Mixed Polymer Superabsorbent Fibers And Method For Their Preparation

Abstract

A method for making mixed polymer composite fibers in which a carboxyalkyl cellulose and a galactomannan polymer or a glucomannan polymer are blended in water to provide an aqueous solution; the aqueous solution treated with a first crosslinking agent to provide a gel; the gel is formed into get fibers using melt blowing, centrifugal spinning, wet spinning or dry-jet wet spinning; and the fibers treated with water miscible solvent to form mixed polymer composite fibers. The fiber has a diameter in the range of 50 μm to 1000 μm.

Description

RELATIONSHIP TO OTHER APPLICATIONS

This application is a continuation-in-part of application Ser. No. 11/537,849, Methods for the preparation of mixed polymer superabsorbent fibers, and application Ser. No. 11/537,989, Mixed polymer superabsorbent fibers, both filed Oct. 2, 2006, and.

BACKGROUND OF THE INVENTION

Personal care absorbent products, such as infant diapers, adult incontinent pads, and feminine care products, typically contain an absorbent core that includes superabsorbent polymer particles distributed within a fibrous matrix. Superabsorbents are water-swellable, generally water-insoluble absorbent materials having a high absorbent capacity for body fluids. Superabsorbent polymers (SAPs) in common use are mostly derived from acrylic acid, which is itself derived from petroleum oil, a non-renewable raw material. Acrylic acid polymers and SAPs are generally recognized as not being biodegradable. Despite their wide use, some segments of the absorbent products market are concerned about the use of non-renewable petroleum oil derived materials and their non-biodegradable nature. Acrylic acid based polymers also comprise a meaningful portion of the cost structure of diapers and incontinent pads. Users of SAP are interested in lower cost SAPs. The high cost derives in part from the cost structure for the manufacture of acrylic acid which, in turn, depends upon the fluctuating price of petroleum oil. Also, when diapers are discarded after use they normally contain considerably less than their maximum or theoretical content of body fluids. In other words, in terms of their fluid holding capacity, they are “over-designed”. This “over-design” constitutes an inefficiency in the use of SAP. The inefficiency results in part from the fact that SAPs are designed to have high gel strength (as demonstrated by high absorbency under load or AUL). The high gel strength (upon swelling) of currently used SAP particles helps them to retain a lot of void space between particles, which is helpful for rapid fluid uptake. However, this high “void volume” simultaneously results in there being a lot of interstitial (between particle) liquid in the product in the saturated state. When there is a lot of interstitial liquid the “rewet” value or “wet feeling” of an absorbent product is compromised.

In personal care absorbent products, U.S. southern pine fluff pulp is commonly used in conjunction with the SAP. This fluff is recognized worldwide as the preferred fiber for absorbent products. The preference is based on the fluff pulp's advantageous high fiber length (about 2.8 mm) and its relative ease of processing from a wetland pulp sheet to an airlaid web. Fluff pulp is also made from renewable and biodegradable cellulose pulp fibers. Compared to SAP, these fibers are inexpensive on a per mass basis, but tend to be more expensive on a per unit of liquid held basis. These fluff pulp fibers mostly absorb within the interstices between fibers. For this reason, a fibrous matrix readily releases acquired liquid on application of pressure. The tendency to release acquired liquid can result in significant skin wetness during use of an absorbent product that includes a core formed exclusively from cellulosic fibers. Such products also tend to leak acquired liquid because liquid is not effectively retained in such a fibrous absorbent core.

Superabsorbent produced in fiber form has a distinct advantage over particle forms in some applications. Such superabsorbent fiber can be made into a pad form without added non superabsorbent fiber. Such pads will also be less bulky due to elimination or reduction of the non superabsorbent fiber used. Liquid acquisition will be more uniform compared to a fiber pad with shifting superabsorbent particles.

A need therefore exists for a fibrous superabsorbent material that is simultaneously made from a biodegradable renewable resource like cellulose that is inexpensive. In this way, the superabsorbent material can be used in absorbent product designs that are efficient. These and other objectives are accomplished by the invention set forth below.

SUMMARY OF THE INVENTION

The present invention provides a method for making mixed polymer composite fibers. In the method, a carboxyalkyl cellulose and a galactomannan polymer or glucomannan polymer are blended in water to provide an aqueous solution; the aqueous solution treated with a first crosslinking agent to provide a gel.

In one embodiment the get is then spun into gel fibers using centrifugal spinning. In another embodiment the gel is extruded into gel fibers using meltblowing. In another embodiment the gel is formed into gel fibers using wet spinning.

In an embodiment the spun or extruded gel fibers are precipitated into solid fibers by being passed into a solvent bath to provide mixed polymer composite fibers. In another embodiment the spun or extruded gel fibers are precipitated into solid fibers by being sprayed with a solvent to provide mixed polymer composite fibers. The solvent bath or spray uses a water miscible solvent.

In another embodiment the bath or spray may contain a second crosslinking agent to provide further crosslinking of the fibers.

The mixed polymer composite fibers may then be dried.

