US2810658A - Process for spinning modified viscose solution - Google Patents

Description

PROCESS FOR SPINNING MODIFIED VISCOSE SOLUTION Eugene Cameron Pontius, Chester, Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 16, 1954, Serial No. 450,255

3 Claims. (Cl. 106--165) This invention relates to the production of artificial filaments, yarns and cords of regenerated cellulose by the viscose process. More particularly, the invention is concerned with improvements in the process of spinning monoamine-modified viscose in the production of rayon.

It has recently been discovered that marked improvements in rayon filaments are obtained by adding monoamine modifiers to the viscose spinning solution or to the spinning bath. The modified filaments obtained by spinning modified viscose solution under suitable conditions, as disclosed in U. S. Patent No. 2,535,044, issued December 26, 1950, to Norman Louis Cox or spinning unmodified viscose into modified baths as disclosed in U. 8. Patent No. 2,535,045; are readily distinguished from unmodified rayon filaments by their smooth surfaces, i. e., the surfaces display no appreciable crenulation whereas the ordinary filaments are highly crenulated. When dyed cross-sections are examined under a microscope, the modified filaments are characterized by having considerably more skin than core, Whereas normal rayon is mostly core with only a very thin skin. Yarn composed of these modified filaments is denser than that from otherwise comparable unmodified filaments, dyes more rapidly and, even more important, has markedly improved tenacity, fatigue resistance and abrasion resistance. Representative yarn and cord properties for filaments spun from unmodified and modified viscose under otherwise comparable conditions are as follows:

To is dry tenacity in grams per denier,

Tw is wet tenacity in grams per denier,

T1. is loop tenacity in grams per denier,

En is percent dry elongation,

To is conditioned tenacity in grams per denier Tom is oven-dry tenacity in grams per denier and D. B. fatigue is the number of minutes required to break the cord with the dynamically balanced fatigue tester.

These tests are conventional with the possible exception of the D. B. fatigue test. In this a cord is conditioned for 48 hours at 24 C. and 54% relative humidity and clamped in jaws set 16.75 inches apart. A load of 1 gram per denier is applied and the cord is brought to 100 C. while in place in the machine for about one-half hour. The

jaws are then oscillated to stretch the cord 3,000 times per minute using a stroke of 0.24 inch.

The amine-modified viscose spinning solutions of the prior art, as described in U. S. Patent No. 2,535,044, have been prepared by adding the amine to completely xanthated alkali cellulose. When added in this way, at least 1 millimole of amine per 100 grams of viscose is required for the modifier to be efiective, and much larger amounts up to 10 millimoles per 100 grams of viscose are usually required. The expense involved in using such large amounts of modifier increases the cost of this rayon to an appreciable extent, and this is obviously undesirable in a commercial process.

smaller amounts of monoamine modifier than have previously been found necessary will be effective for producing rayon having the improved properties described above. Another object is to improve the process of spinning monoamine-modified viscose spinning solution to provide rayon yarns and cords which exhibit a still further marked improvement in properties. Other objects of this invention will become apparent from the following description and claims:

These objects are accomplished by splitting the Xanthation of alkali cellulose, so that not more than of the desired final Xanthation is accomplished by the customary dry phase Xanthation with carbon disulfide, and then incorporating the monoamine modifier during a final stage of Xanthation in which the partial xanthate is mixed with dilute aqueous caustic solution to a cellulose content of 4% to 15% and treated with carbon disulfide to complete the Xanthation. When the viscose solution is prepared in this way a surprising reduction in the amount of mono amine can be made. The amount added per grams of the final viscose solution can be as little as about 0.02 millimole, or less, and not more than about 1 millimole for any of the monoa'mines encompassed by this invention. For best results from 0.1 to 0.85 millimole per 100 grams of viscose is preferred. A further unexpected result of this process is that even better properties are obtained in the spun rayon.

The alkali cellulose used is prepared in the conventional manner, which involves soaking sheets of wood pulp or cotton linter cellulose in caustic alkali solution, draining the caustic solution from the saturated sheets, pressing excess caustic from'the sheets, shredding the resulting alkali cellulose and aging the alkali cellulose to provide the desired viscosity in the viscose ultimately prepared.

