HUT77843A - Absorbent material - Google Patents

Description

The present invention relates to an absorbent material, more particularly to a material commonly known as a "superabsorbent".

Substances currently called "superabsorbents" are weakly cross-linked hydrophilic polymers. Polymers differ in their chemical nature, but they have the property of being able to absorb and retain at moderate pressures an amount of aqueous liquid equivalent to several times its weight. Superabsorbents, for example, can typically contain up to 100 times their own weight or more of distilled water.

Superabsorbents have been proposed for use in a variety of industrial applications where water-absorbing and / or retaining properties are advantageous. Such areas include agriculture, construction, alkaline batteries and filters. However, the most important applications of superabsorbents are hygiene and / or sanitary products such as disposable sanitary napkins and diapers for children or incontinent adults. Such hygiene and / or sanitary products use superabsorbents, generally in combination with cellulosic fibers, to absorb body fluids such as menses or urine. Superabsorbents have a significantly lower body fluid absorbency than deionized water. It is generally believed that this effect is due to the electrolyte content of body fluids and is often referred to as "salt poisoning."

The water-absorbing and water-repellent properties of superabsorbents are due to the presence of ionizable functional groups in the polymer structure. These groups may be carboxyl groups, most of which are in salt form when the polymer is dry but dissociates and solvates upon contact with water. In the dissociated state, the polymer chain has a number of functional groups that have the same electrical charge and thus repel each other. This leads to an expansion of the polymer structure, which in turn allows the absorption of additional water molecules, although this is limited by the crosslinking of the polymer structure and must be sufficient to prevent the polymer from dissolving. It is believed that a significant concentration of electrolyte in water interferes with the dissociation of functional groups and leads to a "salt poisoning effect.

Attempts have been made to counteract the effects of salt poisoning and to improve the absorption efficiency of superabsorbent solutions containing electrolytes such as menses and urine. Thus, Japanese Patent Application Laid-Open 57-4 5057, x, discloses an absorbent consisting of a powder or granule mixture of a superabsorbent such as a cross-linked polyacrylate with an ion exchange resin. EP-A-0210756 relates to an absorbent structure comprising a superabsorbent and an anion exchanger optionally together with a cation exchanger wherein both ion exchangers are fibrous. Combining the superabsorbent material with an ion exchanger aims to reduce the salt poisoning effect by utilizing an ion exchanger, usually in the form of anion exchange and cation exchanger combinations, to reduce the salt content of the liquid. The ion exchanger has no direct effect on the efficiency of the superabsorbent, and it is possible that the salt content may not be sufficiently reduced to achieve an adequate effect on the overall absorption capacity of the combination. In addition to being very expensive, the ion exchanger itself has no absorbent effect and thus acts as a diluent for the superabsorbent.

It is an object of the present invention to provide a superabsorbent having improved efficacy in the presence of an electrolyte, such as menses and urine.

The present invention provides a superabsorbent material which is (1) a cationic superabsorbent having 20 to 100% of the functional groups in basic form;

(2) a cation exchanger in which 50-100% of the functional groups are comprised of a combination of an acidic superabsorbent material.

Preferably 50-100%, more preferably substantially 100% of the functional groups of the cationic superabsorbent are in basic form.

Essentially 100% of the functional groups of the cation exchanger are in acid form.

According to the present invention, it has surprisingly been found that the combination of a basic cationic absorbent and an acid cation exchanger in electrolyte-containing solutions such as menses and urine is particularly effective as a superabsorbent.

While not wishing to be limited to any theory, it is believed that a double effect is achieved if the superabsorbent material of the invention is contacted with the electrolyte-containing material as follows. solution:

(1) converting the cationic superabsorbent from a non-absorbent form to a salt form in which it acts as a superabsorbent; and (2) converting the cationic superabsorbent into a salt form has a deionizing effect on the solution reinforced with the cation exchanger.