The method allows fibers of a specific and predetermined diameter and cross-section to be formed. The fibers may have diameter of 50 μm to 1000 μm. In some instances the diameter of the fibers may vary along the fiber length.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a dry-jet wet process.

FIG. 2 is a diagram of a centrifugal spinning process.

FIG. 3 is a diagram of a meltblow spinning process.

FIG. 4 is a diagram of a meltblow head for the meltblow spinning process.

FIG. 5 is a diagram of a wet spinning process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for making mixed polymer composite fibers. In the method, a carboxyalkyl cellulose and a galactomannan polymer or glucomannan polymer are blended in water to provide an aqueous solution; the aqueous solution treated with a first crosslinking agent to provide a gel; the gel is then spun or extruded into fibers using centrifuge spinning, meltblowing or wet spinning methods. The spun or extruded fibers pass into a solvent bath to provide formed fibers. The solvent is a water-miscible solvent/water mixture. The bath may contain a second crosslinking agent to provide further crosslinking of the fibers.

The mixed polymer composite fiber is a fiber comprising a carboxyalkyl cellulose and a galactomannan polymer or glucomannan polymer. The carboxyalkyl cellulose, which is mainly in the sodium salt form, can be in other salts forms such as potassium and ammonium forms. The mixed polymer composite fiber is formed by intermolecular crosslinking of mixed polymer molecules, and is water insoluble and water-swellable.

As used herein, the term “mixed polymer composite fiber” refers to a fiber that is the composite of two different water soluble polymers (i.e., mixed polymers). The mixed polymer composite fiber is a homogeneous composition that includes two associated polymers: (1) a carboxyalkyl cellulose and (2) either a galactomannan polymer or a glucomannan polymer.

The carboxyalkyl cellulose useful in making the mixed polymer composite fiber has a degree of carboxyl group substitution (DS) of from about 0.3 to about 2.5. In one embodiment, the carboxyalkyl cellulose has a degree of carboxyl group substitution of from about 0.5 to about 1.5.

Although a variety of carboxyalkyl celluloses are suitable for use in making the mixed polymer composite fiber, in one embodiment, the carboxyalkyl cellulose is carboxymethyl cellulose. In another embodiment, the carboxyalkyl cellulose is carboxyethyl cellulose.

The carboxyalkyl cellulose is present in the mixed polymer composite fiber in an amount from about 60 to about 99% by weight based on the weight of the mixed polymer composite fiber. In one embodiment, the carboxyalkyl cellulose is present in an amount from about 80 to about 95% by weight based on the weight of the mixed polymer composite fiber. In addition to carboxyalkyl cellulose derived from wood pulp containing some carboxyalkyl hemicellulose, carboxyalkyl cellulose derived from non-wood pulp, such as cotton linters, is suitable for preparing the mixed polymer composite fiber. For carboxyalkyl cellulose derived from wood products, the mixed polymer fibers include carboxyalkyl hemicellulose in an amount up to about 20% by weight based on the weight of the mixed polymer composite fiber.

The galactomannan polymer useful in making the mixed polymer composite fiber can include any one of a variety of galactomannan polymers. In one embodiment, the galactomannan polymer is guar gum. In another embodiment, the galactomannan polymer is locust bean gum. In a further embodiment, the galactomannan polymer is tar gum. In another embodiment, the galactomannan polymer is fenugreek gum.

The glucomannan polymer useful in making the mixed polymer composite fiber can include any one of a variety of glucomannan polymers. In one embodiment, the glucomannan polymer is konjac gum.

The galactomannan polymer or glucomannan polymer is present in an amount from about 1 to about 20% by weight based on the weight of the mixed polymer composite fiber. In one embodiment, the galactomannan polymer or glucomannan polymer is present in an amount from about 1 to about 15% by weight based on the weight of the mixed polymer composite fiber. In a further embodiment, the galactomannan polymer or glucomannan polymer is present in an amount from about 2 to about 15% by weight based on the weight of the mixed polymer composite fiber.

The preparation of the mixed polymer composite fiber is a multistep process. First, the water-soluble carboxyalkyl cellulose and galactomannan polymer or glucomannan polymer are dissolved in water. Then, a first crosslinking agent is added and mixed to obtain a mixed polymer composite gel formed by intermolecular crosslinking of water-soluble polymers.

Suitable first crosslinking agents include crosslinking agents that are reactive towards hydroxyl groups and carboxyl groups. Representative crosslinking agents include metallic crosslinking agents, such as aluminum (III) compounds, titanium (IV) compounds, bismuth (III) compounds, boron (III) compounds, and zirconium (IV) compounds. The numerals in parentheses in the preceding list of metallic crosslinking agents refers to the valency of the metal.

In one embodiment the gel is formed into fibers through the use of a dry-jet wet spinning process. A diagram of the dry jet wet spinning process is shown in FIG. 1. The gel is pumped through a transfer line 1 through a spinning block 2, through the orifices of spinneret 3 through a layer of gas or air 5 and into a bath 6 where the fibers 4 are conducted by guides 7 and 8 and precipitated into mixed polymer composite fiber 15 which is wound up on a take-up roll 9.

