CA1082866A

CA1082866A - Regenerated cellulose matrix fibres containing n- vinyl amide polymer

Info

Publication number: CA1082866A
Application number: CA239,265A
Authority: CA
Inventors: Frederick R. Smith
Original assignee: Avtex Fibers Inc
Current assignee: Akzo Nobel UK PLC
Priority date: 1975-10-28
Filing date: 1975-11-06
Publication date: 1980-08-05
Also published as: DE2550345C2; FR2330784B1; SE7512061L; FR2330784A1; SE398360B; DE2550345A1; BE835420A; JPS5858441A

Abstract

ABSTRACT OF THE DISCLOSURE

Alloy fibers having high fluid-holding capacity, and a method for making the same, the alloy fibers being comprised of a matrix of regenerated cellulose having polyvinylpyrrolidone dispersed thereon. The polyvinylpyrrolidone may be present in combination with an anionic polymer. The fibers are made by spinning into a coagulating bath a blend of viscose and an N-vinyl amide polymer, the proportions of added polymer being at least about 7% of the total.

Description

The present invention is directed to alloy fibers ~ -having high fluid-holding capacity. -Fluid-holding capacity of fibers may be measured by the pellet test described in Example I below or the Syngyna test referred in Example III below. These tests use a predetermined mass o~ fibers maintained under external pressure and indicate the amount of water absorbed by the fibers themselves as well as the amount of water retained within the interstices of the mass, One aspect of this invention relates to absorbent alloy fibers, each having a matrix of regenerated cellulose and poly-vinylpyrrolidone uniformly dispersed therein, with the regenerated cellulose being the major portion of the fiber mass. These alloy fibers may be prepared by mixing an aqueous solution of polyvinyl-pyrrolidone with a filament-forming viscose, shaping the mixture into fibers, coagulating and regenerating the shaped fibers and thereafter drying the same, Viscose constitutes the major portion of the mixture and the shaped alloy fibers are coagulated and regenerated by known means, and preferably in an acid bath con-taining sulfuric acid and sodium sulfate, The acid bath often contains zinc sulfate as well as other coagulation modifiers as desired.
The present invention provides alloy rayon fibers of higher fluid-holding capacity than non-alloy rayon, which comprises a regenerated cellulose matrix and a water-soluble polymer dis-persed therein--in an amount sufficient to increase the fluid-holding capacity by more than 20%, the water-soluble polymer com-prising an N-vinyl amide polymer.
The present invention also provides a process for making alloy rayon fibers, of higher fluid-holding capacity than non-alloy rayon, comprising a regenerated cellulose matrix and a water-soluble polymer dispersed therein in an amount sufficient to in-crease the fluid-holding capacity by more than 20%, the water-soluble polymer comprising an N-vinyl amide polymer, the process comprising spinning into an aqueous coagulating bath consisting essent:ially of H2S04, Na2S04 and ZnS04 a blend of viscose and the water-soluble polymer to form fibers, the proportions of the dispersed polymer being at least about 7% of the total, Duri~g the spinning of the viscose into the acid bath, hydrogen ions diffuse into the stream of viscose emerging from each spinnerette hole, The reaction of the acid with caustic soda : - -in the viscose produces sodium sulfate and water; the acid also decomposes xanthate groups. The presence of sodium sulfate in the spin bath - - :

; ~ ' .. ~ r -la-~82~66 ZlCtS to induce coagulation of the viscose stream~ owing l:o dehydration from the interiors of the streams. zinc Lons in the ~pin 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 30 to 6~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 temperature such as about 80C to the boiling point, e.g. about 85-95C, and/or to steam, and then to water at a moderate tempera-ture such as about 35 or 45 to 65C. Ir. the high tempera-ture aqueous treatment the fibers may be subjected to stretching, e.g. by about 50-75%. While for most uses the fibers need not have high strength properties, the alloy fibers have been found to retain to a large extent the physical properties of non-alloy rayon, for instance, using spinning and treatment conditions which gave a non-alloy control having a dry (conditioned) tenacity of about 2.9 g/d, dry elongation of about 20%, a dry modulus of about 72 g/d, a wet tenacity of about 1.6, a wet elongation of about 30~0, and a wet modulus of 4.8 g/d, an alloy fiber (made from a spinning solution in which the ratio of cellulose to polyvinylpyrrolidone was about 69:31) showed a dry tenacity of about 2.4 g/d, a dry elongation of about 17%, a dry modulus of about 66 g/d, a wet tenacity of about 1 g/d, a wet elongation of about 27%, and a wet modulus of about 4.1 g/d. With lower 1082~6~; .

