JPH01257026A - High-strength polyvinyl alcohol series hydrogel molded body and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a PVA series hydrogel molded body whose water retention rate and strength are high by a method wherein the title molded body is comprised of polyvinyl alcohol(PVA) whose degree of saponification and that of polymerization are at least a specific value and the water retention rate and breaking strength under a hydrous state are specified. CONSTITUTION:This is a high-strength PVA series hydrogel molded body which is comprised of PVA whose degree of saponification is 99-88mol% and that of polymerization is at least 1500 and a water retention rate and breaking strength under a hydrous state are respectively at least 100wt.% and 10kg/cm<2>. When the degree of saponification is more than 99mol%, the water retention rate of the PVA hydrogel becomes less than 100wt.% and when the degree of saponification is lower than 88mol%, the molded body is swollen and molten remarkably under water of a room temperature and breaking strength also of hydrogel under a hydrous state does not arrive at 10kg/cm<2> into the bargain. Even under a high hydrous state of at least 100wt.%, the high-strength PVA series hydrogel molded body having a breaking strength of at least 10kg/cm<2> is obtained by making use of the PVA whose degree of the polymerization is at least 1500.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to high-strength polyvinyl alcohol, PVA
Regarding the hydrogel molded body and its manufacturing method,
More specifically, the present invention relates to a novel PVA-based hydrogel molded product that has a high water retention rate, high strength, and rubber-like elasticity, and can be applied to fields such as fisheries, agriculture, civil engineering, and medicine, and an industrial method for producing the same.

[Prior Art] In recent years, the functions of molded bodies that do not dissolve in water in a hydrated state and have appropriate mechanical strength, that is, hydrogels, have attracted attention, and the development of their applications has been studied. For example, soft contact lenses, sustained release pharmaceutical carriers, living organisms 111! Medical materials such as recycled wood, artificial keys, artificial skin, water retaining materials, heat medium for cooling, artificial sphagnum moss, artificial soil for hydroponic cultivation, artificial bait for fishing,
Possible industrial uses include soil improvement materials.

Raw materials for such hydrogels include starch, gelatin, natural polymers such as agar, PVA, polyacrylic acid,
Hydrophilic or water-soluble synthetic polymers such as polyacrylamide, polyhydroxyethyl methacrylate, polyvinyl methyl ether, and polyvinyl pyrrolidone are used.

Among these, PVA is the most excellent hydrogel raw material that has high mechanical strength even in a water-containing state, and has been studied extensively. For example, JP-A-60-1770
Publication No. 66 discloses that a high-strength PVA hydrogel is produced by freezing a concentrated aqueous solution of PVA at a low temperature of -5°C or lower for 5 hours or more, and then leaving it to crystallize at a relatively low temperature of 10°C or lower for 10 hours or more. A method for obtaining the information is disclosed. Also,
JP-A No. 61-252261 discloses that by dissolving P'VA in a mixed solvent of water and an organic solvent, freezing and crystallizing it in a -20°C freezer for 3 hours, and washing with water, Tensile strength is 10Kg/cm or more, moisture content is 5
A method for obtaining 0-98% by weight PVA hydrogel is disclosed.

[Problems to be Solved by the Present Invention] However, although the above-mentioned PVA-based hydrogel does have high mechanical strength, it has a low water retention rate (less than 100% by weight) and is suitable for applications requiring a high water retention rate, such as water retention. It was not suitable for industrial uses such as lumber, cold insulation materials, artificial soil, and soil improvement materials.

In addition, the method for producing the PVA-based hydrogel described above is -20°
This manufacturing method has extremely low production efficiency, as it requires treatment at a low temperature of 100% C or more than 10 hours for crystallization at a low temperature, and was not suitable for continuous industrial production of PVA-based hydrokels.

Furthermore, there are many restrictions regarding the shape of the hydrogel obtained by the above-mentioned manufacturing method, and it has been difficult to produce continuous molded products such as films and III, ultrathin and ultrafine molded products of about 1 to 100 microns, and the like.

