US3226461A - Manufacture of regenerated cellulose fibers from viscose - Google Patents

Description

United States Patent 3,226,461 MANUFACTURE OF REGENERATED CELLULOSE FIBERS FROM VISCOSE Harold F. Wise and Elias Klein, Mobile, Donald S. Nelson, Eight Mile, and William C. Richardson, Mobile, Ala., assignors to Courtanlds North America, Inc., New York, N.Y., a corporation of Alabama N0 Drawing. Filed Feb. 25, 1963, Ser. No. 260,847 Claims priority, application Great Britain, Feb. 27, 1962, 7,563/62 1 Claim. (Cl. 264-189) This invention relates to the manufacture of viscose rayon staple fibers having a high initial wet modulus, tenacities greater than g./d. and good processing characteristics on carding machinery.

in recent years a number of patent specifications have described processes for making high intial wet modulus viscose rayon continuous filaments and staple fibers. We have been concerned to increase the strength of such staple fibers, whilst maintaining, or improving, the other inherent properties of the fibers which contribute to good processing on textile machinery.

It is generally appreciated that whilst stretching a filament increases its tenacity, this increase in strength is obtained only at the expense of extensibility. However, both tenacity and extensibility contribute to the resistance of a fiber to breaking under stress. The work of rupture of a fiber is calculated, in fact, as the area under the curve in a stress-strain diagram of a fiber tested to breaking point. Our experience with high initial wet modulus staple fibers shows that it is possible to compare with reasonable accuracy, the performances to be expected in the carding or drawing operations of the cotton system. The product of the tenacity of a fiber in g./denier and the extensibility as a percentage elongation, will be referred to hereafter as the processability index. If the processability index is less than 30, the fiber will suffer excessive breakage during carding, whereas an index above 30 indicates acceptable carding characteristics which improve even more as the index increases.

An object of the present invention is the manufacture of viscose rayon staple fibers having a high initial wet modulus, tenacities greater than 5 g./d. and a processability index of more than 30.

Accordingly, the present invention comprises extruding viscose having a cellulose content between 5% and 9% and a caustic soda to cellulose ratio of 0.6 to 1.5, the cellulose having an average degree of polymerization of at least 300, usually from 300 to 1500, and the viscose having a 7 number (which is an index of the xanthate content of the cellulose) of at least 80, say from 80 to about 120, and a ball fall viscosity of at least 100 seconds, from say 100 to say 500 seconds, into a coagulating bath containing sulphuric acid in a percentage related to the percentage caustic soda content of the viscose by the expression [acid]: (0.77[NaOH] +0.92) 10.5 percent where [acid] is the concentration of H 50 in weight percent and [NaOH] is the concentration of NaOH in weight percent, 6 to percent of sodium sulphat, 0 to 1 percent of Zinc sulphate and 0.5 to 1.5 percent of formaldehyde, the bath having a temperature of between 10 C. and 50 C. and the filaments having an immersion period in the bath of between /3 second and 9 seconds, stretching the filaments whilst they are in contact with a dilute acid liquor containing from a trace to :say 3%, by weight, H 80 at a temperature above 90 C., say 90 C. to 100 C. and thereby increasing the length of the filaents by from 150 percent up to 280 or even up to 350 ICC percent and cutting and relaxing the stretched filaments only after their 7 number has fallen below 10. All proportions are in weight percent unless otherwise stated.

The relationship of acid concentration in the bath and the caustic soda content of the viscose is derived from the necessity to maintain the acid concentration at or above a minimum for trouble-free, continuous spinning. This minimum is characteristic of the viscose and is determined in the main by the caustic soda content.

Certain of the ingredients and conditions of the process act to preserve beyond the spin-bath, a structure more amenable to stretching. Formaldehyde, for example, delays the regeneration reaction, whilst the :relatively short immersion period in the bath limits the contact of the filaments with the sulphuric acid, the main regeneration agent. High caustic soda contents in the viscose also tend to repress regeneration and for this reason, caustic soda/cellulose ratios of from 1:1 to 13:1 are preferred. The 7 number should also be as high as possible and not less than 80.

In examining the capabilities of the present process we have stretched the freshly extruded filaments by 300 percent and more, with the result that very strong (7 g./d.) staple fibers were produced, but frequently these fibers had processability indices of less than 30 and they performed poorly during carding. It was noticeable, however, that the incidence of poor performance fell as the degree of stretching was reduced below 300 percent and at 280 percent and below continuous trouble-free production of staple fibers having processability indices above 30 was possible.

It will be seen that the invention includes the use of zinc sulphate as an optional ingredient of the spin-bath. Whilst the process operates satisfactorily without zinc sulphate, inclusion of zinc sulphate in the bath may lead to the production of fibers in which the rate of loss of extensibility with increasing tenacity is decreased, with a consequent increase in the processability index. There is some evidence that the maximum stretch which can be applied to the filaments is less when those filaments have been coagulated in the presence of zinc sulphate, but stretches of 280 percent are attainable even when the spin-bath contains 1 percent of zinc sulphate.

The freshly-extruded filaments must be heated during the stretching operation and it is convenient to combine the heating medium with a regenerant, because the stretched filaments must be substantially completely regenerated (7 number less than 10) before they are cut into staple fibers, if the fibers are not to be considerably weaker than the unrelaxed filaments. A convenient stretching and regenerating bath comprises a dilute aqueous solution of sulphuric acid at to C.

