JP5202903B2 - Method for producing organic-inorganic composite hydrogel having carboxylic acid group or sulfonic acid group - Google Patents

Description

  The present invention relates to a polymer gel used in the fields of medicine, architecture, civil engineering, machinery, transportation, electronic components, sewing, household goods, sanitary goods, agriculture, foods, and the like.

  Superabsorbent resins are widely used in many fields such as medical, food, horticulture, and architecture, as well as sanitary materials such as disposable diapers and sanitary products. Among such superabsorbent resins, the crosslinked sodium polyacrylate resin (PAc) has a property of absorbing water several hundred to 1000 times its own weight. However, it is a slightly cross-linked sodium polyacrylate, which has the disadvantage that its mechanical properties after water absorption are weak and its shape is difficult to maintain. On the other hand, it has been reported that an organic-inorganic composite hydrogel having a tensile breaking strength of several hundred kPa can be obtained by polymerizing a (meth) acrylamide derivative in the presence of clay mineral uniformly dispersed in water (patented) Reference 1). This organic-inorganic composite hydrogel not only absorbs water and swells greatly, but also has the property of retaining its shape after water absorption. However, the water absorption is lower than that of commercially available high water absorption resins, and there is room for improvement.

  Patent Document 2 discloses a technique related to an organic-inorganic composite hydrogel produced from a polymer of acrylamide monomers, and the polymer can be copolymerized with a monomer having a sulfone group or a carboxyl group as another monomer. Have been described. However, this document does not disclose details of a method for stably producing an organic-inorganic composite hydrogel using such a monomer.

JP 2002-053629 A JP 2006-169314 A

  An object of the present invention is to provide a method for producing a novel organic-inorganic composite hydrogel having not only high mechanical properties but also high water swellability.

  The present inventors have intensively studied to solve the above problems. As a result, a (meth) acrylamide derivative and a (meth) acrylamide derivative in a homogeneous mixed solution of a polymerizable monomer having a carboxylic acid group or a sulfonic acid group, a water-swellable clay mineral (B), and water (C) It was found that the above problems can be solved by an organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group, which is obtained by copolymerizing a carboxylic acid group or a polymerizable monomer having a sulfonic acid group. It came to be completed.

  That is, the present invention is a method for producing the above organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group, comprising (meth) acrylamide or a derivative thereof, a water-swellable clay mineral (B), and water (C And a polymerizable monomer having a carboxylic acid group or a sulfonic acid group is added simultaneously with the polymerization initiator or after the addition of the polymerization initiator, and the (meth) acrylamide or derivative thereof and the above The present invention provides a method for producing an organic-inorganic composite hydrogel characterized by polymerizing a polymerizable monomer having a carboxylic acid group or a sulfonic acid group.

  The organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention retains the high mechanical properties of the organic-inorganic composite hydrogel, and has excellent mechanical strength as compared with conventional organic crosslinked hydrogels. In addition, by introducing a polymerizable monomer having a carboxylic acid group or a sulfonic acid group into the molecular chain, high water swellability was obtained, and application development as a highly water-absorbing resin material became possible.

  For example, high water absorbability (water swellability) is required for paper diapers, contact dehydration sheets for food processing, medical absorbent hydrogels, and the like. In these fields, the organic-inorganic composite hydrogel of the present invention using a polymerizable monomer having a carboxylic acid group or a sulfonic acid group exhibits extremely excellent performance. In particular, the organic-inorganic composite hydrogel using acrylic acid has a significantly increased water swellability as compared with a commercially available superabsorbent resin, and can retain its shape after absorbing water. Development of applications is expected.

  The organic polymer (A) used in the present invention is obtained by copolymerization of a polymerizable monomer having a carboxylic acid group or a sulfonic acid group and (meth) acrylamide and / or a derivative thereof, and is dispersed in water. A three-dimensional network is formed by non-covalent bonds such as hydrogen bonds and ionic bonds with the water-swellable clay mineral (B).

