JPH08218065A - Soil-improving material for preventing salt damage and improvement of soil with the same - Google Patents

Abstract

PURPOSE: To provide a soil-improving material comprising a hydrophilic crosslinked polymer whose swollen volume is changed in response to the change in the concentration of an electrolyte, capable of preventing the accumulation of salt-containing underground water on the surface of the ground, and capable of rapidly allowing water flown in soil to permeate into the underground. CONSTITUTION: This material comprises a hydrophilic crosslinked polymer capable of swell-absorbing an electrolyte aqueous solution having a higher concentration than a critical salt concentration existing in a concentration range of 0.01-2wt.% (the polymer preferably exhibits an absorption ratio of >=10 times for electrolyte aqueous solutions having concentrations of >=1wt.% and also an absorption ratio of <=25 times for the aqueous solutions having concentrations of <=0.01wt.%), and does not swell in a lower concentration range. The polymer is preferably a polymer containing one or more of sulfobetaine type functional group-having vinylic monomers of formulas I-IV [R1 is H, methyl; RCONSTITUTION is 0-6C (hydroxy)alkylene; R3 , R4 are methyl, ethyl; R5 is 1-10C (hydroxy)alkylene; R6 is 1-6C (hydroxy)alkylene; X is ester, amide, (substituted)phenyl] as essential components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soil improvement material for preventing salt damage, which comprises a hydrophilic cross-linked polymer, the swelling volume of which is changed according to the increase or decrease of the electrolyte concentration, and a soil improvement method using the material. The hydrophilic crosslinked polymer of the present invention acts extremely effectively in preventing salt damage and maintaining good soil.

[0002]

2. Description of the Related Art In recent years, desertification of arid areas or green areas has become a big problem on a global scale. As one of the main causes of desertification, the water level of groundwater containing salts rises, the accumulation of salts on the soil surface due to repeated evaporation of water on the soil surface, and the reconstitution of the salt increases the concentration of groundwater salts. The formation of salt soil that is unsuitable for plant growth. Such salt accumulation causes so-called salt damage such as death of crops. In addition,
The electrolyte mentioned here refers to various ionic species widely dissolved in groundwater, and it is known that the influence of sodium ion concentration is large in salt damage.

Methods for preventing such desertification or salt damage have been actively studied. For example, there is a method of arranging an impermeable layer between the groundwater surface and the soil surface to block the rise of groundwater. As the water-blocking material, gravel, super absorbent material, etc. are used. However, when gravel is used as the water-blocking material, the gap between the gravel suppresses the rise of groundwater, but has little effect on salt accumulation. Further, when the superabsorbent material is buried underground, an impermeable layer is formed by the absorbed and swollen superabsorbent material, which prevents the groundwater from rising and prevents the accumulation of salts.

However, when a large amount of water flows into the soil due to rainfall or the like, the water cannot penetrate into the ground due to the impermeable layer, and the drainage deteriorates, so that good soil cannot be maintained. . In addition, the water-absorbing performance of ordinary superabsorbent resins decreases significantly as the salt concentration increases. for that reason,
When groundwater has a high salt concentration, the resin does not swell sufficiently,
A large amount of resin is required to form a good impermeable layer, which is disadvantageous in terms of cost.

There is also a method of burying a porous pipe in the ground and discharging salt-containing groundwater to a drainage channel to prevent salt damage. However, in this method, in order to prevent salt damage, it is necessary to supply irrigation water as needed to prevent accumulation of salt-containing water on the soil surface, which is extremely disadvantageous in terms of cost. If the soil level is lower than the sea level in coastal areas,
Unless it is forcibly discharged using a pump or the like, it is virtually impossible to drain water by this method.

[0006]

In order to overcome the above-mentioned problems, the present inventors have earnestly studied about a method of preventing salt damage and maintaining good soil, and as a result, arrived at the present invention. It is a thing. Providing a soil improvement material that can effectively prevent salt damage and still maintain good soil without impairing drainage and a soil improvement method using the material can reduce work labor in irrigated land and cost. Not only does it bring about a significant reduction, but it also provides an effective means of preventing desertification due to salt accumulation in drylands.

[0007]

The object of the present invention is to absorb and swell a high-concentration electrolyte aqueous solution with a critical salt concentration existing in the range of 0.01 to 2% by weight as a boundary. And, it can be achieved by a soil damage-preventing soil improving material comprising a hydrophilic cross-linked polymer having a characteristic of not swelling in a low-concentration aqueous electrolyte solution and pure water, and the soil improving material is embedded in a sandy soil. Therefore, it is possible to prevent salt damage and maintain good soil by a soil improvement method that forms a gel layer that allows self-control of water permeability / impermeable depending on the electrolyte concentration of groundwater or inflow water to soil. .

