CA1112824A - Alloy rayon (cmc) - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Method for making alloy fibers having high fluid-holding capacity, the alloy fibers being comprised of a matrix of regenerated cellulose having carboxymethyl-cellulose uniformly dispersed therein, as the sole additive for increasing the fluid holding capacity of the fibers.

Description

The present invention is directed to alloy fibers having high fluid-holding capacity, to shaped articles comprising such fibers and a method of preparing them.
Known in the art are alloy fibers consisting of a mat-rix of regenerated cellulose and an additive imparting a fluid-holding capacity to these alloy fibers which is greater than that of conventional regenerated cellulose fibers. This advantage is at least partially offset by their higher manufacturing costs.
As employed throughout the description and claims, the terminology "alloy fibers" refers to cellulose fibers having an additive uniformly dispersed through their re-generated cellulose matrix. Similarly, "fluid-holding capacity" is a measure of liquid absorbed into the fibers of a mass of alloy fibers, together with the liquid re-tained within the interstices or such fiber mass.
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This invention relates to alloy rayon sta~le fibers containing about 10 to 40~ sodium carboxymethylcellulose preferably 15 to 25% based on the weight of cellulose ; ("b.o.c.") and having high fluid holding capacity at least 5.5 cc per gram (such as in the range of up to about 7cc/g) as measured by the Syngyna test. In the ~ '~

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fiber at least about three fourths of the carboxylic ` groups of the carboxymethylcellulose are in sodium salt form. The fibers carry a lubricating finish, ~referably water-soluble polyoxyethylene sorbitan mono-laurate (e.g., AHCO7596T, ICI Ltd.) or similar nonionic ~olyoxyethylene sorbitan monoester of higher fatty acid The ~roportion of finish and the proportion of the carboxyl groups which are in sodium salt form are such that when a mass of the fibers is wetted with 2 or more times its dry weight of water and then dried, without tension, in air at 25C ~he resulting fibers are sub~
stantially non-adherent. The fiber pH Imeasured on a 1~
slurry of these lubric~ted fibers in deionized water) is in the range of about 5 5 to 8.~ preferably about 6 to 8.
Generally the fibers are of about 1 1~2 to 6 denier and the staple fiber length is in the range of about 3/4 to 5 inches (such as about 1 1/2 inches).
Tne fibers .nay be produced by a process which in-cludes the steps of adding carboxymethylcellulose to viscose, spinning the mixture into fiber form into an acid s~in bath, washing to remove adhering acid, de-sulfurizing and treating the fibers with the lubricating finish, the conditions being such that in the course of this treatment at least about three fourths (such as 80%, 90% or more) of the carboxyl groups of the carboxymetnyl-cellulose are converted to the sodium salt form.
Preferably the process is one which yields "chem-ically crimped" fibers, the spinning conditions being

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such that the acidic fibers leaving the acid spin-bath are plastic and stretchable (e.~., stretchable by some 60~ or more of their length) and are then stretched, as in a hot aqueous bath, to a considerable degree (e.g., some 60~ or more such as about 60-70%), after which the stretched acidic fibers are cut to staple length and allowed to relax (e.y., in hot water) and to crimp; then the wet staple fibers are washed, desulfurized and lubri-cated as described above, in a process including a step of supplying sufficient alkali so as to convert at least three fourths of said carboxyl groups to the sodium form.
The fibers may be cut and immediately subjected to the relaxation in hot water at a stage when the regen-eration of the cellulose xanthate (to cellulose) has not been Eully completed, such as when that degree of regen-eration (of the fibers being cut) is less than about 95 but above about 85%, such as about 90 to 95%, or after complete regeneration. The relaxation may take place in a conventional bath of hot water (into which chips or parallel fibers, formed by cutting OL the tow, fall directly from the cutter); this water may be acidic, neutral or alkaline, e.g. made alkaline with NaOH to a pH of 8 to 11, such as about 10 to 11. A desirable crimp level is at least about 8 distinct crimps per inch (such as about 8 to 20). Discussions of chemical crimping of non-alloy rayon fibers are found, for instance, in Merion et al. U.S. 2,517,694; Textile Research Journal Vol. 23 pp. 137-157 and Man-~ade Fibres by Moncrief (6th Edition, 1975, ~ubl. by John Wilev & Sons) pp. 191-193.

