JPS63145345A - Production of porous polyacrylonitrile material - Google Patents

Abstract

PURPOSE:To obtain a porous material excellent in water absorptivity and adsorptivity and having a controllable pore diameter, by coagulating a dope prepared from acrylonitrile (co)polymer and a solvent with a coagulant bath of a specified composition. CONSTITUTION:A dope prepared from an acrylonitrile polymer and/or its copolymer and a solvent is coagulated with a coagulant bath comprising a solvent for the polymers and a coagulant and having a concentration of the solvent in the solution of at least 0.75 time the lower limit (weight fraction) at which the solution can dissolve the polymer. Examples of the solvents include nitric acid, dimethylformamide, ethylene carbonate and succinonitrile. Examples of the coagulants include water, methyl alcohol and acetone. The weight fraction of the acrylonitrile polymer in the dope is preferably in the range of 5-40%, 10-35% for fibers and 5-30% for hollow fibers or films.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a porous body of an acrylonitrile polymer. More specifically, the present invention relates to a method for producing porous fibers having adsorption/water absorption ability, porous hollow fibers having ability to selectively separate substances, and porous films.

[Conventional technology]

Conventionally, as a method for making an acrylonitrile polymer porous, for fibers, for example, Japanese Patent Application Laid-Open No. 47-2541
No. 8, Special Publication No. 47-15901, Special Publication No. 4B-66
As disclosed in Japanese Patent Publication No. 49 and Japanese Patent Publication No. 48-6650, there is a method of making microvoids generated during the manufacturing process of acrylic fibers remain by controlling the drying conditions. Moreover, JP-A No. 47-25416
No., Special Publication No. 48-8285, Special Publication No. 4B-8286
The No. 1 describes a method of obtaining a porous body by filling acrylic fibers with a water-soluble compound, drying and post-processing, and then eluting the filled material. Furthermore, JP-A No. 60-65109 discloses a method for producing porous acrylic fibers by mixing and spinning other polymers. On the other hand, as hollow fibers for substance separation, for example, Japanese Patent Application Laid-Open No. 54-344116
No. 55'-30427 describes a method for producing hollow fibers using water as a coagulant as a main component. When trying to manufacture porous bodies using these methods, in methods that control drying conditions, in order to maintain porosity, it is necessary to leave microvoids generated during the coagulation process by selecting mild drying conditions. There is. In this method, voids disappear due to fluctuations in conditions, and coagulation is performed under conditions where a skin layer is formed on the surface, resulting in a decrease in adsorption and water absorption performance. Furthermore, in the method using a water-soluble filler, manufacturing costs increase and a step for removing the water-soluble filler is required, resulting in a decrease in productivity. When manufacturing hollow fibers, it is best to use a coagulant mainly composed of water, but in this case, the coagulation power of water is very strong, so the pores formed on the surface are 10 to 200 nm. become. At present, hollow fibers with pore diameters in this range are used only for ultrafiltration, and their uses are limited.

As described above, in the conventional method for producing polyacrylonitrile porous materials, not only is the process control complicated, but also the pore size has the greatest effect on the adsorption/water absorption properties or material separation of the resulting porous material. The current situation is that it is extremely difficult to control.

[Problem that the invention seeks to solve]

The present inventors have completed the present invention as a result of intensive research aimed at improving the current situation. According to the method of the present invention, it is possible to easily control the pore size without requiring any special steps, and it is possible to obtain fibers with excellent water absorption and adsorption properties, as well as hollow fibers and films for material separation. It is possible.

Means for Solving Problem C] The present invention provides a dope prepared from an acrylonitrile polymer and/or an acrylonitrile copolymer and its solvent,
Coagulation using a coagulation bath consisting essentially of a polymer solvent and a coagulant, in which the concentration of the solvent in the solution is 0.75 times or more the lower limit concentration (weight fraction) for dissolving the polymer. This is a method for producing a polyacrylonitrile porous material, which is characterized by:

The acrylonitrile polymer used in the method of the present invention is polyacrylonitrile and/or an acrylonitrile copolymer. This acrylonitrile copolymer contains acrylonitrile in a weight fraction of 50% or more, preferably 85% or more. As the copolymerizable heavy substance, vinyl compounds are used, such as acrylic acid and its esters, methacrylic acid and its esters, acrylamide and N-substituted amides, vinyl halides such as vinyl chloride, vinyl acetate, etc. Vinyl esters, vinyl dicarboxylic acids and their esters such as itaconic acid and maleic acid, vinylidene halides such as vinylidene chloride, vinylpyridine and its N-substituted derivatives, vinylpyrrolidone, styrene, allylsulfonic acid,
Examples include sulfonic acid compounds such as methallylsulfonic acid and styrenesulfonic acid, and their salts, and two or more of these can also be used in copolymerization.