~proportions of polyvinylpyrrolidone these physical properties are closer to those of the non-alloy fibers.
Typically, the alloy ibers of this invention are not brittle and can be carded under conditions that cause fiber breakdown of more brittle (e.g. cross-linked) fibers. Also they swell to a greater degree in water than the non-alloy rayon fibers.
The viscose which is employed in making the alloy fibers of the present invention i9 desirably of a compo-sition as is used in making conventional-regenerated cellulose fibers, e.g. a viscose produced by reacting alkali cellulose with carbon disulfide, with the resulting sodium cellulo~e xanthate being diluted with aqueous caustic to provide the resulting viscose with a desired cellulose and alkali content. For example, the viscose composition may contain cellulose ranging from 3 to about 12 wt. percent (e.g. 6 to 10%), caustic from about 3 to 12 wt. percent, and carbon disulfide, based on the weight of cellulose from about 20 to about 60%. Additives or modifiers may be mixed in the viscose if desired.
The polyvinylpyrrolidone preferably has a high molecular weight, such as well above 10,000. Very good results have been attained with polyvinylpyrrolidone of average molecular weight ranging from 100,000 to 400,000 and, more desirably, from 160~000 to 360,000, and a preferred K-value of from 50 to 100. The procedure for determining the K-value of such polymers is known in the art, as disclosed in Modern Plastics, 1945, No. 3, starting on Page 157. Polyvinylpyrrolidone of desired character is commercially available, for example, under .. . . . .

i~8~866 the designation of K~60 and K-90 from GAF Corporation.
Polyvinylpyrrolidone is described in Encyclopedia of Polymer Science and Technology, published in 1971 by John Wiley & Sons, in the article on "N-Vinyl Amide Polymers"
in Volume 14 pages 239-251.
The polyvinylpyrrolidone may be the sole high poly-meric additive in the viscose or it may be used together with other water-soluble (including aqueous alkali-~oluble) high polymers. Preferably these are anionic 10 polymers such as polymeric acids or salts (e.g. alkali metal salts) thereof, e.g. salts of carboxyalkyl cellu-loses (such as sodium carboxymethyl or carboxyethyl cellulose), salts of polyacrylic acids, (including polyacrylic acid or polymethacrylic acid homopolymer, or copolymers of acrylic and/or methacrylic acid with one or more other monomers such as acrylamide or alkyl acrylates, e.g. ethyl acrylate), salts of copolymers of maleic or itaconic acid with other monomers such as methyl vinyl ether, or naturally occurring polycarboxylic polymers, such as algin. These materials are preferably dissolved in aqueous medium before addition to the viscose, the solution being preferably alkaLine, e.g., they may be made with an amount of alkali, such as NaOH, stoichio-metrically equivalent to the amount of acidic (e.g.
carboxyl) groups of the polymer or with an excess of alkali. Less desirably, these materials may be added in acid form (again preferably as aqueous solutions) and be converted to salt form by the action of the alkali present in the viscose. The anionic polymers may be those disclosed in the art as forming complexes with 1(~82~66 . . .. .

