JP6893739B2 - Water-absorbent composite materials and their use - Google Patents

Description

The present invention relates to a composite material derived from carboxymethylated starch, which is suitable as a constituent material for water-absorbing functional products such as disposable diapers.

Various water-absorbing functional products such as disposable diapers, sanitary products, light incontinence pads, wound covering materials, and food freshness-preserving materials are known, and generally, a large amount of liquid (in a short time) is used as a constituent material of such water-absorbing functional products. A polymer material capable of absorbing water, urine, body fluid, blood, etc.) is used. Examples of the highly water-absorbent polymer material include a crosslinked product of a partially neutralized polyacrylic acid, a hydrolyzate of a starch-acrylic acid graft polymer, a saponified product of a vinyl acetate-acrylic acid ester copolymer, an acrylonitrile copolymer, or the like. Examples thereof include those using a hydrolyzate of an acrylamide copolymer, a crosslinked product thereof, a crosslinked polymer of a cationic monomer (acrylamide, ethyleneimine, etc.) as a main raw material. These are synthetic polymers or copolymers based on acrylic acid or acrylamide, which are based on non-renewable petroleum-derived materials and are non-biodegradable or inadequate materials.

In recent years, there has been a demand for the development of water-absorbing materials made from biomass-derived raw materials in response to the demand for reduction of environmental load. To solve such a problem, for example, Patent Document 1 describes a water absorbing material based on carboxymethyl cellulose (CMC) as a water absorbing material made of a biomass-derived raw material. However, in order to use carboxymethyl cellulose (CMC) as a water-absorbing material, it is necessary to form a matrix by reacting with a cross-linking agent, it is difficult to control the predetermined water-absorbing performance, and generally only a material having poor water-absorbing performance can be obtained. There was a problem that there was no.

On the other hand, carboxymethylated starch is a modified starch in which the hydroxyl group in the starch is replaced with the same carboxymethyl group as the above-mentioned carboxymethyl cellulose (CMC), and is an inexpensive and easily available anionic biomass-derived polymer. Since starch has a matrix structure that is inherent in starch, a certain level of water absorption performance can be expected.

A water absorbing material based on this carboxymethylated starch has also been developed. For example, in Patent Document 2, particles containing carboxyalkyl starch permeated with an acid gas having an intramolecular ester bond at least on the surface of the particles. The particles characterized by being in are listed. Then, it is described that the particles are used as a water absorbing material.

Further, on the other hand, Patent Document 3 describes a nanocomposite material in which a layered silicate is dispersed inside a polysaccharide network such as starch, and the layered silicate synergistically contributes to water absorption by the polysaccharide. Is described.

Japanese Unexamined Patent Publication No. 2008-280429 Special Table 2012-518711 Special Table 2007-533780

However, the technique described in Patent Document 2 requires a special device for treating the carboxymethylated starch with an acid gas. Further, in Patent Document 3, the carboxymethylated starch is described only as an example of what can be generally used as a co-absorbing material.

In view of the above prior art, an object of the present invention is to provide a material having excellent water absorption performance by using carboxymethylated starch which is a raw material derived from biomass.

As a result of diligent studies to solve the above problems, the present inventors have found that a composite material having excellent water absorption performance can be obtained by dispersing a layered silicate in carboxymethylated starch, and the present invention has been made. Has been completed.

That is, the first aspect of the present invention is to provide a water-absorbent composite material in which a layered silicate is dispersed in a matrix of carboxymethylated starch.

The composite material according to the present invention is excellent in water absorption performance because the layered silicate is dispersed in the matrix of carboxymethylated starch.

In the composite material according to the present invention, the carboxymethylated starch preferably has a carboxymethyl group substitution degree of 0.1 to 1.0. If the degree of carboxymethyl group substitution is within the above range, the water absorption performance is further excellent.

Further, in the composite material according to the present invention, it is preferable that the layered silicate takes less than 900 seconds to disperse in water under the following condition (A). If the dispersibility of the layered silicate in water is within the above range, the water absorption performance is further excellent.
Condition (A): 100 mL of water at 25 ° C. is put in a 200 mL beaker, a stirrer (width 5 mm × height 5 mm × total length 45 mm) is further put, and this is stirred at 300 rpm, and 5.0 g of layered silicate is added. Is added.

Further, in the composite material according to the present invention, it is preferable that the matrix of the carboxymethylated starch is crosslinked. According to this, the gel strength can be increased by the cross-linking treatment, so that it is more practical.

Further, in the composite material according to the present invention, it is preferable that the layered silicate is dispersed in the matrix of the carboxymethylated starch in the form of microscale aggregates. According to this, the water absorption performance is more excellent than the case where the layered structure of the layered silicate is exfoliated and dispersed in the matrix of carboxymethylated starch on a nanoscale.

Further, in the composite material according to the present invention, it is preferable that the layered silicate is dispersed in a ratio of 1 to 30 parts by mass with respect to 100 parts by mass of the carboxymethylated starch. If the amount of the layered silicate added to the carboxymethylated starch is within the above range, the water absorption performance is further excellent.

On the other hand, the second aspect of the present invention is to provide a water-absorbing composition containing the above-mentioned composite material as an active ingredient of water-absorbing functionality.

Since the composition for water absorption according to the present invention contains a composite material in which layered silicate is dispersed in a matrix of carboxymethylated starch as an active ingredient of water absorption functionality, it is excellent in functionality such as water absorption.

A third aspect of the present invention is to provide a water-absorbing functional product containing the above-mentioned composite material as a constituent material.