The invention is illustrated by the following example.

Example Viscoses were made and spun into spin-baths to form coagulated filaments which were withdrawn from the bath, stretched and regenerated in contact with a hot dilute acid solution and cut into staple fibers. The staple fibers were washed, dried, analyzed and sumbitted to processing on a card under constant conditions, including, for example, concentration and quality of the lubricant. finish, rate of feed to the card and card speed.

The ingredients and their proportions in the viscose, spin bath and stretch-bath, together with the physical and mechanical conditions of the process for a number of spinning runs are set out in the following table.

All the fibers processed well on the card, the quantity of broken fibers never being more than 8 percent.

SPINNING RUN Viscose:

Cellulose, percent 5. 66 5. 55 5. 55 5. 5o 5. 50 5. 55 5. 55 5. 43 5. 55 5. 43 NaOH, percent 7. 12 7. 7. 20 7. 20 7. 20 7. 20 7. 20 7. 04 7. 20 7. 04 NaOH/cellulose 1. 26 1. 3 1. 3 1. 31 1. 31 1. 3 1. 3 1. 23 1. 3 1. 23 Viscosity (seconds) 152 143 143 117 106 143 134 134 132 134 y-number 33 33 30 30 35 86 33 33 33 Spin-bathr H2804, pereent 5. 07 6. 3 6. 27 6. 1 5. 0 6. 07 5. 93 6. 02 6. 10 6. 03 Formaldehyde, peree 0. 7 1. 03 1. 03 0. 3 0. 77 0. 0.90 0. 97 0. 97 1.10 NQQSOA, percent. 3. 5 3. 7 3.7 3. 5 3. 3 3. 3 3. 3 3. 4 3. 3 3. 6 Temperature, 0'; 24 25 25 24. 5 23. 5 25 24. 5 30. 5 25 30.5 Spinning Machine: 20 000 20 000 20 000 20 000 20 000 20 000 20 000 20 000 20 000 20,0001: x X X x x x x x x Jet(NQanddmmetemrhmes) 0.0025" 0.0025" 0. 0025" 0. 0025" 0.0025" 0. 0025" o. 0025" 0.0025" 0. 0025" 0. 0025" Immersion period (second) 0.53 0.57 O. 61 0.61 0.65 0.65 0. 69 0.69 0. 72 0.72 Stretch, percent 200 220 220 240 240 200 260 230 230 Spinning speed (meters/ min. 24 24 24 24 24 24 24 24 24 24 Immersion path (inches) 3 3 3 3 3 3 3 3 3 3 Stretch Bath:

Percent H SO 2 2 2 2 2 2 2 2 2 2 Temperature, C. 93 95 95 95 96 94 95 95 95 94 Fiber properties:

Denier/filament 1. 31 1. 35 1. 32 1. 23 1. 35 1. 34 1. 47 1. 33 1. 29 Air dry tenacity g./d 5. 5 5. 34 5. 46 5. 44 5. 3 5. 72 5. 52 5. 34 6. 05 6. 09 Air dry extensibility, percent. 6. 4 6. 3 6. 1 6.5 6. 2 6.6 6. 2 6.5 6. 1 6. 6 Processability factor 35. 2 33. 4 33. 3 35. 4 36. 0 37. 3 34. 2 33 36. 3 40. 2

What is claimed is: 25 ing the length of the filaments by from percent to 280 A process for making viscose rayon filamentary mapercent and cutting the stretched filaments to form staple terial which comprises extruding viscose having a celluonly after their 7 number has fallen to below 10. lose content between about 5 and about 9 percent, a caustic soda to cellulose ratio of from 0.6 to 1.5, a 'y number of References Clted y the Examine! at least 80 and a ball fall viscosity of at least 100 seconds, 30 UNITED STATES PA N S u n is v r" e de r the cell lose 1 said v cose having an a e age g ee of 2,937,070 5/1960, COX 18 54 polymerization of at laest 300, 1nto an aqueous coagulating 3,107,970 10/1963 Kusunose et al 264-197 bath contammg sulfuric acid 1n a proportion related to 3 109 698 11/1963 Klein et a1 264 197 the caustic content of the viscose by the expression [acid]=(0.77[NaOH]+0.92)i0.5 956 803 ZEE ST reat rltain. Where [acid] is the concentratlon of sulfunc acid in the bath in Weight percent and [NaOH] is the concentration THER REFERENCES of NaOH in the viscose in Weight percent, said bath also d il Encyclopedia, press, bli h d i containing 6 to 15 percent sodium sulfate, 0 to 1 percent 40 1959 b T il B k p bli h I N Y k, 61 zinc sulfate and 0.5 to 1.5 percent formaldehyde, and and 2 are relied UPQIL having a temperature of between 10 C. and 50 C., to form filaments; maintaining the filaments in said coagu- ALEXANDER H. BRODMERKEL, Primary Examiner. lating bath between /3 second and 9 seconds, stretching the MORRIS LIEBMAN xammer. filaments Wh1le 1n contact with a dllute aqueous acid 45 E liquor at a temperature above 90 C. and thereby increas- C. B. HAMBURG, H. W. VERNON, Assistant Examiners.