The alkali cellulose is placed in a rotating drum called a baratte. Carbon disulfide is added and the baratte is rotated to provide mixing. Xanthation of the alkali cellulose occurs and is continued until an absolute xanthate sulfur substitution value of at least 13% is obtained, based on the cellulose content of the material. However, only a partial xanthate sulfur substitution is to be achieved in this step, as the Xanthation must be completed under different conditions in the presence of the modifier. Based on the absolute xanthate sulfur substitution value obtained in the final Xanthation, the Xanthation is split so that not over 90% of the xanthate sulfur substitution occurs in this first step, e. g., if a final absolute Value of 27.0% is desired, the absolute xanthate sulfur substitution value at the conclusion of this first step must not exceed 24.3%. In order to avoid confusion, the propora measured quantity of dilute aqueous caustic soda solu- Patented Oct. 22, 1957,

tion sufiicient to give a cellulose content of 4% to 15% and a cellulose: caustic ratio approximating that of the final viscose solution. Preferably the partial xanthate is added to a conventional viscose mixer filled with the caustic solution in proportions giving a cellulose content of 4% to 10% and a caustic content of 4% to 8% in the final mixture, mixed for about 5 to 30 minutes to dissolve the partial xanthate, and suflicient carbon disulfide is added to complete the xanthation. Other methods of accomplishing this part of the xanthation are disclosed in copending U. S. application Serial No. 351,592 of Andrew Robertson, which is assigned to the assignee of the present application.

The monoamine modifier should be incorporated into the viscose during the final stage of xanthation. For this purpose the addition of the modifier is preferably prior to or within twenty minutes after the start of the final xanthation reaction. The modifier may be added with the caustic solution or with carbon disulfide for the final xanthation step, or may be added separately to the mixture. Suitable modifiers are organic primary or secondary monoamines, i. e., having at least one hydrogen atom attached to the amino nitrogen, said amine having at least two and preferably at least four carbon atoms, but containing no more than eight carbon atoms in any one radical, and should be soluble to the extent of at least 0.1% in 6% caustic soda solution. Illustrative of these modifiers are cyclohexylamine, N-methylcyclohexylamine, N-ethylcyclohexylamine, diethylamine, morpholine and ortho-methyl-N-methylcyclohexylarnine.

The resulting viscose solution is filtered, deaerated and may be permitted to ripen at a temperature of about 18 C. The viscose is then pumped to the spinning machine. The yarn fatigue resistance may be improved by heating the viscose, as by means of a small oil-bath heat exchanger placed between the spinning pump and the spinneret. Heating may be accomplished with any suitable heating medium, such as steam, hot water, oil, or coagulating bath; or an electric heating unit may be inserted in the pipe.

The viscose spinning solution, which may be heated before spinning, preferably to 4080 C., is extruded through a spinneret into a coagulating and regenerating bath maintained at a temperature from 40 C. to 80 C. and containing 4 to 12% sulfuric acid, 13 to 25% sodium sulfate and 2 to 15% zinc sulfate. The zinc sulfate is an essential component of the spinning bath. 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. A spinning tube may be used as described in Millhiser U. S. Patent No. 2,440,057 to confine the filaments in their critical stage of formation so that no substantial tension is imposed upon them. When spinning the monoamine-modified viscose of this invention, the concentration in the spinning bath of modifier or reaction products with the modifier will inevitably build up. Since it is ditficult to determine the form of the modifier in the bath, this concentration is simply expressed in terms of parts per million of nitrogen. In order to obtain the results of my invention, it is important to maintain this level of modifier in the bath below about 200 parts per million of nitrogen by extracting any excess during recirculation of the spinning bath. The bath may contain no nitrogen but in commercial practice it is more likely tocontain between 20 and 200 parts per million. It has been found that the larger the concentration of nitrogen 4 in the bath, the smaller the concentration of modifier required in the viscose.

After extrusion, the filaments are given a travel of 100- 250 inches in the primary bath by means of a multiple roller set-up which gradually applies tension to the traveling filaments and thereby orients them while they are still plastic. The preferred method is to apply a part of the stretch beyond the primary bath in a secondary bath or between feed wheels. The secondary bath may consist simply of water or of dilute (14%) sulfuric acid, or it may be diluted coagulating bath. The temperature of the secondary bath is preferably between 50 C. and 100 C. Total stretches of -105% are preferred for producing high tenacity yarns and 30105% for textile type yarns. From the last feed wheel, the yarn is fed into a rotating bucket to form a cake. The yarn is then washed and slashed. The slashing operation is well-known and consists of stretching the yarn and applying a lubricating solution. The process described is the so-called bucket process. However, the bobbin process or any of the socalled continuous processes may be used with similar results.