polyvinylpyrrolidone; see United States Patent Mo. 2,901,457. Other water-soluble high polymers include ~ubstantially non-ionic polymers such as starch (which may be added as, say an alkaline solution containing some 2-5% of NaOH) or polyvinyl alcohol.
The proportion of polymer added to the viscose should be such a~ to impart improved fluid holding capacity to the rayon. Preferably it is such as to produce fibers whose fluid holding capacity (as measured by the "Syngyna"
test described in Example III below) is at least 5 cc per gram and more, preferabl~ at least 5.5 cc per gram.
As will be seen below, the practice of this invention has made it possible to attain fluid holding capacities which are well above 6 cc per gram and even above ~.5 cc per gram. ~he fluid holding capacities at~ ined in prefer-red forms of the invention are more than 20h better than ~-those of fibers spun and processed under the same condi-tions but in the absence of the added polymer material;
as can be seen from the Examples below this improvement is often greater than 25%, such as about 30, 40, 50, 60 or even 70h. In general the total proportion of added polyvinylpyrrolidone, alone or together with the anionic polymer, is within the range of about 6 to 400/O based on the weight of cellulose in the visco~e, and more desirably in the range of about 10 or 20 to 35%, based on the weight of cellulose. As shown below, higher proportions, e.g. about 50 or 70% may also be used.
Expressed in terms of the total of cellulose and added polymer (hereinafter termed "the total") the proportion of added polymer is generally in the range of about 7 1l)82866 t:o 30% such as about 10, 15 or 200/oJ although higher ~roportions may be employed. The proportion of poly-vinylpyrroli~one, when used in combination with anionic polymer, is advantageously above 1% of the total, preferably above about 2 or 3% of the total such as about 5% or more of the total. In one preferred form the weight ratio of polyvinylpyrrolidone to anionic polymer i8 at least about 10:90, such as about 20:80, 30:70, 50:50, 70:30 or 80:20.
The polyvinylpyrrolidone described exhibits good colubility in water and a~ueous solutions of polyvinyl-pyrrolidone, with or without added polymer, may be incorporated into the visco~e at any stage, then blended and pumped to spinneret~ for extrusion. After the spinning, coagulation, and regeneration stages, the shaped continuous tow of filament~ undergoes the usual processing, which may include stretching if desired, and is then dried by conventional means. Generally, before drying, the continuous tow of filaments is cut into a staple of a desired length. By the practice of the in-vention one can prepare alloy fibers of high fluid holding capacity which do not bond togethar during drying, even in the absence of applied finish, and can be sub~equently carded with no difficulty by the manufacturer of articles incorporating such fibers. To aid in proce3sing one may apply a lubricating finish, preferably of the hydro-philic type, e.g. a non-ionic finish such as a Span or Tween (partial higher fatty acid, e.g. lauric, ester of sorbitan or mannitan or a polyoxyethylene derivative thereof) e.g. ~pan 20 or Tween 20. Such finish may be /f%~Je f~qrk~

- .

108;2866 applied as a dilute a~ueous dispersion thereof before tlrying. One may also treat the fibers with alkaline ~301utions to increase the pH of the dried fiber; treat-ments with alkaline ~olutions are described in some of the Examples and the alkali solution may be blended with the finish. The drying may be effected in any suitable manner, preferably by evaporating off the water by heat, e.g. in a hot air oven at moderate temperature (such as about 70C) or a microwave oven. Typically drying is effected to such degree as to bring the moisture content of the fibers to about 8 to 200/o~ such as about 10-13%.
The alloy fibers of the present invention are adapted for use in a variety of articles, such as sanitary menstrual napkins and vaginal tampons, in which high fluid retention is an essential characteristic. In the manufac-ture of such articles, the alloy fibers necessitate no special technique~ or equipment and they may be blended with other fibers which may or may not enhance the absorbent properties of the resulting articles. Fibers with which the alloy fibers of the present invention may be blended include, for example, rayon, cotton, chemical-ly modified rayon or cotton, cellulose acetate, nylon, polyester, acrylic, polyolefin, etc. Typically a tampon is an elongated cylindrical mass of compressed fibers, supplied within a tube which serves as an applicator;
see United States Patent~ Nos. 2,024,218; 2,587,717;
3,005,456; 3,051,177.
The following examples illustrate the invention further.

