CZ140897A3 - Superabsorptive material - Google Patents

Abstract

The invention provides a superabsorbent material which comprises a combination of (1) a cationic superabsorbent in which from 20 to 100 % of the functional groups are in basic form, and (2) a cationic exchanger in which from 50 to 100 % of the functional groups are in acid form. The combination is particularly effective as a superabsorbent for electrolyte containing solutions such as menses and urine.

Description

The invention relates to an absorbent material of the type referred to as superabsorbent.

In particular, the prior art has t? e9 · i% lDi ¹ f ₅

The substances commonly referred to as superabsorbents are generally slightly crosslinked hydrophilic polymers. Polymers may differ in their chemical nature, but have the common feature of being able to absorb and retain, even at moderate pressure, a quantity of aqueous liquids at several times their own weight. For example, superabsorbents, for example, can absorb up to 100 times their own weight or even more distilled water.

Superabsorbents have already been proposed for various industrial uses where their water absorption and / or water retention capacity can be exploited; Examples include agriculture, the construction industry, the production of alkaline batteries and filters. However, the most important field of application for superabsorbents is the manufacture of sanitary and / or sanitary products such as disposable sanitary pads and disposable diapers for infants or incontinent adults. In such sanitary and / or sanitary products, superabsorbents are generally used together with cellulosic fibers to absorb body fluids such as menses or urine. However, the absorption capacity of superabsorbents for body fluids is dramatically lower than for deionized water. This is probably due to the electrolyte content of body fluids, and this phenomenon is often referred to as salt poisoning.

The water absorption and retention characteristics of the superabsorbents are due to the content of ionizable functional groups in the polymer structure. These groups are generally carboxy groups whose high proportion is in the form of a salt when the polymer is dry, but which dissociate and solvate upon contact with water. In the dissociated state, the polymer chain has a number of chain-linked functional groups, which groups have the same electrical charge and therefore repel each other. This leads to the expansion of the polymer structure, which again allows further absorption of water molecules, although this expansion is limited by the cross-linking of the polymer structure, which must be sufficient to avoid dissolution of the polymer. It is believed that a significant amount of electrolyte in water prevents dissociation of functional groups and leads to a phenomenon referred to as salt poisoning. Although most commercial superabsorbents are anionic in nature, it is also possible to prepare cationic superabsorbents with functional groups such as quaternary ammonium groups. Such materials also need to be in the form of salts to act as superabsorbents, and their characteristics are also influenced by the phenomenon referred to as salt poisoning.

Attempts are known to counteract the phenomenon of salt poisoning and to improve the characteristics of superabsorbents in absorbent electrolyte containing liquids such as menses and urine. For example, Japanese Patent Application Publication No. OPI 57-45057 discloses an absorbent comprising a mixture of a superabsorbent, for example, a cross-linked polyacrylate, with an ion exchange resin in powder or granular form. EP-A0210756 describes an absorbent structure and an anion exchanger, optionally together with a cation exchanger, both of which are in fibrous form. The combination of superabsorbent with an ion exchange resin is intended to reduce the phenomenon of salt poisoning by using an ion exchange resin generally as an anion exchange resin and a cation exchange resin to reduce the salt content of the liquid. The ion exchanger does not directly affect the characteristics of the superabsorbent, and the ion exchanger is not able to sufficiently reduce the salt content to achieve the desired total absorption capacity of the combination. In addition to being expensive, ion exchangers have no absorption capacity as such and therefore act as a superabsorbent diluent.

The invention is therefore directed to overcome the shortcomings of the prior art and to improve the characteristics of the superabsorbent in the presence of an electrolyte, for example in the case of menses and urine.

SUMMARY OF THE INVENTION

The superabsorbent material according to the invention consists of a combination

1) a cationic superabsorbent having 20 to 100% of the functional groups in basic form; and

2) a cation exchanger whose 20 to 100% of the functional groups are in acid form.

The cationic superabsorbent preferably has 50-100% and particularly preferably substantially 100% of the functional groups is in basic form.

The cation exchanger preferably has substantially 100% functional groups in acid form.

