1~91411 The present invention is directed to alkaline alloy fibers having high fluid-holding capacity, to shaped artic-les 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 ~egenexated 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. ~imilarly, "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 of such fiber mass.
In accordance with the present invention, there is provided a high fluid-holding alkaline alloy fiber which comprises a regenerated cellulose matrix and dispersed therein from about 5% to about 30~, based on the weight of the cellulose, of an additive capable of increasing the fluid-holding capacity of the fiber, the proportion of the additive being such that the fluid-holding capacity of
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the fiber is at least 4.79 cc/g, and which is characterized in that the sole additive is an alg~nic acid salt Of an alkali metal~
the fiber preferably has a lubricating finish for cellulose thereon. The ~iber is prepared by mixing a fiber-forming cellulose with from about 5% to 30% by weight of the cellulose with an alginic acid salt oi an alkali metal, forming the mixture into fibers, coagulating and regenerating the shaped fibers, and therea~ter drying the same in an alkaline state, Viscose constitutes the major portion of the mixture and the shaped alloy iibers are coagulated and regenerated by known means, and pre~erably in an acid bath containing sulfuric acid and sodium sulfate. Zinc sul~ate is often incorporated in the bath as well as other coagulation modifiers, as desired.
No 8pecial iinishe8 and/or drying procedures are required to render the alloy ~ibers into a form which can be carded without diiiiculty.
The viscose which is employed in making the alloy iibers is, desirably, oi a composition as is used in making conventional regenerated cellulose ~ibers.
Suitable alkali metal salts of alginic acid give viscosities in the range oi' 20 to 150 seconds and prefer-ably in the range oi 40 to 80 seconds (measurement oi vis-cosity by time ~or a 3mm diameter steel ball to iall 20 cm through the solution) in dilute NaOH or aqueous solutions oi an alginate concentration of 2 to 15%, preferably be-tween 8 and 10%, The pH of the solution is preferably about or above seven.
The alginate containing solution is incorporated '~,:
directly into a viscose and is employed in relatively large quantities, ranging from about 5% to about 30%, preferably at least 10%, based upon the weight of the cellulose in the viscose. Fibers formed from a viscose containing less than about 5% of a useful alginate do not differ appreciably from conventional regenerated cellulose fibers in their fluid-holding capacity.
The aqueous solutions of alkali metal salts of alginic acid may be injected into the viscose as it is pumped to spinnerets for extrusion or, alternately, aqueous solutions of such alginates and viscose may be passed through a blender or homogenizer if it is necessary to secure a more uniform dispersion. After the spinning, coag-ulation and regeneration stages, the shaped continuous multi-filament fiber tow undergoes the usual processing, which may include stretching, if desired, and is then dried by con-ventional means. Generally, before drying, the continuous multifilament fiber tow is cut into staple of a desired length.
In general, the resulting alloy fibers experience no bonding during drying, and can be subsequently carded with no difficulty by the manufacturer of absorbent articles incorporating such fibers. Alternatively, after coagulation and at least partial regeneration, the fibers are stretched, if desired, conventionally wet processed and treated with an aqueous lubricating finish composition. The fibers are then dried to an alkaline, cardable product. In the pre-ferred method of this invention, the sodium ~ -4-\- 1091411 alginate dispersed in viscose, during processing into fibers, is alternately in the alkaline state, the acid state and again the alkaline state. During passage of the modified viscose through the acidic coagulating and regenerating bath, the sodium alginate is acidified. In order to obtain alkaline fibers containing sodium algi-nate, as required by the invention, the wet gel fibers are made alkaline preferably in a bath preceding the finish bath or, if desired, in the finish bath.
Sodium salts of alginic acid, suitable for use in this invention, are commercially available from the Kelco Division of Merck & Co., under the designation *
"Keltex" alginates, sold in various grades as determined by viscosity and concentration in aqueous dispersions.
EXAMPLE I
Using conventional rayon spinning equipment, an alkaline aqueous solution of sodium alginate was sepa-rately injected by a metering pump into a viscose stream during its passage through the blender, and the blend was thereafter extruded into a spinning bath.
Preparation of a 10~ concentration of sodium algi-nate solution was as follows: 300 g. of sodium alginate (KELTEX) high viscosity technical grade "Kelco" alginate were added to 300 ml of 18% concentration of aqueous sodium hydroxide plus 90 ml of 30% concentration hydro-gen peroxide. The peroxide serves to reduce molecular weight and viscosity. This system, after mixing with a spatula, was added to 2250 ml of water, while stirring, *registered trade marks - - -~091411 and mixed for two hours.
