WO1997043480A1 - Composite fibrous structures for absorption of liquids - Google Patents

Abstract

A composite fibrous structure which absorbs liquids is in the form of a yarn or nonwoven fabric which is coated with a superabsorbent polymer in an amount of up to 500 % SAP add-on. The yarn or nonwoven fabric is made of fibers having a non-round cross section. The fibers when in the form of a filament yarn have a specific volume of the filament yarn being greater than or equal to 1.50 cc/gm.

Description

COMPOSITE FIBROUS STRUCTURES FOR ABSORPTION OF LIQUIDS

TECHNICAL FIELD This invention relates to composite fibrous structures for absorption of liquids. More particularly, this invention relates to composite fibrous structures that are yarns or nonwoven fabrics having superabsorbent materials coated thereon and processes for making them.

BACKGROUND OF THE INVENTION Materials that rapidly absorb and retain many times their initial weight in liquids are known as super- absorbent (SA) materials and are available in many different forms such as fibers, powders, yarns and fabrics. Textile Research Institute (SRI) Report Number 34 by T. F. Cooke, June, 1990 describes various types of superabsorbent fibers including modified cellulosic fibers and synthetic fibers. In particular, SA materials are useful in water- blocking components for fiber optic cables. In order to maintain reliable performance for up to 40 years, fiber optic cables must be free from moisture contamination. If the outer sheath of water—proofing plastic is damaged by any of several means, superabsorbent components in an inner layer of the cable wrap can block or retard the penetration of water, both radially and axially, within the fiber optic cable structure. This water-blocking property greatly extends the useful life of the cable to transmit audio and digital signals of high quality. Several types of water-blocking superabsorbent powders, tapes, fibers and yarns are currently in use for fiber optics. However, many have known deficiencies in cost and performance. SA fibers are relatively weak, brittle and sensitive to atmospheric humidity, thus making them difficult to process into many potential articles of commerce. U.S. Patent 5,151,465 discloses uncured polymer compositions that can be made into fibers using conventional fiber forming processes and cured to produce absorbent fibers capable of absorbing at least 60 times their weight of brine. One of these SA fibers, commercially known as FiberDri (trademark) 1038 available from Camelot Superabsorbents, Ltd. of Calgary, Alberta, Canada, has tenacities of about 0.07 grams per denier and elongations of about 40% when measured at a temperature of 70°C and a relative humidity of 65%. FiberDri 1038 fibers appear to become sticky and are not suitable for processing into yarns or nonwoven products when they are exposed to warm and humid environmental conditions for a number of hours.

U.S. Patent 5,298,284 discloses a cable wrap which swells upon contact with water. It is made by coating one side of a nonwoven fabric support with a polyvinyl alcohol binding agent and then with a superabsorber powder, drying the coated fabric between contact surfaces, printing a polyacrylate binding agent paste onto the superabsorber surface, and then drying the coated fabric.

U.S. Patent 5,264,251 discloses an aramid yarn coated with a water swellabie superabsorbent material. The swelling value of the yarn is at least 60. The SA material provides water—blocking capability to the yarn, so that it is suitable for use as a strength member, for example, in water tight optical communication cables. U.S. Patent 5,131,064 discloses a communication cable for use in buried environments in an outside plant. The cable has many functional components including a barrier layer for preventing the longitudinal flow of water within the cable. Such a water-blocking capability may be provided by a barrier layer comprising a laminate having a high temperature resistant tape and at least one other tape with a SA powder therebetween or another tape which has been impregnated with a SA material.

EP—A—0 268 498 discloses a water—absorbent, water- insoluble, linear polymer that may be made into any desired final shape and cross—linked thereafter with controlled and even cross—linking. Films and fibers made from the polymer are disclosed as well as impregnating or coating the polymer as a surface layer onto another substrate. For coating applications, the dry pick—up of the linear polymer to the substrate is typically 2-25 weight percent limiting the absorbency of the final product.

Thus, there exists a need in the art for super- absorbent fibrous structures which have the advantages of excellent performance, production on existing or slightly modified textile equipment, and relatively low cost. Accordingly, it is to the provision of such improved superabsorbent fibrous structures that the present invention is primarily directed.

SUMMARY OF THE INVENTION The present invention which provides for improved superabsorbent characteristics is a composite fibrous structure for absorption of liquids comprising a yarn or a nonwoven fabric coated with a superabsorbent polymer in an amount of up to 500% SAP add—on, as defined below. The yarn and nonwoven fabric comprise a plurality of fibers, each having a non-round cross—section. The fibers in the form of a filament yarn have a specific volume of the filament yarn being greater than or equal to 1.50 cc/gro.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a typical yarn coating and drying unit.

Figure 2 is a side view of a grooved roll for application of SA polymer onto a yarn in accordance with a grooved roll process of the present invention. Figure 3 is a cut—away front view of the grooved roll of Figure 2 during application of SAP precursor solution onto the yarn.

Figure 4 is a cross—sectional side view of the groove in the grooved roll of Figure 2 with SAP precursor solution therein prior to contact with the yarn.

Figure 5 is a cross—sectional side view of the groove in the grooved roll of Figure 2 during contact of the yarn with SAP precursor solution. Figure 6 is a cross—sectional side view of the groove in the grooved roll of Figure 2 after contact of the yarn with SAP precursor solution.

Figure 7 is a frontal view of a stationary V—shaped guide utilized in a stationary groove process of the present invention.

Figure 8 is a side view of the stationary guide of Figure 7 during application of the SAP precursor solution onto a yarn.

Figure 9 is a cross—sectional side view of a closed chamber containing SAP precursor solution in a coating chamber process of the present invention.

Figure 10 is a drawing of a 4DG fiber utilized in the present invention. DETAILED DESCRIPTION OF THE INVENTION A composite fibrous structure for absorption of liquids is comprised of a yarn anαVor a nonwoven fabric coated with a superabsorbent polymer. The yarn or fabric is made from fibers having non—round cross- sections. The superabsorbent polymer is coated onto the yarn or nonwoven fabric as a precursor. "Precursor" refers to the superabsorbent polymer in its uncured or non—cross—linked state. Curing or cross—linking of the superabsorbent polymer follows application of the precursor and typically occurs with the application of heat. Catalysts may be used to increase the rate of cross—linking.

The superabsorbent polymer (SAP) is preferably a cured polymer composition as disclosed in U.S. Patent

No. 5,151,465 to Le—Khac. The polymer composition is a reaction product of:

(a) a partially neutralized aqueous polymer composition prepared by the reaction of a strong base with a polymer containing at least 25 mole percent recurring units of an α, β—unsaturated monomer having in its molecule one or two carboxyl groups or one or two other groups convertible to and converted to carboxyl groups, the degree of neutralization of the partially neutralized polymer being within the range of from about 0.2 to about 0.8 equivalent of total carboxyl groups of the a , β- unsaturated monomer, with

(b) from about 0.1 to about 10 total parts by weight of at least one reactive compound per 100 parts by weight of the partially neutralized aqueous polymer compositions, the reactive compound being a water soluble compound bearing one amine group and at least one hydroxyl group, wherein the reaction product is formed by an ionic bonding reaction between the unneutralized carboxyl groups on the polymer and the amine groups on the reactive compound, and is stable at room temperature. More preferably, the polymer composition is a maleic anhydride and isobutylene copolymer with a molecular weight in the range of 200,000 to 300,000. The polymer composition is applied to the yarn or nonwoven fabric as a precursor in its aqueous, uncured state. Curing is completed by the application of heat to a temperature about 140—210°C causing the formation of ester and amide linkages.