The invention will be more clearly understood by referring to the examples below of preferred embodiments of the invention, and the discussion which follows. In the tables of these examples the meaning of the symbols is as previously defined.

Example I Alkali cellulose, prepared from sheets of wood pulp in the conventional manner, was placed in a baratte. Thirty-two percent carbon disulfide (based on the weight of air-dried pulp) was added in the baratte to achieve a xanthate substitution (percent xanthate sulfur based on the cellulose present) of 21.7. The partially xanthated alkali cellulose was then fed into a mixer which contained dilute caustic solution and also contained cyclohexylamine. Twenty-five minutes later, 7% carbon disulfide (based on the Weight of air-dried pulp) was added to produce a total xanthate substitution of 27.1. Thus 80% of the total xanthate substitution was accomplished during the first xanthation step and the cyclohexylamine modifier was added prior to the second xanthation step. The proportions were controlled to give a viscose solution containing 6.25% by weight of cellulose, 5.75% sodium hydroxide and 0.049% cyclohexylamine (0.49 millirnoles of cyclohexylamine per grams of viscose).

The viscose solution was filtered, deaerated and permitted to ripen to a salt index of 17.5 and to attain a viscosity of 29.5 stokes. Prior to spinning, the solution was passed through a coil-type heater immersed in a tank of hot water. The solution was heated to a temperature of about 44 C. and then extruded into a bath maintained at 60.5 C. containing 9.3% sulfuric-acid, 17.5% sodium sulfate, and 9.5% zinc sulfate. The nitrogen content of the bath was maintained at 40-50 p. p. m. by removing excess during recirculation of the bath.

The filaments were first led through a trumpet-like tube in the bath and then, by means of tension rollers in the bath, they were stretched 70-80%. After leaving the bath the filaments passed over two feed wheels in succession having a differential in speed to stretch the filaments an additional 20%. During this latter stretching, the filaments were treated with diluted bath solution. The filaments were then led into a revolving bucket to form cakes. The cakes were purified, slashed and processed into tire cord in the conventional manner.

The following properties were obtained:

Yarn Properties Cord Properties Denier TD Tw T1. En Ew EL Denier To E15 1b.. Ton D. B.

Fatigue The example was re-run except that the viscose spinning solution was not passed through a heater prior to spinning. Similar results were obtained as indicated by a product displaying in cross-section greater than 85% skin measured radially.

Example II A viscose spinning solution containing 6.25% by weight cellulose, 5.75% by weight sodium hydroxide and 0.07% by weight cyclohexylamine (0.7 millimole per 100 grams of viscose) was prepared from wood pulp sheets by a procedure identical to that described in Example I except for the amount of cyclohexylamine.

The solution had a salt index of 17.3 and a viscosity of 29.5 stokes. It was heated to 44 C. and spun into coagulating and regenerating bath at 60.5 C. The composition of the bath and the ensuing treatments of filaments were those presented in Example I.

The following properties were obtained:

skin measured radially.

Example IV A viscose spinning solution containing 6.25 by weight 10 weight cellulose, 5.75 by weight sodium hydroxide and 0.024% N-methylcyclohexylamine (0.21 millimole per 100 grams of viscose) was prepared from sheets of wood pulp according to the split xanthation process described in Example I.

The solution was heated to 44 C. and spun into the coagulating bath of Example I. The subsequent processing of the filaments was essentially equivalent to that described in Example I.

Yarn Properties Cord Properties Em lbs. Ton

D. B. Fatigue The example was re-run except that the viscose spin- The following properties were obtained:

ning solution was not passed through a heater prior to spinning. Similar results were obtained as indicated by a product displaying in cross-section greater than 85 skin measured radially.

Example 111 A viscose spinning solution containing 6.25% by weight weight cellulose, 5.75 by weight sodium hydroxide and 0.049% by weight cyclohexylamine (0.49 millimole per 100 grams of viscose) was prepared by the split xanthation process of Example I. However, in this example 28% carbon disulfide (based on the weight of air-dried pulp) was added in the baratte to achieve a xanthate Yarn Properties Cord Properties Denier Tn Tw TL En Denier To Elam. Ton D. B.