The present invention will be described in detail below. First, the hydrophilic cross-linked polymer of the present invention is a hydrophilic polymer having a three-dimensional cross-linking structure between the polymers, absorbs and swells with respect to an electrolyte aqueous solution above the upper limit of the specific concentration range, and specific It has the property of not swelling in an aqueous electrolyte solution or pure water below the lower limit of the concentration range. The polymer employed in the present invention is not particularly limited as long as it is a polymer having such properties, specifically, a cross-linked sulfobetaine polymer is known as a salt water-absorbing polymer, Japanese Patent Application 5-
223532 has an "electrolyte aqueous solution absorbing zwitterionic polymer" using a cross-linked product of this sulfobetaine polymer. In the present invention, a crosslinked sulfobetaine polymer can be used particularly preferably. Here, the sulfobetaine polymer is a zwitterionic polyelectrolyte having both a quaternary ammonium group and a sulfonic acid group in the same side chain group in the polymer. Forms an inner salt.

[0009] Ordinary superabsorbent resins, especially superabsorbent resins mainly composed of a cross-linked polyacrylate, show high absorbability with respect to pure water or a low-concentration electrolyte aqueous solution, but with high concentration. The absorbability of an electrolyte aqueous solution or an electrolyte aqueous solution containing polyvalent ions is significantly reduced. This is because the polymer chain contracts due to the electrostatic shielding effect due to the aggregation of counterions with respect to the charged groups in the polymer chain, or the ionic crosslinking due to polyvalent ions.

On the other hand, the sulfobetaine polymer, which is one of the amphoteric polymer electrolytes, has the property of not being dissolved in pure water, but being soluble in an electrolyte aqueous solution having a critical salt concentration or higher. Therefore, the crosslinked product of the sulfobetaine polymer does not swell in pure water or an electrolyte aqueous solution having a critical salt concentration or less, but swells in an electrolyte aqueous solution having a critical salt concentration or more. Here, the critical salt concentration, which is the boundary between swelling and non-swelling, shows different values depending on the difference in molecular structure, particularly the difference in the degree of hydrophilicity. Therefore, by changing the molecular structure, it becomes possible to swell or non-swell with a salt concentration according to the purpose of use, and it is possible to control the concentration of the salt aqueous solution that permeates the soil. That is, in order to prevent salt damage to crops and plants, the critical salt concentration may be set in consideration of the electrolyte concentration of groundwater or the electrolyte concentration of irrigation water or inflow water to soil due to rainfall or the like. However, the critical salt concentration must be set lower than the electrolyte concentration of groundwater. Specifically, the critical salt concentration is set within the range of 0.01 to 2% by weight, and more preferably within the range of 0.05 to 1% by weight. The change from the non-swelling state to the swelling state or the change from the swelling state to the non-swelling state due to the change in the salt concentration is not intermittent but continuous. Therefore, the critical salt concentration in the present invention means the concentration at which the polymer starts to swell when the salt concentration is increased, and the swelling volume changes slightly immediately before and after the concentration.

The absorption capacity of the hydrophilic crosslinked polymer is 1% by weight.
In order to realize the control of water permeation / impermeable to changes in the salt concentration of groundwater, it is 10 times or more for the above electrolyte aqueous solution and 5 times or less for the 0.01% by weight or less electrolyte aqueous solution. desirable. The term "absorption capacity" as used herein means the weight multiple of the absorbed aqueous medium per unit weight of the dried hydrophilic crosslinked polymer.

The crosslinked sulfobetaine polymer is generally obtained by radical copolymerization of the amphoteric vinyl monomer (A) having a sulfobetaine structure and the crosslinkable monomer (B). There are both cases of forming a crosslinked structure during polymerization and cases of postcrosslinking after polymerization, and there is no particular limitation.

In the present invention, a hydrophilic crosslinked polymer is constituted.
As the amphoteric vinyl monomer (A) to be used,
Chemical formula 5 to chemical formula 8 (however, R₁Is a hydrogen atom or methyl
Group, R ₂Is a straight-chain or branched chain having 0 to 6 carbon atoms.
Ruylene group or hydroxyalkylene group, R₃as well as
R_FourAre each independently a methyl group or an ethyl group, R_FiveIs
A straight-chain or branched alkylene group having 1 to 6 carbon atoms
Or hydroxyalkylene group, R₆Is from 1 carbon
6 straight chain or branched alkylene group or hydr
Roxyalkylene group, X is ester group or amide group
Or a substituted or unsubstituted phenylene group, Y is -O- or
Or -NH-. In addition, in the pyridine ring of Chemical formula 7 and Chemical formula 8
To the substituent (R₁And the position of substitution of the polymerizable substituent)
A monomer represented by (1) may be preferably used.