In another preferred embodiment, the superabsorbent polymer is that disclosed in EP 0 268 498. A substantially linear polymer is made by polymerization of a water soluble ethylenically unsaturated monomer blend. The blend comprises a first monomer that provides carboxylic acid groups and a second monomer that provides hydroxyl groups that can react with the carboxylic acid groups to form ester cross-linkages containing only carbon and oxygen atoms in the linkages. The substantially linear polymer is in an uncured stable state prior to coating onto the yarn or nonwoven fabric and is preferably in an aqueous solution. After being coated onto the fiber or nonwoven fabric, the polymer is cross—linked by the reaction of the carboxylic and hydroxylic groups. The reaction occurs by the application of heat to above 150°C.

The yarn or nonwoven fabric is made from fibers having non—round cross—sections which provide relatively high bulk and fiber surface area. These fibers facilitate the application of relatively high amounts of coating with adequate uniformity along the length of the yarn or surface area of the nonwoven fabric. These fibers also provide adequate strength to withstand tensions and other forces to which the yarn or nonwoven fabric may be exposed during its useful life.

Preferably, the fibers which provide for relatively high bulk and fiber surface area are those which when made in the form of a filament yarn have a specific volume of the filament yarn greater than or equal to 1.50 cc/gm. A commercially available fiber which meets this criteria is 'UDG" fiber, available from Eastman Chemical Company of Kingsport, TN. The 4DG fiber is substantially that as shown in Figure 10. For a comparison of round fibers to the fibers of the present invention for specific volume refer to Table V below. The test method for specific volume is set forth below in Test Methods. More preferably, the fibers are those which when made in the form of a filament yarn have a specific volume of the filament yarn of about 2.20 cc/gm and have either (1) a cross—section as that shown in Figure 10 or (2) a cross—section comprising finger—shaped projections such that a shape factor, X, of the fiber cross—section is greater than 1.5. The shape factor of the fiber cross—section satisfies the following equation:

X = E_w ,

4r + (11-2)D wherein P_w is the wetted perimeter of the fiber and r is the radius of the circumscribed circle circumscribing the fiber cross—section and D is the minor axis dimension across the fiber cross—section. A detailed discussion of the shape factor and examples as to its calculations is disclosed in U.S. Patent No.

5,611,981 to Phillips et al., the disclosure of which is incorporated herein by reference.

More preferably, the fibers of the present invention are those that are disclosed in U.S. Patent No. 5,611,981 to Phillips et al. which satisfy the equation

(1-X cos θ_a) < 0, wherein 0_a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment,

X is the shape factor of the fiber cross—section that satisfies the following equation X = P_w

4r + (II-2)D wherein P_w is the wetted perimeter of the fiber and r is the radius of the circumscribed circle circumscribing the fiber cross—section and D is the minor axis dimension across the fiber cross—section.

The basic polymer composition of the fibers may be polyester, polyamide, polyolefin, or other fiber forming polymers.

The yarn is preferably staple/spun or filament yarn. The staple/spun yarn is a product of the spinning frame characterized by a continuous, evenly distributed, coherent arrangement of any type of fibers of varying or similar staple length. The relative positions of the staple fibers are maintained by the introduction of a definite lateral twist to produce strength or coherence. The twist is typically imparted in the final operation. The staple fibers have a wide range of characteristics. The fiber denier may range from about 1 to about 20 denier per filament (D/F) with about 2 to about 15 D/F being more typical. The staple D/F and length of choice depend generally on the application for the yarn and the nature of the fiber type. Typically, the staple fiber has some form of crimp to enhance the cohesion of the fibers during processing to spun yarn and to increase the strength and uniformity of the spun yarn. Selected fiber finishes may also improve the cohesion to enhance fiber properties.

The filament yarn is made from various continuous filaments of the fiber. The characteristics of the filament fibers and yarn also varies depending on the extent of twist, total yarn denier, D/F of the fiber and the application of crimp to the fibers or filament yarn.

The amount of SAP applied to the yarn or nonwoven fabric varies depending on the end use application. The amount is measured as weight percent dry SAP to 100 weight percent dry feed yarn basis and referred to hereinafter as the "% SAP add—on". As low as about 5% SAP add—on to as high as about 500% SAP add—on may be applied to the yarn or nonwoven fabric. For the yarn, the amount of SAP is preferably 50 to 500% SAP add-on and, more preferably, 100 to 400% SAP add—on. For nonwoven fabric, the amount of SAP is preferably as high as about 300% SAP add—on and, more preferably as high as about 100% SAP add-on.

The amounts of SAP needed are readily controllable to the levels required for specific end uses by adjusting process parameters such as solvent concentration, application viscosity and temperature, and application technique as described in more detail below. In particular, the nonwoven fabric has increasing stiffness with increased SAP add-on, which is an important property to consider when evaluating applications. Maximum amounts of % SAP add—on relative to fiber type and application process are shown in Table I. The unusually high bulk of spun 4DG yarn enables the coating of high amounts, up to as much as 500% SAP add-on. Use of the filament 4DG yarn enables a maximum of about 300% SAP add—on to coated yarn. While the % SAP add-on is somewhat lower for filament yarn as compared to spun yarn, the filament yarn offers more uniformity along the yarn axis and higher yarn strength than the corresponding spun yarn. Yarn made from 4DG fibers have higher SAP content and are thus preferred for certain critical applications, such as fiber optic cable wrap where water penetration roust be kept to a minimum. When yarn is made from polyester fibers having round cross- sections, the maximum obtainable amounts of SAP that can be coated thereon is considerably lower by about 20 to

30 percent of that which can be coated onto yarn that is spun from 4DG fibers. However, SA yarn comprised of round or more nearly round fibers may be useful for applications requiring less protection from water penetration.

TABLE I

Case Fiber Yarn Max. SAP Application Max. % SAP

No. Tvoe Type* Solids. % System Add-On Remarks

1 4DG Spun 35 Grooved Roll, 200 Limited by Syrup

2 Round Spun II Syrup at Room 150 Viscosity and

3 4DG Filament II Temperature 100 Waste (<1%) on

4 Round Filament •1 (20-25°C) 50 Drying Rolls

5 4DG Spun 40 Grooved Roll, 300 (Same as 1—4)

6 Round Spun II Syrup at Higher 225 1

7 4DG Filament II Temperature 150 1—'

8 Round Filament II (50-70°C) 65

9 4DG Spun 45 Pumping Heated 400 (Same as 1-4) ,

10 Round Spun II Syrup to Bottom 300 Syrup Warmed to

11 4DG Filament II of Stationary 225 70-100°C before

12 Round Filament •1 Groove 80 Application

13 4DG Spun 50 Pumping Heated 500 (Same as 1-4) ,

14 Round Spun II Syrup to 400 Syrup Warmed to

15 4DG Filament •1 Semi—closed 300 70-110°C before

16 Round Filament II Chamber 100 Application

The coating operation takes place when the SAP is in the precursor stage; that is, the SAP is in a processable, uncured state. The SAP precursor is preferably a viscous solution which is suitable for intimately coating the yarn or nonwoven fabric. The SAP precursor may be further diluted by water or another solvent, referred to in this state as "syrup".

