KR100642032B1 - Polyvinyl alcohol hydrogel and preparation method thereof - Google Patents

Abstract

The present invention relates to a polyvinyl alcohol hydrogel having a network structure formed by intertwining a fibrous material having a diameter of 0.1 to 50 µm as a surface layer. The gel has a large surface area, excellent microbial trapping ability and liquid passage ability, and has an excellent purifying function. The present invention also provides a method for producing such a hydrogel.

Description

Polyvinyl alcohol hydrogel and preparation method thereof

The present invention relates to a hydrogel suitable for a microbial carrier used in wastewater treatment, a bioreactor, and the like, and a method for preparing the same.

Polymer gels include biocatalyst carriers, humectants, refrigerants; It has been actively studied as a substitute for biogels such as eyes, skin, joints, drug release controlling substances and substrates for actuators.

Known polymeric hydrogels consist of agar, alginate, carrageenan, polyacrylamide, polyvinyl alcohol (hereinafter referred to as "PVA") and photocurable resins. Among them, PVA-based gels having high mechanical strength and excellent hydrophilicity (such as water-soluble and microbial habitat) were particularly actively studied and attracted attention as microbial carriers.

Hydrogels used as microbial carriers and bioreactors need to be excellent in their ability to retain microorganisms and water and to capture microorganisms and other fines. Various angles of research have been made regarding the improvement of such properties of hydrogels.

For example, Japanese Laid-Open Patent Publication No. 4416/1995 discloses an aqueous solution containing PVA and sodium alginate in contact with an aqueous calcium chloride solution or the like to solidify at least the sodium alginate present on the surface of the PVA solution, followed by freezing and It describes a PVA gel obtained by repeating the melting operation or contacting with a coagulant for PVA to gel the molded product. However, the gel obtained by contact with the coagulant for PVA has a low microbial trapping ability because the surface is smooth (see FIG. 4). The gel obtained by repeating the freezing and thawing operation forms irregularities on the surface but does not form irregularities inside the gel but forms a dense layer near the surface. Therefore, the microorganisms do not invade the inside of the gel and only live on the surface (see FIG. 5).

Japanese Laid-Open Patent Publication No. 17904/1988 discloses a macroparticulate porous PVA obtained by dispersing a mixed aqueous solution of PVA and a natural gelling accelerator (e.g. sodium chloride) in an organic solvent such as toluene to form spherical particles and spontaneously gel. Is described. By this process, PVA precipitates from the mixed aqueous solution to cause phase separation, giving the precipitate a heterogeneous porous and large PVA particle body. However, in this step, a gel having a smooth surface is formed as in the gel obtained by contact with the PVA coagulant (see FIG. 4).

Japanese Laid-Open Patent Publication No. 276488/1988 describes a process of adding sodium hydrogen carbonate or the like to a PVA aqueous solution to generate fine bubbles, and then freezing and melting the mixture to gelate the mixture. However, the obtained gel is poor in microbial trapping because of its smooth surface. In addition, the gel does not retain microorganisms for a long time because large pores (size: 100 μm or more) are formed from bubbles, and microorganisms easily invade the inside.

Japanese Laid-Open Patent Publication No. 251190/1995 discloses a gel having a structure in which short fibers are present on a surface such as a beard. The gel is obtained by dropwise adding a mixed solution of PVA and sodium alginate to an aqueous calcium chloride solution in which short fibers are dispersed. However, the adhesion of short fibers in such a process deteriorates the gel properties. In addition, the presence of fibers such as whiskers causes the gel particle bodies to become entangled with each other and the particle bodies are easily damaged. In addition, since the network structure made up of a plurality of fibers is not formed on the gel surface, improvement of microbial trapping ability is insufficient.

Accordingly, it is an object of the present invention to provide a PVA gel with excellent properties, including microbial entrapment and microbial habitat.

It is another object of the present invention to provide an efficient method for preparing PVA gel.

The present invention provides:

1) polyvinyl alcohol hydrogel having a network structure formed by interweaving a fibrous material having a diameter of 0.1 to 50 µm as a surface layer;

2) the polyvinyl alcohol hydrogel according to 1), having a spherical shape having a diameter of 1 to 10 mm;

3) the polyvinyl alcohol hydrogel according to 1) or 2), which is further acetalized;

4) a bioreactor comprising a polyvinyl alcohol hydrogel according to any one of 1) to 3);

5) Purification apparatus using the polyvinyl alcohol hydrogel according to any one of 1) to 3);

6) a polyvinyl alcohol molding obtained by removing at least a part of the water contained in the polyvinyl alcohol hydrogel according to any one of 1) to 3);

7) a gel formed by alkali treatment of a polyvinyl alcohol hydrogel having a network structure formed by intertwining a fibrous material having a diameter of 0.1 to 50 µm as a surface layer;

8) A phase separation solution by adding a substance capable of phase-separating the polymer mixed solution (material C) to a polymer mixed solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) which gels upon contact with a cation. Preparing a polymer, contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solid with a coagulation liquid which serves to solidify the polymer A. Method for producing a polyvinyl alcohol hydrogel, comprising the step of;

9) A phase separation solution by adding a substance (substance C) capable of phase separating the polymer mixture solution to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) which gels upon contact with a cation. Preparing a polymer, contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solidified product with a coagulation liquid which coagulates the polymer A. A process for producing a polyvinyl alcohol hydrogel, comprising the step of removing and partially or all of the polymer B from the gel obtained in the above step;

10) A phase separation solution by adding a substance (substance C) capable of phase-separating the polymer mixture solution to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels upon contact with a cation. Preparing a polymer, contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solidified product with a coagulation liquid which coagulates the polymer A. A process for producing a polyvinyl alcohol hydrogel, comprising the step of performing the acetalization reaction simultaneously with or after gelling;

11) A phase separation solution by adding a substance (substance C) capable of phase separating the polymer mixture solution to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) which gels upon contact with a cation. Preparing a polymer, contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solidified product with a coagulation liquid which coagulates the polymer A. And performing acetalation reaction after gelling or gelling at the same time and removing some or all of polymer B from the gel obtained in the above step.

