US 3241553 A
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fluid which can be absorbed by such products.
,pact the material.
United States Patent 3,241,553 SURGICAL DRESSING Fred H. Steiger, East Brunswick, N.J., assignor to Johnson & Johnson, a corporation of New Jersey No Drawing. Filed Aug. 27, 1962, Ser. No. 219,764 13 Claims. (Cl. 128-156) This invention relates to absorbent products for absorbing body fluids and more particularly to fibrous absorbent products having improved fluid-absorbency and fluid-retention characteristics.
Absorbent products for absorbing body fluids, such as tampons, santitary napkins, dressings and dental packing, are usually made from such absorbent fibrous materials as cotton and rayon. The intended use of such absorbent products determines their sizes; in many instances, their sizes cannot exceed certain maximums. For example, tampons and dental packing are made in sizes sufliciently small to permit them to be easily inserted into and removed from the openings within which they are positioned in use. The sizes of sanitary napkins are established by the size of the body area adjacent to which they are placed.
Since the sizes of such products are, to a large extent, predetermined, the amount of absorbent material which they contain and, accordingly the amount of fluid which they can absorb, is also, in etfect, predetermined. Generally, if a product of a given material is made smaller, its absorbing capacity will be reduced. And, conversely, if it is desired to make the product more absorbent, its size is increased. In either event, in the interests of economy, it is desirable to use as little material as possible, consistent with adequate absorbency.
Ways have been sought to increase the amount of This may be accomplished by either increasing the amount of absorbent material in the product, or by increasing the absorbing capacities of the materials used. For example, within limits, by increasing the amout (weight) of the absorbent fibers within a given volume, i.e., by increasing the density of the product, the absorbing capacity of the product may be increased. However, in order to increase the amount of absorbent material present, while maintaining its size constant, it is necessary to compress or com- This compression tends to produce effects which decrease the absorbing capacities of the products. A point can be reached where the reduction in absorbing capacity due to compression exceeds the increase in absorbing capacity obtained due to the additional weight of fibers. Thus, even though such fibers are compressed to increase the absorbing capacity of the product, the size limitations of the product still establish the amount of absorbent fibrous material which may be incorporated therein.
Another factor affects the functioning of these products. In use, they are generally subjected to external pressures. For example, vaginal tampons and sanitary napkins are subjected to body pressures when they are worn. Since most of the absorbed fluid is held Within the interstices between the fibers, externally applied pressures compact the fibers and thereby reduce the size of the interstices. As a result, some of the fluid is squeezed out. An absorbent product for absorbing body fluids should desirably not only be capable of absorbing large amounts of fluid for a given size, but should also be capable of retaining at least a major portion of the fluid absorbed. In addition,
the materials used in such products must be non-toxic and non-irritating, and be otherwise compatable with the conditions of use.
I have discovered that absorbent fibrous products for absorbing body fluids having superior absorbing and fluidretention characteristics may be obtained by including in such products wet cross-linked cellulosic fibers, i.e., cellulosic fibers which have been cross-linked while in a swollen state. In accordance with my invention, there are provided absorbent fibrous products which not only have markedly improved absorbency characteristics, but also have the ability to retain greater amounts of absorbed fluids when subjected to pressures which tend to squeeze out the fluids absorbed. In that form of invention where the absorbent fibrous products are in a compressed form, the products are capable of expanding to a greater extent when they absorb fluids than similar products formed from conventional fibers. This latter characteristic is of particular importance in compressed, absorbent fibrous products, such as tampons.
The fibers which are included in the products incorporating my invention are water-insoluble, wet crosslinked cellulosic fibers and include wet cross-linked natural fibers, such as cotton, wood pulp and cotton linters and wet cross-linked regenerated cellulosic fibers, such as rayon. The cellulosic fibers are subjected to a chemical treatment whereby they are chemically modified to form bonds between the hydroxyl groups in the cellulose molecules which impart to the products within which they are incorporated increased fluid-absorbing and fluidretention characteristics.
