CA1160413A - Production of high performance rayon fibers - Google Patents

Abstract

D.D.Whitney-C.F.Murphy-G.C.Daul 1-14 3 Production of High Performance Rayon Fibers Abstract of the Disclosure:
High tenacity rayon fibers having a wet modulus of at least 0.5 grams per denier are prepared by spinning a viscose solution having a salt index between about 2.5 and 6 into a coagulating spin bath containing sulfuric acid, stretching the resulting incompletely regenerated filaments and completing the regeneration of the cellulosic filaments. The viscose solution is prepared from an unbalanced ratio of sodium hydroxide to cellulose of from 0.60 to 0.87. The spin bath contains from 0.8 to 3.9% of sulfuric acid and the ratio of acid to sodium hydroxide ranges from 0.20 to 0.66.

Description

~ 1~0~13 D.D. I~itney-C.F. Mur~hy-G.C. Daul 1-14-3 This invention relates to a process for the production of high performance, high wet modulus rayon filaments and fibers.
Regular low wet modulus rayons normally are prepared from a viscose containing 8 or 9g cellulose and 5 to 6~ caustic soda; the acid in the spin bath usually being much in excess of that required to neutralize the alkaline caustic soda -6.5% to as high as 9% or more of acid. Low modulus rayons when converted to fabrics have a tendency to shrink when laundered, the principal cause of shrinkaye beipg their low resistance to stretching when wet ti.e. low modulus1. Rayon researchers have found tha~ when the wet modulus of rayon is sufficiently high (over 0.5 g~d), progressive~shrinkage is essentially controlled and a more stable fabric and garment reslllt.
On the other hand, in the production of high wet modulus (HW~) rayon fibers, that is fibers having a wet ;~ `
strength of at least about 0.5 grams per denier, it is customary to use a "rich" viscose composition in which the a~ount of caustic soda is essentially equal to the amount of cellulose. For example, U.S. Patent 3,720,743, assigned to the present assignee, discloses a process for the production of HWM rayon fibers having a number of desirable properties in addition to high ~7et strength. The Patent indicates that~
a balanced ratio, for example, of 7.5~ cellulose and 7.5%