The present inventors conducted intensive studies on PVA-based hydrogel molded products with high water retention and high mechanical strength. After stretching low saponified high polymerization degree PVA at a high magnification, the It was discovered that by relaxing, a new P■, λ hydrogel molded article having a significantly higher water retention rate and higher breaking strength than conventional PVA hydrogels could be obtained, and the present invention was accomplished based on this finding.

In other words, the object of the present invention is that it has an extremely high water retention rate compared to conventional PVA-based hydrogel molded products, has high breaking strength, and exhibits rubber-like elasticity in a water-containing state. Another challenge is to provide a PVA-based hydrogel molded product that can be used in industrial applications such as agriculture, civil engineering, and fisheries that require high performance. The objective is to provide a commercial or commercial manufacturing method.

[Means for Solving the Problems] The above problems to be solved by the present invention are as follows: (1) The degree of saponification is 99 to 88 mol%, and the degree of polymerization is 1500.
It is made of polyvinyl alcohol with a water retention rate of 100%.
Weight% or more, breaking strength in hydrated state is 10Kg/c
A high-strength polyvinyl alcohol-based hydrogel molded body having a size of m2 or more, and (2) a degree of saponification of 99 to 88 mol%
After dry-wet molding or gel molding polyvinyl alcohol with a degree of polymerization of 1500 or more, it is stretched so that the total stretching ratio is 10 times or more, and the temperature TS (°C) of the stretched molded product before water dissolution is This can be achieved by a method for producing a high-strength polyvinyl alcohol-based hydrogel molded body, which is characterized by shrinking the molded body by 50% or more in water at a temperature of Ts -50°C or more and Ts -5°C or less.

The degree of saponification of PVA constituting the high-strength PVA-based hydrogel molded article in the present invention is 99 to 88 mol%, preferably 98 to 90 mol%, and more preferably 97 to 91 mol%. When the degree of saponification exceeds 99 mol%, the water retention rate of the PVA hydrogel will be less than 100% by weight, and when the degree of saponification is less than 88 mol%, it will swell or dissolve significantly in water at room temperature. Moreover, the breaking strength of the hydrogel in a water-containing state does not reach 10 Kg/cm2.

Furthermore, the degree of polymerization of PVA used in the high-strength PVA-based hydrogel molded article of the present invention is 1500 or more, preferably 2000 or more, and more preferably 2500 or more, and it is preferable to use PVA with such a high degree of polymerization. According to
Even in a high water content state of 100% by weight or more, 10kg/
A high-strength PVA-based hydrogel molded article having a breaking strength of cm" or more can be obtained.

As mentioned above, the PVA-based hydrogel molded article of the present invention is made of PvA with a high degree of polymerization and a low degree of saponification, and has improved hydrophilicity without reducing the mechanical performance of the gel, so it has a high water retention rate. is 100% by weight or more, preferably 200% by weight or more, more preferably 250% by weight or more, most preferably 300% by weight or more, and the breaking strength is 10Kg/cm2 or more, preferably 15Kg/Cm
2 or more, more preferably 20 to 3/cm2 or more.

Further, it is desirable that the high-strength PVA-based hydrogel molded article of the present invention also has a breaking elongation of 200% or more.

Preferred forms of the high-strength PVA-based hydrogel molded article of the present invention include fibers, hollow fibers, films, tapes, sheets, tubes, rods, blocks, vibrators, spheres, lenses,
It is possible to raise spirals, etc., but this is not the only option.

The polymerization degree, saponification degree, water retention rate of hydrokel, and breaking strength of PVA in the present invention are defined (measured) as follows.

(a) Polymerization degree of PVA Based on JIS K6726, the degree of polymerization (Pn) was calculated from the intrinsic viscosity of an aqueous solution at 30° C.

log(Pn) = 1.613 log([77]
ml/g (b) Saponification degree of PVA Calculated from the amount of residual acetic acid groups determined by neutralization titration method based on JIS K6726.

(c) Water retention rate of hydrogel After immersing approximately tog of the hydrogel molded body in water at 25°C for 24 hours, centrifugal dehydration for 15 minutes (rotation speed: 1500 rpm)
) After measuring L/, measure the weight ff1 (W). Furthermore, the hydrogel molded body after dehydration was heated to 60°C under reduced pressure (≦1 m
mHg) Dry for 24 hours and measure the absolute dry weight (Wo).