The typical process for applying the SAP either as a precursor or syrup onto a piece of yarn is by the use of a yarn coating and drying unit 10 as shown in Figure 1. Deviations from this process will be primarily directed to the application of SAP precursor or syrup in the Syrup Application Step as detailed below. In a first process, the syrup was added by a horizontal, rotating, grooved roll. In a second process, the syrup was added by pumping syrup to an open—top, stationary, grooved applicator. In a third process, the syrup was added by pumping syrup to a chamber which fully enclosed the moving yarn to enable contact and coating of the full 360 degree circumference of the surface for the yarn. The other process steps, i.e. yarn feed, preheat, syrup drying, polymer cross—linking, and SA yarn collection and storage, apply to all three processes of applying syrup.

Yarn Feed Step.

In the yarn coating and drying unit 10, yarn is supplied from a convenient source 12 with conventional guides and tensioning devices 14 to provide yarn at uniform and relatively low tension to the syrup application unit 16. The guides and tensioning devices 14 may be a series of multiple rolls 18 with adjustable speed. The multiple rolls provide yarn having tensions in the range of about 0.01 to about 0.5 grams (g)/denier of uncoated, feed yarn. Preheat Step.

Optionally, the feed yarn may be preheated by six multiple wraps around the last two supply rolls 18 for the purpose of providing a fraction of the heat needed to evaporate solvent from the coated yarn after the syrup coating step. While preheating is not required for relatively low levels of SAP on the coated yarn, this substep is beneficial for achieving maximum levels of % SAP add—on to the coated yarn. Permissible yarn preheat temperatures include room temperature up to the melting or softening point of the feed yarns. Higher temperatures up to the point of causing damaging effects to the yarn are preferred for highest levels of SAP application to the coated yarn.

Syrup Application Step A/Grooved Roll Process.

From the yard feed or preheat step, the moving yarn next passes over a grooved, rotating roll 40 with the bottom surface immersed into a reservoir 42 of syrup, as shown in Figures 2 and 3. The groove 44 has a width of about one and a half to four times the diameter of the feed yarn. Preferably, the groove width is about twice the diameter of the feed yarn. The depth of the groove 44 may be one to four times, preferably two to three times, the diameter of the feed yarn. The tapered entrance 46 to the groove aids in keeping the yarn in its proper position.

The speed of the grooved roll 40 is adjustable to enable the desired concentration of SAP on the yarn up to the maximum level at which SAP waste becomes excessive. For yarn speeds of about 15 to 30 meters/minute (m/min) , roll speeds of 4 to 40 revolutions/minute (rpm) are preferred. For higher yarn speeds with enhanced syrup drying techniques or lower SAP concentrations on the coated yarn, reasonable variations outside the range of the noted groove dimensions and roll speeds would be obvious to those skilled in the art of fiber and polymer processing. For example, for 5 to about 20% SAP add—on, the grooves would not be necessary.

Application of the SAP to the yarn is shown in Figures 3—6. In Figure 3 the yarn is shown moving across the top portion of the grooved roll. The yarn enters the groove at an angle for maximum contact with and take up of the syrup in the groove. This angle is preferably 20 degrees less than horizontal. The groove is substantially filled with syrup prior to contact with the yarn as shown in Figure 4. When the yarn passes through the groove at the top of the grooved roll it is completely submerged in the syrup as shown in Figure 5. The yarn exits the groove with a substantially even coating of syrup thereon leaving the groove emptied as shown in Figure 6.

Syrup with solids levels of about 10 to 35 weight percent, preferably 22 to 30 weight percent, are used by this application process to make samples having about 50 to 200% SAP add—on depending on the fiber type. Somewhat higher solids syrups may be used if the syrup is heated, but the temperature appears to be limited to about 65°C because of increasing tendency for water (or other solvent) to be evaporated from the rotating roll and the syrup reservoir.

The grooved roll application process provides for a yarn that is coated with an adequate amount of syrup in an economical manner to produce the desired SA yarn. High production rates with minimum waste of SAP along the coating unit are obtainable with this process. Thus, the use of high concentrations of SAP precursor in the syrup enables higher % SAP add—on for a given level of syrup application to the yarn and minimizes the amount of water to be evaporated from the coated yarn during the drying operation.

When SA coated yarn was made by this grooved roll process, operating conditions and SA yarn properties obtained are as shown in Examples 2—6 and 12—15 of Tables III and V.

Syrup Application Step B/Statlonary Groove Process.

The moving yarn from the feed step passes through a stationary V—shaped guide 60 of a stationary groove applicator 62, as shown in Figures 7 and 8. The walls 64 of the groove 66 slope up from the groove. SAP precursor solution or syrup is supplied in a reservoir 68 to a metering pump (not shown) . The pump delivers syrup through a heater to supply the syrup at a desired temperature to the bottom of the stationary groove applicator. Figure 8 shows the yarn prior to and after application of the syrup.

The solids level for the SA syrup may be in the range of about 20 to about 45 weight percent or higher. For the application of high levels of SAP to the yarn, solids levels of about 35 to 45 weight percent are desired to enable high production rates with suitable yarn properties. Suitable temperatures for the syrup feeding the stationary groove applicator are about 60 to about 105°C. Preferred syrup feed temperatures are about 90 to 100°C, which are the temperatures just below the boiling point of the syrup.

The advantages of this system are uniform delivery rate of the syrup to the feed yarn and the ability to heat the syrup to higher temperatures at the point of application to the feed yarn. These factors permit the use of syrup having higher solids levels than that possible with the grooved roll process. Also, the syrup can be applied to the yarn at a higher temperature, thereby enhancing the evaporation of water from the coated yarn during the ensuing drying step.

When SA coated yarn is made by this stationary groove process, operating conditions and SA yarn properties were obtained as shown in Examples 16 and 17 of Table VI.

Syrup Application Step C/Coating Chamber Process.

The syrup application in this step is much the same as that described above for the stationary groove process. For this system, the stationary V—shaped guide is replaced by a substantially closed syrup application chamber 80 as shown in Figure 9. The feed yarn enters and exits the chamber by way of tubes 82 having long, small—diameter bores 84. Hot syrup 86 is pumped from a reservoir (not shown) at a uniform rate to the bottom of the chamber 80. Air may be vented from a tube 88 at the top of the chamber as required at startup and at times of accumulation. The diameter of the supply yarn entrance tube 82a is somewhat smaller than the exit tube 82b to accomplish almost complete flow of syrup to the exiting yarn and very little leakage out the yarn entrance tube 82a.

When SA coated yarn was made by this coating chamber process, operating conditions and SA yarn properties obtained are as shown in Example 18 of Table VI.

Suitable dimensions of the tubes 82 for coating 1250 total denier spun yarn produced from 6 denier per filament 4DG fibers were 38 mm long and 1.1 mm in diameter for the entrance tube 82a and 25 mm long and 1.4 mm in diameter for the exit tube 82b. Syrup Drying Step.

The yarn coated with syrup is preferably dried to about 5 weight percent or less moisture. For relatively high concentrations of greater than about 50% SAP add- on, the syrup surface is preferably dried before contact is made with hot solid rolls. This initial drying is accomplished with hot air jets and infra—red heat lamps in an air chamber 20. Other types of non—contact heating and drying, such as radiant heat or microwave heating, also accomplish this pre—drying need. To complete the drying of the syrup, the coated yarn contacts a set of heated rolls 22 for about one to three minutes. The heated rolls have a surface temperature of about 100 to 150°C, with 140°C being preferred. At lower temperatures the syrup tends to stick to the rolls. At higher temperatures, water vapor bubbles cause problems with SAP waste, and polymer cross—linking begins too soon.