[0014]

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[0015]

[Chemical 6]

[0016]

[Chemical 7]

[0017]

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The zwitterionic vinyl-based monomer (A) is generally known as a sulfobetaine type monomer, and there are many reports on the solution properties of the polymer. For example, P
OLYMER, 1978, Vol. 19, 1157. ,
POLYMER, 1984, Vol. 25, 254. There are documents such as. In many cases, sulfobetaine-type monomers are synthesized by reacting the corresponding tertiary amine-type monomer with sultones. For example, by reacting dimethylaminoethyl methacrylate and 1,3-propane sultone in dimethylformamide at 30 ° C. for 3 days,
N, N-dimethyl-N- (2-methacryloyloxyethyl) -N- (3-sulfopropyl) ammonium inner salt can be synthesized. Further, a tertiary amine type monomer is reacted with a condensate of an aldehyde or ketone and acidic sodium sulfite, or a reaction between a tertiary amine type monomer and a haloalkanesulfonic acid, and a quaternary ammonium type having a hydroxyl group. The amphoteric vinyl monomer (A) of the present invention can also be synthesized by a sulfuric acid esterification reaction of the monomer. In addition, 1-vinyl-3- (3-sulfopropyl) imidazolium inner salt, 1-vinyl-2-methyl-3- (3-sulfopropyl) imidazolium inner salt,
1-vinyl-2-methyl-3- (4-sulfobutyl) imidazolium inner salt, 1-vinyl-3- (2-sulfobenzyl) imidazolium inner salt, 2-vinyl-1- (3
-Sulfopropyl) pyridinium inner salt, 4-vinyl-
1- (3-sulfopropyl) pyridinium inner salt, N,
N-diethyl-N- (2-methacryloyloxyethyl) -N- (3-sulfopropyl) ammonium inner salt,
3- {3- [2- (methacryloyloxy) ethoxycarbonyl] pyridinio} propanesulfonate inner salt,
N, N-dimethyl-N- (2-acryloyloxyethyl) -N- (3-sulfopropyl) ammonium inner salt, N, N-dimethyl-N- (3-acrylamidopropyl) -N- (3-sulfopropyl) ) Ammonium inner salt, N, N-dimethyl-N- (3-methacrylamidopropyl) -N- (3-sulfopropyl) ammonium inner salt, N, N-dimethyl-N- (3-acrylamidopropyl) -N- (2-Sulfoethyl) ammonium inner salt, N, N-dimethyl-N- (3-methacrylamidopropyl) -N- (2-sulfoethyl) ammonium inner salt, N, N-dimethyl-N- (3-acrylamidopropyl) -N- (4-sulfobutyl) ammonium inner salt, N, N-dimethyl-N- (3-methacrylamidopropyl) -N- (4- Ruhobuchiru) sulfobetaine monomers such as ammonium inner salt is, can be suitably used as ampholytic vinyl monomer in the present invention (A).

The present invention also includes a polymer in which a zwitterionic functional group is introduced into the polymer by a polymer reaction with the polymer. That is, a method of introducing a zwitterionic functional group by a polymer reaction between a polymer having a tertiary amino group and a sultone, or a method of introducing a zwitterionic functional group by reacting a polymer with a compound having a zwitterionic functional group, The hydrophilic crosslinked polymer of the present invention can also be obtained by adopting a method of graft-polymerizing the amphoteric vinyl-based monomer (A) into the polymer.

The composition charged at the time of polymerization of the amphoteric vinyl monomer (A) is preferably in the range of 70 to 99.99 mol%. When the charged composition of the amphoteric vinyl monomer (A) is less than 70 mol%, the swelling volume change of the hydrophilic cross-linked polymer with respect to the electrolyte concentration change may not be sufficiently expressed, which is not preferable. Further, when the charged composition of the amphoteric vinyl-based monomer (A) is more than 99.99 mol%, the composition of the crosslinkable monomer (B) becomes low and the crosslink density of the hydrophilic crosslinked polymer decreases. Then, the polymer becomes a solution or a semi-solution when swollen, which is not preferable. However, when the zwitterionic vinyl-based monomer (A) has self-crosslinking properties, the crosslinkable monomer (B) is not always necessary, and the zwitterionic vinyl-based monomer (A) is 100 mol%
It is within the scope of the present invention when the composition is prepared as follows. Also,
In the present invention, the hydrophilic cross-linked polymer is copolymerized with other vinyl-based monomer (C) according to the purpose in addition to the zwitterionic vinyl-based monomer (A) and the cross-linkable monomer (B). be able to. That is, for the purpose of improving the physical properties such as strength of the hydrophilic cross-linked polymer, the radical-polymerizable vinyl monomer can be appropriately selected and used.

