MXPA96003475A - Porous absorbing materials that have modified surface characteristics and methods to make myself - Google Patents

Abstract

The present invention relates to a porous absorbent material comprising an absorbent polymer insoluble in water, swellable with water. The absorbent material comprises a polyether and / or a polycation bound to the absorbent polymer, whereby the contact angle of the blood on a surface of the absorbent material is from about 0 degrees to about 40 degrees. Due to the improved wetting ability with liquids, as well as the porous structure, the absorbent material can provide superior absorbent characteristics with liquids, particularly with the

Description

POROUS ABSORBING MATERIALS THAT HAVE MODIFIED SURFACE CHARACTERISTICS AND METHODS TO MAKE THEMSELVES FIELD OF THE INVENTION The present invention relates to absorbent materials, which, upon contact with liquids such as water or exudates from the body, swell and imbibe such liquids. More specifically, the present invention relates to porous absorbent materials having modified surface characteristics. Said porous absorbent materials have improved absorption characteristics with liquids. The present invention has particular application in absorbent articles such as diapers, incontinence pads for adults, sanitary napkins, and the like. The invention also relates to processes for producing such materials and absorbent articles containing said materials.

BACKGROUND OF THE INVENTION Hydrogel-absorbent, water-insoluble, and water-swellable polymers are capable of absorbing vast quantities of liquids, such as water, blood, exudates from the body (e.g., urine, menstrual fluid). ), industrial fluids and household fluids, and they are also capable of retaining said liquids absorbed under moderate pressures. The absorption characteristics of said polymer materials make them especially useful for incorporating absorbent articles, such as diapers, sanitary napkins, tampons, and the like. In general, polymer, absorbent, conventional materials have good water or urine absorption characteristics, or those required; however, poor distribution and dispersion with certain liquids remain. In particular, they have poor absorption characteristics for certain liquids, specifically for blood or menstrual fluid. More specifically, upon contact with the blood or menstrual fluid, the absorbent polymer materials do not exhibit characteristics of sufficient absorption, especially the rate of absorption of the blood due to poor distribution and dispersion of blood. Said poor distribution and dispersion, of blood, are mainly caused by the low capacity of humidity with the blood. In general, the capacity of distribution and dispersion of the blood can be evaluated by measuring the contact angle of the blood on the surface of the absorbent polymer material. Since the contact angles of conventional absorbent polymer materials are on the scale of about 30 degrees to about 90 degrees, or more, a desired moisture capacity can not be obtained with the blood, so the distribution and dispersion poor, from the blood, are caused in the absorbent polymer materials. An attempt to improve said absorption characteristics is described in the U.S. patent. No. 4,190,563 (Rosley et al.), Issued February 20, 1980, wherein the moisture capacity with the blood is improved by treating, on the surface, the absorbent polymer materials, in particles, using polyethers. The absorbent polymer materials, described, can be effectively moistened with blood; however, the distribution and dispersion of the blood towards and between the absorbent polymer materials is not completely improved, due to its high resistance to the flow of liquids within the polymer materials due to the lack of capillarity or liquid transport channels, and insufficient specific surface area of the polymer materials. Therefore, the absorption characteristics with the blood are not satisfactory and there remains a need to further improve, the distribution and dispersion of the blood through and between the polymer materials, absorbents. In addition, since the polyether is physically placed or bonded onto the surface of the absorbent polymer materials, said polyether can be removed from the polymer materials, absorbers by the good application of liquids.

Consequently, there is a need for further improvements in such absorbent materials. Therefore, an object of the present invention is to provide a porous absorbent material, which has improved absorption characteristics with liquids. Another object of the present invention is to improve the distribution and dispersion of liquids in an absorbent material. Mn, another object of the present invention is to improve the • * The absorption speed of an absorbent material, especially for blood. A further object of the present invention is to provide an absorbent material, which is not affected by the subsequent application of liquids. Still another object of the present invention is to provide a method for making said absorbent materials. A further object of the present invention is to provide disposable absorbent articles, such as diapers, sanitary napkins, tampons, and the like, which have improved absorption characteristics with body exudates.

BRIEF DESCRIPTION OF THE INVENTION Briefly stated, the present invention relates to porous absorbent materials having modified surface characteristics. In one aspect, a porous absorbent material, comprises a water insoluble polymer, swellable with water; wherein the contact angle of the blood on the surface of the absorbent material is from about 0 degrees to about 40 degrees. In another aspect of the invention, a porous absorbent material comprises, a water insoluble polymer, swellable with water; a positively charged filler compound, bound to water insoluble polymer, swellable with water; and a non-ionic hydrophilic compound, bound to water insoluble polymer, swellable with water. The present invention also relates to an absorbent article. The absorbent article comprises: (a) a liquid permeable topsheet; (b) a back sheet impervious to liquid; and (c) an absorbent core positioned between the topsheet and the backsheet. The absorbent core comprises at least one porous absorbent material of the present invention. The present invention also relates to methods for making absorbent materials having modified surface characteristics. In a further aspect of the invention, a porous absorbent material is produced by (a) applying a first surface modification compound on a portion of a water-swellable, water insoluble absorbent polymer surface, wherein the first modification Surface has the function of modifying the surface characteristics of the absorbent polymer; (b) inflating the absorbent polymer by absorbing water; and (c) removing a portion of said water, while maintaining the absorbent polymer in a substantially swollen state, thereby forming a porous structure in the absorbent material. In yet another aspect of the invention, the porous absorbent article is produced by, (aa) making an absorbent polymer insoluble in water, hydrolysable with water from monomers containing acid, unsaturated, polymerizable, using a solution polymerization method watery (bb) applying a first surface modification compound on a portion of a water-swellable, water insoluble absorbent polymer surface, wherein the first surface modification has the function of modifying the surface characteristics of the insoluble absorbent polymer in water, inflatable with water; and (c) removing a portion of said water, while maintaining the absorbent polymer in a substantially swollen state, thereby forming a porous structure in the absorbent material. In a further aspect of the invention, an absorbent material is produced by, (A) making a porous absorbent polymer, insoluble in water, contactable with water; Y (B) applying a first surface modification compound on a portion of a water-insoluble, water-swellable porous absorbent polymer surface, wherein the first surface modification has the function of modifying the surface characteristics of the polymer porous absorbent, insoluble in water, inflatable with water.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an electronic scanning photomicrograph (magnified 250X) of a section of a porous absorbent material of an embodiment of the present invention.

Figure 2 is an enlarged portion (magnified 1000X) of the porous absorbent material shown in Figure 1. Figure 3 is a scanning electron microphotograph (magnified 250X) of a section of a porous absorbent material of another embodiment of the present invention.

Figure 4 is an enlarged portion (magnified 500X) of the porous absorbent material shown in Figure 3.

DETAILED DESCRIPTION OF POROUS ABSORBENT MATERIALS OF THE INVENTION The porous absorbent materials of the present invention are capable of absorbing large amounts of liquids, such as water, blood, body exudates (eg, urine or menstrual fluid), industrial fluids and household fluids, and are capable of retaining said fluids. liquids under moderate pressure. Typically, the porous absorbent materials of the present invention will swell, in general, isotropically, and rapidly absorb liquids. The porous absorbent materials of the present invention comprise a water insoluble polymer, swellable with water, capable of absorbing large quantities of liquids.

(Said absorbent polymer is commonly referred to as a hydrogel, hydrocolloid, superabsorbent polymer). The -. porous absorbent materials preferably comprise absorbent polymers substantially insoluble in water, swellable with water. The specific absorbent polymers for use in the present invention will be described in greater detail, below. In one aspect of the present invention, the porous absorbent materials having modified surface characteristics comprise an absorbent, water-insoluble, water-swellable polymer. The porous absorbent material has a contact angle of the blood on a surface of the porous absorbent material from about 0 degrees to about 40 degrees. It should be noted that, in this aspect of the invention, the porous absorbent material can be used to absorb a variety of liquids, examples of which, non-limiting, are: water, blood, body exudates, industrial fl uids, and fluids. domestic. To describe the characteristic of the absorbent, porous material, blood has been selected, as a representative liquid; An absorbent, porous material, in accordance with this aspect of the invention, will exhibit the specified characteristics with the blood as an absorbed fluid medium. The term "blood", as used herein, should be understood in general. A typical example of the content of "normal blood" is described in a document written by H. Nagorski and others and is entitled "SUPERABSORBENT POLYMERS IN FEMENINE HYGIENE APPLICATIONS" in the American publication called "THE NEW NOWOVENS WORLD" (pages 101-106).; Fall, 1992), which is incorporated herein by reference. As used herein, the term "porous structure" means a structure that forms walls that surround and define cellular voids of absorbent polymers, when they are substantially dry. In general, a porous structure of absorbent material can provide the porous absorbent material with a specific surface area of low and / or high density. Under microscopic observations, the walls formed in a porous absorbent material, for example, show the sponge-like appearance, as shown in Figures 1 and 2, and the walls of another porous absorbent material show a whitish-leaf appearance. , as can be seen especially in Figures 3 and 4. In preferred embodiments, the porous absorbent materials have an overall density of about 0.01 g / cc to about 0.4 g / cc, preferably from about 0.03 g / cc to about 0.35 g. / cc, and most preferably about 0.06 g / cc to about 0.3 g / cc. In alternative preferred modalities, the porous absorbent materials have a specific surface area of at least about 400 cm2 / g, preferably of at least about 600 cm2 / g, and most preferably at least about 1,000 cm2 / g. A method for determining the specific surface area of a sample of porous absorbent materials is described in the TEST METHODS section. The moisture capacity with liquids, such as urine and blood, can be defined in terms of contact angles and the surface tension of the liquids and solids involved. This is discussed, in more detail, in the Publication of the American Chemical Society entitled "Contact Angle, Wettability, and Adhesion "edited by Robert F. Gould and registered in 1964, which is incorporated herein by reference.