12) The process according to any one of 8) to 11), wherein the polymer to be gelled upon contact with a cation (polymer B) is sodium alginate.

Reference will now be made to the following detailed description with reference to the accompanying drawings, in order to facilitate a more complete understanding of the present invention and its numerous attendant advantages.

The present invention has been completed based on the finding that PVA gel (see FIGS. 1 to 3) having a network structure formed by interweaving a fibrous material having a diameter of 0.1 to 50 μm as a surface layer is excellent in various performances. The use of such a gel as a sewage purification material provides the trapping ability of microorganisms and the like and the habitat of microorganisms having an excellent network structure forming a rough surface. Since the gel does not block the passage of the liquid therein, the liquid easily passes therethrough, and the sewage purification ability is further improved.

For this reason, the gel has a remarkably large effective surface area, which is effective as a filter as well as a filler for chromatography. Since the network structure of the surface layer is very loose, it is excellent in moisturizing properties and the gel is effective as a refrigerant or a moisturizing agent.

In terms of microbial entrapment, increase in surface area, liquid permeability and moisture retention, the diameter of the fibrous material forming the network structure should be 0.1 to 50 µm, preferably 0.2 to 20 µm, more preferably 0.3 to 10 µm, respectively. The surface layer may include other fibrous materials and materials other than those described in the specification without departing from the effect of the present invention.

The fibrous materials need not be identical in shape and can differ in thickness and length from one another. Similarly, when looking at a fibrous material, the thickness, shape, etc. may be different in the longitudinal direction.

Various effects can be obtained by the surface layer including the network structure formed by entanglement of such fibrous materials.

The surface of the gel according to the invention does not necessarily need to be completely covered with fibrous material. However, it is preferable that 30% or more, preferably 50% or more, and more preferably 80% or more of the gel surface are composed of a network structure (surface layer) comprising a fibrous substance.

In view of the microbial entrapment and strength and wear resistance of the gel, the thickness of the surface layer is preferably about 0.1 to 20%, preferably about 1 to 10% of the gel diameter (maximum diameter).

In addition, the inside of the gel according to the present invention is preferably made of a sponge-like structure finer than the structure of the surface layer. When the gel is used as a carrier for a biocatalyst, the presence of a fibrous substance as the surface layer facilitates microbial trapping, and the microorganisms can inhabit under favorable conditions in which fibers are present. In this case, if the inside of the gel contains a finer structure, the microorganisms can be improved and the gel strength can be increased, which is preferable in both cases. In terms of gel strength, it is preferable that the interior of the gel does not consist of fibrous material but comprises an internally connected sponge-like structure having a plurality of fine pores.

The micropores of the inner sponge-like structure preferably have a diameter of 0.1 to 100 m, more preferably 0.5 to 50 m and most preferably about 1 to 10 m.

In terms of strength and abrasion resistance of the gel, the dense internal thickness is preferably at least 10%, more preferably at least 40%, especially at least 50% and at most 99.9%, more preferably at most 99% of the gel diameter (maximum diameter). .

The interior of the gel need not have a uniform structure. Thus, the interior may have various structures in part, and may be connected to the surface layer through an intermediate layer having another structure. In the latter case, the intermediate layer preferably has a structure that does not form a barrier film between the surface layer and the inside so that microorganisms can be introduced therein. In terms of liquid permeability, the porosity of the intermediate layer is preferably larger than the porosity of the interior (microporous layer). When the gel is used as a biocatalyst carrier, anaerobic bacteria inhabit the inside of the gel and aerobic bacteria in the middle and surface layers to obtain a better purification effect.

As shown in FIG. 3, it is particularly preferred to provide the gel with an intermediate layer comprising a plurality of finger-shaped voids separated from each other by thin walls extending from the interior to the surface layer. Such a structure is excellent in the invasion and liquid permeation effect of microorganisms. The diameter of the voids is preferably about 10 to 200 μm.

The thickness of the intermediate layer is not particularly limited and may be about 1 to 50% of the gel diameter (maximum diameter). If the pores of the intermediate layer are larger than the pores of the dense inner layer, the strength of the gel is reduced if the thickness of the intermediate layer is too large. Therefore, it is recommended to adjust the thickness of the intermediate layer according to the intended purpose and use of the gel.

The gel of the present invention may have a desired shape such as spherical, elliptical, square, film, columnar, hollow columnar, square columnar, rod or amorphous. In order to use it as a carrier of a bioreactor or the like, it is preferably spherical in view of durability, filling effect, fluidity and ease of handling in a sewage treatment tank. In this case, the diameter (maximum diameter) of the spherical gel is preferably 1 to 10 mm, more preferably 3 to 5 mm in view of the separability from the garbage of the prepared carrier and the activity of the microorganisms.