In order for the water absorbing resin to absorb the aqueous medium and maintain the swollen state without being dissolved in the medium, it is necessary to introduce a crosslinked structure into the polymer by covalent bond, electrostatic bond, hydrogen bond or the like. Is. In the present invention, in order to introduce a crosslinked structure into the hydrophilic crosslinked polymer, a polyfunctional radically polymerizable monomer such as a divinyl compound can be used as the crosslinkable monomer (B). As the polyfunctional radically polymerizable monomer, bisacrylamides, di (meth) acrylic acid esters, diallyl compounds and the like can be preferably used in the present invention.

Examples of such polyfunctional radically polymerizable monomers include N, N-diallylmethacrylamide, diallylamine, N, N-bisacrylamidoacetic acid, N,
N'-bisacrylamide acetic acid methyl ester, N,
N'-methylenebisacrylamide, N, N-benzylidenebisacrylamide, diallyl succinate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, neopentyl glycol di Acrylate, 1,6-hexanediol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,
3-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, glycerin dimethacrylate, neopentyl glycol dimethacrylate, diallyl acrylamide, and the like, which are preferably used in the present invention can do.

Another method of introducing a crosslinked structure into the hydrophilic crosslinked polymer is a crosslinking treatment of a monomer having a functional group capable of being crosslinked after polymerization. When a crosslinkable monomer is used as the crosslinkable monomer (B) in the present invention, a compound that chemically bonds with the monomer (B) to form a crosslinked structure may be used. This compound is referred to as a crosslinking aid. When a monomer that self-crosslinks by heat or the like is used, a crosslinking aid is not always necessary. Further, the crosslinkable monomer (B) may be the same monomer as the other vinyl-based monomer (C), in which case the crosslinkable monomer (B) is the other vinyl-based monomer. It is regarded as a monomer component that contributed to the crosslinked structure in the monomer (C) after the crosslinking treatment.
As the crosslinkable monomer, a carboxyl group, an amide group, a nitrile group, a methylol group, a glycidyl group, a hydroxyl group, a monomer containing an imino group, and an acid anhydride monomer are preferably used in the present invention. Can be used. For example, acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide, acrylonitrile, N-
Methylol acrylamide, glycidyl acrylate,
Examples thereof include glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylamide, hydroxypropyl acrylate, hydroxypropyl methacrylate, and iminol methacrylate.

As the crosslinking aid, for example, when the crosslinkable monomer (B) has a carboxyl group, it reacts with a carboxyl group such as a hydroxyl group, an epoxy group, an amino group and a methylol group to form a chemical bond. Possible polyfunctional compounds having two or more functional groups, for example, ethylene glycol, propylene glycol, glycerin, glycidyl alcohol, diglycidyl ether, glycerin triglycidyl ether, ethylene glycol diglycidyl ether,
Ethanolamine, ethylenediamine, propylenediamine, polyethylene glycol, polyvinyl alcohol, trimethylolmelamine, pentaerythritol,
Examples include trimethylolpropane, polyethyleneimine, urea and the like. Also, cross-linking with formaldehyde,
Crosslinking with polyvalent metal ions is also possible.

When the crosslinkable monomer (B) has a hydroxyl group, two functional groups capable of forming a chemical bond by reacting with a hydroxyl group such as a carboxyl group, an acid anhydride, an aldehyde group and an isocyanate group. A polyfunctional compound having the above, for example,
Malonic acid, succinic acid, glutaric acid, malic acid, propane-1,2,3-tricarboxylic acid and their acid anhydrides,
Glyoxal, glutaraldehyde, hexamethylene diisocyanate, cyclohexane diisocyanate and the like can be mentioned as the crosslinking aid.

Further, when the hydroxyl groups are the same or the hydroxyl groups form a crosslinked structure by hydrogen bond with the carboxyl group, it is not necessary to use a crosslinking aid. For example, when vinyl acetate or (meth) acrylic acid ester is used as the other vinyl-based monomer (C) and a hydroxyl group or a carboxyl group is generated by hydrolysis, a microcrystalline structure by hydrogen bond is used as a cross-linking point. In particular, it is possible to absorb water and maintain a swollen state without introducing a cross-linking structure by a covalent bond, and such a method for introducing a cross-linking structure can also be adopted in the present invention.

Further, using a dehydration catalyst for carboxyl groups, carboxyl groups and hydroxyl groups, or hydroxyl groups,
The crosslinked structure can also be introduced by performing crosslinking by forming an acid anhydride, crosslinking by an ester bond, or crosslinking by an ether bond.