Due to the porous structure of the absorbent materials and the improved wetting capacity with the liquids (ie, the low contact angle on the surface) of the porous absorbent material, the distribution of liquid and the dispersion of blood or other materials can be improved. liquids around and through the porous absorbent material. In this way, the porous absorbent material can swell r-, isotropically and quickly absorb liquids. A method to determine the contact angle of a sample is described in the TEST METHODS section. In preferred embodiments, the porous absorbent materials of the present invention further comprise a hydrophilic compound having a function to modify the surface characteristics of the absorbent materials.

Later, a variety of compounds will be described Hydrophilic that have such surface modifying functions. The term "surface characteristic", as used herein, means a physical characteristic of a surface of a material when it comes into contact with liquids. For example, the wetting capacity of liquids and the contact angle of liquids on a surface of the absorbent material are included in said surface characteristics. The term "modify", as used herein, refers to a change in characteristics, or to an increase or reduction in the degree of characteristics. Both types of reactive and non-reactive hydrophilic compounds can be used as the hydrophilic compound. As used herein, the term "reactive" represents a hydrophilic compound, which can react with the absorbent polymer under the condition of the process of the present invention. In other words, said hydrophilic compound comprises at least one reactive functional group which can, under the conditions of the process, form a covalent bond with the absorbent polymer, or an effective number of cationic groups for the ionic bond to the absorbent polymer through the electrostatic interaction. Therefore, the reactive hydrophilic compound forms a chemical bond between the hydrophilic compound and the absorbent polymer. Any type of chemical bonds, including covalent bonds and ionic bonds, can be formed between the hydrophilic, reactive compound and the absorbent polymer. Such chemical bonds must be strong enough to prevent the reactive, hydrophilic compound on the surface of the porous absorbent material from being removed by the following application of liquids (e.g., solvent, urine, menstrual fluid, etc.). In a preferred embodiment, a covalent bond or an ionic bond can be formed as one of such chemical bonds. For example, the covalent bond generally arises as a result of the formation of ester, amide (imide) or urethane linkages, by reaction of the functional group of the hydrophilic compound with a carboxyl group of the absorbent polymer. On the other hand, the term "non-reactive" represents a hydrophilic compound that does not react with the absorbing polymer under the condition of the process of the present invention. In other words, said hydrophilic compound does not comprise any reactive functional group that can form a covalent bond with the absorbent polymer under the condition of the process, nor any effective number of cationic groups for the ionic bond to the absorbent polymer. Therefore, the non-reactive hydrophilic compounds are merely capable of physically associating with, physically connecting to or physically binding to the absorbent polymer through intramolecular interactions. In some preferred embodiments, a spacer may be present, between the hydrophilic compound and the absorbent polymer, to form a chemical bond between the hydrophilic compound and the absorbent polymer. The separator, used herein, must have at least one atom, capable of making said chemical bond or connection between the hydrophilic compound and the absorbent material. In more preferred embodiments of the present invention, the hydrophilic compound can be either a compound '"" supplier of positive charge or a hydrophilic, non-ionic compound. The hydrophilic, non-ionic compound can be either a reactive polyether having at least one functional group, or a non-reactive polyether which is physically capable of physically associating with, physically connecting to or physically binding to the absorbent polymer through intramolecular interactions.

Preferred non-reactive polyethers are described in greater detail, for example, in the U.S.A. 4,190,563 (Rosley et al.) Issued February 26, 1980, which is incorporated herein by reference. Some of the non-reactive polyethers preferably used are described hereinafter. The base structure of the non-reactive polyethers can be expressed by the following formula: R (C2H40) a (C3H60) b (C2H40) cR where a + c represents the total number of oxyethylene units and b the number of oxypropylene units , and where a + cob can be zero, and R is a non-reactive functional group unable to chemically bind to the absorbent polymer under the conditions of the process of the present invention, and is selected preferably independently of H-, H0-, CH30 -, CH3CH20-, etc. The molecular weight of a non-reactive polyether can typically be from 200 to 20,000. The non-reactive polyether may be a polyexyethylene polymer, that is, a polyethylene glycol, in which case b, in the above formula is zero. Polyethylene glycols are soluble in water. Preferred polyethylene glycols are those having a molecular weight of 200 to 3,000. The non-reactive polyethene may be a polyoxypropylene polymer, ie, a polypropylene glycol, in which case a + c, in the above formula is zero. Polypropylene glycols are not soluble in water. Preferred polypropylene glycols are those having a molecular weight of 400 to 4,000. The non-reactive polyether can also be water-insoluble or water-insoluble polyoxyethylene-polyoxy-copolymer block copolymer. The term water-soluble non-reactive polyether represents one that is soluble to a degree of more than 1% in water at 25 ° C, ie, a solubility greater than 1 gram in 100 grams of water. In water-soluble polyoxyethylene-polyoxypropylene copolymers, the weight of the oxyethylene units exceeds about 15% by weight of the total compound. Preferred polyoxyethylene-polyoxypropylene copolymers are those that are liquid at room temperature. Preferred water-soluble copolymers are those having a molecular weight of 1,000 to 4,000. In highly preferred embodiments, the non-reactive polyether is selected from the group consisting of a non-reactive polyethylene glycol (PEG), a non-reactive polypropylene glycol, and a non-reactive poly (oxyethylene-oxypropylene) copolymer. Preferred reactive polyethers have at least one reactive functional group capable of forming a chemical bond on the surface of the absorbent polymer through a covalent bond or an ionic bond. In preferred embodiments, the reactive polyether capable of forming a covalent bond to the absorbent polymer will have at least one reactive functional group as the terminal group, which has repeating units of oxyethylene or oxypropylene and / or a mixture thereof. The functional group of the reactive polyether can be any chemical group reactive with the absorbent polymer, such as a halogen group, a carboxyl group, an amino group, or an epoxy group. Preferred reactive polyethers are described in greater detail below. The reactive polyether base structure can be expressed by the following formula: X (C2H40) to (C3H60) b (C2H40) cY wherein at least one of X and Y is a reactive functional group capable of binding to the absorbent polymer, that is, a halogen group, a carboxyl group, an epoxy group, etc., where a + c represents the total number of oxyethylene units and b the number of oxypropylene units, and where a + c or b can be zero. X and Y can be from the same functional group or from different functional groups. The molecular weight of the reactive polyethers can typically be from 200 to 20,000. The reactive polymer can be a polyoxyethylene polymer having at least one reactive functional group, ie, a polyethylene glycol terminating with a functional group, in which case b, in the above formula is zero. The reactive polyethylene glycol derivatives are soluble in water. Preferred reactive polyethylene glycol derivatives are those having a molecular weight of 200 to 3,000. The reactive polyether may be a polyoxypropylene polymer having at least one reactive functional group, ie, a reactive polypropylene glycol terminating with a functional group, in which case a + c, in the above formula is zero. The reactive propylene glycol derivatives are generally not soluble in water. Preferred reactive polypropylene glycol derivatives are those having a molecular weight of 400 to 4,000. The reactive polyether may also be a polyoxyethylene-polyoxypropylene block copolymer, soluble in water, or insoluble in water. The term water-soluble reactive polyether represents one that is soluble to a degree not greater than 1% in water at 25 ° C, ie, a solubility greater than 1 gram in water. 100 grams of water. In polyoxyethylene-polyoxypropylene copolymers, soluble in water, the weight of the oxyethylene units exceeds about 15% by weight of the total compound. Preferred polyoxyethylene-polyoxypropylene copolymers are those that are liquid at room temperature. Preferred water-soluble copolymers are those which have a molecular weight of 1,000 to 4,000. In highly preferred embodiments, the reactive polyether is selected from the group consisting of a reactive polyethylene glycol (PEG) a polypropylene glycol, and a reactive poly (oxyethylene-oxypropylene) copolymer. In alternative and preferred embodiments, a positively charged compound as the reactive hydrophilic compound chemically bound to the absorbent polymer can be used. The positively charged supply compound can supply the absorbent polymer with a positive charge, thereby forming an ionic bond between the absorbent polymer and the positively charged supply compound. In other alternative and highly preferred embodiments, a polycation can be used as the positive charge delivery compound chemically bound to the absorbent polymer. Polycation is a polymer that has more than one positively charged group, capable of forming an ionic bond to the absorbent polymer. In preferred embodiments, the polycation preferably used is selected from the group consisting of: (1) polymers having primary amine groups (e.g., polyvinyl amine, polyallylamine); (2) polymers having secondary amine groups (e.g., polyethyleneimine); (3) polymers having tertiary amine groups (e.g., poly N, N-dimethylalkyl amine); and (4) polymers having quaternary amine groups (e.g., polydiallyl dimethyl ammonium chloride). The most preferred polycation to be used is a polyamine which; it has primary or secondary amine groups, such as a polyallylamine, polyvinyl amine, or a poly-imine, such as a polyethylene imine. In other highly preferred embodiments, a polycation having oxyethylene repeating units or oxypropylene repeating units can be used as the positively charged compound. For example, an ethoxylated or propoxylated product of an amino compound having oxyethylene units, oxypropylene units, or both, can also be used as the polycation to form ionic bonds for the absorbent polymer. The oxyethylene or oxypropylene units of said cation can have the same formula described above. The amino compounds useful in the present invention will be described in greater detail below. The most preferred polycation for use is a cationic adduct of amino-epichlorohydrin, which is the reaction product between epichlorohydrin and an amino compound, such as a monomeric or polymeric amine, whereby the resulting reaction product has at least two functional cationic groups. These adducts may be in the form of monomeric compounds (e.g., the reaction product of epichlorohydrin and ethylene diamine), or may be in polymeric form (e.g., the reaction product between epichlorohydrin, and polyap-ida). - oliamines, or polyethyleneimines). The polymeric versions of these cationic amino-epichlorohydrin adducts are typically referred to as "resins". A type of amino compounds which can be used to make the ethoxylated or propoxylated product, and which can react with epichlorohydrin to form adducts useful in the present invention, comprise di-, tri-amines, monomers and higher having primary or secondary amino groups in its structures. Examples of useful diamines of this type include bis-2-aminoethyl ether, N, N-dimethylethylenediamine, piperazine, and ethylene amine. Examples of useful triamines of this type include N-aminoethyl piperazine, and dialkylene triamines, such as diethylenetriamine and dipropylenetriamine. Said amine materials are reacted with epichlorohydrin to form the cationic amino-epichlorohydrin adducts useful as the hydrophilic compound, reactive of the present. The preparation of these adducts, as well as a more complete description thereof, can be found in the patent of E.U.A. 4,310,593 (Gross), issued January 12, 1982, and Ross et al., J. Organic Chemistry, Vol. 29, pp. 824-826 (1964). Both documents are incorporated herein by reference. In addition to the monomeric amines, polymeric amines such as polyethyleneimines can also be used, such as the amino compound. A particularly desirable amino compound, which can be reacted with epichlorohydrin to form preferred cationic polymeric adduct resins, useful herein, comprises certain polyamide-polyamines derived from saturated polyalkylene polyamines and C3-C10 dicarboxylic acids. Epichlorohydrin / polyamide-polyamine adducts of this type are water-soluble, cationic, thermo-physebic polymers which are well known in the art as resins resistant to. the humidity for paper products.