The gel of the present invention is preferably at least 50% by weight, more preferably at least 60% by weight, most preferably at least 90% by weight. When used for sewage treatment, the gel is preferably higher in water content only when the strength is sufficient. In view of the strength of the gel, the water content is preferably adjusted to 98% by weight or less.

The water content is measured as follows. The hydrogel sample is immersed in 25 ° C. water for 24 hours. After removing the water on the surface, measure the wet weight (W1) of the gel. Then, after drying for 4 hours at 105 ℃ the dry weight (W2) of the gel is measured. The water content (%) is calculated from the wet weight (W1) and the dry weight (W2) by the formula water content (%) = (W1-W2) / W1 x 100.

The method for producing the PVC gel having the surface layer containing the fibrous material is not particularly limited, but it is preferable to use the following method for producing the gel efficiently. That is, the process involves adding a vinyl alcohol polymer (polymer A) and a substance (substance C) capable of phase separating the polymer mixture solution to a polymer mixture solution containing a polymer (polymer B) that gels upon contact with a cation. Preparing a separation liquid, contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solid with a coagulation liquid which serves to solidify the polymer A. Gelling to form, or

A phase separation solution was prepared by adding a substance (substance C) capable of phase separating the polymer mixture solution to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels upon contact with a cation. Contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solids with a coagulation liquid which coagulates the polymer A. And removing some or all of the polymer B from the gel obtained in the above step, or

A phase separation solution was prepared by adding a substance (substance C) capable of phase separating the polymer mixture solution to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels upon contact with a cation. Contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solids with a coagulation liquid which coagulates the polymer A. And carrying out the acetalization reaction simultaneously or after gelling, or

A phase separation solution was prepared by adding a substance (substance C) capable of phase separating the polymer mixture solution to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels upon contact with a cation. Contacting the phase separation liquid with a cation-containing liquid to solidify at least polymer B present on the surface of the phase separation liquid, and contacting the obtained solids with a coagulation liquid which coagulates the polymer A. Carrying out the acetalation reaction at the same time or after gelling and removing some or all of the polymer B from the gel obtained in the above step.

All types of polyvinyl alcohol can be used as polymer A without particular limitation. However, it is preferable to use PVA whose average degree of polymerization is at least 1,000, preferably at least 1,500 in terms of strength and water resistance of the gel and at most 20,000, preferably at most 10,000 in terms of processability and cost. The saponification degree is preferably 95 mol% or more, more preferably 98 mol% or more, and most preferably 99.8 mol% or more in terms of water resistance. In the present invention, unmodified PVA can be used without any problem, but various modified PVAs can also be used as long as they do not impair the effects of the present invention.

Preferred examples of polymer B which gels upon contact with a cation, preferably a polyvalent metal ion, are water soluble synthetic polymers such as polyethylene glycol and derivatives thereof and water soluble polyurethanes, water soluble polysaccharides such as alginic acid and salts thereof, carrageenan, Met and chitosan. These polymers can be used in combination as long as the effects of the present invention are not impaired.

Of these polymers, it is suitable to use water-soluble polysaccharides, most of which are gelled upon contact with cations and are excellent in gel formation properties. Modified PVAs, such as itaconic acid modified PVA and maleic acid modified PVA, may also be used, which are functional groups capable of solidifying upon contact with a cation.

The use of alkali metal salts of alginic acid, in particular sodium alginate, is preferred in view of gel formation and network structure formation.

Higher PVA concentrations in the polymer mixed solution result in higher gel strength but poor microbial formatting. Therefore, it is preferable to set PVA concentration to 1 to 40 weight%, More preferably, it is 3 to 20 weight%. The concentration of the polymer B is preferably 0.2 to 4% by weight, more preferably 0.5 to 2% by weight in terms of gel formation.

In terms of gel formation, network formation and gel strength, the mixing weight ratio between polymer A and polymer B is preferably 100: 0.2-30, in particular 100: 1-20, and the total polymer concentration is 1-50% by weight. desirable.

In the solvent used, water is generally used in terms of easy gel formation, but other solvents may also be used in combination with water. Examples of other solvents are alcohols such as ethylene glycol, glycerin and polyethylene glycol, dimethyl sulfoxide, dimethylformamide and diethylenetriamine. One or more of these solvents may be used with water. An aqueous thiocyanate solution can also be used.

When using a solvent mainly containing water, it is preferable to use a water-soluble polymer, especially a water-soluble polysaccharide, as the polymer B.

The temperature of the prepared solution is preferably about 10 to 100 ° C., in particular about 20 to 80 ° C., in terms of thermal stability and solution viscosity of the polymer used.

In the present invention, it is preferable to use a mixed solution containing polymer A and polymer B, but if necessary, polymers other than these two polymers and other additives can be added. Examples of other additives useful are microbial media, reinforcements to increase gel strength and fillers for specific gravity adjustment.

In order to form the surface layer comprising the fibrous material, the polymer mixed solution containing the polymer A and the polymer B must be phase separated. To this end, a phase separation solution is prepared by adding a substance (substance C) capable of phase separating the polymer to a polymer mixed solution containing polymer A and polymer B.