Since the water-absorbing functional product according to the present invention contains a composite material in which layered silicate is dispersed in a matrix of carboxymethylated starch as a constituent material, it is excellent in functionality such as water absorption.

A fourth aspect of the present invention is a water-absorbent composite comprising a step of mixing carboxymethylated starch and layered silicate and homogenizing to disperse the layered silicate in the matrix of carboxymethylated starch. It provides a method of manufacturing a material.

In the method for producing a composite material according to the present invention, carboxymethylated starch and layered silicate are mixed and homogenized to obtain a composite material in which the layered silicate is dispersed in a matrix of the carboxymethylated starch. Since the process is included, a composite material having excellent water absorption performance can be obtained. Further, even when a dehydration step is included in the preparation of the composite material, the layered silicate facilitates pulverization after dehydration.

In the method for producing a composite material according to the present invention, it is preferable that the carboxymethylated starch and the layered silicate are further mixed with a cross-linking agent and subjected to a cross-linking treatment. According to this, the gel strength can be increased by the cross-linking treatment, and a more practical composite material can be obtained.

Further, in the method for producing a composite material according to the present invention, it is preferable that the homogenization treatment is carried out to such an extent that the layered silicate is dispersed in the matrix of the carboxymethylated starch in the form of microscale aggregates. According to this, a composite material having more excellent water absorption performance can be obtained as compared with the case where the layered structure of the layered silicate is peeled off and dispersed in the matrix of carboxymethylated starch on a nanoscale.

Further, in the method for producing a composite material according to the present invention, it is preferable to add the layered silicate at a ratio of 1 to 30 parts by mass with respect to 100 parts by mass of the carboxymethylated starch. When the amount of the layered silicate added to the carboxymethylated starch is within the above range, a composite material having further excellent water absorption performance can be obtained.

Further, in the method for producing a composite material according to the present invention, the carboxymethylated starch preferably has a carboxymethyl group substitution degree of 0.1 to 1.0. When the degree of carboxymethyl group substitution is within the above range, a composite material having further excellent water absorption performance can be obtained.

Further, in the method for producing a composite material according to the present invention, it is preferable that the layered silicate takes less than 900 seconds to disperse in water under the following condition (A). If the dispersibility of the layered silicate in water is within the above range, a composite material having further excellent water absorption performance can be obtained.
Condition (A): 100 mL of water at 25 ° C. is put in a 200 mL beaker, a stirrer (width 5 mm × height 5 mm × total length 45 mm) is further put, and this is stirred at 300 rpm, and 5.0 g of layered silicate is added. Is added.

On the other hand, the fifth aspect of the present invention provides a method for producing a water-absorbing composition, which comprises containing the composite material obtained by the above-mentioned production method as an active ingredient of water-absorbing functionality.

The method for producing a water-absorbing composition according to the present invention is excellent in functionality such as water absorption because it contains a composite material in which layered silicate is dispersed in a matrix of carboxymethylated starch as an active ingredient of water-absorbing functionality. A composition for water absorption can be obtained.

A sixth aspect of the present invention is to provide a method for producing a water-absorbing functional product using the composite material obtained by the above-mentioned production method as a constituent material.

The method for producing a water-absorbing functional product according to the present invention uses a composite material in which layered silicate is dispersed in a matrix of carboxymethylated starch as a constituent material, so that a water-absorbing functional product having excellent functionality such as water absorption can be obtained. Can be done.

The composite material according to the present invention is excellent in water absorption performance because the layered silicate is dispersed in the matrix of carboxymethylated starch.

In the method for producing a composite material according to the present invention, carboxymethylated starch and layered silicate are mixed and homogenized to obtain a composite material in which the layered silicate is dispersed in a matrix of the carboxymethylated starch. Since the process is included, a composite material having excellent water absorption performance can be obtained. Further, even when a dehydration step is included in the preparation of the composite material, the layered silicate facilitates pulverization after dehydration.

FIG. 1 is an electron micrograph of the water absorbing material 5. FIG. 2 is an electron micrograph of the water absorbing material 19. FIG. 3 is an electron micrograph of the water absorbing material 7. FIG. 4 is an electron micrograph of the water absorbing material 20. FIG. 5 is an electron micrograph of the layered silicate. FIG. 6 is an electron micrograph of the water absorbing material 1.

The carboxymethylated starch used in the present invention is modified starch in which the hydroxyl group in the starch is replaced with a carboxymethyl group. There are no particular restrictions on the metal or salt coordinated to the starch, and sodium, calcium, potassium, etc. can be used, but from the viewpoint of availability, sodium is coordinated. (Sodium starch glycolate) is preferably used.

As the carboxymethylated starch used in the present invention, a commercially available starch may be used, but it can be obtained by carboxymethylating the raw material starch by a conventionally known method. For example, sodium monochloroacetate may be added to a starch suspension under alkaline conditions. More specifically, for example, to a starch suspension adjusted to pH 9 to 13 by adding an acid agent such as hydrochloric acid or an alkaline agent such as sodium hydroxide, 0.1 to 100 parts by mass of the dry mass of starch. Carboxymethylation can be achieved by adding 50 parts by mass of sodium monochloroacetate and holding and stirring at 10 to 60 ° C. for 1 to 48 hours. The origin of the starch that is the source of the starch is not particularly limited, and any commonly used starch may be used. Examples thereof include corn starch, tapioca, rice starch, wheat starch, horse belly starch, sweet potato starch, green bean starch, kataguri starch, kudzu starch, sardine starch, sago starch, pea starch, and Oobayuri starch. Of these, tapioca, cornstarch, rice starch, and potato starch are particularly preferable because they are inexpensive and easily available in large quantities. Further, in any starch, in addition to ordinary starch, those improved by breeding method or genetic engineering method such as Uruchi species, Waxy species, and Hyamylose species may be used.