Fatigue The example was re-run except that the viscose spinning solution was not passed through a heater prior to spinning. Similar results were obtained as indicated by a product displaying in cross-section greater than 85% skin measured radially.

Example V Example I was repeated with 0.024% N-methylcylohexylamine in the viscose, instead of the 0.049% cyclohexylamine, and with the addition of suflicient N-methylcyclohexylamine to the spinning bath to maintain a concentration of about 0.056%, corresponding to p. p. m. based on the nitrogen content of the bath.

The following properties were obtained:

Yarn Properties Cord Properties Denier T1) Tw TL ED Denier To E15 lbs. Tom D. B.

Fatigue The example was re-run except that the viscose spinning solution was not passed through a heater prior to spin- 60 ning. Similar results were obtained as indicated by a product displaying in cross-section greater than skin measured radially.

Example VI A viscose spinning solution containing 6.25% by weight 65 cellulose, 5.75 by weight sodium hydroxide and 0.044%

by weight N-methylcyclohexylamine (0.39 millimole per grams viscose) was prepared from wood pulp sheets Yarn Properties Cord Properties Denier T 'Iw T E E E1. Denier Tc E15 lbs. T D. B.

Fatigue 7 according to the split xanthation process described in Example I. The solution was heated to. 44 C. and ex truded into a bath at 63% C. containing 9.1% sulfuric acid, 17.5% sodium sulfate, 9.5% zinc sulfate and .008% N- was prepared from wood pulp sheets according to the split xanthation process. Eighty percent of the xanthation occurred in the baratte and in the mixer with a total of 41% carbon disulfide (based on the air-dried methylcyclohexylamine. 5 pulp) used.

The filaments were stretched 110% and collected on a In this case, the cyclohexylamine was added after the bobbin. They were processed in accordance with the carbon disulfide for the second xanthation step had been conventional bobbin process. The following properties added. The partially xanthated alkali cellulose was fed were obtained: into the mixer which contained dilute caustic solution.

Yarn Properties Cord Properties Denier Tn Tw Tr. ED Denier To E1511". Too B- Fatigue The example was re-run except that the viscose spin- Twenty-five minutes later, 7.4% carbon disulfide was ning solution was not passed through a heater prior to added. Ten minutes'after this addition of carbon disulspinning. Similar results were obtained as indicated by 0 fide, the cyclohexylamine was added.

a product displaying in cross-section greater than 85 The solution was then filtered, deaerated and permitted skin measured radially. to ripen slightly. Prior to spinning, the solution was Exam le VH heated to 44 C. and extruded, processed, etc., in the man- 17 ner described in Example I.

Morpholine and diethylamine, representative of com- The following properties were obtained: The yarn, in mercially accessible secondary amines, were also tested cross-section, exhibited 85-90% skin, based on radial on a smaller scale (so-called blow case spinning). A vismeasurement.

Yarn Properties Cord Properties Denier 'In 'Tw Tr. En Denier Tc Emu. Ton Percent D. B.

Conv. Fatigue cose spinning solution containing 6.25% by weight eellu- The example was re-run except that the viscosespinning lose, 5.75% by weight sodium hydroxide was prepared solution was not passed through a heater prior to spinby the split xanthation process, as described in Example ning. Similar results were obtained as indicated by a I, using 37% carbon disulfide. Eighty percent of the product displaying in cross-section greater than 85% total xanthate sulfur substitution was permitted to occur skin measured radially. in the first xanthation step. In one case, 0.05% by Weight The following monoamines were substituted for cycleof morpholine (0.57 millimole per 100 g. viscose) was hexylamine in the processes described in Example I: used. In the second case, the viscose spinningsolution 9. n-Amylamine 14. Pyridine b% zi gg g gggg gig g g gzg g 10. N-butylethanolamine 15. Piperidine 6p e p g n 11. Diethanolamine 16. Ortho-methyl,N-methyland processing followed, in general, the operatlons de- 1 scribed in Exam le I exce t that no nitro en built u in Ethylethanolamme cyclohexylamme p P g p 13. N-ethylcyclohexylamine l7. Ortho-methyLN-ethylcythe spinning bath.

clohexylamme A filament having a smooth cross-section and composed 50 of from 95 to 100% skin was obtained in both cases. The following physical properties were also obtained:

In all cases, the filaments produced had cross-sections which displayed more than skin measured radially.