The solvent used to prepare the dope is not particularly limited as long as it dissolves the acrylonitrile polymer and/or acrylonitrile copolymer, but preferably nitric acid, dimethylformamide, dimethylacetamide, Dimethyl sulfoxide, ethylene carbonate, γ-butyl lactone, succinonitrile, N-methyl-2-pyrrolidone, hydroxyacetonitrile are used. Furthermore, two or more of these solvents may be used in combination. In order to further impart a suitable porosity, a coagulant may be added to the solvent in a fraction of less than 15% by weight, based on the solvent. Addition of coagulant in excess of this amount reduces solubility. The coagulant used at this time is not particularly limited, but at least one selected from water, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, acetone, ethylene glycol, propylene glycol, glycerin, etc. Seeds are preferably used.

The weight fraction of the acrylonitrile polymer in the dope is preferably used in the range of 5 to 40%, 10 to 35% in the case of fibers, and 5 to 30% in the case of hollow fibers or films. is particularly preferably used. The temperature of the dope is also not particularly limited, but is usually -5℃.
The temperature is preferably within the range of ~80°C.

The most important feature of the method for producing a porous body of the present invention lies in the composition of the coagulation bath. The coagulation bath used in the present invention uses a combination of an acrylonitrile polymer solvent and a coagulant. The solvent is not particularly limited as long as it dissolves the acrylonitrile polymer, but usually the same solvent used to prepare the dope is used. This is to consider industrial productivity. Therefore, at least one of nitric acid, dimethylformamide, dimethylacetamide, dimethylsulfoxide, ethylene carbonate, γ-butyllactone, succinonitrile, N-methyl-2-pyrrolidone, and hydroxyacetonitrile is selected as the solvent.

Particularly preferably, nitric acid, dimethylformamide, dimethylacetamide, and dimethylsulfoxide are used.

As the coagulant, one of water, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, acetone, ethylene glycol, propylene glycol, and glycerin is used. Most preferably, water is used. Ru.

The ratio of the solvent and coagulant forming the coagulation bath is the most important point of the present invention. That is, how much of the solvent occupies the solution forming the coagulation bath? 1 degree needs to be at least 0.75 times the lower limit (weight fraction) of the solvent that dissolves the polymer. More preferably, a concentration range of 0.8 times or more is used. Using concentrations lower than this concentration range will result in
A dense skin layer is formed on the surface, and only a porous body with a minute pore size of about 10 to 20 nm can be obtained.

Here, the lower limit concentration of the solvent is defined as the minimum weight fraction of the solvent in the solution required to dissolve the polymer when the polymer is dissolved in a solution composed of a solvent and a coagulant. This fraction varies depending on the temperature at which the polymer is dissolved and the type of coagulant.

Furthermore, if a coagulant with weak coagulating power is used, the lower limit and concentration will decrease. The most commonly used combinations are nitric acid/water, dimethylformamide/water, dimethylsulfoxide/water, dimethylacetamide/water;
In the case of nitric acid/water, a 38 to 50% by weight aqueous solution is preferably used, and in the case of dimethylformamide, dimethylsulfoxide, and dimethylacetamide, a 65 to 90% by weight water/8 solution is preferably used as the bath composition. Additionally, a third component may be added to modify the porosity.

An important feature of the present invention is that by coagulating the dope in a coagulation bath having the above-mentioned composition, the resulting coagulated product becomes porous. If a solvent weight fraction lower than this composition is used, a dense skin layer will be formed on the surface of the coagulum, as described above, which will impede diffusion when used for adsorption, water absorption, or material separation. .

Another feature of the present invention is that the pore size for use in adsorption, water absorption, or substance separation can be controlled very easily. In conventional methods, this control is hardly possible and the applications are limited. In the method of the present invention, it is possible to control the shape and diameter of the pores by precisely controlling the dope concentration, coagulation bath composition, and coagulation bath temperature. In particular, the pore size can be controlled over a wide range of 10 nm to 5 μm. The dope concentration and coagulation bath composition are preferably within the ranges mentioned above. Temperature has the greatest effect on controlling pore size. In the method of the present invention, the temperature of the coagulation bath is usually set within the range of -20°C to 80°C. Preferably a range of -5°C to 65°C is used. Pore size tends to increase with increasing temperature.

When making hollow fibers, it is necessary to flow a hollow agent to form hollow parts. Like the coagulation bath, this hollow agent consists of a polymer solvent and a coagulant, and the concentration of the solvent in the solution is 0.75 times or more the lower limit concentration (weight fraction) of the solvent that dissolves the polymer. It is common to use a solution with a composition of

Furthermore, when a porous body is formed using the coagulation bath composition of the present invention, the shape of the extrusion die is maintained as it is, and one of the characteristics is that the shape stability is good, and it can be used freely depending on the purpose. Melift's ability to design its form was something that was not expected at all at the beginning.