There is no particular limitation on selecting substance C, but it is preferable to use a salt as substance C. Of the various salts, salts containing divalent or higher anions are preferred in terms of gel formation and have little effect on the acetalization reaction. In this case, it is preferable to use a polymer precipitated by salting out, especially sodium alginate, as polymer B which gels upon contact with polyvalent metal ions in view of gel formation and phase separation liquid formation.

Examples of salts that can be used include carbonates such as sodium carbonate, potassium carbonate, calcium carbonate, ammonium carbonate and magnesium carbonate; Hydrocarbon salts such as sodium hydrocarbon, potassium potassium, hydrocarbon ammonium, calcium hydrogen carbonate and magnesium hydrogen carbonate; Sulfates such as sodium sulfate, potassium sulfate, ammonium sulfate and magnesium sulfate; Phosphates such as sodium phosphate, potassium phosphate, ammonium phosphate and magnesium phosphate and halides such as sodium chloride and potassium chloride. These salts can also be used in combination. Hydrocarbonates and sulfates are particularly preferred in terms of solubility, cost and the fact that they hardly remain after the gel formation process.

When sodium alginate is used as polymer B, preference is given to using sodium bicarbonate and / or sulfate as material C.

The amount of the substance capable of phase separating the polymer is preferably about 0.01 to 1% by weight based on the weight of the polymer mixed solution.

"Phase separation" as used herein means the phenomenon that a homogeneous solution containing at least polymer A and polymer B separates into a plurality of solutions, each with a specific composition when material C is added. The resulting heterogeneous mixture is called "phase separation liquid".

The occurrence of phase separation can be confirmed by the following test. That is, the substance C is added to the polymer liquid mixture containing at least the polymer A and the polymer B, and the mixture is fully stirred. The absorbance of the mixture is then irradiated with an absorbance analyzer 66Onm. The data obtained are plotted against the amount of addition of substance C. The graph shows that phase separation occurred at the point where the rate of increase in absorbance increased rapidly.

Phase separation may be confirmed by visually observing the mixture separating into two or more layers by leaving the mixture at 60 ° C. for 1-7 days.

In view of processability, it is preferable to add substance C to the polymer mixture containing polymer A and polymer B, but the order of addition may be changed.

The state of the network structure (diameter and density of the fibrous material, and thickness of the surface layer) can be determined by the phase separation degree, mixing ratio and viscosity ratio of the polymer used, mixing conditions, the temperature of the mixed liquid, the type and amount of the substance C, the solidification temperature, and the like. Can be controlled by adjusting.

For example, increasing the amount of material C or raising the temperature of the polymer mixture of polymer A and polymer B increases the thickness ratio of the surface layer and the intermediate layer. Conversely, decreasing the amount of substance C or lowering the temperature of the polymer mixture containing polymer A and polymer B increases the content of the inner layer (microporous layer).

When polymer A is PVA (polymerization degree: 1,700; degree of saponification: 99.8 mol%) and polymer B is sodium alginate, the phase separation solution comprising polymer A and polymer B comprises a mixed layer containing polymer A and polymer B and polymer A. Or a single layer containing polymer B alone. In this case, when the specific gravity of the separation layer is made to be similar to each other or a medium value, a fine dispersion is formed to reduce the diameter of the fibrous material forming the surface layer.

The phase separation thus obtained is contacted with a solution containing a cation, preferably a polyvalent metal ion. Generally, an aqueous solution containing a cation is used. At this time, first, the phase separation liquid is sufficiently mixed to obtain a homogeneous dispersion, which is contacted with a cation-containing solution. This process allows the gel obtained to have a uniform structure.

Examples of cations usable for this purpose include alkaline earth metal ions such as calcium ions, magnesium ions, strontium ions and barium ions; Polyvalent metal ions such as aluminum ions, nickel ions and cerium ions; Potassium ions and ammonium ions. Two or more of these cations may be used in combination. In the solvent used, water is generally used in terms of easy gel formation. Calcium chloride is preferred in view of cost, handleability and gel formation. In this case, the use of sodium alginate together is preferable because the gel forming effect is excellent and the resulting gel can have a surface formed by a fine network structure.

The concentration of the cation-containing solution is preferably 0.05 to 1 mol / l, more preferably about 0.1 to 0.5 mol / l in terms of gel formation effect.

Contacting the phase separation with a cation-containing solution solidifies at least the polymer B present on the surface of the phase separation to form a mixture. If a spherical gel particle is required, the spherical phase can be easily obtained by surface tension by dropwise adding or spraying the phase separation solution to the cation-containing solution. At this time, it is preferable to add using an extrusion nozzle. The diameter of the extrusion nozzle can be appropriately selected and is generally about 1 to 10 mm. The mixture may be injected into a mold or the resulting gel may be cut or processed to obtain the desired form.

After the solids have been separated, the desired gel is obtained by contacting with the coagulant and gelling therein. Polymer B present at least on the surface of the phase separation solidifies in the previous step. Contact with the coagulant also gels Polymer A, resulting in a gel comprising Polymer A and Polymer B. Preferably, some or all of the polymer B contained in the gel is removed to produce a gel according to the present invention.