The carboxymethylated starch used in the present invention is not particularly limited as long as it is a starch into which a carboxymethyl group has been introduced, but the degree of substitution of the carboxymethyl group is 0.1 in consideration of its performance as in the examples described later. It is preferably ~ 1.0, more preferably 0.1-0.6. If the degree of carboxymethyl group substitution is less than the above range, the desired water absorption performance tends not to be obtained, and if it exceeds the above range, it becomes difficult to obtain a material having excellent water absorption performance, and dehydration occurs during the preparation of the composite material. When a step is included, it tends to be difficult to pulverize after dehydration. The degree of substitution of the carboxymethyl group means the degree of substitution of the carboxymethyl group with respect to one glucose residue of starch, and can be measured by the following method.

<Degree of substitution>
The dry weight of the sample is precisely weighed, recorded as a (unit: g), wrapped in filter paper, placed in a porcelain crucible, and incinerated at 600 ° C. After cooling, transfer to a 500 mL beaker, add 250 mL of water and b (unit: mL) of 0.05 N sulfuric acid, and boil for 30 minutes. This is cooled, a phenolphthalein indicator is added, and the titration is carried out with 0.1N sodium hydroxide, and the titration amount is defined as c (unit: mL). The degree of substitution can be calculated using the following formula. In the following formula, f indicates the titer of 0.05N sulfuric acid, and f'indicates the titer of 0.1N sodium hydroxide. Further, B indicates the alkalinity or acidity of the sample, and can be measured as described in the latter part.

A = (bf-cf') / a-B
Degree of substitution = (162 × A) ÷ (10000-80 × A)

<Alkaline or acidity>
The sample is placed in a 300 mL glass beaker, weighed precisely, and the dry weight thereof is recorded as d (unit: g), and then 200 mL of distilled water is added to dissolve the sample. To this, 5 mL of 0.05N sulfuric acid is added, boiled for 10 minutes, cooled, a phenolphthalein indicator is added, and the titration is carried out with 0.1N sodium hydroxide, and the titration amount is defined as e (unit: mL). Separately, a blank test is carried out without adding a sample, and the titration amount of the result is g (unit: mL). Alkaliity or acidity can be calculated by the following formula. In the following formula, f indicates the titer of 0.05N sulfuric acid, and f'indicates the titer of 0.1N sodium hydroxide.

B = (gf-ef') / d

The layered silicate used in the present invention is a clay mineral containing silicate in its composition, and in microscopic observation, it has a shape in which flakes having a thickness of about 1 nm and a width and length of about 1 to 500 nm are laminated in layers. It is a clay mineral to be presented. For example, montmorillonite, smectite, bentonite, saponite, nontronite, laponite, byderite, hectorite, saponite, stevenzite, vermiculite, volconscoite, magadite, medmontite, kennyite and the like can be mentioned. The composition varies depending on the raw material, and a mixture of two or more of these compositions can also be used.

The layered silicate used in the present invention is not particularly limited as long as it is a layered silicate having the above-mentioned properties, but it has a certain degree of hydrophilicity in consideration of its performance as in the examples described later. It is preferable to have. That is, for example, it is more preferable to use one having a dispersion time in water measured under the following condition (A) of 900 seconds or less. If the dispersion time in water exceeds the above range, it becomes difficult to obtain a product having excellent water absorption performance, and when a dehydration step is included in the preparation of the composite material, it tends to be difficult to pulverize after dehydration.
Condition (A): 100 mL of water at 25 ° C. is put in a 200 mL beaker, a stirrer (width 5 mm × height 5 mm × total length 45 mm) is further put, and this is stirred at 300 rpm, and 5.0 g of layered silicate is added. Is added.

In the above measurement, it is judged that the layered silicate is dispersed in water without floating on the water surface.

Further, the hydrophilic property of the layered silicate used in the present invention can also be adjusted by treating the raw material such as the clay mineral with a predetermined treatment agent. For example, by using an organic acid such as maleic anhydride, the surface can be adjusted to be hydrophilic, and the hydrophilicity of the layered silicate after the treatment can be enhanced. Alternatively, in some cases, the surface can be adjusted to be hydrophobic by using a long-chain alkylamine such as octadecylammonium.

The present invention provides a composite material in which the layered silicate described above is dispersed in the matrix of carboxymethylated starch described above. Since the composite material having such a structure is excellent in water absorption performance, it can be suitably used as a constituent material of a water absorption function product or the like.

The blending ratio of the carboxymethylated starch and the layered silicate is not particularly limited, but it is preferable that the layered silicate is dispersed at a ratio of 1 to 30 parts by mass with respect to 100 parts by mass of the carboxymethylated starch. It is more preferable that the layered silicate is dispersed in a proportion of 5 to 20 parts by mass. If the amount of the layered silicate added to the carboxymethylated starch is less than the above range, the effect of dispersing the layered silicate tends to be difficult to obtain, and if it exceeds the above range, the layered silicate is added to the carboxymethylated starch. It tends to be difficult to disperse in the matrix. Two or more types of carboxymethylated starch may be used in combination, and two or more types of layered silicate may be used in combination. In that case, the above-mentioned compounding ratio is a value calculated by the total amount of two or more kinds.

