JPS63190012A - Hollow yarn film of polyacrylonitrile and production thereof - Google Patents

Abstract

PURPOSE:To obtain the titled hollow yarn film having high water permeability and small pore diameter (distribution), by spinning a spinning stock solution comprising a specific acrylonitrile polymer by the use of a spinneret for sheath- core type hollow yarn and injecting a solution having low coagulating properties from a core part yarn. CONSTITUTION:An acrylonitrile polymer, preferably a polymer comprising one or more components of acrylonitrile polymer containing acrylonitrile having extremely high polymerization degree, is dissolved in an organic solvent such as dimethyl sulfoxide, etc., to prepare a spinning stock solution having 5-20wt.% total polymer concentration. Then the spinning stock solution is extruded from a sheath part by the use of a spinneret for sheath-core type hollow yarn, a coagulating solution having low coagulating properties is injected from a core part to yarn and the organic solvent is evaporated in a gas phase. Further the extruded yarn is immersed in a coagulating bath, washed and wound to give the aimed hollow yarn film.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polyacrylonitrile hollow fiber membrane and a method for producing the same. More specifically, the present invention relates to a high-performance polyacrylonitrile hollow fiber membrane for ultrafiltration that has high water permeability, small pore size and pore size distribution, and is particularly suitable for supplying a liquid to be treated from the outside of the hollow fiber membrane, and a method for producing the same.

(Prior art) Ultrafiltration membranes made of cellulose acetate, polyacrylonitrile, polyolefin, etc. have been used to concentrate or recover active ingredients, or to create water in many fields such as the food industry, medical field, and electronics industry. Methods are being considered. The performance required of ultrafiltration membranes includes particularly high water permeability and high solute separation ability. Among these, polyacrylonitrile-based ultrafiltration membranes have superior chemical stability than cellulose acetate, have good mechanical properties, and are easily wetted by water despite being a hydrophobic material, making them excellent ultrafiltration membranes. For example, in Japanese Patent Publication No. 52-15072 and Japanese Patent Publication No. 53-3,
It is described in Japanese Patent Publication No. 1106 and Japanese Patent Publication No. 60-39404.

Japanese Patent Publication No. 52-150724 does not have a so-called dense layer and consists of a graded porous layer and a network porous structure, and Japanese Patent Publication No. 53-31106 uses a solution with a relatively high polymer concentration. This is a manufacturing method using However, all of these membranes have insufficient separation or filtration ability, and there is a need for further improvement. In addition, special public service 1986-3
Although Publication No. 9404 has excellent filtration performance due to its dense layer, porous layer, and giant pores, it is still not sufficient and there are considered to be problems with mechanical strength and thermal properties. .

The present inventors have conducted extensive research in view of the current situation, and have now accomplished the present invention.

(Problems to be Solved by the Invention) That is, an object of the present invention is to have higher separation ability and filtration ability than conventional polyacrylonitrile ultrafiltration membranes, to have a good balance between the two, and to have mechanical strength and An object of the present invention is to provide a hollow fiber membrane with excellent thermal properties and a method for producing the same.

(Means for solving problems) The present invention has the following configuration.

(1) The outermost layer of the hollow fiber membrane is composed of a dense layer with a pore size of 500 Å or less, forms a porous layer with the pore size increasing from the outermost layer to the innermost layer, and is characterized by substantially no macropores. Polyacrylonitrile hollow fiber membrane.

(2) The polyacrylonitrile hollow fiber membrane according to claim (1), wherein the hollow fiber membrane is a polymer having at least one component an acrylonitrile polymer containing acrylonitrile with an ultra-high degree of polymerization.

(3) Ultra-high polymerization degree acrylonitrile has an intrinsic viscosity of 2.0
The polyacrylonitrile hollow fiber membrane according to claim (2) above.

(4) When manufacturing a hollow fiber membrane using a sheath-core type hollow fiber die, an organic solvent solution containing an acrylonitrile polymer with a total polymer concentration of 5 to 20% by weight is used as the spinning stock solution, and A method for producing a polyacrylonitrile hollow fiber membrane, which is characterized by injecting a low-coagulable injection liquid.

(5) The method for producing a polyacrylonitrile hollow fiber membrane according to claim (4), wherein the acrylonitrile polymer is a polymer having at least one component an acrylonitrile polymer containing acrylonitrile with an ultra-high degree of polymerization. .

(6) Ultra-high polymerization degree acrylonitrile has an intrinsic viscosity of 2.0
The method for producing a polyacrylonitrile hollow fiber membrane according to claim (5) above.

(7) The method for producing a polyacrylonitrile hollow fiber membrane according to claim (4), wherein the low coagulability injection liquid is an aqueous liquid mainly containing dimethyl sulfoxide.

