JP7113449B2 - Adsorptive foam for adsorbing and removing substances and method for producing same - Google Patents

Description

The present invention relates to adsorbent foams used to reduce or remove substances such as cesium, iodine, thorium, or strontium and methods of making same.

The Great East Japan Earthquake that occurred in 2011 caused the Fukushima nuclear power plant to collapse, causing the problem of radioactive materials flowing into the environment. Among them, cesium-137 is the most problematic. Since cesium is water-soluble and dissolves in rainwater, groundwater, river water, etc., and diffuses, immediate decontamination is required.

A technique using zeolite is generally used as a technique for adsorbing/removing substances (for example, Patent Document 1). Here, if the target substance is a radioactive substance, it is not easy to replace it, so it is desirable to reduce the number of man-hours as much as possible. However, zeolite has low selectivity and takes in substances in the environment other than radioactive substances, resulting in clogging soon. Therefore, the removal efficiency is poor, and it is necessary to replace frequently.

Therefore, an invention using Prussian blue and its analogues as a material with high selectivity to cesium has been proposed (Patent Document 2). Prussian blue is the material that can adsorb cesium most selectively among existing materials, and is expected to be applied to decontamination activities for radioactive substances. However, there was a problem that it easily dissolves in water. Therefore, even if decontamination work is performed using adsorbents carrying these substances, Prussian blue is released into the environment, and the released Prussian blue adsorbs cesium, creating hot spots where cesium is concentrated. .

Patent Document 3 discloses an invention that improves the outflow of Prussian blue into the environment. In order to suppress the elution of Prussian blue into water, a composite (pseudo-complex) is formed with nanocellulose and supported on a hydrophilic substrate such as polyvinyl alcohol. According to this document, the resin used as the base material is selected in consideration of hydrophilicity, and the material is formed into a porous body in order to increase the adsorption efficiency of cesium. Considering the decontamination work in the environment, it is a very excellent technology that suppresses the elution of Prussian blue and improves the adsorption area by the hydrophilic base material and porous material.

However, the preparation of the polyvinyl alcohol aqueous solution, the addition of the core material that forms the voids of the porous body, and the washing process for removing the core material are many steps. This increases time and economic costs and makes mass production difficult. In addition, from the viewpoint of processing speed with the collected matter, it is preferable to form the collected matter into a thin sheet, but it has been difficult to produce such a sheet. Therefore, in reality, there is no choice but to deal with batch molding, and there is room for improvement in terms of processing speed and cost.

Japanese translation of PCT publication No. 2007-526110 JP 2013-057575 A JP 2016-155116 A

The present invention is intended to solve the above problems. That is, the first object of the present invention is to provide a method capable of efficiently producing the collected matter. A second object of the present invention is to produce a sheet-like collected material.

As a result of intensive research by the present inventors on the above problems, it became possible to simplify the process by preparing a raw material containing a nanocellulose composite to a predetermined composition, and in addition, to form an adsorptive foam into a sheet. found that it is possible, and completed the present invention.

That is, the present invention
A method for producing an adsorptive foam containing a composite (pseudo-complex) formed from an adsorbent capable of adsorbing and retaining a target substance and nanocellulose,
A composite (pseudo-complex) formed from an aqueous liquid dispersion medium, a water-dispersible resin, a cross-linking agent, a foaming agent, an adsorbent capable of adsorbing and retaining a target substance, and nanocellulose, A raw material preparation step of obtaining a liquid raw material mixture containing
a foaming step of mechanically foaming the liquid raw material mixture to obtain a foamed mixture;
a molding step of molding the foamed mixture into a sheet on a substrate;
a drying step of heating the sheet-shaped foamed mixture to evaporate the dispersion medium;
A method of making an absorbent foam comprising:

In the manufacturing method of the present invention, the liquid raw material mixture or the foamed mixture may be further blended with a cell stabilizer in at least part of the raw material preparation process, the foaming process, and the molding process.

In the production method of the present invention, at least part of the water-dispersible resin may be one or more selected from urethane emulsions, (meth)acrylic emulsions, and ethylene-vinyl acetate emulsions.

In the production method of the present invention, at least part of the foaming agent may be an anionic surfactant. At least part of the cell stabilizer may be a metal cation source for precipitating the anionic surfactant.

In the production method of the present invention, at least part of the foaming agent may be a sulfosuccinate having a hydrocarbon group with 12 to 18 carbon atoms and a degree of unsaturation of 2 or less.

In the production method of the present invention, at least part of the adsorbent capable of adsorbing and retaining the target substance may be Prussian blue.

In addition, the present invention
An adsorptive foam containing a complex (pseudo-complex) formed from an adsorbent capable of adsorbing and retaining a target substance and nanocellulose,
The absorbent foam has a thickness of 2 mm or less,
The size of the cells of the adsorptive foam is 20 to 250 μm,
The absorbent foam has a skin layer with a thickness of 1 μm or less on at least one side,
The skin layer is a denser area compared to the central part of the foam,
It is an adsorptive foam capable of adsorbing and removing the target substance.

Further, the present invention is a method for adsorbing/removing the target substance using the adsorbent foam. In particular, it is a method of adsorbing and removing cesium using an adsorptive foam whose adsorbent is Prussian blue.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to manufacture the said collected matter efficiently in a short time by a process simpler than before. This can reduce time/economic costs and greatly improve feasibility. Moreover, according to the present invention, since the collected matter can be manufactured in a sheet form, it is possible to increase the rate efficiency of removing the target substance by the collected matter.

The present invention will be described in detail below.

The present invention provides a trap (adsorptive foam) used to reduce or remove substances, a method for producing the same, and a method for removing substances by adsorption using the trap. Substances are not particularly limited as long as they can be adsorbed by any adsorbent, and examples thereof include monatomic molecules, simple substances, compounds, and ions.

The production method of the present invention includes a raw material preparation step for preparing a predetermined liquid raw material mixture.

A predetermined liquid raw material mixture is capable of adsorbing and holding an aqueous liquid dispersion medium, a water-dispersible resin, a foaming agent, a cross-linking agent (curing agent), and a target chemical substance (target substance). It contains a complex (pseudo-complex) formed from an agent and nanocellulose. Some embodiments further contain a cell stabilizer.

The aqueous liquid dispersion medium is typically a hydrophilic solvent. Hydrophilic solvents include, for example, water, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, propylene glycol, glycerin, ethyl carbitol, ethyl cellosolve, and butyl cellosolve; polar solvents such as N-methylpyrrolidone; Mixtures of these are included. The aqueous liquid dispersion medium preferably contains 85% by mass or more of water based on the total amount of the dispersion medium.

The content of the aqueous liquid dispersion medium is not particularly limited, and is the remainder of the liquid raw material mixture excluding other components. Although not intended to limit the present invention, it is preferably less than 70% by mass, less than 65% by mass, or less than 60% by mass based on the total amount of the liquid raw material mixture. On the other hand, it is preferably 35% by mass or more, 40% by mass or more, or 45% by mass or more.

