US2879170A - Chemical composition and process - Google Patents

Description

United States Patent No Drawing. Application October 2, 1957 Serial No. 687,624

9 Claims. (Cl. 106-165) The present invention relates to a novel and useful composition and process for the production of shaped structures of regenerated cellulose. More particularly, it relates to a composition and process for the formation of shaped structures of regenerated cellulose such as filaments, ribbons, films and the like having improved properties. I

It is known that the properties, particularly the strength, of viscose yarns and cords are improved through reduction of the primary swelling of the gel fibers. The great importance of gel swelling in viscose spinning operations has attained full recognition in recent years and it has become common practice to add certain compounds to the viscose, to the coagulating and regenerating bath or both to obtain the maximum reduction in the gel swelling of the freshly regenerated filaments. A number of these coagulations modifiers are described in U. S. Patents 2,535,044, 2,535,045, 2,536,014, 2,696,423, British Patents 762,772, 741,728 and Italian Patent $61,552.- It is also well known that the application of increased stretch during the spinning operation leads to yarns having higher strength. Increased stretch may be attained by increasing the number of xanthate groups present during the spinning operation so that the yarn is more-plastic.

This may be accomplished by the use of spinning baths which coagulate the filaments but do not regenerate the cellulose. When such baths are used however, the gel swelling of the filaments is high and cannot be reduced even by the use of the above-mentioned coagulation modifiers. It is. therefore highly desirable to develop methods by which the xanthate content of the yarn during the spinning operation may be increased sufficiently to permit substantial increases in stretch while at the ,same time maintaining a desirably low level of gel swelling. I

It is an object of this invention therefore to provide a composition and process for producing yarns and cords having improved properties. Another object is to provide a process in which the xanthate content of the filaments during the spinning operation is substantially increased while thegel swelling is maintained at a desirably low level. A further object is to provideaprocess in which the spinning stretch may be increased while maintaining the gel swelling at a low-level. Other objects will become apparent hereinafter from the descriptions, the examples and the claims.

These objects are accomplished by the present invention which provides an improvement in the process of producing a shaped structure of regenerated cellulose by extruding viscose into an acid-zinc sulfate bath in the presence of a coagulation modifier, the improvement comprising adding at least about 0.02% soluble nickel (by weight) to the viscose prior to extrusion. By the term acid-zinc sulfate bath is meant a conventional 2,879,170 5 Pate'ntd Mar. 24, 1959 ice may be used in the practice of this invention are those which are set forth in the hereinbefore mentioned patcuts. The term solublenickel is usedto designate that nickel 'is added tothe viscose in a soluble form (i. e.

it is soluble at least to the required extent,0.02%) or is converted to a soluble form upon its addition to the viscose. In either procedure the concentration of elemental nickel in the viscose must be at least about 0.02% by weight. i e

, The present invention also provides a composition of matter comprising viscose containing at least about 0.02%

of soluble nickel; which composition is useful in carrying out the above described process. I e p In forming thecomposition of the present invention, the nickel is added to the viscose in the form of a water soluble compound such as the acetate, chloride, nitrate, sulfate or as a complex compound such as'the ethylenediamine tetraacetate-nickel complex many of the various nickel ammonium compounds. Preferably the nickel is added as the nickel-ethylenediamine tetraacetate complex since in this form the nickel may be easily added without fear of precipitation as nickel sulfide due to the presence of sulfide in the viscose. Another preferred method of addition is to add the nickel as the nickel trithiocarbonate since this also eliminates the possibility of nickel sulfideprecipitation. When compounds such as the acetate, chloride, nitrate, sulfate, etc.'are employed, the compound must be added to the viscose very slowly as a dilute, aqueous solution 'while stirring the viscose'Vig'drously to prevent precipitation of nickel sulfide. Although the nickel 'is' added in the form of a nickel compound, for convenience the concentrations of nickel are expressed in terms of elemental nickel.

In the followingtexamples the gel swelling of the yarn is'determined on small samples (5-10 grams) of the freshly spun yarn which is collected on a bobbin or feed wheel prior to its entry into the hot secondary bath. The sample is centrifuged at 3600 r.p.m.- for five minutes, weighed, washed free of acid and salt, dried in an oven at 105. C.1l0 C. and weighed again. The ratio of the first weight (i. e. the weight-of .the centrifuged sample) to the final weight provides the grams of gel yarn per grams of dry cellulose and is referred to as the gel swelling.