  The (meth) acrylamide or its derivatives constituting the organic polymer (A) includes N-substituted acrylamide derivatives, N, N-disubstituted acrylamide derivatives, N-substituted methacrylamide derivatives, N, N-disubstituted methacrylamide derivatives. Etc. Specifically, acrylamide, N-methylacrylamide, N-ethylacrylamide, N-cyclopropylacrylamide, N-isopropylacrylamide, methacrylamide, N-methylmethacrylamide, N-cyclopropylmethacrylamide, N-isopropylmethacrylamide, N, N-dimethylacrylamide, N-methyl-N-ethylacrylamide, N-methyl-N-isopropylacrylamide, N-methyl-Nn-propylacrylamide, N, N-diethylacrylamide, N-acryloylpyrrolidine, N-acryloyl Examples include piperidin, N-acryloylmethyl homopiperazine, N-acryloylmethylpiperazine and the like. Among them, N-isopropylacrylamide, N, N-diethylacrylamide, and the like having polymer properties (hydrophilicity and hydrophobicity) in an aqueous solution having LCST (lower critical solution temperature) are preferably used from the viewpoint of functionality.

The polymerizable monomer having a carboxylic acid group or a sulfonic acid group constituting the organic polymer (A) is one for introducing a carboxylic acid group or a sulfonic acid group into the organic-inorganic composite hydrogel. It is preferable to use it.
(1) Monomers having a carboxylic acid group Unsaturated carboxylic acids such as acrylic acid, maleic acid, itaconic acid, crotonic acid, fumaric acid, and salts thereof
(2) Monomers having sulfonic acid groups
2-acrylamido-2-methylpropane sulfonic acid, methacrylamide sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, p-styrene sulfonic acid and their salts, sodium methacryloxyoxyethyl sulfonate, etc. Acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are particularly preferably used from the viewpoint that an excellent organic polymer can be easily obtained.

  The water-swellable clay mineral (B) used in the present invention is one that swells in water and can be uniformly dispersed, and is particularly preferably a layered clay mineral that can be uniformly dispersed in water at a molecular level (single layer) or at a level close thereto. is there. For example, water-swellable smectite or water-swellable mica is used. Specifically, water-swellable hectorite containing sodium as an interlayer ion, water-swellable montmorillonite, water-swellable saponite, water-swellable synthetic mica, etc. Can be mentioned. These clay minerals need to be finely and uniformly dispersed in an aqueous solution before the monomer of the water-soluble organic polymer is polymerized. In particular, the clay mineral must be dispersed at the unit layer level in the aqueous solution. desirable. Here, it is necessary that there is no clay mineral aggregate that causes precipitation of clay mineral in the aqueous solution, more preferably one having a thickness of about 1 to 10 layers dispersed, particularly preferably 1 or It is dispersed with a thickness of about two layers.

  The ratio of the organic polymer (A) and the water-swellable clay mineral (B) that can be uniformly dispersed in water in the organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention is (A) and (B). It is only necessary to prepare an organic-inorganic hydrogel having a three-dimensional network consisting of and is not necessarily limited depending on the types of (A) and (B) used, but is preferable from the viewpoint of the ease and uniformity of hydrogel synthesis. The mass ratio ((B) / (A)) of the water-swellable clay mineral (B) and the organic polymer (A) is 0.01-10. More preferably, the mass ratio of (B) / (A) is 0.01 to 5, particularly preferably 0.03 to 2, and most preferably 0.1 to 1.0.

  When the mass ratio of (B) / (A) is less than 0.01, the stretchability of the hydrogel of the present invention is often insufficient, and when it exceeds 10, production problems such as brittleness of the resulting hydrogel occur. There is a case. On the other hand, the ratio of (C) water to (A) + (B) can be arbitrarily set within a wide range according to the purpose by adjusting the amount of water in the polymerization process or by subsequent swelling or drying.

