JP2013049782A - Gel and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel, wherein: intensity thereof is improved; a polymerization process for producing the gel is reduced; the degradation and yellowing due to long-term use are prevented; corrosion to a metal is reduced; and/or loads on environment and biology, caused during processing, can be reduced.SOLUTION: The gel includes: a first crosslinked network structure (A) obtained by immersing a cellulose solution in a poor solvent for cellulose, wherein the cellulose solution is formed by dissolving a cellulose raw material (a) in a solvent (s); and a molecular chain (B) obtained by introducing a monomer (b) into the first crosslinked network structure (A) and then polymerizing the monomer (b), wherein the monomer has a polymerizable unsaturated bond.

Description

  The present invention relates to a gel using cellulose and a method for producing the same.

Gel materials have been used for high water-absorbing resins, disposable diapers, sanitary products, soft contact lenses, indoor water-containing sheets, etc. . In addition, it has sustained drug release properties and is applied to medical materials such as drug delivery systems and wound dressings. It is also used for shock absorbing materials, vibration control / soundproof materials, etc., and its uses are diverse.
However, such a gel material generally has no strength, and the structure is destroyed by a minute stress. Therefore, the gel material is not suitable for an application requiring strength. In recent years, various gel materials have been proposed in which the strength is greatly improved from the conventional gel materials as described above.

For example, a topological gel in which the cross-linking points move along the main chain (for example, Patent Document 1), a nanocomposite gel using hydrophilic clay as a cross-linking point (for example, Patent Document 2), and a double in which two types of network structures enter each other Network gels (for example, Patent Document 3) and tetrapeg gels having a uniform network structure (for example, Non-Patent Document 1) are called four major high-strength gels and are attracting attention.
These gels are higher in elongation and strength than conventional gels, and various applications and industrial uses are expected.
In particular, the double network gel is excellent in that it can freely design a balance between elongation and strength and is highly transparent. It is also known that a gel having higher elasticity and strength can be obtained by increasing the amount of the crosslinking agent added. Such a double network gel is proposed in Patent Documents 3 and 4, for example.

In Patent Document 3, it is essential to polymerize the first monomer component in order to form the first network structure constituting the double network gel. As the number of polymerization steps included in the manufacturing process increases, variations such as lot shake due to subtle differences in polymerization conditions are more likely to occur. Further, in Patent Document 3, the first monomer component for forming the first network structure contains an anionic monomer containing an acidic group in a certain amount or more. As the amount increases, deterioration or yellowing due to hydrolysis of the gel during long-term use tends to occur. Furthermore, the presence of acidic groups increases the corrosiveness to metals, the environmental load during processing, and the environmental impact.
Patent Document 4 describes the use of bacterial cellulose produced by microorganisms as a polymer constituting a double network gel. However, bacterial cellulose is not readily available and is not easy to prepare.

Japanese Patent No. 3475252 Japanese Patent No. 3914489 Japanese Patent No. 438297 Japanese Patent No. 4709756

Macromolecules, 2008, Vol. 41, No. 14, 5379 Mitsugu-5384 Mitsugu

  The present invention improves the strength of the gel, reduces the polymerization process for producing the gel, suppresses deterioration and yellowing during long-term use, reduces the corrosiveness to metals, and / or burdens on the environment and ecology during processing. It aims at providing the gel which can implement | achieve reduction, and its manufacturing method.

The gel of the present invention comprises a first crosslinked network (A) obtained by immersing a cellulose solution in which a cellulose raw material (a) is dissolved in a solvent (s) in a poor solvent for cellulose, It has a molecular chain (B) obtained by introducing a monomer (b) having a polymerizable unsaturated bond into one crosslinked network structure (A) and polymerizing the monomer (b). It is characterized by that.
The monomer (b) preferably contains an electrically neutral monomer (b1).

  In the present invention, a cellulose raw material (a) is dissolved in a solvent (s) to prepare a cellulose solution, and the cellulose solution is immersed in a poor solvent for cellulose to form a first crosslinked network structure ( A) forming step, introducing the monomer (b) having a polymerizable unsaturated bond into the first crosslinked network structure (A), and polymerizing the monomer (b) There is provided a method for producing a gel characterized by comprising the step of:

According to the present invention, since the first crosslinked network structure (A) can be formed by a method in which a cellulose solution is immersed in a poor solvent to precipitate regenerated cellulose, the first crosslinking is not performed. The formed network structure (A) can be formed. By reducing the number of polymerization steps in the manufacturing process, product variations due to variations in polymerization conditions can be reduced.
According to the present invention, the first cross-linked network structure (A) is composed of cellulose, whereby a mechanical strength is improved and a gel excellent in handleability is obtained.
In addition, by using cellulose, it is possible to reduce the amount of monomers containing acidic groups and charged monomers that have been used in the production of conventional gels. It is possible to suppress deterioration and yellowing due to, and reduce the corrosiveness to metals, the environmental load during processing, and the ecological load.