In the composite material according to the invention, the layered silicate is preferably dispersed in the matrix of carboxymethylated starch in the form of microscale aggregates. According to this, as shown in Examples described later, the water absorption performance is more excellent than in the case where the layered structure of the layered silicate is exfoliated and dispersed in the matrix of carboxymethylated starch on a nanoscale. There is. In addition, "dispersed in the matrix of carboxymethylated starch in the form of microscale aggregates" means that the layered structure of the layered silicate is maintained and the size of the microscale is contained in the matrix of carboxymethylated starch. It means that it is dispersed. As shown in Examples described later, if the degree of homogenization treatment is too strong, the layered structure of the layered silicate is exfoliated due to shear stress (shear stress) and dispersed on a finer nanoscale, thus absorbing water. The sex is reduced. Whether or not the layered silicate is dispersed on a microscale can be confirmed by microscopic observation with, for example, a scanning electron microscope (SEM).

Further, in the composite material according to the present invention, the matrix of carboxymethylated starch is preferably crosslinked. According to this, as shown in Examples described later, the gel strength can be increased by the cross-linking treatment, the gel is not easily crushed even under practical conditions as a constituent material of a water-absorbing functional product, and the absorbed water is re-absorbed. It has the advantage of being difficult to release. The method for cross-linking the carboxymethylated starch is not particularly limited, and the carboxymethylated starch can be treated by a usual method used for the cross-linking treatment of starch.

The cross-linking agent may be any cross-linking agent capable of cross-linking the amylose skeletons of starch with each other, and is ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, 1,3-propanediol, glycerin, polyglycerin, 1,4. Polyhydric alcohol compounds such as −butandiol, 1,6-hexanediol, trimethylpropane, diethanolamine, triethanolamine, polyoxypropylene, pentaerythritol, sorbitol; ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl Epoxy compounds such as ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol; haloepoxy compounds such as epichlorohydrin; ethylenediamine, diethylenetriamine, triethylenetetramine, polyamidepolyamine, polyallylamine, polyethylene Polyvalent amine compounds such as imine; inorganic acids such as silicic acid, phosphoric acid and condensed phosphoric acid; organic acids such as citric acid, succinic acid, maleic anhydride and succinic anhydride; dialdehydes and oxys such as glycal and glutalaldehyde Examples thereof include cross-linking agents such as acidified compounds such as phosphorus chloride.

Hereinafter, the method for producing a composite material according to the present invention will be described in more detail. However, the following description is not intended to limit the scope of the composite material according to the present invention to those according to a specific preparation method.

The composite material according to the present invention can be obtained by mixing carboxymethylated starch and layered silicate, homogenizing the mixture, and dispersing the layered silicate in a matrix of carboxymethylated starch.

In the method for producing a composite material according to the present invention, there is no particular limitation on the method for mixing the carboxymethylated starch and the layered silicate. The mixture may be wet or dry. For the wet method, for example, it is preferable to prepare a paste solution of carboxymethylated starch, add layered silicate to the paste solution, and mix the mixture. The paste solution of carboxymethylated starch is obtained by adding carboxymethylated starch to water, and the concentration of carboxymethylated starch in terms of dry weight with respect to the total mass thereof is typically 1 to 95% by mass, more typically. Can be obtained by mixing so as to be 10 to 40% by mass. At this time, the carboxymethylated starch and the layered silicate may be added to water at the same time or substantially at the same time and mixed. The paste solution of carboxymethylated starch is preferably adjusted to pH 9 or higher, and more preferably pH 10 or higher, by adding a pH adjusting agent (alkaline agent) such as sodium hydroxide. A pH of 10 or higher facilitates dispersion of the layered silicate in the matrix of carboxymethylated starch. In the dry method, for example, a pH adjuster (alkaline agent) such as sodium hydroxide can be added to carboxymethylated starch and layered silicate as needed, and the mixture can be mixed using an extruder or the like. .. In that case, the concentration of the carboxymethylated starch in terms of dry weight with respect to the total mass of the obtained starch kneaded product is typically 1 to 99% by mass, more typically 5 to 97% by mass. Is preferable. Further, the concentration of the layered silicate in terms of dry weight with respect to the total mass of the obtained starch kneaded product is typically 0.01 to 29.7% by mass, more typically 0.05 to 29.1% by mass. It is preferable to mix so as to be%. The pH of the obtained starch kneaded product is preferably adjusted to pH 9 or higher, and more preferably pH 10 or higher. When such a dry reaction is used, the step of gelatinizing the carboxymethylated starch, the step of dispersing the layered silicate, and the step of adding an alkaline agent can be carried out at the same time, so that in terms of industrial production efficiency. Excellent. That is, in this case, the homogenization treatment described later can be performed in one step together with the mixing of the carboxymethylated starch and the layered silicate.

The mixing ratio of the carboxymethylated starch and the layered silicate is not particularly limited, but it is preferable to add the layered silicate at a ratio of 1 to 30 parts by mass with respect to 100 parts by mass of the carboxymethylated starch, and 5 to 5 It is more preferable to add the layered silicate in a proportion of 20 parts by mass. As described above, in the obtained composite material, if the amount of the layered silicate added to the carboxymethylated starch is less than the above range, the effect of dispersing the layered silicate tends to be difficult to obtain, and exceeds the above range. And, it tends to be difficult to disperse in the matrix of carboxymethylated starch. Two or more types of carboxymethylated starch may be used in combination, and two or more types of layered silicate may be used in combination. In that case, the above-mentioned compounding ratio is a value calculated by the total amount of two or more kinds.