  Further, in the monomer composition of the organic polymer (A), when the copolymerization ratio of the polymerizable monomer having a carboxylic acid group or a sulfonic acid group is too high, the mechanical properties of the obtained hydrogel are lowered. On the other hand, if the copolymerization ratio is too low, the high water absorption of the hydrogel of the present invention cannot be exhibited. Therefore, the copolymerization ratio of the polymerizable monomer having a carboxylic acid group or a sulfonic acid group in the organic polymer (A) is preferably 0.1 to 50 mol% with respect to the whole monomer, more preferably 0.3 to It is 40 mol%, particularly preferably 0.5 to 30 mol%, and most preferably 1 to 20 mol%.

  The organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention has a critical temperature (Tc) that is transparent and / or volume swelled on the low temperature side and opaque and / or volume contracted on the high temperature side. And having the characteristic that the transparency and volume can be reversibly changed by changing the temperature above and below Tc. Such an organic-inorganic composite hydrogel can be prepared using an organic monomer exhibiting LCST (lower critical solution temperature) in an aqueous solution as an organic monomer.

  The organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention retains the characteristics of an organic-inorganic hydrogel and has a high water absorption rate as compared with a conventional organic crosslinked gel, as well as excellent mechanical properties, etc. Is shown. For example, the organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention is superior to an organic crosslinked gel in terms of mechanical properties such as strength, elongation, and toughness.

Since the mechanical properties of the organic-inorganic composite hydrogel vary depending on the water content and shape of the hydrogel, the mechanical properties of the organic-inorganic composite hydrogel having a carboxylic acid group or sulfonic acid group of the present invention are within a certain range. It is expressed as a result of testing using a hydrogel having an area. In this specification, specifically, a hydrogel having a cross-sectional area (initial cross-sectional area) of 0.237 cm ² at the start of the test is used as a test material, and an organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group is used. The physical properties of the water (C) having a water content (water content) of 90% by mass were measured.

  The organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention has a tensile strength of 10 to 500 kPa, more preferably 20 to 5 when measured using the hydrogel having the above water content and initial cross-sectional area. It is 450 kPa, particularly preferably 30 to 400 kPa, and further, the tensile elongation at break is 100 to 3000%, more preferably 200 to 2500%, and particularly preferably 300 to 2000%.

  In the organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention, the equilibrium swelling degree Wgel / Wdry is preferably 50 or more. Here, the equilibrium swelling degree Wgel / Wdry is the mass number of the hydrogel swollen per 1 g of the dried gel. Wdry is the solid content of the hydrogel, and Wgel is the mass until the hydrogel is soaked in a large amount of water and does not increase its weight. The equilibrium swelling degree Wgel / Wdry is more preferably 50 to 5000, and particularly preferably 100 to 4000.

  The organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention has a high level of water absorption that cannot be imagined from conventional materials. The commercially available sodium polyacrylate having the most excellent water-absorbing resin absorbs water 100 to 1000 times its own weight, but the swelling degree of Example 1 of the present invention exceeded 2000. That is, it can absorb water 2000 times its own weight (solid content of the gel).

  The organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group of the present invention can be produced by the following method. Water-swellable clay mineral (B) exfoliated in layers after preparing a uniform solution containing the monomer of organic polymer (A), water-swellable clay mineral (B) that can be uniformly dispersed in water, and water (C) The monomer of the organic polymer (A) is polymerized in the presence of. The water-swellable clay mineral (B) acts as a monomer cross-linking agent due to the interaction between the monomer of the organic polymer (A) and the water-swellable clay mineral (B) during the polymerization process, and the organic polymer (A) Complexation at the molecular level with the water-swellable clay mineral (B) is achieved, and an organic-inorganic composite hydrogel having a carboxylic acid group or a sulfonic acid group gelled by three-dimensional network formation is obtained.

