WO1999055767A1

WO1999055767A1 - Mechanically stable hydrogels

Info

Publication number: WO1999055767A1
Application number: PCT/EP1999/002702
Authority: WO
Inventors: Volker Frenz; Rüdiger Funk; Norbert Herfert; Fritz Engelhardt; Ulrich Riegel; Uwe Stüven
Original assignee: Basf Aktiengesellschaft
Priority date: 1998-04-28
Filing date: 1999-04-22
Publication date: 1999-11-04
Also published as: EP1084174A1; JP2002513059A

Abstract

The invention relates to ionically cross-linked hydrogels, characterized by the addition of compounds of the formula (I) Mn[H2n+2AlnO3n+1], in which M is potassium or sodium and n is a whole number between 1 and 10. The compounds are intended for cross-linking and their pH is adjusted to between 3.0 and 9.5.

Description

Mechanically stable hydrogels

description

The present invention relates to ionically crosslinked hydrogels, obtainable by adding aluminates of the formula (I)

Mn [H ₂ n ₊ 2Al _n θ3n ₊ l] ⁽ D, where

M is potassium or sodium and n is an integer from 1 to 10,

to an uncrosslinked or covalently crosslinked hydrogel, the pH after the addition of I being between 3.0 and 9.5, a process for their preparation and their use for the absorption of aqueous liquids.

These are water-insoluble, crosslinked polymers containing carboxyl groups, which are capable of swelling and forming hydrogels in aqueous liquids and body fluids, such as e.g. Take up urine or blood and retain the amount of fluid absorbed under a certain pressure.

The preparation and use of such be for hydrogel ^¬ fähigter polymers is described in numerous patents, such as EP-A-316 792, EP-A-400 283, EP-A-343 427, EP-A-205 674 and DE-A -4 418 818.

In order to produce polymers which are hydrogels with a particularly high liquid absorption capacity, high gel strength and high absorption capacity under pressure, it has proven necessary to subject the polymer particles to a subsequent surface treatment.

Substances are preferably used which contain two or more groups which can form covalent bonds with the carboxyl groups of the hydrophilic polymers (EP-A-0 349 240).

Polyglycidyl ethers, haloepoxy compounds, polyols, polyamines or polyisocyanates can be used as crosslinking agents. Furthermore, DE-A-3 314 019, EP-A-0 317 106 and DE-A-3 737 196 describe polyfunctional azidine compounds, 2

Called alkyl di (tri) halide and oil-soluble polyepoxide compounds.

According to DE-B-4 020 780, improved absorption under pressure is achieved by surface-crosslinking treatment of a polymer with 0.1 to 5% by weight alkylene carbonate.

The surface crosslinking of so-called superabsorbent polymers with polyvalent metal cations is also known. EP-A-386 897, US-A-5 684 106 and US-A-4 798 861 describe the use of aluminum salts for surface crosslinking.

The use of polyvalent metal oxides to Oberflächenver ^¬ networking is described in JP-A-01029257 and US-A-5,399,591 teaches the use of polyvalent metal cations in combination with organic carbonates.

EP-A-372 981, JP-A-03 179 008, US-A-5 314 420 and US-A-4 690 971 describe the use of polyvalent metal ions in general for surface crosslinking.

It is an object of the present invention to provide new hydrogels came near ^¬ extending African particular by an improved mechanical stability of the swollen gel particles ^¬ Pricing Further, the hydrogels improved properties in terms of gel strength and water retention should have.

The invention thus relates to ionically crosslinked hydrogels, obtainable by adding aluminates of the formula (I)

M _n [H _{2n + 2} Al _n 0 _{3n +} l] ⁽ Dz where

M is potassium or sodium and n is an integer from 1 to 10,

to an uncrosslinked or covalently crosslinked hydrogel, the pH being adjusted to between 3.0 and 9.5 by the addition of I.

