MXPA00005002A

MXPA00005002A - Absorbent foam

Info

Publication number: MXPA00005002A
Authority: MX
Inventors: Jian Qin; Raj Ramaswami Wallajapet Palani; Gary D Williams
Original assignee: Kimberly Clark Co
Priority date: 1997-11-25
Filing date: 2000-05-22
Publication date: 2000-11-01
Also published as: GB2347675B; WO1999026670A1; MX229331B; CO5070628A1; BR9815033A; DE19882845T1; GB2347675A; AR017661A1; GB0015476D0; AU1421399A; KR100552032B1; KR20010032398A

Abstract

An absorbent foam is disclosed which exhibits desirable softness and flexibility properties but which is highly absorbent. In one embodiment, the absorbent foam comprises a water insoluble, water swellable polymer wherein the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam and a value of softness that It is less than about 30 grams of force per gram per square meter of absorbent foam. In a second embodiment, the absorbent foam has an average cell size of the cells in the absorbent foam of between about 10 microns to about 100 microns and an average wall thickness of the cells in the absorbent foam of between about 0. .1 microns to around 30 microns. Such an absorbent foam can be used in a disposable absorbent product intended for the absorption of fluids such as body fluids. A process for preparing an absorbent foam is also described. The process generally involves forming a solution of a polymer in a solvent, freezing the solution at a relatively slow cooling rate at a temperature below the freezing point of the solvent, removing the solvent from the frozen solution, and recovering the polymer to form a polymer foam insoluble in water and inflatable on ag

Description

ABSORBENT FOAM Background of the Invention Field of the Invention The present invention relates to an absorbent foam which exhibits a desirable softness and flexible property but which is nonetheless highly absorbent. Absorbent foam can be used in a disposable absorbent product that is intended for the absorption of fluids such as body fluids. The present invention also relates to a process for preparing an absorbent foam. The process generally comprises forming a soluble polymer solution in a solvent, freezing the solution at a relatively slow cooling rate at a temperature below the freezing point of the solvent, removing the solvent from the frozen solution, and recovering the polymer to form a foam. Polymer insoluble in water and inflatable in water.

Description of Related Art Absorbent products currently find widespread use in many applications. For example, in the areas of child and infant care, diapers and underpants have generally replaced reusable fabric absorbent articles. Typical disposable absorbent products include women's care products such as sanitary towels or tampons, adult incontinence products, and health care products such as surgical covers and wound dressings. A typical disposable absorbent product generally comprises a composite structure that includes an upper sheet, a lower sheet, and an absorbent structure between the upper sheet and the lower sheet. These products usually include some type of fastening system for notching the product on the carrier.

It is known to use absorbent materials generally insoluble in water and swellable in water, commonly known as superabsorbents, in personal care products or disposable absorbers. Such absorbent materials are generally employed in the absorbent products in order to increase the absorbent capacity of such products while reducing the overall volume. Such absorbent materials are generally present in the absorbent products in the form of small particles in a fibrous matrix, such as a wood pulp fluff matrix. A matrix of wood pulp fluff generally has an absorbent capacity of about 6 grams of liquid per gram of fluff. The superabsorbent materials generally have an absorbent capacity of at least about 10, preferably around 20, and often up to 100 times their weight in water. Clearly, the incorporation of such absorbent materials into the disposable absorbent products can reduce the overall volume while the absorbent capacity of such products is increased.

As an alternative to the use of a fibrous matrix containing superabsorbent materials, the absorbent foam compositions are also known. One form of absorbent foam composition is where a foam material, such as polyurethane, is prepared to include particulate superabsorbent material within the polyurethane foam structure. Alternatively, a particulate superabsorbent material is located between at least two layers of a polyurethane foam material to form a layered composite structure. Although such foam structures may be useful absorbent materials in specific applications, they have not been shown to be optimal for use in disposable absorbent products because the absorbent properties tend to be limited. In particular, the foam material in such structures, such as polyurethane, generally does not have sufficient absorbent capacity to retain liquids. Therefore, even when particulate superabsorbent material in the foam structure may be capable of retaining a liquid, the overall ability of the foam structure to absorb and retain a liquid is limited. In addition, the overall absorptive properties of foam structure tend to be limited due to the relatively low surface area to mass ratio of the particulate superabsorbent material in relation to the foam portion of the structure.

Absorbent foams are also known because they are prepared comprising essentially all of the superabsorbent material. Typically, a blowing agent is used to form a water swellable and foamed polymeric liquid absorbent material. However, certain absorbent foams prepared using specific blowing agents have been found to have limited use for liquid absorption or liquid distribution. This is typically due to the physical characteristics of the foam structure, which may include discontinuous channels, a very large cell size, an unacceptably large cell size distribution, and / or capillary diameters that vary widely and at the same time they tend to result in undesirable absorbency rates and capacity and undesirable liquid distribution properties. In addition, known absorbent foams that are prepared comprising essentially all of the superabsorbent material have been found to typically have undesirable nonabsorbent physical characteristics, such as a lack of softness or being too brittle. In addition many of the known foams are hydrophobic in nature require a treatment with a wetting agent or other suitable treatment pastes to obtain a hydrophilic nature. Such undesirable nonabsorbent physical characteristics of an absorbent foam tend to limit the utility of the absorbent foams in the products. Disposable absorbers since such disposable absorbent products generally require the s to be essentially flexible to withstand the rigors of use per consumer and also be sufficiently mild to be comfortably acceptable during use.

Therefore, there is a continuing need for improvement for absorbent foams. In particular, there is a need for an absorbent foam which exhibits a relatively high liquid absorbent capacity but still exhibits desirable softness and flexibility properties. In addition, a need for a process for preparing such foam absorbs that is simple, safe and cost-effective.

It is therefore an object of the present invention to provide an absorbent foam which exhibits a relatively high liquid absorbing capacity but which exhibits desirable physical characteristics such as softness and flexibility properties.

It is also an object of the present invention to provide a process for preparing an absorbent foam that is simple, safe and cost effective.

It is also an object of the present invention to provide a disposable absorbent product which includes an absorbent foam exhibiting a relatively high liquid absorption capacity but still exhibits desirable physical characteristics such as softness flexibility properties.

Synthesis of the Invention The present invention relates to an absorbent foam which exhibits a relatively high liquid absorbent capacity but still exhibits desirable physical characteristics such as softness and flexibility properties.

One aspect of the present invention relates to an absorbent foam comprising an insoluble water insoluble polymer in which the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam and a Softness value q is less than about 30 grams of force per gram per square meter of absorbent foam.

In another aspect, the present invention relates to an absorbent foam comprising a water-swellable and water-insoluble polymer wherein the absorbent foam has average cell size of the cells in the absorbent foam between about 10 microns to about 1000 microns and average wall thickness of the cells in the absorbent foam between about 0.1 microns to about 30 microns.

The present invention also relates to a process for preparing an absorbent foam.

An incorporation of such a process comprises forming a solution of a soluble polymer in a solvent to freeze the solution at a relatively slow cooling rate at a temperature below the freezing point of the solvent, remove the solvent from the frozen solution, optionally treat the polymer for form a polymer insoluble in water and inflatable in water.

Another embodiment of such a process comprises forming a gel solution of a cross-linked polymer in a solvent, freezing the gel solution at a relatively slow cooling rate at a temperature below the freezing point of the solvent and removing the solvent from the g of frozen solution, resulting in a water insoluble and water swellable absorbent polymer foam.

In another aspect, the present invention relates to a disposable absorbent product comprising the absorbent foams described herein.

An incorporation of such a disposable absorbent product comprises a liquid permeable upper sheet, or lower sheet attached to the liquid permeable upper sheet, an absorbent foam of the present invention located in the liquid permeable upper sheet and the lower sheet.

Brief Description of the Drawings Figure 1 is an illustration of the equipment employed in determining the values of Absorbency Under Load and Free Inflation of a foam or absorbent material.

Detailed Description of Preferred Additions The present invention is directed to an absorbent foam which exhibits a relatively high liquid absorbent capacity but still exhibits desirable softness properties of flexibility. The absorbent foam comprises a water insoluble and water swellable polymer. As used in the present invention, the water insoluble and swellable polymer in water to a large extent requires providing the absorbent foam with a liquid absorption capacity. As such, the water insoluble and water swellable polymer needs to be effective for providing a desired amount of absorbent capacity of liquid to the absorbent foam.

As used herein, the term "foam" is generally intended to represent a porous polymer matrix which is an aggregate of hollow cells, the boundaries or walls of which cells comprise solid polymeric material. The cells may be interconnected to form capillary channels or vessels within the foam structure wherein such channels or capillary vessels facilitate the distribution of the liquid within the foam.

As used herein, the term "water-insoluble water-swellable" is intended to refer to a material that when exposed to an excess of water, swells at its equilibrium volume but does not dissolve in water. As such, a water-insoluble and water-swellable material generally retains its original identity or physical structure, but in a highly expanded state, during water absorption, and therefore must have sufficient physical integrity-to resist the flow and fusion with neighboring materials.

As used herein, a material will be considered as being "water soluble" when it is essentially dissolved in an excess of water to form a solution, thus losing its initial and essential shape and becoming a molecular dispersion through a solution of water. Water. As a general rule, a water-soluble material will be free of a substantial degree of cross-linking since cross-linking tends to render the material insoluble in water.