Polymer B can be removed by any method without particular limitation as long as the method used does not remove polymer A. For example, Polymer B is removed by treatment with an aqueous solution containing an alkali metal salt or by incubating the gel for a long time to induce microbial degradation. For example, the polymer B can be almost completely removed by immersion in an aqueous sodium hydroxide solution (1 mol / l, 30 ° C.) for 24 hours. As used in claim 7, the term "alkali treatment" means treatment with aqueous sodium hydroxide solution.

Removal of polymer B results in the formation of a surface layer comprising a network structure in which the fibrous material is entangled, and at the same time, pores are formed inside the gel to increase the surface area. This improves the ability to bind microorganisms, microbial habitat and liquid permeability. In order to fully exhibit these effects, the polymer B must be removed by 50% by weight or more, preferably 80% by weight or more. However, the gel can be used with little removal of Polymer B. In this case, polymer B remains part or all at the beginning of use but is gradually removed over time due to the action of microorganisms or alkalis. Therefore, the step of removing polymer B can be determined according to the purpose of use of the gel.

The mechanism associated with the formation of a gel comprising a surface layer having such a specific structure is not clear, but is estimated as follows. In the phase separation of polymer A and polymer B, polymer B forms a dispersed phase (sea portion) and polymer A forms a dispersed phase (island portion). When the phase separation liquid comes into contact with the cation-containing solution, the molecules present at least on or near the surface of the polymer B molecules forming the dispersed phase solidify. Then, in contact with the coagulating liquid, polymer A, which forms islands, coagulates. Removal of polymer B forms a fibrous material.

Examples of coagulants suitable for coagulating vinyl alcohol polymers include sodium sulfate, ammonium sulfate, potassium sulfate, magnesium sulfate, aluminum sulfate, sodium citrate, ammonium citrate, potassium citrate, magnesium citrate, aluminum citrate, sodium tarta Liquids containing at least one compound selected from the group consisting of latex, ammonium tartrate, potassium tartrate, magnesium tartrate and aluminum tartrate. Among them, an aqueous sodium sulfate solution having excellent coagulation property is preferable. In this case, the concentration is preferably at least 50 g / l, more preferably at least 100 g / l and most preferably using a saturated sodium sulfate solution.

Other treatments, such as crosslinking treatments, may be performed at certain stages in the manufacturing process to improve the water resistance of the PVA gel. Acetalization reactions are particularly preferred because they are easy to carry out and can greatly improve the water resistance. The acetalization reaction can be carried out at any stage, but is preferably carried out simultaneously with the coagulation (gelling) treatment with the coagulating solution and / or after the gelling treatment, and in particular in terms of ease of operation, to be carried out simultaneously with the coagulation treatment.

The acetalization reaction is preferably carried out using an aqueous solution containing aldehyde and acid. In view of ease of operation, it is preferable to incorporate aldehyde into the coagulation solution to coagulate (gel) the reaction and to perform the acetalization reaction. The method is more effective because it prevents the hydrogel from swelling or dissolving in the presence of aldehydes or acids due to the presence of coagulant.

Examples of aldehydes used for this purpose are glyoxal, formaldehyde, benzaldehyde, succinate, malondialdehyde, glutaraldehyde, adipinealdehyde, terephthalaldehyde, nonanedial and their acetalization reaction products. In particular, formaldehyde and glyoxal, malondialdehyde and their acetalization reaction products, and glutaraldehyde are preferred.

Examples of acids that can be used include strong acids such as sulfuric acid, hydrochloric acid and nitric acid; Weak acids such as acetic acid, formic acid and phosphoric acid and acid salts such as ammonium hydrogen sulfate. Of these, strong acids, in particular sulfuric acid, are preferred.

The acetalization reaction degree of PVA is preferably 10 to 65 mol%, more preferably 30 to 60 mol% in view of the water resistance of the gel and the habitat of the microorganism. Acetalization reactivity can be controlled by adjusting conditions such as concentration of aldehyde and acid used, reaction time, reaction temperature and the like.

When the acetalization reaction is carried out after the coagulation reaction, the concentrations of aldehyde and acid of the reaction solution are preferably 0.01 g / l or more and 0.5 to 300 g / l, respectively, when formaldehyde and sulfuric acid are used. When the acetalization reaction is carried out simultaneously with the coagulation reaction, the concentrations of aldehyde and acid in the reaction solution are preferably 0.05 to 200 g / l and 1 to 100 g / l, respectively. In this case, if sodium sulfate is used as the coagulant, the concentration of the coagulant is preferably 10 to 300 g / l at the temperature of the treatment solution at 10 to 80 ° C.

When the gel of the present invention is used as a carrier of a bioreactor, it is preferable to wash the coagulated (or further acetalized) gel with water and neutralize. In particular, in order to use as a carrier for a biocatalyst, since aldehyde deteriorates the formatting of microorganisms, it is preferable to wash sufficiently.

Hydrogel of the present invention having a surface including a network structure has a wide surface area and excellent moisturizing properties can be used in various applications. Typically used as filter material (suspended solid removal filter), humectants, refrigerants, substitutes of biogels such as eyes, skin and joints, substances for controlling drug release, substrates of irritants and chromatographic fillers.

In particular, the hydrogel of the present invention can be suitably used in bioreactors for fixing biocatalysts such as enzymes and microorganisms, and can also be used as a sewage purification agent.

If the hydrogel contains a biocatalyst such as a microorganism, the containing method is not particularly limited. For example, an overall fixation method may be used that involves incorporating the microorganisms into a premixed solution. When the gel is later treated with adverse effects on the biocatalyst, such as an acetalization reaction, it is preferable to add the biocatalyst after the gel formation is completed.