When the crosslinkable monomer (B) has a nitrile group, a polyfunctional compound having two or more functional groups capable of reacting with a nitrile group such as an amino group to form a chemical bond, for example, a polyfunctional compound. , Hydrazine, ethylenediamine, propylenediamine, butylenediamine, pentamethylenediamine, hexamethylenediamine, aminated polyethylene glycol at both ends and the like can be mentioned as the crosslinking aid.

The composition of the cross-linkable monomer (B) at the time of polymerization is preferably 0.01 because the hydrophilic cross-linked polymer which has absorbed the aqueous electrolyte solution does not dissolve and has no fluidity.
It is desirable that the content is mol% or more. However, as described above, when the amphoteric vinyl monomer (A) has self-crosslinking property, the crosslinkable monomer (B) is not always necessary. Further, since the swelling volume decreases when the composition of the crosslinkable monomer (B) in the polymer increases, the crosslinkable monomer (B) is preferably 0.5 mol% or less. However, when the other vinyl-based monomer (C) and the crosslinkable monomer (B) are the same monomer, the charged composition of the monomer (C) is followed.

The other vinyl-based monomer (C) is preferably selected from water-soluble monomers having a hydrophilic functional group in order to enhance the ability of the hydrophilic crosslinked polymer to absorb an aqueous electrolyte solution. . Examples of the hydrophilic functional group include a carboxyl group, an amide group, a hydroxyl group, a sulfonic acid group, a phosphoric acid group, an amino group, a quaternary ammonium group, and a polyethylene glycol group. Further, a monomer capable of easily introducing a hydrophilic functional group by hydrolysis or the like can also be used. As such a monomer having a hydrophilic functional group, and as an introducible monomer, for example, acrylic acid and its alkali salt, methacrylic acid and its alkali salt, itaconic acid, acrylonitrile, acrylic acid alkyl ester, methacrylic acid alkyl ester, Acrylamide, methacrylamide, N-substituted alkyl acrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxopropyl methacrylate, hydroxyethyl acrylamide, vinyl acetate, vinyl sulfonic acid and its alkali salt, methallyl sulfonic acid and its alkali salt , Styrene sulfonic acid and its salt, 2-acrylamido-2-methylpropane sulfonic acid and its alkali salt, 2-methacryloyloxyethane sulfone And their alkali salts, mono (2-acryloyloxyethyl) acid phosphate, mono (2-methacryloyloxyethyl)
Acid phosphate, 3-methacrylamidopropyldimethylamine and its salt, 2-methacryloyloxyethyldimethylamine and its salt, 2-methacryloyloxyethyldiethylamine and its salt, 3-methacrylamidopropyltrimethylammonium chloride,
There are N-vinyl-2-pyrrolidone, polyethylene glycol methacrylate, polyethylene glycol acrylate and the like, and these monomers can be used alone or in combination of two or more kinds.

Further, a hydrophobic vinyl-based monomer may be used as the other vinyl-based monomer (C) for the purpose of improving the strength of the swollen gel or controlling the absorption capacity. As such a hydrophobic vinyl-based monomer,
Styrene, vinyl chloride, vinylidene chloride, vinyl acetate,
Examples thereof include methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylonitrile and the like.

The composition of the other vinyl-based monomer (C) at the time of polymerization is 0 mol% to 30 mol% in order to cause a change in the swelling volume of the hydrophilic crosslinked polymer with respect to the change in the concentration of the aqueous electrolyte solution. It is desirable to be within the range. In particular, when the other vinyl-based monomer (C) has high hydrophilicity, it is desirable that the composition charged at the time of polymerization is 5 mol% or less, and if it exceeds 5 mol%, the hydrophilic cross-linking weight is increased. This is not preferable because the coalescence may show a high degree of swelling even with pure water or a low-concentration electrolyte aqueous solution. However, as long as the swelling volume change of the hydrophilic crosslinked polymer is sufficiently exhibited, the charging composition of the other vinyl-based monomer (C) is not particularly limited.