In another embodiment the gel is formed into fibers through the use of centrifugal spinning. FIG. 2 is a diagram of centrifugal spinning. In centrifugal spinning the gel 20 is directed in a generally hollow cylinder or drum 21 with a closed base and a multiplicity of small apertures 22 in its sidewalls 23. As the cylinder rotates, the gel is forced out horizontally through the apertures as thin gel strands or gel fibers 24. As the strands meet resistance from the surrounding air they are drawn or stretched. The amount of stretch will depend on readily controllable factors such as cylinder rotational speed, orifice size of the apertures and the viscosity of the gel. The strands either fall by gravity or are forced down by air flow into a water miscible solvent 25 held in a basin 26 where the gel fibers are precipitated into mixed polymer composite fibers. Alternatively, the fibers 24 may be sprayed with a water-miscible solvent from a ring of spray nozzles 27 fed by line 28.

In another embodiment the gel is formed into fibers through the use of melt blowing technology. FIGS. 3 and 4 are diagrams of melt blowing. In melt blowing the gel is directed to an extruder 32 which forces the gel through an orifice head 34 having a multiplicity of orifices 36. Air or another gas is supplied through lines 38 and surrounds and transports extruded gel fibers 40. The air or gas moves in parallel with the fibers and impinges on the fibers, transporting the fibers, and drawing and stretching the fibers. The gel fibers move into the bath 42 which contains a water-miscible solvent 44 which precipitates the gel fibers to form mixed polymer composite fibers. As in centrifugal spinning the gel fibers may be sprayed with the water-miscible solvent to form the mixed polymer composite fibers instead of being placed in a bath. Below orifice 36 and above bath 42, solvent circulated from bath 42 can be sprayed onto fibers 40 too.

FIG. 4 shows a typical extrusion orifice. The orifice plate 50 is bored with a multiplicity of orifices 36. The plate 50 is held to the body of the extrusion head 51 by a series of cap screws 52. An internal member 53 forms the extrusion ports 54 for the gel. It is embraced by air passages 55 that surround the extruded gel fibers 40 causing them to be drawn and to assist in their transport to the bath. The amount the gel fibers are drawn or stretched will depend on the viscosity of the gel, the speed of the fiber travel and the gas travel, and the angle between the gas and the fiber. Depending on the speed and angle of the fiber and gas, long continuous fibers may be formed or short fibers may be formed.

In another embodiment the gel may be formed into fibers by wet spinning. A diagram of wet spinning is shown in FIG. 5. In wet spinning the gel is passed by a pump 60 through pipe 61 leading into bath 62 containing the water-miscible solvent 63. The gel is extruded through spinneret 64 directly into the bath to form mixed polymer composite fibers 65 which are guided from by the transfer roll 66 to a take up roll. The amount of time of the gel in the bath will depend on the speed of the fibers and the placement of the spinneret in the bath. A short retention time is shown. A different placement of the spinneret will increase the retention time in the bath. The fibers are fixed in the bath. Alternatively, fiber 65 can be collected on a moving screen.

The mixed polymer composite fiber thus obtained may be further crosslinked (e.g., surface crosslinked) by treating with a second crosslinking agent in the treating bath or spray. The second crosslinking agent can be the same as or different from the first crosslinking agent. The need for a second crosslinking step will depend on the amount of crosslinking that has been generated in the initial crosslinking. If the initial crosslinking is light then the fiber generated after first crosslinking has a high level of sliminess when hydrated and forms soft gels and cannot be used in absorbent applications without further treatment. If the crosslinking in the first or initial crosslinking is greater the fiber generated after the first crosslinking will not be slimy and will be a hard gel.

The mixed polymer fibers are substantially insoluble in water while being capable of absorbing water. The fibers are rendered water insoluble by virtue of a plurality of non-permanent intra-fiber metal crosslinks. As used herein, the term “non-permanent intra-fiber metal crosslinks” refers to the nature of the crosslinking that occurs within individual modified fiber (i.e., intra-fiber) and among and between each fiber's constituent polymer molecules.

The fibers are intra-fiber crosslinked with metal crosslinks. The metal crosslinks arise as a consequence of an associative interaction (e.g., bonding) between functional groups (e.g., carboxy, carboxylate, or hydroxyl groups) of the fiber's polymers and a multi-valent metal species. Suitable multi-valent metal species include metal ions having a valency of three or greater and that are capable of forming associative interpolymer interactions with functional groups of the polymer molecules (e.g., reactive toward associative interaction with the carboxy, carboxylate, or hydroxyl groups). The polymers are crosslinked when the multi-valent metal species form associative interpolymer interactions with functional groups on the polymers. A crosslink may be formed intramolecularly within a polymer or may be formed intermolecularly between two or more polymer molecules within a fiber. The extent of intermolecular crosslinking affects the water solubility of the composite fibers (i.e., the greater the crosslinking, the greater the insolubility) and the ability of the fiber to swell on contact with an aqueous liquid.