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The degree and type of fiber lubrication and the degree of conversion of carboxyl groups to sodium carboxylate groups are such that the wet lubricated fibers have considerable re-sistance to compaction and tend to separate from each other after they have been squeezed together (to express excess water) under pressure and then released. Thus when the fibers are dried they show little tendency to adhere to neighboring fibers, and the product (particularly after conventional rayon "opening") is made up substantially entirely out of individual non-bonded fibers.
The Syngyna test involves the following procedure: the fibers are carded into web form and then separated into 2,5 gram portions each about 6 inches long. Each such web portion is then individually rolled in the direction of its width to provide a six inch roll and a string is looped a~out the center thereof. Each such roll is then folded on itself at the string loop and drawn into a 1/2 inch tube within which it is compressed by a clamp and plunger, thus forming a tampon. The resulting tampons are removed, allowed to stand for a period of about 30 minutes (during which the tampons recover to a bulk density of about 0.4 g/cc) and are then evaluated for their capacity to hold water by the Syngyna Method, as described by G.W. Rapp in a June 1958 publicatlon of the Department of Research, Loyola University, Chicago, Illinois.
The alloy fibers of the present invention are adapted for use in a variety of articles, such as surgical dressings, .~

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pads and vaginal tam~ons, in which high fluid retention is an essential characteristic. In the manufacture of such articles, the alloy fibers may be used in the same manner and with the same equipment as employed with conventional rayon fibers. They may be blended with other fibers which may or may not enhance the absorbent properties of the re-sulting articles.
Fibers with which the alloy fibers of the present invention may be blended include, for example, rayon, cotton, chemically modified rayon or cotton, cellulose acetate, nylon, polyester, acrylic, polyolefin, etc.
Typically a tampon is an elongated cylindrical mass of compressed fibers, which may be supplied within a tube which serves as an applicator; see U.S. Patent Nos. .-~
2,024,218; 2,587,717; 3,005,456; 3,0Sl,177. The fiber of this invention has been converted into yarns and woven into fabrics having textile application.
The spin bath is an acid bath containing sulfuric ~ acid and sodium sulfate and usually, zinc sulfate. Other J 20 coagulation modifiers, as desired, may be present. It is preferred that the H2SO4 concentration be on the relatively low side, such as 6.0 or 6.8% or (with appropriate other conditions) in a range OL about 5.5 - 8%. During the spin-ning of the viscose into the acid bath, hydrogen ions diffuse into the stream of viscose emerging from each spinneret hole. The reaction of the acid with caustic soda in the viscose produces sodium sulfate and water; the _5_ -~ - . , ,, . :
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acid also decomposes xanthate groups. The presence of sodium sulfate in the spin bath acts to induce coagulation of the viscose streams owing to dehydration from the interiors of the streams. Zinc ions in the spin bath act, at least at the surfaces of the streams, to convert sodium cellulose xanthate of the viscose to zinc cellulose xanthate which is decomposed more slowly by the acid and thereby keeps the fiber in more stretchable and orientable condition.
Typically the temperature of the acid bath is in the range of about 45 to 65~C (such as about 50-55C) and the fiber, after passing through the acid bath, is subjected to a bath of water (or dilute acid) first at a high temper-ature s~ch as about 80C to the boiling point, e.g. about 85-95C, and/or to steam and then to water at a moderate temperature such as about 40 to 50C. In the high temper-ature a~ueous treatment the fibers are subjected to stretch-ing. While for most uses the fibers need not have high strength properties, the alloy fibers have been found to retain to a very large extent the physical properties of ~ 20 non-alloy rayon. Typically, the alloy fibers of this in-; vention are not brittle and may be processed in about the same ways as ordinary rayon.
While the polyoxyethylene sorbitan monoester of a higher fatty acid (such as the A~CO series) is a preferred finish, it is within the broader scope of the invention ; to employ other lubricating finishes, preferably applied in aqueous solution or dispersion, such as soaps; sulfon-ated oils; ethoxylated fatty acids; ethoxylated fatty ester 32~