In the preparation of polyamide polyamines used to form this preferred class of cationic, polymeric resins, a dicarboxylic acid is first reacted with a polyalkylene polyamine, preferably in aqueous solution under conditions to produce a long-chain, water-soluble polyamide, containing the recurrence groups -NH (CnH2nHN)? - CORCO-, where n and x are each two or more and R is the alkylene group of C, to C8 of the dicarboxylic acid. A variety of polyalkylene polyamines, including polyethylene polyamines (e.g. polyethyleneimine or polyvinyl amine), polypropylene polyamines (e.g., polyallylamine), polybutylene polyamines, etc., can be employed to prepare the polyamide-polyamine, of the which polyethylene polyamines represent an economically preferred class. More specifically, the preferred polyalkylene polyamines, used to prepare the cationic, polymeric resins herein, are polyamines containing two primary amine groups and at least one secondary amine group, wherein the nitrogen atoms are joined together by groups of the formula -CnH2n-, wherein n is a small integer, greater than unity and the number of said groups in the molecule ranges from two to about eight and preferably up to about four. The nitrogen atoms may be attached to the adjacent carbon atoms in the -C n H 2n- group, or to carbon atoms separately, but not to the same carbon atom. Also contemplated is the use of polyamines, such as diethylenetriane, triethylenenetetramine, tetraethylenepentamine, dipropylenetriamine, and the like, which may be obtained in a reasonably pure manner. Of all the above, the most preferred are polyethylene polyamines containing two to four ethylene groups, two primary amine groups, and one to three secondary amine groups. In preferred embodiments, the polycation is selected from the group consisting of: (1) monomeric, ethoxylated amine; (2) ethoxylated polyamine; and (3) ethoxylated poly-imine. For example, the monomeric, ethoxylated amine is tetraethylene pentamine ethoxylated with 15 moles (average) of ethylene oxide) at each hydrogen site on each nitrogen (TEPA-E15); the ethoxylated polyamine is an ethoxylated polyallylamine with 15 moles (average) of ethylene oxide at hydrogen sites on nitrogen atoms; the ethoxylated polyimine is polyethylenimine ethoxylated with 15 moles (average) of ethylene oxide at hydrogen sites on nitrogen atoms. For use herein, polyamine precursor materials containing at least three amino groups are also contemplated, at least one of these groups being a tertiary amino group. Suitable polyamines of this type include methyl bis (3-aminopropyl) amine, methyl bis (2-aminoethyl) amine, N- (2-aminoethyl) piperazine, 4,7-dimethyltriethylene tetramine, and the like.

The dicarboxylic acids which can be reacted with the above polyamines to form the polyamide-polyamine precursors of the preferred cationic, cationic resins useful herein, comprise the saturated aliphatic C3-C10 dicarboxylic acids. Most preferred are those containing from 3 to 8 carbon atoms, such as malonic, succinic, glutaric, adipic, etc., together with diglycolic acid. Of these, the most preferred are diglycolic acid and saturated aliphatic dicarboxylic acids, which have from 4 to 6 carbon atoms in the molecule, particularly, succinic, glutaric and adipic. Mixtures of two or more of these dicarboxylic acids can also be used as well as mixtures of one or more of these with higher, saturated, aliphatic dicarboxylic acids, such as azelaic and sebacic acids, since the resulting long-chain polyamide-polyamine is soluble in water or at least dipersable in water. The polyamide-polyamine materials prepared from the above polyamines and dicarboxylic acids are reacted with epichlorohydrin to form polymeric aminoepichlorhydrone resins, cationic, preferred for use herein as the reactive hydrophilic compound. The preparation of such materials is described in greater detail in the U.S. patent. 2,926,116 (Keim) issued February 23, 1960, patent of E.U.A. 2,926,154 (Keim), issued February 23, 1960, and patent of E.U.A. 3,332,901 (Keim) issued July 25, 1967, all of which will be incorporated herein by reference. A porous absorbent material of another aspect of the present invention comprises a positively charged supply compound bonded to the absorbent polymer, and a nonionic hydrophilic compound bonded to the absorbent polymer. In a preferred embodiment, the contact angle of the blood on a surface of the porous absorbent material is from about 0 degrees to about 40 degrees. Any of the positive charge component compounds, described above, can be used.

Preferred are the polycations described above, which can be attached to the absorbing polymer through the ionic bond. In this aspect of the invention, the nonionic hydrophilic compound may include the above-described reactive hydrophilic compound, which is cae of chemically bonding to the absorbent polymer, as well as non-reactive hydrophilic compounds, which are merely cae of physically associating, physically connecting or physically bind to the absorbing polymer through intermolecular interactions.

It is noted that all of the porous absorbent materials described above of the present invention can have a number of shapes and sizes. For example, porous absorbent materials typically have the form of particles, sheets, cylinders, blocks, fibers, filaments, or other shaped elements. The term "particle" as used herein, describes the porous absorbent materials of the present invention which may be in the form of granules, sprays, spheres, flakes, fibers, aggregates or agglomerates, and the size of the porous absorbent materials generally it will be in the range of between about 1 micron to about 2,000 microns, most preferably from about 20 microns to about 1,000 microns. The term "sheet" as used herein describes the porous absorbent materials of the present invention that can be formed with a thickness of at least about 0.2 mm. The sheets will preferably have a thickness of between about 0.5 mm and about 10 mm, typically from about 1 mm to about 3 mm.