1~82866 EXAMPLE I
Using conventional rayon spinning equipment, aqueous Flolutlons of polyvinylpyrrolidone, designated as K-60 (GAF
C'orporation) and having an average molecular weight of about 160,000 and K-value of 50-62~ were separately injec-ted by a metering pump into a viscose stream during its passage thro~gh a blender and the blend thereafter extru-ded. During this blending, the blend was sub~ected to high mechanical shearing. The viscose composition was 9.0% cellulose, 6~0% sodium hydroxide and 32% (based upon the weight of the cellulose) carbon disulfide. The viscose ball fall was 56 and its common salt test was 7.
The mixtures of viscose and polyvinylpyrrolidone were extruded through a 720 hole spinneret into an aqueous spinning bath consisting of 7. 5% by weight of sulfuric acid, 18% by weight of sodium sulfate, and 3.5%
by weight of zinc sulfate. After passage through the spinning bath, the resulting continuous tow was washed with water, desulfurized with an aqueous solution of sodium hydrosulfide, washed with water, acidified with an aqueous HCl solution, and again washed with water.
The still wet multifilament tow was cut into staple fiberx and, without any further treatment, dried.
The fluid-holding capacity of sample fibers, mads with various approximate proportions (tabulated below~ :.
of cellulose and polyvinylpyrrolidone in the spinning :
solution, was determined using the following test procedure.
Sample staple fibers were carded or otherwise well opened and then conditioned at 75F and 58% relative ~ 8 ~

.
.

1~8Z86~

humidity. Two grams of such alloy fiber~ were placed in one-inch diameter die, pressed to a thickness of 0.127 inch, and maintained in this condition for one minute.
This compressed pellet of fibers was removed from the die and placed on a p~rous plate of a Buchner funnel~
The upper surface of the pellet wa~ then engaged with a plunger which was mounted for free vertical movement, the plunger having a diameter of one inch and a weight of 2.4 pounds.
The funnel stem was connected by a flexible hose to a dropping bottle from wh~ch water was introduced into the funnel to wet the pellet of fibers. control over the water flow was exercised by the position of the dropping bottle. After an immorsion period of two minutes, the water was permitted to drain from the fiber pellet for three minutes, after which the still wet pellet wa3 removed from the funnel and weighed. One-half of the weight of water in the sample pellet is a measure of the fluid-holding capacity of the fibers, expressed in cc/g.
The test results of ~ample fibers, as described above, were as follows:

_ 9 _ .

FLUID-HOLDING
POLYVINYL- CAPACITY % W~TER
SAMPLE CELLULOSE PYRROLIDONE cc/q RE~ENTION
A 100 0 3.06 105 B 95 5 3.16 112 C 90 10 3.52 121 D 80 20 4.15 145 E 70 30 4.69 186 F 65 35 4.68 178 G 60 40 4.65 190 fiWATER RETENTION is the percent water retained by the loose mass of fibers after centrifuging the same at 1 G for 3.5 minutes.
EXAMPLE II
A 20~o aqueous solution of polyvinylpyrrolidone, designated a~ K-90 (GAF Corporation) and having an average molecular weight of 360,000 and a K-value of 80-100 ~ was injected into a viscose having a composition as de~cribed in Example I, after which the mixture was extruded a-~ a continuous tow and processed as described above. The relative propor-tions of cellulose and polyvinylpyrrolidone in the spinning solution were 83:17. The resulting fibers had a fluid-holding capacity (tested as in Ex. I) which was 28% higher than conventional regenerated cellulose fibers.
EXAMPLE III
Aqueous solutions of polyvinylpyrrolidone, desig-nated as K-90 (GAF Corporation) and having an average molecular weight of about 160,000 and K-value of 80-100, -- 10 - , i ~08Z866 : ~

were ~eparately injected into a viscose having a compo-13ition as de~cribed in Example I. In a manner a~
described in Example I, the mixtures of vi~cose and polyvinylpyrrolidone were shaped into a tow, treated ~ ,2~ -with an aqueous solution containing 1.0% Span ~e and then cut into staple fibers.
Two and one-half grams of the different fibers pre-pared as described above were separately made into tampons by the following procedure: The fibers were carded into webs, each having a length of about 6 inches and being of variable thickness and width. Each of these webs wa~ individually rolled in the direction of it3 width to provide a six inch roll and a string was looped about the center thereof. Each such roll was then folded on itself at the string loop and drawn into a l/2 inch tube within which it was compressed by a clamp and plunger. After compression, the resulting tampons were removed, allowed to stand for a period of about 30 minutes during which the tampons recovered to a bulk density of about 0.4 g/cc. and were then evaluated for their capacity to hold water by the Syngyna Method, a~ described by G.W. Rapp in a June 1958 publication of the Department of Research, Loyola University, Chicago, Illinois. The results of such test were as follows, for fibers made with various approximate proportions (tabulated below) of cellulose and polyvinylpyrrolidone in the spinning solution:

-h ~e~ tJ ~r~,/e ~4rk 1~8ZB66 FLUID-HOLDING
POLYVINYL- CAPACITY
~SAMP~E CEL~UIOSE PYRROLIDONE cc/g ~ 100 0 4.36 R 90 10 4 . 84 L 85 15 5 . 3 8 M 80 2 0 5 . 46 N 75 25 5.65 ~XAMPL~ IV
A conventional, non-derivatized viscose, an aqueous solution of polyvinylpyrrolidone and a carboxy-ethyl cellulose (specifically a cyanoethylated viscose) were prepared separately, The compositon of the non-derivatized vi~cose wa~ 9.0% rayon cellulose, 6~0%
sodium hydroxide and 32% carbon di~ulfide, ba~ed on the weight of the cellulose. This viscose had a ball fall of 56 seconds and its common salt test was 7.
The aqueous solution of polyvinylpyrrolidone was prepared simply by dissolving, in water, polyvinyl-pyrrolidone K-60.
Cyanoethylated viscose was prepared by premixing 8.25 lbs. of carbon disulfide and 10. 75 lbs. acrylonitrile (34% and 45%~ respectively, based on the weight of the cellulose), with the mixture then being charged into an evacuated churn by gravity through a valved stainles~
steel line. The churn contained a 77 lb. batch of alkali cellulose crumbs and was kept at a temperature of 15 to 32 C during a two hour reaction or churning period.
Sufficient water and caustic were added to the churn after the two hour reaction period to provide a viscose ~ 12 --' ' ' ~082866 of 8.0% cellulose and 6.0% ~odium hydroxide (caustic) ba~ed on the weight of the viscose, and 34% carbon cli~ulide and 45% acrylonitrile based upon the weight of the cellulose, after mixing in the churn for an additional one and three quarter hours. The resulting cyanoethylated viscose had a common salt test of 17-21 and a ball fall of 40-50 seconds. Its content of cellulose derivative recoverable on spinning into, or precipitation by, a sulfuric acid spin bath was about 90/0; tnis 9% value was used to calculate the proportions of such cellulo~e derivative (termed "CEC", for carboxy-ethyl-cellulose) in the table below.
Using conventional spinning equipment, the alloy-ing materials were injected into the non-derivatized vi~cose as hereafter set forth, with the resulting mixture being extruded through a 720 hole spinneret into an aqueous spinning bath consisting of 7 . 5% by weight of sulfuric acid, 1~3% by weight of sodium sulfate, and 3.5%
by weight of zinc sulfate. After passage through the spinning bath, the resulting continuous tow was wa~hed with water, desulfurized, acidified, and again washed with water in a manner as described in Example I. The still wet tow was cut into staple fibers which were treated with an aqueous solution containing 0.5% Span 20, dried, carded and then conditioned at 75F and 58%
relative humidity.
The fluid-holding capacity of sample unalloyed fibers and fibers containing the alloying components individually and in combination was determined using the test procedure described in Example I. The ~ id ~e ~ 13 ~

108Z8~6 approximate proportions in the spinning solutions u~ed for the unalloyed and alloyed fibers and the results of ~uch test~ were as follow~:

POLYVINYI.- FLUID-HOIil)ING
SAMPLE CELLUIOSE CEC PYRROLIDONE CAPACITIES cc/q.
A 100 0 0 3.06: 3.07; 3.14; 3.16 B 90 10 0 2.50; 2.55 C 80 20 0 2.95;3.3 D 60 40 0 3.35; 3.5 E 90 0 10 3.52, 3.53 F 70 0 30 4.68; 4.70 -G 75 12.5 12.5 5.03; 5.04 H 65 17.5 17.5 5.37; 5.39 It will be noted that conventional rayon fibers (Sample A), as produced from non-derivatized visco~e, exhibit fluid-holding capacities which are lesq than those of alloy fibers produced from a mixture of con-ventional vi~cose and polyvinylpyrrolidone (Samples E

and F) and that the fluid-holding capacities of fibers :
comprised of non-derivatized regenerated cellulose al~
loyed with regenerated cyanoethyl cellulose increase directly with the regenerated cyanoethyl cellulose content (Samples B, C and D). Significantly, notwith-standing the detrimental effects produced when the lower amounts of cyanoethylated viscose are employed alone as alloying agents, as illustrated by Samples B and C, such derivatized viscose, when combined with polyvinylpyr-rolidone, does provide for a synergism, as exhibited by the remarkably improved fluid-holding capacities of the three-component alloy fibers indicated as Samples G