o_ polyhvdric alcohols; fatty acld esters co~bined with emulsif~ing agents or mixtures of various lubricating finishes. Generally, the amount of lubricating finish depoaited on the fiber ~.7ill be well below 1%, and usually more than 0.05~,such as in the range of about 0.1 to 0.5~
or 0.1 to 0.3~. Preferably it is not such as to give the .ibers an oily feel.
The following Exam~les illustrate the invention.
-EX~MPLE 1 Using conventional rayon spinning equipment,an aqueous alkaline solution of sodium carbox~ethylcellulose of 7~. -grade (Hercules) having an avera~e degree of substitution of 0.7 carbo~ymethylunits per anhydroylucose unit of the cellulose, and having a molecul~r weisht such that the viscosity of a 2~ solution thereof in water is about 300 cps) is injected by a metering ~u~-n~ into a viscose stream during its passage through a blender and the blend is there-after ex.ruded. During this the blend is subjected to high --~echanical shearing. The viscose composition is 9.0% cel-lulose, 6.0~ sodium hydroxide and 31~ (based upon the weight OL the cellulose) carbon disulfide. The viscose ball fall is 60 and its common salt test is 7. In making the alkaline CIiC ~eed solution the sodium carboxymethylcellulose (C1lC) is added to a 6% aqueous solution of NaOH to form a uhiform solution having a ball fall viscosity of 120 seconds (which E~
is a viscosity of about 13,000 c~s). The addition amount of L
CMC is such as to provide 20% thereof based on the weight f ~,t cellulose in the spinning solution. -The mixture of viscose and sodium carboxymethylcellu-lose is extruded through a spinneret (having 980 circular holes, each 0.0035 inch in diameter) into an aqueous spinning bath con-sisting of 6.0% by weight of sulfuric acid, 21% by weight of sodium sulfate, and 1.0% by weight of zinc sulfate at 55C.
The tow formed in the spin bath is passed around a driven roll and then pulled (by a second driven roll) through a hot aqueous stretch bath (e.g. containing about 3 to 5% H2SO4 and at about 85C. or higher). The exit speed (i.e., the speed at the surface of the second driven roll) is 40 meters/minute, and the speed ratio of the first and second driven rolls is such that the tow is stretched about 60 to 70% in the stretch bath.
The length of travel of the tow in the spin bath is about 0.4 meter and in the stretch bath about 2 meters. After leaving the second driven roll, the tow drops into a cutter and the resulting cut fibers drop into flowing hot water (about 85 to 90C.) where relaxation (and crimping) occurs. The 3 d.p.f. (denier per filament) staple fibers are taken up as a ~ 20 blanket, washed with hot water for 8 minutes at 90C.; treated ; for 8 minutes in a 0.5% NaOH solution at 40C. (or e~uivalent solution of sodium carbonate or sodium sulfide) to neutralize the adhering acid; washed again in water for 4 minutes at 40C.;
bleached and desulfurized in an aqueous solution of sodium hypochlorite containing about 0.2% available chlorine and about 0.2% NaOH at 40C. for 3 minutes; washed with soft water for 8 minutes at 40C. (if the pH of the final dried product indicates : ~i , `..

the presence of free alkali [e.g. NaOH] in the fiber, the proc2ss may be modified to include addition of dilute H2SO4 to the wash water in amount sufficient to neutralize the free alkali).
To the fibers there is then applied an aqueous solution of 0.3~ AHC07596T,~fter which the fibers are squeezed to remove adhering water and then dried (e.g. at about 90C.) without tension. In squeezing to remove water, the blanket ,,!
(about 2 to 4 inches thick) of the staple fibers is passed between stainless steel pressure rolls, the blanket being in the nip of this pair of rolls for less than 2 seconds and the pressure being such that the average water content of the blanket is reduced thereby to less than about 100%
(e.g. about 80%). The blanket is then ~assed over a beater having a rotating spiked roll which tears it into chunks (e.y. of 1 to 2 inch diameter, or more) of fiber before drying, e.g. in hot air at 70 or 90C.
At a level of CMC additions of twenty per cent, b.o.c., the fluid holding ca~acity was 6.8 cc/g in the Syngyna test.