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1 1~0413 D.D. ~qhitney-C.F. ~lurphy-G.C. Daul 1-14-3 caustic soda should be used. U.S. Patents 3,632,468 and 4,121,012 are similarly directed to ~M rayon fibers prepared from balanced ratios of caustic and cellulose.
So-called polynosic rayons, having high strength 5 and modulus, are prepared from relatively smaller (and unbalanced) amounts of cellulose and caustic. However, the polynosic rayons differ from other ~r,~ rayons in both their properties and their preparation. Because of the high degree of polymerization of the cellulose required for these rayons, high viscosity viscoses are used. High salt indices (about 20) and very large amounts of CS2 are `necessary to effect solubility and good spinnability. Low concentrations of acid at low temperatures in the spin bath are also necessary to form the fibrillar polynosic structure.
Such fibers, while they have high wet modulus properties, have low elongations, in the range of 7 to 10~, which result in difficulties in conversion to yarn and fahric.
~olynosic fibers made by such processes are usually brittIe and have accordingly achieved only limited commercial acceptance.
Thus, it would be desirable to produce dimensionally stable, strong high performance rayons with high wet modulus, using, however, more economical conditions than have heretofore been thought possible.
It is accordin~ly a primary object of this invention D.D. ~lhitney- C.F. Murphy l 160413 G.C. Daul 1-14-3 to provide a process for the production of high wet modulus rayon filaments and fibers with reduced amounts of caustic and acid~
It is an additional object of this invention to provide a process in which the ranges of caustic soda relative to acid can be adjusted to produce HWM fibers with a variety of properties, cross-sections and shapesO
It is still an additional object of this invention to provide a process for producing rayon filaments and fibers which combine more economical process conditions with improved fiber properties.
It has been found quite unexpectedly that high per-formance, HWM rayon fibers having a desirable level of elon-gation may be produced by the use of an unbalanced ratio of cellulose and caustic in the viscose if it is accompanied by ~ reduced amount of acid in the primary spin bath. More specifically, the pxocess of the invention involves the production of crimped high tenacity rayon filaments and fibers having a wet modulus of at least 0.5 g/d and a wet elongation Of about 11-17% comprising preparing a viscose solution containing a mixture of viscose modifiers which substantially retard regenaration, said modified viscose solution having a salt index between 2.5 and 6, prepared from an unbalanced ratio by weight of sodium hydroxide to cellulose ranging from 0,6~ to 0.87, spinning said viscose solution into a coagulating spin ba~l containing from 0.8 to 3.9~ by weight of sulfuric acid, from 1 to 6~ by weight zinc sulfate and from 10-20~ by weight sodium sulfate, the ratio by weight of acid r~ 4 11 6 0 ~ 1 3 D D Whi~ney-C,F Murph~-in the spin bath to sodium hydroxide in the viscose solution ranging from 0.20 to 0,66. The ~esulting incompletely regenerated filaments are immediately stretched and the regeneration is completed in an acid bath maintained above 80C and the tension of said cellulosic filaments relaxed to permit crimp development.
It should be noted that the reduction of only a percentage or two in the amount Gf caustic soda and acid used in the viscose processhas considerable economic significance. These are two of the major raw materials used, which when neutralized, produce water and salts.
Evaporation of the water and recovery of the salt are energy intensive operations. Be reducing the quantities of the raw materials used in the process, significant energy and cost savings are effected.
It was quite surprising to find that HWM fibers of outstanding quality could be spun from leaner viscose compositions, i.e. viscose compositions containing less caustic by weight than cellulose. The key to HWM properties was thought to be high caustic. Ordinarily, when the caustic content is lowered and all other spinning conditions are held constant, the wet elongation increases and the wet modulus properties of the resulting fiber deteriorate dramatically. Most commercially produced HWM fibers are spun at acid levels which cannot be lowered without encoun-tering spinnability problems. o~ten poor spinning, under normal ~M process conditions, can be improved simply by increasing the primary bath acid concentration and this is l 160~13 D . D, ~lhitney-C. F . Murphy-G.C. Daul 1-14-3 frequently done in commercial spinning operations. ~e have now found that for high wet modulus production, the reduced caustic requires less acid, not only less acid resulting from less caustic requiring neutralization, but less acid so that the fibers set up more slowly, an~ stretchability is improved. With balanced ratios of caustic and cellulose, the acid concentration cannot be lowered without adversely impacting fiber spinning, resulting in a condition known to the art as slubbing. The present invention involves the discovery that the caustic level may~be reduced i~ the viscose only if the ~evel of acid in the s~in bath is also reduced. Not only does this prevent adverse impact on spinnability and fiber properties, but the fiber properties, principally wet modulus, are actually improved. ; ~;~
lS Generally, the process of the invention involves the ~;
preparation of a viscose solution from cellulose xanthate.
Purified chemical cellulose, such~as bleached sulfite and prehydrolyzed kraft wood pulps as well as cotton linters having a relatively high uniform degree of polymerization ;~
are converted into alkali cellulose by steeping in sodium hydroxide, aged to a cuene I.V. (intrinsic viscosity) of from 2.0 to 3.6 dl/g (decaliters/gram) and xanthated with 26 to 40% by weight of carbon disulfide, based on oven dried cellulose weight, at approximately ambient temperatures (e.g. 20-30C). The amount of carbon disulfide is not ~ \

l ~ ~0413 D.D. r~lhitney-C.F~ ?-lurphy-G.C. Daul 1-14-3 critical as long as the salt index is correct and viscose filterability is satisfactory. The viscose solution is modified with a regeneratin retardant of ~he type shown, for exam~le, in U.S. Patent 2 t 942,931 and which preferably comprises from 0.5 ~o 2.5~ each of dimethylamine and poly-ethylene glycol. Alternatively, modifiers such as ethoxylated amines sold under the trademarks Ethomeen C-25 and Leomi~-, AC80 can be used in place of dimethylamine, and branched chain polyglycols such as those sold ~nder the trademark Berol Visco 399 may be substituted for polyethylene glycol.