The feature of the present invention is that the outermost layer of the hollow fiber membrane is a dense layer and has a rough texture.
It consists of a porous layer whose pore size increases as it progresses inside the membrane, and although it contains virtually no giant pores,
It has high water permeability.

In addition, ultra-high degree of polymerization acrylonitrile polymer (hereinafter referred to as A
Another important feature of the manufacturing method is that the spinning stock solution with a relatively low polymer concentration is used for spinning with an injection liquid having low coagulability.

The conventional thinking is that membranes with a dense layer, a porous layer, and a network structure layer containing giant pores have excellent water permeability, and membranes without giant pores have good mechanical properties. had low water permeability.

The high water permeability of the hollow fiber membrane of the present invention is due to the use of a spinning dope with a relatively low polymer concentration, and the good mechanical and thermal properties are due to the fiber structure without large pores. This is due to the shape and the use of a polymer with an ultra-high degree of polymerization. The thermal properties mentioned here refer to the thermal contraction rate,
Since the hollow fiber membrane of the present invention has a low thermal shrinkage rate, the decrease in water permeability when hot water is passed through it is smaller than that of conventional membranes.

In addition, among its mechanical properties, it is particularly resistant to bending fatigue, and this property is largely dependent on the use of polymers with an ultra-high degree of polymerization, and these characteristics are useful in the large-scale water treatment field. suitable.

As seen in FIG. 1, the hollow fiber membrane in the present invention has the following features:
The outermost layer (on the left) is a dense layer, and the membrane further consists of a porous layer whose pore diameter increases as it goes inside the membrane. The outermost dense layer has a pore diameter of 500 Å or less as shown in FIG. If it is 500 Å or less, it can be adjusted freely, but especially 10
0 to 300 people is preferable in terms of balance of filtration performance.

In the present invention, a graded porous layer is formed in which the pore diameter increases from the outermost layer to the innermost layer of the membrane. The pore size ranges from 500 to 500,002 as seen from the outer layer (Figure 2), inner layer (Figure 3), and inner layer surface (Figure 4), and is often 1,000 to 20,000. .

Although the hollow fiber membrane of the present invention does not substantially contain giant pores, the term "giant pores" as used herein refers to cavities having a diameter of 5 μm or more, particularly 10 μm or more.

The ultra-high degree of polymerization AN-based polymer contained as the main component in the present invention refers to an intrinsic viscosity of 2.0 or more, preferably 2.5 to 2.5.
It has a specific degree of polymerization of 3.6, more preferably 2.9 to 3.3.

In general, the polymer contains at least 90 mol % AN, preferably 95 to 100 mol %, based on the AN.

AN homopolymer or AN consisting of 5 mol% or less, preferably 0 to 5 mol%, of a vinyl compound having copolymerizability
It is a copolymer.

The vinyl compound is not particularly limited as long as it is a compound that is copolymerizable with various known ANs, but preferred copolymerizable components include acrylic acid, itaconic acid, methyl acrylate, methyl methacrylate, Examples include vinyl acetate, sodium allylsulfonate, sodium methallylsulfonate, and sodium p-styrenesulfonate.

In the present invention, the organic solvent that dissolves the AN-based polymer is
Any solvent used for AN may be used, such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF>
, dimethylacetamide (DMAC), ethylene carbonate, butyl lactone, etc., but DMSO is particularly preferably selected and the obtained polymer solution is used as a spinning dope.

However, the total polymer concentration of this spinning dope is about 5 to
20% by weight, preferably within the range of 10 to 18% by weight. If the total polymer concentration is lower than 5%, not only will it be difficult to form a dense layer, but the mechanical strength will be insufficient, making it difficult to use. I can't stand it anymore. On the other hand, the total polymer concentration is 20%
Exceeding this is not preferable because the dense layer becomes too thick or the pore diameter of the porous layer becomes small, resulting in a significant decrease in filtration ability and an increase in viscosity, which impairs spinnability.

In the present invention, an AN-based copolymer containing a hydrophilic group may be blended with an AN-based polymer having an ultra-high degree of polymerization, but if the amount is too high, the mechanical strength, especially the bending strength, and the filtration ability will decrease. , preferably 40% by weight or less. The AN-based copolymer includes 50% by weight or more of acrylonitrile and one or more known monomers copolymerizable with acrylonitrile.
It is a polymer consisting of ~50% by weight.

Furthermore, in order to increase water permeability, water, alcohols, inorganic salts, or other polymers such as polyethylene glycol and polyvinylpyrrolidone may be added to the polymer solution.

Next, a specific method for producing the polyacrylonitrile hollow fiber membrane of the present invention will be described.

The polyacrylonitrile hollow fiber membrane of the present invention is prepared by preparing a spinning stock solution of an AN polymer containing acrylonitrile with an ultra-high degree of polymerization using the organic solvent at a total polymer concentration of 5 to 20%. , which can be produced by spinning it using a dry-wet method.