Functional groups in cationic superabsorbents are typically quaternary ammonium groups which are strong ion exchangers. Thus, when the cationic superabsorbent is contacted with an electrolyte, such as a saline solution, it swells, the OH / ions of the superabsorbent are partially replaced by the Cl ions of the solution, and the pH of the solution becomes strongly basic. However, the presence of the cation exchange resin prevents the solution from becoming strongly basic by shifting the equilibrium reaction towards the complete conversion of the cationic superabsorbent salt form. In this case, the sodium ions of the solution are replaced by the cation exchange resin, the chloride ions in the solution are replaced by a basic cationic superabsorbent, thus significantly desalting the brine, while the superabsorbent improves its absorption.

This conversion of the anionic superabsorbent into the salt form upon contact with the electrolyte-containing solution and the cation-exchange sodium ion-binding effect exerts a significant desalting effect on the solution, thereby improving the superabsorbent's effectiveness by eliminating the salt-poisoning effect. In contrast to the desalting of the solution, an ion exchange resin is used in combination with a superabsorbent already in salt form (see Japanese Patent Application No. 57-45157, supra). And European Patent Application EP-A-021Q256), the basic cationic superabsorbent also has a desalting effect on the solution. This allows a much greater desalination effect to be achieved by using an ion exchanger and a superabsorbent in salt form. It should be noted that the effect of the electrolyte in the solution on the absorption capacity of the superabsorbent in that solution is non-linear unless the absorption capacity decreases with increasing salinity. Accordingly, in certain concentration ranges, a relatively large increase in absorbency must be achieved by a relatively small reduction in the salinity of the solution.

The cationic superabsorbent can be any material having superabsorbent properties in which the functional groups are cationic. Functional groups generally bind to the weakly cross-linked acrylate base polymer. The base polymer may be, for example, a polyacrylamide, a polyvinyl alcohol, an ethylene-maleic anhydride copolymer, a polyvinyl ether, a polyvinylsulfonic acid, a polyacrylic acid, a polyvinylpyrrolidone or a polyvinylmorpholine. Copolymers of these monomers may also be used. Starch and cellulose based polymers such as hydroxypropyl cellulose, carboxymethyl cellulose and acrylate-grafted starches may also be used. Specific base polymers include crosslinked polyacrylates, hydrolyzed acrylonitrile-grafted starch, starch polyacrylates, and isobutylene-maleic anhydride copolymers. Particularly preferred base polymers are starch polyacrylates and cross-linked polyacrylates.

Suitable cationic functional groups include, for example, quaternary ammonium groups or primary, secondary or tertiary amines which must be present in basic form. For cellulose derivatives, the degree of substitution (DS) of a derivative containing a functional group is defined as the number of functional groups (usually quaternary ammonium groups) per cellulose anhydroglucose unit. The DS is usually 0.1 to 1.5. Analogously, DS can be defined as the number of functional groups per monomer or comonomer unit for synthetic polymers. The DS value is usually 1, for example 1 quaternary ammonium group / polyacrylate monomer unit. Preferred base polymers include polysaccharides and polymers based on dimethyldiallyl ammonium chloride.

In one embodiment, the cationic superabsorbent may be a polysaccharide superabsorbent prepared by reacting a fibrous polysaccharide, such as cellulose, with an excess of a quaternary ammonium compound having at least one substituent having polysaccharide hydroxyl groups and having from 0.5 to 1.1 substituents. containing a quaternary ammonium compound. The quaternary ammonium compound can be represented by the general formula (I), (II), wherein f 'n 1 is a number from 1 to 16, X is a halogen atom; Z is an anion, such as an alkali or a hydroxy group; and R, R, R and R are the same or different and each is hydrogen, alkyl, z 2 -hydroxyalkyl, alkenyl or aryl, and the substituent R is a radical of formula (III) or (IV) wherein p is a number from 2 to 10 and n, R, R ¹ , R ³ , X and Z are as defined above. That's it

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Type II cationic polysaccharide superabsorbents are described in more detail in International Patent Application 92/19652.