.
:

and H.
q~he terminology "cyanoethylated viscose" as used herein refers to a viscose to which acrylonitrile i8 added or viscose prepared by the simultaneous cyanoethy-lation and xanthation of alkali cellulose. The latter procedure i9 preferred from the standpoint of economy and is described in United States Patents Nos. 3,143,116 to A.I. Bates and 3,525,733 to I.K. Miller. Regeneration of such cyanoethylated viscose is accomplished by use of a conventional acidic type coagulating and regenerating bath, as described above. Hydrolysis of the cyanoethyl group on the cellulose during aging and processing pro-duces predominantly carboxyethyl substituent groups on the cellulose in place of the cyanoethyl groups in the resulting regenerated product. The term "regenorated cyanoethyl cellulose" as employed herein refers to a regenerated product as produced by the cyanoethylated viscose described.
Reference to the average degree of substitution (D.S.) of the cyanoethyl cellulose as used herein in-cludes products wherein the anhydroglucose units of the cellulose molecules have an average substitution from about 0.25 to about 0.65 of cyanoethyl groups or chemical groups derived from said cyanoethyl groups by hydrolysis or other chemical change which occurs during manufacture and aging of the material. Thus, the recitation of cyanoethyl cellulose is also meant to include cellulose having carboxyethyl groups and some amidoethyl substituent groups.

-EXAMPLE v Example I was repeatedJ but instead of injecting the polyvinylpyrrolidone alone there was injected a blend of equal volumes of a ~h solution of the poly-~inylpyrrolidone in water with a ~/0 solution of sodium carboxymethyl cellulose ("CMC") (Hercules grade 7 MF :-~
in 6% NaOH, D.S. of 0.7). Various amounts of thi~ blend ~:
were used, specifically the proportions of cellulose;
polyvinylpyrrolidone, and carboxymethylcellulose were varied as follaws: 100:00; 95:2 1/2: 2 1/2; 90:5:5;
85:7 1/2: 7 1/2; 80:10:10. A portion of the resulting fibers was finished with a 1/2% water aolution of Span 20 (sorbitan monolaurate~; and then dried; a second portion was made somewhat alkaline by washing in 1% aqueous solution of ~odium bicarbonateJ then rinsed in water before finishing with the 1/2% Spa ~20 solution and drying. The presence of the additive gave improved fluid holding capacity (measured by the Syngyna test as in Example III above); for instanceJ the 80:10:10 blend treated with sodium bicarbonate gave a fluid holding capacity well above 6 cc/g.
EX~MPLE VI
Example I was repeatedJ but instead of injecting polyvinylpyrrolidone ("PVP") alone there was injected a blend of about 450 parts of a 6.7% aqueous solution of the polyvinylpyrrolidone K-90 and 550 parts of a 5.5%
aqueous alkaline solution of polyacrylic acid ("PAA").
The latter was made by diluting 120 gxams of Rohm &
Haas "Acrysol A-5" (a 25% aqueous solution of a poly-acxylic acid) with 338 ml of water, then adding a r~ rks 16 .