' The xanthate content of the filaments is'dete'rmined as follows:

acetone and then given a final wash with the buffer solution. The washed yarn samples are then: dissolved. in a ml.. volume of 8% sodium hydroxide solution; I The weight ofcellulose isdetermined on a measured portion of the solution by the well-known dichromate oi idation procedure. The xanthate content of the sample is then determined by measuring the absorbance of'the's'olution at 302 i'nmu usingafBeckman model DU- spectrophotometer. The spectrophotometer is calibrated using eth'yl xanthat'esince the absorbance'of the-xanthate group at fate. The term coagulation modifier is used to desig- --nate-a chemical compound which reduces the primary this wave lengthis independent of, the radicai "to which it L. as;

3 EXAMPLE I Viscose containing 5% recoverable cellulose and 6.5% total alkali, calculated as sodium hydroxide, is prepared in the conventional manner using 60% carbon disulfide and a xanthation period of 4% hours at 26 C. While mixing the viscose, suflicient polyethylene glycol, having an average molecular weight of 600, is added to give a concentration in the viscose of 0.2% by weight. The viscose is filtered, deaerated and ripened to a salt index of .26 and a-viscosity of 42 poises. The viscose is then extruded into a coagulating and regenerating bath containing about 10.0% sulfuric acid, 9.5% zinc sulfate and 17.5% sodium sulfate, the bath being maintained at a temperature of 60 C. The yarn is passed for a distance of 20 inches through the primary coagulating and regenerating bath and then for a further distance of inches through a hot secondary bath consisting of 2% sulfuric acid in water and maintained at a temperature of 95-97 C. The. yarn is stretched 110% in the secondary bath by means of a power driven roller. After passing through the secondary bath the yarn is wound on a bobbin at a speed of 28 y.p.rn. The yarn is subsequently purified,

slashed and dried in the conventional manner. Part of the yarn, which has a denier of 1100, is twisted into 2-ply cord having a denier of 2450 for testing. The gel swelling and xanthate content of the yarn are determined as described above on samples of yarn taken just before the yarn passes into the hot secondary bath.

Properties of the yarn and cord are given in Table I, test A below. Test B of Table I shows the result obtained when test A is repeated except that 0.04% of nickel, in the form of the nickel-ethylenediamine tetraacetate complex, is added to the viscose during mixing. The nickel complex is formed by dissolving 286 g. Tetrasodium Tetraene (tetrasodium salt of ethylene diamine tetraacetic acid and 325 g. NiSO -6H O in water and diluting to a volume of 2 liters. Test C shows the efiect of omitting the coagulation modifier.

Table 1 Te t A B O Coagulation Modifier, percent 0.2 0.2 None Nickel, percent None 0.0 0. 03 .XanthateSulfur in yarn, perce 8. 0 5. 0 Spinning Stretch, percent- 110 152 121 "Stretch at break, percent- 140 180 Gel Swelling 2. l 2. t 3. 2 Yarn:

Tenacity, g.p.d, dry 5.00 5. 32 4.88

Tenacity, g.p.d. wet. 3. 84 4. 09 2. 60 C ('llenacity, g.p.d., loop- 8. 68 3. 8? 2. 98

Tenacity, g.p.d., conditioned 4. 39 4. 62 3. 34 Tenacity, g.p.d., oven dry 4. 78 5. 06 3. 98

Whenthe polyethylene glycol is replaced by a quaternary ammonium compound such as benzyltrirnethylam- .monium hydroxide, substantially the same results are obtained.

EXAMPLE H 1 given in Table H. Test C shows the result obtained when no nickel is'added to this .viscose. Test D shows the improved results obtained whennickel is added to the visco e intli manner'described in Example I,

The triethanol amine is replaced with hexamethylene diamine. The resulting yarns have substantially the same properties shown above.

EXAMPLE III Modified viscose prepared as described in Example I is extruded into a coagulating and regenerating bath containing 9.0% sulfuric acid, 9.5% zinc sulfate and 17.5% sodium sulfate, the bath temperature being 60 C. In test B no nickel is added to the viscose. In tests F and G nickel is added to the viscose in the form of the nickelethylenediamine tetraacetate complex, in concentrations of 0.02 and 0.04%, respectively. The xanthate sulfur content of the yarn and the gel swelling is determined as described in Example I. The results shown in Table III illustrate the effectiveness of low concentrations of nickel in increasing the xanthate content of the yarn while the gel swelling is held at a low level.