Polymer Cross-Linking Step.

After the SAP precursor is dried on the coated yarn, the cross—linking step may be accomplished immediately by exposure of the coated yarn to required times and temperatures on heated rolls 24 as shown in Figure l. Alternatively, the coated yarn may be collected on a moving belt or suitable frame and passed through a hot oven for the required time and temperature to achieve the cross-linked SA yarn.

The cross-linking step converts water soluble, uncured SAP precursor to cured SAP that is water insoluble, yet water swellabie or water absorbing, thereby providing for a superabsorbent composite fibrous structure, i.e., SA yarn. This cross-linking operation is achieved by exposing the coated yarn to temperatures of about 150 to 220°C for about 2 to 20 minutes. Longer times are required for lower ranges in temperature. Some range in the temperature is permissible to select the extent of cross—linking which provides for desired SA yarn properties. For example, SA yarn with relatively low extents of cross-linking may have somewhat greater extents of water absorption but lower gel strength than the respective properties of SA yarn with relatively high extents of cross-linking. The conditions required for cross—linking may also be affected by the chemical types of multifunctional cross- linking molecules used in the various SA polymers available.

After the SAP precursor is dried on the coated yarn, the yarn may be collected and stored for a few hours or for several weeks prior to the cross—linking operation. Should this coated yarn collect moisture during this storage period, it must be redried to about 5 weight percent or lower moisture at temperatures up to about 140°C before the cross—linking operation. The cross—linking may then be achieved by exposure of the coated, dry yarn to temperatures of about 150 to 220°C for 2 to 20 minutes as described above.

SA Yarn Collection and Storage. After the cross-linking step, the SA yarn is preferably wound onto cones or tubes or is stored in a satisfactory manner to enable future processing into an article for commercial use. Typically the SA yarn is passed over an oil roll 26, providing lubrication, prior to entering the winding machine 28. In most cases, the dry, SA yarn should be packaged in such a way as to minimize the likelihood for water or other chemical species to reach the yarn until the final articles for commercial use are fabricated and put into actual service. Alternatively, the SA yarn could be directly processed into an article for commercial use immediately after the cross—linking step.

EXAMPLES

Specific combinations of yarn type, syrup solids content, yarn speed, % SAP add—on to the coated yarn and application processes are given in the examples. The 4DG fibers preferably have a processing lubricant on the surface as those disclosed in U.S.

Patent No. 5,372,739 to Neal et al. In particular, the lubricant used for the examples was 98 weight percent polyethylene glycol 880 sorbitan monolaurate and 2 weight percent 4—ethyl, 4—cetyl, morpholinium ethosulfate (antistat agent) .

Example 1

A 15 weight percent (wt %) aqueous solution of SAP precursor was prepared by diluting a solution of 25 wt % FiberSorb (trademark) SA 7200, which is an aqueous SAP precursor available from Camelot Superabsorbents, Inc. , of Charlotte, NC. The composition of the SAP precursor solution was approximately as follows.

Component Composition. %

Water 74.5

50 mol % Maleic anhydride/50 mol % isobutylene copolymer 19.5

Sodium Hydroxide 5.0

Glycerol 1.0

Two superabsorbent yarn samples, A and B, were made in the following manner. For Sample A, a polyester [poly(ethylene terephthalate)] feed yarn consisted of 9 plies of 150 denier/30 filament fully oriented filament yarn without intentional twisting. This provided a nominal 1350 denier feed yarn having fibers of round cross—section. This feed yarn was processed through a research fiber tow line consisting of sub—units arranged as shown by Figure l. The feed yarn passed over the feed rolls at a surface speed of 30 m/min, contacted a 5.08-cm (2-inch)—diameter roll which was rotating at 20 rpm for the application of SAP precursor solution (syrup) , passed over a set of eight drying rolls at a surface temperature of 90°C (not shown) , passed through a 2.438 meter (8-feet) length hot air chamber at 130°C, passed over a second set of eight drying rolls at a surface temperature of 110°C, passed over set of seven heat treatment rolls at a surface temperature of 190°C, and was wound onto a winder package. In the set of heat treatment rolls, the SAP coated yarn was guided so as to achieve multiple wrappings on the roll set and a contact time of about 6 minutes thereby allowing for some cross— linking of the SAP. The coated yarn was given additional heat treatments and selected fiber tests in a fiber testing laboratory. A summary of the heat treatments and fiber tests is shown in Table II.

For Sample B, a polyester feed yarn consisted of a four cotton count spun yarn prepared from 6 denier per filament x 3.81-cm (1.5-inch)-length 4DG staple fiber. This provided a nominal 1350 total denier spun yarn. This 4DG spun yarn was processed through the research fiber tow line at the same conditions as those described for the Sample A. The coated 4DG spun yarn was given the same additional heat treatments and selected fiber tests as that given to Sample A.

For Sample C, a third yarn without SAP was prepared for comparison of fiber properties. This feed yarn was the 9—ply polyester filament feed yarn described for Sample A. This yarn was passed through the research tow line at the same speed and temperatures as Samples A and B except that it was not contacted with the SAP syrup. A water absorbency test, as described in detail below, was conducted on each of the samples. This test measured the amount of water that a 1—gram to 5-gram sample of yarn or nonwoven fabric absorbs in a 3 minute period, and the results were expressed in grams of water per gram of initial dry fiber retained 10 seconds after the fiber was removed from the water. The tensile properties of the fiber were determined by standard process using an Instron Tensile Tester.

The following are observations from Table II concerning fiber properties of Sample A—C. The spun 4DG yarn was coated by about 20% more SAP than the filament round yarn under comparable processing conditions. The untreated filament yarn absorbed only 2.1 g water per g of fiber, while the SAP coated filament and spun yarns absorbed 11.6 and 15.6 g water per g of sample, respectively, without additional laboratory heat treatment. The lab treatment in hot air ovens at 170 and 190°C significantly increased the water absorbency of the yarn samples. Apparently, the SAP was not adequately heat treated during the continuous processing stage. The most severe heat treatment of 20 minutes at 190°C resulted in somewhat lower water absorbency than that for the two other conditions. This was consistent with excessively cross-linking the SAP to give a polymer structure that will not expand to absorb as much water as SAP structures that have somewhat lower levels of cross-linking. The tensile strength of the filament round cross—section yarn was significantly higher than that of the spun 4DG fiber yarn at all comparable conditions. However, the strength of the SA spun 4DG yarn was still much higher than commercial 100% superabsorbent yarns and was sufficient for many commercial applications. Additionally, it is believed that the strength of spun 4DG yarn can be increased by optimization of fiber and yarn preparation conditions.