In the method for producing a composite material according to the present invention, there is no particular limitation on the method of mixing carboxymethylated starch and layered silicate and homogenizing the mixture. For example, it is possible to use a homogenizing means usually used for preparing modified starch, such as a stirring type, an ultrasonic type, and a pressure type. Further, as described above, this homogenization treatment can also be achieved by mixing the carboxymethylated starch and the layered silicate using an extruder or the like. However, in a preferred embodiment of the present invention, in the obtained composite material, it is preferable that the layered silicate is dispersed in the matrix of carboxymethylated starch while maintaining the shape of microscale aggregates. According to this, as shown in Examples described later, the water absorption performance is more excellent than in the case where the layered structure of the layered silicate is exfoliated and dispersed in the matrix of carboxymethylated starch on a nanoscale. There is. In that case, by adjusting the degree of homogenization treatment, the layered silicate can be dispersed in the matrix of carboxymethylated starch while maintaining the shape of the microscale aggregates.

The temperature conditions during the above mixing and homogenization treatment are not particularly limited, but from the viewpoint of not denaturing the matrix structure of the carboxymethylated starch as much as possible, it is preferably about 20 to 150 ° C., preferably 25 to 130 ° C. It is more preferably about 30 to 70 ° C., and even more preferably about 30 to 70 ° C.

In a preferred embodiment of the present invention, as described above, the matrix of carboxymethylated starch is preferably crosslinked from the viewpoint of increasing the gel strength of the obtained composite material. The method for cross-linking the carboxymethylated starch is not particularly limited, and the starch can be treated by a usual method used for the cross-linking treatment of starch. There is no limitation on the order of addition of the raw materials of the carboxymethylated starch, the layered silicate and the cross-linking agent, and the cross-linking agent is added before the carboxymethylated starch and the layered silicate are brought into contact with each other to carry out the cross-linking treatment. Alternatively, the carboxymethylated starch and the layered silicate may be mixed, the layered silicate may be dispersed by the homogenization treatment, and then a cross-linking agent may be added to carry out the cross-linking treatment. And the dispersion treatment of the layered silicate may be performed in parallel. However, if it is difficult for the layered silicate to disperse in the matrix of the carboxymethylated starch after cross-linking, the carboxymethylated starch and the layered silicate are mixed, homogenized, and then the cross-linking agent is added and mixed. Then, it is more preferable to carry out a cross-linking treatment. Further, the temperature conditions during the mixing and homogenization treatment are not particularly limited, and as described above, the temperature is preferably about 20 to 150 ° C. from the viewpoint of not denaturing the matrix structure of the carboxymethylated starch as much as possible. It is more preferably about 25 to 130 ° C., and even more preferably about 30 to 70 ° C.

The amount of the cross-linking agent added may be appropriately selected depending on the gel strength of the desired cross-linking treatment, the type of the cross-linking agent, and the like, and is not particularly limited. Typically, for example, it is about 0.01 to 60% by mass with respect to the dry weight of starch, and more typically, it is about 0.1 to 50% by mass with respect to the dry weight of starch. In order to carry out the cross-linking treatment more efficiently, the reaction can be carried out after adjusting to the optimum pH using an acid or an alkali.

More specifically, for example, a case where phosphorus oxychloride is used as a cross-linking agent will be described. The carboxymethyl starch is mixed with water so that the concentration of the carboxymethyl starch in water in terms of dry weight is 10 to 30% by mass. To obtain a paste solution of carboxymethylated starch. At this time, the paste solution of the carboxymethylated starch is adjusted to the pH range of 11 to 12 by adding an alkaline agent such as sodium hydroxide. The amount of phosphorus oxychloride added as the cross-linking agent may be appropriately selected according to the desired gel strength and the like, and is not particularly limited, but is typically 0.01 to 60 with respect to the dry weight of starch, for example. It is about% by mass, and more typically about 0.1 to 50% by mass with respect to the dry weight of starch. The cross-linked mixture prepared in this way is allowed to stand for 6 to 24 hours in an environment at a temperature of 20 to 50 ° C. to carry out a cross-linking treatment having a structure in which the hydroxyl groups of the carboxymethylated starch are phosphoric acid-crosslinked. To.

On the other hand, for example, to explain the case where epichlorohydrin is used as the cross-linking agent, the carboxymethylated starch is added to water so that the concentration of the carboxymethylated starch in water in terms of dry weight is 10 to 30% by mass. Addition and mixing to obtain a paste solution of carboxymethylated starch. At this time, the paste solution of the carboxymethylated starch is adjusted to the pH range of 11 to 12 by adding an alkaline agent such as sodium hydroxide. The amount of epichlorohydrin added as the cross-linking agent may be appropriately selected according to the desired gel strength and the like, and is not particularly limited, but typically, for example, 0.01 to 0.01 to the dry weight of starch. It is about 60% by mass, and more typically about 0.1 to 50% by mass with respect to the dry weight of the starch. A cross-linking treatment having a structure in which the hydroxyl groups of carboxymethylated starch are cross-linked with epichlorohydrin by allowing the mixture of the cross-linking treatment thus prepared to stand for 6 to 24 hours in an environment of a temperature of 20 to 50 ° C. Is made.

