CN1171797A - Absorbent 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

absorbent material

This invention relates to absorbent materials, and more particularly to materials of the class commonly referred to as "superabsorbents".

Materials commonly referred to as "superabsorbents" are generally lightly crosslinked hydrophilic polymers. The chemistry of these polymers can vary, but they all have the ability to absorb and retain many times their own weight in aqueous fluid, even under moderate pressure. For example, superabsorbents typically can absorb up to 100 times their own weight or more in distilled water.

Superabsorbents have been proposed for many different industrial applications where the advantages of their water absorption and/or retention properties can be exploited, examples include agriculture, construction, production of alkaline batteries and filters. A primary field of application for superabsorbent materials is however the production of hygiene and/or hygiene products, such as disposable sanitary napkins and disposable diapers for incontinent children or adults. In these health and/or hygiene products, superabsorbents are often used in combination with cellulose fibers to absorb bodily fluids (such as menses or urine). However, the absorption capacity of superabsorbents for body fluids is significantly lower than for deionized water. It is generally believed that this effect comes from the electrolyte content of the body fluids, and this effect is called "salt poisoning".

The water absorption and water retention properties of superabsorbents are due to the presence of ionizable functional groups in the polymer structure. These groups are usually carboxylate groups, and high levels of carboxylate groups are in the form of salts when the polymer is in the dry state, but when in contact with water, dissociation and solvation occur. In its dissociated state, the polymer chain has a series of functional groups attached to the chain which have the same charge and therefore repel each other. This results in swelling of the polymer structure, which allows further uptake of water molecules, although this swelling is limited by crosslinking in the polymer structure, where sufficient crosslinking is necessary to prevent dissolution of the polymer. It is believed that the presence of large concentrations of electrolytes in water interferes with the dissociation of these functional groups and produces a "salt poisoning" effect. Although most commercially available superabsorbents are anionic, it is equally possible to prepare cationic superabsorbents having functional groups such as quaternary ammonium groups. Such materials must also be in salt form to function as superabsorbents, and their performance is also affected by salt poisoning.

Many attempts have been made to inhibit the effects of salt poisoning and to improve the absorption properties of superabsorbents for electrolyte-containing fluids such as menses and urine. Japanese patent application OPI No. 57-45,057 therefore discloses an absorbent which is a mixture of a superabsorbent such as crosslinked polyacrylate and a powdered or granular ion exchange resin. EP-A-0210756 relates to an absorbent structure comprising a superabsorbent and an anion exchanger, optionally also a cation exchanger, wherein both ion exchangers are in the form of fibers. Combining superabsorbents with ion exchangers has attempted to reduce the salt poisoning effect by using ion exchangers, usually a combination of anion exchangers and cation exchangers, to reduce the salt content of the liquid. The ion exchanger has no direct influence on the properties of the superabsorbent, nor is it possible to reduce the salt content sufficiently to have the desired influence on the overall absorption properties of the composition. In addition, besides being expensive, the ion absorbents are not absorbent by themselves and thus act as diluents to the superabsorbent.

It is an object of the present invention to provide a superabsorbent with improved performance in the presence of electrolytes, as in the case of menses or urine.

The present invention provides a superabsorbent material comprising a combination of the following materials:

(1) a cationic superabsorbent in which 20-100% of the functional groups are in the form of bases; and

(2) A cation exchanger in which 50-100% of the functional groups are in the form of acids.

The cationic superabsorbent material preferably has 50-100%, more preferably substantially 100%, of the functional groups in the base form.

The cation exchanger preferably has essentially 100% of the functional groups in the acid form.

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

While not wishing to be bound by any particular theory, it is believed that the superabsorbent materials of the present invention have the following two-fold effect when contacted with a solution containing an electrolyte:

(1) converting the cationic superabsorbent from a nonabsorbent form to a salt form for use as a superabsorbent; and

(2) The conversion of the cationic superabsorbent to its salt form has a deionizing effect on the solution enhanced by the cation exchanger.

The functional groups in cationic superabsorbents are usually quaternary ammonium groups of strong ion exchangers. Therefore, when the cationic superabsorbent comes into contact with an electrolyte solution such as common salt solution, it swells and the OH ions in the superabsorbent are partially replaced by Cl in the solution, and the pH of the solution becomes strongly alkaline. But the presence of cation exchange resin prevents the solution from becoming strongly basic by shifting the equilibrium reaction in favor of complete conversion of the cationic superabsorbent to its salt form. In this case, the sodium ions in solution are replaced by cation exchange resins and the chloride ions in solution are replaced by cationic superabsorbents in the form of bases, thus causing sufficient desalination of the common salt solution, thereby increasing the superabsorbent The absorbency of the agent.