<Gel>
The gel of the present invention is a gel in which water or an organic solvent is incorporated as a solvent in a network structure composed of a polymer.
The network structure means a network-like structure stretched in three dimensions by chemically or physically cross-linking polymers. The network structure is different from the entanglement of linear or branched polymer, and can incorporate a solvent into the network. Hereinafter, a network structure obtained by chemically or physically cross-linking polymers is referred to as a “crosslinked network structure”.

The gel of the present invention generally includes a first crosslinked network structure (A), a molecular chain (B) formed in the first crosslinked network structure (A), and a solvent (hereinafter referred to as gel). It may also be a solvent.) In addition to these, additives such as known colorants, plasticizers, stabilizers, reinforcing agents, inorganic fillers, impact modifiers, and flame retardants may be blended as necessary. The amount and type of additive to be blended, presence / absence of mixing, mixing ratio and the like are not particularly limited, and can be appropriately selected according to the use environment to be used.
The first crosslinked network structure (A) is made of regenerated cellulose obtained by immersing and precipitating a cellulose solution in which cellulose is dissolved in a poor solvent. The regenerated cellulose thus obtained has a network structure composed of crosslinked cellulose.
The molecular chain (B) is a molecular chain formed by the polymerization reaction of the monomer (b).
In the gel of the present invention, the structure formed by the first crosslinked network structure (A) and the molecular chain (B) may be an interpenetrating network structure or a semi-interpenetrating network structure.
The interpenetrating network structure is such that the molecular chain (B) forms a crosslinked network structure (hereinafter referred to as a second crosslinked network structure (B1)), and the first crosslinked network structure. It means a structure in which (A) and the second crosslinked network structure (B1) are overlapped and intertwined with each other.
The semi-interpenetrating network structure is such that the molecular chain (B) is a non-crosslinked molecular chain (B2) having no crosslinking point, and the first crosslinked network structure (A) and the non-crosslinked molecular chain (B2) means a structure intertwined with each other.

The amount and type of the gel solvent taken into the gel, the presence / absence of mixing, the mixing ratio, and the like are not particularly limited, and can be appropriately selected according to the use environment to be used. The gel solvent may be one kind of single solvent or two or more kinds of mixed solvents. For example, water or a mixture of water and an organic solvent is preferably used.
The organic solvent may be an organic substance that is in a liquid state at room temperature. For example, monohydric alcohols such as methanol and ethanol, dihydric alcohols such as ethylene glycol and propylene glycol, amines such as dimethylformamide and dimethylacetamide, acetone And ketones such as methyl ethyl ketone, dimethyl sulfoxide, tetrahydrofuran, benzene, toluene, xylene, acetic acid, ethyl acetate, butyl acetate, acetic anhydride and the like.

In the gel of the present invention, the gel solvent content (sometimes referred to as water content) is preferably 40 to 99% by mass, and more preferably 60 to 80% by mass.
In the present specification, the solid content in the gel is expressed as a mass after drying when the gel is dried at a temperature of 100 ° C. and a pressure of 50 mmHg (6.67 kPa) or less for 24 hours to remove the solvent in the gel. The content [% by mass] (also referred to as moisture content) of the solvent present in the gel is a value obtained from the following formula from the change in the mass of the gel before and after the drying.
Content of solvent in gel = (mass before drying−mass after drying) / mass before drying × 100

In the gel of the present invention, when the mass of the first crosslinked network structure (A) composed of cellulose is 1, the monomer (b The mass ratio of the molecular chain (B) formed by the polymerization reaction is preferably 0.1 to 500, more preferably 1 to 500, and particularly preferably 2 to 500. If the degree of polymerization of cellulose increases, the mechanical strength of the cellulose gel is high, and a gel having a high water content can be prepared, so that the mass ratio of the molecular chain (B) to be introduced can be increased. Therefore, if a gel having high ductility or the like is to be prepared, the mass ratio of the molecular chain (B) formed by the polymerization reaction of the monomer (b) may be increased. When the mass ratio of the molecular chain (B) formed by the polymerization reaction of the monomer (b) was 0.1 or more, the monomer (b) was easy to form a network structure by the polymerization reaction, and was obtained. Gel strength is easily developed.
In the present invention, the gel is composed of the first crosslinked network (A), the molecular chain (B), a solvent and, if necessary, an additive. The solid content mass in the gel having the network structure (A) is regarded as the mass of the first crosslinked network structure (A), and the solid content mass in the gel of the present invention is regarded as the first crosslinked network structure. Considered as the sum of (A), molecular chain (B), and additives. The mass of the molecular chain (B) formed by the polymerization reaction of the monomer (b) is a value obtained from the following formula.
Mass of molecular chain (B) = (mass after drying of gel of the present invention−mass after drying of gel having first crosslinked network structure (A)) × (mass of monomer (b) / (single The mass of the monomer (b) + the mass of the additive))
The mass after drying is the mass after drying when the gel is dried at a temperature of 100 ° C. and a pressure of 50 mmHg (6.67 kPa) or less for 24 hours to remove the solvent in the gel.