The polymers which are suitable for use in the present invention are generally any polymer which is initially soluble in a solvent so that soluble polymer can be formed in a solution by mixing it with a liquid solvent, such as water, and therefore the polymer is treated to render the material water insoluble and water swellable so that an absorbent foam comprising such an insoluble polymer in water-swellable water exhibits the desired physical absorbency characteristics.

The polymers which are suitable for use in the present invention include a wide variety of anionic, cationic and nonionic materials. Suitable polymers include polyacrylamides, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinyl ethers, polyacrylic acids, polyvinylpyrrolidones, polyvinylmorpholinones, polyamines, polyethyleneimines, polyacrylamides, polyquaternary ammoniums, polysaccharide polymers of natural base such as carboxymethylcelluloses, carboxymethyl starches, hydroxypropyl celluloses, algines, l alginates, carrageenan , acrylic grafted starches, acrylic grafted celluloses, chitin and chitosan and synthetic polypeptides such as polyaspartic acid, polyglutamic acid, polyaspargins, polyglutamines, polylysines and polyarginines, as well as salts, copolymers and mixtures of any of the above polymers.

In an embodiment of the present invention, it is desired that the polymer used be a glazed polymer. As used herein, the term "glazed polymer" is intended to refer to a polymer having a glass transition temperature.

(Tg) above about 23 ° C (around the ambient temperature) at a relative humidity of about 30 percent less. Examples of the glazed polymers include, but are limited to, sodium polyacrylate, polyacrylic acid, sodium carboxymethylcellulose, and chitosan salt polymers. Examples of the non-glazed polymers, include but are not limited to polyethylene oxide, polyvinyl acetat and polyvinyl ether polymers.

One property of the water-swellable water-insoluble polymer which is relevant to its effectiveness in providing a desired amount of the liquid absorbent capacity to an absorbent foam is its molecular weight. Generally, a water-insoluble, water-swellable polymer with higher molecular weight will exhibit a superior liquid absorbent capacity as compared to a water-insoluble, water-swellable polymer with a lower molecular weight.

The water insoluble and swellable polymer useful in the absorbent foam of the present invention may generally have a broad range of molecular weights. A water-insoluble, water-swellable polymer having a relatively high molecular weight is often beneficial for use in the present invention. Notwithstanding this, a wide range of molecular weights is generally suitable for use in the present invention. Water-insoluble and water-swellable polymers suitable for use in the present invention beneficially will have a weight average molecular weight of greater than about 10,000, more beneficially greater than about 100,000, even more beneficially of about 200,000, suitably more about 500,000, more adequately greater than 1,000,000 to around 20,000,000. Methods for determining molecular weight of a polymer are well known in the art.

It is generally desired that the polymer is present in the absorbent foam in an effective amount to result in the absorbent foam exhibiting the desired properties. The polymer will be present in the absorbent foam in an amount by weight that is between about 50 percent by weight to 100 percent by weight, beneficially from about 60 percent by weight to about 100 percent by weight, more beneficially between about 70 percent by weight to about 100 percent by weight, suitably between about 80 percent by weight to about 100 percent by weight, more adequately between about 90 percent by weight about 100 percent by weight, and still m suitably between about 95 percent by weight about 100 percent by weight, wherein all p-hundreds by weight are based on the amount of total weight of the polymer, any agents cross linking any other optional components present in the absorbent espu. In an embodiment of the present invention, it is desired that the absorbent foam consists essentially of the polymer and, optionally, any crosslinking agent used to crosslink the polymer. As will be appreciated by one of skill in the art, such absorbent foam may also comprise an insubstantial amount of solvent retained for the preparation process and / or an insubstantial amount of water vapor absorbed from the air. In general, the presence of any materials in the absorbent foam which is not the water-insoluble and water-swellable polymer will tend to reduce the absorbency of the overall liquid of the absorbent foam. The water insoluble and swellable polymer useful in the absorbent foam will generally be cross-linked. The amount of crosslinking generally must be above a minimum amount sufficient to make the polymer insoluble in water but also somewhat below the maximum amount to allow the polymer to be sufficiently water-swellable so that the water insoluble and swellable poly Water absorbs a desired amount of liquid absorption.

The crosslinking of the polymer can generally occur either while the polymer is in solution after the solvent has been removed from a solution used to prepare the absorbent foam. Such cross-linking of polymer can generally be achieved by any type of different types of cross-linking agents. Tale cross-linking agents will generally be soluble in the solvent that is being used such as water.

One type of cross-linking agent is a latent cross-linking agent. The latent crossover agents are generally either internal latent crossover agents or external latent crossover agents. An internal latent crosslinking agent is generally copolymerizable to the monomer monomers used to prepare the polymer and, therefore, generally comprises at least one vinyl group and a functional group or functionality that is capable of reacting with the side groups on the base polymer such as a carboxyl group (-C00") on a sodium polyacrylate polymer or carboxylic acid group (-COOH) on a polyacrylic acid polymer Examples of suitable copolymerizable crosslinkable agents include ethylenically unsaturated monomers, such as ethylene glycol vinyl eth and amino propyl vinyl ether.

An external latent cross-linking agent generally cross-links the polymer itself after, for example, that a polymer has been formed from a monomer specific monomers used to prepare the polymer and / or polymer has been mixed with a solvent to form a solution. The latent cross-linking agents generally take part in the overall polymerization process, but instead are reactive to the polymer at a later point in time when an adequate cross-linking condition is provided. Suitable cross-sections include the use of heat treatment, such as a temperature above about 60 ° C, exposure to ultraviolet Lu, exposure to micronades, co-steam treatment or high humidity, high-temperature treatment. pressure, oe treatment with an organic solvent.

Suitable external latent cross-linking agents are any organic compound having at least two functional groups or functionalities capable of reacting with the carboxyl, carboxylic acid, amino or hydroxyl group of a polymer. It is desired that such an organic cross-linking agent has been selected from the group consisting of diamines, polyamines, diols, polyols and mixtures thereof; particularly of the group consisting of primary diols, primary polyols, primary diamines and primary polyamines and mixtures thereof. Of the diols and the polyols, those having long carbon chain lengths, such as four or greater, are generally beneficial. Specifically, the cross-linking agent can be selected from the group consisting of chitosan glutamate gelatin type A , diethylene triamine, ethylene glycol, butylene glycol, polyvinyl alcohol, hyaluronic acid, polyethylene and its derivatives and mixtures thereof. Other suitable organic cross-linking agents include monochloroacetic acid, sodium chloroacetate, citric acid, and butanetetracarboxylic acid, and amino acids such as aspartic acid, and mixtures thereof. Another suitable latent cross-linking agent comprises a meta ion with more than two positive charges, such as Al3", Fe3t, Ce +, Ce4" Ti4", Zr4 + and Cr3 *. Suitable ion-cross-linking agents include those of the transition elements which generally have vacant d-orbitals.The suitable metal ion cross-linking agents include A1C FeCl3, Ce2 (S04) 3, Zr (NH4) 4 (CO,) 4 and Ce (NH4) 4 (S04) 4 »2H20, other well-known metal ion compounds and mixtures thereof. Such metal ion cross-linking agents, when used with a particular polymer, are believed to form ionic bonds with the carboxyl, carboxylic groups , amino hydroxyl on the polymer Metal ions with only d positive charges such as Zn + m Ca2 +, or Mg2 +, are also suitable as cross-linking agents for polymer cements.

When the polymer is a cationic polymer, cross-linking agent is a polyanionic material t such as a sodium polyacrylate, a carboxymethyl cellulose or polyphosphate.

A second type of cross linking mechanism that certain polymers are capable of undergoing involves macromolecular rearrangement of the polymer chains during the polymer solidification process so that the polymer forms a superior ordered structure with a high gra of crystallinity which is generally insoluble. in water Suitable polymers for such a crosslinking approach include, but are not limited to, polyvinyl alcohol, chitosan, and carboxymethylcellulose with a relatively low degree of carboxymethylation. The additional strong bond polymer can be established between the polymer chains during the solidification process which results in a material generally soluble in water. An example of this behavior is the union of strong hydrogen in polyvinyl alcohol to form an insoluble material.

Cross-linking agents suitable for a polymer solution gel process are also generally of two different types: either external cross-linking or internal polymerizable agent. The internal cross-linking agent ti is a polymerizable agent but cross-linked in the instant The polymerizable cross-linking agents suitable for the monomer or monomers used to prepare the polymer are generally reactive and, therefore, generally comprise at least two groups functional or functions that are able to react with the monomers. Examples of suitable polymerized crosslinking agents include ethylenically unsaturated monomers such as N, N'-methyl bis-acrylamide for the free-radical polymerization, and polyamines or polyols for condensation polymerization. The second type of cross-linking agent is a reactive compound having at least two functional groups capable of reacting with: a carboxyl, carboxylic acid, amino or hydroxyl groups of a polymer er? _ solution phase wherein such cross-linking is not latent, in the sense of that additional conditions are not necessary to initiate the cross-linking reaction. Suitable cross-linking agents can be selected from the group consisting of aldehydes, such as glutaraldehyde or glycidyl ethers, such as polyethylene glycol diglycidyl ether.

Another approach to forming a cross-linking polymer network in either a polymer solution or a recovered polymer is the use of an energy treatment such as microwave radiation or electron beam radiation to form free radicals in the polymer. which are used to generate cross-linking points. This approach is applicable but is not limited to cases where a cross-linking agent is not used to prepare the absorbent foam.

