mono fatty allrly hydrazines and mixtures thereof, the fatty alkyl radical containing from 6 to 24 carbon atoms, the adducts containing at least alkylene oxide units per mole of mono fatty alkyl hydrazinqthe alkylene oxide being selected from the group consisting of ethylene oxide and propylene oxide, said small amount of the modifier being a quantity sutficient to impart a smooth, non-crenulated surface and a substantially all skin structure to products formed by spinning the viscose at a sodium chloride salt test of at least 8 into an aqueous bath containing from to 22% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric acid in an amount not exceeding. 8%, but the quantity being insufiicient to adversely affect the physical properties of such products.

2. A viscose spinning solution containing from about 0.25 to about 4%, based on the weight of the cellulose in the viscose, of a modifier selected from the group consisting of alkylene oxide adducts of mono fatty alkyl hydrazines and mixtures thereof, the fatty alkyl radical containing from 6 to 24. carbon atoms, the adducts containing at least about 10 alkylene oxide units per molecule of monofatty alkyl hydrazine, the alkylene oxide being selected from the group consisting of ethylene oxide and propylene oxide.

3. A viscose spinning solution as wherein the alkylene oxide adducts. l

defined in claim 2 adducts are ethlylene oxide 4. A viscose spinning solution as defined 'in claim 2 wherein the selected modifier is a mixture of ethylene oxide adducts of mono fatty alkyl hydrazines in which the individual fatty alkyl radicals represent the fatty alkyl radicals derived from the fatty acids of coconutoil.

'5. A viscose spinning solution as defined in claim 2 wherein the selected substance is an ethylene oxide adduct of lauryl hydrazine. V 6.-A viscose spinning solution as defined in claim 2. wherein the selected substance is an ethylene oxide adduct of oleyl hydrazine. p 7. A viscose spinning solution as defined in claim 2 wherein the selected substance is an ethylene oxide adduct of stearyl hydrazine. v

8. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.25 to about 4%, based on the weight of the cellulose, of a modifying agent into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8%, the modifying agent being selected from the group of substances consisting of alkali-soluble alkylene oxide adducts of mono-fatty alkyl hydrazines and mixtures thereof, the fatty alkyl radical having from 6 to 24 carbon atoms, the alkylene oxide being selected from the group consisting of ethylene oxide and"pr0pylene oxide, and the adducts containing at least about 10 alkylene oxide units per molecule of mono-fatty alkyl hydrazine.

9. The step in the method as'defined in claim 8 wherein the modifying agent is an ethylene oxide adduct. 10. The step in the method as defined in claim 8 wherein the modifying agent is a mixture of ethylene oxide adducts in which the fatty alkyl radicals of the individual adducts are obtained from the fatty acids of coconut oil.

11. The step in the method as defined in claim 8' wherein the modifying agent is an'ethylene oxide adduct 'of'lauryl hydrazine.

l 12. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in viscose from about 0.25% to about 4%, based on the weight of the cellulose, of a'modifying agent and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3%,to 15 zinc sulfate and sulfuric acid, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 8%, the modifying agent being selected from the group of substances consisting of alkali-soluble alkylene oxide adducts of mono-fatty alkyl hydrazines and mixtures thereof, the fatty alltyl radical having from 6 to 24 carbon atoms, the alkylene oxide being selected from the group consisting of ethylene oxide and propylene oxide, and the adducts containing at least about 10 alkylene oxide units per molecule of monofatty alkyl hydrazine. Y

13. The method as defined in claim 12 wherein the modifying agent is a mixture of ethylene oxide adducts in which the fatty 'alkyl radicals of the individual adducts are obtained from the fatty acids of coconut oil.

14. The method as defined in claim 12 wherein the modifying agent is an ethylene oxide adduct of lauryl hydrazine. 1 e

15. The method of producing shaped bodiesof'regen erated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in viscose from about 0.25% to about 2%, based on the weight of the cellulose, of a modifying agent, ripening the viscose to a sodium chloride salt point of not lower than about 9 and extruding the viscose into an aqueous spinning bath containing from 16% to 20% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric'acid,- the sulfuric References Cited in the file of this patent UNITED STATES PATENTS 2,335,980 Waltmann Dec. 7, 1943 5 2,792,281 Castellan May 14, 1957 2,852,334 Hollihan et a1 Sept. 16, 1958 OTHER REFERENCES Hackhs Chemical Dictionary, third edition (1944), 15 pages 33, 332, 333 and 417.

Claims (1)

1. A VISCOSE SPINNING SOLUTION CONTAINING A SMALL AMOUNT OF A MODIFIER SELECTED FROM THE GROUP CONSISTING OF ALKYLENE OXIDE ADDUCTS OF MONO FATTY ALKYL HYDRAZINES AND MIXTURES THEREOF, THE FATTY ALKYL RADICAL CONTAINING FROM 6 TO 24 CARBON ATOMS, THE ADDUCTS CONTAINING AT LEAST 10 ALKYLENE OXIDE UNITS PER MOLE OF MONO FATTY ALKYL HYDRAZINE, THE ALKYLENE OXIDE BEING SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDE AND PROPYLENE OXIDE, SAID SMALL AMOUNT OF THE MODIFIER BEING A QUANTITY SUFFICIENT TO IMPART A SMOOTH, NON-CRENULATED SURFACE AND A SUBSTANTIALLY ALL SKIN STRUCTURE TO PRODUCTS FORMED BY SPINNING THE VISCOSE AT A SODIUM CHLORIDE SALT TEST OF AT LEAST 8 INTO AN AQUEOUS BATH CONTAINING FROM 15% TO 22% SODIUM SULFATE, FROM 4% TO 9% ZINC SULFATE AND SULFURIC ACID IN AN AMOUNT NOT EXCEEDING 8%, BUT THE QUANTITY BEING INSUFFICIENT TO ADVERSELY AFFECT THE PHYSICAL PROPERTIES OF SUCH PRODUCTS.