WATER INSULINABLE POLYMER MATERIALS, WATERABLE WITH WATER The absorbent polymers for use in the present invention are hydrogel formers. Preferably, absorbent polymers suitable for use can be an interlaced polyelectrolyte. Most preferably, the crosslinked polyelectrolyte can have a multitude of anionic functional groups, such as sulfonic acid, and very typically carboxyl groups. In preferred embodiments, the crosslinked polyelectrolyte is selected from the group consisting of an entangled polyacrylate-sodium, an entangled polymethacrylate-sodium, a crosslinked potassium-polyacrylate, an interlaced polymethacrylate-potassium, a polyacrylate grafted with starch, interlaced, a polymethacrylate grafted with starch, interlaced, a polyacrylate grafted with polyvinyl alcohol, interlaced, a polymethacrylate grafted with polyvinyl alcohol, interlaced, an interlaced carboxy-methyl-cellulose, a polyacrylate grafted with cellulose, interlaced, and a methacrylate grafted with cellulose, interlaced. Some of the preferred crosslinked polyelectrolytes are made from monomers containing polymerizable, unsaturated acid. In this way, such monomers include the olefinically unsaturated acids and anhydrides, which contain at least one olefinic carbon-to-carbon double bond. More specifically, these monomers can be selected from carboxylic acids and olefinically unsaturated acid anhydrides, olefinically unsaturated sulfonic acids, and mixtures thereof. Some monomers without acid, usually in minor amounts, may also be included to prepare the crosslinked polyelectrolyte herein. Such monomers without acid may include, for example, esters soluble in water or water dispersible from acid-containing monomers, as well as monomers containing no carboxylic or sulfonic acid group. Thus, optional non-acidic monomers include monomers containing the following types of functional groups: esters of carboxylic acid or sulfonic acid, hydroxyl groups, amine groups, amino groups, nitrile groups, and quaternary ammonium salt groups. These monomers without acid are well known materials and are described in greater detail, for example, in the patent of E.U.A. 4,076,663 (Masuda et al.) Issued on February 28, 1978, and in the U.S. patent. 4,062,017 (Westerman), issued December 13, 1977, both incorporated herein by reference. The olefinically unsaturated carboxylic acid and carboxylic acid anhydride monomers include acrylic acids illustrated by the same acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylic acid, b-methylacrylic acid (crotonic acid) , α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid, chlorosorbic acid, angelic acid, cinnamic acid, p-chloro cinnamic acid, b-sterilacrylic acid, itaconic acid, citroconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic acid anhydride. Olefinically unsaturated sulfonic acid monomers include aliphatic or aromatic vinylsulfonic acids, such as vinylsulfonic acid, allylsulfonic acid, vinyltoluenesulfonic acid, and styrene sulfonic acid; acrylic and methacrylic sulfonic acid, such as sulfoethyl acrylate, sulphoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropyl sulfonic acid and 2-acrylamide-2-methylpropane-sulfonic acid. The preferred crosslinked polyelectrolyte for use herein contains carboxy groups. These polymers include hydrolyzed starch-acrylonitrile graft copolymers, partially neutralized starch-acrylonitrile copolymer copolymers, starch-acrylic acid graft copolymers, partially neutralized starch-acrylic acid graft copolymers, vinyl acetate copolymers. acrylic ester, saponified, hydrolyzed acrylonitrile or acrylonitrile copolymers, lightly entangled polymers in their network of any of the above copolymers, partially neutralized polyacrylic acid, and slightly interlocked polymers in their partially neutralized polyacrylic acid work network. These polymers can be used either alone or in the form of a mixture of two or more different polymers. Examples of these polymer materials are described in the U.S.A. 3,661,875, patent of E.U.A-. 4,076,663, patent of "E.U.A. 4,093,776, patent of E.U.A. 4,666,983, and US patent. 4,734,478. The highly preferred crosslinked polyelectrolyte for use in the invention are slightly interlaced polymers in their network of partially neutralized polyacrylic acids and their starch derivatives. Most preferably, the crosslinked polyelectrolyte comprises from about 50 to about 95%, preferably about 75%, of polyacrylic acid, lightly entangled in its neutralized working net (i.e. poly (sodium acrylate / acrylic acid)). As described above, the crosslinked polyelectrolyte are polymer materials that are slightly interlaced in their network of work. The network interlacing serves to make the polymer materials water-soluble, and, in part, determines the absorptive capacity and the characteristics of the extractable polymer content of the absorbent material. The procedures for network interworking of polymers and typical network interlacing agents are described in more detail above with reference to the US patent. 4,076,663. The interlaced polyelectrolyte particles can be formed in any conventional manner. Typical and preferred methods for producing the crosslinked polyelectrolyte are described in the US patent. Re. 32,649 (Brant et al.), Issued April 19, 1988, patent of E.U.A. 4,666,983 (Tsubakimoto et al.) Issued January 19, 1987, and the US patent. 4,625,001 (Tsubakimoto et al.), Issued November 25, 1986, all of which are incorporated herein by reference. Preferred methods for forming the crosslinked polyelectrolyte are those involving aqueous solution methods or other solution polymerization methods. As described in the patent of E.U.A. Re. 32,649, mentioned above, the polymerization of aqueous solution involves the use of an aqueous reliction mixture to carry out the polymerization in order to form the interlaced polyelectrolyte. The aqueous reaction mixture is then subjected to polymerization conditions which are sufficient to produce in the mixture a slightly interlaced polymer material in its working network, substantially insoluble in water. More specifically, the method of polymerizing aqueous solution to produce the crosslinked polyelectrolyte comprises the preparation of an aqueous reaction mixture, wherein the polymerization is carried out to form the desired crosslinked polyelectrolyte. One element of said reaction mixture is the monomer material containing an acid group, which will form the "base structure" of the crosslinked polyelectrolyte to be produced. The reaction mixture will generally comprise about 100 parts by weight of the monomer material. Another component of the aqueous reaction mixture comprises a working network interlacing agent. The network interlacing agents useful for forming the interlaced polyelectrolyte are described in more detail in the U.S. Re. 32, 649, patent of E.U.A. 4,666,983 and the patent of E.U.A. 4,625,001, mentioned above. The working network interlacing agent will generally be present in the aqueous reaction mixture in an amount of about 0.001 mol% to about 5 mol% based on the total moles of the monomer present in the aqueous mixture (from about 0.01 to about 20). parts by weight, based on 100 parts by weight of the monomer material). The free radical initiator includes, for example, peroxygen compounds, such as sodium, potassium, and ammonium persulfates, caprylyl peroxide, benzoyl peroxide, hydrogen peroxide, cumene hydroperoxides, tertiary butyl diperphthalate, butyl perbenzoate. tertiary, sodium peracetate, sodium percarbonate, and the like. Other optional components of the aqueous reaction mixture comprise the various non-acidic co-monomer materials, including esters of the monomers containing an unsaturated acid functional group, or the other co-monomers that do not contain any carboxylic acid functionalities or sulfonic. The aqueous reaction mixture is subjected to polymerization conditions, which are sufficient to produce in the mixture, polymer materials slightly interlaced in its working network, hydrogel formers, absorbents, insoluble in water. The polymerization conditions are also discussed in more detail in the three patents mentioned above. Said polymerization conditions generally involve heating (thermal activation techniques) at a polymerization temperature of from about 0 ° C to about 100 ° C, most preferably from about 5 ° C to about 40 ° C. The polymerization conditions, under which the aqueous reaction mixture is maintained, can also include, for example, subjecting the reaction mixture, or portions thereof, to any conventional form of polymerization that activates the irradiation. Radioactive, electronic, ultraviolet or electromagnetic radiation are conventional, alternative polymerization techniques. The resulting polymerization product is a swollen hydrogel, insoluble in water. The swollen, water-insoluble hydrogel is used in some preferred methods to make porous absorbent materials, as described hereinafter. The acid functional groups of the polymer materials formed in the aqueous reaction mixture are also preferably neutralized. The neutralization can be carried out in any conventional manner, which results in at least about 25 mol%, and most preferably about 50 mol%, of the total monomer used to form the polymer material, being monomers containing an acid group , which are neutralized with a salt-forming cation. Said salt-forming cations include, for example, alkali metals, ammonium, substituted ammonium and amines, as discussed in greater detail in the U.S. patent. Re. 32,649, mentioned above. Since it is preferred that the entangled polyelectrolyte be manufactured using an aqueous solution polymerization process, it is also possible to carry out the polymerization process using multi-phase polymerization proceeding techniques, such as inverse emulsion polymerization or polymerization procedures. of reverse suspension. In the inverse emulsion polymerization or inverse suspension polymerization processes, the aqueous reaction mixture, as described above, is suspended in the form of very small droplets in a matrix of an inert organic solvent, immiscible with water, such as cycloexan. The resulting interlaced polyelectrolyte has a generally spherical shape. The reverse suspension polymerization processes are described in greater detail in the U.S.A. 4,340,706 (Obaysashi and others), issued July 20, 1982, patent of E.U.A. 4,506,052 (Flesher et al.), Issued March 19, 1985 and US patent. 4,735,987 (Morita et al.) Issued April 5, 1988, all of which are incorporated herein by reference. The preferred crosslinked polyelectrolyte of the present invention is one that exhibits a high absorption capacity. The absorption capacity refers to the ability of a given polymer material to absorb liquids with which it is in contact. The absorption capacity can vary significantly with the nature of the liquid that is being absorbed and with the way in which the polymer material makes contact with the liquid. For the purposes of this invention, the absorptive capacity is defined in terms of the amount of Synthetic Urine (as defined herein below) absorbed by any given polymer material, in terms of grams of Synthetic Urine per gram of polymer material in a procedure defined later in the Test Methods section. The preferred crosslinked polyelectrolyte of the present invention is one having an absorption capacity of at least about 20 grams, most preferably at least about 25 grams of Synthetic Urine per gram of polymer material. Typically, the polymer materials of the interlaced polyelectrolyte herein have an absorption capacity of about 20 grams to about 70 grams of Synthetic Urine per gram of polymer material.

Since all the interlaced polyelectrolytes are preferably formed from the same polymer material with the same properties, this is not the case. For example, some entangled polyelectrodes may comprise a starch-acrylic acid graft copolymer, while other entangled polyelectrolytes may comprise a slightly interlaced polymer in their partially neutralized polyacrylic acid work network. In addition, the interlaced polyelectrolyte may vary in size, shape, absorption capacity, or any other property or characteristic. In a preferred embodiment of the present invention, the entangled polyelectrolyte consists essentially of slightly interlaced polymers in its partially neutralized polyacrylic acid work network, each entangled polyelectrolyte having similar properties.