The fibers include non-permanent intrafiber metal crosslinks formed both intermolecularly and intramolecularly in the population of polymer molecules. As used herein, the term “non-permanent crosslink” refers to the metal crosslink formed with two or more functional groups of a polymer molecule (intramolecularly) or formed with two or more functional groups of two or more polymer molecules (intermolecularly). It will be appreciated that the process of dissociating and re-associating (breaking and reforming crosslinks) the multi-valent metal ion and polymer molecules is dynamic and also occurs during liquid acquisition. During water acquisition the individual fibers and fiber bundles swell and change to gel state. The ability of non-permanent metal crosslinks to dissociate and associate under water acquisition imparts greater freedom to the gels to expand than if the gel was restrictively crosslinked by permanent crosslinks that do not have the ability to dissociate and re-associate. Covalent organic crosslinks, such as ether crosslinks, are permanent crosslinks that do not dissociate and re-associate.

The fibers have fiber widths of from about 2 μm to about 100 μm and coarseness that varies from soft to rough. Melt blown fibers have diameters that vary along the length of the fiber to give an undulating cross section to the fiber.

The fibers are highly absorptive fibers. The fibers can have a Free Swell Capacity of from about 25 to about 60 g/g (0.9% saline solution), a Centrifuge Retention Capacity (CRC) of from about 15 to about 35 g/g (0.9% saline solution), and an Absorbency Under Load (AUL) of from about 15 to about 30 g/g (0.9% saline solution).

The fibers can be formed into pads by conventional methods including air-laying techniques to provide fibrous pads having a variety of liquid wicking characteristics. For example, pads can absorb liquid at a rate of from about 10 ml/sec to about 0.005 ml/sec (0.9% saline solution/10 ml application). The integrity of the pads can be varied from soft to very strong.

The mixed polymer composite fibers are water insoluble and water swellable. Water insolubility is imparted to the fiber by intermolecular crosslinking of the mixed polymer molecules, and water swellability is imparted to the fiber by the presence of carboxylate anions with associated cations. The fibers are characterized as having a relatively high liquid absorbent capacity for water (e.g., pure water or aqueous solutions, such as salt solutions or biological solutions such as urine). Furthermore, because the mixed polymer fiber has the structure of a fiber, the mixed polymer composite fiber also possesses the ability to wick liquids. The mixed polymer composite fiber advantageously has dual properties of high liquid absorbent capacity and liquid wicking capacity.

Mixed polymer fibers having slow wicking ability of fluids are useful in medical applications, such as wound dressings and others. Mixed polymer fibers having rapid wicking capacity for urine are useful in personal care absorbent product applications. The mixed polymer fibers can be prepared having a range of wicking properties from slow to rapid for water and 0.9% aqueous saline solutions.

The mixed polymer composite fibers are useful as superabsorbents in personal care absorbent products (e.g., infant diapers, feminine care products and adult incontinence products). Because of their ability to wick liquids and to absorb liquids, the mixed polymer composite fibers are useful in a variety of other applications, including, for example, wound dressings, cable wrap, absorbent sheets or bags, and packaging materials.

In one aspect of the invention, methods for making mixed polymer composite fibers are provided. In the methods, the mixed polymer composite fibers are formed by spinning or extruding the gel into a fiber and then precipitating the fiber to form a mixed polymer composite fiber by a water-miscible solvent bath or spray.

In one embodiment, the method for making the mixed polymer composite fibers (crosslinked fibers) includes the steps of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form) and a galactomannan polymer or a glucomannan polymer in water to provide an aqueous solution; (b) treating the aqueous solution with a first crosslinking agent to provide a gel; (c) forming a fiber from the gel by centrifugal spinning; and (d) treating the gel fiber in a water-miscible solvent bath or by water-miscible solvent spray to provide to precipitate the mixed polymer composite fibers.

In another embodiment, the method for making the mixed polymer composite fibers (crosslinked fibers) includes the steps of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form) and a galactomannan polymer or a glucomannan polymer in water to provide an aqueous solution; (b) treating the aqueous solution with a first crosslinking agent to provide a gel; (c) forming a fiber from the gel by melt blowing; and (d) treating the gel fiber in a water-miscible solvent bath or by water-miscible solvent spray to provide mixed polymer composite fibers.

In another embodiment, the method for making the mixed polymer composite fibers (crosslinked fibers) includes the steps of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form) and a galactomannan polymer or a glucomannan polymer in water to provide an aqueous solution; (b) treating the aqueous solution with a first crosslinking agent to provide a gel; (c) forming a fiber from the gel by wet spinning; and (d) treating the gel fiber in a water-miscible solvent bath to provide mixed polymer composite fibers.

In another embodiment, the method for making the mixed polymer composite fibers (crosslinked fibers) includes the steps of: (a) blending a carboxyalkyl cellulose (e.g., mainly salt form) and a galactomannan polymer or a glucomannan polymer in water to provide an aqueous solution; (b) treating the aqueous solution with a first crosslinking agent to provide a gel; (c) forming a fiber from the gel by jet-dry wet spinning; and (d) treating the gel fiber in a water-miscible solvent bath to provide mixed polymer composite fibers.

