JPH0657012A - Production of polyvinyl-alcoholic gel formed articles - Google Patents

Abstract

PURPOSE:To obtain polyvinyl-alcoholic formed articles of a desired shape having high strength and water resistance by bringing a specific polyvinyl alcohol aqueous solution into contact with a liquid containing a boric acid compound to effect forming followed by insolubilization treatment. CONSTITUTION:(A) A polyvinyl alcohol aqueous solution of 0.3 to 40wt.% concentration having a pH of over 8, preferably 9 to 13 adjusted by adding an alkaline substance, suitably calcium hydroxide is brought into contact with (B) a liquid, preferably an aqueous solution containing 1g/l of a boric acid compound, suitably an inorganic acid of boric acid, to effect forming (for example, the component A is dripped from a cylindrical nozzle to form liquid drops and the drops are brought into contact with the component B), then the polyvinyl alcohol is insolubilized (for example, frozen lower than -5 deg.C, preferably lower than -10 deg.C, kept more than 1, preferably 10 hours, then thawed, and these operations are repeated more than once to give the objective formed polyvinyl alcohol gel, particularly spherical drops of polyvinyl-alcohol gel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyvinyl alcohol gel molding having a high affinity for biocatalysts such as enzymes and microorganisms.

[0002]

2. Description of the Related Art Polymer hydrogels are used in recent years with regard to biocatalyst immobilization carriers, water retention materials, cold insulation materials, alternatives to biogels such as eyes, skin and joints, drug sustained release materials, actuator base materials, etc. The research is active. Examples of the polymer material used as a raw material for these hydrogels include agar, alginate, carrageenan, polyacrylamide, polyvinyl alcohol, and photocurable resin. Of these, polyvinyl alcohol (hereinafter abbreviated as PVA) hydrogel is
It has a high water content, excellent permeability for enzymes and substrates, high affinity with living organisms, and is particularly excellent among high molecular water-containing gels.
As the shape of this polyvinyl alcohol-based hydrogel,
In consideration of fluidity, filling effect, and handleability, spherical shape is often required.

Conventionally, as a method for molding a PVA gel,
A method in which a mixed aqueous solution of PVA and sodium alginate is brought into contact with an aqueous solution of calcium chloride to be spheroidized, and then the PVA is gelled (JP-A-64-43188), and a method in which the aqueous PVA solution is brought into contact with a saturated boric acid aqueous solution and gelled. (Sewerage Association, 23, 41 (1986); water and wastewater,
30, p. 36 (1986)) is known.

[0004]

In order to produce a PVA gel, a method of bringing a mixed aqueous solution of PVA and sodium alginate into contact with a calcium chloride aqueous solution is as follows. When metal ions such as magnesium ions, strontium ions, barium ions, aluminum ions, potassium ions, cerium ions, and nickel ions are mixed, the mixed aqueous solution immediately gels, and it is impossible to mold it into a desired shape. It was In the method of dropping the PVA aqueous solution into the boric acid aqueous solution, the dropped droplets were stuck to each other, and a molded product having a desired shape could not be obtained. Further, gelation with boric acid is a reversible reaction, and the gel is easily dissolved due to a change in pH, etc., which makes practical application difficult.

[0005]

Means for Solving the Problems As a result of intensive studies by the present inventors in order to solve the above problems, the hydrogen ion exponent (p
The present invention finds a method for producing a PVA-based gel molded article, which comprises subjecting a PVA aqueous solution having H) of 8 or more to contact with a liquid containing a boric acid-based compound, and then insolubilizing the PVA. Came to complete. The PVA gel obtained according to the present invention has excellent affinity with biocatalyst, strength and durability applicable to various reaction types, and excellent characteristics such as high water resistance and chemical resistance. have.