That is, specifically, the solution is discharged from the sheath part using a sheath-core type hollow fiber nozzle, the coagulation liquid is injected from the core part, and the organic solvent is evaporated in the gas phase for 0 to 20 minutes. This was immersed in a mixture of water and an organic solvent (so-called coagulation bath), and then
It is produced by processing in water or a mixture of water and a non-solvent at a temperature below 0°C. As the organic solvent in the coagulation bath, the solvent used for the spinning stock solution is used, and DMSO is particularly preferably selected. The concentration of the organic solvent is 0 to 50% by weight, preferably 0 to 30%, because if it is too high, it becomes difficult to form a dense layer in the outermost layer.

Furthermore, the temperature of the coagulation bath is selected between b and 2, since if it is too high, the membrane will shrink and the water permeability will decrease.

In the present invention, a hollow fiber membrane is manufactured by discharging a spinning stock solution from a sheath part using a sheath-core type hollow fiber nozzle and injecting a coagulating liquid with low coagulability from a core part, as described above. The coagulating liquid to be injected consists of the solvent used in the spinning dope and its non-solvent. Examples of the solvent include those mentioned above,
In particular, DMSO is preferably selected. As a non-solvent,
Examples include water, alcohols, aliphatic ketones, glycerin, polyethylene glycol, and water is particularly preferably selected. The concentration of the solvent is 70% by weight or more, but the optimum range varies depending on the combination of solvent and nonsolvent. That is, if it is less than 70% by weight, coagulability is high;
A relatively dense layer is formed in the innermost layer of the hollow fiber, and giant pores are formed inside it, but if the concentration of the same solvent as the spinning stock solution is increased to 70% by weight or more to lower coagulation,
Since the solidification rate of the innermost layer is low and the pore size becomes large, a graded porous layer containing no giant pores is formed inside the innermost layer.

Examples will be shown below, but the invention is not limited thereto.

(1) Water permeability ff1 (UFR) refers to the amount of water that flows outside through the hollow fiber membrane when water or an aqueous solution flows through the hollow part of the hollow fiber membrane, and the effective area (outer surface) of the membrane and the time. The unit is d/hr.
-mHO・butt. Here, water-UFR refers to the water permeability when using pure water.

(2) ΔS (%) is a value expressed by the following formula when a hollow fiber of length LO is immersed in water at 60°C for 10 minutes under no tension, and the length is Ll, A small value indicates that the thermal shrinkage rate is small and the decrease in water permeability when hot water is poured is small.

0-Ll ΔS (%)-X100 (3) Strength and elongation is TENSI LON/UTM-111
(manufactured by Toyo Baldwin Co., Ltd.), the measurement was carried out at a sample length of 50 M and a tensile speed of 50 m/1 inch, and the cross-sectional area of the membrane excluding the hollow portion was used as the cross-sectional area of the thread.

(4) The bending fatigue test was conducted at a bending angle of 180 degrees and a bending speed of 90 degrees.
I went round trip/n+in.

(5) The intrinsic viscosity of the polymer is determined by Journal ofPo
lymer 5science (A-1>Volume 6, Volume 1
47-157 (1968), dimethylformamide (DMF) was used as a solvent, and the measurement was performed at 30°C.

(Example) ``Example 1 A polymer of 100 mol% acrylonitrile and [ηconi 3゜2] was polymerized in DMSO and roughly diluted to a polymer concentration of 1.
A 3.0% by weight spinning dope was obtained.

Inner diameter 0.25agt, slit width 0. This spinning stock solution was discharged from the sheath at a speed of 1°4rd/1IIin using a sheath-core type hollow fiber nozzle, and DMS0 from the core.
An 80% by weight aqueous solution was injected as a coagulating liquid. The temperature of the nozzle was 50℃, and the discharged yarn was placed in the air (room temperature) for 8
After passing through 0 m, it was introduced into a coagulation bath consisting of water at 30°C to coagulate, washed in water at 35°C, and then wound up.
A hollow fiber membrane as shown in Figs. to 4 was obtained. The obtained hollow fiber membrane has an inner diameter of 207 μm and a membrane thickness of 35 μm, and the membrane structure has a dense layer with a pore size of 100 to 300 people in the outermost layer, and the pore size increases toward the inside of the membrane, but it is 1 to 2 μm. There were no large holes at all.

The properties of the obtained hollow fiber membrane are as shown in Table 1, and it was a hollow fiber membrane with high water permeability, strong resistance to bending fatigue, particularly low thermal shrinkage rate, and little deterioration.