13toichiometric amount of alkali, namely 92 grams of 18%
aqueou~ Na0~ solution. The K-90 solution was then added to the polyacrylate solution with stirring and the resulting blend was a clear solution containing about 3%
of each of the polymers. Various amounts of the blend were used; specifically the proportions of cellulose;
polyvinylpyrrolidone; polyacrylic acid; were varied a~
follows: 100:00: 95:2 1/2: 2 1/2, 90:5:5, 85:7 1/2:
7 1/2: 80:10:10. A portion of the resulting fiber~ was finished with a 1/2% water solution of Span 20 and then dried. A second portion was made somewhat alkaline by washing in a 1% aqueous solution of sodium bicarbonate, then rin~ed in water before finishing with the 1/2%
Span 20 solution and drying. The presence of the addi-tives gave improved fluid holding capacity (measured by the Syngyna test as in Example 3 above); for instance, the 90:5:5; 85:7 1/2: 7 1/2; and 80:10:10 blends each gave a fluid holding capacity well above 6 cc/g.
When the polyacrylic acid was only partially neutra-lized (e.g. neutralized with only 70% of the stoichio-metric proportion of ~aOH) before blending with the polyvinylpyrrolidone the improvement was not as marked.
Thus with 85 parts cellulose, 7 1/2 parts PVP, 7 1/2 parts PAA (or 10 PVP and 5 PAA; or 5 PVP and 10 PAA the fluid holding capacity was about 20-25% better than the control (100 cellulose) when such partially neutralized PAA was used. It is therefore preferred that the amount of alkali present in the system be at least equal to or greater (e.g. 20-30% greater) than the amount necessary to neutralize all the acidic groups of the added ~¢~ c/e ~7~4 - 17 ~082866 anionic polymers.
EXAMPLE VII
Example I was repeated except that the solution injected was prepared as follows: A carboxyethyl starch ("CES") solution containing 9/0 starch was prepared (see Ex. 1 of ~ -U.S. 3,847,636) with enough acrylonitrile added to give a degree of substitution of 0.7. To a volume of this solu-tion was added an equal volume of 9% aqueous solution of PVP K-60. The resulting blend of polymer solution~ (as tabulated below) was used for injection into viscose and --subsequent spinning of fibers. The fibers were processed as described in Example I. To one portion a 1/2% Spa~20 was finish solution/applied and then the fibers were dried.
A second portion was immersed in 1% aqueous NaHC03, then in 1/2% Span~20 and dried.
The evaluation for fluid holding by the Syngyna test gave the following results.
FLUID HOLDING CAPACITY
CES (EXPRESSED WITHOUT WI~H
IN TERMS OF NaHC03 NaHC03 --SAMPLE CELLULOSE STARCH CONTENT PVP TREATMENT T~EATMENT
A 100 0 0 4.3 4.0 B 90 5 5 4.8 4.2 C 80 10 10 4.7 5.2 D 70 15 15 4.9 5.2 EXAMPLE VIII
Example I was repeated with the following changes:
The solutions for injection into the viscose were bo~
prepared as follows. A ~rbo~ starch (CES) solution was prepared as stated in Example VII. One solution for injection comprised equal parts of the J e h~ 18 above CES solution with 9/0 aqueous PVP K-90. A second l301ution for injection comprised three parts of the above CES ~olution with one part of a 9~/0 aqueous solution of PVP K-90. Fibers were then spun by blending with viscose (as tabulated below). ~he fibers were processed a~
described in Example I and finished in an aqueous solu-tion of 1/2% Na2HP04 and 1/2% Span 20. The fibers were dried and then evaluated.

CES
(EXPRESSED
rN TERMS OF FLUID HOLDING
SAMPLE CELLULOSE STARCH CONTENT) PVP CAPACITY
.
A 100 0 0 4.08 B B9.2 5.4 5.4 4.80 C 80 10 10 5.44 D 80 15 5 5.40 E 89.2 8.1 2.7 4.80 The more preferred fibers of this invention show a pH (measured in a mixture of 100 parts distilled water and one part of fibers) of well above 6 and generally at least about 7, such as about 8, 9 or 9.5.
It is within the broader scope of this invention to employ in place of all or part (e.g. 1/3, 1/2 or 2/3), of the polyvinylpyrrolidone, one or more other N-vinyl amide polymers, e.g. N-vinyl lactam polymers, N-vinyl-

2 oxazolidinone polymers or N-vinyl-3-morpholinone polymers such as the polymers (including copolymer~) listed in united States Patent 2,931,69~ issued April 5, 1960.
It will be noted that in the foregoing Examples, lOl~Z866 ~ ~ ~

the fibers, as spun, are unpigmented and undyed. It is of course within the broader scope of the invention, ~lthough not at all nocessary for practicing it, to incorporate pigments or dye into the spinning solution.
Fibers described in the above Examples had a denier per filament of about 3. It will be understood, of course, that the spinning may be effected to produce other deniers such as 1.5, 4, 5.5 and 8 denier per filament.
"

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Alloy rayon fibers of higher fluid-holding capacity than non-alloy rayon, which comprises a regenerated cellulose ma-trix and a water-soluble polymer dispersed therein in an amount sufficient to increase the fluid-holding capacity by more than 20%, the water-soluble polymer comprising an N-vinyl amide polymer.