In another embodiment, the cationic superabsorbent may be a cross-linked cellulose based, in particular, a fibrous cationic polysaccharide having superabsorbent properties, substituted with quaternary ammonium groups and having a degree of substitution of at least 0.5 and sufficiently water insoluble. Superabsorbents of this type are described in more detail in our pending patent application.

In another embodiment, the cationic superabsorbent may be a water-swellable, water-insoluble polymer which is a diallyl quaternary ammonium salt monomer crosslinked with a suitable polyfunctional vinyl compound, characterized in that the polymer is radicalized in an aqueous medium using a free radical catalyst. Such superabsorbents are described in more detail in our pending patent application.

Ion exchange is the reversible exchange of ions between a solid and a liquid, in which the structure of the solid _{,, η} „,. .,. , ”Ί which is the ion exchange material, there is no permanent structural change.

'—......... ...... - .....

Ion exchange occurs in many materials such as silicates, phosphates, fluorides, humus, cellulose, wool, proteins, alumina, resins, lignin, cells, glasses, barium sulfate, and silver chloride.

However, they are used as ion exchange agents which depend on properties other than ion exchange between the liquid and solid phase. Ion exchange has been used industrially since 1910.

since the introduction of water softening, initially with natural and later synthetic zeolites.

The introduction of synthetic organic ion exchange resins in 1935 was the result of the synthesis of phenolic condensation products containing sulfone or amine groups which can be used for reversible exchange of cations or anions.

Inorganic ion-exchange agents include both naturally occurring substances such as mineral zeolites (e.g. cliptonite), green sands and clays (e.g. montmorillonite group), and synthetic products such as gel zeolites, aqueous oxides of polyvalent metals, and polybasic acids with multivalent metals salts.

Synthetic organic products include strong and weak types of cation and anion exchange resins.

The weak acid cation exchange resins are primarily based on acrylic methacrylic acid crosslinked with a bifunctional monomer such as divinylbenzene (DMB). Other weak acid resins have been prepared with phenolic or phosphonic acid functional groups.

The weak acid resin has a high affinity for hydrogen ions, so it can be easily regenerated with strong acids. However, this property limits the range where the salt cleavage can take place to a pH greater than 4.

Highly acidic resins of commercial importance are sulfonated styrene dVB ¹ copolymers using sulfonic acid, sulfur trioxide and chlorosulfonic acid for sulfonation.

These materials are characterized by the ability to exchange cationic compounds or cleave neutral salts and can be used throughout the pH range.

Preferably, the cation exchanger is a cationic resin having acidic functional groups. Suitable functional groups include carboxylic or sulfonic acid groups.

The following cation exchange resins may be used in the practice of the present invention:

Amberlite IR 120

It is a strong cation exchange resin which has the functionality of H ⁺ sulfonic acid. The total ion exchange capacity is 4.4 meq / g dry resin.

Amberlite IRC 76

It is a weak cation exchange resin which has the carboxyl functionality in acid form. The total ion exchange capacity is 10 meq / g dry resin.

Dowex 50W YZ

It is a strong cation exchange resin available in H ⁺ form and having sulfonic acid functionality. It has a total ion exchange capacity of 10 meq / g dry resin.

The weight ratio of the cationic superabsorbent to the cation exchanger is 1:20 to 1: 1, preferably 1: 3 to 1: 1, depending on the molecular weight and ion exchange capacity.

The absorbent material of the present invention is particularly advantageous for applications where it is desired to absorb electrolyte-containing aqueous fluids. Such liquids are, for example, menses and urine, and the absorbent material may be used as a filler for pads and diapers, generally in the form of a mixture with a fibrous absorbent such as a curled cellulose. For this purpose, the absorbent granules of the present invention may be in the form of granules or fibers.