The salt in~ex of the viscose spinning solution should be between 2.5 and 6 and the gamma number between about 20 and about 45 when spun with ripening selected to attaLn~
this level. The specific salt index~and gamma~number depend lS upon the amount of carbon disulfide used in xanthation~and~
the temperature and time of ripening used. The viscos~ity of the spinning solution is not particularly critical and ~ : ~
can range between about 50 and 150 ball fall seconds, or between 75 and 225 poise, measured at 20C. The viscose solution is prepared from an unbalanced ratio by weight of sodium hydroxide to cellulose ranging from 0.60 to 0.87 and preferably from 0.65 to 0.80. The amount of cellulose should be from 5-9%, preferably 6-~%, by wei~ht of the solution. The amount of sodium hydroxide should be from 4-7%, preerably from 5-6~, also by weight of the solution.

_ 7 _ l ~60~13 D,D. ~itney-C.F. '~urp~y-G.C. Daul 1-14-3 The coagulating spin bath contains a sulfuric acid concentration of from 0 R to 3.9%, preferably 2.5 to 3.5%
by wei~nt of the bath. The ratio by weight of acid in the spin bath to sodi~ hydroxide in the viscose spinning solution should range from 0.20 to 0.66, preferably from 0.40 to 0.60. The spin bath should also contain about l to 6% by weight of zinc sulfate and from 10-20% by weight of sodium sulfate. It may also contain from 0.01 to 0.1 percent by weight of a surface active agent or lubricant such as lauryl pyridinium chloride, and a modicum of regeneration retardants carried in with th.e tow.
The deaerated viscose is spun through a spinnerette into a coagulating spin bath at about 30 to 45C. Travel of the filament through the primary spin bath should be li~ited to that re~uired to develop sufficient strength for stretching, in order to avoid any unnecessary regene-ration, with the greater percentage of stretch achieved prior to substantial reseneration. Immediately after leaving the spin bath, the filaments as a group or towj and ~hile thev are substantiall~ soluble in dilute alkali, are stretched from about lO0 to 300 percent. ~o effect this stretch, the tow is drawn frorl the bath the desired distance, passed several times around a driven godet to ~revent slippage and then several times around one or more stretch rolls driven at a sufficiently greater speed to .
l 1~0413 D.D. I~hitney-C.F. ~lurphy-G.C. Daul 1-14-3 g _ provi~e the ~esired continuous stretching.
Since filaments made by the procedures described above are highly plastic and relatively strong immediately upon extrusion into the coagulation bath, it is important to stretch as quickly and as much as possible prior to reqeneration in order to obtain the desired high wet modulus. The strongest filaments with the highest wet modulus are produced when the stretching takes place immediately after the onset of coagulation in a gradual fashion. For example, when only one godet and one stretch roll are used, the stretching occurs on, or as the tow ;
leaves, the first roll and is then completed as the tow of filaments passes through the regeneration bath or baths.;~
To facilitate stretching and to regenerate the coagulated filament tow, it is conducted through one or more hot regeneration baths of suffIcient length which contain hot dilute acid. We prefer dilute acid baths for our purpose, maintained at 80 to 100C (preferably about 95-98C), in any event, sufficiently hot to substantially regenerate the newly formed filaments in the tow. The stretch bath or baths contain from about O.5 to 3.0 percent sulfuric acid and a stabilized modicum of salts carried over from the preceding coagulation bath.
After the filaments are substantially regenerated, tension is reduced or removed to permit crimp development.