Example 2 A polymer containing 100 mol% acrylonitrile and [η]=3°2 was polymerized in DMSO to obtain a spinning dope with a polymer concentration of 15.5% by weight. Inner diameter 0.67111° Slit width 0.
This spinning stock solution was discharged from the sheath at a speed of 2.8 d/min using a sheath-core type hollow fiber nozzle No. 1711111, and an 80% by weight aqueous solution of DMS0 was injected as a coagulation liquid from the core. The die temperature was 60° C., and the subsequent treatments were carried out in the same manner as in Example 1.

The obtained hollow fiber membrane had an inner diameter of 298 μm and a membrane thickness of 50 μm.
The membrane structure was composed of a dense layer and a graded porous layer similar to the membrane of Example 1, but the pore diameter was smaller than that of Example 1 due to the high polymer concentration. The properties of this hollow fiber membrane are summarized in Table 1. Although its water permeability is somewhat inferior, it is an excellent membrane with good mechanical properties and a fairly low heat shrinkage rate.

Comparative Example 1 Acrylonitrile 93.1 mol%, methyl acrylate 5
．． 8 mol%, sodium methallylsulfonate 0.3 mol%,
[η]-1,2 copolymer was polymerized in DMSO and roughly diluted to obtain a 16% by weight spinning stock solution. Inner diameter 0.25
Using a sheath-core type hollow fiber spindle with m+ and a slit width of 0°075J111, yarn was produced in the same manner as in Example 1, except that water was injected into the core.

The obtained hollow fiber membrane has an inner diameter of 205 μm and a membrane thickness of 56 μm, has a dense layer in the outermost layer and an innermost layer, and has a diameter of 10 μm in the inner layer.
It had huge pores larger than μm.

The properties of the hollow fiber membranes are summarized in Table 1. The membrane not only had low water permeability, but also was susceptible to bending fatigue, easily broke, and had a high thermal shrinkage rate.

Comparative Example 2 Spinning was carried out in the same manner as in Example 1, except that the same spinning dope as in Example 1 was used and water was injected from the core.

The obtained hollow fiber membrane had an inner diameter of 205 μm, a membrane thickness of 56 μm, a dense layer in the outermost layer and an innermost layer, and a diameter of 10 μm in the inner layer.
It had huge pores larger than μm.

The properties of this hollow fiber membrane are summarized in Table 1. Since the elongation was lower than that of Example 1, it was easily broken, and the heat shrinkage rate was large, so it could not exhibit sufficient performance in hot water.

<Effects of the Invention> The polyacrylonitrile hollow fiber membrane of the present invention has excellent separation ability and filtration ability, and has a good balance between the two.
It has ultrafiltration performance, is hard to break, and is resistant to heat.

In particular, it can be applied to various industrial fields more than conventional hollow fiber membranes. For example, food field, pharmaceutical field, microorganism field,
Examples include water and other liquid treatment fields such as the electronic industry and nuclear power generation, and are particularly suitable for the electronic industry and nuclear power generation fields.

[Brief explanation of the drawing]

1 to 4 are scanning electron micrographs of the hollow fiber membrane obtained in Example 1. Figure 1 is a cross-sectional photograph of a hollow fiber membrane (10
00 times). Figures 2 and 3 are cross-sectional photographs (5000x magnification) of the inner and outer layers of the hollow fiber membrane, respectively. FIG. 4 is a photograph (5000x magnification) of the inner layer surface of the hollow fiber membrane.

Claims (7)

[Claims] (1) The outermost layer of the hollow fiber membrane is composed of a dense layer with a pore size of 500 Å or less, forms a porous layer with the pore size increasing from the outermost layer to the innermost layer, and is characterized by substantially no macropores. Polyacrylonitrile hollow fiber membrane. (2) The polyacrylonitrile hollow fiber membrane according to claim (1), wherein the hollow fiber membrane is a polymer having at least one component an acrylonitrile polymer containing acrylonitrile with an ultra-high degree of polymerization. (3) Ultra-high polymerization degree acrylonitrile has an intrinsic viscosity of 2.0
The polyacrylonitrile hollow fiber membrane according to claim (2) above. (4) When manufacturing a hollow fiber membrane using a sheath-core type hollow fiber die, an organic solvent solution containing an acrylonitrile polymer with a total polymer concentration of 5 to 20% by weight is used as the spinning stock solution, and A method for producing a polyacrylonitrile hollow fiber membrane, which is characterized by injecting a low-coagulable injection liquid. (5) The method for producing a polyacrylonitrile hollow fiber membrane according to claim (4), wherein the acrylonitrile polymer is a polymer having at least one component an acrylonitrile polymer containing acrylonitrile with an ultra-high degree of polymerization. . (6) Ultra-high polymerization degree acrylonitrile has an intrinsic viscosity of 2.0
The method for producing a polyacrylonitrile hollow fiber membrane according to claim (5) above. (7) The method for producing a polyacrylonitrile hollow fiber membrane according to claim (4), wherein the low coagulability injection liquid is an aqueous liquid mainly containing dimethyl sulfoxide.