Hereinafter, the method for producing the PVA-based gel molded article of the present invention will be described in more detail. First, the components used in the present invention will be described. The average degree of polymerization of PVA used in the present invention is preferably 1,000 or more, more preferably 1700 or more. The saponification degree of PVA is preferably 98.5 mol% or more, and fully saponified PVA of 99.85 mol% or more.
Is more preferable from the viewpoint of gel formation. As the PVA of the present invention, in addition to non-modified PVA, various known modified PVA can be used as long as the effects of the present invention are not impaired. The higher the concentration of the PVA aqueous solution, the stronger the gel is formed, but if the required gel strength is obtained, PV
A lower concentration of the aqueous solution A is more advantageous from the viewpoint of raw material cost. Types and amounts of additive components other than PVA, PVA
Although it is necessary to select an appropriate concentration depending on the liquid temperature of the mixed aqueous solution and the molding method, when the PVA mixed aqueous solution is dropped at room temperature, PVA will be formed from the viewpoint of moldability and gel strength.
The concentration of the aqueous solution is preferably 0.3 to 40% by weight. In the present invention, the method for adjusting the hydrogen ion index (pH) to 8 or more is not particularly limited, but the pH of the PVA aqueous solution is 8 or more, preferably pH 9 to 9 by adding an alkaline substance.
The method of adjusting to 13 is preferable. Examples of the alkaline substance include calcium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, barium hydroxide, aluminum hydroxide, calcium carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, calcium oxide and the like. Among them, calcium hydroxide, calcium carbonate and calcium oxide are particularly preferable. The boric acid compound in the present invention is not particularly limited as long as it generates a borate ion, and examples thereof include boric acid, borate salts, and borate esters. Among them, boric acid or an inorganic salt of boric acid is included. preferable. The concentration of the liquid containing the boric acid compound (the liquid is preferably an aqueous solution) is 1
It is preferably g / liter or more, more preferably 10 g / liter or more, and a saturated solution may be used. Further, an alkaline substance may be added to the liquid containing the boric acid compound to adjust the pH to near neutral.

Next, one example of a method of molding using the above-mentioned respective components (manufacturing method in the case of molding into a spherical shape) will be described more specifically. An alkaline substance is added to the PVA aqueous solution to adjust the pH to 8 or more. Alternatively, an alkaline substance may be added in advance to water in which PVA is dissolved, the pH may be adjusted to 8 or more, and then PVA may be dissolved. The PVA aqueous solution contains biocatalysts such as microorganisms and enzymes, a culture medium of the microorganisms, a reinforcing material for increasing the strength of the spherical gel, a filler for adjusting the specific gravity of the produced gel, etc. within a range that does not inhibit the gelation of PVA. You may add. The PVA aqueous solution obtained by the above method is dropped, for example, from a tubular die,
Alternatively, a droplet is formed by spraying from a spray nozzle and then brought into contact with a liquid containing a boric acid compound.
When the droplets of the PVA aqueous solution come into contact with a liquid containing a boric acid compound, they become spherical due to the surface tension, and the outermost surface of the sphere solidifies into a thin film to form a spherical molded product of the PVA aqueous solution. The diameter of the spherical molded product is the diameter of the die, spray pressure, PVA
By adjusting the viscosity of the aqueous solution, a diameter of 1 mm to 2
It can be arbitrarily changed to 0 mm. The liquid containing the boric acid compound may be allowed to stand, but by forcibly stirring it with a stirrer or the like, the reaction between the molded product of the PVA aqueous solution and the boric acid compound is promoted, and the spherical molded products are completely agglomerated. It can be prevented. Practically, in the case of producing a large amount of PVA gel, the diameter of the spherical molded article can be made uniform by using a pump or the like for the extrusion for dropping the PVA aqueous solution. For example, by using a roller pump that compresses and feeds a flexible tube, the discharge amount from the die becomes constant, and a uniform spherical molded product is easily obtained. The above method is an example of a method of forming a sphere,
The shape of the molded product obtained by the production method of the present invention is not particularly limited, and any shape such as spherical shape, fibrous shape, rod shape, square shape, elliptical shape, disk shape, cylindrical shape, and columnar shape is possible. PVA molded in liquid boric acid compound
The molded product is separated from the liquid containing the boric acid compound and then PV
Insolubilization treatment of A is performed. For the insolubilization treatment of PVA, any known method can be used. For example, (1) Freezing at −5 ° C. or lower, preferably −10 ° C. or lower, holding for at least 1 hour or longer, preferably 10 hours or longer, and then thawing is repeated at least once, preferably twice or more. (2) Contact with a liquid containing a compound having a syneresis action of PVA. Immersion time is 10 minutes or more, preferably 3
0 minutes or more is good. Examples of the compound having a synergic action of PVA include sodium sulfate, ammonium sulfate, potassium sulfate, magnesium sulfate, aluminum sulfate, sodium citrate, ammonium citrate, potassium citrate,
Examples of the liquid include at least one compound selected from the group consisting of magnesium citrate, aluminum citrate, sodium tartrate, ammonium tartrate, potassium tartrate, magnesium tartrate, aluminum tartrate and the like, and an aqueous solution of sodium sulfate is particularly preferable. The concentration is 100g
/ Liter or more is preferable, and a saturated aqueous solution is particularly preferable. (3) After being dried to a water content of 20% by weight or less, preferably 5% by weight or less, it is immersed in water. Examples of the drying method include all methods such as natural drying, blast drying, heat drying, vacuum drying and freeze drying. After drying, in order to further strengthen the bonds between PVA molecules, heat treatment at 150 ° C. or higher, preferably 200 ° C. or higher, or crosslinking operation with formaldehyde or glutaraldehyde may be performed. Among the above methods, the method (1) is more preferable,
Two or more of the methods (1) to (3) may be used in combination. The PVA-based gel molded product thus obtained has a strength that does not deform or damage for a long period of time, and can be continuously used without being attacked by water or various chemicals. Is high.