Cross-linked cellulosic fibers may be obtained by reacting cellulosic fibers with a material one molecule of which is capable of combining with at least two hydroxyl groups in the cellulose molecule, or in adjacent cellulose molecules. The reactive groups of the cross-linking agent which combine with the hydroxyl groups may exist prior to the reaction with cellulose, as in the case of glyoxal, or they may be generated during the reaction with the cellulose, as in the case of the sodium thiosulfate derivative of divinyl sulfone. In order to cross-link cellulose, the cross-linking agent must be at least difunctional with respect to cellulose, e.g., it must react with at least two hydroxyl groups. Formaldehyde, for example, is monofunctional with regard to many substances; it is, however, difunctional with respect to cellulose. In many polyfunctional materials of the type that react with two or more hydroxyl groups, one reactive group of the polyfunctional material may react more rapidly than other groups. Consequently, within a given reaction time, not all of the reactive groups on a molecule of the polyfunctional material may react with the hydroxyl groups in the cellulose molecule to form cross-links; only one of the reactive groups may so react. Cross-linking occurs when at least two of the reactive groups in a molecule of the polyfunctional material react.
Cellulose can be cross-linked in a number of ways and, in accordance with current concepts, may be dry crosslinked or wet cross-linked. The two types of cross-linking refer to the manner in which the cross-linking is done.
Dry cross-linked cellulose is obtained when the cellulose is in a collapsed state at the time of cross-linking. A collapsed state is obtained by removing most or all of the water which causes the fiber to swell. In one known procedure, the cellulose is passed through a boric acid solution, dried, and then heated in a sealed tube in the presence of paraformaldehyde. The fibers are then washed free of unreacted material. A more common technique is to apply the cross-linking agent and a catalyst to the cellulose in an aqueous bath, drive off the water in a drying step, and react the Cross-linking agent with the cellulose in a subsequent curing step.
Wet cross-linked cellulose is obtained when the crosslinking agent is reacted with the cellulose while the cellulose is in a swollen state. Ordinarily, the cellulose is maintained in a swollen state by water which is present during the reaction. However, techniques have been developed whereby the cellulose can be maintained in a swollen state in the absence of water by using in lieu thereof an inert, nonvolatile substance. Cellulose fibers so treated have the properties of wet cross-linked cellulose even though the reaction takes place in the absence of significant amounts of water.
Wet cross-linked and dry cross-linked cellulosic fibers can be distinguished. The strain recovery of a dry crosslinked cellulosic fiber, the crease recovery of a fabric of such fibers, and the compressional recovery of a bat of such fibers is significantly greater than that of untreated cellulose, both in a conditioned dry state and in a wet state. In the conditioned dry state, these characteristics of wet cross-linked cellulose are essentially the same as those of untreated cellulose. When in the wet state, how ever, wet cross-linked cellulose is much more resilient than untreated cellulose in the wet state.
A dyeing test may also be used to distinguish wet crosslinked from dry cross-linked cellulosic fibers. In this test, samples of wet cross-linked cellulose, dry cross-linked cellulose and untreated cellulose, all in the same moisture state, either conditioned dry or dripping wet, are immersed into a boiling solution containing one percent of Calcomine Sky Blue FF EX. Conc., a dye supplied by American Cyanamid Company. After one minute of thorough agitation, the samples are removed and rinsed in cold water until the rinse water is free from traces of the dye. Wet cross-linked cellulosic fibers dye darker than untreated cellulosic fibers while dry cross-linked fibers dye lighter.
The following are illustrative examples of ways of making wet cross-linked fibers which are incorporated into the products of this invention:
Example I 200 grams of #2 peeler comber, bleached cotton staple having an average fiber length of about /2 inch are immersed for ten minutes at 80 C. in a glass vessel containing 7 /2 liters of an aqueous solution containing, by volume, 95% Formalin and concentrated sulphuric acid. The fibers are then removed from the treating solution and thoroughly rinsed, first with hot water, and then with cold water. The treated fibers are then airdried, or dried in a forced-air oven at 240 F.