The water-dispersible resin is not particularly limited as long as it is water-dispersible. Examples include urethane emulsions, (meth)acrylic emulsions, ethylene vinyl acetate emulsions and mixtures thereof. The water-dispersible resin preferably has a hydrophilic group so that it can be easily dispersed in water. Hydrophilic groups include sulfonic acid groups, carboxyl groups, and hydroxyl groups.

The urethane emulsion is obtained by dispersing spherical urethane resin particles having a diameter of 0.01 to 5 μm in water. Urethane resin means a copolymer (polyurethane) produced from polyisocyanate and polyol.

Any polyisocyanate that is commonly employed as a raw material for urethane resins may be used. Examples thereof include bifunctional polyisocyanates, trifunctional or higher polyisocyanates, and mixtures thereof. Examples of polyisocyanates include aromatic polyisocyanates, alicyclic polyisocyanates, and alkylene polyisocyanates.

Examples of bifunctional aromatic polyisocyanates include 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), m-phenylene diisocyanate, p- Phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethanedianate (2,4'-MDI), 2,2'-diphenylmethane diisocyanate (2,2'-MDI ), hydrogenated MDI, xylylene diisocyanate, 3,3′-dimethyl-4,4′-biphenylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate, polymethylene polyphenyl polyisocyanate, 1 , 5-naphthalene diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, tetramethylxylene diisocyanate (TMXDI) and the like.

Examples of the bifunctional alicyclic polyisocyanate include cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexane diisocyanate and the like.

Examples of bifunctional alkylene-based polyisocyanates include butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, and lysine diisocyanate.

Tri- or higher functional polyisocyanates include, for example, 1-methylbenzol-2,4,6-triisocyanate, 1,3,5-trimethylbenzol-2,4,6-triisocyanate, biphenyl-2,4,4 '-triisocyanate, diphenylmethane-2,4,4'-triisocyanate, methyldiphenylmethane-4,6,4'-triisocyanate, 4,4'-dimethyldiphenylmethane-2,2',5,5'tetraisocyanate, triphenylmethane-4,4′,4″-triisocyanate, polymeric MDI, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, bicycloheptane triisocyanate, 1 ,8-diisocyanatomethyloctane and the like, and modified products and derivatives thereof.

Any polyol that is commonly employed as a raw material for urethane resins may be used. Examples include polyether polyols, polyester polyols, polyester ether polyols, polycarbonate polyols and mixtures thereof.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol obtained by polymerizing cyclic ethers such as ethylene oxide, propylene oxide and tetrahydrofuran, respectively, and copolyethers thereof. It can also be obtained by polymerizing the above cyclic ether using a polyhydric alcohol such as glycerin or trimethylolethane.

Examples of polyester polyols include aliphatic dicarboxylic acids (succinic acid, adipic acid, sebacic acid, azelaic acid, etc.), aromatic dicarboxylic acids (phthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, etc.), alicyclic dicarboxylic acids, Acids (hexahydrophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, etc.), or their acid esters or acid anhydrides, ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,3 -butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,8-octanediol, 1,9 -Nonanediol and the like, or polyester polyols and the like obtained by a dehydration condensation reaction with a mixture thereof. Alternatively, polylactone diols obtained by ring-opening polymerization of lactone monomers such as ε-caprolactone and methyl valerolactone are included.

Polyester ether polyols include, for example, aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid and azelaic acid, aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid, alicyclic Dicarboxylic acids such as hexahydrophthalic acid, hexahydroterephthalic acid and hexahydroisophthalic acid, or their acid esters or acid anhydrides and glycols such as diethylene glycol or propylene oxide adducts, or mixtures thereof Examples thereof include those obtained by dehydration condensation reaction.

Examples of polycarbonate polyols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexane. Diol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, at least one polyhydric alcohol such as diethylene glycol, diethylene carbonate, dimethyl carbonate, diethyl Examples thereof include those obtained by reacting with carbonate and the like.

The (meth)acrylic emulsion is, for example, spherical (meth)acrylic resin particles having a diameter of 0.01 to 5 μm dispersed in water. (Meth)acrylic resin means a polymer or copolymer produced from one or more of (meth)acrylic acid and its derivatives. The notation "(meth)acrylic" means that either acrylic or methacrylic may be used. Similarly, the notation "(meth)acrylate" means that either acrylate or methacrylate may be used.

(Meth)acrylic acid derivatives include, for example, alkyl (meth)acrylates and hydroxyalkyl (meth)acrylates.

Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, and (meth)acrylic acid. heptyl, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate , dicyclopentanyl (meth)acrylate, phenyl (meth)acrylate, and benzyl (meth)acrylate.

Examples of hydroxyalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 2-hydroxybutyl (meth)acrylate. , 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and the like.

The ethylene-vinyl acetate emulsion is obtained by dispersing, for example, spherical ethylene-vinyl acetate resin particles having a diameter of 0.01 to 5 μm in water. Ethylene vinyl acetate resin means a copolymer made from ethylene and vinyl acetate.

The method for producing the ethylene-vinyl acetate emulsion (ethylene-vinyl acetate copolymer resin emulsion) that can be used in the present invention is not particularly limited. agent or the like as an emulsifying dispersant, and copolymerizing ethylene and a vinyl acetate monomer by emulsion polymerization.

The ethylene-vinyl acetate copolymer resin emulsion may be obtained by further copolymerizing a vinyl monomer having a functional group such as a carboxyl group, an epoxy group, a sulfonic acid group, a hydroxyl group, a methylol group, or an alkoxy acid group. good.

The content of the water-dispersible resin is not particularly limited, but is preferably 25% by mass or more, 30% by mass or more, 35% by mass or more, and 60% by mass or less and 55% by mass or less, based on the total amount of the liquid raw material mixture. Preferably.

The cross-linking agent (curing agent) is not particularly limited. A necessary amount may be added depending on the application. A specific cross-linking method can be selected according to the type of water-dispersible resin. As the cross-linking agent, a known cross-linking agent can be used, and the resin formulation system used contains an epoxy-based cross-linking agent, a melamine-based cross-linking agent, an isocyanate-based cross-linking agent, a carbodiimide-based cross-linking agent, an oxazoline-based cross-linking agent, and the like. An appropriate amount can be used depending on the type of functional group and the amount of functional group.

More specifically, the cross-linking agent (curing agent) includes ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol di( meth)acrylate, glycerin tri(meth)acrylate, N,N'-methylenebis(meth)acrylamide, diallyl phthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, trimethylolpropane tri (Meth)acrylate, tetramethylolmethane tri(meth)acrylate, and dipentaerythritol hexaacrylate.