<Method for producing gel>
In the method for producing a gel of the present invention, a cellulose raw material (a) is dissolved in a solvent (s) to prepare a cellulose solution, the cellulose solution is immersed in a poor solvent for cellulose, and the first crosslinking is performed. Forming the formed network structure (A), introducing the monomer (b) having a polymerizable unsaturated bond into the first crosslinked network structure (A), and the monomer (B) is polymerized.

[Formation of the first crosslinked network structure (A)]
First, the cellulose raw material (a) is dissolved in the solvent (s) to prepare a cellulose solution.
A cellulose raw material (a) is a composition which consists of a cellulose and the impurity which originates in a raw material or in the middle of manufacture, and can use a well-known cellulose raw material suitably.
As the cellulose raw material (a), for example, plant-derived cellulose, animal-derived cellulose (eg, squirt cellulose), regenerated cellulose and the like can be used. The cellulose in the cellulose raw material (a) may be a cellulose that has been chemically modified within a range that does not hinder dissolution in the solvent (s).
As the cellulose raw material (a), it is preferable to use a cellulose raw material having a cellulose purity of 90% or more from the viewpoint of hydrogen bonding property that expresses gel strength.
The form of the cellulose raw material (a) is not particularly limited, and various forms such as powder, thread, paper, and film can be used.
The average degree of polymerization of the cellulose raw material (a) is preferably 100 or more, more preferably 200 or more, and particularly preferably 400 or more, from the viewpoint of easily expressing the viscosity of the cellulose solution and the good strength of the obtained regenerated cellulose gel. In addition, the average degree of polymerization of the cellulose raw material (a) is preferably 30000 or less from the viewpoint of easy availability and handling.
The value of the average degree of polymerization of the cellulose raw material (a) in the present specification is a value obtained by using a published value or a well-known Mark-Houwink-Sakurada formula.

As the solvent (s) for dissolving the cellulose raw material (a), a known solvent can be used in the production of regenerated cellulose. For example, an aqueous caustic solution, an aqueous solution in which caustic and urea are dissolved in water (sometimes referred to as caustic / urea aqueous solution), a copper ammonia solution in which copper (II) hydroxide is dissolved in concentrated ammonia, lithium chloride Examples thereof include a solution dissolved in N, N-dimethylacetamide.
Among these, a caustic / urea aqueous solution is preferable because it is easily available, low in cost, and has a low environmental load and ecological load. The caustic / urea aqueous solution is more preferably an aqueous solution containing (i) 2 to 20% by mass or more of caustic and (ii) 2 to 40% by mass of urea or thiourea. When one or both of (i) and (ii) are not satisfied, the cellulose solubility of the aqueous caustic / urea solution is greatly reduced.
The caustic alkali is preferably potassium hydroxide, sodium hydroxide or lithium hydroxide, more preferably sodium hydroxide or potassium hydroxide from the viewpoints of storage stability of the cellulose solution, solubility of cellulose and the like. Lithium hydroxide is more preferable in terms of the storage stability of the cellulose solution and the solubility of cellulose. Sodium hydroxide is also used for food processing, and is particularly preferable in that the load on the environment and ecology is particularly small.

As a method for dissolving the cellulose raw material (a) in the solvent (s), a known method can be used.
The cellulose raw material (a) is added to the solvent (s) in terms of easy melting of the cellulose, and the mixture is cooled at around −20 ° C. with stirring and completely frozen, and then in the refrigerator (for example, 10 to 0 ° C.). It is preferable to use a method of gradually melting in step (b).
0.1-30 mass% is preferable and, as for the solid content concentration of the cellulose raw material (a) in a cellulose solution, 0.2-15 mass% is more preferable. When the cellulose solution is less than the lower limit of the above range, it is difficult for the celluloses to have a network structure when the cellulose solution is immersed in a poor solvent, and it is difficult to form a crosslinked structure. Exceeding the upper limit is not preferable from the viewpoint that the viscosity of the solution is too high, only cellulose having a low molecular weight can be dissolved, and the cellulose solution is not uniform.

Next, the cellulose solution is immersed in a poor solvent for cellulose to precipitate cellulose to obtain a regenerated cellulose gel. The poor solvent used at this time is not particularly specified as long as it does not dissolve cellulose. For example, alcohols, alkaline aqueous solutions, acidic aqueous solutions, water and the like can be used. Alcohol is desirable, and methanol is particularly preferable from the viewpoint of cost and the surface uniformity of the regenerated cellulose obtained by dipping.
A method for immersing the cellulose solution in the poor solvent is not particularly limited, and examples thereof include a method of immersing the cellulose solution in a poor solvent in a state where the cellulose solution is coated in a film form; a casting method and the like.
The regenerated cellulose gel thus obtained has a physical cross-linked structure due to hydrogen bonding between celluloses. Physical crosslinking differs greatly from chemical crosslinking in that it is reversible with environmental changes. A gel formed by physical crosslinking is called a physical crosslinking gel, and is a gel having a network structure (called a physical crosslinking network structure) formed by physical crosslinking of polymer chains.