Example II 200 grams of 3 denier, bleached, crimped, dull rayon staple, 1 /8 inches long, such as the type available from American Viscose Corporation under the designation SN- 2269, are immersed in 7 /2 liters of aqueous solution containing, by volume, Formalin, 50% concentrated hydrochloric acid and water at room temperature for a period of twenty minutes, and then removed, rinsed and dried in accordance with Example I.
The Formalin referred to in both examples contains 37% formaldehyde and 63% water.
In each instance, the unreacted formaldehyde is removed by thoroughly rinsing the treated fibers. The time and conditions of treatment of the fibers may be varied to provide fibers having varying characteristics with respect to absorbency. For example, it was noted that by treating the rayon staple in the solution described in Example II for a period of four minutes, the absorbing capacity of the fibers is markedly improved. Treating for a period of eight minutes produced a still greater increase in absorbing capacity. Treating for a period of fifteen minutes produced fibers with a slightly greater absorbing capacity than that obtained in the eight-minute treatment. Still longer treatment times produced fibers whose absorbing capacities were not distinguishable from that of the fibers which were treated for fifteen minutes.
By treating at elevated temperatures, the time of treatment may be reduced and, conversely, by reducing the temperature, the time of treatment should be extended to obtain fibers having equivalent characteristics. Generally, for practical purposes it is desirable to treat the fibers at room temperatures. The procedure set forth in Example II is preferred because elevated temperatures are not required, although the time of treatment may be somewhat longer than that described in Example I, and although the concentration of the acid catalyst is higher. Rayon is preferred because it appears more susceptible to wet cross-linking.
The nature of the bond which results from cross-linking cellulose is believed generally to be represented by the following formula:
-CELLULOSE- This linkage, which in the illustration is a methylene bridge between hydroxyl groups, does not necessarily occur uniformly or completely throughout the cellulosic fiber.
The illustration does not distinguish between dry crosslinked and wet cross-linked cellulose. According to present theories, it is believed that the difference between dry cross-linked cellulosic fibers and wet cross-linked cellulosic fibers is in the distribution of the cross-links within the fibers. For example, in the case of cotton fibers, it is believed that dry cross-linking takes place between the lamellae, while wet cross-linking occurs within or at the surface of the microfibrils.
The absorbing capacities of compressed bodies made from wet cross-linked, dry cross-linked and untreated cellulosic fibers have been compared. It was determined that the absorbing capacities of products made from dry cross-linked cellulosic fibers are about the same as the absorbing capacities of products made from untreated cellulosic fibers and that the absorbing capacity of each is considerably lower than that of products made from wet cross-linked cellulosic fibers.
The fibers treated in accordance with Examples I and II were formed into articles embodying the invention which were then tested to compare their absorbing capacities with the absorbing capacities of like articles containing untreated fibers. T 0 this end, a series of tampons were made by carding both treated and untreated fibers, forming the card webs into strips six inches long, and weighing 40 and 50 grains, tying each strip with a piece of string at the midpoint of their length, folding the strips in half at the midpoint of their length, placing the folded strips into a cylindrical die having an inside diameter of 0.533 inch and then compressing the strips mainly in the direction of their length into the elongated, cylindrical shape of a tampon. The 40 grain tampons so made were approximately 0.56 inch in diameter and 1.6 inches long and the 50 grain tampons were approximately 0.58 inch in diameter and 1.6 inches long. The tampons were then tested by measuring the amount of fluid absorbed by each in the apparatus and in accordance with the method de scribed below.