The hydrophilic crosslinked polymer of the present invention may be prepared by any of the conventional radical polymerization methods. That is, any of bulk polymerization, aqueous precipitation polymerization, suspension polymerization, reversed-phase suspension polymerization, emulsion polymerization, and solution polymerization may be used, and depending on the purpose, the morphology of the resulting polymer is appropriately considered. Just select it. However, a polymerization system using water as a medium is generally preferable from the viewpoint of cost and environment. Examples of the method of generating radicals include a method using a radical polymerization catalyst, a method of irradiating radiation, an electron beam, and an ultraviolet ray. Examples of the radical polymerization catalyst include peroxides such as hydrogen peroxide, benzoyl peroxide, cumene hydroperoxide, azo compounds such as azobisisobutyronitrile and azobiscyanovaleric acid, and persulfates such as ammonium persulfate and potassium persulfate. Examples thereof include radical generators such as salts, and redox type initiators composed of a combination of these radical generators and a reducing agent such as sodium hydrogen sulfite and L-ascorbic acid. Examples of the polymerization medium include water, an aqueous electrolyte solution, methanol, acetone, dimethylformamide, and the like, which may be appropriately selected depending on the polymerization method. Examples of the form after the polymerization include a swollen body, a solution, a dispersion, and the like, and a drying operation or a post-crosslinking operation may be performed as necessary.

The soil damage-preventing soil-improving material comprising the hydrophilic cross-linked polymer is used as a dry powder or an aqueous solution of the hydrophilic cross-linked polymer alone, or is mixed with a non-woven fabric, a sandy medium or the like, and further a film. It can be used in any form, such as being processed into a fiber or the like and used. Thus, the soil improvement material for preventing salt damage of the present invention is embedded in sandy soil to form a water-absorbing gel layer capable of self-control of water permeability / impermeable according to the electrolyte concentration of groundwater or inflow water to the soil. By so doing, the soil improvement method of the present invention can be achieved. The reversible permeable / impermeable layer can be buried in a single layer or multiple layers under the surface of general sandy soil and at any depth depending on the purpose.

As a method for embedding a soil improving material for preventing salt damage in sandy soil, a sandy soil on the soil surface is dug up to a predetermined depth, and then a dry powder of a hydrophilic cross-linked polymer or water swelling of the powder is swelled. There is a method in which a body or an aqueous dispersion, or a mixture of a hydrophilic cross-linked polymer, a processed product such as a film or a fiber is surface-sprayed, and the sandy soil is filled again. Further, it can be generally formed by a method of extruding the water-swelling body or the water dispersion into sandy soil, for example, a pouring method. However, the present invention is not limited to these burying methods, for example, after injecting an aqueous solution of a hydrophilic polymer that is a precursor of the hydrophilic cross-linked polymer into the sandy soil, the cross-linking reaction. By a method of introducing a cross-linked structure, or alternatively, by injecting each monomer, which is a raw material constituting the hydrophilic cross-linked polymer, into sandy soil, a method of performing a polymerization and / or a cross-linking reaction, or the like, A gel layer of hydrophilic crosslinked polymer can be formed in the ground. Furthermore, it is also possible to embed various organic or inorganic porous or bulky substances such as perlite, vermiculite, peat moss and the like in the coexisting state, and the point is that the hydrophilic cross-linked polymer as described above in sandy soil. Any method can be adopted as long as a gel layer based on the soil improvement material can be formed.

The amount of the soil improving material comprising the hydrophilic cross-linked polymer of the present invention to be used depends on the required water-stopping ability and the degree of swelling of the hydrophilic cross-linked polymer, but is at least about 20 g / m ^{2 in} terms of solid content weight. The amount of water used is desirable, and if it is less than this, the water-stopping ability decreases, which is not desirable.
The use amount exceeding 1000 g / m ² is not preferable in terms of practicality.

[0037]

The hydrophilic cross-linked polymer of the present invention shows a large change in swelling volume in response to changes in the concentration of the electrolyte and exhibits a low swelling property in pure water or a low-concentration aqueous electrolyte solution, and a high-concentration electrolyte. The reason why it exhibits a high swelling property in an aqueous solution has not been fully clarified, but it can be considered as follows. That is, a homopolymer of a linear sulfobetaine-type monomer that is not crosslinked is not soluble in pure water and an aqueous electrolyte solution having a critical salt concentration less than, and since it is soluble in an electrolytic aqueous solution having a critical salt concentration or more, It is considered that even in a polymer having a crosslinked structure, a reversible change in swelling / contraction of the water-absorbent gel with respect to a change in salt concentration is exhibited with an electrolyte aqueous solution near the critical salt concentration as a boundary. Further, as the salt concentration increases from the critical salt concentration, the swollen volume of the water-absorbent gel also tends to continuously increase, and the higher the salt concentration, the higher the water blocking effect. As described above, the critical salt concentration strongly depends on the molecular structure of the hydrophilic crosslinked polymer, and the amphoteric vinyl monomer (A) to be used for the polymerization may be appropriately selected according to the purpose of use. it can.

[0038]

The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to these examples.