It has now surprisingly been found that the combination of a cationic absorbent in basic form with an acid cation exchanger is particularly effective as a superabsorbent in electrolyte-containing solutions such as menses and urine.

While not intending to be bound by theory, the twofold effect of the superabsorbent of the invention in contact with an electrolyte-containing solution is explained as follows:

1. the cationic superabsorbent is converted from a non-absorbent form to a salt form in which it acts as a superabsorbent; and

2. Conversion of the cationic superabsorbent to the salt form has a deionizing effect on cation exchange promoter solutions.

The functional groups in the cationic superabsorbents are generally quaternary ammonium groups, which are strong ion exchangers. When a cationic superabsorbent is contacted with an electrolyte solution, for example, a salt solution, the swelling and hydroxyl ions of the superabsorbent are partially replaced by chloride ions from the solution and the pH of the solution becomes strongly basic. However, the presence of a cation exchange resin prevents the solution from becoming a strongly basic shift of the equilibrium reaction in favor of the complete conversion of the cationic super absorbent to the salt form. Sodium ions in solution are replaced by a cation exchange resin, chloride ions in solution are replaced by a cationic superabsorbent in a basic form, thereby achieving substantial desalting of the brine solution, thereby improving the absorbency of the superabsorbent.

This conversion of the anionic superabsorbent to the salt form upon contact with an electrolyte-containing solution and cation exchange sodium ion has a strong desalting action on the solution, thereby improving the utility properties of the superabsorbent by eliminating the phenomenon of salt poisoning. In contrast to the use of an ion exchange resin for desalting a solution in combination with a salt already superabsorbent (Japanese Patent Application Publication No. OPI 57-45057 and EP-A-0210756, as mentioned above), the cation exchange superabsorbent has a basic in the form of a desalting action on the solution. This allows for much more desalination than the use of ion exchange resin and superabsorbent in the form of a salt. It is recalled that the action of the electrolyte in solution on the absorption capacity of the superabsorbent for the solution is not linear, so that the absorption capacity does not decrease regularly with increasing salt content. Above a certain concentration range, a relatively large increase in absorption capacity is possible with a relatively small decrease in the salt content of the solution.

The cation exchange superabsorbent can be any material with superabsorption and properties having a cationic functional group. In general, the functional groups are bonded to a slightly crosslinked acrylic base polymer. For example, the parent polymer may be polyacrylamide, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinyl ether, polyvinyl sulfonic acid, polyacrylic acid, polyvinylpyrrolidone and polyvinyl morpholine. Copolymers of these monomers may also be used. Starch and cellulose based polymers may also be used, for example, hydroxypropylcellulose, carboxymethylcellulose and acrylic grafted starches. Preferred base polymers include crosslinked polyacrylates, hydrolyzed acrylonitrile grafted starches, starch polyacrylates, and isobutylene-maleic anhydride copolymers. Starch polyacrylates and crosslinked polyacrylates are particularly preferred.

Examples of suitable cationic functional groups are the quaternary ammonium groups of the primary, secondary or tertiary amines to be contained in basic form. For cellulose derivatives, the degree of substitution (DS) of a functionalized derivative is defined by the number of functional groups (generally quaternary ammonium groups) on the anhydroglucose cellulose unit. The degree of substitution is generally 0.1 to 1.5. Similarly, the degree of substitution for synthetic polymers can be defined as the number of functional groups per monomer or comonomer unit. The degree of substitution is generally 1, for example one quaternary ammonium group per polyacrylate monomer unit. Preferred base polymers include polysaccharides and dimethyldiallylammonium chloride polymers.