PROCESS FOR MAKING ABSORBENT-POROUS MATERIALS OF THE INVENTION The present invention also involves a method for producing the absorbent material with modified surface characteristics, as described hereinafter, comprising the steps of: (a) applying a first compound modifying the surface on a portion of a water-swellable, water-insoluble absorbent polymer surface, wherein the first surface modification has the function of modifying the surface characteristics of the absorbent polymer; (b) inflating the absorbent polymer by absorbing water; and (c) removing a portion of said water, while maintaining the absorbent polymer in a substantially swollen state, thereby forming a porous structure in the absorbent material. Preferably, in step (c) substantially all of the free water (ie, the water that has not chemically bound to the absorbent polymer) is removed substantially, thus leaving the porous structure substantially dry to the touch. The free water may include water that is retained within the passages of the absorbent material before said removal step. The portion of water removed from the swollen absorbent polymer can be removed by any means that results in a stable, porous structure. Such means may include methods that are well known in the art of removing water from solid or semi-solid materials. One method for removing water is to extract moisture using an extraction solvent, which is substantially miscible with water, which will not readily absorb or sublimate the surface modifying agent, which is easily removed from the swollen absorbent polymer, by evaporation. (ie, having a low boiling temperature), and / or having no substantial affinity or reactivity for the absorbent polymer material. A very preferred method is to use high mass transfer media, at high speed, such as high velocity air or gases, or low ambient pressures (such as partial or total voids) or any combination of these to remove the water directly from the polymer swollen absorbent Said procedure is preferred, since the water is removed without the need to introduce other chemicals or solvents to extract the water. Most preferably, a procedure will remove the free water, quickly, before the particle is dried, and the open passages in it have the opportunity to be crushed. The rapid removal of water from hydrogel absorbent polymer materials, without crushing the passages, requires special processing conditions. Without being bound by any theory, it is believed that the crushing of the particle, more specifically the crushing of the passages between particles in the absorbent polymer, occurs due to the high capillary retention of water in such passages, while the water is removed. The removal of water from the passage moves the passage inwards, due to the high capillary forces with the attraction of the water towards the surfaces of the polymer. By removing the last amounts of free water from the capillary or passage, the surfaces of the polymer, which include carboxyl and hydroxyl groups, can be chemically bound, together; this procedure is commonly referred to as "hydrogen bonding". This phenomenon is commonly found in the drying water of cellulose fibers and cellulosic structures having small diameters of capillaries and / or fibers. The effect of hydrogen bonding can be demonstrated by using a tissue paper or towel, filling a ball with the paper, and letting the paper dry. After drying, which usually takes several days, or using forced heat drying, the dry paper becomes a compact, hardened and inflexible structure. Therefore, special drying procedures are required to quickly remove water from the typical hydrogel absorbent polymer materials without crushing the passages. Said methods may include, but are not necessarily limited to: instantaneous vacuum drying; dried with counter-current air or in current, at high temperature; fluid bed drying; dielectric or infrared drying; freeze drying; and combinations thereof. Said methods are described in the following references, the descriptions of which are incorporated herein by reference: Handbook of Industrial Drying, Marcel Dekker Inc. (Arun S. Mujumdar, Ed.), 1987 (ISBN 0-8247-7606); Flash Drying Bilgin Kisakurek (pp. 475-400); Microwave and Dielectric Drying, Robert F. Schiffmann (pp. 327-356); Freeze Drying, Athanasios Liapis (pp. 295-326); and Application of infrared radiation for drying or particulate materials, Jakobsen & Driscoll (pp. 704-711), Drying '92 (Arun S. Mujumdar, Ed.), Elsevier Sci. Publ. (ISBN 0-444-89393-8). It is usually sufficient to remove enough free water, quickly and without substantial crushing, by such procedures, which can then be removed, then minor amounts of moisture, without additional plating, by drying methods, including air drying, fluid bed drying, and the like. In other preferred embodiments, the method for producing the absorbent material, having modified surface characteristics, comprises the steps of: (a) applying a first surface modification compound on a portion of a surface of a water-insoluble absorbent polymer, inflatable with water, wherein the first surface modification compound has the function of modifying the surface characteristics of the absorbent polymer; (b) inflating the absorbent polymer by absorbing water; (cl) freezing the swollen absorbent polymer; and (c2) removing a portion of water from the swollen, frozen absorbent polymer, thereby forming a porous structure in the absorbent material.

In preferred embodiments, the absorbent polymer material as a precursor also has a number of shapes and sizes. For example, said absorbent polymer material, precursor, may typically be in the form of particles, sheets, films, cylinders, blocks, fibers, filaments or other shaped elements. Preferably, discrete units are used, most preferably precursor particles of the absorbent polymer. In a preferred, alternative embodiment, it can be used as the precursor, a macrostructure or absorbent sheet comprising a multitude of absorbent, interconnected particles of the absorbent polymer. In preferred embodiments, a variety of reagents can be used to modify the surface characteristics of the absorbent polymer, such as the first surface modification compound. Preferably, said reagents include chemical compounds to improve the distribution and dispersion of liquids in absorbent polymer materials. In highly preferred embodiments, one of the pyl ethers described above, which includes non-reactive polyethers and reactive polyethers, can be used as the first modification compound. Said polyethers can be applied by any technique and apparatus used to apply materials to the other materials, including coating, draining, dripping, condensing, spraying or dipping the reactive polyether onto the absorbent polymer material. As used herein, the term "applied on" means that the reactive polyether will be on at least a portion of the surface area of the -,. Absorbent polymer material. Preferably, the reactive polyether is applied over the entire surface of the absorbent polymer material. In a preferred embodiment, the reactive polyether is combined with the absorbent polymer, and the two components are mixed, preferably mixed thoroughly, using any number of mixing techniques and apparatus, including various mixers, sprinklers or kneaders, as are known in the art. The technique. Therefore, in one embodiment, the reactive polyether is bonded to the surface of the absorbent polymer through a covalent bond, in another embodiment, another reactive polyether is attached to the surface of the absorbent polymer via an electrostatic interaction, and still in another embodiment, another non-reactive polyether is attached to the surface of the absorbent polymer via intermolecular interactions, as described hereinbefore. In another preferred, alternative embodiment, one of the polycations described above can be used as the first surface modification compound. In a preferred embodiment, step (a) is carried out before step (b), so that the first surface modification compound is attached to at least a portion of the surface of the absorbent polymer before it is bloat The absorbent polymer is swollen by the application of water. The amount of water applied at least is sufficient to cause the absorbent polymer to swell by S-water bsorption. Preferably, the ratio of the water to the absorbent polymer will be on the scale of about 1: 1 about 50: 1, preferably about 3: 1 to about 20: 1. In a preferred embodiment, the first surface modification compound (ie, a polyether or a polycation) is dissolved in water to make an aqueous liquid mixture comprising the water and the first surface modification compound. The first surface modification compound can be dissolved in water by any of the various techniques and apparatuses, known in the art, used to dissolve materials to solutions. The aqueous liquid mixture may contain an additional solvent and / or an additional material, which adversely affects the absorbency or wettability of the liquid, of the absorbent polymer. For example, low molecular weight alcohols, such as methanol, ethanol, propanol or acetone, can be contained in the liquid mixture, as well as the first surface modification compound. After preparing the aqueous liquid mixture, it is applied on the absorbent polymer. The aqueous liquid mixture can be applied on the absorbent polymer. The aqueous liquid mixture can be applied by any of the various techniques and apparatuses used to apply solutions to materials including coating, pouring, dripping, spraying, atomizing, condensing or immersing the aqueous liquid mixture on the absorbent polymer. In this way, the aqueous liquid mixture can be applied on only some of the absorbent polymer, especially the absorbent polymer, on only a portion of a part or all of the absorbent polymer. In some preferred embodiments, the first surface modification compound (ie, a polyether or a polycation) is dissolved in an organic solvent to make an organic solution. The first surface modification compound can be dissolved in the organic solvent by any of the various techniques and apparatuses known in the art, used to dissolve materials to solutions. The organic solution is applied on the surface portion of the absorbent polymer. In a preferred, alternative embodiment, step (a) is carried out after step (b). More specifically, the water or other aqueous solution is first applied to an unswollen absorbent polymer. After the absorbent polymer has swelled, the first surface modification compound is applied onto the swollen absorbent polymer, whereby the first surface modification compound is attached to the surface of the swollen absorbent polymer. When contacting the aqueous liquid mixture or with. water, the absorbent polymer begins to swell by absorbing water. Substantially, most of the swelling of the absorbent material is conducted during and / or after applying the aqueous liquid mixture or water on the absorbent polymer. In preferred embodiments, more than about 60%, preferably more than about 80%, most preferably more than about 95% of the applied water, will be absorbed by the swelling of the absorbent polymer. The actual temperature used for the swelling will vary depending on the specific polymer materials used herein. The preferred swelling conditions will involve a temperature of about -5 ° C to 60 ° C. Most preferably, the swelling is carried out at a temperature of about -2 ° C to 30 ° C, most preferably about 0 ° C to 10 ° C. In a preferred embodiment, wherein the reactive polyether is mixed with a solvent such as an organic solvent or an aqueous solvent mixture, the reactive polyether is reacted with the absorbent polymer. In one embodiment, wherein the reactive polyether includes a plurality of cationic groups to make the ionic bond, the reaction can be carried out at room temperature, while in another embodiment, a higher temperature will be required to achieve chemical bonding. For example, in an embodiment wherein the reactive polyether includes a halogen terminal group or an epoxy end group to make the covalent bond, heating the aqueous liquid mixture and the absorbent polymer is required to achieve an effective chemical bond. Preferably, the temperature of the aqueous liquid mixture and the absorbent polymer is maintained in the range from about 60 ° C to about 250 ° C, most preferably from about 80 ° C to about 200 ° C. In some embodiments, a catalyst, such as a Lewis base, is used to promote the reaction between the reactive polyether and the absorbent polymer. In preferred modalities, alternatives, the absorbent, swollen, water-insoluble, water-swellable polymer can be made directly from acid-containing, polymerizable, unsaturated monomers using an aqueous solution polymerization method, such as that described in the POLYMER MATERIALS section. INSOLUBLES IN WATER, IHINCHABLES WITH WATER. Said swollen absorbent polymer is also used to make porous absorbent materials of the present invention. After making the absorbent polymer swollen, it is frozen; for example, by applying cooling media. The freezing of the swollen absorbent polymer can be done by any of the various techniques and apparatuses used to freeze materials. For example, the swollen absorbent polymer is carried or passed into an externally cooled compartment and remains there until it freezes. Alternatively, the swollen absorbent polymer can be circulated around a cooling source, such as cooling tubes or a bath containing a cooler, e.g., liquid nitrogen, dry ice, a solution of alcohol or the like, and the slurry frozen is collected. In preferred embodiments, the freezing of the swollen absorbent polymer is effected by cooling to a temperature below about -10 ° C, most preferably below about -30 ° C, for a sufficient time to achieve freezing. If the temperature is too high or the time too short, the swollen absorbent polymer will not freeze completely. Typically, more than about 60%, preferably more than about 80%, preferably more than about 95%, preferably all by weight of the swollen absorbent polymer, will be frozen. After freezing of the swollen absorbent polymer, the portion of the frozen water contained in the frozen absorbent polymer is removed or dried by applying any drying means without passing through the liquid state, ie, the ice is converted to the gaseous state maintaining the Absorbent polymer below the melting temperature of the ice. In other words, the resulting ice in the frozen absorbent polymer is sublimated and the water vapor is carried away, leaving a material substantially free of water. Sublimation of the ice is achieved by generally subjecting the swollen, frozen absorbent polymer to a low pressure environment. In preferred embodiments, to obtain effective rates of sublimation and removal of water to the vapor phase, the frozen absorbent polymer is subjected to an environment of subatmospheric pressure, under such conditions, the water is sublimed directly from the solid phase to the phase steam. In the freeze drying technique, the vacuum means for providing said subatmospheric pressure environment are well known. Typically, said subatmospheric pressure is less than about 5.0 Torr and, preferably, less than about 1 Torr. In preferred embodiments, more than about 80%, preferably more than about 90%, most preferably about 97% by weight of the water or ice contained in the frozen absorbent polymer will be removed. In a highly preferred embodiment step (c2) is carried out by drying the swollen, swollen absorbent polymer while maintaining the frozen state of the frozen absorbent polymer. Therefore, preferably the drying step of the swollen, frozen absorbent polymer is conducted in the same apparatus used for the cooling means. It should be noted that in some embodiments, the swollen absorbent polymer can be directly subjected to a subatmospheric pressure environment without pre-freezing.