Table II Sample A B__ C

Yarn Type Filament Spun Filament Fiber Type or Cross Section Round "4DG" Round

SAP Precursor Solution 15 15 (None) Solids, %

TESTS ON YARNS AS PROCESSED ON TOW LINE

Total Denier (g/9000 m) 1703 1820 1410 % SAP Add-On 20.8 25.8 0

Tenacity, g/denier 4.11 1.22 4.9

Elongation, % 28.9 30.3 29.1

Elastic Modulus, 49 9.6 62 g/denier Water Absorbency, g/g fiber 11.6 15.5 2.1

TESTS ON YARNS ADDITIONALLY HEATED 10 MINUTES AT 190°C

Tenacity, g/den. 4.03 1.04

Elongation, % 29.6 30.9 Elastic Modulus, g/denier 44 8.7

Water Absorbency, g/g fiber 21.3 29.4

TESTS ON YARNS ADDITIONALLY HEATED 20 MINUTES AT 190°C

Tenacity, g/den. 4.02 l.ll Elongation, % 30.2 30.4

Elastic Modulus, g/den. 42 7.9

Water Absorbency, g/g fiber 17.4 19.8

TESTS ON YARNS ADDITIONALLY HEATED 10 MINUTES AT 170°C Tenacity, g/den. 1.15

Elongation, % 32.9

Elastic Modulus, g/den. 6.8

Water Absorbency, g/g fiber 16.5 TESTS ON YARNS ADDITIONALLY HEATED 20 MINUTES AT 170°C

Tenacity, g/den. 1.30

Elongation, % 36.4

Elastic Modulus, g/den. 9.3

Water Absorbency, g/g fiber 21.4 Examples 2 through 7

Six yarn samples were made from a similar type of polyester yarn on the research fiber tow line of Example 1, except as noted in the following descriptions for these examples. The feed yarn was spun yarn processed from 15 denier/filament x 15.24-cm (6-inch) 4DG staple. The staple fiber had been processed into four cotton—count single—ply yarn which was nominally 1350—total denier yarn. The aqueous solutions of SAP precursor were prepared at the concentrations noted in Table III by diluting a 46.5 wt % solution of Fibersorb SA 7200. The application roll was modified by machining a circumferential groove onto it to enhance the uniform additions of relatively large amounts of SAP syrup to the yarn.

The six yarn samples were prepared in the following manner. The feed yarn passed over initial feed rolls at a surface speed of 14.7 m/min, contacted the 5.08—cm (2-inch)-diameter SAP application roll with groove which was rotating at the noted speeds (Table III) , passed through a 1.219 meter (4—feet) length heated air heat exchanger, passed under five 250—watt infra-red heat lamps, passed through a 2.438 meter (8—feet) length hot air chamber at 165°C, and passed onto a set of eight drying rolls which were heated to a surface temperature of 140°C and operated at a surface speed of 15.0 m/min. The minimum contact drying units between the SAP precursor application roll and the set of drying rolls were used to sufficiently dry the SAP precursor solution thereby enabling the remaining drying operation to occur without excessive coating out of SAP precursor solution onto the drying rolls. Additionally, multiple wraps were made on an adjacent pair of initial feed rolls which were heated to a surface of 180°C to facilitate the evaporation of water from the SAP precursor solution after being applied to the yarn. After the set of eight drying rolls, the yarn passed over a set of seven drying rolls at a surface temperature of 140°C and were wound onto winder tubes. Three wrapping cycles were made on this last drying unit to provide about three minutes of drying time and assure that the water concentration in the processed yarn was below about 5 wt % water. The yarn was given additional heat treatments and tested for selected physical properties. Table III shows the sample preparation conditions and the laboratory test results for yarn samples for Examples 2 through 7. Preparation conditions differed by SAP precursor concentration and SAP application roll speed. The SAP precursor solutions ranged from 10.5 wt % solids for Examples 2 and 3 to 31.7 wt % solids for Examples 5 and 6. The yarn for Example 7 was processed through the unit without applying SAP precursor.

Viscosities were estimated for the SAP precursor solution, i.e., syrup, at the point of application to the yarns. These viscosities ranged from 0.95 p (poise) for the 10.5 wt % solids syrup to 29 p for the 31.7 wt % solids syrup. The syrup temperature was 23°C for all of these examples. For Example 3 with 10.5 wt % solids, there was significant waste (4.4%) on the drying rolls, although only 37.2% SAP was added to the yarn. For

Example 6 with 31.7 wt % solids, there was only slight waste (0.4%) on the drying rolls, although 233% SAP was added to the yarn.

The viscosities of syrup were measured with a laboratory cone and cup viscometer under a range of syrup solids (10 to 48 wt %) and temperatures (25 to 75°C) . These viscosity values were plotted onto a nomogram from which viscosities could be estimated with reasonable accuracy within the ranges of 10 to 50 wt % solids and 20 to 97°C temperature for the SAP syrup. The SAP waste from drying rolls and moisture after the first set of drying rolls are important characteristics of the SAP application process. Minimum SAP waste on drying rolls is desirable to limit material losses and provide for clean housekeeping. With other preparation conditions comparable including level of % SAP add—on to the coated yarn, higher SAP precursor solution solids minimized drying roll waste. Lower moisture content on the coated yarn is also desirable to reduce drying costs and possibly increase operating rates.

The combinations of SAP solution solids and SAP application roll speeds resulted in a relatively wide range of % SAP add—on to the SA yarns ranging from 29.1% for Example 2 to 233% for Example 6.

Total deniers of the SA yarns increased as the levels of SAP increased as compared to the control yarn of Example 7. The SA yarn tenacity decreased slightly as the % SAP add—on increased. However, the presence of the SAP apparently added to the total strength of the SA yarn, as indicated by the general increase in mean yarn strength in Newtons (pounds) .

SA yarn swell properties were determined by The Swell Test Procedure described in detail below. The swell height increased as the SAP content of the SA yarns increased. The swell time increased as the SAP content of the SA yarns increased. Higher swell heights and shorter swell times are typically desired for many commercial applications of absorbent products. Consequently, if swell height and swell time requirements for an absorbent product are known, the % SAP add-on can be adjusted to meet these requirements. For example, a commercial yarn was obtained which was reported to be suitable for use as a water-blocking component in fiber optic cable. This yarn had a swell height of about 2 cm/g and a swell time of about 240 seconds. The SA yarn of Example 5 with a swell height of 2.81 cm/g and a swell time of about 114 seconds has better swell properties than those of the commercial yarn.

Table III Preparation Conditions and Yarn Properties for Examples 2 through 7 Example Number 2 3 4 5 6

PREPARATION CONDITIONS AND RESPONSES SAP Precursor Solutions Solids, wt % 10.5 10.5 22.7 31.7 31.7 N/A SAP Application Roll Speed, rpm 18.9 27.5 13.0 6.2 9.0 (19) Est. Syrup Viscosity at Application 0.95 0.95 6.8 29 29 N/A

Roll, p SAP Waste from Drying Rolls, % 0.2 4.4 13.0 0.2 0.4 0.0 Moisture after First Set of Drying 24 36 46 33 46 0.0

Rolls, wt %

YARN TESTS AFTER HEAT TREATING FOR 15 MINUTES AT 195°C NJ -^1

Tensile Properties & Estimate of SAP Content

Total Denier (g/9000 m) 1730 1838 2619 3429 4459 1336

Apparent % SAP Add-On 29.1 37.2 95.5 155.9 233 (0.0)

Tenacity, g/den. 1.39 1.36 0.92 0.82 0.51 1.43

Elongation, % 37 36 33 34 29 28

Elastic Modulus, g/den. 11.8 11 8.7 6.8 8.3 11.7

Mean Yarn Strength, N 23.5 24.6 23.6 27.6 26.8 18.6

Mean Yarn Strength, Pounds 5.29 5.54 5.31 6.2 6.03 4.19

Yarn Swell Tests with Distilled Water at 414 Pa (0.06 psi)