  Specifically, a (meth) acrylamide derivative is added to an aqueous solution of a water-swellable clay mineral (B) finely dispersed in water, a polymerizable monomer having a carboxylic acid group or a sulfonic acid group at a low temperature, and a radical polymerization initiator. Then, polymerization is performed at a predetermined temperature. Here, the addition order of the polymerizable monomer having a carboxylic acid group or a sulfonic acid group is important. When a polymerizable monomer having a carboxylic acid group or a sulfonic acid group is first added together with the acrylamide derivative, the clay mineral is aggregated due to a strong interaction with the carboxylic acid group or the sulfonic acid group. The hydrogel obtained in this way not only becomes cloudy but also exhibits a tendency to greatly reduce the mechanical properties. In addition, the reaction system may remarkably thicken and gel due to the interaction between the clay mineral and the carboxylic acid group or sulfonic acid group. Therefore, the polymerization initiator cannot be dispersed in the reaction system, and a uniform hydrogel cannot be obtained. In order to minimize the aggregation of clay minerals, (meth) acrylamide (derivative) is first added to the clay mineral aqueous dispersion, followed by a polymerizable monomer having a carboxylic acid group or a sulfonic acid group and a polymerization initiator at once. Effectively used is a method in which radical polymerization is carried out together with the dispersion of the monomer by adding a polymerizable monomer having a carboxylic acid group or a sulfonic acid group after adding or adding a polymerization initiator, and gelling the entire system. It is done. When adding a polymerization initiator and a polymerizable monomer having a carboxylic acid group or a sulfonic acid group separately, it is preferable to add the monomer immediately after adding the polymerization initiator. When the polymerization initiator is added, polymerization of (meth) acrylamide (derivative) previously added to the aqueous dispersion starts. Therefore, when a polymerization initiator is added, it is preferable to add a polymerizable monomer having a carboxylic acid group or a sulfonic acid group as soon as possible to promote random copolymerization and exhibit the effects of the present invention.

  The above radical polymerization reaction can be performed by a known method such as radical polymerization initiator and / or radiation irradiation. As the radical polymerization initiator and the catalyst, known and commonly used radical polymerization initiators and catalysts can be appropriately selected and used. Preferably, those having water dispersibility and uniformly contained in the entire system are used.

  Specifically, as the polymerization initiator, water-soluble peroxides such as potassium peroxodisulfate and ammonium peroxodisulfate, water-soluble azo compounds such as VA-044, V-50, V-501, And water-soluble radical initiators having an ethylene oxide chain. On the other hand, as the catalyst, tertiary amine compounds such as N, N, N ′, N′-tetramethylethylenediamine and β-dimethylaminopropionitryl are of course used, but in the present invention, they are used as monomers. Since the polymerizable monomer having a carboxylic acid group or a sulfonic acid group functions as a catalyst, the above-mentioned radical polymerization catalyst may not be added.

  The polymerization temperature can be set in the range of 0 ° C. to 100 ° C. according to the type of initiator. The polymerization time varies depending on other polymerization conditions, and is generally carried out for several tens of seconds to several tens of hours.

The invention is further illustrated by the following examples.
(Measurement condition)
In the following examples and comparative examples, the tensile test was performed by sliding an unpurified round bar-shaped hydrogel (diameter = 5.5 mm) at the chuck part using a desktop universal testing machine AGS-H manufactured by Shimadzu Corporation. The sample was mounted on a tensile test apparatus so that the distance between the gauges was 30 mm and the tensile speed was 100 mm / min. The temperature dependence of the light transmittance was measured using a UV-visible spectrophotometer V-530 manufactured by JASCO Corporation as it was by synthesizing a hydrogel in a prismatic transparent polystyrene cell. The degree of water swelling was determined from the time dependence of the mass increase of about 0.2 g of a round rod-shaped hydrogel having a diameter of 5.5 mm immersed in a large amount of water.