According to the invention, the ionic crosslinking by means of aluminate ions takes place homogeneously in the gel form of the polymeric hydrogels before drying to form powders or granules. 3

These hydrogel structures are produced by adding aluminumates I, preferably [Al (OH) ₄ ] ^" , to polymers containing carboxyl groups and / or alkali metal or ammonium carboxylate groups, aqueous gels, so-called hydrogels, which can be uncrosslinked or pre-crosslinked by covalent bonds. AI (OH) ₃ dissolves as an amphoteric hydroxide both in acid

AI (OH) 3 + 3H ⁺ → Al ³⁺ + 3H ₂ 0 (a)

with formation of aluminum salts (a), as well as in bases

AKOH ₃ ) + OH → AI (OH) ₄ - (b)

with formation of aluminate (b)

AI (OH) ₃ + NaOH? NaA10 ₂ + 2 H ₂ 0 (c)

As such, the Alumination [AI (OH) ₄ ] ^" is not stable and condenses easily to higher molecular weight oxo compounds under water. Instead of condensation, the Alumination [AKOH ₄ )] - like the isolation of sodium salts of the composition 3 Na ₂ 0 -Al ₂ θ ₃ -6H ₂ 0 shows can also be stabilized by taking up 2 OH ions

Na [Al (OH) ₄ ] + 2 NaOH 5 Na ₃ [Al (OH) ₆ ].

As the first stage in the condensation of the alumination under water leakage, the Di -Alumination is created

[AI (OH) ₃ -0-Al (OH) ₃ ] ² -

which e.g. in the form of the potassium salt

K ₂ [H ₆ A1 ₂ 0 ₇ ] = K ₂ 0 ^• A1 ₂ 0 ₃ ^• 3 H ₂ 0

can be isolated.

Further condensation leads to polyaluminations of the general formula

[H _{2n + 2} Al _n 0 ₃ n ₊ li ⁿ -

n = 3 trial illuminations n = 4 tetra illuminations 4 which in the form of their salts

Na ₃ [H ₈ Al ₃ Oι ₀ ] and Na [H10AI ₄ O13]

are known.

Preference is given to using covalently crosslinked hydrogels which are obtained by polymerizing 90-99.99 mol% of a monounsaturated monomer containing carboxyl groups and / or alkali metal or ammonium carboxylate groups and 0.01-10 mol% of a crosslinking agent.

Suitable crosslinkers are in particular methylenebisacryl or methacrylamide, esters of unsaturated mono- or polycarboxylic acids of polyols, such as diacrylate or triacrylate, e.g. Butanediol or ethylene glycol diacrylate or methacrylate as well as triethylolpropane triacrylate and allyl compounds such as allyl (meth) acrylate, tri-allylcyanurate, maleic acid diallyl ester, polyallyl ester, tetraallyloxyethane, triallylamine, tetraallyl ethylene diphosphate such as phosphate and allyl ester diamine, for example allyl esters, A-0 343 427. However, hydrogels which are prepared using polyallyl ethers as crosslinking agents and by acidic homopolymerization of acrylic acid are particularly preferred. Suitable crosslinkers are pentaerythritol tri- and tetraallyl ether, polyethylene glycol diallyl ether, monoethylene glycol diallyl ether, glycerol di- and tri-allyl ether, polyallyl ether based on sorbitol, and alkoxylated variants thereof.

Monounsaturated monomers are, for example, vinyl acetic acid and preferably acrylic acid and methacrylic acid and their alkali metal or ammonium salts, e.g. Sodium, potassium and ammonium acrylates. Preference is given to ionically crosslinked hydrogel structures which are composed of 50 to 99.99% by weight of structural units which are derived from acrylic acid.

Such hydrogels are generally known and are produced by conventional processes.

The ionically crosslinked hydrogel structures according to the invention are preferably obtained by free-radically polymerizing aqueous acrylic acid solutions with the addition of polyolefinically unsaturated compounds, for example the above-mentioned crosslinking agents. The polymerization process gives water-containing hydrogels, which are then added to pH values between 3.0 and 9.5, preferably between 4.0 and 7.5, by adding illuminations as described above in connection with bases such as sodium or potassium hydroxide. 5 places. The bases can be added either before the addition of the aluminate or together with the aluminate. In the former case, neutralized or partially neutralized gels are crosslinked. It is also possible to polymerize partially neutralized aqueous acrylic acid solutions, preferably in the presence of a crosslinking agent, and then to crosslink them with aluminates, if appropriate with the addition of a base.

The amount of aluminates used is 0.05 to 80 mol%, preferably 0.05 to 30 mol% of aluminum, based on the sum of carboxyl groups and alkali metal or ammonium carboxylate groups, preferably based on the acid units to be neutralized in the hydrogel.