Swell Height, cm/g 0.615 0.99 1.93 2.81 3.31 0.0

Time to 90% Maximum Swell Height, s 8.8 23.8 31 113.8 146

Initial Sample Thickness, mm 1.22 1.3 1.5 1.8 1.95 1.5

Maximum Increase in Height, mm 1.55 2.50 4.88 7.21 8.48 0.0

Swell Rate, cm/(g-Min) 3.80 2.25 3.36 1.34 1.25

Examples 8 through 11

Two nonwoven fabrics were prepared on a development textile processing unit by conventional process. In each case, polyester staple fiber that was 6 denier/filament and 5.08-cm (2-inch) length was opened to a uniform web, coated with 15 wt % of a low melting polyester copolymer and then heated and calendared to form nonwoven fabrics of about 36 g/sq. m density. One fabric was made from a standard round fiber cross— section polyester staple fiber while the other fabric was made from a 4DG polyester staple fiber. Sections of these fabrics were then coated with a 15 wt % solids SAP precursor solution on a laboratory coating unit. Excess SAP precursor solution was removed by passing the fabric through a pair of spring loaded nip rolls. Identifi¬ cations of the pair of coated composite fabrics and the respective uncoated control fabrics are shown in Table IV.

The SA composite fabric composed of round fibers gained 36.7 wt % of SAP, and the SA composite fabric composed of 4DG fibers gained 46.7 wt % of SAP. The absorbency for distilled water was 54.1 g/g and 59.1 g/g for the round and 4DG SAP composite fabrics, respectively. The absorbency for distilled water was 29.7 g/g and 39.3 g/g for the uncoated control fabrics composed of round and 4DG fibers, respectively. Under these fabric treatment conditions, the actual thickness under low pressure was less for the coated fabrics than the uncoated fabrics. This result was caused by the combination of the compressing action of the nip rolls after coating and the tendency of the SAP to "plaster" the individual fibers together into a relatively dense fabric structure. Table IV Preparation Conditions and Fabric Properties for Examples 8-11

Example Number 10 11

Fiber Type or Cross Section Round 4DG Round 4DG

FABRIC COATING CONDITIONS AND MEASUREMENTS

SAP Precursor Solution Solids, % 15 15 None None Wet Pick-up of SAP Solution, % 220 271 0 0

TESTS ON FABRICS AFTER HEAT TREATMENT FOR 16 MINUTES AT 180°C

Apparent Weight Gain of SAP, 36.7 46.7 0 P

N3 Water Absorbence, g/g Fabric 54.1 59.1 29.7 39.3 v£> Fabric Thickness at 138 Pa 1.59 1.52 2.71 1.89 , (0.02 psi) , mm

Examples 12 through 15

Four samples of SA yarns were prepared under the conditions and with the properties as set forth in Table V. The coating conditions were similar to those described for Examples 2—6, except for the yarn types, the SAP precursor solids levels and the SAP precursor application roll speeds. Both the filament and spun yarns were processed from fibers that were about 6 denier per filament. The staple fiber length used for preparing the two feed spun yarns were 152.4 mm (6 inches) . Both the filament yarn samples were twisted 1.38 turns/cm or 3.5 turns/inch before coating. After the continuous coating and drying process, skeins of coated yarns were heat treated for 15 minutes in a circulating hot air oven at 195°C to cross—link the SAP. These examples demonstrated that SAP may be coated onto a variety of yarn types such as filament and spun yarns and onto a variety of fiber types such as round and 4DG cross-sections. Because of differences in the bulk and surface area of the yarn types and fiber types, there were systematic differences in the amounts of SAP coated onto the fibers. The bulk of the feed yarn is described in Table V as the volume (cm³) per unit mass (g) when wound under relatively low tensions into a circular groove. Accordingly, the filament yarn of Example 12 having round cross—section fibers had the lowest % SAP add-on of 50.2. The use of spun yarns and/or the use of the 4DG fiber cross-section resulted in higher % SAP add-on. These effects resulted in the highest % SAP add-on of 125.3 for Example 15 having a base yarn of spun 4DG fiber. Nevertheless, all superabsorbent yarn samples had enhanced water absorption properties relative to the respective properties of uncoated yarns as indicated by the significant swell heights of the yarns with distilled water. The filament yarns and fibers of round cross- section had generally higher tenacities. Consequently, yarn strengths may be balanced with amount of % SAP add—on and other practical absorbent product properties when selecting absorbent yarns or nonwoven fabrics of this invention.

Table V Preparation Conditions and Yarn Properties for Examples 12-15

Example Number 12 13 14 15

Yarn Type Filament Spun Filament Spun

Fiber Type or Cross Section Round Round 4DG 4DG

SAP Precursor Solution Solids, % 24.48 25.74 25.74 24.48

SAP Application Roll Speed, rpm 10.5 10.5 10.5 10.5

TESTS ON YARNS AS PROCESSED ON TOW LINE Total Denier of Uncoated

Feed Yarns, (g/9000m) 1485 1267 1426 1240 Specific Volume of Uncoated

Yarn, cu. cm/g 1.26 1.64 2.18 2.41 1 Total Denier after CO

Conditioning, (g/9000m) 2477 ho

2947 3361 3347

TESTS ON YARNS ADDITIONALLY HEATED 15 MINUTES AT 190°C

Total Denier after Heat 2230 2519 2852 2794

Treatment, (g/9000 m)

Apparent % SAP Add-On 50.2 98.8 100.0 125.3

Tenacity, g/den. 2.77 1.65 0.93 1.33

Elongation, % 47.4 40.0 19.1 27.8

Elastic Modulus, g/denier 14.6 9.6 10.8 12.1

Mean Yarn Strength, N 60.5 40.6 26.0 36.4

Mean Yarn Strength, Pounds 13.61 9.15 5.84 8.19

Yarn Swell Tests with Distilled Water at 414 Pa (0.06 psi 1)

Swell Height, cm/g 1.90 2.39 2.46 2.84

Time to 90% Maximum Swell Height, s 91 104 158 123

Initial Sample Thickness, mm 1.05 1.35 1.52 1.61

Example 16-18

The preparation and properties of SA yarns by the Stationary Groove Process were shown by Examples 16 and 17. The use of SAP syrup having 40% solids and being heated to 100°C resulted in the respective SA yarns having 154% and 406% SAP add-on. Only slight waste of 0.2% was on the drying rolls for the higher % SAP add¬ on. The estimated syrup viscosity was 18 p for Example 16 and 15 p for Example 17 of which both were less than the viscosity for Example 6. Apparently, the combination of higher temperature and higher solids for Example 17 enabled the addition of more SAP without excess waste. The water absorbing properties for the SA yarn with the 406% SAP add-on had higher levels of swell heights reaching 3.52 cm/g and 0.895 cm/g in distilled water and synthetic sea water, respectively.