The water retention rate was calculated from the following formula.

Water retention rate = ((W - Wo) / Wo) x 100
(%) (d) Breaking strength of hydrogel After immersing the hydrogel molded body in water at 25°C for 24 hours,
After centrifugal dehydration for 15 minutes (rotation speed: 1500 rpm), the breaking strength was measured using a tensile tester under conditions of a sample length of 100 mm and a tensile speed of 100 mm/min.

Next, a manufacturing example of the high-strength PVA-based hydrogel molded article of the present invention will be explained.

That is, in the present invention, the highly polymerized and low saponified PVA is stretched and oriented at a high magnification to improve the crystallinity of the molded product, thereby forming crystal crosslinking points in the molded product and further making it hydrophilic in water. By highly relaxing only the highly oriented amorphous phase with water, a hydrogel molded product that does not swell or dissolve even in water at room temperature, has high water retention, and has high mechanical strength is obtained. There is. Therefore, in the present invention, it is necessary to stretch the above-mentioned low saponified high polymerization degree PVA so that the total stretching ratio is 10 times or more, preferably 12 times or more, and more preferably 15 times or more. If the total stretching ratio is less than 10 times, the crystallinity of the stretched molded product will be low, and the breaking strength of the hydrogel will be lower than 10 kg/kg.
cm2, the shrinkage rate in water is less than 50%, and the water retention rate does not reach 100% by weight. In the present invention, as described above, high polymerization degree low saponification degree PVA
It is necessary to draw and orient the material to a high degree, and wet-dry molding or gel molding is necessary as a molding method that enables such high-magnification stretching.

Therefore, wet-dry molding and gel molding in the present invention will be explained.

First, wet-dry molding is a process in which a molding solution is first discharged from a die (a die if the molded object is a fiber, a slit if it is a film) into an inert atmosphere such as air, nitrogen, helium, argon, etc. This is a method in which this extrusion molding solution is introduced into a coagulation bath and coagulated.

At this time, the molding solvent for the wet-dry molding is dimethyl sulfoxide (hereinafter abbreviated as DMSO), water, glycerin, ethylene glycol, diethylene glycol, triethylene glycol, J raw aqueous solution of sodium thiocyanate, and a mixed solvent thereof. Among them, DMSO, water, glycerin, and ethylene glycol are preferable, and DMSO is more preferable.

Furthermore, in the present invention, it is inevitable that the saponification degree of PVA described above is maintained even in the final molded product,
To this end, when preparing the molding solution, it is necessary to use a solvent that does not allow the saponification reaction to proceed even if it is left at a temperature of 80°C or higher for a long time (for example, 6 hours or more).
It is desirable to use DMSO adjusted with an acid so that the hydrogen ion concentration (pH) at 5° C. is 6 to 8.

In addition, as the coagulation bath in the present invention, low saponification degree PV
Since A is water-soluble, alcohols such as methanol, ethanol and butanol, organic solvents such as acetone, benzene and toluene, and mixed solvents of one or more of these solvents and the above-mentioned molding solvents are preferred. is a mixed solvent of methanol and DMSO (mixing ratio is methanol/DMSO = 10010 to 15/85 weight ratio,
Preferably, the weight ratio is 10010-10/90).

Next, gel molding involves discharging the molding solution from a die into a microscopic space in an inert atmosphere, and then introducing the discharged molding solution into a cooling bath consisting of a solvent that is immiscible with the solvent of the molding solution. This is a method of cooling and gelling (without substantially changing the polymer concentration of the extruded molded body solution).

As a solvent for the molding solution in this gel molding, PVA
It is preferable to use a polymer that gels when the solution obtained by heating and dissolving the polymer at a high temperature is cooled. Specifically, examples include polyhydric alcohols such as glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane, and solvents that are non-volatile at room temperature such as benzenesulfonamide and caprolactam. However, glycerin and ethylene glycol are preferred.