In a preferred embodiment of the present invention, after the dispersion treatment of the layered silicate by the homogenization treatment and the cross-linking treatment with the cross-linking agent are completed, an organic solvent such as ethanol is appropriately added, and the present invention is used as a precipitate. The composite material according to the invention may be recovered. According to this, impurities other than the composite material in which the layered silicate is dispersed in the matrix of carboxymethylated starch can be efficiently removed. For the treatment of precipitation with an organic solvent, for example, an organic solvent such as ethanol having a volume of about 1 to 5 times that of the post-treatment mixture after the dispersion treatment of the layered silicate by the homogenization treatment and the cross-linking treatment with the cross-linking agent is used. It can be carried out by adding and stirring. Such a cleaning treatment with an organic solvent may be repeated a plurality of times. Further, it is preferable to add an appropriate pH adjusting agent (acid agent) such as acetic acid to adjust the pH to about 6 to 9. According to this, the cleaning efficiency at the time of the cleaning treatment with such an organic solvent is further enhanced.

In a preferred embodiment of the present invention, after the dispersion treatment of the layered silicate by the homogenization treatment and the cross-linking treatment with the cross-linking agent are completed, an organic solvent such as ethanol is appropriately added, and the present invention is used as a precipitate. The composite material according to the invention may be recovered and further powdered. That is, the precipitate on the lump can be crushed and dried by a vacuum dryer or the like to be pulverized. Further, the particle size may be further reduced by an appropriate pulverizing means such as a homogenizer. The form after pulverization preferably has a water content of about 0 to 7%, and more preferably a water content of about 0.5 to 5%. Further, those having a particle size of 16 mesh (JIS standard, opening size 1 mm) and turning on a mesh of 60 mesh (JIS standard, opening size 0.25 mm) are 50% by mass or more per mass. It is preferable that the particle size passes through the mesh of 16 mesh and is turned on in the mesh of 60 mesh, and it is more preferable that the particle size is 60% by mass or more per mass.

The composite material according to the present invention described above is excellent in water absorption performance as shown in Examples described later. Specifically, for example, in the water absorption test shown below in accordance with JIS K 7223, the water absorption performance is 25 or more, more preferably 26 or more, and even more preferably 27 or more. Have.

<Water absorption test>
Weigh about 0.3 g (sample weight: h) of the test material into a 5 x 10 cm size tea bag made of nylon cloth with an opening of 57 μm, seal it, and measure the weight (weight before immersion:). i). After immersing in 1,000 mL of physiological saline (0.9 mass% sodium chloride aqueous solution) for 60 minutes, the mixture is vertically suspended and drained for 15 minutes. The weight after draining (weight after immersion: j) is measured, and the water absorption ratio is calculated by the following formula.

Water absorption ratio = (j-i) / h

The composite material according to the present invention may be used alone or in combination with other materials. Other materials are not particularly limited, but are, for example, alkyl cellulose derivatives such as CMC, cross-linked polyacrylic acid partially neutralized products, hydrolyzates of starch-acrylic acid graft polymers, and vinyl acetate-acrylic acid ester copolymer weights. Examples thereof include coalesced saponates, acrylonitrile copolymers or hydrolysates of acrylamide copolymers or crosslinked products thereof, and other water absorbing materials such as crosslinked polymers of cationic monomers (acrylamide, ethyleneimine, etc.).

The composite material according to the present invention may be used alone or in combination with other materials as described above as a water-absorbing composition intended to exhibit water-absorbing functionality. In this case, the composite material is preferably contained in the water-absorbing composition in an amount of 1 to 100% by mass, more preferably 10 to 100% by mass. When the content is in the above range, the absorption functionality of the composite material can be effectively exhibited. Specifically, the absorption functionality of the water absorption composition thus prepared can be evaluated, for example, by a water absorption test based on JIS K 7223 described above.

The composite material according to the present invention includes paper diapers, sanitary napkins, light incontinence pads, wound dressings, food freshness preservatives, medical equipment, soil conditioners for civil engineering, artificial snow, seed coating agents, water retention agents for plant cultivation, etc. It is suitably used as a constituent material for various water-absorbing functional products.

The details of the present invention will be described below with reference to examples, but the technical scope of the present invention is not limited to the following examples. In the following, when simply described as%, it means mass%.

[Test Example 1] (Comparison by the amount of layered silicate added)
16 g (dry weight) of carboxymethylated starch (carboxymethyl group substitution degree 0.4) was weighed in a 500 mL glass tall beaker, and distilled water was added to prepare 160 g of a 10% paste solution. 39.5 g of a 10% aqueous sodium hydroxide solution was added to the paste solution, and the mixture was stirred with a homogenizer (Hiscotron NS-50S manufactured by Nichion Medical Science Instruments Mfg. Co., Ltd.) at 20,000 rpm for 1 minute.

Layered silicate (SIGMA-ALDRICH) was added to each ratio shown in Table 1 (as the ratio of the mass of the layered silicate added to 100 parts by mass of the dry weight of starch, no addition, 1% to starch, 3%, 5%, 10%, 20%, 30%) was added, and the layered silicate was dispersed by stirring for 1 minute in the same homogenization treatment as described above. Then, epichlorohydrin was added as a ratio of the mass of the added epichlorohydrin to 100 parts by mass of the dry weight of the starch to 30% of the starch, and distilled water was further added until the total amount reached 400 g. After stirring for 1 minute in the same homogenization treatment, the cross-linking treatment was performed by allowing the mixture to stand in a water bath at 32 ° C. for 24 hours. After the cross-linking treatment, the obtained gel was transferred to a 2,000 mL stainless steel beaker, 1,600 mL of ethanol was added, and the mixture was stirred with a stirring rod until it became cloudy, and the pH was adjusted to about 7.5 with acetic acid. After allowing the solution to stand and decanting, 800 mL of ethanol was added to the precipitate again, and the precipitate was pulverized by stirring for about 1 minute using a homogenizer. The pulverized precipitate was suction filtered, and the obtained precipitate was transferred to a 500 mL glass beaker and dried in a vacuum dryer at 40 ° C. overnight. After drying, the obtained powder was sieved, passed through a mesh of 16 mesh, and those that turned on the mesh of 60 mesh were collected to obtain water absorbing materials 1 to 7.