2. Alloy fibers according to Claim 1, wherein the N-vinyl amide polymer is a polymer of one or more of the monomers vinylpyrrolidone, an N-vinyl-2-oxazolinone or an N-vinyl-3-mor-pholinone.

3. Alloy fibers according to Claim 1, wherein the N-vinyl amide polymer is polyvinyl-pyrrolidone.

4. Alloy fibers according to Claim 1, wherein a water-soluble anionic polymer is also dispersed in the matrix and where-in the weight ratio of N-vinyl amide polymer to anionic polymer is in the range of from 20:80 to 80:20.

5. Alloy fibers according to Claim 4, wherein the anio-nic polymer is a carboxylic group-containing polymer.

6. Alloy fibers according to Claim 5, wherein the anio-nic polymer is selected from salts of carboxyalkyl cellulose, salts of polyacrylic acids, salts of copolymers of acrylic acid and co-polymers of methacrylic acid with one or more other monomers, salts of copolymers of maleic or itaconic acid with vinyl methyl ether and naturally occurring algins.

7. Alloy fibers according to Claim 5, wherein the N-vinyl amide polymer is polyvinylpyrrolidone and the anionic polymer is carboxymethyl cellulose.

8. Alloy fibers according to Claim 5, wherein the N-vinyl amide polymer is polyvinylpyrrolidone and the anionic polymer is a salt of a polyacrylic acid.

9. Alloy fibers according to Claim 5, wherein the N-vinyl amide polymer is polyvinylpyrrolidone and the anionic polymer is a salt of a maleic copolymer.

10. Alloy fibers according to Claim 1, wherein the fluid-holding capacity in a Syngyna test is at least 5 cc/g.

11. Alloy fibers according to Claim 1, wherein the fluid-holding capacity in a Syngyna test is at least 5.5 cc/g.

12. Process for making alloy rayon fibers, of higher fluid-holding capacity than non-alloy rayon, comprising a regene-rated cellulose matrix and a water-soluble polymer dispersed there-in in an amount sufficient to increase the fluid-holding capacity by more than 20%, the water-soluble polymer comprising an N-vinyl amide polymer, said process comprising spinning into an aqueous coagulating bath consisting essentially of H2SO4, Na2SO4 and ZnSO4, a blend of viscose and the water-soluble polymer to form fibers, the proportions of said dispersed polymer being at least about 7% of the total.

13. The process according to Claim 12 in which said dispersed polymer is at least about 10% of the total.

14. The process according to Claim 12, wherein the fluid-holding capacity in the Syngyna test is at least 5cc/g and the N-vinyl amide polymer is a polymer of one or more of the monomers vinylpyrrolidone, N-vinyl lactam, a N-vinyl-2-oxazolidinone or a N-vinyl-3-morpholinone.

15. The process according to Claim 12, wherein the water-soluble polymer includes a water-soluble anionic polycarboxylic po-lymer selected from the group consisting of salts of carboxyalkyl cellulose, salts of copolymers of acrylic acid and copolymers of methacrylic with one or more other monomers, salts of copolymers of maleic or itaconic acid with vinyl methyl ether and naturally occurring algins, and wherein the weight ratio of N-vinyl amide polymer to anionic polymer is in the range of from 20:80 to 80:20.

16. The process according to Claim 15, in which said N-vinylamide polymer comprises polyvinylpyrrolidone.

17. The process according to Claim 16, in which the anionic polymer comprises carboxymethyl cellulose.

18. The process according to Claim 16, in which the anionic polymer comprises a salt of polyacrylic acid.

19. The process according to Claim 16, in which the anionic polymer comprises a vinyl methyl ether-maleic acid co-polymer.

20. Alloy fibers according to Claim 1, when formed into a shaped article.

21. Alloy fibers according to Claim 1, when formed into a vaginal tampon.

22. The process according to Claim 16, wherein a mass of the alloy rayon fibers are formed into a vaginal tampon.