g _ ~ ~60413 D.D. '!Ihitney-C.F. Murphy-G.C. Daul 1-14-3 Following rela~ation, the filaments are treated with hot dilute acid, desulfurized, neutralized, washed, finished and dried by conventional techniques.
Alternatively, the filaments can be cut into staple fibers which develop a high degree of crimp on relaxation.
~hese highly crimped staple fibers are acidified, desul-f~rized, neutralized, washed, finished and dried by conventional techniques. Cutting of the tow into staple t fibers is usually performed in the acid state.
The finishing of the crimped filaments and staple fibers should be balanced to preserve crimp, high ~odulus and high strength, while building adequate elongation for good conversion properties and good wear and abrasion-resistance in end-products. Use of a commercially available staple fiber finishing agent is advantageous to insure processability for efficient conversion to yarn and fabric.
Fibers produced in accordance with the invention may have a variety of cross-sectional configurations and degrees of crimp, primarily dependent on the amount of acid used in the spin bath for a given caustic to cellulose ratio in the viscose. The cross-sectional configuration may vary from essentially circular and with the least amount of crimp, spun at acid concentrations within the lower portio.; of the claimed range, to bilobal filaments at l 160413 D.D. Whitney-C.F. ilurphy-G.C. Daul 1-14-3 intermediate acid levels having the most crimp. At the higher end of the acid range, multilobal cross-sections are obtained. The properties or the fibers produced in accordance with the invention are at least the equivalent of high performance fibers produced from prior art, rich caustic, viscose solutions and higher acid spin baths, while the wet modulus properties are in many instances higher. Properties of the fibers of the invention will have the following general ranges:

Wet modulus 0,5-1.2 g/d S6.5 maximum 12%
Conditioned Tenacity 3-4 g/d Conditioned Elongation lQ-15 Wet Tenacity 2-3 g/d Wet Elongation Ll-l7%

Wet modulus as measured herein LS the ~et tenacity in grams per denier at 5~ elongation. The minimu~ and maximum wet modulus values have been roun~ed off to the ~ ;

first decimal place. ~hus, a wet modulus value of 0.46 is considered to fall within the above range. "S6.s" is a measure of the fiber's resistance to laundering and specifically the solubility of the fiber in 6.5~ ~laOH at 20C, he tenacity values axe in accordance with AST!-I
test number D-1577-66, using 1~2 inch gauge length. The ~5 elongation values are in accordance with ASTM test number -- 11 -- .

D.D ~itney-C.~. Murphy-G.C. Daul 1-14-3 D-540-64.
The following examples illustrates the practice of the invention. Unless other~7ise indicated, all parts and percentages are by weight.

E~.~LE 1 This example shows the preparation of a prior art H~l fiber produced by a process similar to that described in the aforesaid U.S. Patent 3,720,743. A modified v scose spinning solution was produced from chemical cellulose whlch was prepared by steeping a high purity wood pulp, having an Slo of 2.~ percent and an S18 of 1.4 percent. (Slo and S18 are a measure of the solubility of the fiher in~l0~
and 18~ NaO~, respectively, at 25C~. The thus formed alkali cellulose contained, after being pressed,~34% ~;
lS cellulose and 15~ sodium hydroxide. The alkali cellulose was shredded and aged to a cuene I.V~ of about 3.0 dl/g.
It was then reacted with 32% carbon disulfide, based on the weight of cellulose, at 30C to form cellulose xanthate~
~lhich was dissolved in sodium hydroxide at 10C and mixed for two hours to rovide a balanced viscose soluticn con-taining 7.5% cellulose and 7.5~ sodium hydroxide. To this viscose solution, 1.3~ dimethylamine and 1.3~ polyethylene glycol of ~l.l7. 1540 (both based on the weight of cellulose) were added. The viscose solution was ripened to a salt (~aCl) index of 5Ø