Mixtures of sodium or potassium hydroxide solution with mono-, di-, tri- or tetra-aluminates, or else higher polyaluminates of the general formula (I), have proven to be particularly suitable for the preparation of the novel polymeric hydrogels.

M _n [H _{2n + 2} Al _n 0 _{3n +} l] ⁽ I ⁾ , where M, Na or K and n is a number from 5 to 10, and mixtures thereof.

The polymerization can be triggered by radical formers, such as organic or inorganic peroxides and azo compounds. Examples are benzoyl peroxide, tert. -Butyl hydroperoxide, cumene hydroperoxide, (H) ₂ S ₂ 08, K ₂ S ₂ 0β, H ₂ S ₂ 0 ₈ , H ₂ 0 ₂ or azodiisobutyronitrile. Redox systems are also outstandingly suitable as polymerization initiators. Finally, the polymerization can also be triggered by high-energy radiation.

If compounds of the general formula I are first added to an uncrosslinked pre (co) polymer, this is usually done before drying by homogeneous mixing, for example by kneading an aqueous polymer gel in a kneader. However, preference is given to using covalently pre-crosslinked hydrogel structures, which are then used with compounds of the formula I, preferably in mixtures with bases, such as sodium or potassium hydroxide, for neutralization to the desired pH values.

After the ionically crosslinked hydrogel has been produced, which can be carried out in suitable apparatuses such as kneaders, extruders or after comminution in conventional mixing units, such as ploughshare or screw mixers, the gel particles are subjected to a drying process to remove the water. 6, then grind and set a desired particle size distribution by sieving.

The polymer particles produced in this way are able to absorb many times their own weight in aqueous liquids. Hydrogel particles are formed, which are characterized by special physical properties.

If hydrogel particles, which have been produced in a similar way by polymerizing unsaturated water-soluble acids with the addition of polyolefinically unsaturated compounds, are subjected to repeated mechanical stress, such as exposure to strong shear forces, irreversible degradation of the hydrogel network structure takes place through the destruction of covalent bonds under mechanical stress. This has the result that the mechanical stability of the gel particles that is, the so-called gel ^¬ strength drastically decreases.

The hydrogel structures according to the invention, which in addition to covalent crosslinking elements are crosslinked according to an ionic mechanism, do not show this disadvantage since the ionic crosslinking elements are capable of recombination.

The hydrogels according to the invention are outstandingly suitable as absorbents for aqueous liquids, for the formulation of cosmetic preparations, as consolidators and / or binders of fibrous sheet-like structures containing reactive groups, and as drilling fluids and cement sludge in the production of petroleum.

Hydrogels according to the invention based on acrylic acid are particularly suitable for use as so-called "super absorbing polymers" (SAP) for the use of hygiene articles, for example diapers, tampons or sanitary napkins. These preferably contain 50 to 99.99, in particular up to 98% by weight of structural units which are derived from acrylic acid. Particularly preferred are hydrogels, which are copolymers of acrylic acid and di- or polyunsaturated compounds, which have been prepared in aqueous solution.

Hydrogels according to the invention based on carboxymethyl polysaccharides are also outstandingly suitable for use as SAP.

Since the compounds of the general formula I are soluble in aqueous alkaline systems, water-swellable hydrogels according to the invention can be achieved with a network which is more homogeneous than compounds of the prior art. As a result, the 7

In addition to high absorption capacity, hydrogels also have high gel strength.

By post-crosslinking with compounds of the general formula I of already covalently pre-crosslinked polymers which are intended for use as SAP, their performance with regard to absorption under pressure, and in particular the mechanical stability of the gel structures after mechanical stress, can be increased due to the recombination ability of the ionic crosslinking elements be significantly improved.

The improved mechanical property profile of the hydrogel structures according to the invention compared to conventional covalently crosslinked products can be shown by measuring the gel recovery index.