In another embodiment step (d) in each of the above methods may include treating the fibers with a second crosslinking agent (e.g., surface crosslinking) by having the second crosslinking agent in the bath or spray to provide mixed polymer composite fibers.

The fibers may have a diameter of 50 μm to 1000 μm. Melt blown fibers may be nonuniform in diameter along the fiber length.

The mixed polymer composite fibers so prepared can be dried.

The fibers may have a diameter of 50 μm to 1000 μm.

In the process, a carboxyalkyl cellulose and a galactomannan polymer or a glucomannan polymer are blended in water to provide an aqueous solution.

Suitable carboxyalkyl celluloses have a degree of carboxyl group substitution of from about 0.3 to about 2.5, and in one embodiment have a degree of carboxyl group substitution of from about 0.5 to about 1.5. In one embodiment, the carboxyalkyl cellulose is carboxymethyl cellulose. The aqueous solution includes from about 60 to about 99% by weight carboxyalkyl cellulose based on the weight of the product mixed polymer composite fiber. In one embodiment, the aqueous solution includes from about 80 to about 95% by weight carboxyalkyl cellulose based on the weight of mixed polymer composite fiber.

Suitable galactomannan polymers include guar gum, locust bean gum, tara gum, and fenugreek gum. Suitable glucomannan polymers include konjac gum. The galactomannan polymer or glucomannan polymer can be from natural sources or obtained from genetically-modified plants. The aqueous solution includes from about 1 to about 20% by weight galactomannan polymer or glucomannan polymer based on the weight of the mixed polymer composite fibers, and in one embodiment, the aqueous solution includes from about 1 to about 15% by weight galactomannan polymer or glucomannan polymer based on the weight of mixed polymer composite fibers.

In the method, the aqueous solution including the carboxyalkyl cellulose and galactomannan polymer or glucomannan polymer is treated with a suitable amount of a first crosslinking agent to provide a gel.

Suitable first crosslinking agents include crosslinking agents that are reactive towards hydroxyl groups and carboxyl groups. Representative crosslinking agents include metallic crosslinking agents, such as aluminum (II) compounds, titanium (IV) compounds, bismuth (III) compounds, boron (III) compounds, and zirconium (IV) compounds. The numerals in parentheses in the preceding list of metallic crosslinking agents refers to the valency of the metal.

Representative metallic crosslinking agents include aluminum sulfate; aluminum hydroxide; dihydroxy aluminum acetate (stabilized with boric acid); other aluminum salts of carboxylic acids and inorganic acids; other aluminum complexes, such as Ultrion 8186 from Nalco Company (aluminum chloride hydroxide); boric acid; sodium metaborate; ammonium zirconium carbonate; zirconium compounds containing inorganic ions or organic ions or neutral ligands; bismuth ammonium citrate; other bismuth salts of carboxylic acids and inorganic acids; titanium (IV) compounds, such as titanium (IV) bis(triethylaminato) bis(isopropoxide) (commercially available from the Dupont Company under the designation Tyzor TE); and other titanates with alkoxide or carboxylate ligands.

The first crosslinking agent is effective for associating and crosslinking the carboxyalkyl cellulose (with or without carboxyalkyl hemicellulose) and galactomannan polymer molecules. The first crosslinking agent is applied in an amount of from about 0.1 to about 20% by weight based on the total weight of the mixed polymer composite fiber. The amount of first crosslinking agent applied to the polymers will vary depending on the crosslinking agent. In general, the fibers have an aluminum content of about 0.04 to about 0.8% by weight based on the weight of the mixed polymer composite fiber for aluminum crosslinked fibers, a titanium content of about 0.10 to about 1.5% by weight based on the weight of the mixed polymer composite fiber for titanium crosslinked fibers, a zirconium content of about 0.09 to about 2.0% by weight based on the weight of the mixed polymer composite fiber for zirconium crosslinked fibers, and a bismuth content of about 0.90 to about 5.0% by weight based on the weight of the mixed polymer composite fiber for bismuth crosslinked fibers.

The gel formed by treating the aqueous solution of a carboxyalkyl cellulose and a galactomannan polymer with a first crosslinking agent is then spun or extruded into a gel fiber by centrifugal spinning, meltblowing or wet spinning.

The spun or extruded gel fibers are then precipitated to form mixed polymer composite fibers by treatment by a water-miscible solvent in either a bath or spray.

Suitable water-miscible solvents include water-miscible alcohols and ketones. Representative water-miscible solvents include acetone, methanol, ethanol, isopropanol, and mixtures thereof. In one embodiment, the water-miscible solvent is ethanol. In another embodiment, the water-miscible solvent is isopropanol.

If the fibers formed from the spinning or extrusion step are treated in a mixture of water and a water miscible solvent, the proportions of water and solvent must be such that the fibers do not lose their fiber form and form a gel.