The example was re-run except that the viscose spinning solution was not passed through a heater prior to spinning. Similar results were obtained as indicated by a product displaying in cross-section greater than skin measured radially.

Example VIII A viscose spinning solution containing 6.25% by weight cellulose, 5.75 by Weight sodium hydroxide and .05 6% cyclohexylamine (0.56 millimole per grams viscose) 75 Since this quantity of skin had produced the excellent properties in the yarns and cords of this invention, this was considered to be sufficient evidence that the above monoarnines could be used with similar results in the process of my invention.

Preferred primary and secondary monoamine modifiers for the purpose of this invention are those in which the amino nitrogen is attached to hydrocarbon groups, preferably alkyl groups, and/ or hydroxy alkyl groups. Suitable modifying agents in addition to those illustrated in the examples include butylamine, hexanolamine, dipropylamine, dipropanolamine, N-ethylethanolamine, N -propylethanolamine, N-amylethanolamine, N -hexylethanolamine, N- cyclohexylethanolamine, N-propylpropanolamine, N- ethylcyclohexylamine or derivatives, such as ortho-methyl- N-methylcyclohexylamine and ortho-methyl-N-ethylcyclohexylamine. These contain at least 4 carbon atoms and have no radical of more than 8 carbon atoms. Larger radicals, in addition to decreasing the solubility of the amine, tend to produce surface activity which is not desirable in the process of this invention.

For effective results and for the most economic operation, very small quantities of amine modifiers are used. It is undesirable to use more than 1 millimole of agent per 100 grams of viscose; the generally preferred range being from 0.1 to 0.85 millimole per 100 grams of viscose. The optimum concentration of any given agent depends on its particular effectiveness and on its molecular weight. For example, smaller concentrations of N-methylcyclohexylamine will be as effective as larger concentrations of cyclohexylamine. The optimum concentration of modifier in the viscose also depends to some extent on process variables such as the spinning speed and the level of modifier concentration maintained in the bath. At the high spinning speeds used in industrial practice, less agent is desirable than at lower speeds. The amount of agent in the viscose should also be less With higher concentrations in the bath, but the nitrogen content of the bath should not exceed 200 p. p. m.

In practicing this invention, the viscose spinning solutions are prepared by the split xanthation process. The viscose solutions can contain from 4 to cellulose and 4 to 8% alkali, preferably 5 to 7% cellulose and 4 to 6.5% alkali. The sum of carbon disulfide used in the two xanthation steps can be from to 60% (based on the air-dried pulp).

The split xanthation process, besides being essential in the process of this invention, provides several inherent advantages. Split xanthation results in a shorter xanthation cycle. A reduced xanthation cycle results in greater productivity for the baratte. Furthermore, since less carbon disulfide is used in the baratte, cleaning the baratte, which had been time consuming and difficult, can be performed relatively quickly and easily. Splitting xanthation also provides more efficient reaction with carbon disulfide and a reduction in the problem involved in ventilating to remove poisonous carbon disulfide.

This invention permits the use of viscose displaying salt indices above 5, preferably above 10. The use of higher salt indices means a corresponding decrease in ripening time. Partially ripened and, in some cases, unripened viscoses may be spun by this process. Thus, economies are effected by shortening the viscose preparation cycle and by reducing the space required for this operation.

The high tenacity yarns and cords of this invention display outstanding fatigue resistance which is so important in the reinforcement of rubber goods, such as automobile tires, belts used in commercial operation and 10 the like. The abrasion characteristics and durability of the yarns can be advantageously utilized in preparing textile fabrics of exceptionally high launderability. These easily launderable fabrics can be prepared from yarns composed of either continuous filaments or staple fibers.