EXAMPLE II
A viscose solution is prepared to contain 9% cellulose, 6% NaOH and 31% CS2 based on cellulose content, and aged, for spinning, to a ball-fall viscosity of 44 seconds and salt index of 5.8.
A solution of sodium carboxymet~.ylcellulose (CMC7L, Hercules, Inc.) is prepared to contain 9% CMC dissolved in 6% NaOH.
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~-.e ~'C solution is mixed with the viscose solution, _ jus. ~e ore s?inning, by use of a metering pump. The mixed solu,-o~s ~re ?u.~ ed througn a 980 hole jet at a rate to ~a~e 3 ~enier fila,ments, the jet being immersed in a spin ~a~n~ co~taining 6% H2SO4, 0~785o ZnSO~ and 21.3~ Na2SO4 at ~C. lfter .ra~elling 20 inches through the spin bath the ~a n ~ dle is ~2ssed around a guide, a godet wheel, t~rough a _2sc2~e trough and around a pair of wash drums. The casca'e trough contains an aqueous 2 to 3% H2SO~ solution 1~ at g0C. ~he wash crums ha~e a ~eripheral speed sufficiently higher thzn tnat of the godet wheel that the yarn is stretc~ed about 76~. Tne yarn is washed with water until free of spin-~C~:~A che~icals.
Portions of ,he yarn are cut about 1 1/2 inches long, .-ezt2c with suf~icient 1/2~ NaO~ to convert all the ccrbox~-l grou?s to sodiu~ form, washed with water and ~-~ersed in a 0.3% AHCO 7596T,solution. Excess solutions are removec. by centrifuging. The samples are dried and eval-u~.ec -or fluid ;nolcing ca~acity using the Syngyna test.
23 Tne s~e ~rocess is carried out with a control and w-t:~ d~ffere~t ~r~ortions of CMC injected into the viscose s?l~tion, with ~e following results in terms of fluid hol-~in5 czpacit~:

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â~le b.o.c* Fluid held cc/g A 0 4.32 B lO Q.94 C 20 5.86 D 30 6.63 ~ * Sodi~m carboxymethylcellulose, based on ; cellul~se; calculated by dividing the weight of ~e sodiu~ carboxymethylcellulose added to ~he viscose solution by the weight of the cel-; lulose in that ~iscose solution (prior to the adaition OL CMC).

EX~ P E III
r. ~T- scose solution, similar to that used in Example II, as useci with a solution of carboxy~ethylcellulose (Hercules ~;6S~ i~ which 540 g of C`~C 4M6SF weré dispersed in lO00 ml o- iso~_o~anol and then mixed with a solution of 2000 g of 18~ so~ hycroxide and 2675 ml of water. The solution th~s ~_e~ared W25 mixed in various proportions with viscose ænc s~u~. Tne spun ibers were treated as in the ~revious ex~r,?les ~o convert ~C in the fiber to a salt form.AHCO 7596T
~as -~ e rinish em?loyed here. Portions of the fiber were ',hen evalu2te2 for fluid holding ca~acity, using the Syngyna ~est. The results were as follows:
~ CMC 4~16SF Fluid Held _m?le b.o.c. cc/g ~ 0 3.6 B lO 5.7 C 20 6.2 D 30 7.3 E 40 7.7 .s~