A tampon to be tested was placed into a porous plate Buchner funnel. A resilient rubber surface which snugly fits within the funnel is lowered to contact the tampon and pressure equal to about 24 inches of water is applied to the tampon through the resilient rubber surface. The test fluid (sp. gr. 1.04) is introduced upwardly through the stem of the funnel and just covers the test tampon. Absorption is permitted to take place at the 24 inch water pressure for 5 minutes. The test fluid is then removed and the test tampon is permitted to drain for 1 minute under the 24 inch water pressure. The pressure is then removed and the wet tampon is removed and quickly weighed. The volume of fluid absorbed by the tampon is determined by subtracting the weight of the tampon before testing from its weight after testing and dividing the difference by the density of the fluid.
The following results were obtained:
The above results conclusively establish the vast improvement in absorbing capacities of tampons made in accordance with invention as compared to tampons made from like, untreated fibers.
I have arrived at a tentative hypothesis as to the reason for the observed differences between the absorbing capacities of bodies made from untreated cellulosic fibers and fibers which have been cross-linked in the wet state. The absorbing capacity of a fibrous body does not depend to any large extent upon the amount of fluid which may be held within the fiber but is determined primarily by the amount of fluid which can be held within the interstices between fibers. When the fibers are compressed in forming the body, the volume of these interstices is reduced. If the fibrous body remains in its compressed form when wet, the quantity of fluid which can fill the interstices is limited. Therefore, it is desirable to use in such bodies fibers which have such resiliency as to cause the body to expand when wet.
On the other hand, if the fibers have such resilience that the volume of the body increases immediately after it is compressed when dry, it is diflicult to maintain the volume of the body constant. In order to compress such resilient fibers, it may be necessary to use compressive forces of such magnitude that the resilience of the fibers when Wet is appreciably reduced. Thus, it is not only desirable that the fibers can be compressed to form a fibrous body which will maintain a substantially constant volume after compression, but also that such fibers have a high resilience in the wet state to permit the body to expand. Untreated cellulose has a relatively low resilience both in the dry state and wet state, and thus, although easily compressible when dry, does not expand as much as either wet or dry cross-linked cellulose when wet. With respect to untreated cellulose, dry cross-linked cellulose has a relatively high resilience both in the dry state and in the wet state and is therefore more difficult to compress when dry. Wet cross-linked cellulose, however, has, with respect to untreated cellulose, about the same low resilience in the dry state and can thus be easily compressed, and has a relatively high resilience in the wet state, and thus expands to a greater extent after compression.
Other agents for cross-linking cellulose may be used in place of form-aldehyde. Examples of such materials are dichloroacet-ic acid, dichloropropanol-Z, diepoxides, such as butadiene, diepoxide, and polyepoxides, such as the com-pound marketed by Shell Chemical Company under the name EPONITE 100, N-methylol acrylamide, and
divinyl sulfone. All of the above materials require alkaline catalysts, such as sodium hydroxide, to produce wet cross-linked cellulose. It is preferred, however, to use formaldehyde in making wet cross-linked cellulose, because, first, several of the above alkaline catalyzed materials have limited storage stability. In contrast, treatment baths of the type indicated in Example II containing acid catalysts can be used after storing for as long as six weeks without significant loss of cross-linking effectiveness. Second, materials such as dichloropropanol-Z, butadiene diepoxide and divinyl sulfone .tend to be unpleasant and difiicult to handle; they may also be toxic. While formaldehyde does have an unpleasant odor, industry, through long association with formaldehyde and resins made from formaldehyde, has learned how to handle it. Third, formaldehyde is comparatively inexpensive.
It is important that the fibers be in a swollen state at the time of cross-linking in order to obtain wet crosslinked cellulose. Preferably, this swelling is achieved by cross-linking in the presence of water. While other swelling agents for cellulose are known, water is preferred because it is economical, non-toxic, and does not require solvent recovery systems. At least about 18% of water, or equivalent amounts of another swelling agent, should be present in the treating bath.
In the tampons tested, in addition to the increase in their absorbing capacity, a further unexpected and much desired characteristic was noted. After the tampons containing wet cross-linked fibers absorbed fluid, they expanded to a greater extent than those containing like, untreated fibers. The increase in expansion was measured in the following manner.