[0008]

The function of the present invention is not always clear, but when the pH of the boric acid compound is 8 or more, chemical cross-linking with PVA is easily formed, and P
It is considered that the chemical cross-linking is instantaneously formed by the contact between the VA aqueous solution and the liquid containing the boric acid compound, so that no sticking occurs and the desired shape, particularly the spherical shape, can be formed.

[0009]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Example 1 PVA (average degree of polymerization: 4100, saponification degree: 99.85 mol%) was washed with warm water at 40 ° C. for about 1 hour, and then PVA was adjusted to have a PVA concentration of 5% by weight (hereinafter abbreviated as wt%). Water is added to make the total amount 792 g, and calcium hydroxide 8 g
Was added. The pH was 12. While stirring this,
It was treated at 110 ° C. for 2 hours to dissolve PVA. Internal diameter 2 with an injection needle with an internal diameter of 1 mm attached to the end of these mixed solutions
1m with a roller pump that uses one mmφ vinyl tube
The solution was fed at a rate of 1 / min and added dropwise to a 30 g / l boric acid aqueous solution stirred with a stirrer from a height of 5 cm of the water surface. The dropped droplets were immediately spheroidized in an aqueous boric acid solution. Separating these spheroidized PVA mixed molded products from the aqueous boric acid solution,
After washing lightly with distilled water, saturated N stirred with a stirrer
a ↓ 2 SO ↓ 4 By immersing in an aqueous solution for 90 minutes,
An opaque white flexible spherical gel was obtained.
The gel is spherically shaped and non-sticky. Particle size is 3 ~
It was 3.5 mmφ. PVA thus obtained
The gel was examined for durability in water. 300 g of water was added to 30 g of the gel, and the mixture was stirred at 30 ° C. No change in particle size or strength was observed even after 1 month.

Example 2 The same PVA as in Example 1 was washed with warm water at 40 ° C. for about 1 hour, water was added to PVA to make the concentration of PVA 5 wt% to make the total amount 792 g, and 8 g of calcium hydroxide was added. It was The pH was 12. 110 while stirring this
It was treated at 2 ° C. for 2 hours to dissolve PVA. Internal diameter 2 mmφ with these mixed liquids attached to the tip with an injection needle with an internal diameter of 1 mm
The solution was fed at a rate of 1 ml / min with a roller pump using one vinyl tube of No. 1, and added dropwise to a 30 g / l boric acid aqueous solution stirred by a stirrer from a height of 5 cm of water surface. The dropped droplets were immediately spheroidized in an aqueous boric acid solution. These spheroidized PVA mixed moldings were separated from the boric acid aqueous solution, washed lightly with distilled water, and then stirred with a stirrer to obtain saturated Na ↓ 2
After soaking in SO ↓ 4 aqueous solution for 10 minutes, saturated Na ↓ 2SO ↓ 4
It was separated from the aqueous solution and dried at 105 ° C. for 4 hours. When this was re-immersed in water, an opaque white, flexible, spherical gel was obtained. This gel is formed into a spherical shape and is not sticky. The particle size was 3 to 3.5 mmφ. The PVA gel thus obtained was examined for durability in water. 300g of water is added to 30g of gel, 30 ℃
It was stirred at. No change in particle size or strength was observed even after 1 month.