The absorbent materials of the present invention exhibit particularly good electrolyte-containing aqueous solution absorption, as illustrated by the following examples, in which saline (1% sodium chloride solution) and synthetic urine are used.

Preparation

Crosslinked poly (dimethyl diallyl ammonium hydroxide) (Fai

OH) based cationic superabsorbent

Preparation of Fai 7 OH

133 g of 60% aqueous dimethyldiallyl ammonium chloride (DMAC, available from Fluka) was weighed into a 250 ml flask.

0.2 g of bis (acrylamide) (BAC, available from Fluka) was weighed separately into a 5 ml test tube and dissolved in 2 ml of distilled water.

0.12 g of ammonium persulfate (free radical initiator) was dissolved in 2 mL of distilled water in a 5 mL test tube.

The monomer solution was degassed with a vacuum pump.

Then, while stirring, the curing solution ·· · ·

12 and the free radical initiator were added to the monomer solution and the temperature was adjusted to 60 ° C for four hours by placing the flask in a thermostatic bath.

The solid product was cut with a spatula and filled into a 5 liter beaker containing 4 liters of distilled water. After 2 hours of swelling, the gel was filtered through a nonwoven fabric. The gel was dried in an air circulation oven at 60 ° C for 12 hours. 60 g of dry gel was collected and named Fai 7 Cl. 20 g of Fai 7 Cl was placed in a 10 liter beaker, 4 liters of distilled water was added with constant stirring. When the polymer was swollen (after 2 hours) 500 ml of 0.01 M sodium hydroxide solution was added and after 30 minutes the gel was filtered through a nonwoven fabric. These operations (alkalization and filtration) were repeated until chloride ion was no longer detectable in the wash water (chloride ions detected by silver nitrate reaction). At this time, the gel was washed with distilled water until the wash water was no longer alkaline.

The gel was then dried in an air circulation oven at 60 ° C for 12 hours. 10 g of dry polymer was collected, called Fai 7 OH.

Example 1

Liquid absorption comparison study

A study was conducted to demonstrate that the use of both a cationic superabsorbent and a cation exchange resin can improve the effectiveness of the cationic superabsorbent due to the desalination effect produced by the ion exchange mixture.

- 13 in.

In a 250 mL beaker, 150 mL of a 1% sodium chloride solution was contacted with 2.23 g IR 120 (H ⁺ ) cation exchange resin for one hour with continuous stirring. The sodium ions of the solution had to be replaced by the H ⁺ ions of the resin. The solution was aspirated with a Pasteur pipette and added dropwise to another 250 mL beaker containing 0.11 g of Fai 7 OH while stirring; stirring was stopped when the gel was no longer swollen. At this point, the gel was placed in a "tea bag" made of nonwovens and the absorbance measured at 60 g for 10 minutes:

A = (weight of _dry weight - _wet weight) / G where

A = absorbance after centrifugation in g / g, _wet weight = mass of wet / AGM bag after centrifugation in g, weight _dry = mass of dry AGM bag in g,

G = mass, in g, of AGM used for the test.

The assay was performed with both Fai 9 OH and Fai 9 Cl each, without the cation exchange resin.

The results are as follows:

- 14 ·· · * ··· · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

absorption, g / g (tea bag absorption, g / g (centrifuge) quantity, (G) H ₂ O 1% NaCl H ₂ O 1% NaCl Fai-7 OH 0.11 351 55 300 42 Fai-7 Cl 0.11 340 54 290 43 Fai-7 OH + IR 120 (H ⁺ ) 0.11 + 2.23 96, 7 55

The above results show that the basic form of the cationic superabsorbent Fai-7 OH and the salt form of Fai-7 Cl show limited absorption in 1% sodium chloride solution compared to deionized water. However, when combined with the acid-form IR 120 (H ⁺ ) cation exchanger, the material exhibits a significant increase in absorption.

It should be noted that 1% sodium chloride is a rigorous superabsorbent assay. Studies in the literature have shown that urinary salt content varies depending on a number of factors, but 1% by weight is the maximum value in practice.