When the polyethylene glycol of this example is replaced with an N-substituted dithiocarbamic acid such as sodium N-methylcyclohexyl dithiocarbamate, improved yarn properties are also obtained.

EXAMPLE IV Modified viscose prepared as in Example I is extruded on a small scale into a coagulating and regenerating bath containing 9.85% sulfuric acid, 9.40% zinc sulfate and 17.35% sodium sulfate, the temperature of the bath being 60 C. The xanthate sulfur content and gel swelling of the filaments are determined after the filaments had traveled through the bath for a distance of 20 inches. The results shown in Table IV below illustrate the effectiveness of various nickel compounds in achieving the results of the present invention. The compounds are added to the viscose during the mixing operation except for the nickel sulfate which is added to the dilute sodium hydroxide solution, used to dissolve the xanthate, in the mixing tank prior to addition of the xanthate. When added in this manner the nickel sulfate reacts with the sodium hydroxide to give a finely dispersed precipitate of the hydroxide. On addition of the xanthate to the sodium hydroxide solution, the nickel hydroxide precipitate dissolves as evidenced by the absence of a precipitate in the viscose.

Table IV Nickelin Xanthate -Gel Viscose, Nickel Compound Added S ur, Swellmg Percent Percent s2 is 1. die inecom ex .7 22.0 2.20 Ammonia Complex, Nickel Trithio- 14. 6 2. 10

' carbonate, Nickel sulfate.

to precipitate the nickel.

preferred that it not exceed about 0.10%.

The polyethylene glycol of this example is replaced with phenoxyethanol. Improved yarn properties similar to those above are obtained.

As mentioned previously the nickel may be added to the viscose in the form of any water-soluble compound. It is most conveniently added as a complex with compounds such as the sodium salt of ethylenediamine tetraacetic acid. This compound is sold commercially under the trade name Versene and under the trade name Sequestrene. Other compounds which may be'used to form nickel complexes are ethylenediamine, various ammonium compounds and sodium trithiocarbonate. Nickel trithiocarbonate may be readily formed by adding the nickel-ethylenediamine tetraacetate complex to a sodium trithiocarbonate solution; the sodium trithiocarbonate solution being prepared byreacting carbon disulfide With an aqueous sodium hydroxide solution.

.It hasbeen observed, that the nickelethylenediamine tetraacetate complex converts to the nickel trithiocarbonate complex when two solutions of these are mixed. In view of the fact that viscose contains appreciable quantities of sodium trithiocarbonate, it is believed that the nickel added to the viscose is substantially all converted to a nickel trithiocarbonate complex and that this,

accounts for the solubility of the nickel in spite ,of the presence of sulfide which would ordinarily be expected I If, however, the nickel is addedrapidly to the viscose in the form of a compound such as nickel sulfate or nickel chloride, then a substantial amount of the nickel will beprecipitated as nickel sulfide and once-precipitated in this form the nickel is not easilyconverted back to the trithiocarbonate complex. Therefore, if the' nickel is added in the form react with the trithiocarbonate in the xanthate crumb and thus prevent the precipitation of the nickel sulfide.

For efiective results the nickel should be present in the viscose in a concentration of at least about 0.02% by weight of the viscose. High concentrations of nickel should be avoided since this leads to gel formation in the viscose. dependent on the composition of the viscose but it is In general, the range for most effective results is about. 0.04 to about 0.10% nickel. n

The coagulation modifiers which serve to reduce the gel swelling of the filaments, are generally present in course, be used but it seldom gives any further improvement in the product.