A regenerated cellulose gel (physically crosslinked gel) obtained by immersing a cellulose solution in a poor solvent incorporates the poor solvent in a crosslinked network structure.
This regenerated cellulose gel may be immersed in another solvent (for example, water or an organic solvent) different from the poor solvent, and the poor solvent incorporated in the crosslinked network structure may be exchanged with another solvent.
For example, a regenerated cellulose hydrogel can be obtained by immersing a regenerated cellulose gel obtained by immersing a cellulose solution in a poor solvent in water and completely exchanging the poor solvent in the regenerated cellulose gel with water. It is done.
When the poor solvent used for the production of the regenerated cellulose gel is different from the gel solvent in the gel to be obtained, it is preferable to replace the poor solvent with a gel solvent.

  As a preferable embodiment for forming the first crosslinked network structure (A), the solvent (s) of the cellulose solution contains (i) 2 to 20% by weight of caustic alkali, and (ii) 2 or 2 of urea or thiourea. A methanol-containing regenerated cellulose gel obtained by using a caustic / urea aqueous solution containing 40% by mass, using methanol as a poor solvent, and immersing the cellulose solution in methanol, which is a poor solvent, is added to water without drying. Regenerated cellulose hydrogel obtained by immersing and solvent substitution is preferred.

  The content of the solvent in the gel (regenerated cellulose gel) having the first crosslinked network structure (A) used in the next step (sometimes referred to as water content) is preferably 70 to 99.9% by mass, 80-99.8 mass% is more preferable.

[Formation of molecular chain (B)]
After the monomer (b) having a polymerizable unsaturated bond is introduced into the first crosslinked network structure (A) formed using the cellulose raw material (a), the monomer (b) is polymerized. To form a molecular chain (B).
Method (1): In the step of polymerizing the monomer (b), the monomer (b) is polymerized to form a molecular chain (B) and is crosslinked to form the first crosslinked network. A second crosslinked network structure (B1) is formed in the structure (A), and an interpenetrating network structure gel is obtained.
Method (2): In the step of polymerizing the monomer (b), only the monomer (b) is polymerized, and if it is not crosslinked, the first crosslinked network structure (A) is not cross-linked polymer chain. (B2) is formed, and a gel having a semi-interpenetrating network structure is obtained.

  The monomer (b) is a monofunctional unsaturated monomer having one polymerizable unsaturated bond. It is preferably one or a mixture of two or more selected from electrically neutral monomers (b1), anionic monomers (b2), and cationic monomers (b3). These can use a well-known monomer suitably. The monomer (b) contains at least an electrically neutral monomer (b1), which suppresses deterioration and yellowing due to hydrolysis of the gel during long-term use, corrosiveness to metals and during processing. It is preferable at the point which can prepare the gel which can reduce the burden on an environment and the burden on life.

As the electrically neutral monomer (b1), a known nonionic monomer can be used, and one kind may be used alone, or two or more kinds may be used in combination.
Examples of the electrically neutral monomer (b1) include acrylamide derivatives (acrylamide, dimethylacrylamide, N-isopropylacrylamide, N-methylolacrylamide, acryloylmorpholine, etc.), methacrylamide derivatives (methacrylamide, dimethylmethacrylamide, N -Isopropyl methacrylamide, N-methylol methacrylamide, methacryloyl morpholine, etc.), acrylate (hydroxyethyl acrylate, hydroxypropyl acrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, polyethylene glycol monoacrylate, methoxypolyethylene glycol monoacrylate, polyethylene glycol polypropylene) Glycol monoacrylate, polyethylene Glycol monoacrylate esterified product, polyethylene glycol monoacrylate derivative, etc.), methacrylate (hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, polyethylene glycol monomethacrylate, methoxypolyethylene glycol monomethacrylate, polyethylene glycol polypropylene glycol mono Methacrylates, polyethylene glycol monomethacrylate esterified products, polyethylene glycol monomethacrylate derivatives, etc.), acrylonitrile, 2-vinylpyridine, 4-vinylpyridine, N-vinylpyrrolidone, vinyl acetate, and other water-soluble materials such as alkyl (meth) acrylate ( Methyl (meta) Chryrate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, polypropylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate esterified product, polypropylene Nonionic monomers having poor water solubility such as glycol mono (meth) acrylate derivatives and (meth) acrylates having a reactive functional group (such as 2-hydroxyethyl (meth) acrylate and glycidyl (meth) acrylate) may be mentioned. It is not limited to this.

