US 3844287 A
A mass of alloy fibers of polyacrylic acid salt of alkali-metals or ammonium and regenerated cellulose, useful for absorbing fluids, are prepared by mixing a caustic solution of polyacrylic acid with viscose, spinning the mixture into fibers and obtaining dry fibers in the alkaline state. The fibers are advantageously dried with an alkaline lubricating finish thereon and then processed into dressings, sanitary napkins, tampons and diapers.
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Elite rates Smith Get. 29, 1974 ABSORBENT MASS 0F ALLUY FIBERS OF REGENERATED CELLULOSE AND POLYACRYLHC ACllD SALT 0F ALKALll-METALS 0R AMMONIUM  Inventor: Frederick R. Smith, Wilmington,
 Assignee: FMC Corporation, Philadelphia, Pa.
 Filed: June 5, 1972  Appl. No.1 259,944
 U5. Cl 128/285, 128/270, 128/296, 260/17.4
 Int. Cl. A611 13/20  Field of Search 128/263, 270, 285, 284, 128/290, 296; 260/174  References Cited UNITED STATES PATENTS 2,993,018 7/1961 Steinlin 260/17.4
3,187,747 6/1965 Burgeni et a1. 128/285 3,628,534 12/1971 Donohue 128/285 3,669,103 6/1972 Harper et a1.... 128/284 3,670,731 6/1972 Harmon 128/284 3,686,024 8/1972 Nankee et al 117/140 Primary Examiner-Dalton L. Truluck 5 7 ABSTRACT 5 Claims, No Drawings ABSORBENT MASS OF ALLOY FIBERS OF REGENERATED CELLULOSE AND POLYACRYLIC ACID SALT F ALKAlLl-METALS 0R AMMONHUM Alloy fibers consisting of sodium carboxymethyl cellulose and regenerated cellulose have been used as absorbent fibers in articles designed to absorb body fluids. While these alloy fibers are quite useful for this purpose, they are relatively expensive. The carboxymethyl cellulose-regenerated cellulose fiber is difficult to dry down to cardable form from an aqueous system. These fibers may be readily finished and dried by solvent exchange but this adds considerably to the cost of manufacturing the fibers.
It is an object of this invention to provide a highly fluid absorbent mass of alloy fibers of sodium polyacrylate and regenerated cellulose.
It is another object of this invention to provide a method of preparing absorbent alloy fibers of sodium polyacrylate and regenerated cellulose.
These and other objects are accomplished in accordance with this invention which is an article of manufacture comprising a highly fluid absorbent mass of alloy fibers, said fibers comprising a matrix of regenerated cellulose and sodium polyacrylate uniformly dispersed therein.
The alloy fibers are prepared by mixing an aqueous solution of sodium polyacrylate or aqueous solution of sodium hydroxide and polyacrylic acid with viscose at any stage of ripening, forming the mixture into fibers, coagulating and regenerating the fibers, and drying the fibers in the alkaline state. Advantageously, the fibers are coagulated and regenerated in an acid bath, washed, finished by application of an aqueous alkaline finish composition for cellulose, and dried. These fibers are now alkaline and cardable, and are prepared in a conventional manner into articles for absorbing body fluids.
Sodium polyacrylate solutions or polyacrylic acid emulsions are readily commercially available and need not be described in detail. The solutions which are mixed with the viscose preferably have solids concentrations of from about 2.5 to about 42 I3 percent. Sodium hydroxide is added to polyacrylic acid emulsions to obtain the sodium polyacrylate solutions.
The filament-forming viscose used herein is also well known and need not be described in detail. In general, alkali cellulose is reacted with carbon disulfide and the resulting sodium cellulose xanthate is diluted with sodium hydroxide to produce the viscose which is aged to spinning viscosity. Additives or modifiers may be mixed with the viscose, if desired.
The alloy fiber which is formed predominantly from viscose is coagulated and regenerated by known means and preferably in an acid bath containing sulfuric acid and sodium sulfate. Zinc sulfate is often incorporated in the bath as well as other coagulation modifiers, as desired.
The sodium polyacrylate solution may be mixed with the viscose will preferably range from about 6 to about lOpercent based on the weight of the viscose solution.
After injection or mixing of the sodium polyacrylate into the viscose, the mixture may be run through a blender or homogenizer to assure a thorough mix, if desired. The mixture is then pumped to the spinneret and extruded in the form of fibers into a coagulating medium. 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 preferred method of this invention, the sodium polyacrylate containing viscose during processing into fibers is alternately in the alkaline state, the neutralized state and the alkaline state. During passage of the viscose solution through the acid coagulating and regenerating bath, the sodium polyacrylate is neutralized. In order to obtain fibers containing sodium polyacrylate as required by the invention, the wet gel fibers are made alkaline preferably in the finish bath. An alkaline bath preceding the finish bath may also be used, if desired.