In the present invention, the porous body is usually formed by a wet spinning method or a dry-wet spinning method.

After the dope is extruded from the spinneret into the coagulation bath, it is drawn out by a take-up roller, then washed with water and dried.
In some cases, it may be used as is after being washed with water. In order to impart strength, it may be stretched or heat treated before or after washing with water.

A wide range of pore sizes can be set for the porous body obtained by the method of the present invention. There is no conventional method that can produce such a large pore size range for polyacrylonitrile-based porous materials, and considering the chemical stability of acrylonitrile-based polymers, this porous material can be used for clothing that is conventionally used. It is thought that it can be used in a wider range of fields, including water-absorbing fibers for industrial use, enzyme carriers that utilize adsorption properties, and hollow fibers and films for substance separation.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 91.5% by weight of acrylonitrile, 8% by weight of methyl acrylate
% by weight and 0.5% by weight of sodium methallylsulfonate were dissolved in dimethylformamide at 25°C to prepare a 16% by weight dope.

This dope was extruded into a coagulation bath using a nozzle with a hole diameter of 0.08*mφ and 100 holes, and pulled up at a speed of 1 m/min to obtain a porous fiber. The composition of the coagulation bath at this time was 75% by weight, 80% by weight, or 85% by weight dimethylformamide aqueous solution, and the temperature was 25°C. After washing with water, it was air-dried under a fixed length, and the surface structure was observed using a scanning electron microscope. As a result, it was observed that fine pores were present throughout the surface.

The diameter of the pores is 0.1-0.5 when solidified at 75% by weight.
μm, 0.5 to 5 μm when solidified at 80% by weight185
The weight percentage was 0.5 to 4 μm. Furthermore, when the fractured surface was observed in liquid nitrogen, it was revealed that pores similar to those on the surface were present throughout the interior.

Further, in order to impart strength to the fibers, after washing with water, the fibers were stretched three times in hot water, resulting in porous fibers having a structure in which the pores were elongated along the fiber axis.

The water supply rate of these fibers is 25-50%, compared to 4% of conventional products.
was very high compared to

Example 2 Using the same copolymer as in Example 1, it was dissolved in dimethylformamide at 25°C to prepare a 16% by weight dope. This dope was extruded into a coagulation bath using a nozzle with a hole diameter of 0.08 mmφ and 100 holes at a rate of 0.5 m/min.
pulled up at a speed of At this time, the temperature of the coagulation bath was set to -5℃.
, 0℃, 10℃, 20℃, 30'C, 40℃, 50℃,
The temperature was changed to 60°C and 65°C. The resulting fibers were highly porous, with pore diameter varying with temperature. −
0.1-1.5μm at 5℃, 0.1-2μm at 0℃
, 0.1~2μm at 10℃, 0.2~3# at 20℃
m, 0.2 to 4 μm at 30℃, 0.3 to 5 at 40℃
μm, 0.5 to 6 μm at 50℃, 0 at 60℃
．． It was 3-5 micrometers, and 0.1-0.5 micrometers at 65 degreeC.

Example 3 The same copolymer as in Example 1 was used and dissolved in dimethylformamide at 25° C. to give concentrations of 5% by weight, 12% by weight, 14% by weight, 16% by weight, and 18% by weight.

20% by weight, 21% by weight, 23% by weight and 25% by weight
Got the dope. These dopes have a pore diameter of 0.08u+φ
, extruded into a coagulation bath using a nozzle with 100 holes,
It was pulled up at a speed of 0.5 m/1 lIin.

The coagulation bath at this time was at 25° C. and consisted of 80% dimethylformamide. After washing the obtained fibers with water, they were air-dried at 60°C under a fixed length. When the surface of this fiber was observed with a scanning electron microscope, it was found that when 5 to 20% dope was used, the granulated copolymer aggregated to form a porous body. The pore size increases with doping concentration;
It was within the range of 0.081 to 5 μm. At 21-25%, pores were observed on the smooth surface of the copolymer.

The pore diameter was in the range of 0.1-1 μm and decreased with increasing doping concentration.

Example 4 The same copolymer as in Example 1 was used, dissolved in dimethylformamide at 25°C, and 100 g of 20% by weight dope was added.
1 liter was made. A 90% dimethylformamide aqueous solution was added to this to make a 16% by weight dope. After this dope was cast onto a glass plate, it was coagulated by immersing it in a coagulation bath consisting of an 80% by weight dimethylformamide aqueous solution at 25°C.

After washing with water, it was air-dried at room temperature. The front and back surfaces of the obtained film were observed using a scanning electron microscope. 0.1~2μ on the surface
It was confirmed that pores of 0.1 to 1 μm were present throughout the back surface.