Any biocatalyst may be used for this purpose, and available biocatalysts include bacteria, antinomysheets, fungi, yeast, sludge cultured and activated in pure or mixed form.

Examples of microorganisms that can be used are Mucor, Fusarium, Cladothrix, Sphaerotilus, Zoglea, Leptomitus, Aspergillus, Microorganisms belonging to the genus Ryzopus, Pseudomonas, Escherichia, Saccharomyces and Candida. In addition, there are Staphylococcus aureus, methane bacteria, butyric acid bacteria, lactic acid bacteria, Bacillus subtilis, slime mold, incomplete fungi, nitrate bacteria, nitrite bacteria and denitrification bacteria.

When the hydrogel of the present invention is used for sewage treatment, it is preferable to fix bacteria that produce protease, glucosidase and lipase. More specifically, aerobic bacteria such as nitrogenated bacteria and anaerobic bacteria such as denitrogen bacteria, sulfate reducing bacteria and methane bacteria are mentioned. When using enzymes, enzymes of specific origin, ie enzymes derived from animals and enzymes derived from microorganisms, may be appropriately selected.

The hydrogel thus obtained is excellent in effect, but if necessary, is used after drying at least a part of the water contained in the hydrogel, or after immersion in water again after drying. Removing at least some of the water makes it lighter and easier to transport. In principle, the gel can be used not only in the state of containing water but also in the state of not containing water.

The term "containing water" is not limited to containing water, but includes a state containing a mixture of water and other liquids and / or solids.

Other features of the invention will be apparent from the description of the following exemplary embodiments, but are not intended to be limiting.

In the following examples and comparative examples, various properties can be obtained according to the following methods.

Gel structure

The surface and the cut surface of the gel are taken with an electron micrograph. The diameter of the fibrous material of the surface layer and the thickness of the surface layer are observed.

Formalization

PVA hydrogel samples are dried at 105 ° C. for 2 hours. 0.2 g of the sample is accurately weighed and placed in a distillation apparatus filled with 25% sulfuric acid solution. Steam is introduced while the distillation apparatus is heated. The separated formaldehyde is distilled with water and taken up in a 2% NaHSO ₃ aqueous solution. Excess NaHSO ₃ is back titrated with I ₂ to determine the amount of free formaldehyde. The degree of formalization is then calculated from the molar ratio of free formaldehyde to the hydroxyl group content of the PVA gel.

Water content

The hydrogel sample is immersed in water at 25 ° C. for 24 hours. After removing the water on the surface, the wet weight (W1) of the sample is measured. The sample is then dried at 105 ° C. for 4 hours to weigh the dry weight (W2). The water content (%) is calculated by the following equation.

[Equation 1]

Water content (%) = (W1-W2) / W1 × 100

TOC removal rate (mg-TOC / l -gel · h)

The TOC removal rate is higher for gels with better microbial habitat.

500 g of hydrogel samples are immersed in the sewage treatment tank of Kuraray Okayama Plant for one month. Next, 100 g of the sample is taken and immersed in 1 L of wastewater adjusted to TOC 500 mg / l. The wastewater is vented and the rate of TOC removal per gel weight is measured.

durability(%)

Hydrogel sample (500 g) is immersed in the sewage treatment tank of a Kurere Okayama plant. After one year the weight retention is tested.

Example 1

8% by weight of PVA (average degree of polymerization: 1,700; saponification degree: 99.8 mol%), 1% by weight of sodium alginate (DUCK ALGIN NSPL, manufactured by Kibun Food Chemifa Co.) and sodium hydrogencarbonate 0.3 A mixed aqueous solution containing% by weight is prepared. The mixed aqueous solution causes a phase separation such as a suspension and becomes cloudy. A phase separation solution was supplied at a rate of 5 ml / min by a roller pump equipped with a silicon tube having an internal diameter of 4 mm and a nozzle having an internal diameter of 3 mm, and added dropwise to an aqueous solution of 0.1 mol / l calcium chloride while stirring with a stirrer. Droplet added is precipitated because at least the sodium alginate present on its surface solidifies in the aqueous solution of calcium chloride. The obtained solid is spherical.

The spherical solids are immersed in an aqueous solution containing 20 g / l formaldehyde, 20 g / l sulfuric acid, and 100 g / l sodium sulfate at 40 ° C. for 60 minutes to acetalize and solidify with gel particle sieves. The acetalized gel granules are washed with water to obtain spherical hydrogel granules having a diameter of about 5 mm with excellent flexibility.

Observing the structure of the obtained gel, it can be seen that the surface layer has a network structure formed by entangled fibrous materials having a diameter of about 0.3 to 10 μm, and the thickness of the surface layer is about 5% of the maximum diameter of the gel.

It was found that a dense inner layer with micropores having a thickness of about 75% of the maximum diameter of the gel and a diameter of about 1 to 10 μm was formed inside the gel.

It has also been found that there is an intermediate layer between the surface layer and the inner layer which is formed of a plurality of finger-shaped pores from the surface layer to the inner layer and has pores having a diameter of about 100 μm. The thickness of the intermediate layer is about 20% of the maximum diameter of the gel.