The content of the cross-linking agent (curing agent) is not particularly limited, but is preferably 2% by mass or more and 3% by mass or more, and is preferably 6% by mass or less and 5% by mass or less, based on the total amount of the liquid raw material mixture. preferable.

The foaming agent is not particularly restricted. Some surfactants function as foaming agents. Any of nonionic surfactants, anionic surfactants and amphoteric surfactants may be used as long as they function as foaming agents. It is preferable to use an anionic surfactant and an amphoteric surfactant in combination, since the air bubbles can be more stabilized, the size of the air bubbles can be reduced, and the delamination strength can be improved.

The HLB of the foaming agent is preferably 10 or more, more preferably 20 or more, and particularly preferably 30 or more, in order to facilitate dispersion in the aqueous liquid dispersion medium.
In the present invention, the HLB value means a hydrophilic-hydrophobic balance (HLB) value and is determined by the Oda method. How to determine HLB by the Oda method, "Shin Surfactant Introduction" pp. 195-196 and published by Maki Shoten on March 20, 1957 Oda Ryohei et al. 502, and can be determined by HLB=(inorganic/organic)×10.

Nonionic surfactants that function as foaming agents (nonionic foaming agents) include, for example, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene styrenated phenyl ether, polyoxyethylene sorbitol tetraole and the like.

Examples of anionic surfactants (anionic foaming agents) that function as foaming agents include saturated or unsaturated fatty acid salts having 12 to 18 carbon atoms such as stearic acid and oleic acid, Sulfuric acid ester salts, benzenesulfonates, sulfosuccinates, sulfonate salts, diphenyl ether sulfonates, naphthalene sulfonates, etc., having a linear or branched hydrocarbon group with a degree of unsaturation of 2 or less. . When one molecule has a plurality of hydrocarbon groups, the hydrocarbon groups may be the same or different. Among these, sulfosuccinates having the above hydrocarbon group are preferred. Particularly preferred are alkyl/alkenyl sulfosuccinates in which the hydrocarbon radical is an alkyl or alkenyl radical. The alkyl/alkenyl sulfosuccinate means all sulfosuccinates containing one or more alkyl groups, sulfosuccinates containing one or more alkenyl groups, and sulfosuccinates containing one alkyl group and one alkenyl group.

There are no restrictions on the cations contained in these anionic surfactants. They are usually alkali metal cations such as lithium ions, sodium ions, potassium ions, and ammonium ions. Typical examples of anionic surfactants are therefore alkali metal salts such as lithium salts, sodium salts, potassium salts and ammonium salts.

Examples of straight or branched hydrocarbon groups having 12 to 18 carbon atoms and having a degree of unsaturation of 2 or less include straight or branched alkyl groups, alkenyl groups and cycloalkyl groups. The hydrocarbon group is preferably an alkyl group or an alkenyl group.

More specifically, the anionic surfactants that function as foaming agents include sodium laurate, sodium myristate, sodium stearate, ammonium stearate, sodium oleate, potassium oleate, potassium castor oil soap, coconut Potassium oil soap, sodium lauroyl sarcosinate, sodium myristoyl sarcosinate, sodium oleyl sarcosinate, sodium cocoyl sarcosinate, sodium coconut oil alcohol sulfate, sodium polyoxyethylene lauryl ether sulfate, sodium dialkyl sulfosuccinate such as sodium dilauryl sulfosuccinate, dioleyl sulfosuccinate sodium dialkenylsulfosuccinate, sodium laurylsulfoacetate, sodium dodecylbenzenesulfonate, sodium α-olefinsulfonate and the like.

As the anionic surfactant functioning as a foaming agent, sodium alkyl/alkenyl sulfosuccinate having a linear or branched alkyl group or alkenyl group having 12 to 18 carbon atoms or a mixture thereof is particularly preferred.

An anionic surfactant that functions as a foaming agent functions as a foaming agent for an aqueous liquid dispersion medium. insolubilized or insoluble in

The anionic surfactant is a component that is initially dissolved in the dispersion medium, but becomes poorly soluble or insoluble in the dispersion medium when the anionic surfactant is precipitated. Means for making such an anionic surfactant poorly soluble or insoluble are not particularly limited. It can be exemplified by blending agents, etc. By making the anionic surfactant less soluble or insoluble, it becomes possible to form a resin foam having a fine and uniform cell structure without limiting the types of water-dispersible resins and dispersants used as main ingredients. . Furthermore, since the anionic surfactant is rendered poorly soluble or insoluble, it becomes difficult to extract with water or the like (that is, bleeding can be prevented). In addition, since the gelling strength is high, coalescence of the cells in the foaming step is strongly suppressed, thereby stabilizing the cells.

Amphoteric surfactants that function as foaming agents (amphoteric foaming agents) include, for example, amino acid type, amine oxide type, betaine type amphoteric surfactants, and the like. Betaine-type amphoteric surfactants are preferred because the aforementioned effects are higher.

Examples of amino acid-type amphoteric surfactants that function as foaming agents include sodium lauryl diaminoethylglycinate, sodium trimethylglycine, sodium cocoyl taurate, sodium cocoyl methyl taurate, sodium lauroyl glutamate, potassium lauroyl glutamate, lauroyl methyl-β- Alanine etc. are mentioned.

Examples of the amine oxide type amphoteric surfactant functioning as a foaming agent include lauryldimethylamine-N-oxide and oleyldimethylamine-N-oxide.

Examples of betaine-type amphoteric surfactants that function as foaming agents include alkylbetaine, imidazolinium betaine, carbobetaine, amidocarbobetaine, amidobetaine, alkylamidobetaine, sulfobetaine, amidosulfobetaine, phosphobetaine, and the like. There is Alkylbetaines, imidazolinium betaines and carbobetaines are particularly preferred.

More specifically, lauryl betaine, stearyl betaine, betaine lauryldimethylaminoacetate, betaine stearyldimethylaminoacetate, betaine lauramidopropyldimethylaminoacetate, betaine isostearamideethyldimethylaminoacetate, betaine isostearamidepropyldimethylaminoacetate , Isostearamide ethyl diethylamino acetate betaine, Isostearamide propyl diethylamino acetate betaine, Isostearamide ethyl dimethylamino hydroxysulfobetaine, Isostearamide propyl dimethylamino hydroxysulfobetaine, Isostearamide ethyl diethylamino hydroxysulfobetaine, Isostearamide ethyl diethylamino hydroxysulfobetaine, Isostearamide propyl diethylaminohydroxysulfobetaine, N-lauryl-N,N-dimethylammonium-N-propylsulfobetaine, N-lauryl-N,N-dimethylammonium-N-(2-hydroxypropyl)sulfobetaine, N-lauryl-N, N-dimethyl-N-(2-hydroxy-1-sulfopropyl)ammoniumsulfobetaine, laurylhydroxysulfobetaine, dodecylaminomethyldimethylsulfopropylbetaine, octadecylaminomethyldimethylsulfopropylbetaine, 2-alkyl-N-carboxymethyl- N-hydroxyethylimidazolinium betaine (2-lauryl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine 2-stearyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine, etc.), coconut oil fatty acid amide Propyl betaine, coconut oil fatty acid amidopropyl hydroxysultaine, and the like.