A group of preferred coagulation modifiers which are suitable for use in the process of this invention are as follows:

A. Quaternary ammonium compounds of the formula Rf R1-'-II\TR4X ti l: 7 wherein the Rs are organic groups which contain no more than four aliphatic carbon atoms, at least three of the said groups containing only aliphaticcarbon atoms and the fourth of the said'groups containing no The maximum concentration employed is .ethylammonium hydroxide, tetramethylammonium chloride, phenyltrimethylammonium hydroxide, tetraethanolammonium hydroxide, tetraethylammonium bromide, tetramethylammonium iodide, tetrapropylammonium hydroxide, tetrabutylamrnonium chloride, tributylpropylammonium hydroxide tri(beta-hydroxyethyl)-methylammonium hydroxide, tributyl (betahydroxyethyl)-ammonium iodide, etc. The preferred agents of this class are those in which 'all four organic groups attached to the nitrogen atom are hydrocarbon groups or hydroxylsubstituted hydrocarbon groups and in which the radical X is hydroxyl or halogen of. atomic weight above 19, i.e., chlorine, bromine or iodine. The .most useful modifiers of this group-are the quaternary ammonium hydroxides having a total of not. more than ten carbon atoms in the molecule and in which all organic groups are hydrocarbon or hydroxyl-substituted hydrocarbon.

B. Aliphatic monoamines having at least four carbon atoms but containing no radical of more than six carbon atoms. The use of these compounds is disclosed in U.S. Patent 2,535,044. Suitable compounds in this group which may be mentioned are triethanolamine, triethylamine, diethanolamine, butylmonoethanolamine, diethylaminoethanol, n-amylamine, diethylamine, dipropylamine, n-butylamine, ethyldiethanolamine, dipropanolamine, propylpropanolamine, hexanolamine, amyldiethanolamine, butylmethylethanolamine, propylethanolof a compound other than a fairly stable complex, it 1 amine, cyclohexylethanolamine, N methylcyclohexylamine, hexamethyleneimine, piperidine, hexyldiethanolamine, etc. The preferred modifiers of this group are those in which the amino nitrogen is attached to hydrocarbon groups, preferably alkyl groups, and/or to hydroxyalkyl groups.

C. Aliphatic diamines containing two amino nitrogen atoms separated only by carbon atoms and containing a total of at least three carbon atoms, said diamines having the amino groups attached to aliphatic carbon atoms, any monovalent substituent on the amino nitrogens being alkyl groups of 1 to 6 carbon atoms. The use of these compounds is disclosed in British Patent 762,772. Among the aliphatic diaminesmay be mentioned the following: hexamethylenediarnine, tetramethylenediamine, N methyltrimethylenediamine, N,N dimethylethylenediarnine, N,N diisobutylhexamethylenediamine, N,N dimethyltrimethylenediamine, 4,4,-dimethylhexamethylenediamine, N,N diethyl 1,4-cyclohexanediamine, 3 ethoxyethoxyhexamethylenediamine, pentamethylenediamine, octamethylenediamine, N-cyclohexyltetramethylenediamine, N,N-diallylhexamethylene diamine, N-methylnonamethylenediamine, N,- hex-yltrimethylenediarnine, N,N-dimethylpiperazine, N-butylhexamethylenediamine, etc. The preferred agents of this class are the wholly aliphatic, including cycloaliphatic,

diamines which contain only carbon and hydrogen besides the two amino nitrogens and which have a total number of carbon atoms between 4 and 14, inclusive, in addition to fulfilling the other requirements stated above. Still more preferred are the polymethylenediamines of 4 to 14 total carbon atoms having from 4'to 8 methylene groups between the amino groups, and their N-alkyl substituted derivatives where the N-alkyl groups have from 1 to 4 carbon atoms inclusive.

D. The salts of N-substituted ,dithiocarbamic acids. The use of these compounds is disclosed in U.S.; Patent 2,696,423. Among the salts of N-substituted dithiocarbamic acids may be mentioned, sodium amyl dithiocarbamate, sodium butyl monoethanol' dithiocarbamate, sodium hexamethylene bis(dithiocarbamate), potassium pentamethylene dithiocarbamate, sodium methyl dithiocarbamate, sodium benzyl dithiocarbamate, sodium sheets.

ethylene bis (dithiocarbamate), sodium 1,3-cyclohcxane bis (dithiocarbamate), sodium dibutyldithiocarbamate, sodium dimethyledithiocarbamate, sodium dioctyl dithiocarbamate, sodium lauryl dithiocarbamate, sodium cyclohexyldithiocarbamate, lithium cyclohexyl dithiocarbamate, sodium N-methylcyclohexyldithiocarbamate, the sodium dithiocarbamates of a mixture of 10% hexadecylamine, 10% octadecylamine, 35% octadecenylamine and 45% octadecadienylamine, sodium hexamethylene bis (methyl dithiocarbamate), sodium ethylene bis(methyl dithiocarbamate), sodium 1,4-cyclohexane bis (ethyl dithiocarbamate), sodium xylylene bis (dithiocarbamate), etc. The preferred modifiers of this class are the alkali metal salts of monoor di-N-substituted dithiocarbamic acids containing no more than 10 carbon atoms in any radical and in which the nitrogen is attached to aliphatic carbon.