This conversion of the cationic superabsorbent to its salt form when in contact with an electrolyte-containing solution, and the action of the cation exchanger to bind sodium ions, has a significant desalting effect on the solution, thereby increasing the performance of the superabsorbent. Contrary to the use of ion exchange resins to desalt the solution and bind superabsorbent material already in salt form (see Japanese Patent Applications OPI No. 57-45057 and EP-A-0210756 cited above), the cations in the base form The superabsorbent also has a desalination effect on the solution. This results in a much greater desalination effect than using ion exchangers and superabsorbents in salt form. It should be noted that the effect of the electrolyte in solution on the absorption capacity of the superabsorbent in the solution is not linear, since the absorption capacity does not decrease regularly with increasing salt content. Thus, over a certain concentration range, by producing a relatively small decrease in the salt content of the solution, a relatively large increase in absorbency can result.

The cationic superabsorbent can be any material having superabsorbent properties in which the functional groups are cationic. Typically these functional groups are attached to a lightly crosslinked acrylic base polymer. For example, the base polymer may be polyacrylamide, polyvinyl alcohol, ethylene-maleic anhydride copolymer, polyvinyl ether, polyvinylsulfonic acid, polyacrylic acid, polyvinylpyrrolidone, and polyvinylmorpholine. Copolymers of these monomers may also be used. Starch and cellulose based polymers can also be used, including hydroxypropyl cellulose, carboxymethyl cellulose and acrylic acid grafted starch. Specific base polymers include crosslinked polyacrylates, hydrolyzed acrylonitrile grafted starches, starch polyacrylates, and isobutylene/maleic anhydride copolymers. Particularly preferred base polymers are starch polyacrylates and crosslinked polyacrylates.

Examples of suitable cationic functional groups include quaternary ammonium groups or primary, secondary or tertiary amine groups, these groups should be in the form of bases. For cellulose derivatives, the degree of substitution (DS) of derivatives with functional groups is defined as the number of functional groups (usually quaternary ammonium groups) per cellulose anhydroglucose unit. Its DS is usually 0.1-1.5. In a similar manner, the DS of a synthetic polymer can be defined as the number of functional groups per monomer or comonomer unit. Its DS is usually 1, such as one quaternary ammonium group per polyacrylate monomer unit. Preferred base polymers include polysaccharides and dimethyldiallylammonium chloride based polymers.

其中n为1-16的整数；X是卤素；Z是如卤化物或羟基的阴离子；且R、R¹、R²和R³，可相同或不同，每一个是氢、烷基、羟烷基、链烯基或芳基，并且R²可另外代表下式残基：或

其中p是2-10的整数，n、R、R¹、R³、X和Z定义如上。在WO 92/19652中更详细介绍了这种阳离子多糖超吸收剂。According to one embodiment, the cationic superabsorbent may be a polysaccharide superabsorbent prepared by reacting a cellulosic polysaccharide such as cellulose with an excess of a quaternary ammonium compound containing at least one group and have a degree of substitution of 0.5-1.1. The quaternary ammonium compound has the general formula: or

wherein n is an integer from 1 to 16; X is halogen; Z is an anion such as halide or hydroxyl; and R, R ¹ , R ² and R ³ , which may be the same or different, are each hydrogen, alkyl, hydroxyalkane radical, alkenyl or aryl, and ^R may additionally represent a residue of the formula: or

wherein p is an integer of 2-10, and n, R, R ¹ , R ³ , X and Z are as defined above. Such cationic polysaccharide superabsorbents are described in more detail in WO 92/19652.

According to another experimental variant, the cationic superabsorbent may be a superabsorbent based on crosslinked cellulose, in particular a superabsorbent fiber cationic polysaccharide substituted by quaternary ammonium radicals and having a degree of substitution of at least 0.5, the The polysaccharide is cross-linked to a sufficient degree that it is insoluble in water. Such superabsorbents are described in more detail in our co-pending patent application .... (internal reference DR44).

According to yet another embodiment, the cationic superabsorbent may be a water-swellable, water-insoluble polymer containing a polymer derived from a diallyl quaternary ammonium monomer crosslinked by a suitable multifunctional vinyl compound. A unit characterized in that the polymer has been prepared by free-radical polymerization in aqueous phase using a free-radical catalyst. Such superabsorbents are described in more detail in our co-pending patent application . . . (internal reference DR43).

Ion exchange is the reversible exchange of ions between a solid and a liquid in which there is no significant change in the solid structure of the ion exchange material.

Ion exchange occurs on a variety of substances such as silicates, phosphates, fluorides, humus, cellulose, silk, proteins, alumina, resins, lignin, cells, glass, barium sulfate, and chlorine Silver.

However, the use of these materials as ion exchange materials depends on properties other than ion exchange between liquid and solid phases. Ion exchange has been used in industry since 1910 with the introduction of water softening using natural and later synthetic zeolites.