Among these, stearyl betaine, lauryl betaine, and 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine are preferred.

The content of the foaming agent is not particularly limited, but is preferably 1% by mass or more and 1.5% by mass or more, and 4% by mass or less and 3.5% by mass or less based on the total amount of the liquid raw material mixture. is preferred.

The complex (pseudo-complex) according to the present invention is formed or composed of an adsorbent capable of adsorbing and retaining a target chemical substance and nanocellulose.

A target chemical substance in the present invention means a chemical substance or the like contained in a fluid (for example, a liquid such as water or a gas such as air) or soil. Examples include cesium, thorium, strontium, and iodine, and particularly radioactive substances such as radioactive cesium, radioactive thorium, radioactive strontium, and radioactive iodine.

An adsorbent capable of adsorbing and retaining a target chemical substance means one or more types of adsorbents having high binding strength or selectivity to the target chemical substance. Examples of such adsorbents include chelate-forming substances such as Prussian blue and alginic acid. Prussian blue (PB) is suitable as an adsorbent for cesium (especially radioactive cesium).

As Prussian blue, iron hexacyano(II) chloride, iron(III) ferrocyanide, a cyano complex called iron(II) ferrocyanide, and analogues thereof can be used. It only needs to have a property of being able to form a complex (complex or pseudo-complex) with a target chemical substance with a high binding constant for a target chemical substance such as cesium ions, and a specific coordination state is not limited to complexes or quasi-complexes with a coordination number. The Prussian blue used in the present invention may have an average particle size of 1 nm to 200 nm, preferably 10 nm to 20 nm.

Nanocellulose means cellulose that has been refined to an average fiber length of 10 μm to 1000 μm and an average fiber diameter of 1 nm to 800 nm. Nanocellulose is also called cellulose nanofiber (CNF). Any production method may be used. For example, commercially available cellulose (α-cellulose, cellulose acetate, etc.) may be pulverized using a pulverizing device such as an attritor, ball mill, sand mill, or bead mill. Nanocellulose dispersions are obtained by dispersing commercially available cellulose (α-cellulose, cellulose acetate, etc.) together with deionized water or other dispersion media using a micronization device such as an attritor, ball mill, sand mill, or bead mill, in a solvent. It can be obtained by performing a treatment for dispersing cellulose in (hereinafter referred to as "dispersion treatment").

A dispersion medium for the nanocellulose dispersion is not particularly limited, but typically includes a hydrophilic solvent. Hydrophilic solvents include, for example, water, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, propylene glycol, glycerin, ethyl carbitol, ethyl cellosolve, and butyl cellosolve; polar solvents such as N-methylpyrrolidone; Mixtures of these are included. The dispersion medium preferably contains 85% by mass or more of water based on the total amount of the dispersion medium.

Dispersion treatment of nanocellulose is performed, for example, by adjusting nanocellulose and deionized water so that the amount of cellulose is 0.01 to 10 wt% with respect to deionized water, and using an attritor, a ball mill, a sand mill, a bead mill, or the like. can be prepared by mixing using The term "dispersion" as used herein means dispersion in a broad sense including dissolution and suspension. is suspended.

Any method may be used to prepare a nanocellulose/adsorbent complex (pseudocomplex) or to support an adsorbent on nanocellulose. Since nanocellulose has many hydroxyl groups, nanocellulose and adsorbents (eg, chelate-forming substances such as Prussian blue and alginic acid) may be chemically bonded.

More specifically, after binding cations such as iron (III) ions to nanocellulose to form a complex (pseudo-complex) of nanocellulose and cations, the complex (pseudo-complex) is On the other hand, nanocellulose/adsorbent composites (pseudocomplexes) may be prepared by binding complex ions such as hexacyanoferrate(II) acid. By this method, for example, nanocellulose/Prussian blue composites (pseudocomplexes) can be prepared.

In particular, the nanocellulose/Prussian blue complex (pseudocomplex) has a concentration of 0.01 to 10 wt% of the nanocellulose dispersion and a concentration of 1.0 mM to 0.5 M of Prussian blue (MW = 859.23 g / mol). By setting the ratio of Prussian blue to 0.1 to 100 parts by mass with respect to 1 part by mass of nanocellulose before dispersion treatment, it can be prepared in an appropriate medium. Further, it can be prepared by mixing preferably in water. No special conditions are required for the mixing step. For example, when the total amount of the mixture is 10 liters, the temperature can be appropriately adjusted within the range of 4° C. to 45° C. for 30 to 120 minutes. The liquid containing the complexes (pseudocomplexes) prepared in this way can also be described as a solution or colloidal solution of the nanocellulose/Prussian blue complexes (pseudocomplexes).

The mass ratio of nanocellulose and adsorbent in the nanocellulose/adsorbent complex (pseudo-complex) is not particularly limited and varies depending on the type of adsorbent. The ratio of the mass of the adsorbent to the mass of nanocellulose may be 1/5 or more, or 1/3 or more. On the other hand, it may be 5 or less, or 3 or less.

The content of the nanocellulose/adsorbent composite (pseudo-complex) is not particularly limited, but is preferably 1% by mass or more, 2% by mass or more, 3% by mass or more, and 10% by mass, based on the total amount of the liquid raw material mixture. % or less, 8 mass % or less, and 6 mass % or less.

The content of the adsorbent is not particularly limited, but is preferably 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 9% by mass or less, 8% by mass or less, and 7% by mass, based on the total amount of the liquid raw material mixture. % by mass or less, preferably 6% by mass or less, and 5% by mass or less.

A predetermined liquid raw material mixture may further contain a cell stabilizer (gelling agent).

In one embodiment, a foam stabilizer (gelling agent) is blended in the raw material preparation step. In another embodiment, a cell stabilizer (gelling agent) is blended in the foaming step or molding step, which will be described later. Blending in the raw material preparation process is preferable in that the process can be simplified.

Foam stabilizers (gelling agents) include metal cation sources for gelling the foamed mixture described below in combination with the anionic surfactants described above as foaming agents. A metal cation source (or metal cation source compound) supplies metal cations. The supplied metal cation reacts with the anionic surfactant dissolved in the liquid raw material mixture to form a salt (poorly soluble salt, insoluble salt) with relatively lower solubility than the anionic surfactant. . This precipitates the salt with relatively low solubility.

The metal cations supplied by the metal cation source are not particularly limited, and are determined according to the combination with the anionic surfactant. Typical examples include polyvalent metal cations such as beryllium ions, magnesium ions, calcium ions, strontium ions, barium ions, radium ions and aluminum ions.