  As the anionic monomer (b2), a known anionic monomer can be used. For example, an unsaturated monomer having a sulfonic acid group (2-acrylamido-2-methylpropanesulfonic acid, p- Styrene sulfonic acid, vinyl sulfonic acid, etc.), unsaturated monomers having carboxylic acid groups (acrylic acid, methacrylic acid, maleic acid, succinic acid, itaconic acid, etc.), unsaturated monomers having phosphoric acid groups (methacrylic acid) Oxyethyl trimellitic acid and the like) and salts thereof. These anionic monomers may be used individually by 1 type, and may use 2 or more types together.

  As the cationic monomer (b3), a known cationic monomer can be used, and examples thereof include unsaturated quaternary ammonium salts represented by methacrylamidopropyltrimethylammonium chloride. A cationic monomer may be used individually by 1 type, and may use 2 or more types together.

Of the whole monomer (b), the content of the electrically neutral monomer (b1) is preferably 30% by mass or more, more preferably 50% by mass or more, and most preferably 100% by mass. preferable. As the content of the monomer (b1) is larger, deterioration or yellowing due to hydrolysis of the gel during long-term use is less likely to occur.
As the electrically neutral monomer (b1), a nonionic monomer having a molecular weight of 300 or less is preferably used. When such a monomer is used, it becomes easy to introduce a sufficient amount of the monomer (b) into the first crosslinked network structure (A), the polymerization is easy, and Since the molecular weight is likely to increase, it is easy to produce a high-strength gel.
As the electrically neutral monomer (b1), acrylamide is particularly preferable in terms of imparting high toughness (ductility) to the gel.

Examples of the method for polymerizing the monomer (b) include a radical polymerization method using a thermal polymerization initiator and a photopolymerization method using a photopolymerization initiator.
Examples of the thermal polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate, peroxides such as benzoyl peroxide, and azo initiators.
Examples of the photopolymerization initiator include general photopolymerization initiators such as alkylphenone initiators and acylphosphine oxide initiators.
In addition, when the 1st bridge | crosslinked network structure (A) is opaque and does not permeate | transmit light enough, the radical polymerization method by a thermal-polymerization initiator is preferable. In addition, when an unsaturated monomer whose behavior changes with temperature is used, a photopolymerization method using a photopolymerization initiator may be preferable.

[Method (1): Formation of Second Crosslinked Network Structure (B1)]
As a method of crosslinking the molecular chain (B) formed by polymerization of the monomer (b) to form a second crosslinked network structure (B1), a crosslinking method by chemical bonding, a crosslinking method by ionic bonding, Examples include a physical crosslinking method.
Specifically, the following crosslinking methods are mentioned. The method (α) is preferable because it does not require special equipment, the manufacturing process is not complicated, the operation is simple, and the network structure is easy to control, but these methods can also be used in combination.
(Α) A method in which a polyfunctional unsaturated monomer (c) having at least one or more carbon-carbon double bonds in one molecule is used together with the monomer (b) and crosslinked simultaneously with polymerization. .
(Β) A method in which after the monomer (b) is polymerized, a radical is generated in the molecular chain (B) formed by the polymerization of the monomer (b) by radiation irradiation to crosslink.
(Γ) A method in which after the monomer (b) is polymerized, functional groups of side chains of units derived from the monomer (b) constituting the molecular chain (B) are directly reacted.
(Δ) A method of polymerizing the monomer (b) and then cross-linking functional groups of side chains of units derived from the monomer (b) constituting the molecular chain (B) with a crosslinking agent.
(Ε) A method in which polyvalent metal ions (copper ions, zinc ions, calcium ions, etc.) are used for crosslinking by ionic bonds or coordinate bonds.

The polyfunctional unsaturated monomer (c) means an unsaturated monomer having two or more polymerizable functional groups. The polymerizable functional group is a functional group that forms a crosslinking point in the polymer, and examples thereof include a group having a polymerizable unsaturated bond such as a (meth) acryloyl group or a vinyl group.
As the polyfunctional unsaturated monomer (c) used for crosslinking, a known crosslinking agent can be used, and examples thereof include those shown below.

  Examples of the bifunctional unsaturated monomer include N, N-methylenebisacrylamide, monoethylene glycol dimethacrylate, diethylene glycol dimethacrylate, monopropylene glycol dimethacrylate, polyethylene glycol di (meth) acrylate, and polypropylene glycol di (meth) acrylate. , Polytetramethylene glycol di (meth) acrylate, ethoxylated polypropylene glycol di (meth) acrylate, ethoxylated bisphenol A di (meth) acrylate, propoxylated bisphenol A di (meth) acrylate, ethoxylated propoxylated bisphenol A di (meth) ) Acrylate and the like.