Measurement of the gel recovery index:

The gel recovery index is measured using a Creep Meter, model RE-3305 from Yamaden Co., Ltd. This device is a penetrometer, which can be used to carry out investigations of changes in structure and consistency over time or due to changing load factors. The centerpiece of the device is a measuring slide that can be moved in the vertical direction with a force transducer and a stamp as a test specimen. The force transducer measures the compressive or tensile forces that act on the test specimen when the slide is moved from the sample. To carry out various measurements, either the maximum penetration depth of the test specimen (when measuring the force) or the maximum force absorption (when measuring the penetration depth) can be specified. To carry out the measurement of the gel recovery index, 0.2 g of SAP with a sieved grain fraction of 400-500 μm are placed in 7 g of 0.9% strength by weight saline solution and the gel is kept at room temperature for 3 hours in order to obtain a to achieve homogeneous swelling. 0.2 g of this gel are distributed evenly on the sample plate and without mechanical stress using a spatula. The stamp is now lowered so far that it just touches the surface of the swollen SAP particles. From this starting position, the stamp is then moved into and out of the gel in 20 cycles at a speed of 0.5 mm / s. The force absorption decreases from cycle to cycle, since this mechanical load destroys part of the gel structure and thus the elastic modulus of the gel decreases. The depth of penetration of the star apex is selected so that the force absorption in the 20th cycle (50 "3%) is the force absorption in the 1st cycle, and must therefore be individually determined for each product through preliminary tests. 8 be averaged. After the first 20 cycles, the gel is left on the sample plate for 20 minutes at room temperature. During this time, the gel has the opportunity to recover and repair the network defects caused by the mechanical stress. After this time the test program is repeated (2nd cycle series), the depth of penetration of the stamp remains unchanged. Tables 1 and 2 show the force absorption data for gels that do not have a repair effect or a complete repair effect to clarify the test method. The 0 gel recovery index is calculated as follows:

Gel recovery index = 1 [2 / A]

A = Force absorption during the 1st cycle of the 1st cycle 5 C = Force absorption during the 1st cycle of the 2nd cycle

The force absorption is given in the following tables in relative units.

0 Table 1:

Measurement of the gel recovery index for a sample with repair effect (example according to the invention)

Cycle Force absorption Force absorption 1st cycle series 2nd cycle series b 1 100 100

2 94.5 94.5

3 90 90

4 86 86 0 5 82 82

6 78.5 78.5

7 76 76

8 73 73

9 70.6 70.6 5 10 68 68

11 65.2 65.2

12 63 63

13 60.6 60.6

14 58.5 58.5 0

15 56.5 56.5

16 54.8 54.8

17 53.3 53.3

18 52 52

5 Cycle Force absorption Force absorption 1st cycle row 2nd cycle row

19 50.7 50.7

20 50 50

Gel recovery index = l- [2- (100-100) / 100] = 1

Table 2:

Measurement of the gel recovery index for a sample without repair effect (state of the art)

Cycle Force take-up Force take-up 1st cycle row 2nd cycle row

1 100 49

2 94.5 48.03

3 90 47, 09

4 86 46.18

5 82 45.3

6 78.5 44.45

7 76 43.63

8 73 42.84

9 70.6 42.08

10 68 41.35

11 65.2 40.65

12 63 39.98

13 60.6 39.34

14 58.5 38.73

15 56.5 38.15

16 54.8 37.6

17 53.3 37.08

18 52 36.59

19 50.7 36.13

20 50 35.7

Gel recovery index = l- [2- (100-49) / 100] = - 0.02

Gels with a complete repair effect show a gel recovery index of 1.0, gels without a repair effect show a gel recovery index of <0.

example 1

3677.4 g of demineralized water are placed in a polyethylene vessel with a capacity of 10 l, well insulated by foamed plastic material, and slowly 1300 g of acrylic 10 acid added. Now 10 g of pentaerythritol triallyl ether is added as a covalent crosslinker. At a temperature of 4 ° C the initiators, a redox system consisting of 2.2 g 2, 2 '-azobisamidinopropane dihydrochloride, dissolved in 20 g demineralized water, 4 g potassium peroxodisulfate, dissolved in 150 g demineralized water and 0 , 4 g of ascorbic acid, dissolved in 20 g of demineralized water, added in succession and stirred. The reaction solution is then left to stand without stirring, a solid gel being formed by the onset of polymerization, in the course of which the temperature rises to approximately 89.degree. This is then mechanically comminuted and simultaneously adjusted to a pH of 5.8 with an aqueous solution of 30% NaOH, which contains 10% by weight Na aluminate (Riedel-de Haen), and dried at 120 ° C. and ground. The product described here has a GR index of 0.5.