The gel obtained in Example 1 having a network structure in which the surface layer is formed of a fine fibrous material has a large surface area, so that microorganisms are easily attached and have excellent sewage treatment ability.

Gel having a dense inner layer having fine pores therein has a high gel strength and is suitable for incubating anaerobic bacteria and the like, and exhibits excellent purifying function.

In addition, the gel obtained in Example 1 having an intermediate layer formed of a plurality of finger-shaped pores directed from the surface layer to the inner layer is suitable for microorganisms to enter therein and inhabit. This structure allows sewage to easily pass through the gel, resulting in better purification properties.

The results are shown in Table 1.

Example 2

A mixed aqueous solution containing 5% by weight of PVA (average degree of polymerization: 4,000; saponification degree: 99.8 mol%), 1% by weight of sodium alginate (DUCk ALGIN NSPL, manufactured by Mood Food Chemipa Company) and 0.25% by weight of sodium sulfate was prepared. do. The mixed aqueous solution causes a phase separation such as a suspension and becomes cloudy. Subsequently, the solution was treated in the same manner as in Example 1 to produce spherical hydrogel particles having a diameter of about 5 mm with excellent flexibility.

Observing the structure of the gel, it can be seen that the surface layer has a network structure formed by entangled fibrous materials having a diameter of about 0.3 to 10 μm, and the thickness of the surface layer is about 5% of the maximum diameter of the gel.

It was found inside the gel that a dense inner layer with micropores having a thickness of about 80% of the maximum diameter of the gel and a diameter of about 2 to 20 μm was formed.

It has also been found that an intermediate layer is formed between the surface layer and the inner layer with a large number of finger-shaped pores from the surface layer to the inner layer and having pores having a diameter of about 50 μm. The thickness of the interlayer is about 15% of the maximum diameter of the gel.

The gel obtained in Example 2 shows excellent properties similar to the gel obtained in Example 1. The results are shown in Table 2.

Example 3

The finger hydrogel was obtained by repeating the method of Example 1 except that the phase separation solution was extruded into an aqueous calcium chloride solution. The resulting finger gel was cut to give columnar hydrogel chips 5 mm in diameter and 5 mm in length.

Observing the structure of the obtained gel, it can be seen that the surface layer has a network structure formed by entangled fibrous materials having a diameter of about 0.3 to 10 μm, and the thickness of the surface layer is about 5% of the maximum diameter of the gel.

It was found inside the gel that a dense inner layer with micropores having a thickness of about 80% of the maximum diameter of the gel and a diameter of about 1 to 10 μm was formed.

It has also been found that an intermediate layer is formed between the surface layer and the inner layer, which is formed of a plurality of finger-shaped pores from the surface layer to the inner layer and having pores having a diameter of about 80 μm. The thickness of the interlayer is about 15% of the maximum diameter of the gel.

Comparative Example 1

A mixed aqueous solution containing 8% by weight of PVA (average degree of polymerization: 1,700; saponification degree: 99.8 mol%) and 1% by weight of sodium alginate was used in the same manner as in Example 1 except that The method is repeated to produce a hydrogel particle having a diameter of about 5 mm.

Gels prepared without the use of a separation solution had a smooth surface without a surface layer made of fibrous material (see FIG. 4). As a result, the gel has poor microbial adhesion, reduced surface area and insufficient purification properties.

The results are shown in Table 1.

Comparative Example 2

Instead of the phase separation used in Example 1, a mixed aqueous solution containing 8% by weight of PVA (average degree of polymerization: 1700; degree of saponification: 99.8 mol%) and 1% by weight of sodium alginate is used. The solution was added dropwise to the same aqueous calcium chloride solution used in Example 1 in the same manner as in Example 1. The dropwise added droplets precipitate because at least the sodium alginate present on its surface solidifies in the aqueous solution of calcium chloride. The obtained solid is spherical.

The spherical particles are separated from the aqueous calcium chloride solution, washed with water and placed on a tray. Particle sieves are frozen in a freezer at −20 ° C. for 24 hours and thawed to room temperature to produce spherical hydrogel granules of about 5 mm in diameter. The gel obtained had a rough surface with irregularities such as craters (see FIG. 5). The gel has good microbial adhesion but poor cleaning properties due to the dense structure that prevents microorganisms from penetrating inside.

The results are shown in Table 1.

Comparative Example 3

A mixed aqueous solution containing 8% by weight of PVA (average degree of polymerization: 1,700; saponification degree: 99.8 mol%) and 5% by weight of sodium alginate (DUCK ALGIN NSPL, manufactured by Mood Food Chemipa Co., Ltd.) was prepared. The mixed aqueous solution is added dropwise to a 0.5 mole / l calcium chloride solution through a nozzle having an internal diameter of 0.8 mm. In the calcium chloride aqueous solution, PVA short fibers (Kuraray Co., Ltd.) of 6 mm in length and 2 denier in size were previously dispersed. The dropwise mixed aqueous solution solidifies into a spherical shape, while 1.3% by weight of PVA fibers bind like a beard to the solidified surface.

After washing the solid sufficiently with water, the process of freezing at −20 ° C. for 20 hours and melting at room temperature over 12 hours was repeated three times to obtain a PVA hydrogel in which PVA fibers were bound like a beard. The amount of fiber bound to the gel is 2% by weight based on the weight of the hydrogel. The length of the fiber from the gel surface is 2 to 5 mm. The gel has poor microbial adherence because a fine fibrous material that is not as fine as in the present invention adheres to the surface.