The metal cation source is not particularly limited as long as it is a compound that supplies metal cations as described above, and may be an inorganic compound or an organic compound. Such compounds include, for example, sulfates, nitrates, chlorides, oxides, hydroxides, acetates, and the like.

More specifically, the metal cation source includes beryllium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate, radium sulfate, aluminum sulfate, beryllium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, and radium nitrate. , aluminum nitrate, beryllium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride, radium chloride, aluminum chloride, beryllium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, radium oxide, aluminum oxide, beryllium hydroxide, Magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, radium hydroxide, aluminum hydroxide, beryllium acetate, magnesium acetate, calcium acetate, strontium acetate, barium acetate, radium acetate, aluminum acetate and the like.

The content of the foam stabilizer (gelling agent) is not particularly limited, but is preferably 1% by mass or more and 1.5% by mass or more, and 4% by mass or less and 3.5% by mass, based on the total amount of the liquid raw material mixture. The following are preferable.

The order and timing of mixing these are arbitrary and not particularly limited as long as the effects of the present invention are not impaired.

The liquid raw material mixture may contain other ingredients as long as they do not impair the effects of the present invention. Examples of such other components include water-soluble polymers such as DNA and alginic acid.

The content of these optional additional components is not particularly limited, but is preferably 0.1 to 10% by mass based on the total amount of the liquid raw material mixture.

The production method of the present invention includes a foaming step of foaming a liquid raw material mixture to obtain a foamed mixture.

In the foaming step, a foaming fluid is added to the liquid raw material mixture obtained in the raw material preparation step, and these are sufficiently mixed to form a state in which many bubbles are present in the liquid raw material mixture (foaming mixture). This foaming step is usually carried out by sufficiently mixing the liquid raw material mixture obtained in the raw material preparation step and the foaming fluid using a mixing device such as a mixing head.

The foaming fluid mixed with the liquid raw material mixture in the foaming step forms the cells of the absorbent foam. Density is determined. To adjust the density of the adsorptive foam, the desired adsorptive foam density and the volume of the adsorptive foam material (e.g., the internal volume of the mold into which the adsorptive foam material is poured) are combined. From this, the weight of the required absorbent foam raw material can be calculated, and the amount of foaming fluid can be determined so as to obtain the desired volume based on this weight.

Air is mainly used as the type of bubbling fluid, but inert gases such as nitrogen, carbon dioxide, helium, and argon can also be used. A supercritical fluid or a subcritical fluid (for example, supercritical/subcritical nitrogen or carbon dioxide) that can reduce the foam cell diameter is preferable in terms of forming a thin foam. Air is preferable in terms of simplification of the process and thereby improvement in production efficiency.

As a foaming means, a mechanical froth (mechanical foaming) method is used. The mechanical froth method is a method of stirring a liquid raw material mixture with a stirring blade or the like to mix a foaming fluid such as air in the atmosphere into the liquid raw material mixture to foam the mixture. As the stirrer, any stirrer generally used in the mechanical froth method can be used without particular limitation, and for example, a homogenizer, a dissolver, a mechanical froth foamer and the like can be used. According to this mechanical froth method, by adjusting the mixing ratio of the liquid raw material mixture and the foaming fluid, it is possible to obtain an adsorptive foam having a density suitable for various uses.

The mixing time of the liquid raw material mixture and the bubbling fluid is not particularly limited, but is usually 1 to 10 minutes, preferably 2 to 6 minutes. Although the mixing temperature is not particularly limited, it is usually room temperature. Moreover, the stirring speed in the above mixing is preferably 200 rpm or more or 500 rpm or more in order to make air bubbles fine. On the other hand, 2000 rpm or less, 1200 rpm or less or 800 rpm or less is preferable in order to smoothly discharge the foam from the foaming machine.
The room temperature means 5 to 35°C, 15 to 30°C or 20 to 25°C.

In the foaming step, the liquid raw material mixture obtained in the raw material preparing step may be subjected to a predetermined gelation means to obtain a gelled liquid raw material mixture. When a gelling agent is used, the liquid raw material mixture obtained in the raw material preparation step, the foaming fluid, and the gelling agent are sufficiently mixed with a mixing device such as a mixing head. The term "gelled liquid raw material mixture" as used in the present invention refers to both a liquid raw material mixture in the process of gelling and a liquid raw material mixture that has been completely gelled.

Upon completion of gelling, the foaming fluid present in the gelled liquid raw material mixture is retained as air bubbles. Since these cells become the cells of the resin foam to be finally obtained as they are, the size of these cells determines the cell diameter.

In the present invention, it is preferable to adjust the cell size (foam cell diameter) of the foam to 20 to 250 μm or 30 to 200 μm. If the cell diameter is too small, the flow rate of the fluid per unit time will be restricted when purifying a fluid (for example, water) contaminated with the target chemical substance, which is not preferable because it will lead to a decrease in the processing speed. On the other hand, if the cell diameter is too large, pinholes are likely to occur when the cell is formed thin. In this case, there is a problem with mechanical strength, and when the target substance is removed by allowing the fluid containing the target substance to pass through, the probability of contact is lowered, which is not preferable. That is, it is not preferable to form a sheet because it causes problems.

The means for gelling the liquid raw material mixture is not limited at all, and may be appropriately selected according to the application. By blending a metal cation source together with an anionic surfactant contained as a foaming agent, the anionic surfactant may be precipitated (insolubilized or insolubilized) to cause gelation. Alternatively, gelation may be achieved by blending a plurality of surfactants with different HLB values. The staggered orientation of the surfactant improves the density of the surfactant, increases the hydrogen bond between the hydrophilic group and water, and reduces the fluidity of the aqueous liquid dispersion medium, leading to gelation. Alternatively, a plurality of surfactants with different micelle shapes may be blended to form a micelle network to cause gelation.

When a metal cation source that precipitates an anionic foaming agent (an anionic surfactant that functions as a foaming agent) is added to the liquid raw material mixture, the timing of addition is not particularly limited. As described above, it may be blended in the raw material preparation process or may be blended in the foaming process. Blending in the raw material preparation process is preferable because the process can be simplified.

If the gelation time is short or if a water-soluble salt with a high solubility is used, adding it during the preparation of the raw material reduces the amount of foaming fluid that can be mixed in due to thickening due to gelation, resulting in a high-density foam. Addition immediately before or during foaming is preferred.

On the other hand, when the gelation time is long or when a slow-release sparingly soluble salt is used, if added immediately before or during foaming, a fine cell structure cannot be formed due to the coalescence of cells, so it is preferable to add the salt during the preparation of the raw material. . Adding the metal cation source at the time of raw material preparation also has the advantage of simplifying the process.