  Examples of trifunctional unsaturated monomers include ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, ethoxylated propoxylated trimethylolpropane tri (meth) acrylate, and ethoxylated pentaerythritol. Tri (meth) acrylate, propoxylated pentaerythritol tri (meth) acrylate, ethoxylated propoxylated pentaerythritol tri (meth) acrylate, ethoxylated isocyanuric acid tri (meth) acrylate, propoxylated isocyanuric acid tri (meth) acrylate, ethoxylated Examples include propoxylated isocyanuric acid tri (meth) acrylate.

Examples of tetrafunctional unsaturated monomers include ethoxylated pentaerythritol tetra (meth) acrylate, propoxylated pentaerythritol tetra (meth) acrylate, ethoxylated propoxylated pentaerythritol tetra (meth) acrylate, ethoxylated ditrimethylolpropane tetra ( And (meth) acrylate, propoxylated ditrimethylolpropane tetra (meth) acrylate, and the like.
These polyfunctional unsaturated monomers (c) may be used individually by 1 type, and may use 2 or more types together.

The step of forming the second cross-linked network structure (B1) includes first, in the first cross-linked network structure (A), a monomer (b), a polymerization initiator, and, if necessary, a plurality of By introducing a cross-linking agent such as a functional unsaturated monomer (c), the monomer (b) and the like are homogeneous in the solvent contained in the first cross-linked network structure (A). In a diffused state.
Specifically, a monomer solution in which the monomer (b) is dissolved in a solvent is prepared, and the gel having the first crosslinked network structure (A) is immersed in the monomer solution. A method of absorbing the monomer (b) and the like in the gel by solvent substitution is preferable. The solvent of the monomer solution is preferably the same as the gel solvent in the gel to be obtained.
Next, the monomer (b) is polymerized by applying heat or light to the first crosslinked network structure (A) into which the monomer (b) or the like has been introduced to form a molecular chain (B). . The crosslinking of the molecular chain (B) can be performed by the above-described method, and may be performed simultaneously with the polymerization of the monomer (b) or after the polymerization.

As described above, a gel having an interpenetrating network structure can be obtained by forming the second crosslinked network structure (B1) in the first crosslinked network structure (A).
In the interpenetrating network structure, the reactive functional group of the cellulose in the first crosslinked network structure (A) reacts with the monomer (b) to form a polymer such as a graft. You may,
The first crosslinked network structure (A) and the second crosslinked network structure (B1) may be partially crosslinked by the polyfunctional unsaturated monomer (c),
The monomer (b) is partially polymerized in the first crosslinked network structure (A) to form a polymer chain, and the polymer chain part and the second crosslinked network structure (B1) are polyfunctional. May be partially crosslinked by unsaturated monomer (c),
The reactive functional group of the cellulose in the first crosslinked network structure (A) and the second crosslinked network structure (B1) are partially crosslinked by the polyfunctional unsaturated monomer (c). The form of the interpenetrating network structure can be variously selected.
The reactive functional group possessed by the cellulose in the first crosslinked network structure (A) is a hydroxyl group derived from cellulose, a terminal aldehyde group or the like, or a carboxymethyl group or hydroxyethyl possessed by a chemically modified cellulose derivative. Means a group or the like.

[Method (2): Formation of non-crosslinked molecular chain (B2)]
The step of forming the non-crosslinked molecular chain (B2) is performed by first introducing the monomer (b) and the polymerization initiator into the first crosslinked network structure (A). The monomer (b) and the like are uniformly diffused in the solvent contained in the network structure (A). No cross-linking agent is used.
Specifically, in the same manner as in the above method (1), a monomer solution in which the monomer (b) and the like are dissolved in a solvent is prepared, absorbed in the gel, and then exposed to heat or light. To polymerize the monomer (b) to form a non-crosslinked polymer chain (B2).
By forming the non-crosslinked polymer chain (B2) in this way, the non-crosslinked polymer chain (B2) is formed in the first crosslinked network structure (A), and these are intertwined with each other. An interstitial network structure is obtained.
The non-crosslinked polymer chain (B2) can take the same form except that it has no crosslinking point with the second crosslinked network structure (B1). That is, in the semi-interpenetrating network structure, the reactive functional group possessed by the cellulose in the first crosslinked network structure (A) reacts with the monomer (b) to partially overlap the graft body or the like. A coalescence may be formed.

EXAMPLES Hereinafter, although a synthesis example, an Example, and a comparative example demonstrate this invention further more concretely, this invention is not limited to these synthesis examples and a Example.
<Test method>
[Measuring mechanical strength]
The gel formed to a thickness of 0.4 mm was punched into a dumbbell mold using a dumbbell mold (JIS-6251, No. 3) manufactured by TOYOSEIKI, and used as a test piece.
The test piece was subjected to a tensile test based on JIS K 6251 using a Tensilon universal testing machine (model: RTC-1350A-PL) to measure the breaking stress [unit: MPa] and the breaking strain [unit:%]. did. The measurement conditions were a temperature of 25 ° C. and a relative humidity of 65%.