The introduction of synthetic organic ion exchange resins in 1935 arose from the synthesis of phenol condensation products containing sulfonate or amino groups that could be used for the reversible exchange of cations or anions.

Inorganic ion exchange materials include natural materials (such as mineral zeolites (such as cliptonite), green sands, and clays (such as montmorillonite)) and synthetic products (such as gelatinous zeolites, hydrous oxides of polyvalent metals, and polyvalent metal salts with polyvalent metals). insoluble salt of barium acid).

Synthetic organic products include cationic and anionic ion exchange resins, both available in strong and weak forms.

The weak acid cation exchange resins are primarily based on acrylic or methacrylic acid cross-linked with bifunctional monomers such as DVBC (divinylbenzene). Other weak acid resins have been prepared with phosphonic acid functional phenolic groups.

The weak acid resin has a strong affinity for hydrogen ions, so it is easy to regenerate with strong acid. However, this property limits the range in which salts can decompose above pH 4.

Strong acid resins of commercial interest are sulfonated copolymers of styrene and DVB which have been sulfonated with sulfonic acid, sulfur trioxide and chlorosulfonic acid, respectively.

These materials are characterized by their ability to exchange cations or decompose neutral salts and are available over the entire pH range.

The cation exchanger is preferably a cationic resin containing functional groups in the form of an acid. Suitable functional groups include carboxylate or sulfonate.

The following cation exchange resins can be used in the practice of this invention: Amberlite IR 120: This is a strong cation exchanger with sulfonic acid functionality which can be in the H ⁺ form. Its total exchange capacity for dry resin is 4.4 milliequivalents per gram (meq/g). Amberlite IRC 76: This is a weak cation exchanger with carboxylic acid functionality which can be in acid form. Its total exchange capacity for dry resin is 10 meq/g. Dowex 50W YZ: This is a strong cation exchanger which is available in the H ⁺ form and contains sulfonic acid functionality. Its total exchange capacity for dry resin is 5 meq/g.

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

The absorbent material of the present invention is particularly suitable for use in applications where it is desired to absorb aqueous liquids containing electrolytes. Examples of such liquids include menses and urine in particular, and the absorbent material can be used as a padding material for catamenial pads and diapers in admixture with fibrous absorbents such as cellulose fluff. For this purpose, the absorbents according to the invention can be present in granular or fibrous form.

The absorbent material of the present invention particularly exhibits good absorption of aqueous liquids containing electrolytes, as shown in the following examples, which were tested with saline solution (1% NaCl) and synthetic urine. Preparation: Cationic superabsorbent based on cross-linked polydimethyldiallylammonium chloride, called Fai7OH. Preparation of Fai7OH

133 g of a 60% aqueous solution of dimethyldiallylammonium chloride (DMAC, ex fluka) were weighed into a 250 ml flask.

Separately, 0.2 g of bisacrylamide (BAC, purchased from fluka) was weighed into a 5 ml test tube and dissolved in 2 ml of distilled water.

Dissolve 0.12 g of ammonium persulfate (free radical initiator) in 2 ml of distilled water in a 5 ml test tube.

The monomer solution was evacuated with a vacuum pump.

Afterwards, under continuous stirring, the crosslinker solution and 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 constant temperature bath.

The resulting solid product was cut with a spatula and transferred to a 5 liter beaker with 4 liters of distilled water, and after two hours the swollen gel was filtered through a non-woven tissue filter cloth. The gel was dried in a ventilated oven at 60°C for 12 hours. 60 g of dried polymer was collected and called Fai7Cl. Put 20 g of Fai 7 Cl in a 10-liter beaker and add 4 liters of distilled water to swell with continuous stirring. When the polymer had swelled (2 hours), 500 ml of 0.01 M NaOH solution was added and after 30 minutes the gel was filtered through a non-woven tissue filter cloth. These operations (basification and filtration) were repeated until there were no chloride ions in the wash water (chloride ions could be checked by the _AgNO3 reaction). At this point the gel was washed with distilled water until there was no evidence of alkali reaction in the wash water.

The gel was then dried in a vented oven at 60° C. for 12 hours. 10 g of dried polymer was collected and called Fai7OH.

Example 1. Comparative test of liquid absorbency

Experiments were carried out to show that the use of a cationic superabsorbent and a cation exchange resin improves the absorption performance of the cationic superabsorbent due to the desalination obtained by the ion exchange mixture.

A 1% NaCl solution (150 ml) was contacted with 2.23 g of cation exchange resin IR120 (H ⁺ ) in a 250 ml beaker for 2 hours with continuous stirring. The sodium ions of the solution should be replaced by hydrogen ions in the resin. The solution was then aspirated with a Pasteur pipette and transferred, while stirring, into another 250 ml beaker containing 0.11 g Fai 7OH; the addition of the solution was stopped when the gel no longer swelled. At this time, put the gel in a small envelope of non-woven tissue paper "tea bag" type, centrifuge at 60 × g for 10 minutes, and calculate its absorbency according to the following formula:

A = (W _wet - W _dry ) / G where: A = absorbency after centrifugation, g/gW _wet = weight of envelope containing wet AGM after centrifugation, gW _dry = weight of envelope containing dry AGM, gG = the Weight of AGM used in the test, gAGM = absorbent gelling material

The test was also repeated using Fai9OH and Fai9Cl alone without the cation exchange resin.