(reagent)
・ Clay minerals
XLG: Water-swellable synthetic hectorite (Trademark LAPONITE XLG, manufactured by Nippon Silica Co., Ltd.)
Kunipia F: High-purity montmorillonite (Kunimine Industries Co., Ltd.)
·monomer
DMAA: Used after removing the polymerization inhibitor using dimethylacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.) and activated alumina.
NIPAM: N-isopropylacrylamide (manufactured by Kojin Co., Ltd.), recrystallized using a mixed solvent of toluene and hexane and purified to colorless needle crystals before use.
AAc: Acrylic acid (Wako Pure Chemical Industries, Ltd.)
MAc: Maleic acid (Wako Pure Chemical Industries, Ltd.)
AMPS: 2-acrylamido-2-methylpropanesulfonic acid (Wako Pure Chemical Industries, Ltd.)
BIS: N, N'-methylenebisacrylamide (manufactured by Kanto Chemical Co., Inc.)
・ Polymerization initiator
KPS: potassium peroxodisulfate (manufactured by Kanto Chemical Co., Inc.), diluted with pure water at a ratio of KPS / water = 0.2 / 10 (g / g) and used as an aqueous solution.
・ Polymerization catalyst
TEMED: N, N, N ', N'-tetramethylethylenediamine (manufactured by Wako Pure Chemical Industries, Ltd.)

(Example 1)
A uniform solution was prepared by stirring 19 g of pure water and 0.6 g of Kunipia F in a flat bottom glass container having an inner diameter of 25 mm and a length of 80 mm. DMAA 1.8g was added to this, and nitrogen bubbling was carried out for 15 minutes. Subsequently, immediately after adding 0.2 g of KPS aqueous solution with stirring in an ice bath, 0.2 g of AAc (13 mol% with respect to the total amount of monomers) was added to obtain a uniform solution. The obtained uniform solution was immediately transferred to a glass tube container having an inner diameter of 5.5 mm and a length of 150 mm with a closed bottom so as not to come into contact with oxygen, and the upper part was sealed and subjected to stationary polymerization at 20 ° C. After 15 hours, a uniform rod-like hydrogel having elasticity and toughness was formed in the glass tube container. The hydrogel was purified by immersion in a large amount of water. The obtained purified hydrogel was dried at 100 ° C. under reduced pressure to obtain a dried hydrogel from which moisture was removed. It was confirmed that when the dried gel was immersed in water at 20 ° C., it returned to a stretchable hydrogel having the same shape as before drying. Also, thermogravimetric analysis of the dried gel (TG-DTA220 manufactured by Seiko Denshi Kogyo Co., Ltd .: raised to 600 ° C. at 10 ° C./min under air flow) gave B / A = 0.3 (mass ratio). .

  From the above, the gel obtained in this example is a hydrogel composed of an organic polymer (a copolymer of N, N-dimethylacrylamide and acrylic acid), a clay mineral, and water having a component ratio according to the charged composition. Even if no cross-linking agent is added in the synthesis of the organic polymer, it becomes a uniform hydrogel, and the gel dried product obtained by removing water from the hydrogel is immersed in water again. From returning to the shape of the hydrogel, it was concluded that a three-dimensional network composed of organic polymers and clay minerals at the molecular level was formed in water.

  The organic polymer synthesized under the same conditions except that no clay mineral coexists became a polymer aqueous solution and did not become a hydrogel.

  A tensile test was conducted on an unpurified round rod-shaped hydrogel, and the results are shown in FIG. In addition, the measurement result of water swellability is shown in FIG.

  In Comparative Example 1 having the same composition as that of Example 1, AAc was added to an aqueous solution of Kunipia F and DMAA with stirring. The solution immediately thickened significantly. Thereafter, an aqueous KPS solution was added, but the aqueous KPS solution could not be uniformly dispersed in the reaction system, and a tensile measurement sample could not be made.

(Examples 2, 3 and Comparative Example 2)
A hydrogel having the carboxylic acid group of Examples 2 and 3 was synthesized in the same manner as in Example 1 with the composition shown in Table 1. These hydrogels had higher strength and elastic modulus than the hydrogel of Comparative Example 2 containing no carboxylic acid group (FIG. 1). Moreover, in the water swellability, the examples of hydrogels having carboxylic acid groups greatly exceeded the comparative examples, and showed excellent water absorption (FIG. 2).