A second crosslinking agent may be used in the bath or spray. The second crosslinking agent is effective in further crosslinking (e.g., surface crosslinking) the mixed polymer composite fibers. Suitable second crosslinking agents include crosslinking agents that are reactive towards hydroxyl groups and carboxyl groups. The second crosslinking agent can be the same as or different from the first crosslinking agent. Representative second crosslinking agents include the metallic crosslinking agents noted above useful as the first crosslinking agents.

The second crosslinking agent can be applied at a relatively higher level than the first crosslinking agent per unit mass of fiber. This provides a higher degree of crosslinking on the surface of the fiber relative to the interior of the fiber. As described above, metal crosslinking agents form crosslinks between carboxylate anions and metal atoms or hydroxyl oxygen and metal atoms. These crosslinks can migrate from one oxygen atom to another when the mixed polymer fiber absorbs water and forms a gel. However, having a higher level of crosslinks on the surface of the fiber relative to the interior provides a superabsorbent fiber with a suitable balance in free swell, centrifuge retention capacity, absorbency under load for aqueous solutions and lowers the gel blocking that inhibits liquid transport.

The second crosslinking agent is applied in an amount from about 0.1 to about 20% by weight based on the total weight of mixed polymer composite fibers. The amount of second crosslinking agent applied to the polymers will vary depending on the crosslinking agent. The product fibers have an aluminum content of about 0.04 to about 2.0% by weight based on the weight of the mixed polymer composite fiber for aluminum crosslinked fibers, a titanium content of about 1.0 to about 4.5% by weight based on the weight of the mixed polymer composite fiber for titanium crosslinked fibers, a zirconium content of about 0.09 to about 6.0% by weight based on the weight of the mixed polymer composite fiber for zirconium crosslinked fibers; and a bismuth content of about 0.09 to about 5.0% by weight based on the weight of the mixed polymer composite fiber for bismuth crosslinked fibers.

The second crosslinking agent may be the same as or different from the first crosslinking agent. Mixtures of two or more crosslinking agents in different ratios may be used in each crosslinking step.

The resultant fibers, either with one crosslinking agent or surface crosslinked with a second crosslinking agent, are then washed with a water-miscible solvent and air dried or oven dried below 80° C. to provide the mixed polymer composite fibers.

The preparation of representative mixed polymer composite fibers are described in Examples 1-2.

Test Methods

Free Swell and Centrifuge Retention Capacities

The materials, procedure, and calculations to determine free swell capacity (g/g) and centrifuge retention capacity (CRC) (gig) were as follows.

Test Materials:

Japanese pre-made empty tea bags (available from Drugstore.com, IN PURSUIT OF TEA polyester tea bags 93 mm×70 mm with fold-over flap. (http:www.mesh.ne.jp/tokiwa/)).

Balance (4 decimal place accuracy, 0.0001 g for air-dried superabsorbent polymer (ADS SAP) and tea bag weights); timer; 1% saline; drip rack with clips (NLM 211); and lab centrifuge (NLM 211, Spin-X spin extractor, model 776S, 3,300 RPM, 120 v).

Test Procedure:

1. Determine solids content of ADS.

2. Pre-weigh tea bags to nearest 0.0001 g and record.

3. Accurately weigh 0.2025 g±0.0025 g of test material (SAP), record and place into pre-weighed tea bag (air-dried (AD) bag weight). (ADS weight+AD bag weight=total dry weight).

4. Fold tea bag edge over closing bag.

5. Fill a container (at least 3 inches deep) with at least 2 inches with 1% saline.

6. Hold tea bag (with test sample) flat and shake to distribute test material evenly through bag.

7. Lay tea bag onto surface of saline and start timer.

8. Soak bags for specified time (e.g., 30 minutes).

9. Remove tea bags carefully, being careful not to spill any contents from bags, hang from a clip on drip rack for 3 minutes.

10. Carefully remove each bag, weigh, and record (drip weight).

11. Place tea bags onto centrifuge walls, being careful not to let them touch and careful to balance evenly around wall.

12. Lock down lid and start timer. Spin for 75 seconds.

13. Unlock lid and remove bags. Weigh each bag and record weight (centrifuge weight).

Calculations:

The tea bag material has an absorbency determined as follows:

Free Swell Capacity, factor=5.78

Centrifuge Capacity, factor=0.50

Z=Oven dry SAP wt (g)/Air dry SAP wt (g)

Free Capacity (g/g):

$\frac{\begin{array}{c}\left[\left(\mathrm{drip}\mathrm{wt}\left(g\right)-\mathrm{dry}\mathrm{bag}\mathrm{wt}\left(g\right)\right)-\left(\mathrm{AD}\mathrm{SAP}\mathrm{wt}\left(g\right)\right)\right]-\\ \left(\mathrm{dry}\mathrm{bag}\mathrm{wt}\left(g\right)*5.78\right)\end{array}}{\left(\mathrm{AD}\mathrm{SAP}\mathrm{wt}\left(g\right)*Z\right)}$

Centrifuge Retention Capacity (g/g):

$\frac{\begin{array}{c}\left[\mathrm{centrifuge}\mathrm{wt}\left(g\right)-\mathrm{dry}\mathrm{bag}\mathrm{wt}\left(g\right)-\left(\mathrm{AD}\mathrm{SAP}\mathrm{wt}\left(g\right)\right)\right]-\\ \left(\mathrm{dry}\mathrm{bag}\mathrm{wt}\left(g\right)*0.50\right)\end{array}}{\left(\mathrm{AD}\mathrm{SAP}\mathrm{wt}*Z\right)}$

Absorbency Under Load (AUL)

The materials, procedure, and calculations to determine AUL were as follows.