After overnight standing at room temperature, it was mixed again for two more hours. The ball-fall viscosity after 48 hours was 24 seconds. The polymer was added to the viscose and spun by injection, as described above. During this stage, the blend was subjected to high mechanical shearing. The viscose composition was 9.0% cellulose, 6.0%
sodium hydroxide and 32% carbon disulfide (based upon weight of cellulose). The viscose ball-fall viscosity was 61 and its common salt test was 6.6.
The mixtures of viscose and sodium alginate were extruded through a 980 hole spinneret into an aqueous spin-ning bath consisting of 7.5% by weight of sulfuric acid, 20%
by weight of sodium sulfate, and 1.5% by weight of zinc sulfate. After passage through the spinning bath, the result-ing continuous fiber tow was washed with water, d~sulfurized with an aqueous solution of sodium hydrosulfide, and again washed with water. The still wet multifilament fiber tow was cut into staple fibers and finished with a solution com-prising 1% NaHC03, 0.5% "Span 20"* sorbitan monolaurate sur-factant and water. The fiber was then dried.
The fluid-holding capacity of sample fibers, made with various approximate proportions (tabulated below) of cellulose and sodium alginate in the spinning solution, was determined by the following test procedure.
Two and one-half grams of the different fibers pre-pared as described above were separately made into vaginal *registered trade mark ~ 1091411 tampons by the following procedure: The fibers were carded into webs, each having a length of about 15cm and being of variable thickness and width. Each of these webs was individually rolled in the direction of its width to provide a 15cm 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 12mm 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 b~lk density of about 0.4 g/cc. and were then evaluated for their capacity to hold water by the Syngyna Method, as described by G. W.
Rapp in a June 1958 publication of the Department of Research, Loyola University, Chicago, Illinois. The re-sults of such test are set forth in Table I for fibers made with various approximate proportions (as tabulated in Table i) of cellulose and sodium alginate in the spin-ning solution.
EXAMPLE II
An aqueous solution of sodium alginate (prepared from a granular form supplied by Kelco)was made by dis-solving "Keltex" in water to give 3% solution. The solu-tion was injected into viscose, whereby the spinning solution contained 11.1% sodium alginate, based on cellu-lose. The fibers produced were subsequently processed in different ways and evaluated for fluid-holding cap-acity.
*registered trade mark 7 .. .
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, 1C~91411 A portion of the resulting rayon tow was treated with 1% aqueous Na2CO3 and 1% "Span 20" * in one solution, and dried. Sample staple fibers were carded, or otherwise well opened, and then conditioned at 24C and 58% relative humidity. Two grams of such alloy fibers were placed in a 25mm diameter die, pressed to a thickness of 3.2mm, and main-tained in this condition for one minute. This compressed pellet of fibers was removed from the die and placed on a porous plate of a Buchner funnel. The upper surface of the pellet was then engaged with a plunger which was mounted for free vertical movement, the plunger having a diameter of 25mm and a weight of l.lkg.
The funnel stem was connected by a flexible hose to a dropping bottle from which 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 immersion period of two minutes, the water was per-mitted to drain from the fiber pellet for three minutes, after which the still wet pellet was 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. This measurement is defined as ~ the potential ratio.
; A blend of equal parts of this sample fiber with a i three denier crimped rayon had a potential ratio for 4.28 cc/g when measured by known procedures such as that dis-closed in U.S. Patent No. 3,046,983 to Smith. The rayon control sample had a potential ratio of 2.7 cc/g when measured in the same manner with no alginate loading.
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The aqueous alkaline l~bricating finish is often a bath containing an agueous solution of sodium carbonate and soxbitan monolaurate; however, other alkaline agents and lubricating agents may be employed as taught in the art for ordinary rayon yarn. Alternatively, good con-trol of product and process is maintained by separating the alkalizing and finishing treatment steps.
Some examples of finishes for cellulose fibers in-clude partial higher fatty acid esters of sorbitan or mannitan and their polyoxyethylene derivatives, sodium oleate and oleic acid. Some examples of alkaline agents for alkalizing the fibers include dibasic ammonium phos-phate, dibasic sodium phosphate, tribasic sodium phos-phate, and sodium tetraborate.
The alloy fibers are adapted for use in a variety of articles, such as sanitary napkins and tampons, in which high fluid retention is an essential characteristic. In the manufacture of 8uch articles, the alloy fibers neces-sitate no special techniques or equipment and they may be blended with other fibers which may or may not enhance the absorbent properties of the resulting articles.
_g_ 1C~91411 TABL~ I
FLUID-HOLDING
SODIUM CAPACITY
SAMPLE CELLULOSE ALGINATE cc/g A 100 0 4.0 B 90 10 4.79 C 80 20 5.34 D 70 30 4.92 E 60 40 4.51