Example 5 Using the same copolymer as in Example 1, it was dissolved in dimethylformamide at 25°C to prepare a 16% by weight dope. This dope was taken out into a coagulation bath using a nozzle with a hole diameter of 0.08 mmφ and a number of holes of 100, and was heated at a rate of 0.5 m/win.
pulled up at a speed of The temperature of the coagulation bath at this time was 25°C.
It was an 86% by weight dimethyl sulfoxide aqueous solution. After washing with water, it was air-dried under a fixed length, and the surface structure was observed using a scanning electron microscope. As a result, it was found that pores with a diameter of 0.1 to 2 μm were present throughout the fibers on the surface.

Example 6 Using the same copolymer as in Example 1, it was dissolved in dimethylacetamide at 25°C to prepare a 16% by weight dope. This dope was extruded into a coagulation bath using a nozzle with a hole diameter of 0.08 mm and a number of holes of 100, at a rate of 0.5 m/min.
pulled up at a speed of The coagulation bath at this time was 25°C and 8°C.
It was a 0% by weight dimethylacetamide aqueous solution. After washing with water, the fibers were air-dried under a fixed length, and the surface structure was observed using a scanning electron microscope, and it was found that pores with a diameter of 0.1 to 0.5 μm were present throughout the fibers.

Example 7 Using the same copolymer as in Example 1, 67% by weight at 0°C
A 16% by weight dope was prepared by dissolving it in an aqueous nitric acid solution.

This dope was extruded into a coagulation bath using a nozzle with a hole diameter Q of 4 wφ and 100 holes, and pulled up at a speed of 0.5 s/win. The coagulation bath at this time was a 39% by weight nitric acid aqueous solution at 0°C.

After washing with water, the fibers were air-dried under a fixed length, and the surface structure was observed using a scanning electron microscope. As a result, pores with a diameter of 0.2 to 2 μm were present throughout the fibers.

Example 8 Using the same copolymer as in Example 1, it was dissolved in dimethylformamide at 1.25°C to prepare a 18% by weight dope. This dope was extruded into a coagulation bath using a hollow fiber manufacturing nozzle. The diameter of the nozzle is 3.4 m*φ-1,
It was 6*mφ-2, Otmφ. The coagulation bath at this time is
It was an 80% by weight aqueous dimethylformamide solution at 25°C. After being pulled up from the coagulation bath at a rate of 3 m/min, 25
℃, the film was stretched twice in a stretching bath composed of an 80% by weight dimethylformamide aqueous solution, and washed with water. At this time,
An 80% by weight dimethylformamide aqueous solution was flowed into the hollow part as a core liquid at 25°C. The obtained hollow fibers are
It was cut to 0cf11 and air-dried to length.

When the outer wall, inner wall, and cross section of this fiber were observed using a scanning electron microscope, spindle-shaped pores of 0.1 to 3 μm in diameter were observed on the outer wall, and nearly circular pores of 0.1 to 5 μm in diameter were observed in the inner wall. observed throughout. Further, in the cross section, pores of 0.1 to 1 μm were observed throughout the thickness direction from the outer wall to the inner wall.

Claims (1)

[Scope of Claims] 1. A dope prepared from an acrylonitrile polymer and/or an acrylonitrile copolymer and its solvent is made up of a polymer solvent and a coagulant, and the concentration of the solvent in the solution is high. The lower limit concentration (weight fraction) for dissolving coalescence is 0.
A method for producing a porous polyacrylonitrile material, the method comprising coagulating it using a coagulation bath with a coagulation bath of 75 times or more. 2. The solvent forming the dope is nitric acid, dimethylformamide, dimethylacetamide, dimethyl sulfoxide,
The method according to claim 1, characterized in that it consists of at least one selected from ethylene carbonate, γ-butyllactone, succinonitrile, N-methyl-2-pyrrolidone, and hydroxyacetonitrile. 3. A patent characterized in that the coagulant used in the coagulation bath consists of at least one selected from water, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, acetone, ethylene glycol, propylene glycol, and glycerin. A method according to claim 1 or 2. 4. The method according to claim 1, wherein the temperature of the coagulation bath is within the range of -20 to 80°C. 5. The method according to claim 1, wherein the concentration of the polymer in the dope is 5 to 40% by weight. 6. The method according to claim 1, wherein the porous body is a fiber or a film. 7. The method according to claim 6, wherein the porous body is a hollow fiber. 8. The core liquid for forming the hollow part consists of a polymer solvent and a coagulant, and the concentration of the solvent in the solution is 0.75 times or more the lower limit concentration (weight fraction) of the solvent that dissolves the polymer. The method according to claim 7.