Test Materials;

Mettler Toledo PB 3002 balance and BALANCE-LINK software or other compatible balance and software. Software set-up: record weight from balance every 30 sec (this will be a negative number. Software can place each value into EXCEL spreadsheet.

Kontes 90 mm ULTRA-WARE filter set up with fritted glass (coarse) filter plate. clamped to stand; 2 L glass bottle with outlet tube near bottom of bottle; rubber stopper with glass tube through the stopper that fits the bottle (air inlet); TYGON tubing; stainless steel rod/plexiglass plunger assembly (71 mm diameter); stainless steel weight with hole drill through to place over plunger (plunger and weight=867 g); VWR 9.0 cm filter papers (Qualitative 413 catalog number 28310-048) cut down to 80 mm size; double-stick SCOTCH tape; and 0.9% saline.

Test Procedure:

1. Level filter set-up with small level.

2. Adjust filter height or fluid level in bottle so that fritted glass filter and saline level in bottle are at same height.

3. Make sure that there are no kinks in tubing or air bubbles in tubing or under fritted glass filter plate.

4. Place filter paper into filter and place stainless steel weight onto filter paper.

5. Wait for 5-10 min while filter paper becomes fully wetted and reaches equilibrium with applied weight.

6. Zero balance.

7. While waiting for filter paper to reach equilibrium prepare plunger with double stick tape on bottom.

8. Place plunger (with tape) onto separate scale and zero scale.

9. Place plunger into dry test material so that a monolayer of material is stuck to the bottom by the double stick tape.

10. Weigh the plunger and test material on zeroed scale and record weight of dry test material (dry material weight 0.15 g±0.05 g).

11. Filter paper should be at equilibrium by now, zero scale.

12. Start balance recording software.

13. Remove weight and place plunger and test material into filter assembly.

14. Place weight onto plunger assembly.

15. Wait for test to complete (30 or 60 min)

16. Stop balance recording software.

Calculations:

A=balance reading (g)*−1(weight of saline absorbed by test material)

B=dry weight of test material (this can be corrected for moisture by multiplying the AD weight by solids %).

AUL (g/g)=A/B (g 1% saline/1 g test material)

EXAMPLES

The following examples are provided for the purpose of illustrating, not limiting, the invention. In the following examples a laboratory extruder was used. It has a cylinder for the material being extruded and a motor driven piston for extruding the material at a controlled rate. The piston delivers the material through a spin pack with a spinneret having a selected diameter. The diameter of the spinneret can be changed. In the present examples the spinneret discharged directly into a bath.

Example 1

A solution of CMC 9H4F 10.0 g OD in 450 ml deionized (DI) water was prepared with vigorous stirring to obtain a CMC solution. Guar gum (0.6 g) was dissolved in 25 ml DI water and mix well with the CMC solution. The solution was stirred for one hour to allow complete mixing of the two polymers.

The polymer mixture was blended in the blender. Fully dissolve basic dihydroxy aluminum acetate stabilized with boric acid (purchased from Sigma-Aldrich Fine Chemicals) 0.125 g in 25 ml DI water. Transfer the aluminum acetate stabilized with boric acid solution to the polymer solution and blend for five minutes to mix to provide a gel. Leave the gel at ambient temperature (25° C.) for one hour.

Example 2

A solution of CMC 9H4F 10.0 g OD in 950 ml deionized (DI) water was prepared with vigorous stirring to obtain a CMC solution. Guar gum (0.6 g) was dissolved in 25 ml DI water and mix well with the CMC solution. The solution was stirred for one hour to allow complete mixing of the two polymers.

The polymer mixture was blended in the blender. Fully dissolve basic dihydroxy aluminum acetate stabilized with boric acid (purchased from Sigma-Aldrich Fine Chemicals) 0.125 g in 25 ml DI water. Transfer the aluminum acetate stabilized with boric acid solution to the polymer solution and blend for five minutes to provide a gel. Leave the gel at ambient temperature (25° C.) for one hour.

Example 3

The aqueous gels described above in Examples 1 and 2 were extruded in a wet spinning extruder to form a gel fiber. The gel from the Example 1 was a 2% by weight solution and the gel from Example 2 a 1% by weight solution. The get fiber was placed in a denatured ethanol solvent to precipitate the fibers. There was no second crosslinking. The filaments formed were 700 μm in diameter. The following table gives the amount of gel in solution and the free swell, centrifuge capacity and AUL of the fibers. Free swell, centrifuge capacity and AUL are in grams absorbed per gram of fiber.