The preparation and properties of SA yarn by the Coating Chamber Process were shown by Example 18. The use of SA syrup having 45% solids and being heated to 102°C resulted in SA yarn having 424% SAP add—on and only very slight waste of <0.2% on the drying rolls. The estimated syrup viscosity was 29 p at the point of application. This was the same as the viscosity of the unheated syrup of Example 6 in which more roll waste was obtained at lower % SAP add—on. The SA yarn had swell heights of 3.61 cm/g and 0.922 cm/g in distilled water and sea water, respectively. Table VI

Preparation Conditions and Yarn Properti .es for Examples 16-18

Example Number 16 17 18

Yarn Type Spun Spun Spun

Fiber Type or Cross Section 4DG 4DG 4DG

SAP Precursor Solution Application Method Stationary Stationary Coating

Groove Groove Chamber

SAP Precursor Solution Solids, wt % 40 40 45

SAP Application Metering Pump Speed, rpm 13.5 33.4 31.1

Temperature of Syrup after Heater, °C 100 100 102

Estimated Temperature of Syrup Entering ,

Coating Applicator, °C 92 95 97

Estimated Viscosity of Syrup Entering 4>

Coating Applicator, p 18 15 29 ,

SAP Precursor Waste on Drying Rolls,

% of Feed Yarn <0.2 0.2 <0.2

Temperature of Cross-Link Rolls, °C 200 200 200

Time of Cross-Linking, Minutes 14 14 14

TESTS ON YARNS AS PROCESSED ON TOW LINE

Total Denier of Uncoated Feed

Yarns, (g/9000 m) 1311 1240 1240

Specific Volume of Uncoated Yarn,

CU. cm/g 2.41 2.41 2.41

Table VI (Cont'd.)

TESTS ON YARNS DRIED 10 MINUTES AT 120°C

Total Denier after Heat Treatment,

(g/9000 m) 3327 6275 6498 % SAP Add-On 154 406 424

Tenacity, g/den. 0.865 0.469 0.462 Elongation, % 20.6 20.7 21.2 Elastic Modulus, g/den. 7.3 4.7 4.1 Yarn Strength, N 28.2 28.8 29.0 Yarn Strength, Pounds 6.34 6.48 6.61

Yarn Swell Tests with Distilled Water at 414 Pa (0.06 psi) OJ

Ul

Swell Height in 5 Min., cm/g 1.82 3.52 3.61 Time to 90% Swell Height, s 135 229 235 Initial Sample Thickness, mm 1.58 2.52 2.62

Yarn Swell Tests with Sea Water at 414 Pa (0.06 psi)

Swell Height in 5 Min. , cm/g 0.513 0.895 0.922

Time to 90% Maximum Swell Height, s 218 235 240

Initial Sample Thickness, mm 1.48 2.45 2.60

The SA composite fibrous structures may be blended or otherwise combined with other functional materials in the manufacture of articles of commercial use. For example, SA yarns of this invention may be an annular layer in the wrap of a fiber optic cable in which other functional components may include one or more optical fibers with appropriate cladding, metallic strength members, metallic electrical conductor(s) , fibrous bedding materials, and/or a polyolefin outer sheath. The SA composite fibrous structures may be in the form of nonwoven fabrics, as in Examples 8—11, that are useful as components in filters, waste recovery wipes and other absorbent articles.

The SA composite fibrous structures of the present invention offer significant advances over prior art SAP materials. They retain the relatively strong properties of the polymer fiber substrate and also the super- absorbent properties of the SA material. This results in SA composite fibrous structures that are readily handled by conventional fiber and yarn processing equipment at normal environmental conditions such as a relative humidity of 65% and a temperature of 70°C.

This invention has been described in detail with particular reference to preferred embodiments and processes thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. TEST METHODS

Absorbency Test of Fibers and Fabrics for Water

This test is conducted to measure the absorbency time in seconds and the absorptive capacity in grams of distilled water per gram of dry fiber or fabric sample. The test is a modification of ASTM Method D 1117, Section 5.2, "Absorbency Time Test", and Section 5.3, "Absorptive Capacity Test (for Small Test Specimens)". A general description of this test and the changes from the stated ASTM Method D 1117 are given below.

The designated weight of fiber or fabric is placed into a wire basket that is 8 cm high and 5 cm in diameter with one end open. For superabsorbent fibers or fabrics, the 5-g sample specified by the ASTM method can swell to larger size than this basket.

Consequently, a 1—g or a 2—g +/—o.l g sample of material is specified.

The basket with fiber or fabric sample is dropped from a height of 2.54 cm (1 inch) into distilled water at the same time a stop watch is started. The time for the sample to sink completely below the surface of the water (or completely wet out the specimen) is recorded as the value of the absorbency time.

When the sample and basket sink completely below the surface of the water, a second stopwatch is started. For superabsorbent materials, the basket is left submerged for 3 minutes to enable the absorption of the large amounts of water that is characteristic of this class of materials. (The time of submergence for conventional textile materials in the ASTM method is 10 seconds.)

The basket is then lifted with open end up and allowed to drain for 10 seconds. The basket and wet material are then placed in a 127-mm (5-inch) watch glass and weighed immediately. The weight of the water held by the specimen is calculated by subtracting the sum of the weights of the watch glass, the wetted basket, and the dry specimen from the total. The absorptive capacity is calculated as the ratio of the water held by the specimen to the weight of the dry sample. The average of three to five test specimens is reported as the value for the absorptive capacity in this test.

Swell Test of Fibers and Fabrics by Water

This test is conducted to measure the fluid absorption and swelling capabilities of superabsorbent fiber. The test equipment/procedure is called the "FIRET test method" and was developed by the Lantor Corporation. Specifically, this test measures the vertical displacement of a perforated ram which covers a 0.25—g sample of superabsorbent material which is uniformly spread over an 80—mm diameter cup.

Test Procedure, Preparation:

1. Pour 70 ml of distilled water at 25 +/— 3 Celsius into a graduated cylinder.

2. Cut a piece of covering tissue (bridal net) that is 2 mm less in diameter than ram.

3. Place tissue in cup and place ram on top of tissue. (Ram should weigh 88.3 grams, which is 0.06 psi pressure on superabsorbent material during test.)

4. Align pointer on ram with mark on ruler (use a cathetometer) to set zero to measure initial fiber sample thickness.

5. Weigh 0.25+/—0.02 g of the superabsorbent fiber. Record weight. Place superabsorbent fiber sample in cup. Arrange sample in cup so that the fiber or yarn uniformly covers the entire area or the cup.

Place covering tissue (bridal net) on top of the sample.

Gently place measuring ram over the tissue in the cup.

Set cup on jack stand. Align ram and record thickness of dry fiber sample in cm.

Procedure for Measuring Swell Parameters:

1. Realign pointer on ram with zero mark on ruler by lowering the jack stand.

2. Simultaneously pour approximately 70 ml distilled water on ram and start stopwatch.

3. Record expanding height (cm) every 10 seconds for minutes. Continue recording heights for up to 20 minutes, if the material is still swelling.

4. During the test period, add additional fluid to maintain the level near the mid range of the open volume in the upper section of the ram.

Calculations:

1. Calculate and record Maximum Swell Height (cm/g) by dividing the maximum ram displacement (cm) by the dry sample weight (g) . 2. Calculate and record Swell Height in 5 Min. (cm/g) by dividing the ram displacement (cm) at 5 min. by the dry sample weight (g) . 3. Multiply Maximum Swell Height by 0.9 = 90% of Max.

Swell Height (cm) . 4. Look on data sheet to find time at 90% of Max. swell height = Time to 90% Maximum Swell Height

(sec.) and record the time.

Specific Volume The specific volume (SV) is of the yarn is determined by winding the yarn at a specified tension (normally 0.1 grams/denier) into a cylindrical slot of known volume (normally 8.044 cm³). The yarn is wound until the slot is completely filled. The weight of yarn contained in the slot is determined to the nearest 0.1 mg. The specific volume is then defined as

SV (at 0.1 G/D tension) = 8.044 cm³ . wt of yarn in gms

Claims

CLAIMS We claim:

1. A composite fibrous structure for absorption of liquids comprising a yarn or nonwoven fabric coated with a superabsorbent polymer in an amount of up to 500% SAP add—on, said yarn or nonwoven fabric comprising a plurality of fibers having a non—round cross—section.