In addition, when the gel particle bodies are in contact with each other, the coarse fibers are in contact with each other to generate a large friction force. As a result, the fluidity of the gel particle body becomes poor and damage by contact is caused, resulting in insufficient durability.

The results are shown in Table 1.

In view of the above teachings, the invention is susceptible to various modifications and variations. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

TABLE 1

The hydrogel according to the present invention is excellent in sewage purification effect due to the large microorganism trapping and microbial habitat.

1 is a scanning electron micrograph (magnification: 60) showing an example of a PVA (polyvinyl alcohol) hydrogel surface structure according to the present invention.

Figure 2 is a scanning electron micrograph (magnification: 1000) showing the shape of the fibrous material forming the PVA hydrogel surface layer according to the present invention.

3 is a scanning electron micrograph (magnification: 60) showing an example of a cross section (internal structure) of a PVA hydrogel according to the present invention.

4 is a scanning electron micrograph (magnification: 60) showing the surface structure of a PVA hydrogel having a smooth surface obtained in Comparative Example 1. FIG.

FIG. 5 is a scanning electron micrograph (magnification: 60) showing the surface structure of PVA hydrogel obtained in Comparative Example 2 and having a rough surface with irregularities such as craters.

Claims (12)

A phase separation solution was prepared by adding a substance (substance C) capable of phase-separating the polymer mixture solution to a polymer mixture solution containing a polymer (polymer B) and gelling polymer (polymer B) upon contact with a cation. Steps, Contacting the phase separation liquid with a cation-containing drug to solidify Polymer B present on or near the surface of the phase separation liquid, Contacting the obtained solid with a coagulant which coagulates the polymer A and gelling it; and A polyvinyl alcohol hydrogel having as a surface layer a network structure formed by entangled fibrous materials having a diameter of 0.1 to 50 µm, produced by a method comprising the step of removing some or all of the polymer B from the obtained gel. The polyvinyl alcohol hydrogel according to claim 1, wherein the polyvinyl alcohol hydrogel has a spherical shape having a diameter of 1 to 10 mm. The polyvinyl alcohol hydrogel of claim 1 or 2, which is further acetalized. Bioreactor comprising a polyvinyl alcohol hydrogel according to claim 1 Purification apparatus using the polyvinyl alcohol hydrogel of Claim 1. A polyvinyl alcohol molding obtained by removing some or all of the water contained in the polyvinyl alcohol hydrogel according to claim 1. A phase separation solution was prepared by adding a substance (substance C) capable of phase-separating the polymer mixture solution to a polymer mixture solution containing a polymer (polymer B) and gelling polymer (polymer B) upon contact with a cation. Steps, Contacting the phase separation liquid with a cation-containing liquid to solidify Polymer B present on or near the surface of the phase separation liquid, and Polyvinyl alcohol having as surface layer a network structure formed by entanglement of a fibrous material having a diameter of 0.1 to 50 µm, prepared by a method comprising contacting and gelling the obtained solidified product with a coagulant liquid which coagulates polymer A. Gel characterized in that the hydrogel is formed by alkali treatment. A phase separation solution was prepared by adding a substance (substance C) capable of phase-separating the polymer mixture solution to a polymer mixture solution containing a polymer (polymer B) and gelling polymer (polymer B) upon contact with a cation. Steps, Contacting the phase separation liquid with a cation-containing liquid to solidify Polymer B present on or near the surface of the phase separation liquid, and A method for producing a polyvinyl alcohol hydrogel, comprising the step of contacting and gelling the obtained solidified product with a coagulating solution which coagulates polymer A. A phase separation solution was prepared by adding a substance (substance C) capable of phase-separating the polymer mixture solution to a polymer mixture solution containing a polymer (polymer B) and gelling polymer (polymer B) upon contact with a cation. Steps, Contacting the phase separation liquid with a cation-containing liquid to solidify B, the polymer present on or near the surface of the phase separation liquid, Contacting the obtained solid with a coagulant which coagulates the polymer A and gelling it; and A process for producing a polyvinyl alcohol hydrogel, comprising removing some or all of polymer B from the obtained gel. A phase separation solution is prepared by adding a substance capable of phase-separating the polymer mixture solution (material C) to a polymer mixture solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that is gelled in contact with a cation. , Contacting the phase separation liquid with a cation-containing liquid to solidify Polymer B present on or near the surface of the phase separation liquid, Contacting the obtained solid with a coagulant which coagulates the polymer A and gelling it; and A method for producing a polyvinyl alcohol hydrogel, comprising performing the acetalization reaction simultaneously with or after gelling. A phase separation solution was prepared by adding a substance (substance C) capable of phase-separating the polymer mixture solution to a polymer mixture solution containing a polymer (polymer B) and gelling polymer (polymer B) upon contact with a cation. Steps, Contacting the phase separation liquid with a cation-containing liquid to solidify Polymer B present on or near the surface of the phase separation liquid, Contacting the obtained solid with a coagulant liquid which coagulates polymer A, and gelling the same, Carrying out the acetalization reaction simultaneously or after gelling; and Method for producing a polyvinyl alcohol hydrogel, comprising the step of removing some or all of the polymer B from the gel obtained in the above step. The process according to claim 8, wherein polymer B is sodium alginate.

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