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Tne in~ention has been illustrated more ~articularly in con~ecti~n witn sodium carboxymethylcellulose having a degree o' suDstitution in the range of about 0.6 to 1 such as ~er_ules 7~5 (having about 0.65 - 0.85 carboxyrnethyl grou~s ?er 2nhydro~1ucose unit, and a degree of polymerizatioh (nD.P.~) of about 1100; or Hercules 7L (also having about 0.6~-0.8~ carboxymethyl groups per anhydroglucose unit, ~ut ~hose D.P. is about 400; or Hercules 4M (having about 0 3~ - 0 55 carboxymethyl grou~s per anhydroglucose unit 1~ and a D.P. of about 1000. It is also within the broader ~co?e of the invention to employ CJ~C of higher degrees of s~bsti.ution such as about 0.9 or even 1.2 or 1.4, and C~C
of ;~isher or lower molecular weight (e.g. a D.P. of about 3200 or about 200, or even 100).
It is known in the art (U.S. Patent 3,005,456 to Graham) tha_ c2rboxyme.hylcellulose (C~IC), in fibrous form, and of a lo~- ~egree o substitution, (i.e., not more than 0.35 czr~ox~alkyl radicals ~er glucose residue in cellulose), are suDstantially insoluble in water, may increase the 2~ lu-c 2bsorbency of pads or tampons prepared therefrom.
The present invention provides a means of using CMC of .~igher degree of substitution (DS) than 0.35, including DS of 0.4 to 1.2, to make fibers which have, in the form of ~2ds or tam?ons, higher fluid absorbency. The fibers of the ?resent invention are a mixed polymer composition, wherein cel7ulose is the major component and CI~C is the minor ccm?onent. These fibers are insoluble in water, and even though the CMC component is soluble in ~ater, most of it isprevented from going into solution by bein~ trapped in the cellulose matrix.

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Claims (11)

CLAIMS:

1. Alloy rayon staple fibers containing about 10 to 40%
sodium carboxymethylcellulose b.o.c., at least about three fourths of the carboxyl groups of said sodium carboxymethyl-cellulose being in sodium salt form, said fibers having a denier of about 1 1/2 to 6, said fibers carrying a lubri-cating or protective finish in amount of less than one percent, and said fibers having a fluid holding capacity of at least about 5.5 cc per gram as measured by the Syngyna test.

2. Alloy rayon staple fibers as in claim 1 in which said lubricating finish is water-soluble.

3. Alloy rayon staple fibers as in claim 1 in which said lubricating or protective finish is a nonionic poly-oxyethylene sorbitan monoester of a higher fatty acid.

4. Alloy rayon staple fibers as in claim 1 produced by incorporating sodium carboxymethylcellulose in said pro-portion into a viscose solution, spinning the mixture into fiber form into an acidic spin bath containing sulfuric acid and sodium sulfate, to form a stretchable fiber, stretching said fiber in a hot aqueous medium, cutting said stretched fibers into staple form and relaxing said cut fibers in a hot water bath, washing said cut fibers and applying said finish in aqueous medium, the acidity of said stretched fibers being neutralized to such an extent during said process that at least about three fourths of said carboxyl groups are in sodium salt form.

5. An article of manufacture comprising a highly fluid absorbent mass of alloy rayon staple fibers comprising a matrix of regenerated cellulose and about 10 to about 40 percent of sodium carboxymethylcellulose b.o.c., at least about three-fourths of the carboxyl groups of said carboxy-methylcellulose being in sodium salt form, said fibers having a denier of about one and one-half to six; said fibers car-rying a lubricating or protective finish in an amount of less than one percent, and said fibers having a fluid holding capacity of at least about 5.5 cc. per gram of fiber as measured by the Syngyna test.

6. The article of claim 5 wherein said sodium salt is present in the regenerated cellulose in an amount ranging from about 15 to 25 weight percent based on the weight of the cellulose.

7. The article of claim 5 wherein the fibers have a lubricating finish for cellulose thereon.

8. The article of claim 5 in the form of surgical dressing.

9. The article of claim 5 in the form of a tampon.

10. An article as in claim 5 wherein said lubricating or protective finish comprises a nonionic polyoxyethylene sorbitan monoester of a higher fatty acid.

11. An article as in claim 5 wherein said fibers are staple fibers, said article comprising a non-woven array of said staple fibers.