Tampons were formed of card webs of wet cross-linked rayon prepared in accordance with Example II. The card webs were folded and cut into strips 4 inches long and strips 6 inches long. Each strip weighed 40 grains. Strips of the same length and weight were made from webs of untreated rayon fibers. Each strip was tied with a piece of string at the midpoint of the length, folded at the midpoint, and placed into a cylindrical die having an inside diameter of 0.533 inch, and compressed mainly in the direction of the length of the strip to form a tampon. The tampons made from the six inch strips were approximately 1.6 inches long and 0.56 inch in diameter and those made from the four inch strips were approximately 1.5 inches long and 0.58 inch in diameter. The tampons so formed were then subjected to the absorbency test described above and their length and diameter then measured. The following results were obtained:
Length (inches) Diameter (inches) The results establish that a compressed tampon made in accordance with the present invention expands more both in length and diameter than a similar tampon made from untreated fibers. This is an especially desirable characteristic in such products as tampons since they must be made of a size sufliciently small to permit them to be easily introduced intravaginally, and to be easily removed after use. Thus, tampons embodying the invention may be made smaller than tampons containing conventional fibers while still having equivalent absorbing capacities. Further, because of their increase in size due to expansion upon absorbing fluid, the tampons made in accordance with this invention when inserted intravaginally will provide a more effective barrier to the flow of menstrual fluid.
The ability of the products embodying the invention to resist deformation caused by externally applied pressures was determined in the following manner.
A never-dry tow of AVRIL rayon (Fiber 40) available from American Viscose Corporation was treated in accordance with Example I and another portion of the tow was permitted to air-dry. Tampons were made from six inch lengths of the wet cross-linked tow and the air-dried tow, each combed and weighting 50 grains. The lengths of tow were tied with a string at the midpoint of their length and doubled upon themselves at the midpoint to form uncompressed tampons of generally parallel, aligned filaments arranged in a cylindrical shape. When the tampons were tested for their absorbing capacities as described above, the tampons of the untreated rayon tow had an average absorbing capacity of about 6.1 cc. In addition, the tampons, after removal from the test apparatus, had assumed a flat, mop-like appearance and did not retain their original cylindrical shape, apparently due to the externally applied pressures. The tampons formed of the wet cross-linked rayon tow had an average absorbing capacity of about 11.6 cc., i.e., about a 5.5 cc. increase over the tampons made from untreated rayon tow and, in contrast to the tampons formed of the untreated tow, more nearly retained their original cylindrical shape. Thus, a tow tampon made in accordance with the present invention not only has greater absorbing capacity, but also is more capable of resisting deformation caused by externally applied pressures. This characteristic of resistance to deformation is especially desirable in such articles at tampons, sanitary napkins and similar absorbent products which are subjected to externally applied pressures in use.
The fibrous absorbent articles made in accordance with the present invention may be composed entirely of wet cross-linked cellulosic fibers, or may be blended in various combinations with other natural or synthetic fibers, such as cotton, flax, jute, rayon cellulose acetate, nylon, Orlon acrylic fiber, Dacron polyester fiber, depending upon the particular end characteristics desired.
In View of their increased absorbent capacity, the products incorporating the invention may contain lesser amounts of absorbent fibrous material while still having the same absorbing capacities as those containing untreated cellulosic fibrous materials. In addition, smaller products having absorbent capacities equivalent to products made from conventional fibers may be made. If desired, equivalent absorbent capacities can be obtained by blending untreated fibers with wet cross-linked fibers. For example, it has been determined that a tampon containing 20 grains of untreated cotton and 20 grains of wet cross-linked rayon is capable of absorbing about 10.6 cc., whereas a tampon of the same size and weight containing only untreated cotton absorbs about 7.9 cc. A tampon containing a blend of equal amounts of wet crosslinked rayon and unmodified cotton thus has an increase in absorbing capacity of 2.7 cc. over that of the all cotton tampon.