Due to the latent heat of evaporation / sublimation, the swollen absorbent polymer can freeze spontaneously. In a most preferred embodiment, step (a) is carried out after step (c2). More specifically, after making an absorbent polymer material having a porous structure, the first surface modification compound is applied to the porous absorbent polymer material, whereby the first surface modification compound is bonded to the surface of the absorbent, porous polymer material. In a further preferred embodiment, the method further comprises the step of (e) applying a second surface modification compound on a portion of a surface of the absorbent polymer, thereby bonding the second surface modification compound to the absorbent polymer. The second surface modification compound has the additional function of modifying the surface characteristics of the absorbent polymer. The additional function may be the same function that is provided by the first surface modification compound. In this way, the same compound as the first surface modification compound, can also be used as the second surface modification compound. Therefore, in a preferred embodiment, one of the polyethers described above, including non-reactive polyethers and reactive polyethers can be used as the second surface modification compound. In another preferred, alternative embodiment, one of the polycations, described above, can be used as the second surface modification compound, thereby attaching the second surface modification compound to the absorbent polymer via the electrostatic interaction. In a highly preferred embodiment, the first surface modification compound is one of a polyether and a polycation, while the second surface modification compound is the other of the polyether and the polycation. In a preferred embodiment, step (e) is carried out before step (b). More specifically, after application of the first surface modification compound on the absorbent polymer, the second surface modification compound is applied, subsequently on the absorbent polymer, in this way, the second surface modification compound is also attached to the surface of the absorbent polymer before the absorbent polymer swells. In a preferred, alternative embodiment, step (e) is carried out after step (b). More specifically first the water is applied on a swollen absorbent polymer. After the absorbent polymer swells, the second surface modification compound is applied onto the swollen absorbent polymer, whereby the second surface modification compound is attached to the surface of the swollen absorbent polymer. In a preferred, alternative, additional embodiment, step (e) is carried out after step (c2). More specifically, after making an absorbent polymer material having a porous structure, the second surface modification compound is applied to the porous absorbent polymer material, whereby the second surface modification compound is attached to the surface of the absorbent, porous polymer material. Still in preferred embodiments, the method for producing the absorbent material with modified surface characteristics comprises the steps of (A) making a porous absorbent polymer; (B) applying a first surface modification compound on a surface of the porous absorbent polymer, wherein the first surface modification compound has the function of modifying the surface characteristics of the porous absorbent polymer. In a preferred embodiment, step (A) for making a porous absorbent polymer comprises the steps of: (1) forming a reaction mixture comprising, (i) an unsaturated, substantially water-soluble monomer comprising neutralized carxyl groups, (ii) an internal, water-soluble interlacing agent capable of reacting with the monomer to form an absorbent polymer material, -, - and ( iii) a solvent substantially soluble in water, (2) dispersing a blowing agent substantially insoluble in water in the reaction mixture to form a dispersion of blowing agent batches in the reaction mixture, (3) expanding the agent particles. of blowing to form an expanded structure in the reaction mixture, and (4) reacting the monomer and the internal interlacing agent to form a porous absorbent polymer. A preferred method of steps (1) to (4) and a further preferred process are described in the application of E.U.A. Series No. 08 / 038,580, issued to Dean V. Phan et al. On March 26, 1993, entitled "Superabsorbent Polymer Foam", case No. 4838, the description of which is incorporated herein by reference. In a preferred embodiment, step (A) for making a porous absorbent polymer comprises the steps of: (1) forming a reaction mixture comprising, (i) an unsaturated monomer, substantially soluble in water comprising neutralized carboxyl groups, ( ii) an internal, water-soluble interlacing agent capable of reacting with the monomer to form the absorbent polymer material, (iii) a solvent substantially soluble in water, (2) dispersing a substantially insoluble water separating agent, in the reaction mixture to form a dispersion of particles of the separation agent in the reaction mixture, (3) to react the monomer and the internal interlacing agent to form an absorbent polymer, and (4) to remove the dispersion of the agent particles. of separating the insoluble water polymer, swellable with water, to form a water-insoluble, water-swellable, porous polymer. The resulting material of the present invention is a porous absorbent material, which has a surprisingly improved wetting ability and dispersibility with liquids, in particular with urine and blood, as compared to those of the conventionally derived porous absorbent material, while they maintain substantially the same capacity for absorption and retention of liquids. Under microscopic observations, the freeze-dried absorbent material is in the form of discrete platelets, flakes or sheets. Freeze-dried absorbent materials tend to look like walls surrounding and defining cell holes. Macroscopically, it is believed that this morphology results in the sponge-like or porous appearance of the freeze-dried absorbent material. It was also noted that while the cells are apparently surrounded by loose sheet-like polymer flakes, the sheets are to some degree discontinuous and exhibit holes and, in general, resemble a sheet-like structure.