2. The composite fibrous structure of claim 1 wherein said yarn is coated with said superabsorbent polymer in an amount of 50 to 500% SAP add—on.

3. The composite fibrous structure of claim 2 wherein said yarn has 100 to 400% SAP add-on.

4. The composite fibrous structure of claim 1 wherein said yarn is a filament yarn having up to 300% SAP add¬ on.

5. The composite fibrous structure of claim 4 wherein said filament yarn has 50 to 250% SAP add-on.

6. The composite fibrous structure of claim 1 wherein said yarn is spun yarn having up to 500% SAP add—on.

7. The composite fibrous structure of claim 6 wherein said spun yarn has 150 to 400% SAP add-on.

8. The composite fibrous structure of claim 1 wherein said nonwoven fabric is coated with said superabsorbent polymer in an amount of 5 to 300% SAP add-on.

9. The composite fibrous structure of claim 8 wherein said nonwoven fabric has 5 to 100% SAP add—on.

10. The composite fibrous structure of claim 1 wherein said fibers made in the form of a filament yarn have a specific volume of said filament yarn being greater than or equal to 1.50 cc/gm.

11. The composite fibrous structure of claim 10 wherein said filament yarn has a specific volume of 2.20 cc/gm and said fibers have a cross—section as that shown in Figure 10.

12. The composite fibrous structure of claim 10 wherein said filament yarn has a specific volume of 2.20 cc/gm and said fibers have a cross—section comprising a plurality of finger—shaped projections such that a shape factor of the fiber cross-section is greater than 1.5, wherein X is the shape factor of the fiber cross- section that satisfies the following equation

* = Ew .

4r + (II-2)D wherein P_w is the wetted perimeter of the fiber and r is the radius of the circumscribed circle circumscribing the fiber cross—section and D is the minor axis dimension across the fiber cross—section.

13. The composite fibrous structure of claim 1 wherein said fibers are synthetic fibers which satisfy the equation

(1-X cos *_a) < 0, wherein θ_a is the advancing contact angle of water measured on a flat film made from the same material as the fiber and having the same surface treatment,

X is the shape factor of the fiber cross—section that satisfies the following equation X =

4r + (ϋ-2)D wherein P_w is the wetted perimeter of the fiber and r is the radius of the circumscribed circle circumscribing the fiber cross—section and D is the minor axis dimension across the fiber cross—section.

14. The composite fibrous structure of claim l wherein said fibers are made from a polymer selected from the group consisting of polyester, polyamide, and polyolefin.

15. The composite fibrous structure of claim 1 wherein said superabsorbent polymer is a reaction product of: (a) a partially neutralized aqueous polymer composition prepared by the reaction of a strong base with a polymer containing at least 25 mole percent recurring units of an α, β—unsaturated monomer having in its molecule one or two carboxyl groups or one or two other groups convertible to and converted to carboxyl groups, the degree of neutralization of the partially neutralized polymer being within the range of from 0.2 to 0.8 equivalent of total carboxyl groups of the a , β— unsaturated monomer, with

(b) from 0.1 to 10 total parts by weight of at least one reactive compound per 100 parts by weight of the partially neutralized aqueous polymer compositions, the reactive compound being a water soluble compound bearing one amine group and at least one hydroxyl group, wherein the reaction product is formed by an ionic bonding reaction between the unneutralized carboxyl groups on the polymer and the amine groups on the reactive compound, and is stable at room temperature.

16. The composite fibrous structure of claim 15 wherein said superabsorbent polymer is a maleic anhydride and isobutylene copolymer with a molecular weight in the range of 200,000 to 300,000.

17. The composite fibrous structure of claim 1 wherein said superabsorbent polymer is a substantially linear polymer made by polymerization of a water soluble ethylenically unsaturated monomer blend, said blend comprising a first monomer that provides carboxylic acid groups and a second monomer that provides hydroxyl groups that react with said carboxylic acid groups forming ester cross—linkages containing only carbon and oxygen atoms.

18. A process for preparing a yarn coated with superabsorbent polymer comprising the steps of: a) feeding an uncoated yarn comprised of a plurality of fibers having a non—round cross—section to a syrup application unit having a grooved, rotating roll with a bottom surface immersed into a reservoir containing a superabsorbent polymer precursor, b) passing the uncoated yarn across a top portion of the grooved roll with the yarn contacting the groove at an angle sufficient for maximum contact and take up of the superabsorbent polymer precursor in the groove, c) drying the coated yarn to remove moisture, and d) applying a sufficient amount of heat to the coated yarn to convert the superabsorbent polymer precursor to a cured superabsorbent polymer.

19. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 18 wherein step a) the groove has a width of 1.5 to 4 times the diameter of the uncoated yarn and a depth of 1 to 4 times the diameter of the uncoated yarn.

20. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 18 wherein step b) the angle is 20 degrees less than horizontal.

21. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 18 wherein the superabsorbent polymer precursor is in the form of a syrup comprising a diluted amount of the superabsorbent polymer precursor.

22. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 21 wherein the syrup has a solids level of 10 to 35 weight percent and the coated yarn has a 50 to 200% SAP add-on.

23. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 18 wherein said fibers in the form of a filament yarn have a specific volume of said filament yarn being greater than or equal to 1.50 cc/gm.

24. A process for preparing a yarn coated with superabsorbent polymer comprising the steps of: a) feeding an uncoated yarn comprised of a plurality of fibers having a non—round cross-section to a syrup application unit having a stationary V-shaped guide contacting a reservoir containing a syrup comprising a superabsorbent polymer precursor, b) passing the uncoated yarn through the guide for contact and take up of the superabsorbent polymer precursor in the guide, c) drying the coated yarn to remove moisture, and d) applying a sufficient amount of heat to the coated yarn to convert the superabsorbent polymer precursor to a cured superabsorbent polymer.

25. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 24 wherein the superabsorbent polymer precursor is in the form of a syrup comprising a diluted amount of the superabsorbent polymer precursor.

26. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 25 wherein the syrup has a solids level of 20 to 45 weight percent.

27. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 24 wherein said fibers in the form of a filament yarn have a specific volume of said filament yarn being greater than or equal to 1.50 cc/gm.

28. A process for preparing a yarn coated with superabsorbent polymer comprising the steps of: a) feeding an uncoated yarn comprised of a plurality of fibers having a non—round cross-section through an entrance tube into a substantially closed syrup application chamber containing a superabsorbent polymer precursor, b) withdrawing a coated yarn from the chamber through an exit tube having a larger diameter than the entrance tube, c) drying the coated yarn to remove moisture, and d) applying a sufficient amount of heat to the coated yarn to convert the superabsorbent polymer precursor to a cured superabsorbent polymer.

29. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 28 wherein the superabsorbent polymer precursor is in the form of a syrup comprising a diluted amount of the superabsorbent polymer precursor.

30. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 29 wherein the syrup has a solids level of 20 to 60 weight percent.

31. The process for preparing a yarn coated with superabsorbent polymer as recited in claim 28 wherein said fibers in the form of a filament yarn have a specific volume of said filament yarn being greater than or equal to 1.50 cc/gm.