In the present invention, the term "water-soluble" means that the amount dissolved or dispersed in 100 g of water at 25°C is 1 g or more. The term "sparingly soluble" means that the amount that dissolves or disperses in 100 g of water at 25° C. is 1 to 5 g. The term "insoluble" means that the amount dissolved or dispersed in 100 g of water at 25°C is less than 1 g.

The deposition step of the anionic surfactant mainly provides thixotropy to the system by precipitating the anionic surfactant (anionic foaming agent) as a foaming agent after foaming. As a deposition step, a method different from this is also conceivable.

For example, after foaming, water-soluble components present in the system (e.g., metal cations derived from anionic foaming agents, components contained in water-soluble resins, previously added water-soluble A method of precipitating a mold component) can be mentioned. For example, a method of depositing using a metal cation derived from an anionic foaming agent can be realized by adding another component that binds to the metal cation and deposits. A more suitable example is a method of adding an anionic surfactant other than the anionic surfactant which is a foaming agent. The solubility of anionic surfactants in water is generally determined by polyvalent metal salts {e.g., alkaline earth metal salts (e.g., calcium salts)} < alkali metal salts (e.g., sodium salts) < ammonium or amine salts, is the order. Using this property, for example, as an anionic foaming agent, a highly water-soluble salt (e.g., sodium salt of the first anionic surfactant) forms a sparingly soluble or insoluble salt with the water-soluble cation. By using a second anionic surfactant (for example, an ammonium salt), the second anionic surfactant forms a sodium salt through a cation exchange reaction and is discharged out of the system. The first anionic foaming agent maintains its foamability without becoming poorly soluble or insoluble. Here, for example, in the above example, the second anionic surfactant is soluble in water as an ammonium salt, but poorly soluble or insoluble in water as an alkali metal salt. By adding such a second anionic surfactant to the system, the second anionic surfactant undergoes cation exchange (for example, ammonium → sodium ion), water-soluble → sparingly water-soluble or water Change to insoluble form. As a result, the fluidity of the system is lowered, and it becomes possible to produce a foam having a low cell diameter and the like, as in the case of depositing an anionic foaming agent as described in detail above. The timing of blending the first anionic surfactant and the second anionic surfactant may be changed depending on the combination thereof. After blending both before foaming, foaming may be performed while gelling. Alternatively, after blending the first anionic surfactant, foaming may be performed, and the second anionic surfactant may be blended and gelled during or after foaming.

For example, it is assumed that at least an alkali metal salt (eg, sodium salt) is used as an anionic foaming agent (of course, other surfactants may be used in combination). In this case, if a long-chain fatty acid (eg, C 16-22) ammonium (eg, ammonium stearate) is used as the second anionic surfactant, an alkali metal ion derived from an anionic foaming agent (eg, sodium ion) reacts with the long-chain fatty acid derived from the second anionic surfactant to precipitate a fatty acid alkali metal salt (eg, sodium salt) as a poorly soluble or insoluble salt. As an anionic foaming agent, it is also assumed to use an alkali metal salt (for example, sodium dodecanoate) of a medium-chain fatty acid (for example, 8 to 15 carbon atoms) (in this case, the anion (corresponds to an aspect in which a non-soluble foaming agent is rendered insoluble or insoluble). In this case polyvalent metal ions (eg calcium ions) are added to the foamed system. As a result, the polyvalent metal ion and the short-chain fatty acid derived from the anionic foaming agent react to precipitate a fatty acid polyvalent metal salt (for example, calcium salt) as a sparingly soluble or insoluble salt.

In addition, as the deposition step of the anionic surfactant, the above-described methods may be appropriately combined.

The production method of the present invention includes a molding step of molding the foamed mixture into a sheet on a substrate between the foaming step described above and the drying step described below.

The substrate is not particularly limited, and those commonly used as substrates for resin foams can be used. A sheet-like base material with low stretchability that does not allow the raw material components of the adsorptive foam to permeate is preferred.

From this point of view, the substrate is preferably a PET film, nonwoven fabric, woven fabric, paper, or the like. Among them, a nonwoven fabric having a basis weight of 30 to 150 g/m ² and a thickness of 50 to 500 µm is particularly preferable.

"Sheet-like" means that the thickness is sufficiently smaller than the depth and width among the depth, width and thickness. For example, if the ratio of depth and width to thickness is 5 or more, 10 or more, or 15 or more, it may be expressed as a sheet.
In particular, with regard to the absorbent foam, when the depth and width are 5 cm or more and the thickness is 2 mm or less, 1.5 mm or less, or 1 mm or less, the absorbent foam is expressed as a sheet.

The means for molding on the substrate is not particularly limited, and known means can be used. It is usually molded by coating on a base material. The semi-solid foamed mixture coated on the base material is molded to a desired thickness with high accuracy by means such as a doctor knife and a doctor roll.

The production method of the present invention includes a drying step of heating the foamed liquid raw material mixture (foaming mixture) to evaporate the dispersion medium.

The drying method in the drying step is not particularly limited. For example, hot air drying or the like may be used. The temperature and time of the drying process can be adjusted as appropriate, but for example, the temperature may be about 80° C. for about 1 to 3 hours.

In the drying process, the dispersion medium evaporates from the foamed mixture, and the path through which this vapor escapes communicates from the inside to the outside of the adsorptive foam. Therefore, in the adsorptive foam of the present invention, the passageway through which vapor escapes remains as open cells, so that at least some of the cells present in the adsorptive foam become open cells.

When the bubbling fluid mixed in the bubbling step remains as it is, the resulting adsorptive foam becomes closed cells, and the mixed bubbling fluid is communicated when steam escapes in this step. If so, open cells are present in the resulting adsorptive foam. In the present invention, some of the cells in the adsorptive foam may be open cells, or all the cells may be open cells.

When a cross-linking agent (curing agent) is added, the drying process proceeds and completes the cross-linking (curing) reaction of the raw material. Specifically, the raw materials are cross-linked by the above-described cross-linking agent (hardening agent) to form a hardened foam. The heating means at this time is not particularly limited as long as it can sufficiently heat the raw material and crosslink (harden) the raw material. For example, a tunnel heating furnace or the like can be used. Also, the heating temperature and heating time may be any temperature and time at which the raw material can be crosslinked (cured), for example, about 1 hour at 80 to 150 ° C. (especially about 120 ° C. is preferable). .

According to the production method of the present invention described above, it is possible to produce a sheet-like adsorptive foam.

In the conventional manufacturing method, it was not possible to form the absorbent foam into a sheet shape, and there was no choice but to produce an absorbent foam having a certain size. In order to capture the target substance from a fluid containing the target substance (eg, a liquid such as water) and purify the fluid, the fluid must be passed through an absorbent foam. However, the applied pressure must be considerably high to pass through a non-sheet-like adsorptive foam. This is disadvantageous in terms of cost, such as the need for a booster device, and is also disadvantageous in terms of time efficiency, since the flow rate of the fluid is reduced due to the resistance of the adsorptive foam, and the cleaning speed of the fluid is greatly restricted. Furthermore, for example, when used to collect radioactive substances such as radioactive cesium, there was a concern that conventional products would unintentionally collect a large amount of radioactive substances, resulting in workers being exposed to more radiation than expected. The manufacturing method of the present invention enables the adsorptive foam to be formed into a sheet. Molding into a sheet shape leads to avoiding or reducing these problems.