D.D. I~hitney-C.~. ~'urphy-G.C. Daul 1-14-3 The well-deaerated viscose then was extruded through a cluster of spinnerettes with 24,200 holes -0.0025 inch diameter each, into a primary acid coagulating-type spin bath containing 5.0% sulfuric acid, 15~ sodium sulfate, and 2.8~ zinc sulfate at a temperature of 40C.
The coagulated filament tow was wrapped around a godet and led through a hot secondary acid bath to a wash reel on which it was wrapped several times to prevent slippage.
The secondary acid bath contained 3.0~ sulfuric acid and residues of salts carried over from the primary bath. It was maintained at about 95 to 98C. The tow was spun at 30 meters per minute and stretched through the secondary bath at 120%.
The tow was collected wet, cut in~to staple fiber lengths, washed, desulfurized, and finished in the usual manner with a staple fiber finish. After dryina and conditioning, single filament test were run under standard pxocedures. The sin~le filament fiber physical property ~
test results are sho~m in Table I. ~ ;
The ratio of ~laOH/cellulose in this E~ample was 1:1 and the ratio of H2SO4 in the spin bath to NaOH;ln the viscose was 0.67.

E ~ ~I2 2 The process of Example 1 was substantially repeated 2s except that the primary bath sulfuric acid concentration l 160413 D,D, Whitney-C.F. ~ur?hy-G.C. Daul 1-14-3 was reduced to 3.5%. The lower acid level resulted in unacceptable extrusion occurring at~the spinnerette face in the primary bath (i.e. slubbing) which resulted in unregenerated, uncoagulated viscose in the tow which prevented it from being cut into staple or processed properly.

EX~LE 3 The rayon fiber of this example is typical of commercially produced regular rayon staple. ~
A viscose spinning solution was produced by steeping a chemical cellulose wood pulp, ha~ing an Slo~ of 8.8 and an Slg of 4.4. The thus formed alkali cellulose was pressed,~
shredded, and aged to a cuene I.V. of 2.2 dl/g. It was then reacted with 28% carbon dlsulfide, based on ~the~-eight of cellulose, to orm cellulose xanthate which was dissolved in sodium hydroxide and mixed to produce a viscose solution containing 9.0% cellulose and 5.0~ sodium hydroxide.
The viscose was ripened to a salt (,~aCl) inde~ of 4.0 and deaerated.
It was then extruded through a spinnere~tte into a primary acid coaguIating-type spin bath containing 6.8 sulfuric acid, 21~ sodium sulfate, and 1.0% zinc sulfate at a temperature of 55C. The coagulated to~7 was wrapped around a godet several times to prevent slippage and ~5 stretched 50~ while spinning at lOO meters per minute.

l ~6~413 D.D. Whitney-C.F. Murphy-G.C. Daul 1-14-3 The tow was collected wet, cut into staDle fiber lengths, washed, desulfurized, and finished in the usual manner with a staple fiber finish. After drying and conditioning, single filament fiber physical tests were run under standard procedures. The results are given in Table I.
The ratio of NaOI-I to cellulose in this Exam~le was 0.56 anA the ratio of H2SO4 in the spin bath to NaOH ln the viscose was 1.36.

E ~ ~LE 4 This example illustrates the practice of the present~
invention. The H~M rayon of this example was ~roduced by the process of Example l except that an unbalanced vis~cose composition of 7 . 5Qo cellulose and 4.5% sodium hydroxide was used.
It was spun under the same conditions e~cept that 1.0~ sulfuric acid was contained in the primary spin bath.
All other process variables were the same. Flber physical ~est results are listed in Table I.
The ratio of l~laOH to cellulose was 0.6 and the ratio :
of H25O4 in the spin bath to NaOH ln the viscose was 0.22.