In addition, in the present invention, since low saponification PVA has low thermal stability (decomposes at 190 to 230°C), the solution temperature is set to 190°C or less, preferably 190°C or less during solution preparation and molding.
It is desirable to keep the temperature below 80°C.

The cooling bath for gel molding may be one that is not miscible with the solvent of the molding solution and is a non-solvent for PVA polymers, such as decalin, trichlorethylene, carbon tetrachloride, paraffin oil, etc. is used.

In the present invention, when molding into multi-filament fibers as the form of a hydrogel molded body, since the coagulation and gelation speed of low saponification degree pvA is extremely slow and the fibers tend to adhere to each other, a molding solution is used to prevent adhesion. It is desirable that the polymer concentration of low saponification degree PVA is 12 to 30% by weight, preferably 15 to 25% by weight.

Furthermore, in order to avoid adhesion between yarns, the residence time of the coagulated yarn or gelled yarn in the coagulation bath or cooling bath is preferably 5 seconds or more, preferably 10 seconds or more.

In the present invention, in order to highly stretch the obtained solidified molded product or gelled molded product, the temperature is 180 to 230°C.
℃5 Preferably, stretching is carried out using a heating tube, heating furnace, hot plate, heat medium bath, etc. at 190 to 225°C.

Further, in the present invention, the solidified/gelled molded product may be cold-stretched and hot-stretched by 1 to 7 times before the above-described hot stretching.

In the present invention, the stretched molded product thus obtained has a temperature of Ts-50°C or more and Ts-5°C or less, preferably Ts, where the water dissolution temperature of the stretched molded product is Ts (°C).
-40℃ or more and Ts-10℃ or less, more preferably Ts
It is necessary to shrink by 50% or more, preferably 55% or more in water at -35°C or more and Ts -10°C or less.

Here, the water dissolution temperature (Ts
) refers to the temperature at which the molded product is fused and cut by applying a load of g/cm2 to the molded product, placing it in water at a temperature of 5°C, increasing the temperature at a rate of 1°C/min.

If the water temperature when shrinking the stretched molded product is below Ts -50°C, it will take a long time for the stretched molded product to reach a shrinkage rate of 50% or more. production becomes difficult.

Furthermore, when the water temperature exceeds Ts-5°C, although the time required for the shrinkage rate to reach 50% is extremely short, the difference from the water solubility temperature (Ts) is extremely small, and the hydrophilic non-containing material in the stretched product is Since not only the crystalline phase but also the crystalline crosslinked phase is hydrated, the breaking strength of the resulting hydrogel molded article is reduced.

In the present invention, it is necessary to shrink the stretched molded article by 50% or more, preferably 55% or more at the above-mentioned specific water temperature. If the shrinkage rate is less than 50%, the water retention rate of the hydrogel molded product produced will not reach 100% by weight.

In addition, methods for shrinking the stretched molded product in water include continuous shrinkage using double rollers, multiple rollers, etc., division and cutting of the stretched molded product into each unit, and complete relaxation in a shrinking treatment bath. Methods such as fixing it to a frame or the like and contracting it discontinuously can be mentioned, but the method is not limited to this.

In this way, by using specific molding methods such as dry-wet molding and gel molding for low-saponification and high-polymerization PVA,
By highly stretching-oriented crystallization and further shrinking the obtained stretched molded product in water at a specific temperature, it is possible to achieve a high water retention rate of 100% by weight or more and a weight of 10kg.
The high-strength PVA-based hydrogel molded article of the present invention, which also has a high breaking strength of /cm2 or more, can be obtained.

[Examples] Hereinafter, the present invention will be explained in more detail based on Examples.

Example 1 PVA with a degree of saponification of 95 mol% and a degree of polymerization of 2800 was dissolved in DMSO so that the polymer concentration was 20% by weight,
A spinning stock solution was prepared. Prior to dissolution, p-toluenesulfonic acid was added to DMSO to adjust the hydrogen ion concentration (pH; 25°C) of the stock solution to 6.4.