1E. The ethers of the formula RO-(CH CH O) where R is alkyl or aryl n is an integer from 1 to 4 inclusive; and R is hydrogen, alkyl or aryl. The use of these compounds as coagulation modifiers is disclosed in British Patent 741,728. Among the ethers may be mentioned phenoxyethanol, ethoxyethanol, butoxyethanol, methoxyethoxyethanol, butoxyethanol, phenoxyethoxyethanol, ethoxyethoxyethoxyethanol, butoxyethoxyethoxyethanol, phenoxyethoxyethoxyethanol, butoxyethoxyethoxyethoxyethanol, phenoxyethoxyethoxyethoxyethanol, 1 ethenyloxy-Z-methoxyethylene, ethylene glycol diethyl ether, triethylene glycol diethyl ether, tetramethylene glycol diethyl ether, triethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc. With this class of coagulation modifiers, it has been found that those compounds which, in addition to being soluble in viscose, are difficultly soluble in the coagulating bath, i.e., to the extent of less than 05%, give the best results.

F. The polyethylene glycols of formula HO(CH CH O) H where n is an integer greater than 3. The use of these compounds is disclosed in Italian Patent 561,552. The polyethylene glycols of formula HO(CH CH O),,H (ethyleneoxide polymers) include all such compounds where n is at least equal to 4, i.e., polymers which have a molecular weight of at least 200, and which in addition have the required solubility in viscose. Such compounds are available commercially in various molecular weight ranges, such as 600, 1500 or 2500. For use as coagulation modifiers, the polyethylene glycols having molecular weights between about 300 and about 1000 are preferred.

Other coagulation modifiers, as are known in the art, may also be employed in place of the listed compounds. Various suitable ones are described in U.S. Patents 2,777,775; 2,792,278; 2,792,279; 2,792,280 and 2,792,- 281; British Patents 723,435; 730,451; 748,147 and 765,905, and French Patents 1,102,898 and 1,111,580.

In the process of this invention the viscose solution is prepared in the conventional manner. Alkali cellulose is first prepared by soaking sheets of wood pulp or cotton linters pulp in sodium hydroxide solution. The excess alkali is then drained and pressed from the saturated The resulting alkali cellulose is shredded and then aged to provide the desired viscosity in the prepared viscose. The shredded alkali cellulose is dropped into a rotatable drum called a barratte where xanthation occurs.

The alkali cellulose may be completely xanthated in the barratte or partially xanthated in the barratte and partially in the mixer. Splitting xanthation so that not over 90% is completed in the barratte is described in U.S. Patent 2,801,998, issued August 6, 1957, to A. Robertson.

In either conventional or split xanthation, at least 30% carbon disulfide, based on the cellulose content of the alkali cellulose, should be used.

.Thexauthated or partially xanthated alkali cellulose is now added to a tank where it is mixed with a measured quantity of dilute aqueous sodium hydroxide solution. The amount of sodium hydroxide solution is sufficient to provide a final viscose solution containing 4% to 9% cellulose or more and 4% to 9% or more total alkali calculated as sodium hydroxide. The standard viscoses of the industry, i.e., those having between 5% and 8% cellulose and between 5% and 7% alkali, are preferably used.

The viscose solution is filtered, deaerated and may be permitted to ripen at a temperature of about 18 C. to the desired salt index. While the process of this invention yields improved properties with ripe viscoses it is preferable to restrict ripening and spin the viscose in an 'unripened or a partially ripened state, i.e., salt indexes of 10 and higher.

The viscose may be extruded hot or cold. Heating may be accomplished by passing the viscose solution through a heat exchanger using hot oil, hot water, steam, or heated coagulating bath as the source of heat; or an electric heating unit may be inserted in the pipe.