If the cross-linking agent is used, do you generally want the cross-linking agent to be used in an amount that is beneficial from around? 0.01 percent by weight to about 20 percent by weight more beneficially from about 0.05 percent by weight to about 10 percent by weight, and appropriately from about 0.1 percent per weight to about 5 percent by weight by weight, based on the total weight of the polymer and the crosslinking agent present in an absorbent foam.

In general, a cross-linking catalyst will not be necessary, but will be beneficial, to assist in cross-linking the polymer in order to prepare the absorbent espu of the present invention. For example, if citric acid is used as the cross-linking agent, sodium hypophosphite is beneficially used as a cross-linking catalyst. If a cross-linking catalyst is used, it is generally desired that the cross-linking catalyst be used in an amount of from about 0.01 about 3 percent by weight, suitably from about 0.1 to about 1 percent by weight, based on the total pe of the polymer used.

Although the main absorbent foam components of the present invention have been described above, such absorbent foam is not limited thereto and may include other components that do not adversely affect the desirable properties of the absorbent foam. The example materials which may be used as additional components may include, without limitation, the pigments, the antioxidants, the stabilizers, the plasticizers, the nucleating agents, the surfactants, the waxes, the flow promoters, the solid solvents, the particles, and the materials added to increase the processing of the absorbent foam. Such additional components are included in an absorbent foil, it is generally desired that such additional components be used in an amount that is beneficially less than about 10 percent by weight, more beneficially less than about 5 percent by weight, and suitably less of about 1 percent by weight, wherein, all l percent by weight are based on the total amount of pe of the amount of the polymer, of any cross-linking agents, and any other optional components present in the absorbent foam.

The absorbent foam of the present invention suitably has the ability to absorb a liquid, aq mentioned as the value of Free Swelling (FS). The method p by means of which the value of free inflation is determined is set below in relation to the examples. The Free Inflation values determined as stated below and as reported here refer to the amounts in grams of an aqueous solution, which contains 0.9 percent by weight of sodium chloride, one gram of a material can be absorbed in about 1 hour under a load negligible around 0.01 lb. per square inch (psi). As a general rule, it is desired that the absorbent foam of the present invention have a Free Swell value, for a load of about 0.01 pounds per square inch of at least about 1 beneficially of at least about 15, m beneficially of at least about 20, suitably of at least about 25, more suitably of less than about 30, and up to about- 200 grams per gram of absorbent foam.

The absorbent foam of the present invention also suitably has the ability to absorb a liquid while the absorbent composition is under an external pressure or load, here referred to as the Absorbency Under Load (AUL) value. The ability of the material to absorb liquid while the absorbent composition is under an external load or pressure has been found to be frequently an important feature of an absorbent material used in a disposable absorbent product, since even when used and / or used for a consumer, the disposable absorbent product and frequently subjected to an external pressure or load that may negatively impact the capacity of the absorbent material that is being used to effectively absorb any liquid that is discharged into the disposable absorbent product. The method by which the Absorbency is determined Low Load is established below in relation to the examples. The Absorbency Under Load values determined as stated below and reported here refer to the amount in grams of an aqueous solution containing 0.9 percent by weight sodium chloride, one gram of a material can absorb in 1 hour under a load around 0.3 pounds per square inch (psi). As a general rule, it is desired that the absorbent foam of the present invention have a Low Absorbency value, for a load of about 0.3 pounds per square inch, of at least 10, beneficially of at least 15, more beneficially of at least 20, suitably at least about 25, more suitably at least about 30, and up to about 100 grams per gram absorbent foam.

It has been found that the conditions under which an absorbent foam is stored can potentially impact the absorbent properties of the absorbent foam upon aging. Even conditions relatively soft, such as environmental conditions, such as around 24 ° C and at least about 3 percent relative humidity, suitably between about 30 to about 60 percent relative humidity, can result in a degradation of the absorbent properties of an absorbent foam as it ages. Typically, storage conditions, such as relatively higher temperatures and / or relatively high humidity, compared to environmental conditions, can result in a more rapid and / or more severe degradation of absorbent properties of an absorbent foam as it ages. this.

In an embodiment of the present invention, the absorbent foam of said invention will tend to retain its Free Swell and Absorbency Under Load values after aging. Specifically, an absorbent foam of the present invention can retain more than about 50 percent, suitably more than about 70 percent of its Free Inflation or Absorbency Under Load values after aging for about 60 days. Typically, the aging conditions are at ambient conditions such as about 24 ° C and at least about 3 percent relative humidity. For example, if an absorbent foam of the present invention has an initial Absorbency Under Load value of about 20, that the absorbent foam may have an Absorbency Under Load value of at least about 10, and suitably about 14, after aging for about 60 days at about 24 ° C and at least about 3Q percent relative humidity. Other similar absorbent foams may tend not to retain their Free Inflate or Low Absorbency values after the aging under similar conditions.

Suitably, the absorbent foam of the present invention retains more than about 50 percent, and suitably more than about 70 percent of its initial d Free Blocking and Initial Low Absorbency values after aging for about 60 days to about of 24 ° C_ around 10 Q percent relative humidity.

As used herein, the term "Initial Lib Swelling" or "Initial Underflow Absorbency" is intended to refer to the value of Free Swell or Low Car Absorbency exhibited by an absorbent foam as measured within about 1 day after the Preparation of an absorbent foam when the absorbent foam is stored at ambient conditions, such as about 24 ° C and about 30 to about 60 percent relative humidity.

It is also desirable that the absorbent foam of the present invention exhibit liquid handling properties such as suitable liquid absorption rate or liquid vertical transmission values.

The absorbent foam of the present invention also suitably exhibits desired softness characteristics, here quantified by the use of a softness value. It is generally desired to have an absorbent foam that is soft and flexible so that a disposable absorbent product comprising the absorbent foam it will provide a good entall to a wearer or carrier of the disposable absorbent product as to avoid a premature liquid run-off, or a certain degree of comfort and a reduced packing volume because a soft material generally provides maximum compression and bending capacity . The method by which the Softness value was determined is established below in relation to the examples. The softness values determined as s establish below and are reported here for the force value that relates to the stiffness of a material. Using this method d test described here, the Softness value of a material gives an average of the rigidity of the material in all directions, is a measurement of the force exerted on the material at a rate of 50 centimeters per minute, in a circular bend test. In general, the greater the force value needed to bend a material, the more rigid the material will be. As a general rule, it is desired that the absorbent foam of the present invention exhibit a softness value that is beneficially less than about 30. , more beneficially d less than around 25, even more bene fi cially less than about 20, suitably less than about 15, suitably less than about 10, and yet more adequately less than about 15 grams of force per gram per square meter of absorbent foam.

A typical foam will comprise open spaces open cells within the structure of the foam. In the development of the present invention, it has been determined that the size of the cells of an absorbent foam generally affects certain liquid transport properties, such as vertical liquid transmission values, but that the size of the cells of a foam Absorbent generally has a minimal effect on the overall flexibility or softness of the absorbent foam. This has been found to be particularly true when the polymer that is being used to prepare the absorbent foam is a glazed polymer. Instead, the softness or flexibility of an absorbent foam is found to depend generally on the thickness of the cell walls. In general, the thinner the wall thickness the cells of an absorbent foam, the softer and / or more flexible the absorbent foam will be. In order to achieve the desired physical and absorbency characteristics of the absorbent foam of the present invention, it has been found that both the average cell size and the average thickness of the absorbent foam cell walls require careful control, preferably the optimize.

In an embodiment of the present invention, it is generally desired that the average cell size of the cells in an absorbent foam be beneficially about 1 micron to about 100 micron and suitably about 10 micron to about 50 micron. . Such a range of average cell size of the cells in the absorbent foam has found that it generally results in an effective channel system for distributing the liquid within the structure of the absorbent foam. The method by which the cell size of the pores is determined in an absorbent foam is set below in relation to the examples.

In an embodiment of the present invention, it is generally desired that the average wall thickness of the cells in a absorbent foam be beneficially from around? 0.1 microns to around 30 microns and suitably from around 0.5 microns to around 10 microns. Such a range of wall thicknesses of the cells in an absorbent and found foam generally results in the achievement of desired physical properties, such as softness and / or flexibility, of the absorbent foam. The method by which the average wall thickness of the pores in an absorbent foam is determined is set below in relation to the examples.

As used herein, the term "hydrophobic" refers to a material having a contact angle of water and air of at least 90 °. In contrast, as used herein, the term "hydrophilic" refers to a material having a contact angle of water in air of less than 90 °. For the purposes of this application, contact angle measurements are determined as established in the work of Rober J. Good and Robert J. Stromberg, editions, in "Science of Coloid and Surface - Experimental Methods", volume II, ( Prens Plenum, 1979). The absorbent foams of the present invention are generally hydrophilic as they are prepared and generally do not require any subsequent treatment to make them hydrophilic. This is in contrast to many absorbent foams known in the art in which the polymeric material of the foam is not inherently hydrophobic but becomes hydrophilic by a suitable treatment such as mediating the addition of a surfactant.

The absorbent foam of the present invention has found that it is capable of being prepared by means of a relatively simple, safe and cost-effective process. In incorporation, the process generally comprises forming a solution of a solvent-soluble polymer, freezing the solution at a relatively slow cooling rate at a temperature below the freezing point of the solvent, removing solvent from the frozen solution, and optionally Treating polymer to form a water-insoluble and water-swellable polymeric absorbent foam.