In one embodiment, the cationic superabsorbent may be a polysaccharide superabsorbent obtainable by reaction of a fibrous polysaccharide, for example, cellulose. with an excess of a quaternary ammonium compound comprising at least one group capable of reacting with polysaccharide functional groups and having a degree of substitution of 0.5 to 1.1. The quaternary ammonium compound may have the general formula I or II

CH 2 -CH- (CHR) η 1 I

X OH

Rl

L

R2 (I)

CH 2 -CH- (CHR) Π0

Rl

L

R 2 z (II) wherein n is an integer from 1 to 16, X is halogen, Z is an anion such as halide or hydroxyl group, and R, R, R ² and R ³ are the same or different, are hydrogen or benzylthio alkyl, hydroxyalkyl, alkenyl or aryl; and R ² additionally a group of formula III or IV

R (III) (CH _{2) p} N - (CHR) Ni3

CH

AND

OH

CH2

AND

X

Z (CH ₂ ) p R 1

- - (CHR) nCH

CH 2 from (IV) wherein p is an integer from 2 to 10 and n, R, R 1, R ² and R ³ , X and Z are as defined above. The cationic polysaccharide superabsorbents of this type are described in detail in WO92 / 19652.

In another embodiment, the cationic superabsorbent may be a cross-linked cellulose superabsorbent, particularly a fibrous cationic polysaccharide having superabsorbent properties, the polysaccharide being substituted with quaternary ammonium groups and having a degree of substitution of at least 0.5, the polysaccharide being cross-linked sufficiently to be insoluble in water . Superabsrobes of this type are described in detail in the co-pending patent application (internally designated DR44).

In yet another embodiment, the cationic superabsorbent may be a water-swellable, water-insoluble polymer containing units derived from a diallyl quaternary ammonium salt monomer cross-linked with a suitable polyfunctional vinyl compound, wherein the polymer is prepared by free-radical polymerization in aqueous phase. Superabsorbents of this type are described in detail in the co-pending patent application (internally designated DR43).

Ion exchange is a reversible exchange of ions between a solid and a liquid, without permanently changing the structure of the solid that is an ion exchange resin.

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

These substances, however, have been used for ion exchangers, where there is no ion exchange between liquid and solid. Ion exchange has been used industrially since 1910, when it was introduced to soften water using 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 either sulfone or amino groups, which can be used for reversible cation and anion exchange.

Inorganic ion exchange materials include both naturally occurring materials such as natural zeolites (e.g., clipronite), uncleaned sands and clay (e.g., from the montmorillonite group), as well as synthetic products such as gel zeolites, aqueous polyvalent oxides and insoluble polyvalent salts. acids with polyvalent metals.

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

The weakly acidic cation exchange resin is based primarily on acrylic or methacrylic acid, which is crosslinked with a difunctional monomer such as divinylbenzene (DVB). Other weakly acidic resins are prepared with phenolic or phosphonic functional groups.

The weakly acidic resin has a high affinity for hydrogen ions and is therefore easily regenerated by strong acids. However, this property limits the field of application in which cleavage may occur beyond pH 4.

Strongly acid resins of commercial importance are sulfonated copolymers of styrene and divinylbenzene, using sulfonic acid, sulfur trioxide and chlorosulfonic acid for sulfonation.

These materials are characterized by the ability to change cations or cleave neutral salts and are useful throughout the pH range.

The cation exchangers are preferably cation exchange resins containing functional groups in acid form. Suitable functional groups include carboxylic or sulfonic acid groups.

According to the invention, cation exchange resins selected from the group consisting of the following resins may be used:

Amberlite IR 120, which is a strong cation exchange resin having sulfone functional groups, available in H ⁺ form. The total exchange capacity is 4.4 meq / g dry resin.

Amberlite IRC 76, which is a weak cation exchange resin having carboxyl functional groups, which is available in acid form. The total exchange capacity is 10 meq / g dry resin.

Dowex 50W YZ, which is a strong cation exchange resin having sulfone functional groups, available in H ⁺ form. The total exchange capacity is 5 meq / g dry resin.

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

The absorbent material of the present invention is particularly suitable for purposes where it is necessary to absorb aqueous electrolyte-containing liquids. Examples of such liquids are in particular menses and urine, and the absorbent material may be used as a filling for sanitary napkins and diapers in general in admixture with a fibrous absorbent material such as cellulosic lint. For this purpose, the absorbent according to the invention may be in the form of granules or fibers.

The absorbent material of the invention has a particularly good absorbency for electrolyte-containing aqueous liquids, as exemplified below in tests carried out using brine (1% sodium chloride solution) and synthetic urine.