EX~ E 5 The HWM rayon of this example was produced by a process similar to that in Example 4 except that an unbalanced viscose composition of 9.0~ cellulose and 6.0%

l 160~13 D.D. ~itney-C.F. ~urphy-G.C. Daul 1-14-3 sodium hydroxide was used and was prepared at a cellulose I.V. of 2.3 dl/g and ripened to a 4.9 salt (~aCl) index.
It was spun under the same conditions except that the primar~ bath contained 3.5~ sulfuric acid. All other process variables were the same except that stretch was 130~, Fiber physical test results are given below in Table I with results from fibers produced as described in Examples 1-4.

TABLE I

Ex. 1Ex. 2 Ex. 3Ex. 4 Ex. 5 Ratio~
~aOH/Cellulose in viscose 1.0 1.0 0.560.6 ~ 0.67 Ratio:
H2SQ4 in spin bath~NaOH in viscose 0.670.47 1.360.22 0.42 ;
Tenacity g/d Conditioned 3.5 would 2.8 3.5 3.7 Wet 2.2 L.5 2.2 2.4 Elongation Conditioned 13 not 20 13 12 Wet 15 25 15 13 Wet Modulus g/d 0.5 0.2 0.5 0.8 25 Full ~ave s~in Crimps/in. 15 10 20 18 ::

l 160413 D~D~l~hitney-c~F~Mur~h G.C.Daul 1-14-3 E ~ ~LE 6 A process similar to that of Example 4 was used to produce the fiber of this example except that an unbalanced viscose composition of 8.5~ cellulose and 6.0~ soaium hydroxide was used to prepare the viscose. The cellulose in viscose was at I.V. 2.2 dl/g; it was ripened to a 5.1 salt (NaCl) index, and 1.3% Ethomeen C-25 (an ethoxylated amine) and 1.3% polyethylene glycol were added (based on -the weight of cellulose) as regeneratlon retardants.
The viscose was spun into~a primary bath contain1ng 2.9~ sulfuric acid. All other process variables were the .
same. Fiber physical test results are given in Table II.
The ratio of acid in the spin bath to NaOH in the visoose ;
was 0.48. ;

lS E~A~T~ 7 The ~IW~ rayon produced in this example was prepared similar to that of Example 6, using similar viscose composi-tion, cellulose cuene I.V., and other parameters, except that the regeneration retardants used were dimethylamine an~ a branched polyglycol, Berol Visco 399 (1.3% of each~.
All other viscose and spinning conditions were the same.
The fiber physical ~est results are listed in Table II
together with those of ~xample 7.

~ 160413 D . D . Whitney-C.F. Murphy-G.C. Daul 1-14-3 TABLE II
Example 6Example 7 Ratio:
NaOHfCellulose in viscose 0.71 0.71 S Ratio:
H2So4 in spin bath/
NaOH in viscose 0.48 0.48 Modifiers Ethomeen C-25 dimethylamine polyethylene serol Visco 399 glycol Tenacity~ g/d Conditioned 3.5 3.6 Wet 2.2 2.3 Elongati~n,% . ~ :
Conditioned 15 13 : :
Wet 17 15~ ~ :