In another embodiment, the process comprises forming a monomer solution in a solvent, polymerizing the monomers to form a solution gel of a polymer crosslinked in the solvent, freezing the solution gel at a relatively slow cooling rate au temperature below the freezing point of the solvent, remove the solvent from the frozen solution gel Optionally, the solution gel of the crosslinking polymer can be subjected to additional swelling, mediate the use of additional solvent, before freezing the solution gel.

The absorbent foam of the present invention is also believed to be capable of being formed by a process comprising generally forming a solution of a soluble polymer in a solvent, adding a blowing agent to solution, starting the blowing agent, removing the solvent of solution, and optionally treating the polymer to form an insoluble polymer water-insoluble and water-swellable absorbent foam.

As used herein, the term "solvent" is intended to represent a substance particularly in a liquid form, which is capable of dissolving the polymer used herein to form an essentially uniformly dispersed mixture at a molecular level. In an embodiment of the present invention, the solvent used to prepare the absorbent foam requires being able to first freeze and then be capable of undergoing sublimation where the solvent passes directly from its frozen state to its vapor state. As such, the solvent used to prepare the absorbent foam must have a freezing point at which the solvent changes from a liquid to a solid. The freezing point of water and other solvents is generally known in the art. However, as will be recognized by one skilled in the art, the freezing point of a particular solvent can be affected by such factors as the particular solvent, the polymer and cross-linking agents being used as well as the relative concentrations of the respective components of the solution.

The soluble polymer or monomers are typically dissolved in a solvent comprising at least about 30 percent by weight of water, beneficially about percent by weight of water, suitably about 75 percent by weight of water, and more Properly 100 percent p weight of water. When a co-solvent with water is employed other suitable solvents include methanol, ethanol, acetone, isopropyl alcohol, ethylene glycol, glycerol and other solvents known in the art. However, when a water soluble polymer is used, the use or the presence of such other nonaqueous solvents may prevent the formation of a homogeneous mixture so that the polymer does not effectively dissolve in the solvent to form a solution.

In general, a solution of the polymer, solvent and optionally of a cross-linking agent and / or other optional components is prepared, wherein the polymer can be added to the solution as a polymer or it can be formed as a polymer in the solution of the monomers. In the present invention, it has been found that controlling the concentration of the polymer in the solution is important in order to achieve an absorbent foam exhibiting the desired properties. In general, if the concentration of the polymer in the solution is very high, the resultant absorbent foam prepared is found that does not exhibit the desired properties particularly the softness, due to the formation of relatively thick cell walls. Without attempting to be united by this, it is theorized that the use of a very large polymer concentration in the solution results in a relatively small volume of space occupied by the solvent molecules compared to the overall solution volume. In general, if the concentration of the polymer in the solution is very low, the resultant absorbent foam prepared has been found not to exhibit the desired properties, particularly the absorbent properties and the liquid distribution capacity., due to the formation of cell walls that are very thin and l cells that are very large. Without attempting to be united by this, it is theorized that the use of a very small concentration of polymer in the solution results in a large volume of space occupied by the solvent molecules. It has generally been found that the higher the polymer concentration the solution, the resulting absorbent foam exhibits a smaller average cell size and average thick cell walls as compared to an absorbent foam prepared from a solution with a lower polymer concentration in solution.

Therefore, it is generally desired that the solution comprises from about 0.1 to about ^ percent by weight, beneficially from about 0.5 about 20 percent by weight, and suitably from about 1 to about 10 percent by weight. percent by weight, based on the total solution weight of the polymer. The solution will generally comprise from about 99.99 to about 70 percent, beneficially from about 99.5 about 80 percent by weight and suitably from about 99 to about 90 percent by weight of solvent.

In an embodiment of the present invention, the dissolution of a soluble polymer in a solvent is believed to result in the entanglement of individual segments of the polymer chains with one another. Such entanglement results in the polymer chains interpenetrating one another in the mixture, so that a random entangled molecular configuration will occur which is believed to effectively provide cross-linking points and which helps to allow an additional crosslinking of the polymer. with an additional treatment, for example with a heat treatment. To allow effective entanglement of the individual segments of the polymer with each other, the solution is suitably allowed to form a homogeneous and stable solution in equilibrium prior to further processing steps to insure effective dissolution of polymer in the solvent. It will be appreciated that a relatively minor amount of a non-soluble part of the polymer may exist that will typically not dissolve in the solvent. For example, the crystalline areas retained by a crystalline cross-linked polymer typically will not dissolve in ag while the non-crystalline areas will.

Generally, the order of mixing of the polymer or the monomers of the solvent, and optionally of any cross-linking agents is not critical. As such, either the polymer, the monomers or the crosslinking agent can be added to the solvent and then the remaining components subsequently added, or all the components can be added together at the same time. However, it may be beneficial, when certain cross-linking agents are used to first add the polymer or monomers from the solvent and then add the cross-linking agent to the solution.

The solution of the polymer or of the solvent monomers, and optionally, of a cross-linking agent can generally be formed at any temperature at which the polymer or monomer is soluble in the solvent. Generally, such temperatures will be within the range of from about 10 ° C to around 1D0 ° C.

The solution can be acidic (a pH of less than 7), neutral (a pH of 7), or basic (a pH greater than 7). If desired, the solution can be acidified by the addition of an aqueous solution of an inorganic acid, such as the hydrochloric acid or nitric acid, or an aqueous solution of organic acid, such as acetic acid. Similarly, if you want to provide the solution with a basic pH, a base t such as an aqueous solution of sodium hydroxide, potassium hydroxide or ammonia can be added to the solution.

The solution will generally have a pH within range of from about 2 to about 12, beneficially from about 4 to about 9, more beneficially from about 4 to about 7.5 and properly from about 6 to about 7.5. The resulting absorbent foam will generally have the same pH as the solution. - When the absorbent foam of the present invention is intended for use in personal care products such as diapers, training underpants, women's care products, it is typically desired that the absorbent foam have a generally neutral character. For this reason, it is generally beneficial that the solution was formed with a generally neutral pH. If the solution is formed with a basic acidic pH, the recovered-absorbent foam can be acidic or basic, respectively, but can be neutralized. A recovered absorbent foam which is acidic can be neutralized, for example, by contact with a base gassings such as ammonia. A recovered absorbent foam which is basic can be neutralized, for example, by contact with an acidic gas such as carbon dioxide.

After the formation of the solution comprising the polymer or monomers, the solvent optionally a cross-linking agent, the solution is beneficially stirred, moved or otherwise mixed so as to effectively combine the components so as to form a solution essentially homogeneous.

If the monomers are being used, said monomers are suitably then treated to form the desired polymer in the solution.

The solution is then cooled to a temperature below the freezing point of the solvent so that the solvent freezes and a solid phase is made in the solution. Since the polymer and, optionally, a cross-linking agent are essentially homogeneously dispersed in the solution, it is generally desired that the polymer and, optionally, the cross-linking agent form an essentially continuous matrix within the frozen solution when the solvent freezes and a solid phase is made. As such, the essentially continuous matrix of the polymer and optionally, the cross-linking agent is essentially enclosed by the frozen solvent, forming an essentially uniform bicontinuous structure. As used herein, the term "enclose" and related terms is intended to mean that the frozen solvent phase essentially encloses or surrounds the essentially continuous matrix of the polymer and optionally cross-linking agent.

As will be recognized by one with skill in the art, the temperature at which the solution is cooled in order to freeze the solvent will typically depend on such factors as the solvent, the polymer and the cross-linking agent which is being used as well. of the relative concentrations of the respective components in the solution. In general, it has been found that if the temperature at which the solution is eventually cooled is very close to the freezing point of the solvent, the frozen polymer solution may not exhibit sufficient resistance and the additional processing steps may be deformed. as under a vacuum treatment to remove the frozen solvent. In addition, the freezing point of the solvent can be depressed due to the effect of the dissolved polymer and / or the cross-linking agent. As such, if the solution is merely cooled to the freezing point of the pure solvent, then some of the solvent present in the solution It may not be frozen at this temperature. In general, it has also been found that if the temperature at which the solution is eventually cooled is well below the freezing point of the solvent, the solvent molecules in the solution may tend to form a non-uniform crystalline phase through the solution. solution which has been found to frequently cause cracking in the polymer matrix and thus in the absorbent foam that is being prepared. Such cracks tend to reduce the mechanical properties of the absorbent foam, such as tensile strength and softness or flexibility. In addition, the use of very low temperatures tends to decelerate the rate of sublimation of the frozen solvent.

In an embodiment wherein the solvent used to prepare the absorbent foam is essentially all water an aqueous solution comprising mostly water, but also another solvent, it is generally desired that the temperature at which the solution is eventually cooled, be within around -50 ° C and around 0 ° C, beneficially between -50 ° C and around -5 ° C, more beneficially d between around -40 ° C and around -10 ° C, and suitably d between about -30 ° C and around -U0 ° C. ___ _ It has also been found that the rate at which the solution is cooled from a temperature above the freezing point of the solvent at a temperature below the freezing point of the solvent is important to achieve an absorbent foam exhibiting the desired properties described herein.

In a qualitative manner, the rate of cooling used should be so rapid that visible cracks or non-uniformities visible in the freezing solution begin to form. As such, there is generally a critical cooling rate that will exist for a particular solution in order to achieve a desired absorbent foam of the present invention. Using a cooling rate that is faster than such a critical cooling rate will generally result in an undesirable absorbent foam that will exhibit a relatively non-uniform po structure and a cracked polymer matrix. In contrast, the use of a cooling rate that is greater than such a critical cooling rate will generally result in a desirable absorbent foam having a relatively uniform po structure and in the absence of any significant cracking deformities in the polymer matrix.