TABLE 1
	gel in		centrifuge
Example	solution, %	Free swell	capacity	AUL
1	2	31.2	13.32	18.71
1	2	27.16	14.03	22.95
2	1	34.51	17.07	13.23

Example 4

In this example, the preparation of representative mixed polymer composite fibers crosslinked with fresh aluminum sulfate and fresh aluminum sulfate is described. A solution of Weyerhaeuser pine pulp CMC (40 g OD) in 900 ml deionized water was prepared with vigorous stirring to obtain a CMC solution. Guar gum (2.4 g) was dissolved in 50 ml DI water and mixed with the CMC solution. The solution was stirred for one hour to allow complete mixing of the two polymers.

Weigh 0.8 g of fresh aluminum sulfate octadecahydrate and dissolve in 50 ml DI water. Transfer aluminum sulfate solution to the polymer solution and blend for 5 minutes to mix well. Leave the gel at ambient temperature (25° C.) for one hour.

The gel was formed into fibers using wet spinning (one orifice with hole diameter of 500 micron).

The gel fibers entered a water-miscible solvent bath containing 1200 ml water and 3600 ml isopropanol containing a second crosslinker. The crosslinker concentration in the following table is based on the amount of crosslinker per 4 g dry gel extruded. The second crosslinker was also fresh aluminum sulfate. Each portion of precipitated fiber was then soaked in 500 ml of isopropanol and mixed for 10 minutes. The fibers were then dried.

The following table gives the speed of the gel through the orifice, the amount of crosslinker in the bath, and the free swell, and centrifuge capacity of the composite fiber. Free swell, centrifuge capacity and AUL are in grams absorbed per gram of fiber.

	TABLE 2
	gel rate.			centrifuge
	g/min	crosslinker %	free swell	capacity
	30	0.05	35.4	18.54
	30	0.072	41.09	25.16
	30	0.084	40.83	26.71
	30	0.148	29.3	13.69
	10	0.2	38.79	21.15

While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

Claims

1. A method for making mixed polymer composite fibers, comprising:

(a) blending a carboxyalkyl cellulose and a galactomannan polymer or glucomannan polymer in water to provide an aqueous solution;

(b) treating the aqueous solution with a first crosslinking agent to provide a gel;

(c) forming gel fibers from the get using melt blowing, centrifugal spinning, wet spinning, or dry-jet wet spinning,

(d) treating the gel fibers with a water-miscible solvent to provide mixed polymer composite fibers.

2. The method of claim 1 wherein in step (d) the gel fibers are treated in a solvent bath.

3. The method of claim 1 wherein in step (d) the gel fibers are treated by a solvent spray.

4. The method of claim 1 further comprising drying the fiberized fibers to provide dried crosslinked mixed polymer composite fibers.

5. The method of claim 1, wherein the carboxyalkyl cellulose has a degree of carboxyl group substitution of from about 0.3 to about 2.5.

6. The method of claim 1, wherein the carboxyalkyl cellulose is carboxymethyl cellulose.

7. The method of claim 1, wherein the galactomannan polymer is selected from the group consisting of guar gum, locust bean gum, tara gum, and fenugreek gum.

8. The method of claim 1, wherein the glucomannan polymer is konjac gum.

9. The method of claim 1, wherein the aqueous solution comprises from about 60 to about 99 percent by weight carboxyalkyl cellulose based on the total weight of mixed polymer composite fibers.

11. The method of claim 1, wherein the aqueous solution comprises from about 1 to about 20 percent by weight galactomannan or glucomannan polymer based on the total weight of mixed polymer composite fibers.

12. The method of claim 1, wherein the first crosslinking agent is a carboxyl group crosslinking agent.

13. The method of claim 1, wherein the first crosslinking agent is a hydroxyl group crosslinking agent.

14. The method of claim 1, wherein the first crosslinking agent is selected from the group consisting of aluminum (III) compounds, titanium (IV) compounds, bismuth (III) compounds, boron (III) compounds, and zirconium (IV) compounds.

15. The method of claim 1, wherein the first crosslinking agent is applied in an amount from about 0.1 to about 20 percent by weight based on the total weight of mixed polymer composite fibers.

16. The method of claim 1, wherein the water-miscible solvent is an alcohol.

17. The method of claim 1, wherein the water-miscible solvent is selected from the group consisting of methanol, ethanol, isopropanol, and mixtures thereof.

18. The method of claim 1 further comprising treating the gel fibers with a second crosslinking agent during step (d).

19. The method of claim 18, wherein the second crosslinking agent is selected from the group consisting of aluminum (III) compounds, titanium (IV) compounds, bismuth (III) compounds, boron (III) compounds, and zirconium (IV) compounds.

20. The method of claim 18, wherein the second crosslinking agent is applied in an amount from about 0.1 to about 20 percent by weight based on the total weight of crosslinked fibers.

21. A mixed polymer composite fiber, comprising a carboxyalkyl cellulose and a galactomannan polymer or a glucomannan polymer, having a diameter in the range of 50 μm to 1000 μm.