When the dispersion time of the layered silicate used in this test example in water was measured by the measurement test described below, it was dispersed in water in 14 seconds, and the layered silicate was not suspended on the water surface. Became.

<Measurement test of dispersion time of layered silicate>
The time required for dispersion in water is measured under the following condition (A).
Condition (A): 100 mL of water at 25 ° C. is put in a 200 mL beaker, a stirrer (width 5 mm × height 5 mm × total length 45 mm) is further put, and this is stirred at 300 rpm, and 5.0 g of layered silicate is added. Is added.

The water absorption materials 1 to 7 obtained were subjected to the water absorption test described below.

<Water absorption test>
The test was conducted in accordance with JIS K 7223. About 0.3 g of water absorbing material (sample weight: h) was weighed on a 5 x 10 cm size tea bag made of nylon cloth with an opening of 57 μm, sealed, and then weighed (weight before immersion:). i). After immersing in 1,000 mL of physiological saline (0.9 mass% sodium chloride aqueous solution) for 60 minutes, the mixture was vertically suspended and drained for 15 minutes. The weight after draining (weight after immersion: j) was measured, and the water absorption ratio was calculated by the following formula.

Water absorption ratio = (j-i) / h

In addition, the workability of the obtained water absorbing materials 1 to 7 at the time of preparation was evaluated according to the criteria described below.

<Workability evaluation>
Considering the handleability in the dehydration step at the time of preparing the water-absorbent material, the workability of the dehydration work at the time of preparing various water-absorbent materials was evaluated on a 6-point scale of 1 to 6. Specifically, in the dehydration step with ethanol after the cross-linking treatment, the easier it is to powder, the higher the evaluation score, and the more difficult it becomes to form a rice cake, the lower the evaluation score. Aggregated.

Table 1 shows the results of the water absorption test and workability evaluation.

As shown in Table 1, all of the water-absorbing materials 2 to 7 in which the layered silicate was dispersed were superior in terms of water-absorbing performance as compared with the water-absorbing material 1 to which the layered silicate was not added. In particular, the water-absorbing materials 3 to 5 in which 3 to 10% by mass of layered silicate was dispersed with respect to the dry weight of starch showed remarkable water-absorbing performance. Further, the water absorbing materials 4 to 7 in which 5 to 30% by mass of the layered silicate was dispersed with respect to the dry weight of the starch had good dehydration workability.

[Test Example 2] (Comparison by type of raw material biomass material)
Same as the water absorbing material 5 of Test Example 1 except that hydroxypropylated oxidized starch (EXTRAFIL802 manufactured by EIAMHENG) or carboxymethyl cellulose (CMC) (cellogen F-SA manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was used instead of carboxymethylated starch. The water absorbing materials 8 to 9 were obtained.

The obtained water absorbing materials 8 to 9 were subjected to a water absorption test and workability evaluation in the same manner as in Test Example 1. The results are shown in Table 2.

As shown in Table 2, the water-absorbing material 8 using hydroxypropylated oxidized starch instead of carboxymethylated starch was significantly inferior in water absorption ratio to the water-absorbing material 5 using carboxymethylated starch. Further, the water-absorbing material 9 using carboxymethyl cellulose (CMC) changed to pulp when dehydrated with ethanol after cross-linking, and could not be sufficiently pulverized, making it impossible to prepare the water-absorbing material itself.

[Test Example 3] (Comparison of presence / absence of cross-linking)
A water absorbing material 10 was obtained by operating in the same manner as the water absorbing material 5 of Test Example 1 except that the carboxymethylated starch was not crosslinked with epichlorohydrin.

The obtained water absorbing material 10 was subjected to a water absorption test and workability evaluation in the same manner as in Test Example 1. The results are shown in Table 3.

As shown in Table 3, the water-absorbing material 10 which was not subjected to the cross-linking treatment showed substantially the same water-absorbing performance as the water-absorbing material 5 which was subjected to the cross-linking treatment. However, since the water absorbing material 10 had a significantly lower gel strength than the water absorbing material 5, the water absorbing material 5 subjected to the cross-linking treatment was preferable in consideration of its practicality as a water absorbing material.

[Test Example 4] (Comparison of layered silicates having different dispersion times)
The same procedure as for the water absorbing material 5 of Test Example 1 was carried out except that various layered silicates (SIGMA-ALDRICH) having different dispersibility in water were used to obtain water absorbing materials 11 to 13. The dispersion time of each layered silicate in water measured under the above condition (A) was as shown in Table 4.

The obtained water absorbing materials 11 to 13 were subjected to a water absorption test and workability evaluation in the same manner as in Test Example 1. The results are shown in Table 4.

As shown in Table 4, the water-absorbing materials 5, 11 and 12 using the layered silicate, which take less than 900 seconds to disperse in water, are particularly excellent in water-absorbing performance, and are particularly excellent in water-absorbing performance at the time of preparation. The workability in the dehydration process was also good. On the other hand, the layered silicate used for the water absorbing material 13 floats on the water surface even after stirring for 900 seconds and does not completely disperse. The workability in the dehydration step was inferior to that of the water absorbing materials 5, 11 and 12.