From the foregoing, it is apparent that products embodying the invention initially have a greater absorbing capacity than conventional products and, when subjected to pressures such as those commonly encountered in the use of tampons, sanitary napkins, dental packing and the like, retain greater amounts of fluid. Further, when in compressed form, they have greater expansion characteristics which permit the use of products which are initially smaller.
It is also apparent that variations in and modifications of the foregoing illustrative embodiments of the invention may be made while still remaining within the spirit of the invention.
What is claimed is:
1. An improved fibrous absorbent dressing for absorbing body fluids comprising as a fluid-absorbing and retaining means a preformed body of nonwoven, water-insoluble cellulosic fibers moveable with respect to each U other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said preformed body of fibers being deformation resistant to externally applied pressure.
2. A fibrous absorbent dressing in accordance with claim 1 wherein said cellulosic fibers are cotton.
3. A fibrous absorbent dressing in accordance with claim I wherein said cellulosic fibers are rayon.
4. An improved fibrous absorbent dressing for absorbing body fluids comprising as a fluid-absorbing and retaining means a preformed compressed body of nonwoven water-insoluble cellulosic fibers moveable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said preformed compressed body of fibers being deformation resistant to externally applied pressure and being expansible when wetted with body fluid.
5. An improved fibrous absorbent dressing for absorbing body fluids comprising as a fluid-absorbing and retaining means a preformed body of nonwoven, water-insoluble cellulosic fibers moveable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said crosslinks being methylene bridges, said preformed body of fibers being deformation resistant to externally applied pressure.
6. A catamenial dressing for absorbing menstrual fluid comprising as a fluid-absorbing and retaining means a preformed pad of nonwoven water-insoluble cellulosic fibers moveable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said preformed pad of fibers being deformation resistant to externally applied pressure.
7. A catamenial dressing in accordance with claim 6 wherein said preformed pad of nonwoven cellulosic fibers is compressed and which is expansible when wetted with menstrual fluid.
8. A tampon for absorbing body fluids comprising as a fluid-absorbing and retaining means a preformed, compressed elongated cylindrical body of nonwoven, waterinsoluble cellulosic fibers moveable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said elongated cylindrical body of fibers being deformation resistant to externally applied pressure and expansi ble when wetted with body fluid.
9. A tampon in accordance with claim 8 wherein said cellulosic fibers are cotton.
10. A tampon in accordance with claim 8 wherein said cellulosic fibers are rayon.
11. A tampon for absorbing body fluids comprising as a fluid-absorbing and retaining means a preformed elongated cylindrical body consisting of a tow of water-insoluble cellulosic fibers moveable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state and being substantially parallelized lengthwise in said preformed cylindrical body, said preformed cylindrical body of fibers being deformation resistant to externally applied pressure.
12. A sanitary napkin for absorbing menstrual fluid comprising as a fluid-absorbing and retaining means a preformed compressed pad of nonwoven water-insoluble cellulosic fibers movable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said preformed pad of fibers being deformation resistant to externally applied pressure and expansible when wetted with menstrual fluid.
13. A bandage for absorbing body fluid comprising as a fluid-absorbing and retaining means a preformed compressed pad of nonwoven, water-insoluble cellulosic fibers movable with respect to each other to vary the size of the interstices between fibers, said cellulosic fibers being crosslinked in the wet state, said preformed pad of fibers being deformation resistant to externally applied pressure and expansible when Wetted with body fluid.
References Cited by the Examiner UNITED STATES PATENTS Morton 8-116.4 Pinkney 8116'.4 Walker -1 8--116 .4 Lewing 128285 Sieger 128296 1 0 OTHER REFERENCES Textile Research Journal, Cotton Cross-Linked at Various Degrees of Fiber Swelling, vol. 30, pp. 179-192, 5 Reeves et 211. March 1960.
RICHARD A. GAUDET, Primary Examiner.
JORDAN FRANKLIN, Examiner.