The aqueous alkaline lubricating finish is preferably a bath containing an aqueous solution of sodium carbonate and sorbitan monolaurate, however, other alkaline agents and lubricating agents may be employed as taught in the art for ordinary rayon yarn. Some examples of finishes for cellulose fibers include 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 phosphate, dibasic sodium phosphate, tribasic sodium phosphate, sodium tetraborate and the like.
The fiber is usually cut in the form of staple before drying, dried and shipped to the manufacturer of the absorbent articles. The absorbent articles may require carding of the fibers which is accomplished in the usual manner without difficulty.
ln tampon application, the fibers are formed into the tampon in accordance with any desired procedure. They may be blended with any other fibers which may or may not serve to enhance the properties of the absorbent articles. Some fibers with which the alloy fibers of this invention may be blended include rayon, cotton, chemically modified rayon or cotton, cellulose acetate, nylon, polyester, acrylic, polyolefin and similar fibers.
The fluid holding capacity of the alloy fibers of this invention was determined in accordance with the following procedure.
Sample staple fibers are carded or well opened, conditioned and two grams placed in a 1 inch diameter die.
' The fibers in the die are then pressed to 0.127 inches the viscose at any stage of the viscose ripening. Con- I thickness for one minute, removed and placed on a porous plate (e.g., a Buchner funnel) so that the 1 inch diameter foot of a plunger weighing 2.4 pounds rests on the test pellet. (The plunger is held in a vertical position and is free to move vertically). The pellet is then wetted with water which flows into the funnel from the stem which is connected by a flexible tube to a dropping bot tle, the flow of water being controlled by the position of the dropping bottle. After two minutes immersion, the water is drained for three minutes, the wet pellet is removed and weighed. The fluid holding capacity of the fibers in cc./g. is one-half the weight of water in the test pellet.
To demonstrate this invention, the following example is set forth.
Example A sodium polyacrylate solution (12.5 percent solids having 10,000 to 20,000 cps. viscosity) was injected through a metering pump into the viscose stream of a spinning machine. The viscose composition was 9.0 percent cellulose, 6.0 percent sodium hydroxide and 32 percent carbon disulfide, based on the weight of the cellulose. The viscose ball fall was 70 and its common salt test was 8.
The mixture was spun through a 720 hole spinneret into an aqueous spinning bath consisting of 7.5 percent by weight of sulfuric acid, 18 percent by weight of sodium sulfate and 3.5 percent by weight of zinc sulfate. The alloy fibers passed through the bath and were washed with water, desulfurized and washed again with water. The wet gel fibers were then passed through an alkaline finish bath consisting of 1 percent by weight of sodium carbonate and 1 percent by weight of sorbitan monolaurate (Span 20). The fibers were cut, dried and carded. The fluid holding capacity was tested for fibers having different amounts of sodium polyacrylate in the alloy fibers in the previously described test procedure. The results are set forth in the following table along with results for other fibers prepared as above except that these alloy fibers were prepared with polyacrylic acid without the formation of the sodium salt in the dried fiber product.
Table Sodium polyacrylate. 71 B.O.C.*
Fluid held, ccjg. 2.75 4.55 6.05 Polyacrylic acid. B.O.C.* 0 I0 20 Fluid hcld. :c./gv 2.50 3.25 3.85
B.O.C. Based on the weight ol the cellulose in the alloy fiber.
From the above data, it is seen that the absorbent mass of alloy fibers, as disclosed herein, has good fluid holding capacity and the sodium salt is necessary to provide distinctly better fluid holding results.
While this invention has been described in terms of sodium polyacrylate, polyacrylate salts of other alkalimetals such as potassium and lithium, and ammonium are also included and may be successfuly used to replace sodium polyacrylate in the example.
Various changes and modifications may be made in practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.
1. An article of manufacture comprising a highly fluid absorbent mass of alloy fibers, said alloy fibers comprising a matrix of regenerated cellulose and polyacrylic acid salt of alkali-metals or ammonium uniformly dispersed therein.
2. The article of claim 1 wherein the polyacrylic acid salt of alkali-metals or ammonium is present in the regenerated cellulose in an amount ranging from about 5 to about 35 percent, based on the weight of the cellulose.
3. The article of claim 1 wherein the fibers have a lubricating finish for cellulose thereon.
4. The article of claim 1 in the form of a pad.
5. The article of claim 1 in the form of a tampon.
. UNITED- STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3.844.287 Dated October 29, 1974 Inv nt Frederick R. Smith pears in the aboveidentified patent It is certified that error ap rected as shown below:
and that said Letters Patent are hereby cor "42" should be omitted.
"successfuly" should read --successfully-.
Col. 1, line 44, C01. 4, line 13,
Signed and sealed this 11th day of February 1975.
, (SEAL) 'Attest:
C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks FORM PO-1050 (10- 9) I USCOMM-DC 60376-P69 LLS. GOVERNMENT PRINTING OFFICE: i969 0-366-33,
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