Since many diiferent embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

What is claimed is:

l. A process for spinning modified viscose to provide improved rayon yarns and cords comprising the steps of partially xanthating alkali cellulose with carbon disulfide in a dry phase in the absence of a monoamine modifier to an absolute sulfur substitution value of at least 13%, based on the cellulose content, and a relative xanthate sulfur substitution value of up to based on the absolute value obtained in the final xanthation; mixing the partially xanthated alkali cellulose with aqueous caustic solution to a cellulose content of 4% to 15% and a cellulose to caustic ratio approximating that of the final viscose solution; completing the xanthation with carbon disulfide in the presence of at least about 0.02. but less than 1 millimole of an organic monoamine modifier per grams of final viscose solution, said organic monoamine modifier having at least one hydrogen atom attached to the amino nitrogen, containing at least four carbon atoms, having a maximum of eight carbon atoms in any one radical, and being soluble to the extent of at least 0.1% in 6% caustic soda solution; preparing a viscose solution containing 4% to 10% of cellulose and 4% to 8% of caustic from the modified cellulose xanthate mixture; and spinning the modified viscose solution into a spinning bath containing 4% to 12% sulfuric acid, about 13% to 25% sodium sulfate, 2% to 15% zinc sulfate and less than 200 parts per million of combined nitrogen at 40-80 C.

2. A process as defined in claim 1 in which the organic monoamine modifier is selected from the group consisting of cyclohexylamine, N-rnethylcyclohexylamine, N-ethylcyclohexylamine, diethylamine, morpholine, namylamine, N-butylethanolamine, diethanolarnine, ethylethanolamine, pyridine, piperidine, ortho-rnethyl-N- methylcyclohexylamine, and ortho-methyl-N-ethylcyclohexylamine.

3. A process as defined in claim 1 in which the amount of organic monoamine modifier added is from 0.1 to 0.85 millimole of modifier per 100 grams of viscose.

References Cited in the file of this patent UNITED STATES PATENTS 1,929,868 Haller Oct. 10, 1933 2,393,817 Schlosser et al Jan. 29, 1946 2,397,454 Woodward Mar. 26, 1946 2,481,692 Schlosser et al Sept. 13, 1949 2,535,044 Cox Dec. 26, 1950 2,535,045 Cox Dec. 26, 1950

Claims (1)

1. A PROCESS FOR SPINNING MODIFIED VISCOSE TO PROVIDE IMPROVED RAYON YARNS AND CORDS COMPRISING THE STEPS OF PARTIALLY XANTHATING ALKALI CELLULOSE WITH CARBON DISULFIDE IN A DRY PHASE IN THE ABSENCE OF A MONOAMINE MODIFIER TO AN ABSOLUTE SULFUR SUBSTITUTION VALUE OF AT LEAST 13%, BASED ON THE CELLULOSE CONTENT, AND A RELATIVE XANTHATE SULFUR SUBSTITUTION VALUE OF UP TO 90%, BASED ON THE ABSOLUTE VALUE OBTAINED IN THE FINAL XANTHATION; MIXING THE PARTIALLY XANTHATED ALKALI CELLULOSE WITH AQUEOUS CAUSTIC SOLUTION TO A CELLULOSE CONTENT OF 4% TO 15% AND A CELLULOSE TO CAUSTIC RATIO APPROXIMATING THAT OF THE FINAL VISCOSE SOLUTION; COMPLETING THE XANTHATION WITH CARBON DISULFIDE IN THE PRESENCE OF AT LEAST ABOUT 0.02 BUT LESS THAN 1 MILLIMOLE OF AN ORGANIC MONOAMINE MODIFIER PER 100 GRAMS OF FINAL VISCOSE SOLUTION, SAID ORGANIC MONOAMINE MODIFIER HAVING AT LEAST ONE HYDROGEN ATOM ATTACHED TO THE AMINO NITROGEN, CONTAINING AT LEAST FOUR CARBON ATOMS, HAVING A MAXIMUM OF EIGHT CARBON ATOMS IN ANY ONE RADICAL, AND BEING SOLUBLE TO THE EXTENT OF AT LEAST 0.1% IN 6% CAUSTIC SODA SOLUTION; PREPARING A VISCOSE SOLUTION CONTAINING 4% TO 10% OF CELLULOSE AND 4% TO 8% OF CAUSTIC FROM THE MODIFIED CELLULOSE XANTHATE MIXTURE; AND SPINNING THE MODIFIED VISCOSE SOLUTION INTO A SPINNING BATH CONTAINING 4% TO 12% TO SULFURIC ACID, ABOUT 13% TO 25% SODIUM SULFATE, 2% TO 15% ZINC SULFATE AND LESS THAN 200 PARTS PER MILLION OF COMBINED NITROGEN AT 40*-80*C.