<Synthesis Example 1: Preparation of regenerated cellulose hydrogel (A-1)>
In 100 g of an aqueous solution in which 4.6 g of lithium hydroxide, 15 g of urea and 80.4 g of water are dissolved, powdered cellulose (product name: CF11, manufactured by Whatman, derived from cotton linter, cellulose purity of 98% or more, average polymerization degree 200) 6 The solution with .4 g added was placed in a container and sealed. The vessel was immersed in liquid nitrogen, cooled with stirring, and stirring was continued until the solution was completely frozen. The solution was completely melted by leaving it in a refrigerator (3 to 7 ° C.) overnight to obtain a transparent cellulose solution in which cellulose was dissolved. A small amount of the cellulose solution was cast on a glass plate and stretched with a glass rod to form a film having a uniform thickness, and then immersed in an aqueous methanol solution having a concentration of 100% by mass. After 10 minutes, the gelled film was immersed in water and washed to obtain a regenerated cellulose hydrogel (A-1) having a first crosslinked network structure.
About regenerated cellulose hydrogel (A-1), moisture content [unit: mass%], content of total solid content (mass after drying) [unit: mass%], mechanical strength (breaking stress and breaking strain; hereinafter the same). ) Was measured. The results are shown in Table 1 (hereinafter the same).
The total solid content (mass after drying) of the regenerated cellulose hydrogel (A-1) is regarded as the content of the first crosslinked network (A) composed of cellulose.

<Example 1: Production of gel (PG-1) having an interpenetrating network structure>
200 g of pure water, 100 g of acrylamide (AAm) as the monomer (b), 0.1 g of N, N′-methylenebisacrylamide (MBAAm) as the crosslinking agent, and 2-hydroxy-2-methyl-1-as the initiator 0.01 g of phenyl-propan-1-one (product name: dar 1173, manufactured by BASF) was added and mixed to prepare a monomer solution.
In this monomer solution, the regenerated cellulose hydrogel (A-1) obtained in Synthesis Example 1 was immersed all day and night, and the monomer solution was absorbed into the gel by solvent substitution.
The soaked regenerated cellulose hydrogel (A-1) is taken out, sandwiched from the upper surface with a glass plate, and polymerized by irradiation with a chemical lamp (TOSHIBA, fluorescent lamp for insect trap, 20W, model number: FL20S · BL) for 1 hour. As a result, a gel (PG-1) having an interpenetrating network structure was obtained.
About gel (PG-1), moisture content [unit: mass%], content [unit: mass%] of total solid content (mass after drying), and mechanical strength were measured.
The total solid content (mass after drying) of the gel (PG-1) was regarded as the sum of the masses of the first crosslinked network structure (A) and the molecular chain (B), and obtained in Synthesis Example 1. Considering the total solid content of the regenerated cellulose hydrogel (A-1) as the content of the first crosslinked network (A), the content of the molecular chain (B) [unit: mass%], and The mass ratio [(B) / (A)] of the molecular chain (B) when the mass of the first crosslinked network structure (A) was 1 was calculated.
These results are shown in Table 1 (hereinafter the same).

<Synthesis Example 2: Preparation of regenerated cellulose hydrogel (A-2)>
Regenerated cellulose hydrogel (A-2) was obtained by the same method except that the mass of the powdered cellulose in Synthesis Example 1 was changed from 6.4 g to 9.8 g. Measurement was performed in the same manner as in Synthesis Example 1.
<Example 2: Production of gel (PG-2) having interpenetrating network structure>
A gel (PG-2) having an interpenetrating network structure was obtained by the same method except that the regenerated cellulose hydrogel (A-2) was used instead of (A-1) in Example 1. Measurements were performed in the same manner as in Example 1.

<Synthesis Example 3: Preparation of Regenerated Cellulose Hydrogel (A-3)>
A regenerated cellulose hydrogel (A-3) was prepared in the same manner as described above except that 6.4 g of powdered cellulose in Synthesis Example 1 was changed to 6.4 g of ashless pulp (manufactured by Advantec, cellulose purity of 98% or more, average polymerization degree 800). ) Measurement was performed in the same manner as in Synthesis Example 1.
<Example 3: Production of gel having interpenetrating network structure (PG-3-1)>
A gel (PG-3-1) having an interpenetrating network structure was obtained by the same method except that regenerated cellulose hydrogel (A-3) was used instead of (A-1) in Example 1. Measurements were performed in the same manner as in Example 1.

<Example 4: Production of gel (PG-3-2) having semi-interpenetrating network structure>
In Example 3, a gel (PG-3-2) having a semi-interpenetrating network structure was obtained by the same method except that MBAAm as a crosslinking agent was not used. Measurements were performed in the same manner as in Example 1.
<Example 5: Production of gel (PG-4) having an interpenetrating network structure>
A gel (PG-4) having an interpenetrating network structure was obtained in the same manner as in Example 3 except that the amount of acrylamide (AAm) as the monomer (b) was changed from 100 g to 200 g. Measurements were performed in the same manner as in Example 1.