(Examples 4, 5 and Comparative Example 3)
Hydrogels having carboxylic acid groups of Examples 4 and 5 were synthesized in the same manner as in Example 1 with the compositions shown in Table 1. Further, an organic crosslinking gel having a carboxylic acid group of Comparative Example 3 was synthesized using an organic crosslinking agent instead of the clay mineral. The gel of Comparative Example 3 was extremely fragile and an attempt was made to conduct a tensile test, but most of the samples were broken before being attached to the chuck. Moreover, even those lightly attached to the chuck were broken immediately after the test, and no physical property values were obtained. In contrast, Examples 4 and 5 exhibited excellent mechanical properties (FIG. 3). Further, as shown in FIG. 4, the water swellability of Examples 4 and 5 was larger than that of Comparative Example 3. When the temperature dependence of the light transmittance was measured, Examples 4 and 5 showed clear LCST (FIG. 5).

(Examples 6, 7, 8 and Comparative Example 4)
Hydrogels having carboxylic acid groups or sulfonic acid groups of Examples 6, 7, and 8 were synthesized in the same manner as in Example 1 with the compositions shown in Table 1. As shown in FIGS. 6 and 7, the hydrogels of Examples 6, 7, and 8 showed excellent mechanical properties and water swellability.

  In Comparative Example 4 having the same composition as that of Example 6, an AAcNa aqueous solution was added to an aqueous solution of XLG and DMAA with stirring. The solution immediately gelled. Even if an aqueous KPS solution was added after gelation, the aqueous KPS solution could not be dispersed in the reaction system, and a tensile measurement sample could not be made.

FIG. 4 is a diagram showing the strength and elongation of hydrogels obtained in Examples 1, 2, 3 and Comparative Example 2. 2 is a graph showing the water swelling degree of hydrogels obtained in Examples 1, 2, 3 and Comparative Example 2. FIG. FIG. 4 is a view showing the strength and elongation of the hydrogel obtained in Examples 4 and 5. FIG. 4 is a graph showing the water swelling degree of hydrogels obtained in Examples 4 and 5 and Comparative Example 3. FIG. 4 is a graph showing the temperature dependence of the light transmittance of the hydrogels obtained in Examples 4 and 5. FIG. 4 is a graph showing the strength and elongation of hydrogels obtained in Examples 6, 7, and 8. FIG. 6 is a graph showing the water swelling degree of the hydrogels obtained in Examples 6, 7, and 8.

Claims (7)

A method for producing an organic-inorganic composite hydrogel in which an organic polymer (A) and a water-swellable clay mineral (B) form a three-dimensional network, comprising (meth) acrylamide or a derivative thereof, and the water-swelling property After preparing a homogeneous solution containing clay mineral (B) and water (C), a polymerizable monomer having a carboxylic acid group or a sulfonic acid group is added simultaneously with the polymerization initiator or after the addition of the polymerization initiator, A method for producing an organic-inorganic composite hydrogel, characterized in that the organic polymer (A) is produced by polymerizing the (meth) acrylamide or a derivative thereof and the polymerizable monomer having a carboxylic acid group or a sulfonic acid group. . 2. The method for producing an organic-inorganic composite hydrogel according to claim 1, wherein a mass ratio ((B) / (A)) of the water-swellable clay mineral (B) and the organic polymer (A) is 0.01 to 10. 3. The method for producing an organic-inorganic composite hydrogel according to claim 1, wherein the polymerizable monomer having a carboxylic acid group is acrylic acid or a salt thereof, or maleic acid or a salt thereof. The method for producing an organic-inorganic composite hydrogel according to any one of claims 1 to 3, wherein the polymerizable monomer having a sulfonic acid group is 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof. The method for producing an organic-inorganic composite hydrogel according to any one of claims 1 to 4, wherein a copolymerization ratio of a polymerizable monomer having a carboxylic acid group or a sulfonic acid group in the organic polymer (A) is 50 mol% or less. . An organic-inorganic composite hydrogel obtained by the production method according to any one of claims 1 to 5, wherein the tensile strength is 10 kPa to 500 kPa when the content (water content) of water (C) is 90% by mass. An organic-inorganic composite hydrogel having an elongation at break of 100% to 3000%. The organic-inorganic composite hydrogel according to claim 6, wherein the equilibrium swelling degree Wgel / Wdry with water is 50 to 5,000.

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