Furthermore, according to the manufacturing method of the present invention, on at least one side, the absorbent foam has a skin layer (relatively dense layer). The presence of this skin layer can impart appropriate mechanical strength to the adsorptive foam. This makes it difficult for the sheet-like adsorptive foam to break even when the fluid to be purified is passed through it.

Thus, the sheet-like adsorptive foam produced by the above production method has the following configuration.

The sheet-like adsorptive foam comprises a nanocellulose/adsorbent composite. Therefore, the adsorptive foam has a scavenging ability derived from the adsorbent, and can capture the target substance of the adsorbent. By choosing a suitable adsorbent, the adsorbent foam can adsorb and retain, for example, cesium, thorium, strontium, iodine (especially radioactive cesium, radioactive thorium, radioactive strontium, radioactive iodine). Prussian blue can be mentioned as such an adsorbent. Prussian blue is an excellent adsorbent for cesium. Thus, a typical adsorbent foam contains a nanocellulose/Prussian blue composite and is capable of adsorbing and retaining cesium (particularly radioactive cesium) by means of the contained Prussian blue.

Further, in relation to the manufacturing method, the adsorptive foam also contains the water-dispersible resin and the cross-linking agent. These form a network structure.

The thickness of the absorbent foam is 2 mm or less, 1.5 mm or less, 1 mm or less, 0.8 mm or less, 0.6 mm or less or 0.5 mm or less. From the viewpoint of ensuring a certain degree of mechanical strength, the thickness of the adsorptive foam is preferably 0.01 mm or more, 0.05 mm or more, or 0.1 mm or more.

The apparent density (JIS K6401) of the adsorptive foam is not particularly limited. For example, it may be 50 to 500 kg/m ³ or 100 to 300 kg/m ³ . If the density is too low, the mechanical strength of the adsorptive foam may decrease, and the amount (concentration) of the adsorbent per volume may decrease, resulting in a decrease in adsorption treatment efficiency. Conversely, a high density means that the structure is close to a closed cell structure and that there are few open cells. As a result, there is a risk that the amount and speed at which the fluid penetrates into the adsorptive foam will decrease, and the adsorbent inside the adsorptive foam will not be in sufficient contact with the target substance, resulting in reduced adsorption efficiency.

The cell size (foam cell diameter, cell size) of the adsorptive foam is 20 to 250 μm or 30 to 200 μm. In the present invention, the cell size of the adsorptive foam is measured by taking a photograph of a cross section in the thickness direction of the adsorptive foam using a scanning electron microscope (SEM) (manufactured by Keyence Corporation, VHXD-500). do. For the cells in the photograph, the diameter of each cell was measured using image processing software Image-Pro PLUS (manufactured by Media Cybernetics, 6.3ver), and the average value was defined as the size of the bubble.

The absorbent foam is provided with a skin layer on at least one side. The skin layer is a region in which resin or the like exists at a higher density than in the central portion when the foam is cut in the thickness direction. This is because the cell density is lower and/or the average foam cell diameter is smaller than in the central portion of the foam when the foam is cut in the thickness direction. The presence of this skin layer can be confirmed by observing a cross section in the thickness direction with a scanning electron microscope (SEM). This skin layer is very thin, less than 1 μm at most. The presence of a skin layer that is denser than the center of the foam and very thin allows for adsorption while minimizing adverse effects on fluid flow through the absorbent foam and on the scavenging ability of the absorbent foam. Suitable mechanical strength is given to the elastic foam.

As described above, the adsorbent foam of the present invention can adsorb substances targeted by the adsorbent due to the adsorbent contained in the adsorbent foam. Therefore, according to the present invention, a method for adsorbing/removing the target substance (capturing method) using the adsorbent foam sheet is provided. The substrate may be removed from the absorbent foam when the absorbent foam is used in the adsorption-removal method.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

The absorbent foams of the Examples and Comparative Examples were prepared by the following procedure.

First, a nanocellulose/Prussian blue composite (pseudocomplex) was formed according to the method described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2016-155116).

Next, liquid raw material mixtures (with pure water as the dispersion medium) having the compositions shown in Tables 1 and 2 were prepared (numbers mean parts by weight). Foam stabilizers were incorporated prior to foaming. A gas such as air in the atmosphere was employed as a foaming fluid, and the respective liquid raw material mixtures were stirred and foamed using a mechanical foaming method. The foamed mixture (foamed mixture) was cast on a release-treated PET film (substrate), and then formed into a sheet by a coater. This was heated/dried at 150° C. for 10 minutes to evaporate the dispersion medium. A sheet-like adsorptive foam was thus produced. The following evaluation tests were performed on these adsorptive foams, and the results are also listed in Tables 1-2.

The compounds used are as follows.
Water-dispersible resin 1: urethane emulsion (solid content 60% by mass)
Water-dispersible resin 2: acrylic emulsion (solid content 54% by mass)
Water-dispersible resin 3: ethylene vinyl acetate emulsion (solid content 54% by mass)
Anionic foaming agent 1: sodium sulfosuccinate having a hydrocarbon group (pH 9.3, solid content 35% by mass, hydrocarbon group is alkyl group having 12 to 18 carbon atoms, alkenyl group)
Anionic foaming agent 2: ammonium stearate (pH 11, solid content 30% by mass)
Amphoteric foaming agent 1: coconut oil fatty acid amidopropyl betaine (pH 7.5, solid content 30% by mass)
Amphoteric foaming agent 2: myristyl betaine (pH 6.5, solid content 36% by mass)
Nonionic foaming agent: polyoxyethylene alkyl ether (pH 6.5, solid content 50% by mass)
Bubble stabilizer (metal cation source): calcium nitrate aqueous solution with a concentration of 30% by mass (pH 6.1)
Adsorbent complex: nanocellulose (CNF) and Prussian blue (PB) complex (pseudo complex) solution (pH 3.0, solid content 50% by mass, mass ratio of CNF and PB is 1:1)
Cross-linking agent (curing agent): Hydrophobic HDI isocyanurate (number of functional groups: 3.5)

<Evaluation method>
Each adsorbent foam produced was evaluated for performance by the following evaluation tests.

The thickness of the absorbent foam was measured with a thickness gauge.

(Density evaluation)
The apparent density of the adsorptive foam was measured according to JIS K6401.