Example 1 In this example, as the zwitterionic vinyl monomer (A), N, N-dimethyl-N- (2-methacryloyloxyethyl) -N- (3-sulfopropyl) ammonium internal salt was used. (Hereinafter, abbreviated as DMPS), N, N-dimethyl-
N- (2-acryloyloxyethyl) -N- (3-sulfopropyl) ammonium inner salt (DAPS), N,
N-dimethyl-N- (3-acrylamidopropyl)-
N- (3-sulfopropyl) ammonium internal salt (DP
PS), N, N-dimethyl-N- (2-methacryloyloxyethyl) -N- (4-sulfobutyl) ammonium inner salt (DMBS) was added to POLYMER, 1977, V.
ol. 18,1058. In the same manner as in the method described in 1, the corresponding tertiary amine type monomer of each monomer and propane sultone or butane sultone in dimethylformamide,
It was synthesized by reacting at 30 ° C. for 5 days. As the crosslinkable monomer (B), N, N′-methylenebisacrylamide (MBAAm) was used. In addition, acrylic acid (AA) and acrylamide (AAm) were used as the other vinyl-based monomer (C).

A predetermined amount of the monomer mixture and ammonium persulfate (APS) as an initiator are dissolved in ion-exchanged water (total monomer concentration = 30% by weight), polymerized at 70 ° C. for 6 hours, dried and pulverized. Thus, a powdery hydrophilic cross-linked polymer was obtained. Further, a polymer not containing the amphoteric vinyl monomer (A) outside the scope of the present invention was also polymerized under the same conditions as above to obtain a polymer. The composition of the charged monomers of each polymer is shown in Table 1.

[0041]

[Table 1]

The absorption capacity of each of the obtained polymers for ion-exchanged water and aqueous electrolyte solution was measured by the following method. 0.5 g of each dried polymer was immersed in 500 ml of ion-exchanged water and various aqueous electrolyte solutions for 2 hours, filtered through a 200-mesh wire net, drained for 10 minutes, and then the weight of the polymer on the wire net absorbing the aqueous medium. Was measured, and the absorption capacity was defined as the number of grams of the aqueous medium absorbed per 1 g of the dried polymer. As the electrolyte aqueous solution, 0.01 wt% and 0.5 wt% and 1.0 wt% and 5.0 wt% NaCl aqueous solutions were used. Table 2 shows the results.

[0043]

[Table 2]

Polymers 1 to 3 are obtained by changing the composition of the crosslinkable monomer (B). Polymer 1 had a small charge composition of the crosslinkable monomer (B), and although it swelled in the aqueous electrolyte solution, it had many dissolved components and had a relatively low absorption capacity. Polymers 4 and 5 are copolymers of AA and AAm as the other vinyl-based monomer (C), and are added to pure water and an aqueous electrolyte solution, respectively.
The absorption capacity is slightly increased. Polymers 6 and 7 are copolymers of AN as the other vinyl-based monomer (C), and the absorption capacity is slightly lowered. However, by copolymerizing AN, the gel strength after swelling was stronger than other polymers. The polymers 8 to 10 are different in the type of the amphoteric vinyl-based monomer (A), and DMP
DAPS (polymer 8) and DPP, which are more hydrophilic than S
When S (polymer 9) is used, it exhibits a high absorption capacity even for a low-concentration aqueous electrolyte solution, and the absorption capacity is high as a whole. When DMBS (polymer 10) is used, it exhibits a relatively low absorption capacity for a low-concentration electrolyte aqueous solution, and also has a low absorption capacity as a whole. Polymers 11 and 12 are comparative examples AA and A
As a cross-linked polymer of Am, the polymer 11 has a high absorption capacity for pure water and a low-concentration electrolyte aqueous solution, but has an extremely low absorption capacity for a high-concentration electrolyte aqueous solution. Polymer 12 showed almost no change in absorption capacity with respect to changes in electrolyte concentration, and exhibited a low absorption capacity as a whole.

All the polymers 1 to 10 have an absorption capacity of 5 times or less for an aqueous electrolyte solution of 0.01% by weight or less, and an absorption capacity of 10 or more for an aqueous electrolyte solution of 1% by weight or more. It shows that the hydrophilic cross-linked polymer in the present invention has a property that it swells in high-concentration salt water and does not swell in low-concentration salt water.