ABSORBENT ARTICLES MADE FROM POROSOS ABSORBENT MATERIALS The porous absorbent materials according to the present invention can be used for many purposes in many fields of use. For example, porous absorbent materials can be used to pack containers; drug delivery devices; devices for cleaning wounds; devices for the treatment of burns; ion exchange column materials; Construction materials; agricultural and horticultural materials, such as sheets for seeds or materials to retain water; and industrial uses, such as mud-forming agents or oil water removers, materials to prevent dew formation, desiccants, and materials for moisture control. Due to the unique absorbent properties of the porous absorbent materials of the present invention, they are especially suitable for use as absorbent cores in absorbent articles, especially disposable absorbent articles. As used herein, the term "absorbent article" refers to articles that absorb and contain exudates from the body, and more specifically refers to articles that are placed against or from the user's body to absorb and contain the various exudates. discharged from the body. In addition, "disposable" absorbent articles are those that are intended to be discarded after a single use (i.e., the additional absorbent article in its entirety does not intend to be washed, or otherwise restored or reused as an absorbent article, although certain materials or all the absorbent article can be recirculated, reused or compound). In general, an absorbent article comprises: (a) a liquid-permeable topsheet, which is located adjacent to the wearer's body; (b) a liquid impermeable backsheet, which is located away from the wearer's body and adjacent to the wearer's clothing; and (c) an absorbent core positioned between the topsheet and the backsheet. The absorbent core comprises at least one of the porous absorbent materials described above. Preferably, the absorbent core further comprises a web of substrate bonded to the porous absorbent material. Alternatively, the absorbent core further comprises a wrapping band that encloses the porous absorbent material. In highly preferred embodiments, the porous absorbent material in the absorbent core has a basis weight of from about 60 g / m2 to about 1,500 g / m2, preferably from about 100 g / m.2 to about 1,000 g / m2, most preferably a about 150 g / m2 to about 500 g / m2 of the absorbing material. In some preferred embodiments, the absorbent core may further comprise fibers or fluff pulp (fibrous or fiber material), more specifically, non-absorbent gelling fibers. Said fiber material can be used as reinforcing members in the absorbent core, improving the handling of the core liquid, as well as a co-absorbent with the absorbent polymers. Preferably, the absorbent core includes from about 20% to about 90% by weight of absorbent material and from about 80% to about 10% by weight of said non-absorbent, gelled fiber material distributed within the porous absorbent material. Any type of fiber material, which is suitable for use in conventional absorbent products, can be used in the absorbent core herein. Specific examples of said fiber material include cellulose fibers, modified cellulose fibers, rayon, polypropylene fibers, and polyester, such as polyethylene terephthalate (DACRON), hydrophilic nylon (HYDRIFIL), and the like. Examples of other fiber materials for use in the present invention, in addition to those already discussed, are hydrophobic, hydrophilic fibers, such as thermoplastic fibers treated with a surfactant or treated with silica derived from, for example, polyolefins such as polyethylene or polypropylene, polyacrylics, polyamides, polystyrenes, polyurethanes and the like. In fact, hydrophilic, hydrophilic fibers, which are in and by themselves are not very absorbent, and which, therefore, do not provide bands of sufficient absorbent capacity to be useful in conventional absorbent structures, are suitable for use in the absorbent core by virtue of its good movement properties by wicking effect. This is because, in the absorbent core of the present, the inclination of movement due to the wicking effect of the fibers is very important, if not more important than the absorbing capacity of the same fiber material due to the high speed of fluid consumption and the lack of gel blocking properties of the absorbent core. Synthetic fibers are generally preferred for use herein as the fiber component of the absorbent core. Most preferred are polyolefin fibers, preferably polyethylene fibers. Other cellulosic fiber materials that may be useful in certain absorbent cores herein are chemically hardened cellulosic fibers. Preferred chemically hardened cellulosic fibers are hardened, twisted, curled cellulosic fibers which can be produced by internally interlacing cellulose fibers with an entanglement agent. The hardened, twisted, crimped cellulose fibers useful as the hydrophilic fiber material herein are described in greater detail in the U.S. patent. 4,888,093 (Dean et al.), Issued December 19, 1989; patent of E.U.A. 4,889,595 (Herrón et al.) Issued December 26, 1989; patent of E.U.A. 4,889,596 (Schoggen et al.), Issued December 26, 1989; patent of E.U.A. 4,889,597 (Bourbon et al.) Issued December 26, 1989; and patent of E.U.A. 4,898,647 (Moore et al.) Issued February 6, 1990, all of which are incorporated herein by reference. A preferred embodiment of the disposable absorbent article is a diaper. As used herein, the term "diaper" refers to a garment, generally worn by infants and incontinent persons that is worn around the wearer's lower torso. A preferred diaper configuration, eg, a diaper comprising an absorbent core is generally described in US Pat. 3,860,003 (Buell), issued on January 14, 1975, which is incorporated herein by reference. The alternatively preferred configurations for disposable diapers of the present are also described in the US patent. 4,808,178 (Aziz et al.) Issued February 28, 1989; the patent of E.U.A. 4,695,278 (Lawson), issued September 22, 1987; the patent of E..U.A. 4,816,025 (Foreman) issued on March 28, 1989; the patent of E.U.A. 5,151,092 (Buell et al.) Issued September 29, 1992, all of which are incorporated herein by reference. Another preferred embodiment of the disposable absorbent article is a catamenial product. Preferred catamenial products comprise an apertured top sheet of formed film, as described in U.S. Pat. 4,285,343 (McNair) issued August 25, 1981; the patent of E.U.A. 4,608,047 (Mattingly) issued August 26, 1986; and the patent of E.U.A. 4,687,478 (Van Tilburg) issued August 18, 1987, all of which are incorporated herein by reference. Preferred catamenial products may comprise wings, side tabs, and other structures or elements, as described in the co-pending, commonly assigned US application, Series No. 984,071 issued to Yasuko Morita, entitled "Absorbent Article Having Elasticized Side Flaps", No. of Agent JA-09RM, filed November 30, 1992 incorporated herein by reference It should be understood, however, that the present invention can also be applied to other absorbent articles commercially known under other names, such as incontinence briefs. , adult incontinence products, trainers, diaper inserts, facial tissues, paper towels and the like.

PREPARATION OF ARTIFICIAL BLOOD To prepare the specific artificial blood used in the test methods of the present invention, they are dissolved 3 grams of gastric mucin in 460 ml of phosphate pH regulator saline with a pH of 7.2. After heating the resulting solution at 50-80 ° C, for about 2.5 hr, 2.0 ml of 8% lactic acid is applied to the resulting solution. The resulting solution is mixed with an equal volume of defibrinated, sterile, fresh sheep blood, as a result, the resulting mixture is obtained as the blood that is used in the test methods.

TEST METHODS A. Contact Angle Measurement An absorbent material is made to absorb a certain amount (approximately 5-8%) of moisture and then placed on a horizontal support plate and compressed at 5-20 kg / cm2 to form a sheet consisting of the compressed absorbent material. By supplying a drop of blood on the surface of the sheet, the contact angle defined by the drop of blood and the surface of the sheet is measured simultaneously by means of a contact angle meter (type: CA-A, obtained from Kyowa Kaimen Kagaku Co., Ltd., Tokyo) equipped with a camera. The measurement is conducted under normal laboratory conditions at approximately 23 ° C. B. Measurement of the Specific Surface Area After the absorbent material is completely dried in a vacuum oven at 50 ° C for 24-40 hr, the specific surface area is measured using the Brunauer gas absorption method. Emmet-Teller (BET). This method involves absorbing a monolayer of a gas (Krypton) over a known mass of a sample of absorbent material at the temperature of liquid nitrogen. The absorbed Krypton is then desorbed by increasing the temperature of the sample (thermal desorption) and is detected by a thermal conductivity detector (TCD), whose output is connected to an integration register. In this way the peak area of the desorbed Krypton is known. The specific equipment used for these measurements is Belsorp 36, obtained from Nippin Bel K.K. 0.0-1.5 grams + 0.005 grams of the sample of absorbent material is weighed to the sample cell of the apparatus. The cell, which contains the sample, is then placed in the gas flow of the instrument. The samples are purified with gas, with a helium flow of 30 ml / min, to remove any gas other than helium, from the sample, typically a minimum of 4 hr. After purifying with gas, the gas flow is changed to a specific mixture of Krypton-Helium gas. The sample cell is immersed in liquid nitrogen so that it can reach equilibrium. An absorption curve is generated. Afterwards, the absorbed Krypton is desorbed by removing the liquid nitrogen and submerging the flask in hot running water. Absorbed Krypton generates a desorption curve and a peak value. The specific surface area is obtained from the BET graph. C. Measurement of Global Density. After the absorbent material is completely dried in a vacuum oven at 50 ° C, for 24 hr, the sample is packed in a 10 ml graduated cylinder. During packing, the graduated cylinder is kept on the table without being covered. The weight of the packed sample is measured and the overall density is obtained by dividing the measured weight of the sample by the volume of the sample (10 ml). D. Measurement of Absorbency Time. 0.25 grams of absorbent material is placed in a petri dish, and 5 ml of the artificial blood is applied to the absorbent material. The mixture is stirred with a spatula to keep the absorbent material in contact with the artificial blood. The time required for the liquid to disappear is recorded as the absorbency time.

EXAMPLE OF PRECURSORY PARTICLE.

An aqueous monomer solution consisting of 40 grams of partially neutralized acrylic acid, having a portion thereof, of 75 mol% neutralized with caustic soda, 0.37 grams of N, N'-methylene-bis-acrylamide and 60 grams, is prepared. -. grams of water The aqueous monomer solution is fed to the reaction vessel, which is subsequently purged with nitrogen gas to remove trapped air remaining from the reaction system. The mixture is then stirred and heated to about 45 ° C, and a solution of 0.23 grams of 2,2'-azo-bis- (2-amidinopropane) dihydrochloride is added thereto as a polymerization initiator. , in a gram of water. The polymerization starts approximately 15 minutes after the addition of the polymerization initiator. With the progress of the polymerization, the aqueous monomer solution gives rise to a gel containing soft water. The internal temperature of the reaction system is maintained at 80-90 ° C for hours to completely complete the polymerization. A swollen gel polymer is formed. This swollen gel polymer is used in the following examples. The resulting swollen gel polymer, thus obtained, is spread on a metal gauge with a size of # 50, normal, and dried with hot air at 150 ° C. The dry particles are pulverized in a hammer-type crusher and sifted with a normal # 20 sieve (850 microns) to obtain particles that pass through the normal # 20 sieve. As a result, white, dry precursor particles of the absorbent polymer are obtained.

EXAMPLE 1 A solution consisting of 2 grams of polyethylene glycol (molecular weight 600), 3.3 grams of Kymene Plus (30% active resin) and 1,500 grams of distilled water is prepared. The polyethylene glycol is two parts by weight and the Kymene Plus is 1 part by weight for 100 parts by weight of precursor particles of the absorbent polymer. The solution is applied to 100 grams of precursor particles, made according to the Example of Precursor Particle. The precursor particles have a particle size such that the precursor particles pass through a # 20 normal screen (850 microns) and are retained on a # 100 normal screen (150 microns). The mixture is thoroughly mixed with a stirring spatula until all the precursor particles come into contact with the previous solution. Upon contacting the solution, the absorbent polymer begins to swell by absorbing the water included in the solution. The mixing temperature is about 2 ° C. The swollen absorbent polymer, which is then obtained, is freeze dried using a freeze drying apparatus (available from TOKYO RIKAKIKAI CO., LTD., Tokyo). The swollen absorbent polymer is introduced into stainless steel trays, which are then placed in a freezer at an effective cooling temperature of about -20 ° C. The frozen absorbent polymer is then placed in the freeze drying apparatus, and the water is removed by sublimation under a vacuum of about 0.05 Torr. The dry absorbent material is pulverized with a hammer-type crusher and is sifted with a normal # 20 sieve (850 microns) to obtain particles that pass through the normal # 20 sieve. As a result, white particles of the absorbent material are obtained. The contact angle of the blood on the resulting absorbent material is less than about 10 degrees. The absorbency time of the resulting absorbent material is about 6 seconds. The specific surface area of the resulting absorbent material is approximately 1,200 cm 2 / g. The overall density of the resulting absorbent material is approximately 0.1 gram / cc.