As with the freezing point of a solvent, the critical freezing rate to be used for a particular solution will typically depend on such factors as the solvent, the polymer and the cross-linking agent being used as well as the relative concentrations of the solvent. The respective components in the solution. In one embodiment the present invention, wherein the water is the solvent or an aqueous solution comprising mostly water but also comprising another solvent and, more particularly, wherein the polymer is used at a concentration of between about Q.

At about 2 percent by weight where the weight percent is based on the total weight of the solvent, the critical freezing rate has been found to be a decrease in temperature from about 0.4 ° C to about 0.5 ° C. per minute. In such an embodiment, it is therefore desired that the cooling rates used to freeze the solvent be less about 0.4 ° C per minute, beneficially less about 0.3 ° C per minute, and suitably less about 0.1 ° C per minute. .

As will be recognized by one skilled in the art in addition to the approach of using a slower cooling rate than a critical cooling rate to achieve an essentially uniform cell structure, in an absorbent foam, other methods may also be applied. Other methods include, but are not limited to, the inclusion of small air bubbles or the use of a nucleating agent. If attempting to be bound by this, it is speculated that the use of nucleating agent will increase the number of cores to ensure an essentially uniform crystallization of the solvent molecules during the cooling process. The use of a nucleating agent generally increases the rate of critical cooling After the solution has cooled so that the solvent freezes and a solid phase is made in the solution and the solution has ben- eficially reached a relatively stable temperatur, the frozen solvent is then essentially removed from the solution. In the present invention, the use of a suitable vacuum to sublimate the frozen solvent has been found to generally result in a desired absorbent foam. As will be appreciated by one skilled in the art, the vacuum to be used as a frozen particulate solution will typically depend on such factors as the solvent, polymer and cross-linking agent that is being used, the relative concentrations of the components in the solution, and the temperature of the solution frozen. The desirable vacuum conditions are beneficially less than about 500 millitor, more bene fi cially less than about 300 millitor, suitably less than about 200 millitor, and more suitably less than about 100 millitor. In general, the higher the vacuum, the faster the sublimation rate of the frozen solvent.

As used herein, the sublimation, by the use of or vacuum, of the frozen solvent of the frozen solution is meant to essentially represent that all the solvent is removed from the frozen solution before, if necessary, any additional treatment steps. It will be appreciated, however, that after the removal of essentially all of the solvent, it can remain in a small amount of the solvent trapped within the structure of the remaining polymer matrix. The amount of the remaining solvent trapped within the structure of the polymer matrix will typically depend on the method and conditions under which the frozen solvent is sublimated. Generally, less than about 20 percent by weight beneficially less than about 15 percent. by weight, suitably less than about 10 percent by weight, of the original amount of the solvent in the solution remaining trapped within the remaining polymer matrix of the absorbent foam.

After the frozen solvent has been sublimated essentially from the frozen solution, the polymer and optionally, any crosslinking agent will remain, with the polymer generally forming a polymer matrix comprising generally the interconnected cells to achieve a foam structure. The polymeric matrix formed the cell walls with the open cells having been created by the sublimation of the frozen solvent. As discussed thus far, it is generally desired that the resulting foam structure exhibits a desired average pore size and the desired average thickness of the cell walls.

The recovered foam structure can and exhibits the desired physical and absorbent properties so that the recovered foam structure is an absorbent foam of the present invention and does not require any additional treatment steps. As will be appreciated by one of ordinary skill in the art, this will generally depend on the particular polymer and, if used, the particular cross-linking agent used in the preparation of the foam. The methods of preparation wherein the recovered foam structure can already exhibit the desired absorber physical properties include where the monomers are polymerized from the solution to form a crosslink and therefore an insoluble polymer gel solution, a binding agent. cross-linked which is capable of reacting with the polymer at a relatively low temperature, such as d around room temperature or lower, if used; and the polymer used, such as polyvinyl alcohol or chitosan, is capable of forming a highly ordered structure during freezing and the solidification process.

If the recovered foam structure does not yet exhibit the absorbent and physical properties, it may be necessary to treat the recovered polymeric foam structure with an additional process step. For example, if the cross-linking agent is a latent cross-linking agent, such a cross-linking agent may still not have reacted with the polymer because the proper cross-linking condition has not yet been provided to the polymer mixture and cross linking agent. As such, an effective cross-linking condition may still be necessary to be provided in order to cross-link the polymer to achieve a water-insoluble, water-swellable polymer. Such post-treatment conditions include the use of heat treatment, exposure to ultraviolet light, exposure to microwaves, exposure to an electronic ray, to steam, or to a high-moisture treatment, or high-pressure treatment, or to a treatment with an organic solvent.

In general, if co-heat treatment is necessary, any combination of temperature and time is effective to achieve a desired degree of cross-linking, without undesirable damage to the polymer, so that the polymer and the absorbent foam exhibit the properties Described herein is suitable for use in the present invention As a general rule, when a cross-linking agent is used, the polymer will be heat treated at a temperature d between about 50 ° C to about 250 ° C, beneficially d from about 80 ° C to about 250 ° C, more beneficially from about ICLCL ^ C to about 2Q0 ° C, and suitably from about 100 ° C to about 160 ° C. The higher the temperature used, the shorter the period of time generally necessary to achieve the desired degree of cross-linking. It has been found that if very high temperatures are used with an effective length of time, ta as a temperature of between about 10D ° C and about d 250 ° C for a duration of time between about 5 seconds and about 500 minutes. , Free Inflate and Effective Absorbency values can be achieved for certain polymers, such as carboxyalkyl polysaccharide without the use of a cross-linking agent.

Generally, the heat treatment process will extend over a period of time ranging from about 1 minute to about 600 minutes, beneficially from about 2 minutes to about 200 minutes, suitably from about 5 minutes. to around 10 minutes.

If used, a heat treatment process, any other acceptable recovery treatment process, generally causes the polymer to cross-link or cross-link additionally and to be generally insoluble in water but swellable in water. If attempting to be linked by this, it is believed that the process of subsequent recovery treatment causes the polymer to undergo a degree of cross-linking, unrelated to the presence of a cross-linking agent, through the formation of cross-links between either the polymer functional groups and the external cross-linking agent or between the functional groups in the polymer when it contains more than one type of functional groups. An example of a cross-linked self-attaching polymer is carboxymethylcellulose which contains both carboxylic acid groups and hydroxy groups and is capable of forming ester bonds. This cross-linked self-linking may be in addition to any cross-linked linkage caused by the presence of a cross-linking agent. Further, when the crosslinking agent is a diamine or polyamine, it is believed that the crosslinking occurs through the amidation of any carboxyl groups on the polymer through the formation of an ammonia salt. Esterification, through a cross-linked self-entanglement process, is thought to occur primarily in a weakly acidic, neutral or slightly basic condition. Esterification, through a cross-linking process, is not believed to process to a significant degree under conditions Relatively basic cross-linking due to the cross-linking agent can occur under both acidic and basic conditions.Therefore, the presence of cross-linking agent allows the crosslinking to occur over a wide pH range.

There is generally an optimum degree or amount of crosslinking of a particular polymer that optimizes the absorbency properties of the bonded polymer in particular crosslinked form. If very little crosslinking occurs, the polymer may have relatively low absorbency properties, such as the Absorbency Under Load values due to the lack of gel strength. If too much crosslinking occurs, the polymer can similarly possess relatively low absorbency properties, such as Free Swell values, due to the lack of ability of the polymer to absorb the liquid.

Those skilled in the art will recognize that the presence of the cross-linked bonds formed by the esterification or amidation, ionic bonding, or other types of bonds can be detected through various analytical techniques. For example, infrared spectroscopy and magnetic resonance can be used. to verify the presence of cross-linked ester and amide bonds.

The absorbent foams of the present invention are suitable for use in disposable products which include disposable absorbent products such as diapers, adult incontinent products, and bed pad; in catamenial devices such as sanitary napkins and plugs; and other absorbent products such as cleansing cloths, bibs, wound dressings and surgical covers or layers. Therefore, in another aspect, the present invention relates to a disposable absorbent product comprising the absorbent foams of the present invention.

In an embodiment of the present invention, it provides a disposable absorbent product, which disposable absorbent product comprises a liquid permeable topsheet, a lower sheet attached to the liquid permeable topsheet, and an absorbent structure placed between the liquid-permeable upper sheets and lower sheet wherein absorbent structure comprises an absorbent foam of the present invention.

The absorbent products and structures according to all aspects of the present invention are generally subjected, during use, to multiple discharges of a body fluid. Therefore, absorbent products structures are desirably capable of absorbing multiple discharge of body fluids in amounts to which the products and absorbent structures will be exposed during use. The downloads are usually separated one to ot for a period of time.

Test Methods Free Bloated Free Swelling Capacity (FS) is a test which measures the amount in grams of an aqueous solution, which contains 0.9 percent by weight of sodium chloride, a gram of a material can absorb in 1 hour under a restriction force or of negligible applied load, such as about 0.01 pounds per square inch.