Means

Cationic superabsorbent based on cross-linked polydimethyldi10 allylammonium hydroxide trade name Fai 7 OH

Preparation of Fai 7 OH

Weigh 133 g of a 60% aqueous solution of dimethyldiallylaroonium chloride (DMAC of F1 at k a) into a 250 ml flask.

Separately weigh 0.2 g of bisacrylamide (BAC from Fluka) into a 5 ml tube and dissolve in 2 ml of distilled water.

Weigh 0.12 g of ammonium persulphate (free radical initiator) into a 5 ml test tube and dissolve in 2 ml of distilled water.

Air is removed from the monomer solution using a vacuum pump.

While stirring, the crosslinking solution and the free radical initiator are added to the monomer solution, the temperature is adjusted to 60 ° C by placing the flask in a thermostatic bath for four hours

The resulting solid product was cut using a spatula and transferred to a 5 liter flask containing 4 liters of distilled water, after two hours the swollen gel was filtered through a bonded fabric filter. The gel is dried in a ventilated oven at 60 ° C for 12 hours. 60 g of dried Fai 7 Cl polymer are obtained. Place 20 g of Fai 7 Cl in a 10 liter flask and swell by adding 4 liters of distilled water while stirring. When the polymer swells (after two hours), 500 ml of 0.01 M sodium hydroxide solution is added and after 30 minutes the gel is filtered using a bonded fabric filter. These operations (alkalization and filtration) are repeated until no more chloride ions are present in the wash water (chloride ions can be detected by reaction with silver nitrate).

At this point, the gel was washed with distilled water until the basic wash water reaction disappeared.

The gel was dried in a ventilated oven at 60 ° C for 12 hours. 10 g of dried Fai 7 OH polymer is obtained.

The invention is illustrated by the following examples, but parts and percentages are by weight unless otherwise indicated.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

1. Comparative tests of liquid absorption

A test is performed to demonstrate that the use of a cationic superabsorbent and cation exchange resin can improve the absorbency characteristics of the cationic superabsorbent due to the removal of the salt that is achieved by the ion exchange mixture.

A 1% solution of sodium chloride (150 ml) and 2.23 g of IR120 (H ⁺ ) cation exchange resin in a 250 ml beaker were contacted for two hours with stirring. Sodium ions in the solution should be replaced by hydrogen ions H ⁺ resin. The solution was withdrawn with a Pasteur pipette and dropped into another 250 ml beaker containing 0.11 g of Fai 7 OH with stirring. The addition is terminated as soon as the gel no longer swells. At this point, the gel is placed in a small bag of the bonded fabric tea bag and the absorbency after centrifugation of 60 xg for 10 minutes is determined as follows:

A = (Wmokra - Wsucha / G where

And absorbency after centrifugation in g / g

Wmokra weight of envelope containing wet AGM after centrifugation in g

Wsucha mass of envelope containing dry AGM after centrifugation in g G mass of AGM used in g test.

The test is repeated using both Fai 7 OH ”and Fai 7 Cl alone without using cation exchange resin. The results are given in Table I below (column II shows the quantity in g)

Table I

Fai 11 Absorption g / g (tea bag) H 2 O 1% NaCl 535 55 Absorption g / g (centrifuge) H2O 300 1% NaCl 42 7 OH 0.11 Fai 7 Cl 0.11 340 54 290 43 Fai 7 0H 0.11 96.7 - 55

+ IR 120 (H ^< + & gt ^; ) + 2.23

The results obtained show that the cationic superabsorbent in the basic form Fai 7 OH 'and in the form of the salt Fai 7 Cl show limited absorption in 1% sodium chloride solution compared to deionized water. However, when combined with an acid cation exchange resin IR120 (H ⁺ ), the material exhibits a substantial increase in absorbency.

It is also recalled that 1% sodium chloride solution is a strict text of superabsorbent. Published studies have shown that the salt content in urine varies depending on numerous factors, but 1% is the maximum we experience in practice.

Industrial applicability

A superabsorbent material consisting of a combination of a cationic superabsorbent having 20 to 100% functional groups in basic form and a cation exchanger having 20 to 100% functional groups in acid form is suitable for absorbent products, particularly for sanitary napkins and incontinent diapers.