The spinning bath is preferably maintained at a temperature between 40 C. and C. and contains 4% to 10% sulfuric acid, 5% to 25% sodium sulfate and 3% to 15% zinc sulfate. If desired, other divalent metal salts known to reinforce or supplement the action of zinc sulfate may also be used. These include ferrous sulfate, manganese sulfate, nickel sulfate or chromic sulfate.

The filaments may be extruded through a spinning tube to confine the filaments in the critical stage of formation as described in U.S. Patent 2,440,057 to F. R. Millhiser. After extrusion, the filaments may travel through about 25 to 150 inches in the primary bath where they may be confined to a small area by means'of a multiple roller set-up. The rollers are designed to apply tension to the traveling filaments in gradual increments and thereby orieat them while they are still plastic. A preferred method is to apply a part of the stretch beyond the primary bath by passing the filaments through a secondary bath or shower located between two power driven rollers. The secondary bath may consist simply of water or of dilute (1% to 4%) sulfuric acid, or it may be diluted spinning bath at a temperature between 50 C. and C. Total stretches of 80% or more are preferred for producing high tenacity yarns and as low as 30% may be acceptable for textile type yarns. From the last roller, the yarn may be wound on a bobbin or fed into a rotating bucket to form a cake and then Washed and slashed. The slashing operation is well known and consists of stretching the yarn and applying a lubricating solution.

The yarns and cords of this invention have outstanding properties and may be used for any purpose where regenerated cellulose fibers are finding application, such as for reinforcement of rubber articles, automobile tires and in various textile fields.

Many other equivalent modifications will be apparent to those skilled in the art from a reading of the foregoing without a departure from the inventive concept.

What is claimed is:

1. In the process of producing a shaped structure of regenerated cellulose by extruding viscose into an acidzinc sulfate bath in the presence of a coagulation modifier, the improvement which comprises adding at least about 0.02% by Weight, based on viscose, of soluble nickel to the viscose prior to extrusion.

2. The process of claim 1 wherein the coagulation modifier is added to the viscose in amounts of from about 0.1 to about 10 millimoles per 100 grams of viscose.

3. The process of claim 1 wherein the soluble nickel is present in amounts of from about 0.04 to about 0.10% by weight based on the viscose.

4. The process of claim 2 wherein the soluble nickel is present in amounts of from about 0.04 to about 0.10% by weight based on the viscose.

5. The process of claim 4 wherein the coagulation modifier is a polyethylene glycol having an average molecabout 0.04 to about 0.10% by weight, based on the viscose ular weight of about 600. of soluble nickel.

6. The process of claim 4 wherein the coagulation mo7difi lelrl' is triethanfolzimine. h th d If 5 References Cited in the file of this patent e process 0 c aim 4 w erein e aci -zinc su ate bath is at a temperature of from about 40 C. to about UNITED STATES PATENTS 80 C. 1,885,878 Whitehead et a1. Nov. 1, 1932 8. As a composition of matter, viscose containing at 2,206,278 Dreyfus July 2, 1940 least about 0.02% by weight, based on the viscose, of 2, 2,969 Cramer Dec. 24, 1946 soluble nickel. 0 2,535,044 Cox Dec. 26, 1950 9. As a composition of matter, viscose containing from 2,696,423 Dietrich Dec. 7, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,879,170 March 24, 1959 Ivan Keith Miller It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 31, for "coagulations" read coagulation column 3 line 37, after "acid" insert a closing parenthesis; same column 3, in the table, in the column headed "B", second item, for "01,0" read F 0606 ea; same table, first column thereof,r last line, for "dry read dry line '73, for "this" read we the column 7, line 24, for "butoxye'thanol" read butoxyethoxye'thanol line 56, for British Patent N06 "730,451" read Signed and sealed this 21st day of July 1959a (SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. IN THE PROCESS OF PRODUCING A SHAPED STRUCTURE OF REGENERATRED CELLULOSE BY EXTRUDING VISCOSE INTO AN ACIDZINC SULFATE BATH IN THE PRESENCE OF A COAGULATION MODIFIER, THE IMPROVEMENT WHICH COMPRISES ADDING AT LEAST ABOUT 0.02% BY WEIGHT, BASED ON VISCOSE, OF SOLUBLE NICKEL TO THE VISCOSE PRIOR TO EXTRUSION.