The obtained stock solution was kept at a temperature of 100°C, and the caliber was 0.08.
It was discharged into the air at a discharge rate of 150 cc/min from a nozzle with a diameter of 500 mm and 500 holes, and after traveling through a 10 mm space (distance between the nozzle surface and the liquid level of the coagulation bath), 2% by weight of DMSO was added. The mixture was introduced into a methanol coagulation bath at a temperature of 15° C. and coagulated, and then withdrawn at a rate of 10 m/min. In this case, the residence time of the coagulated thread in the coagulation bath was 15 seconds.

The obtained undrawn yarn was washed with methanol, cold-stretched by a double roller to four times its original size, and passed through an oil solution containing 1% by weight of a silicone oil (TE-1002, manufactured by Toshi Silicone Co., Ltd.) dissolved in methanol. After drying, it was dried using a heated roller at 60°C. The dried yarn was stretched 4.5 times through a heating tube with a nitrogen stream at 220° C., and wound up with a winder. The total stretching ratio of the obtained drawn yarn was 18.0 times, there was no adhesion between single yarns, and the water dissolution temperature (Ts) was 52 ° C.
The shrinkage rate in water at 30°C was 77%. This drawn yarn was continuously shrunk by 70% in a 30°C water bath,
A hydrogel fiber bundle having rubber elasticity was obtained. The water retention rate of the obtained hydrogel molded body was 418%, and the breaking strength was 39K.
g/cm2.

Examples 2, 3, 4, Comparative Example 1 The 4-fold cold-drawn yarn obtained in Example 1 was passed through a heating tube with a nitrogen stream at 220°C to give a total stretching ratio of 7 times, 12 times, 16 times, and 19 times. The stretched yarn was stretched to double its original size, and the resulting stretched yarn was shrunk in water at 30°C for 5 minutes to produce a hydrogel fiber bundle. Table 1 shows the shrinkage rate of each drawn yarn, the water retention rate, and the breaking strength of the obtained hydrogel fiber bundle.

(The following is a blank space) Table 1 Comparative Example 2 A yarn was produced in the same manner as in Example 1, except that PVA with a degree of saponification of 95 mol% and a degree of polymerization of 800 was used at a polymer concentration of 25% by weight. However, the stretchability was lower than in Example 1, and the total stretching ratio was only 15 times. The temperature of the obtained drawn yarn before dissolution in water was 56°C, and the shrinkage rate in water at 30°C was 46%. The water retention rate of the hydrogel fibers after shrinkage was 96%, and the breaking strength was 8 Kg/cm''.

Examples 5 and 6, Comparative Examples 3 and 4 Using α,αゝ-azobisisobutyronitrile as an initiator, bulk polymerization of vinyl acetate was carried out at a polymerization temperature of 50°C to obtain highly polymerized polyvinyl acetate. Ta.

By changing the full cali saponification conditions when converting this polyvinyl acetate into PVA, four types of PV with a polymerization degree of 4000 and a saponification degree of 86.92.96.99.5 mol% were produced.
A was created.

4 in the same manner as in Example 1, except that the obtained PVA was dissolved in DMSO so that the polymer concentration was 17.
A double cold drawn yarn was produced. Each of the obtained cold-drawn yarns was
It was stretched 3.8 times through a heating tube with a nitrogen stream at 5° C. and wound up in a winder.

Table 2 shows the temperature before water dissolution (Ts) of the obtained drawn thread, and the water retention rate and breaking strength of the hydrogel fiber obtained by shrinking the drawn thread by 70% at a water temperature of Ts -20°C.

(The following is a blank space) Table 2 Wood: Dissolved in water at 25°C Wood: Does not gel at 100°C or lower and cannot be measured Examples 7 and 8, Comparative Examples 5 and 6 Saponification degree 96 mol % and a degree of polymerization of 4800 was dissolved in glycerin so that the polymer concentration was 15% by weight to prepare a spinning stock solution.

The obtained stock solution was kept at a temperature of 170 °C, and the caliber was 0.12.
From a nozzle with mmφ and 100 holes, it was discharged into the air at a rate of 45 cc/min, and after traveling through a 20 mm space (distance between the nozzle surface and the cooling bath liquid level), decalin at a temperature of 5°C was discharged. The mixture was introduced into a cooling bath consisting of 300 ml of water to form a gel, and the mixture was drawn off at a rate of 10 m/min. In this case, the residence time of the gelled yarn in the cooling bath was 20 seconds.