<Comparative Example 1>
In this example, the first crosslinked network structure (A) was formed by a method using no cellulose.
That is, 100 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as a monomer, 4 g of MBAAm as a cross-linking agent, and 0.1 g of the dar1173 (product name) as an initiator are mixed in 400 g of pure water and mixed. An aqueous solution was prepared. A circular silicon frame is affixed on a glass plate, an AMPS aqueous solution is poured inside, a glass plate is sandwiched from the top so that the liquid does not leak, and a chemical lamp is irradiated for 15 hours to polymerize. A gel (B-1) having one crosslinked network structure was obtained.
The obtained gel (B-1) was immersed in the same monomer solution used in Example 1 all day and night, and the monomer solution was absorbed into the gel by solvent substitution.
The soaked gel (B-1) is taken out, sandwiched from the upper surface with a glass plate, and polymerized by irradiation with a chemical lamp for 1 hour in the same manner as in Example 1 to obtain a gel having an interpenetrating network structure (PB-1). )
About gel (PB-1), the moisture content [unit: mass%], content [unit: mass%] of total solid content (mass after drying), and mechanical strength were measured.

<Comparative example 2>
A gel (PB-1) having an interpenetrating network structure was obtained in the same manner as in Comparative Example 1 except that the amount of MBAAm, which was a cross-linking agent, used for preparing the AMPS aqueous solution was changed from 4 g to 6 g. Measurements were performed in the same manner as in Comparative Example 1.

In Examples 1 to 5, it was not necessary to polymerize the monomer by using cellulose to form the first crosslinked network structure, and a high-strength gel could be obtained. In addition, compared to the regenerated cellulose hydrogel obtained in Synthesis Examples 1 to 3, the molecular chain (B) was formed to form an interpenetrating network structure or a semi-interpenetrating network structure, so that the values of the breaking stress and breaking strain were The cellulose-containing gel which improved and was excellent in durability was able to be obtained.
In Example 2, when the cellulose concentration in the gel was increased as compared with Example 1, the breaking stress was improved. Moreover, the mass ratio of (B) / (A) became small, and the value of elongation at break decreased.
In Example 3, the rupture stress and the rupture strain were improved by using ashless pulp having an average degree of polymerization of cellulose higher than that of powdered cellulose used in Example 1. It can be seen that the higher the degree of polymerization of cellulose, the higher the strength of the gel.
In Example 4, a high-strength gel was obtained even as a semi-interpenetrating network structure in which the molecular chain (B) was not crosslinked.
In Example 5, the amount of the monomer (b) used was larger than that in Example 3 to increase the mass ratio of (B) / (A), and the values of the breaking stress and breaking strain were further improved. . Therefore, a high-strength gel can be easily obtained by increasing the average degree of polymerization of the cellulose used and further increasing the content of the monomer (b) in the gel.

In Comparative Examples 1 and 2, which did not use cellulose, it is necessary to polymerize a monomer in order to form the first crosslinked network structure. For this reason, cost increases and there is a high possibility that lot blurring occurs due to subtle differences in polymerization conditions. Moreover, a fracture stress is inferior compared with Examples 1-5.
The gel of the present invention does not need to be polymerized to form the first network structure by using cellulose in the first crosslinked network structure, and it is difficult to obtain a cellulose material such as bacterial cellulose. The present inventors have found that a high-strength gel can be realized by using a simple method of dissolving and reprecipitating cellulose without the need to use the slag.
In addition, without using the electrolyte monomer represented by AMPS used in Comparative Example 1 and Comparative Example 2 for forming the first cross-linked network structure, by using cellulose instead of this, a gel is obtained. It is possible to obtain a gel with less deterioration over time and corrosiveness to metals, and less burden on the environment and ecology. Therefore, the gel of the present invention can be widely developed as an earth-friendly bio-based polymer that has been demanded in recent years.

Claims (3)

A first crosslinked network structure (A) obtained by immersing a cellulose solution in which a cellulose raw material (a) is dissolved in a solvent (s) in a poor solvent for cellulose;
A molecular chain (B) obtained by introducing a monomer (b) having a polymerizable unsaturated bond into the first crosslinked network structure (A) and polymerizing the monomer (b); A gel characterized by comprising:   The gel according to claim 1, wherein the monomer (b) contains an electrically neutral monomer (b1). Dissolving cellulose raw material (a) in solvent (s) to prepare a cellulose solution;
Immersing the cellulose solution in a poor solvent for cellulose to form a first crosslinked network (A);
Introducing the monomer (b) having a polymerizable unsaturated bond into the first crosslinked network structure (A);
A method for producing a gel, comprising a step of polymerizing the monomer (b).