Claims (17)

1.1. 1) of a cationic superabsorbent having from 20 to 100% of the group of groups in the basic form | Λ i What is claimed is: 1. A superabsorbent material characterized in that it is composed of a combination. F Superabsorbent material according to claim 1, characterized in that the cationic superabsorbent has 50 to 100X and particularly preferably substantially 100X of functional groups in basic form and the cation exchanger has substantially 100X of functional groups in acid form. 2) a cation exchanger whose 20 to 100% functional groups are in the ------ form. A superabsorbent material according to claim 1 or 2, wherein the functional groups of the cationic superabsorbent are primary, secondary or tertiary amine groups or quaternary ammonium groups. 4. The superabsorbent material of claim 3 wherein the functional groups of the cationic superabsorbent are quaternary ammonium groups. 5. The superabsorbent material of claim 1, wherein the functional groups are bonded to a base polymer selected from the group consisting of polyacrylamide, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinyl ether, polyvinyl sulfonic acid, polyacrylic acid, polyvinylpyrrolidone, polyvinyl pyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone. their copolymers and polymers based on starch and cellulose. 6. The superabsorbent material of claim 5 wherein the starch or cellulose-based base polymer is hydroxypropylcellulose, carboxymethylcellulose or acrylic grafted starch. 7. A superabsorbent material according to claim 5 or 6, wherein the base polymer is a cross-linked polyacrylate or a polymer of isobutylene and maleic anhydride. 8. The superabsorbent material of claim 7 wherein the base polymer is starch polyacrylate or cross-linked polyacrylate. 9. The superabsorbent material of claim 1, wherein the cationic superabsorbent is a polysaccharide superabsorbent obtainable by reacting a filamentous polysaccharide with an excess of a quaternary ammonium compound comprising at least one group capable of reacting with the polysaccharide functional groups and having a degree of substitution of 0.5. 10, A superabsorbent material according to claim 9, wherein the quaternary ammonium compound has the general formula I or II CH 2 —CH— (CHR) _n II X OH Rl L b R2 Z (I) CH2-CH- (CHR) n0 R ¹ AND N R3 R2 Z (II) wherein n is an integer from 1 to 16, X is halogen, Z is an anion such as a halide or hydroxyl group and R, R ¹ , R ² and R ³ are the same or different hydrogen, alkyl, hydroxyalkyl, alkenyl or aryl; and R ² additionally a group of formula III or IV R 1 (CH 2) p - N - (CHR) n - CH - CH 2 L ^{1 1} R ³ OH X + (III) ZR 1 (CH 2) p - N - (CHR) n - CH - CH 2 Ø ³ 0 wherein p is an integer from 2 to 10 and n, R + Z (IV) Rl, R2 and R ^3, X and Z are as defined above. 11. The superabsorbent material of claim 1, wherein the cationic superabsorbent is a filamentous cationic polysaccharide having superabsorbent properties, wherein the polysaccharide is substituted with quaternary ammonium groups and has a degree of substitution of at least 0.5 and is crosslinked sufficiently to be insoluble. in the water. 12. The superabsorbent material of claim 1, wherein the cationic superabsorbent is a water-swellable, water-insoluble polymer comprising units derived from a diallyl quaternary ammonium salt monomer crosslinked with a suitable polyfunctional vinyl compound, wherein the polymer is capable of free radical polymerization. in the aqueous phase using a free radical catalyst. 13. The superabsorbent material of claim 1, wherein the cation exchange resin is a cation exchange resin containing functional groups in acid form. 14. The superabsorbent material of claim 13, wherein the functional group is a carboxyl group or a sulfonic acid group. 15. The superabsorbent material of claim 1, wherein the weight ratio of cationic superabsorbent to cation exchange resin is from 1:20 to 1: 1. 16. The superabsorbent material of claim 15 wherein the weight ratio of cationic superabsorbent to cation exchange resin is from 1: 3 to 1: 1. Superabsorbent material according to claims 1 to 16, useful for absorbing aqueous electrolyte-containing liquids.