After extracting glycerin from the obtained gelled yarn in a methanol washing bath at 20°C, it was cold-stretched to 4 times its original size using a double roller, and was coated with a silicone oil agent (Toshi Silicone Co., Ltd. TE-1).
002) was dissolved in 1% by weight methanol, and then dried with a heated roller at 50°C. 4. The dried yarn is passed through a heating tube with a nitrogen stream at 225°C.
It was stretched to 1x and wound up on a winder. The total stretching ratio of the obtained drawn yarn was 16.4 times, there was no adhesion between the single yarns, and the temperature before water dissolution (Ts) was 61°C.

The temperature of the obtained drawn yarn was 15.30.45.58°.
Table 3 shows the time required for shrinkage (shrinkage time), water retention rate, and breaking strength of the hydrogel fiber bundle after shrinkage.

(The following is a margin) Table 3 *...Example 9 that does not shrink by 70% even in 24 hours PVA with a degree of saponification of 97 mol% and a degree of polymerization of 2200 is dissolved in DMSO so that the polymer concentration is 20% by weight. Prior to dissolution, para-toluenesulfonic acid was added to DMSO to adjust the hydrogen ion concentration (pH; 25°C) of the solution to 6.
The resulting solution was kept at a temperature of 100°C, and was slit through a slit cap with a width of 0.2 mm and a length of I 0 mm.
After traveling through a space of 15 mm (distance between the nozzle surface and the coagulation bath liquid level) at a discharge rate of 00 cc/min, 3% by weight of DM
It was introduced into a methanol coagulation bath containing SO at a temperature of 17°C to coagulate it, and was withdrawn at a rate of 10 m/min.

The obtained unstretched film was washed with methanol, cold-stretched to 4 times with double rollers, and dried with heated rollers at 60°C. The dried film was stretched four times through a heating tube with a nitrogen stream at 225°C and wound up with a winder.

The temperature before water dissolution (Ts) of the obtained uniaxially stretched film was 65
The hydrogel film obtained by shrinking 60% in a water bath at 40°C had a water retention rate of 370% and a breaking strength of 41.3/cm2.

[Effects of the Invention] The high-strength PVA-based hydrogel molded article of the present invention exhibits rubber-like elasticity in a water-containing state, has a water retention rate of 100% by weight or more, and has excellent properties such as a breaking strength of 10 kg/cm2 or more. In addition, it can be freely formed into fibers, films, tubes, rods, etc., so it can be used for artificial elbows, artificial muscles,
Artificial skin, artificial blood vessels, artificial joints, denture bases, biological repair materials,
catheters, soft contact lenses, antithrombotic materials,
In addition to medical materials such as sustained-release carriers for pharmaceuticals, carriers for immobilizing enzymes and microbial cells, we also provide water retention materials, cold insulation materials, thermal media for cold storage, artificial sphagnum moss, artificial soil for hydroponic cultivation, fishing lures, soil conditioner,
It is highly anticipated that it will be used in industrial applications that require high water retention, such as algae-proofing materials, antifouling materials, materials for printing rolls, and sustained-release carriers for fragrances.

Claims (2)

[Claims] (1) Saponification degree is 99-88 mol%, polymerization degree is 1500
It is made of polyvinyl alcohol with a water retention rate of 100%.
Weight% or more, breaking strength in hydrated state is 10Kg/c
A high-strength polyvinyl alcohol-based hydrogel molded article having a tensile strength of m^2 or more. (2) Saponification degree is 99-88 mol%, polymerization degree is 1500
After dry-wet molding or gel molding the above polyvinyl alcohol, it is stretched so that the total stretching ratio is 10 times or more, and the water dissolution temperature of the stretched molded product is Ts (℃).
A method for producing a high-strength polyvinyl alcohol-based hydrogel molded article, which comprises shrinking the molded article by 50% or more in water at a temperature of Ts-50°C or more and Ts-5°C or less.