Wet Modulus, g/d 0.5 0.7 Full Wave Crimps/in~ 22 18 EXAMP~E 8 In this example, fibers were prepared with progressive-ly decreasing amounts of acid and acid to caustic ratios.
A modified ~iscose spinning solution was produced in much the same manner as in Example 1 including steeping, pressing, shredding, aging, xanthating, and mixing l 1~0413 D.D. I~lhitney-C.F. ~urphy-G.C. Daul 1-14-3 operations. IIowever, an unbalanced viscose composition of 7.5% cellulose and 6.0~ sodium hydroxide was used. The viscose was ripened to a salt (.laCl) index of 5.2 with a cuene I.V. of 2.8 dl/g resulting in a viscosity of 100 ball ~all seconds at 20C. The modifiers~, dimethylamine and polyethylene glycol were added to the viscose at 1.3~ each based on the weigh~ of cellulose. 30% carbon~disulfide was injected durlng xanthation. ~ ~
The deaerated viscose was extruded throu~h a cluster of spinnerettes with 24,200 holes (0.0020 inch diameter each) into a primary acid coagulating-type spin bath containing~
2.9~ sulfuric acid, 15% sodium sulfate, and 2.~ zinc sulfate at a temperature o 40C. The coaguIated~tow~was~
wrapped around a godet and led through a hot secondary acid bath to a wash reel on which it was wrapped~several times to prevent slippage.
The secondary acid bath contained about 2.0~ suIfuric acid and residues of salts carried over from the primary bath. It was maintained at about 95 to 98C, and the tow was spun at 30 meters per minute and stretched 130%
through the secondary bath.
The tow was collected wet, cut into staple fiber lengths, washed, desulfurized, an~ finished in the usual manner with a staple fiber finish. After drying and con-ditioning, single filament tests were run under standard -- lg --1 ~60~13 D.D. T~h~ tney-C.F. ~ur~hy-G.C. Daul 1-14-3 procedures. The single filament fiber physical property test results are shown in Table III as a family of fibers with different primary bath acid concentrations. The acid level had a direct effect on secondary bath stretch ancl fiber wet elongation and modulus; i.e., the lower the acid concentration with respect to caustic in viscose, the hi~gher the ~odulus.
In Table III, Sample 1 is outside the scope of the invention. At acid levels of 4% and higher, the wet elongation is too high a~ there is some sacrifice of wet modulus. It will be noted from this table that wet modulus and wet elongation propertles are directly related to acid level.
The lower the acid, the lower the wet elongation and the higher the wet modulus. The relationship is essentially linear with respect to both of these properties. The invention thus makes possible the ability ~o control wet elongation and modulus by control of aci~ level. Insofar' as is known, this has never previously been possi~le.

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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of crimped high tenacity rayon filaments and fibers having a wet modulus of at least 0.5 g/d and a wet elongation of about 11-17% comprising preparing a viscose solution con-taining a mixture of viscose modifiers which substantially retard re-generation, said modified viscose solution having a salt index between about 2.5 and 6, spinning said viscose solution into a coagulating spin bath containing sulfuric acid, from 1 to 6% by weight zinc sulfate and from 10-20% by weight sodium sulfate, immediately stretching the result-ing incompletely regenerated filaments and completing the regeneration in an acid bath maintained above 80°C and relaxing the tension of said cellulosic filaments to permit crimp development, characterized in that said viscose solution is prepared from an unbalanced ratio by weight of sodium hydroxide to cellulose ranging from 0.60 to 0.87 and said spin bath contains from 0.8 to 3.9% by weight of sulfuric acid, the ratio by weight of acid in said spin bath to sodium hydroxide in said viscose solution ranging from 0.20 to 0.66.

2. The process of Claim 1 in which the ratio by weight of sodium hydroxide to cellulose is from 0.65 to 0.80.

3. The process of Claim 1 in which from 5 to 9% by weight of cellulose is present in the viscose solution.

4. The process of Claim 3 in which from 4 to 7% by weight of sodium hydroxide is present in the viscose solution.

5. me process of claim 1 in which from 2.5 to 3.5% by weight of acid is present in the spin bath.

6. me process of claim 1 in which the acid to sodium hydroxide ratio is from 0.40 to 0.60.

7. The process of claim 1 in which the viscose spinning solution has a cuene I.V. of from 2.0 to 3.6 dl/g and is prepared from 26 to 40% by weight of CS2, based on cellulose weight.

8. The process of claim l in which the fiber has at least 12 full-wave crimps per inch.

9. The process of claim 1 in which the acid bath in which stretching and completion of regeneration occurs is maintained between 95 to 98°C.

10. m e process of claim 4 in which from 5-6% by weight of sodium hydroxide is present in the viscose solution.

11. The process of claim l in which the mixture of viscose modifiers consist of from 0.5 to 2.5% each of dimethylamine and polyethylene glycol.