Next, the water-stopping ability of each polymer for electrolyte-containing groundwater and the water permeability of pure water were evaluated. Diameter 1
A cylindrical column made of acrylic resin having a length of 0 cm and a length of 60 cm was packed with sand, and 0.5 g of the dry polymer (weight per unit area: about 64 g / m ² ) was applied to the cylindrical cross section at a depth of 25 cm from the ground surface. It was buried so as to be uniform. afterwards,
The column was installed in a constant temperature and humidity room at a temperature of 25 ° C. and a relative humidity of 50%, and a groundwater level of 35 cm below the ground surface was set. The groundwater used was a 1.0 wt% NaCl aqueous solution. A heat bulb is irradiated from a position 30 cm above the surface of the column to accelerate evaporation of water from the upper surface of the column, and after 5 days, 5c below the surface of the ground.
The salt concentration at the position of m was measured. The salt concentration was measured using a salt concentration meter manufactured by Asahi Life Science. still,
The groundwater level was always kept constant by supplementing with a 1.0 wt% NaCl aqueous solution. Also, when the polymer was not embedded as a blank, the salt concentration was measured in the same manner. The results are shown in Table 3.

Further, the water permeability to pure water is JIS A
The water permeability coefficient K (cm / sec) was evaluated in accordance with the water level change method of 1218 (soil water permeability test method). The water permeability coefficient K is expressed as -logK. The results are shown in Table 3.

[0048]

[Table 3]

It is understood that all of the polymers 1 to 10 of the present invention have an extremely low salt concentration at 5 cm below the ground surface and effectively prevent the accumulation of salts. On the other hand, the polymers 11 and 12 which are comparative examples show a high value which is not much different from the salt concentration of the blank, and it can be seen that it is not effective in preventing salt accumulation. Further, in order to express good water permeability, it is desirable that the water permeability coefficient (−logK) is 3 or less, and all the polymers of the present invention satisfy this condition and have sufficient water permeability. It can be said that On the other hand, the polymers 11 and 12, which are comparative examples, were poor in water permeability, and thus were extremely poor in drainage. As described above, it was confirmed that the soil improving material comprising the hydrophilic cross-linked polymer of the present invention can achieve both excellent salt accumulation preventive property and good drainage property at a high level.

[0050]

The hydrophilic cross-linked polymer of the present invention described above has the property that the swelling volume of the water-absorbent gel changes with changes in the concentration of the aqueous electrolyte solution. By burying the soil improvement material for sand in the sandy soil, accumulation of salt-containing groundwater on the soil surface can be prevented, and inflow water to the soil can be promptly infiltrated underground. Therefore, the soil damage-preventing soil improving material comprising the hydrophilic cross-linked polymer of the present invention is for helping good cultivation of agricultural crops in soil where salt damage is likely to occur, or for preventing desertification and restoring green spaces. It provides an effective measure and exerts an excellent effect for such applications.

Claims (5)

[Claims] 1. A high concentration electrolyte aqueous solution which absorbs and swells at a critical salt concentration existing within a concentration range of 0.01 to 2% by weight, and a low concentration electrolyte aqueous solution and pure water. A soil improving material for preventing salt damage, which comprises a hydrophilic cross-linked polymer and is characterized in that it does not swell. 2. The hydrophilic crosslinked polymer exhibits an absorption capacity of 10 times or more for an aqueous electrolyte solution of 1% by weight or more,
The soil improvement material for preventing salt damage according to claim 1, which exhibits an absorption capacity of 5 times or less for an aqueous electrolyte solution of 0.01% by weight or less. 3. The soil improving material for preventing salt damage according to claim 1, wherein the hydrophilic cross-linked polymer is a polymer containing an amphoteric vinyl monomer (A) as an essential component. . 4. The amphoteric vinyl monomer (A), which is an essential component of the hydrophilic crosslinked polymer, is a compound represented by Chemical Formula 1 to Chemical Formula 4 (wherein R ₁ is a hydrogen atom or a methyl group, and R ₂ is a carbon number). A linear or branched alkylene group or hydroxyalkylene group of 0 to 6, R ₃ and R ₄ are each independently a methyl group or an ethyl group, and R ₅ is a linear or branched group of 1 to 10 carbon atoms Is an alkylene group or a hydroxyalkylene group, R ₆ is a linear or branched alkylene group or a hydroxyalkylene group having 1 to 6 carbon atoms, X is an ester group or an amide group, or a substituted or unsubstituted phenylene group, and Y is Represents -O- or -NH-, wherein a substituent (R
₁ and a polymerizable substituent) may be selected at any position), and is selected from vinyl monomers having a sulfobetaine-type functional group. 2. A soil improving material for preventing salt damage according to. Embedded image Embedded image Embedded image [Chemical 4] 5. A soil improving material for preventing salt damage, which comprises the hydrophilic cross-linked polymer according to any one of claims 1 to 4, is embedded in a sandy soil, and the ground water or the influent concentration of inflow water into the soil is adjusted according to the concentration of the electrolyte. The method for improving soil is characterized by forming a gel layer capable of self-controlling water permeability / water impermeability.