[Test Example 5] (Comparison by degree of carboxymethyl group substitution)
The same procedure as for the water absorbing material 5 of Test Example 1 was carried out except that the carboxymethylated starch having various degrees of carboxymethyl group substitution shown in Table 5 was used to obtain water absorbing materials 14 to 18.

The obtained water absorbing materials 14 to 18 were subjected to a water absorption test and workability evaluation in the same manner as in Test Example 1. The results are shown in Table 5.

As shown in Table 5, the water-absorbing materials 16, 5, and 17 using the carboxymethylated starch having a degree of substitution of 0.2 to 0.8 were particularly excellent in water absorption performance.

[Test Example 6] (Comparison based on homogenization conditions)
Layered Kay prepared by adding an aqueous sodium hydroxide solution to the paste of carboxymethylated starch and then stirring with a homogenizer for 2 minutes, and stirring the layered silicate with 100 g of distilled water in advance with a homogenizer for 1 minute. The acid salt dispersion was used, the stirring treatment with a homogenizer after adding the layered silicate to the carboxymethylated starch paste was set for 2 minutes, and then a homomixer (TK HOMOXER manufactured by Primix) was further used. The operation was carried out in the same manner as in the water absorbing material 5 and the water absorbing material 7 of Test Example 1 except that the mixture was stirred at 20,000 rpm for 2 minutes using MARK II) to obtain the water absorbing material 19 and the water absorbing material 20, respectively.

In order to confirm the dispersed state of the layered silicate in each water absorbing material, it was observed with a scanning electron microscope (FIGS. 1 to 4). Further, the layered silicate used and the water-absorbing material (water-absorbing material 1) to which the layered silicate of Test Example 1 was not added were also observed with a scanning electron microscope (FIGS. 5 and 6).

Table 6 shows the results of the water absorption test and workability evaluation of the water absorbing materials 19 to 20 in the same manner as in Example 1.

As a result, as seen in FIGS. 1 and 3, in the water absorbing material 5 and the water absorbing material 7, agglomerates having a layered structure of the layered silicate as seen in FIG. 5 remain and are observed. It was. From this, it was confirmed that the layered silicate was present in the matrix of the carboxymethylated starch on a microscale maintaining the layered structure and dispersed in the form of microscale aggregates. On the other hand, as seen in FIGS. 2 and 4, the water-absorbing material 19 and the water-absorbing material 20 subjected to the homogenization treatment under stronger conditions provided a layered structure of the layered silicate as shown in FIG. No aggregates were observed. As a result, it was considered that the layered structure of the layered silicate was exfoliated and dispersed in the carboxymethylated starch on a finer nanoscale.

Further, as shown in Table 6, the water-absorbing materials 19 and 20 in which the layered silicates are dispersed on the nanoscale are inferior in water absorption performance to the water-absorbing materials 5 and 7 in which the layered silicates are dispersed on the microscale. there were.

Claims (12)

A water-absorbent composite material in which layered silicates made of clay minerals are dispersed in the form of microscale aggregates in a matrix made of crosslinked products of carboxymethylated starch. The composite material according to claim 1, wherein the carboxymethylated starch has a degree of carboxymethyl group substitution of 0.1 to 1.0. The composite material according to claim 1 or 2, wherein the layered silicate composed of the clay mineral takes less than 900 seconds to disperse in water under the following condition (A).
Condition (A): 100 mL of water at 25 ° C. is placed in a 200 mL beaker, a stirrer (width 5 mm × height 5 mm × total length 45 mm) is further added, and this is stirred at 300 rpm to form a layered silicic acid composed of clay minerals. Add 5.0 g of salt. The composite material according to any one of claims 1 to 3 , wherein the layered silicate composed of the clay mineral is dispersed in a ratio of 1 to 30 parts by mass with respect to 100 parts by mass of the carboxymethylated starch. A water-absorbing composition containing the composite material according to any one of claims 1 to 4 as an active ingredient having water-absorbing functionality. A water-absorbing functional product containing the composite material according to any one of claims 1 to 4 as a constituent material. A layered silicate composed of carboxymethylated starch and a clay mineral is mixed and homogenized to the extent that the layered silicate composed of the clay mineral is dispersed in the matrix of the carboxymethylated starch in the form of microscale aggregates. , The step of dispersing the layered silicate composed of the clay mineral in the matrix of the carboxymethylated starch, and the layered silicate composed of the carboxymethylated starch and the clay mineral are further mixed with a cross-linking agent for cross-linking. A method for producing a water-absorbent composite material, which comprises a step of treating. The method for producing a composite material according to claim 7 , wherein the layered silicate composed of the clay mineral is added at a ratio of 1 to 30 parts by mass with respect to 100 parts by mass of the carboxymethylated starch. The method for producing a composite material according to claim 7 or 8 , wherein the carboxymethylated starch has a carboxymethyl group substitution degree of 0.1 to 1.0. The composite material according to any one of claims 7 to 9 , wherein the layered silicate composed of the clay mineral takes less than 900 seconds to disperse in water under the following condition (A). Manufacturing method.
Condition (A): 100 mL of water at 25 ° C. is placed in a 200 mL beaker, a stirrer (width 5 mm × height 5 mm × total length 45 mm) is further added, and this is stirred at 300 rpm to form a layered silicic acid composed of clay minerals. Add 5.0 g of salt. A method for producing a water-absorbing composition, wherein the composite material obtained by the production method according to any one of claims 7 to 10 is contained as an active ingredient of water-absorbing functionality. A method for producing a water-absorbing functional product, which uses the composite material obtained by the production method according to any one of claims 7 to 10 as a constituent material.

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