Comparative example

The procedure is analogous to Example 1, except that only a 30% aqueous solution of NaOH is used to adjust the acidic gel to a pH of 5.8.

Example 2

The procedure is analogous to example 1, but now becomes

Adjusting the acidic gel used at a pH of 6.1 30% aqueous KOH containing 15 wt .-% dissolved sodium aluminate ent ^¬ holds. The resulting product has a GR index of 0.7, is ideal for use in baby diapers and is characterized by good fluid retention.

Example 3

Under adiabatic conditions, 1287 g of demineralized water cooled to 15 ° C. are placed in a 1.5 1 cylindrical wide-neck reaction flask and 225 g of acrylic acid and 128 g of tetraallyloxyethane are dissolved therein. Nitrogen is introduced into the monomer solution (approx. 2 l / min. For approx. 20 min.) In order to reduce the oxygen content. At a content of 1.5 ppm 0 ₂ , 7.7 g of a 10% strength aqueous solution of 2,2'-azobis (2-amidinopropane) dihydrochloride are added, after further N ₂ introduction and a 0 ₂ - Content of 1.3 ppm, 2.6 g of a 1% H ₂ 0 ₂ solution are added, and finally at a 0 content of 1.0 ppm, 6.4 g of a 0.1% ascorbic acid solution are added. The onset of polymerization, in the course of which the temperature rises to approx. 65 ° C, results in a solid gel which is then mechanically comminuted. 400 g of the crushed 11

A product is obtained, essentially characterized by the following physical data, all measured in NaCl 0.9%: extractables (16 h value) 1.1%, absorption under pressure (20 g / cm ² ) = 23.8 g / g, GR index = 0.3.

Table 3

Extractable absorption with gel recovery

Proportions of pressure (20 g / cm ² ) index

16 h value (%) ⁽ g / g ⁾

Comparative 10.2 9.4 0 example

Example 1 7.5 25.2 0.5

Example 2 7.1 32.9 0.7

Example 3 7.7 23.8 0.3

All values are measured in 0.9% NaCl

Claims

12 Patent claims

1. Ionically crosslinked hydrogels, obtainable by adding aluminates of the formula (I)

M _n [H _{2n + 2} Al _n 0 _{3n + 1} ] (I),

wherein

M potassium or sodium and

n is an integer from 1 to 10,

to an uncrosslinked or covalently crosslinked hydrogel, the pH after addition of I being between 3.0 and 9.5.

2. Ionically crosslinked hydrogels according to claim 1, characterized in that the hydrogel used carries carboxyl groups and / or alkali or ammonium carboxylate groups.

3. Ionically crosslinked hydrogels according to claim 1 or 2, characterized in that they are made up of 50 to 99.99% by weight of structural units which are derived from acrylic acid.

4. Ionically crosslinked hydrogels according to one of claims 1 to 3, characterized in that the hydrogel used was produced by a radical copolymerization.

5. Ionically crosslinked hydrogels according to one or more of claims 1 to 4, characterized in that they are prepared by adding compounds of the formula (I), in which n is an integer from 2 to 4.

6. Ionically crosslinked hydrogels according to one or more of claims 1 to 5, characterized in that the pH is adjusted to 4.0 to 7.5 when compounds of the formula (I) are added.

7. Ionically crosslinked hydrogels according to one or more of claims 1 to 6, characterized in that the amount of aluminates is 0.05 to 80 mol-AI based on acid units to be neutralized in the hydrogel. 13

8. Ionically crosslinked hydrogels according to one or more of claims 1 to 7, characterized in that a covalently crosslinked hydrogel is used.

9. The ionically crosslinked hydrogels according to one or more of the at ^¬ claims 1 to 8, characterized in that the hydrogel used were represents by copolymerization of acrylic acid with di- or poly-unsaturated compounds in aqueous solution Herge ^¬.

10. A process for the preparation of ionically crosslinked hydrogels according to claims 1 to 9 by reacting an uncrosslinked or covalently crosslinked hydrogel with aluminates I in such a way that a pH of 3.0 to 9.5 is established.