EXAMPLE 2 A solution is prepared consisting of 2 grams of polyethylene glycol (molecular weight 600), 3.3 grams of Kymene (30% active resin) and 1, 200 grams of distilled water. The polyethylene glycol is two parts by weight and the Kymene Plus is 1 part by weight for 100 parts by weight of the absorbent polymer. The solution is sprayed onto the swollen gel polymer made before the drying step according to the Precursor Particle Example and mixed together. A sprayer is used (type: 24-182-04, available from Iuchi Seieido Co., Ltd., of Osaka, Japan). The resulting mixture is then freeze-dried using the freeze-drying apparatus. The swollen absorbent polymer mixture is introduced into stainless steel trays, which are then placed in a freezer at an effective cooling temperature of about -20 ° C. The frozen absorbent polymer is then placed in the freeze drying apparatus, and the water is removed by sublimation under a vacuum of about 0.05 Torr. The dry absorbent material is pulverized with a hammer-type crusher and is sifted with a normal # 20 sieve (850 microns) to obtain particles that pass through the normal # 20 sieve. As a result, white particles of the absorbent material are obtained. The contact angle of the blood on the resulting absorbent material is less than about 10 degrees. The absorbency time of the resulting absorbent material is approximately 10 seconds. The specific surface area of the resulting absorbent material is approximately 1,500 cm 2 / g. The overall density of the resulting absorbent material is approximately 0.1 gram / cc.

EXAMPLE 3 A solution consisting of 2 grams of reactive polyether (TEPA-E15), and 1,000 grams of distilled water is prepared. The reactive polyether is two parts by weight for 100 parts by weight of the absorbent polymer. The solution is sprayed onto 100 grams of the precursor particles made according to the Precursor Particle Example and mixed together. The precursor particles absorb the water from the solution and begin to swell. The resulting swollen mixture is then freeze-dried using the freeze-drying apparatus. The absorbent polymer mixture is introduced to stainless steel trays, which are then placed in a freezer at an effective cooling temperature of about -20 ° C, for about 5 hours. The frozen absorbent polymer is then placed in the freeze drying apparatus, and substantially all the water is removed by sublimation under a vacuum of about 0.05 Torr. The dry absorbent material is pulverized with a hammer-type crusher and is sifted with a normal # 20 sieve (850 microns) to obtain particles that pass through the normal # 20 sieve. As a result, white particles of the absorbent material are obtained. The contact angle of the blood on the resulting absorbent material is less than about 10 degrees. The absorbency time of the resulting absorbent material is approximately 11 seconds. The specific surface area of the resulting absorbent material is approximately 1,500 cm 2 / g. The overall density of the resulting absorbent material is approximately 0.1 gram / cc.

EXAMPLE 4 1,500 grams of distilled water are applied to 100 grams of precursor particles made according to the Precursor Particle Example. The precursor particles have a particle size such that the precursor particles pass through a # 20 normal screen (850 microns) and are retained on a # 100 normal screen (150 microns). The mixture is thoroughly mixed with a stirring spatula until all the precursor particles come into contact with the previous solution. Upon contacting the solution, the absorbent polymer begins to swell by absorbing the water included in the solution. The mixing temperature is about 2 ° C. The swollen absorbent polymer, which is then obtained, is freeze dried using a freeze drying apparatus (available from TOKYO RIKAKIKAI CO., LTD., Tokyo). The swollen absorbent polymer is introduced into stainless steel trays, which are then placed in a freezer at an effective cooling temperature of about -20 ° C, for about 5 hours. The frozen absorbent polymer is then placed in the freeze drying apparatus, and substantially all the water is removed by sublimation under a vacuum of about 0.05 Torr. As a result, white particles of the absorbent material are obtained. 100 grams of the absorbent polymer is placed in a 2 liter flask. A solution consisting of 2 grams of polyethylene glycol (molecular weight 600), 1 gram of polyallylamine and 500 grams of methanol is prepared. The solution is introduced into the flask. The mixture is thoroughly mixed with a stirring spatula until all the absorbent polymer particles are wetted with the above solution. After the methanol, included in the resulting mixture, is evaporated by means of a rotary evaporator, the resulting product is dried under vacuum at 40 ° C to obtain the absorbent material. The dry absorbent material is pulverized with a hammer-type crusher and is sifted with a normal # 20 sieve (850 microns) to obtain particles that pass through the normal # 20 sieve. As a result, white particles of the absorbent material are obtained. The contact angle of the blood on the absorbent material is less than about 10 degrees. The absorbency time is approximately 6 seconds. The specific surface area of the resulting absorbent material is approximately 1,200 cm 2 / g. The overall density of the resulting absorbent material is approximately 0.1 gram / cc.

Claims (13)

NOVELTY OF THE INVENTION CLAIMS

1. - A porous absorbent material having modified surface characteristics, characterized in that it comprises: a water insoluble polymer, swellable with water; wherein the contact angle of the blood on a surface of said absorbent material is from 0 degrees to 40 degrees.

2. The porous absorbent material according to claim 1, characterized in that further comprises a hydrophilic compound bound to said water-insoluble, water-swellable polymer, said hydrophilic compound is selected from the group consisting of a charge-supplying compound positive, and a non-ionic hydrophilic compound, preferably a polyether.

3. - The porous absorbent material according to claim 2, further characterized in that said positively charged filler compound is a polycation having a plurality of positively filler groups, said polycation is preferably selected from the group consisting of (1) polymers that they have primary amine groups; (2) polymers having secondary amine groups; (3) polymers having tertiary amine groups; and (4) polymers having quaternary amine groups.

4. - The porous absorbent material according to claim 2, further characterized in that said polyether is selected from the group consisting of polyethylene glycol, a polypropylene glycol, and a copolymer of poly (oxyethylene-oxypropylene).

5. The porous absorbent material according to any of claims 1 to 4, further characterized in that said porous absorbent material has an overall density of 0.01 g / cc at 0.4 g / cc, preferably 0.03 g / cc to 0.35 g. / cc, and most preferably 0.06 g / cc at 0.3 g / cc.

6. - The porous absorbent material according to any of claims 1 to 5, further characterized in that said porous absorbent material has a specific surface area of at least 400 cm2 / g, preferably of at least 600 cm2 / g , and most preferably at least 1,000 cm 2 / g.

7. The porous absorbent material according to any of claims 1 to 6, further characterized in that said water-insoluble, water-swellable polymer is an interlaced polyelectrolyte, said entangled polyelectrolyte is preferably selected from the group consisting of a polyacrylate- interlaced sodium, an interlaced polymethacrylate-sodium, an interlaced polyacrylate-potassium, an interlaced polymethacrylate-potassium, a polyacrylate grafted with starch, interlaced, a polymethacrylate or grafted with starch, interlaced, a -, polyacrylate grafted with polyvinyl alcohol, interlaced, a polymethacrylate grafted with polyvinyl alcohol, interlaced, an interlaced carboxy-methyl-cellulose, a polyacrylate grafted with cellulose, interlaced, and a methacrylate grafted with cellulose, interlaced.

8. An absorbent article comprising: (a) a liquid-permeable top sheet; (b) a posterior back sheet impervious to liquid; and (c) an absorbent core positioned between said topsheet and said backsheet, said absorbent core characterized in that it comprises at least one porous absorbent material of any of claims 1 to 7. The absorbent article according to claim 8 , further characterized in that said porous absorbent material in said absorbent core has a basis weight of 60 g / m2 to 1,500 g / m2 of said porous absorbent material, preferably from 100 g / m2 to 1,000 g / m2 of said material - porous absorbent, most preferably from 150 g / m2 to 500 g / m2 of said porous absorbent material. 10. A method for making a porous absorbent material having modified surface characteristics, characterized in that it comprises the steps of: (a) applying a first surface modification compound on a portion of a surface of an absorbent polymer insoluble in water, inflatable with water, said first surface modification compound having a function of modifying the surface characteristics of the absorbent polymer; (b) inflating the absorbent polymer by absorbing water; and (c) removing a portion of said water, while maintaining the absorbent polymer in a substantially swollen state, thereby forming a porous structure in the absorbent material. 11. The method method for making a porous absorbent material having modified surface characteristics, according to claim 10, further characterized in that said step (c) comprises the steps of: (cl) freezing the water insoluble polymer, swellable with the water, swollen; and (c2) removing a portion of water from the water-insoluble, water-swellable, swollen, frozen polymer, thereby forming a porous structure in the absorbent material. The method method for making a porous absorbent material having modified surface characteristics, according to any of claims 10 or 11, characterized in that it further comprises the step of applying a second surface modification compound on a portion of a surface of the water-insoluble, water-swellable polymer, thereby attaching said second surface-modification compound to the water-insoluble, water-swellable polymer, and said second surface-modification compound having the additional function of modifying the surface characteristics of the water insoluble polymer, inflatable with water. 13. - The method method for making a porous absorbent material having modified surface characteristics, according to any of claims 10 or 11, further characterized in that said first surface modification compound is one of polyether and a polycation, and , second surface modification compound is one of the other said polyether and said polycation.