Example 3 The same PVA as in Example 1 was washed with warm water at 40 ° C. for about 1 hour, water was added to PVA so that the concentration of PVA was 5 wt% to make the total amount 792 g, and 8 g of calcium hydroxide was added. It was The pH was 12. 110 while stirring this
It was treated at 2 ° C. for 2 hours to dissolve PVA. Internal diameter 2 mmφ with these mixed liquids attached to the tip with an injection needle with an internal diameter of 1 mm
The solution was fed at a rate of 1 ml / min with a roller pump using one vinyl tube of No. 1, and added dropwise to a 30 g / l boric acid aqueous solution stirred by a stirrer from a height of 5 cm of water surface. The dropped droplets were immediately spheroidized in an aqueous boric acid solution. All of these spherical PVA mixed moldings were separated from the boric acid aqueous solution, lightly washed with distilled water, and then frozen at -20 ° C for 20 hours,
Thaw at room temperature. An opaque white, flexible, spherical gel was thus obtained. The gel is spherically shaped and non-sticky. The particle size was 3 to 3.5 mmφ. The PVA gel thus obtained was examined for durability in water. 300 g of water was added to 30 g of the gel, and the mixture was stirred at 30 ° C. No change in particle size or strength was observed even after 1 month.

Comparative Example 1 The same PVA as in Example 1 was washed with warm water at 40 ° C. for about 1 hour, and water was added to PVA so that the concentration of PVA was 5 wt% to make the total amount 800 g. No calcium hydroxide was added. The pH was 7. 110 while stirring this
It was treated at 2 ° C. for 2 hours to dissolve PVA. Internal diameter 2 mmφ with these mixed liquids attached to the tip with an injection needle with an internal diameter of 1 mm
The solution was fed at a rate of 1 ml / min with a roller pump using one vinyl tube of No. 1, and added dropwise to a 30 g / l boric acid aqueous solution stirred by a stirrer from a height of 5 cm of water surface. The dropped liquid droplets were immediately solidified in the boric acid aqueous solution, but the liquid droplets were stuck to each other and a spherical molded product could not be obtained.

Comparative Example 2 The same PVA as in Example 1 was washed with warm water at 40 ° C. for about 1 hour, water was added to PVA so that the concentration of PVA was 5 wt% to make the total amount 792 g, and 8 g of calcium hydroxide was added. It was The pH was 12. 110 while stirring this
It was treated at 2 ° C. for 2 hours to dissolve PVA. Internal diameter 2 mmφ with these mixed liquids attached to the tip with an injection needle with an internal diameter of 1 mm
The solution was fed at a rate of 1 ml / min with a roller pump using one vinyl tube of No. 1, and added dropwise to a 30 g / l boric acid aqueous solution stirred by a stirrer from a height of 5 cm of water surface. The dropped droplets were immediately spheroidized in an aqueous boric acid solution. All of these spherical PVA mixed moldings were separated from the boric acid aqueous solution and lightly washed with distilled water. The subsequent PVA insolubilization treatment was not performed. An opaque white, flexible, spherical gel was thus obtained. This gel is formed into a spherical shape and is not sticky. The particle size was 3 to 3.5 mmφ.
The PVA gel thus obtained was examined for durability in water. Add 300g of water to 30g of gel,
The mixture was stirred at 30 ° C. After 3 days, it was found that the gel was dissolved and there was a problem in durability.

[0014]

As is apparent from the above examples, according to the present invention, it is possible to easily obtain a polyvinyl alcohol gel molding having a desired shape, particularly a spherical shape, and the obtained molding is Because of its high strength and sufficient water resistance, it is useful as a bioreactor, a carrier for wastewater treatment, a water retention material, a cold insulation material and the like.

Claims (2)

[Claims] 1. A polyvinyl alcohol which is formed by bringing an aqueous polyvinyl alcohol solution having a hydrogen ion index (pH) of 8 or more into contact with a liquid containing a boric acid compound, and then subjecting the polyvinyl alcohol to an insolubilization treatment. A method for producing an alcohol-based gel molded article. 2. The method for producing a polyvinyl alcohol-based gel molded article according to claim 1, wherein the molded article has a spherical shape.