Referring to Figure 1, the apparatus and method for determining Free Inflating and Low Absorbency will now be described. A perspective view of the apparatus in position during a test is shown. A laboratory jack 1 having an adjustable knob 2 for raising or lowering the platform 3 is shown. A laboratory support 4 supports a spring 5 connected to a modified gros measuring probe 6, which passes through the box 7 of the meter, which is held rigidly by the laboratory support A plastic sample cup 8, which contains the sample absorbent foam material to be tested, has a liquid permeable bottom and rests within a Petri dish 9 and which contains the salt water solution to be absorbed For the determination of only the Absorbency Low Load values, a weight 10 rests on the top of a disc spacer (not visible) resting on top of the sample of Absorbent foam material (not visible).

The sample cup consists of a plastic cylinder that has an inside diameter of one inch and an outer diameter of 1.25 inches. The bottom of the sample cup is formed by adhering a 100 mesh metal grid that has 150 micron openings to the cylinder end by heating the grid above the molten point of the plastic and pressing the plastic cylinder against the the hot grid to melt the plastic and join the grid to the plastic cylinder.

The modified thickness gauge used to measure the expansion of the sample while the salt water solution is absorbed is a Mitutoyo Digimatic Indicator IDC Series 54 Model 543-180, which has a range of 0-0.5 inches and an accuracy of 0.00005 inches (from Mitutoyo Corporation, 31-19 Shiba 5-chome, Minato-ku, Tokyo 108, Japan). As supplied by Mitutoyo Corporation, the bulk meter contains a spring attached to the probe inside the meter box. This spring is removed to provide a free drop probe which has a downward force of about 27 grams. In addition, the cap on top of the probe located on top of the meter box is also removed to allow the probe to be attached to the suspension syringe 5 (available from McMaster-Carr Supply Co., Chicago) , Illinois, Article No. 9640K41), which serves to counterattack or reduce the downward force of the probe to about gram + 0.5 grams. A wire hook can be attached to the upper part of the probe for attachment to the suspension spring. The lower tip of the probe is also provided with an extension needle (Mitutoyo Corporation, Part No. 131279) to allow the probe to be inserted into a sample cup.

To carry out the test, a sample of absorbent foam material was cut into circular discs with a diameter of about 1 inch. A total of about 0.160 grams of the sample of absorbent foam material typically around 3 to 4 layers of circular discs, placed in the sample cup. The sample is then covered with a plastic spacer disk, weighing 4.4 grams and having a diameter of around 0.995 inches, which served to protect the sample from being disturbed during the test also to uniformly apply a load on the entire sample. The sample cup with the material sample and the spacer disk is then weighed to obtain its dry weight. L sample cup is placed in the Petri dish on the platform and the laboratory jack is raised until the upper side of the plastic spacer disk makes contact with the tip of the probe. The meter is reset. A sufficient amount of the salt water solution is added to the Petri dish (50-10 milliliters) to begin the test. The distance at which the plastic spacer disk is raised by the expansion sample when absorbing the salt water solution is measured by the probe. This distance, multiplied by the cross-sectional area within the sample cup, is a measure of the volume of expansion of the sample due to absorption. L Factoring in the density of the salt water solution and weight of the sample, the amount of room water solution absorbed is easily calculated. The weight of the salt water solution absorbed after about 1 hour is the value of Free Swelling expressed as salt water solution in grams absorbed per gram of absorbent foam sample. If desired, the readings of the modified thickness meter can be imputed continuously to a computer (Mitutoyo Digimati Microprocessor DP-2 DX) to perform the calculations and provide the Free Swell readings. As a cross-check, Free Inflation can also be determined by determining the difference in weight between the sample cup before and after the test, the difference in weight being the amount of solution absorbed by the sample.

Absorbency Under Load Absorbency Under Load (AUL) is a test which measures the amount in grams of an aqueous solution, which contains 0.9 percent by weight of sodium chloride, which can be absorbed by 1 gram of material in 1 hour under a force of restriction or of applied load of about 0.3 pounds per square inch. The procedure for measuring the Absorbency Under Load value of an absorbent composition and essentially identical to the procedure for measuring the values of Free Blocking, except that a weight of 100 grams was placed on top of the plastic spacer disk thus applying a load about 0.3 pounds per square inch in the absorbent foam when absorbing this salt water solution.

Smoothness The Softness value in a material is determined by a test which is modeled according to the ASTM D4032-82 Circular Bending Procedure. This modified test is used for the purposes of the present invention and is hereinafter simply referred to as the "Circular Bending Procedure". The Circular Bending Procedure is a simultaneous multidirectional deformation of a material in which one face of a material becomes concave and the other face becomes convex. The Circular Bending Procedure gives a force value which is related to the stiffness of the material, simultaneously averaging the stiffness in all directions and here given as being inversely related to the material softening.

The apparatus needed for Procedure d Circular Bending is a Modified Bending Rigidity Tester that has the following parts: a smooth polished steel plate platform which is 102.0 mm (length) by 102.0 millimeters (in width) by 6.35 millimeter (in depth) having an orifice of 18.75 millimeters diameter. The edge of the hole should be at an angle of degrees to a depth of 4.75 millimeters. A plunger having the following dimensions is used: overall length of 72. millimeters, a diameter of 6.25 millimeters, a ball nose q has a radius of 2.97 millimeters and a needle point that extends 0.88 millimeters from the nose of the ball with a base diameter of 0.33 millimeters and a point that has a range of 0.5 millimeters. The plunger is concentrically mounted with the hole having equal spacing above all on the sides. The needle tip is merely used to prevent lateral movement of a sample during the test. The bottom of the plunger must be well above the top 1 of the hole plate. From this position, the blow down the ball nose is down to the exact bottom of the plac An inverted compression load cell having a load range of from about 0.0 to about 2000.0 grams was used as a force measurement meter. The compression tester used was an Instron Compression Load Cell Model No. 1122, available Instron Engineering Corporation of Canton, Massachusetts.

After calibrating the load cell, the measuring length for the piston displacement was set to 25 millimeters. To perform the test, an absorbent foam sample was cut into a 38.1 x 38.1 square millimeter sample using a die cutter. The sample was placed on the test platform and the plunger was lowered onto the specimen by a measuring length of 25.4 millimeters at a crosshead speed of 500 millimeters per minute. During the movement of the plunger, the absorbent foam sample was deflected towards down to a hole of 18.75 mm by the plunger and the force exerted by the compression tester to deflect the foam sample during the displacement of measuring length of 25.4 mm from the plunger was measured by the load cell and recorded. The force measured by the load cell divided by the base weight of the sample is reported in units of grams force / grams per square meter of sample (g / gsm). This value is used as the Softness value to obtain a quantitative measurement of the softness of the sample. The higher the softness value (in g / gsm), the stiffer and po the less soft the specimen.

Measurements of Cell Pore Size and Cell Wall Thickness A sample of foam was cut by a sharp knife. The cut foams were attached to metal stumps using a copper tape and imaging in an environmental electronic scanning microscope using a 12 kV beam voltage. The instrument used was an environmental electronic scanning microscope, Model E-20 from Electroscan Corporation of Wilmington, Massachusetts. Sample chamber pressure was around 1.2 torr. Electronic return spreader detector was used to collect images, which has the advantage of being able to discern any variations in the composition. Amplification varied depending on the scale of the sample object, with an amplification of 150 used for a general investigation of the sample and an amplification of 2500 used to measure cell wall thickness and cell size. L measurements of cell size thickness and cell size were taken directly on the environmental electronic scanning microscope. It was not possible to apply automatic image analysis routines to these complex structures for the measurement of the cell wall thickness. L Manual measurement was required. The cell wall thickness and cell size of each sample were averaged out of at least 2 measurements.

EXAMPLES For use in the following examples, s obtained the following polymer materials: Polymer 1: A carboxymethyl cellulose having a weight average molecular weight of greater than 1,000,000 and a degree of substitution of carboxymethyl groups on the anhydride unit of the cellulose material of about 0.7 was obtained from Aqualon of Wilmington, Delaware, a subsidiary of Hercules, Inc., under the designation carboxymethylcellulose B313. L carboxymethylcellulose is an anionic polymer.

Polymer 2: A polymer of polyacrylate sodium having a weight average molecular weight of about 4,000,000 and a degree of neutralization of about 70 percent was obtained from Polysciences of Warrington, Pennsylvania, under catalog number 06501. The Polyacrylate sodium polymer is an anionic polymer.

Polymer 3: A polymer of polyacrylate sodium having a weight average molecular weight of about 240,000 d and a degree of neutralization of about 70 percent was obtained from Polysciences of Warrington, Pennsylvania, under the catalog number of 18613. The polymer Polyacrylate sodium is an anionic polymer.

Polymer 4: A sodium polyacrylate polymer having a weight average molecular weight of about 60,000 and a degree of neutralization of about 70 percent was obtained from Polysciences of Warrington, Pennsylyania, under catalog number 18611. The polymer Sodium polyacrylate is an anionic polymer.

Polymer 5: A chitosan acetate having a weight average molecular weight of about 11,000,000 and a degree of acetylation of about 80 percent was obtained from the Vanson Company of Seattle, Washington, under the designation Chitosan VNS-608. Chitosan acetate is a cationic polyme.

Polymer 6: A polyethylene oxide having a weight average molecular weight of about 4,000,000 was obtained from Union Carbide Corporation, of Danbury, Connecticut, under the designation polyethylene oxide WSR-301. Polyethylene oxide is a nonionic polymer.