Claims (16)

PATENT CLAIMS 1) a cationic superabsorbent having a functional group of 20 to 100% basic form, and A superabsorbent material, characterized in that: 2) consists of a combination of a cation exchanger with a functional group of 50 to 100% acid form. The superabsorbent material according to claim 1, characterized in that the functional groups of the cationic superabsorbent are in the form of 50 to 100%, preferably substantially 100% of the basic form and substantially 100% of the functional groups of the cationic exchanger are acidic. Superabsorbent material according to claim 1 or 2, characterized in that the functional groups of the cationic superabsorbent are primary, secondary or tertiary amine or quaternary ammonium groups. A superabsorbent material according to claim 3, characterized in that the functional groups are quaternary ammonium .X -. ~~~ ~~ groups. 5. A superabsorbent according to any one of claims 1 to 5, characterized in that the functional groups as the basic polymer are polyacrylamide, polyvinyl alcohol, ethylene-maleic anhydride copolymer, polyvinyl ether, polyvinylsulfonic acid, - 16 »W» ««. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · About polyacrylic acid, polyvinylsulfonic acid, polyacrylic acid, polyvinylpyrrolidone, polyvinylmorpholine or copolymers thereof, or a starch or cellulose based polymer such as the parent polymer. The superabsorbent material of claim 5, wherein the starch or cellulose-based polymer is hydroxypropyl cellulose, carboxymethyl cellulose or acrylate-grafted starch. A superabsorbent according to claim 5 or 6, characterized in that the base polymer is a crosslinked polyacrylate or an isobutylene-maleic anhydride copolymer. The superabsorbent according to claim 7, wherein the base polymer is a starch polyacrylate or a crosslinked polyacrylate. 9. A superabsorbent material according to any one of claims 1 to 5, characterized in that the cationic superabsorbent is a polysaccharide superabsorbent which is prepared by reacting a fibrous polysaccharide with an excess of a quaternary ammonium compound capable of reacting with at least one of the hydroxyl groups of the polysaccharide. Contains 1 degree of substitution. 10. The superabsorbent material of claim 9, wherein the quaternary ammonium compound (I) or (ϊI)) is a monohydrate. · · 9 »··« loc / phthalane - where n is a number from 1 to β; X is halogen; Z is an anion such as a halide or hydroxyl ion; and R, R ¹ , R ² and R ³ may be the same or different and are hydrogen, alkyl, hydroxyalkyl, alkenyl or anlyl, and R is a group of formula (III) or (IV) wherein p is an integer from 2 to 10 and n, R, R ¹ , R ³ , X and Z are as defined above. 11. A superabsorbent material according to any one of claims 1 to 5, characterized in that the cationic superabsorbent is a fibrous, cationic, polysaccharide having superabsorbent properties, the polysaccharide is substituted with quaternary ammonium groups, the degree of substitution is at least 0.5 and the polysaccharide is '. remain insoluble. 12. The superabsorbent material of any preceding claim, wherein the cationic superabsorbent is a water-swellable, water-insoluble polymer comprising units derived from ta diallyl quaternary ammonium salt monomer, ^r? which is crosslinked with a suitable polyfunctional vinyl compound and characterized in that the polymer is prepared in water using a free radical catalyst. 13. any one of claims ^r bens material, characterized in that the kationc t Cationic resin containing functional groups. The superabsorbent material of claim 13, wherein 15. A superabsorbent material according to any one of claims 1 to 5, characterized in that the weight ratio of the cationic superabsorbent to the cation exchanger is in the range of 1:20 to 1: 1. 16. The superabsorbent material of claim 15, wherein the weight ratio of the cationic superabsorbent to the cationic ion exchanger is 1: 3 to 1: 1. 1-16. Use of a superabsorbent material according to any one of claims 1 to 4 for absorbing aqueous liquids containing electrolyte.