The above results show that the cationic superabsorbents Fai-7 OH in base form and in salt form (Fai-7Cl ⁺ ) exhibit limited absorption in 1% NaCl solution compared to deionized water. But when combined with a cation exchanger in the acid form IR120 (H ⁺ ), this material exhibits a significantly increased absorption.

It should be understood that 1% NaCl represents an exact test for this superabsorbent. Literature studies have shown that the salt content of urine varies with a number of factors, but 1% by weight represents the maximum value likely to be encountered in practice.

Claims (17)

1. superabsorbent material, it comprises the combination of following material:

I) a kind of positively charged ion super-absorbent, wherein the functional group of 20-100% is the form of alkali; With

Ii) a kind of cationite, wherein the functional group of 50-100% is the form of acid.

2. the described superabsorbent material of claim 1, wherein this positively charged ion super-absorbent has 50-100%, preferably is essentially the functional group of 100% the form that is alkali, and wherein this cationite has basically 100% functional group that is the form of acid.

3. claim 1 or 2 described superabsorbent materials, wherein the functional group in this positively charged ion super-absorbent be primary, the second month in a season or tertiary amine groups or quaternary ammonium root.

4. the described superabsorbent material of claim 3, wherein this functional group is the quaternary ammonium root.

5. each described superabsorbent material among the claim 1-4, wherein this functional group is connected on polymeric amide, polyvinyl alcohol, ethene-copolymer-maleic anhydride, polyvinyl ether, polyvinyl sulfonic acid, polyacrylic acid, polyvinylpyrrolidone or the polyethylene morpholine as base polymer or on its co-polymer, and on the polymkeric substance of starch or cellulose base.

6. the described superabsorbent material of claim 5, wherein the polymkeric substance of this starch or cellulose base is hydroxypropylcellulose, carboxymethyl cellulose or acrylic acid-grafted starch.

7. claim 5 or 6 described super-absorbent, wherein this base polymer is crosslinked polyacrylic ester or iso-butylene/copolymer-maleic anhydride.

8. the described superabsorbent material of claim 7, wherein this base polymer is starch polyacrylic ester or crosslinked polyacrylic ester.

9. each described super-absorbent among the claim 1-8, wherein this positively charged ion super-absorbent is the polysaccharide super-absorbent that is prepared as follows: with fiber polysaccharide and the reaction of excessive quaternary ammonium compound, this compound contains at least one can and have the substitution value of 0.5-1.1 with the group of polysaccharide hydroxyl reaction.

10. the superabsorbent material described in the claim 9, wherein this quaternary ammonium compound has general formula: Or Wherein n is the integer of 1-16; X is a halogen; Z is the negatively charged ion as halide ions or hydroxyl; And R, R ¹, R ²And R ³, can be identical or different, each is hydrogen, alkyl, hydroxyalkyl, alkenyl or aryl, and R ²Can represent the following formula residue in addition:

Or

Wherein p is the integer of 2-10, n, R, R ¹, R ³, X and Z definition as above.

11. each described superabsorbent material among the claim 1-10, wherein this positively charged ion super-absorbent is the fiber cation polysaccharide with superabsorbent energy, this glycocalix quaternary ammonium root replaces and has and is at least 0.5 substitution value, and the crosslinked enough degree of this polysaccharide make it keep insoluble in water.

12. each described superabsorbent material among the claim 1-10, wherein this positively charged ion super-absorbent is water swellable, water-insoluble polymkeric substance, this polymkeric substance contains from diallyl quaternary ammonium salt monomer deutero-, by the crosslinked unit of suitable polyfunctional vinyl compound, it is characterized in that this polymkeric substance prepares by cationoid polymerisation at aqueous phase with free radical catalyst.

13. each described superabsorbent material among the claim 1-12, wherein this cationite is the resin cation (R.C.) that contains the functional group of the form that is acid.

14. the superabsorbent material described in the claim 13, wherein this functional group is carboxylic acid or sulfonic group.

15. each described superabsorbent material among the claim 1-14, wherein the weight ratio of positively charged ion super-absorbent and cationite is 1: 20-1: 1.

16. the superabsorbent material described in the claim 15, wherein the weight ratio of positively charged ion super-absorbent and cationite is 1: 3-1: 1.

17. each described superabsorbent material absorbs and contains electrolytical liquid, aqueous purposes among the claim 1-16.