Example 1 Quantities by weight of the various polymer samples were dissolved in separate charges of about 200 grams of distilled water at a temperature of about 23 ° C. For the solutions of carboxymethylcellulose (Polymer 1) and polyethylene oxide (Polymer 6), it was also They added about 0.2 grams of citric acid to the solutions as a cross-linking agent. For the polyacrylate sodium solutions (Polymers 2-4), about 0.75 grams of the aqueous solution comprising about 40 weight percent zirconium ammonium carbonate were also added to the solutions as a cross-linking agent. The various solutions were mixed for about 2 to 3 hours to ensure a complete mixture of the components. About 500 grams of prepared solution was placed in separate stainless steel trays, where the trays had dimensions of 1 inch (width) by 20 inches (length) by one flea (depth). The trays contained the respective solutions where they were placed in a freeze drier, available from The VirTis, Inc., of Gardiner, New York, under the designation of frozen dryer VirTis Génesi model 25EL. The various solutions of the trays were then cooled to about -15 ° C at various rates of cooling in order to freeze the water in the solutions. The various tray solutions were maintained at about -15 ° C for about 1 hour to ensure an essentially complete freezing of the water The frozen solutions were left in the freeze dryer and then subjected to a vacuum of about 105 millitor , provided by a vacuum bomb which had a condenser set at a temperature d around -60 ° C to around -70 ° C for about 1 hour.The resulting foam structures were then treated at various temperatures for various periods. of time to aid in the cross-linking of the polymers The final foam structures were then evaluated for the values of Free Swelling, Absorbency Under Load and Softness The various process conditions and the results of the evaluations for the various samples are summarized in Table 1 The foam sample prepared using Polymer 4 (Sample 7 was soluble in water and therefore did not exhibit any Hin values). Chado Free and of Absorbency Under Load measurable.

A sample of comparative foam (Sample 10 was also prepared follows.) About 250 grams of the aqueous acrylic acid solution containing 50 weight percent acrylic acid was neutralized using a 1 N sodium hydroxide solution to form an acrylate solution. Sodium with 75 percent degree of neutralization The neutralization was carried out slowly using a gall bath taking care to keep the temperature of the solution around 5 ° C to avoid any polymerization.S transferred to about 200 milliliters of this solution A 2-liter reaction vessel equipped with a heating cover and a high-cut mixer (an Ultra Turrax T25 mixer from Janke &Kunkel GmbH of Staufen, Germany.) The solution in the reaction vessel was added 0.5 grams d N , N'-methylenebisacrylamide, to about 1.3 grams of 2,2'-azobis- (2-amidopropane) monomer-polymeric hydrochloride &Daj to Labo ratories, Inc., of Feastervilie, Pennsylvania, and about 20 grams of polyethylene glycol of 600 weight average molecular weight from Union Carbide Company, maintaining the mixture at 22 ° C About 3.5 grams of sorbitan monolaurate and about 6.5 grams of ethoxylated sorbitan monolaurate were mixed with about 60 grams of 1,1-trichlorotrifluoroethane and this mixture was then added to the solution in the reaction vessel. The high-cut mixer was turned on and the mixture was combined at a rate of about 8,000 revolutions per minute for about 10 minutes after which the mixer was removed from the reaction vessel and the temperature was increased to about 60 ° C and it was maintained for about 1 hour to form the foam, followed by the increase and maintenance of the temperature at about 80 ° C for about 30 minutes and finally increasing and maintaining the temperature at around 120 ° C for about 30 minutes E reactor that then cooled to around 22 ° C. A mixture consisting of about 5 grams of glycerol and about 25 grams of isopropyl alcohol were added to the foam in the reactor and the temperature was increased to about 180 ° C and maintained for about 1 hour. The reactor was then cooled to room temperature, the foam was removed from the reactor and placed in a chamber at about 80 percent relative humidity for about 6 hours to obtain the final foam material. This foam sample was then evaluated with respect to the values of Free Inflate, Absorbenci Under Load and Softness, with the results of such evaluations also summarized in Table 1.

Table 1 * It is not an example of the present invention.

Example 2 Similar foam samples were prepared as follows. About 10 grams of Polymer 1 (carboxymethylcellulose) were dissolved in about 2000 grams of distilled water at a temperature of about 23 ° C. About 0.2 grams of citric acid was also added to the solution as a crosslinking agent. The solution was mixed for about 2 to 3 hours to ensure thorough mixing of the components. About 50 grams of the solution was placed in a stainless steel tray, where the tray had dimensions of 10 inch (width) by 20 inches (length) by 1 inch (depth). The tray containing the solution was then placed in a freezing dryer available from The VirTis Inc., of Gardiner, New York, under the designation d Frozen dryer VirTis Genesis model 25EL. The solution in the patent leather was then cooled to about -15 ° C at a cooling rate of about 0.04 ° C / minute in order to freeze the water in the solution. The solution in the tray was maintained around -15 ° C for about 1 hour to ensure essentially complete freezing of the water. The frozen solutions were left in the freeze dryer and then subjected to a vacuum of about 105 millitor, supplied by a vacuum pump which had a condenser set at a temperature of about -60 ° C to about -70 °. C po around 15 hours.

The resulting foam structures were then treated at various temperatures for various periods of time in order to assist in the cross-linking of the polymers. The final foam structures were then evaluated with respect to the values of Free Inflate, Absorbenci Under Load and Softness. The various process conditions and the results of the evaluations for the various samples are summarized in Table 2.

Table 2 It is not an example of the present invention.

Those skilled in the art will recognize that the present invention is capable of many modifications without departing from the scope thereof. Therefore, the detailed description and examples set forth above are intended to be illustrative only and are not intended to limit in any way the scope of the invention as set forth in the appended claims.

Claims

R E I V I N D I C A C I O N S

1. An absorbent foam comprising water insoluble and water swellable polymer wherein the water insoluble and water swellable polymer is present in the absorbent foam in an amount by weight of between about 50 percent by weight to 100 percent by weight. weight, based on the total weight of the absorbent foam, and wherein the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam and a Softness value that is less than about of 30 grams d force per gram per square meter of absorbent foam.

2. The absorbent foam as claimed in clause 1, characterized in that the polymer is selected from the group consisting of polyacrylamides, polyvinyl alcohole, ethylene maleic anhydride copolymer, polyvinyl ethers, polyacrylic acids, polyvinyl pyrrolidones polyvinyl morpholinones, polyamines, polyethylene imines polyacrylamides, polyquaternary ammoniums, carboxymethylcelluloses, carboxymethyl starches, hydroxypropyl celluloses, alginates alginates, carrageenans, acrylic grafted starches, grafted acrylic celluloses, chitin, chitosan, polyaspartic acid, polyglutamic acid, polyglutamine polyglutamines, polylysines, polyarginines, and the copolymer salts and mixtures of any of the above polymer.

3. The absorbent foam as claimed in clause 2, characterized in that the polymer is selected from the group consisting of polyacrylic acids, carboxymethyl celluloses, chitin, chitosans and the salts, copolymers and mixtures of any of the above polymer.

4. The absorbent foam as claimed in clause 3, characterized in that the water insoluble and water swellable polymer is selected from the group consisting of polyacrylic acids and their salts.

5. The absorbent foam as claimed in clause 1, characterized in that the water insoluble and water swellable polymer is present in the absorbent foam in an amount of weight of between about 60 weight percent to 100 weight percent .

6. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam further comprises a cross-linking agent.

7. The absorbent foam as claimed in clause 6, characterized in that the crosslinking agent is selected from the group consisting of an organic compound having at least two functional functional groups capable of reacting with the polymer and a meta ion. with two or more positive charges.

8. The absorbent foam as claimed in clause 6, characterized in that the cross-linking agent is present in the absorbent foam in an amount by weight of between about 0.01 percent by weight to about 20 percent by weight, based on on the total weight of the absorbent foam.

9. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam exhibits a Free Swell value of at least about 15 grams of liquid per gram of absorbent foam.

10. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam exhibits a softness value that is less than about 2 grams of force per gram per square meter of the absorbent foam.

11. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam exhibits an Absorbency Under Load value of at least about 10 grams of liquid per gram of absorbent foam.

12. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam comprises cells and where the average cell size of the cells is between about 10 microns to about 10 microns

13. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam comprises cells comprising walls having a thickness and e where the average wall thickness of the cells is from about 0.1 microns to about 30 microns.

14. The absorbent foam as claimed in clause 1, characterized in that the water insoluble and water swellable polymer is selected from the group consisting of polyacrylic acids, carboxymethyl celluloses, chitin, chitosan, and the salts, copolymers and mixtures of any d The above polymers, wherein the absorbent foam comprises cells comprising cells having a thicknwherein the average cell size of the cells is between about 10 microns to about 100 microns, and wherein the average wall thicknof the cells are between about 0.1 miera to around 30 micras.

15. An absorbent foam comprising water insoluble and water swellable polymer wherein the water insoluble and water swellable polymer is present in the absorbent foam in a weight amount of between about 50 percent by weight to 100 percent by weight. weight, wherein the absorbent foam comprises cells comprising walls having a thicknwherein the average cell cell size is between about 10 microns to about 10 microns, and wherein the average wall thicknof the cells e from around 0.1 microns to around 30 microns.

16. The absorbent foam as claimed in clause 15, characterized in that the polymer is selected from the group consisting of polyacrylamides, polyvinyl alcohole, ethylene maleic anhydride copolymer, polyvinyl ethers, polyacrylic acids, polyvinyl pyrrolidones, polyvinyl morpholinones, polyamines, polyethylene imines, polyacrylamides, polyquaternary ammoniums, carboxymethylcelluloses, carboxymethyl starches, hydroxypropyl celluloses, algins, alginates, carrageenans, grafted acrylic starches, grafted acrylic celluloses, chitin, chitosan, polyaspartic acid, polyglutamic acid, poliaspargins, polybutamines, polylysines, polyarginines, and the salts, copolymers and mixtures of any of the above polymer.