(Cell size evaluation)
Using a scanning electron microscope (SEM) (manufactured by Keyence Corporation, VHXD-500), a photograph of a cross section in the thickness direction of the adsorptive foam was taken. For the cells in the photograph, the diameter of each cell was measured using image processing software Image-Pro PLUS (manufactured by Media Cybernetics, 6.3ver), and the average was calculated. At this time, a skin layer having a thickness of 1 μm or less was confirmed on both sides of each of the adsorptive foams.

(Water absorption evaluation)
One drop (0.033 mL) of ion-exchanged water was dropped on the test piece of the adsorptive foam, and the time required for complete penetration was measured. The test piece is a sheet with a width of 5 cm and a depth of 5 cm, and the average time required for water absorption is calculated at 5 points in the center and four corners. Evaluation criteria are as follows.
○: Average water absorption time within 10 seconds △: Average water absorption time from over 10 seconds to 60 seconds ×: Average water absorption time over 60 seconds

(Appearance evaluation)
The state of the cells and the surface of the adsorptive foam were evaluated visually. Evaluation criteria are as follows.
〇: Cells are uniform and the surface is not rough △: There are uneven cells, or the surface is rough ×: No cells (not foamed), uneven cells, or very rough surface

(Prussian blue elution test)
1 g of the adsorptive foam sheet of Example 2 (PB content: 2.5 wt %) was put into 40 mL of deionized water with a predetermined pH and stirred at 20° C. and 300 rpm for 24 hours. The pH of the ion-exchanged water was adjusted to 1 to 13 (in increments of 1) by adding an aqueous sodium hydroxide solution or an aqueous sulfuric acid solution.
After agitation, the absorbent foam was removed and the remaining liquid was evaluated for total cyanide concentration (the amount of Prussian blue eluted) and free cyanide concentration. A total cyan concentration (low concentration) set (type: WA-CNT (L)) manufactured by Kyoritsu Rikagaku Kenkyusho Co., Ltd. was used to measure the total cyan concentration. Digital Packtest Multi (Lambda-9000) manufactured by Kyoritsu Rikagaku Kenkyusho Co., Ltd. was used to measure the concentration of free cyanide.

The total cyanide concentration was below the detection limit in the pH range of 1-11. 98 ppm was detected at pH 12 and 135 ppm at pH 13.
The concentration of free cyanide was below the detection limit in the pH range of 1-9. It was 0.015 ppm at pH 10, 0.017 ppm at pH 11, 0.10 ppm at pH 12, and 0.32 ppm at pH 13.
It was confirmed that Prussian blue was not eluted at all in the low pH range (acidic range, neutral range, weakly alkaline range). It was also confirmed that the elution amount was very small even in the high pH range. This result means that Prussian blue is strongly retained on nanocellulose, and their complexes (pseudo-complexes) are strongly retained on the adsorptive foam.

(Cesium adsorption test)
A cesium aqueous solution was prepared by dissolving cesium nitrate in deionized water and seawater, respectively. The cesium ion concentrations were 100 ppb, 200 ppb, 300 ppb, 500 ppb, 1000 ppb (1.0 ppm), 3.0 ppm, 5.0 ppm, 10 ppm, 20 ppm, 50 ppm and 100 ppm.

About 200 mg of the adsorptive foam sheet of Example 2 was added to 30.0 mL of the above cesium aqueous solution, respectively, and then shaken at room temperature for 24 hours. Thereafter, changes in the concentration of cesium ions in the solution were measured using ICP-MS, and the adsorption capacity of the adsorptive foam sheet for cesium ions was calculated (the average value of three samples was used). The adsorbent foam of the present invention (PB content: 2.5 wt%) had a saturated adsorption amount of 1.17 mg/g in the case of a cesium aqueous solution prepared using deionized water. On the other hand, in the case of the cesium aqueous solution prepared using seawater, the saturated adsorption amount was 1.08 mg/g.
The adsorption capacity of the adsorptive foam sheet of Comparative Example 1 (sheet-like adsorptive foam containing no Prussian blue) was similarly measured. The adsorption capacity was about μg/g, and the trapping performance was greatly inferior to that of the adsorptive foam of the present invention. It was confirmed that the sheet-like adsorptive foam produced by the method of the present invention has adsorption performance derived from the adsorbent.

Thus, it was possible to produce an absorbent foam in the form of a sheet by the method of the present invention. The adsorbent (Prussian blue) was firmly retained in the produced sheet-like adsorptive foam. Furthermore, the adsorbent foam was able to adsorb the target substance (cesium) of its adsorbent (Prussian blue). By selecting an appropriate adsorbent for the target substance, the production method of the present invention can produce a sheet-like adsorptive foam capable of capturing the target substance.

Claims (8)

A method for producing an adsorptive foam comprising a composite formed from an adsorbent capable of adsorbing and retaining a target substance and nanocellulose, comprising:
A liquid containing a water-based liquid dispersion medium, a water-dispersible resin, a cross-linking agent, a foaming agent, and a composite formed from an adsorbent capable of adsorbing and retaining a target substance and nanocellulose a raw material preparation step of obtaining a raw material mixture;
a foaming step of mechanically foaming the liquid raw material mixture to obtain a foamed mixture;
a molding step of molding the foamed mixture into a sheet on a substrate;
a drying step of heating the sheet-shaped foamed mixture to evaporate the dispersion medium;
A method of making an absorbent foam comprising: 2. The method for producing an adsorptive foam according to claim 1, wherein the liquid raw material mixture or the foamed mixture is further blended with a cell stabilizer in at least part of the raw material preparation process, the foaming process, and the molding process. 3. The method for producing an adsorptive foam according to claim 1, wherein the water-dispersible resin is one or more selected from urethane emulsion, (meth)acrylic emulsion, and ethylene vinyl acetate emulsion. the foaming agent is an anionic surfactant,
4. The method for producing an adsorptive foam according to claim 2, wherein the cell stabilizer is a metal cation source for precipitating the anionic surfactant. The adsorptive foam according to any one of claims 1 to 4, wherein the foaming agent is a sulfosuccinate having a hydrocarbon group with 12 to 18 carbon atoms and a degree of unsaturation of 2 or less. manufacturing method. The method for producing an adsorptive foam according to any one of claims 1 to 5, wherein the adsorbent capable of adsorbing and holding the target substance is Prussian blue. An adsorptive foam comprising a composite formed from an adsorbent capable of adsorbing and retaining a target substance and nanocellulose,
The absorbent foam has a thickness of 2 mm or less,
The size of the cells of the adsorptive foam is 20 to 250 μm,
The absorbent foam has a skin layer with a thickness of 1 μm or less on at least one side,
The skin layer is a denser area compared to the central part of the foam,
An adsorptive foam capable of adsorbing and removing the target substance. A method of adsorbing/removing the target substance using the adsorptive foam produced by the production method according to any one of claims 1 to 6 or the adsorptive foam according to claim 7.