17. The absorbent foam as claimed in clause 16, characterized in that the water insoluble and water swellable polymer is selected from the group consisting of polyacrylic acids, carboxymethyl celluloses, chitosan chitosan and the salts of the copolymers and mixtures of any of the previous polymers.

18. The absorbent foam as claimed in clause 17, characterized in that the water insoluble and water swellable polymer is selected from the group consisting of polyacrylic acids and their salts.

19. The absorbent foam as claimed in clause 15, characterized in that the water insoluble and water swellable polymer is present in the absorbent foam in an amount by weight of between about 60 weight percent to 100 weight%.

20. The absorbent foam as claimed in clause 15, characterized in that the absorbent foam further comprises a cross-linking agent.

21. The absorbent foam as claimed in clause 20, characterized in that the cross-linking agent is selected from the group consisting of an organic compound having at least two functional functional groups capable of reacting with the polymer and the metal ion. with two or more positive charges.

22. The absorbent foam as claimed in clause 21, characterized in that the crosslinking agent is present in the absorbent foam in an amount by weight of between about 0.01 percent by weight to about 20 percent by weight, based on on the total weight of the absorbent foam.

23. The absorbent foam as claimed in clause 1, characterized in that the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam and a softnvalue that is lthan about of 30 grams of po gram force per square meter of absorbent foam.

24. A disposable absorbent product comprising a liquid-permeable top sheet, a lower leaf attached to the upper sheet, and an absorbent core placed between the liquid permeable upper sheet and the lower leaf, wherein the absorbent core comprises an absorbent foam, wherein the absorbent foam comprises a water-insoluble and inflatable polymer in water wherein the water-insoluble, water-swellable polymer is present in the absorbent foam in an amount by weight of between about 50 percent by weight to 100 percent by weight, based on the total weight of the absorbent foam, and wherein the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of the absorbent foam and a value of Softness that is less than about 30 grams of pogram force per square meter of water. the absorbent foam.

25. A disposable absorbent product comprising a liquid-permeable top sheet, a lower sheet attached to the upper sheet, and an absorbent core positioned between the liquid-permeable sheet and the lower sheet, wherein the absorbent core comprises an absorbent sheet, wherein the absorbent foam comprises a water-insoluble, water-swellable polymer wherein said water-insoluble, water-swellable polymer is present in the absorbent foam in an amount by weight of between about 50 percent by weight to 100 percent by weight weight, wherein the absorbent foam comprises cells comprising walls having a thickness where the average cell size of the cells is d between about 10 microns to about 100 microns, and where the average cell wall thickness is from around 0.1 microns to around 30 micras.

26. A process for preparing an absorbent foam wherein the absorbent foam comprises a water insoluble and water swellable polymer, the process comprising: to. forming a solution comprising a quantity by weight of water and a polymer, wherein the polymer is present in the solution in an amount by weight of about 0.1 to about 30 weight percent, based on the weight of total solution; b. cool the solution to a temperature of about -50 ° C and about 0 ° C at a rate of cooling that is less than about 0.4 ° C per minute under effective conditions to freeze the water; c. remove essentially the frozen water from the solution; Y d. recover a polymeric foam.

27. The process as claimed in clause 26, characterized in that the frozen water is removed from the solution by using a vacuum of less than about 500 millitor.

28. The process as claimed in clause 27, characterized in that less than about 20 percent by weight of the amount of water weight in the solution remains in the recovered absorbent foam.

29. The process as claimed in clause 26, characterized in that the process further comprises treating the polymer foam under effective conditions to achieve a water insoluble and water swellable polymer.

30. The process as claimed in clause 29, characterized in that the polymeric foam is treated with a treatment selected from the group consisting of heat treatment, exposure to ultraviolet light, exposure to microwaves, exposure to an electronic beam treatment with steam, treatment with high humidity, treatment with high pressure, and treatment with an organic solvent.

31. The process as claimed in clause 30, characterized in that the polymeric foam is treated with a temperature between about 50 ° C and about 250 ° C.

32. The process as claimed in clause 26, characterized in that the solution also comprises a cross-linking agent.

33. The process as claimed in clause 32, characterized in that the cross-linking agent is selected from the group consisting of an organic compound having at least two functional groups functionalities capable of reacting with the polymer and a metal ion with two or more positive charges.

34. The process as claimed in clause 26, characterized in that the polymer is a water-soluble polymer.

35. The process as claimed in clause 26, characterized in that the polymer is selected from the group consisting of polyacrylamides, polyvinyl alcohols, ethylene maleic anhydride copolymer, polyvinyl ethers, polyacrylic acids, polyvinyl pyrrolidones, polyvinyl morpholinones polyamines, polyethylene imines, polyacrylamides, polyquaternary ammonium, Carboxymethylcelluloses, carboxymethyl starches, hydroxypropyl celluloses, algins, carrageenan alginates, grafted acrylic starches, grafted acrylic cellulose, chitin, chitosan, polyaspartic acid, polyglutamic acid, polyaspargins, polyglutamines, polylysins, polyarginines, and the salts, copolymers and mixtures of any of the previous polymers.

36. The process as claimed in clause 35, characterized in that the polymer is selected from the group consisting of polyacrylic acids, carboxymethylcelluloses, chitin, chitosan and the salts, copolymers and mixtures of any of the above polymer.

37. The process as claimed in clause 26, characterized in that the water insoluble and swellable polymer is present in the absorbent foam in an amount by weight of between about 50 percent by weight 100 percent by weight, based on on the total weight of the absorbent foam.

38. The process as claimed in clause 26, characterized in that the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam and a value of Smooth that is less than about 30 grams of force per gamo per square meter of absorbent foam.

39. The process as claimed in clause 38, characterized in that the absorbent foam comprises cells comprising walls having a thickness wherein the average cell size of the cells is between about 10 microns to about 100 microns, and where the average wall thickness of the cells is between about 0.1 mier to about 30 microns.

40. The process as claimed in clause 26, characterized in that the absorbent foam comprises cells comprising walls having a thickness where the average cell size of the cells is between about 10 microns to about 100 microns, and in where the average wall thickness of the cells is between about 0.1 miera to about 30 micras.

41. The process as claimed in clause 26, characterized in that the polymer is selected from the group consisting of carboxymethylcelluloses polyacrylic acids, chitin, chitosan, and the copolymer salts and mixtures of any of the above polymer; the solution further comprises a cross-linking agent; Frozen water is removed from the solution by using a vacuum of less than about 50 milliters and less than about 20 percent by weight of the amount by weight of water and the solution remains in the recovered absorbent foam; The process further comprises treating the polymeric foam with a treatment selected from the group consisting of heat treatment, exposure to ultraviolet light, exposure to microwaves, exposure to an electronic ray, steam treatment, high humidity treatment, high treatment. pressure, and treatment with an organic solvent; the water insoluble and water swellable polymer is present in the absorbent foam in an amount by weight between about 50 weight percent to 100 weight percent, based on the total weight of the absorbent foam; The absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam, an Absorbency Under Load value of at least about 10 grams of liquid per gram of absorbent foam and a Softness value which is less than about 30 gram of force per gram per square meter of the absorbent foam and the absorbent foam comprises cells comprising a thickness where the average cell size of the cells is around from 10 microns to around 10 microns and the average wall thickness of the cells is from around 0.1 microns to around 30 micras.

42. An absorbent foam prepared by the process as claimed in clause 26.

43. The absorbent foam as claimed in clause 42., characterized in that the polymer is selected from the group consisting of polyacrylic carboxymethylcellulose acids, chitin, chitosan and the copolymer salts and mixtures of any of the above polymer, the water insoluble polymer and swellable in water is present in the absorbent foam in an amount by weight d between about 50 percent by weight at 100 percent by weight, based on the total weight of the absorbent foam; The absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam, an Absorbency Under Load value of at least about 10 grams of liquid per gram of absorbent foam, and a Softness value that is less than about 30 grams d force per gram per square meter of the absorbent foam; and the absorbent foam comprises cells comprising walls having a thickness wherein the average cell cell size is between about 10 microns to about 10 microns and the average cell wall thickness is about 0.1 microns to around 30 micras. SUMMARY An absorbent foam is described which exhibits properties of desirable softness and flexibility but which is highly absorbent. In one embodiment, the absorbent foam comprises a water insoluble and water swellable polymer where the absorbent foam exhibits a Free Swell value of at least about 10 grams of liquid per gram of absorbent foam and a value of Softness that It is less than about 30 grams of force per gram per square meter of absorbent foam. In a second embodiment, the absorbent foam has an average cell size of the cells in the absorbent foam of between about 10 microns to about 100 microns and an average wall thickness of the cells in the absorbent foam of about 100 microns. 0.1 microns to about 30 microns. Such an absorbent foam can be used in a disposable absorbent product intended for the absorption of fluid such as body fluids. A process for preparing an absorbent foam is also described. The process generally comprises forming a solution of a polymer in a solvent, freezing the solution at a relatively slow cooling rate at a temperature below the freezing point of the solvent, removing the solvent from the frozen solution, and recovering the polymer for forming a polymeric foam which is insoluble in water and swellable in water.