JPS5962311A - Production of hollow yarn-like semipermeable membrane made of aromatic polysulfone - Google Patents

Abstract

PURPOSE:To produce a titled semipermeable membrane having excellent mechanical strength and high water permeability by dissolving arom. polysulfone in a liquid mixture of a polar org. solvent and a nonsolvent, and allowing an aq. soln. of electrolyte to coexist. CONSTITUTION:Arom. polysulfone is dissolved in a soln. mixture of a polar org. solvent (for example, N-methyl pyrolidone, etc.) which dissolves arom. polysulfone and a solvent (for example, dimethyl sulfoxide, etc.) which is intimately mixed with the polar org. solvent but does not dissolve arom. polysulfone. An aq. soln. of electrolyte (for example, common salt, etc.) is further allowed to coexist in the soln., and the soln. is molded to a hollow yarn shape. The yarn is then brought into contact with a liquid which is mixed intimately with the solvent mixture but does not dissolve arom. polysulfone (for example, water, etc.) to remove the solvents, whereby a hollow yarn-like semipermeable membrane is obtd. The concn. of the polymer soln. as a raw liquid for forming is preferably about 5-35wt% and the film thickness is about 10-450mu.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a novel hollow fiber semipermeable membrane made of aromatic polysulfone.

Conventionally, a large number of polymer compounds have been used as materials for semipermeable membranes, and many of them are actually produced industrially, such as cellulose acetate, polyacrylic acid, and polyamide.

Aromatic polysulfone is originally used as an engineering plastic, but because of its good heat resistance and chemical resistance, it is also being used as a material for semipermeable membranes. There are many patents and documents regarding aromatic polysulfone flat membranes, but hollow fiber semipermeable membranes are known by Amicon Corporation (Japanese Unexamined Patent Publication No. 1-231g3) and Gulf South Co., Ltd.
Research Institute (Journal of Applied Polymer Science, Volume 20, 1.23k ~
, 2.39'l pages and 239! ; N, 21101
．． Page, 7776, 2/vol., 1gg3~/900 Hesi, /9ri7) is known.

However, the structure of Amicon Corporation's aromatic polysulfone hollow fibers has a surface layer on the inside, but no surface layer on the outside, and when forming a membrane, the polymer is missing in areas exceeding 70 μm in diameter. Since the cavity is open to the outside, /) mechanical strength is low, c) backwashing is not possible, 3.
) It has practical drawbacks such as clogging. In addition, Gulf South Research Institute's polysulfone hollow fiber was originally developed as a support for reverse osmosis, and despite its large surface pore size ranging from 2!01 to Al17μ, its water permeability is low. It is extremely small, at most /3+n'/m'・day・short, and depending on the manufacturing method, the surface pore size is 10 to 10θA, and the water permeability is 1) i l! m'/rn"・day・y or higher, and it is impractical as an ultrapolar membrane.Furthermore, compared to the case of flat membranes, a high viscosity is required to make hollow fibers. A polymer solution is required, but if a highly concentrated aromatic polysulfone solution is used for this purpose, the water permeability will be significantly reduced by the usual method, making it practically meaningless.Furthermore, in general, polyacrynitrile or sulfone Semipermeable membranes made of relatively hydrophilic polymers such as aromatic polysulfone have high water permeability due to their strong affinity for water, but semipermeable membranes made of hydrophobic polymers such as aromatic polysulfone Water permeability is generally low, and in order to obtain a semipermeable membrane with high water permeability, various special methods are required.Means usually taken to improve water permeability include, for example, acrylonitrile, sulfonated polysulfone, polycarbonate, etc. This is a means of forming an anisotropic semipermeable membrane consisting of a surface layer and a supporting layer, as in the case of Cellpose/Secuto, etc. In an anisotropic semipermeable membrane, a thin surface layer that defines water permeability and a thin surface layer that defines water permeability are used. , has a support layer that has no resistance to water permeability and serves as a support for the surface layer, but it is inconvenient to use because it has low compaction resistance and changes greatly during various operations, and also has low mechanical strength. .

The present inventors developed a highly water permeable aromatic polysulfone hollow fiber semipermeable membrane that does not have the above-mentioned drawbacks! ! ! As a result of extensive research on the structure, a mixed solvent was used as the aromatic polysulfone solution, and an aqueous electrolyte solution was added.

As a result, the hollow fibers have layers with no cavities on both the inner and outer surfaces, and have high consolidation resistance and mechanical strength. The inventors have discovered that an aromatic polysulfone hollow fiber semipermeable membrane having high water permeability can be obtained through a water permeation mechanism different from that of the previous method, and have completed the present invention.

The aromatic polysulfone applicable to the present invention has the following general formula (I
) is a polymer having a repeating unit represented by

However, in the formula, x, x', -, nz O is O
or represents an integer less than or equal to da. Generally 1, nl, ns
Those in which all o's are O are easily available.

Such an aromatic polysulfone polymer is mixed with a polar organic solvent that well dissolves the aromatic borisulpo:/ in which an appropriate medicinal substance or its aqueous solution is dissolved, but does not dissolve the aromatic polysulfone. liquid (hereinafter referred to as
The hollow fiber-like semipermeable membrane of the present invention can be obtained by dissolving the membrane in a mixed solution with a non-solvent (referred to as a non-solvent), extruding it through an annular nozzle for manufacturing hollow fibers by a conventional method, and coagulating it from the inside and outside. When forming a hollow fiber semipermeable membrane, aromatic polysulfone dissolved in a polar organic solvent enters the coagulation solution from both the inner and outer surfaces, causing precipitation around the non-solvent droplets as nuclei. It is estimated that the parts that touch each other form pores. The presence of a non-solvent is significant as a nucleus for the formation of pores, and contributes greatly to the improvement of water permeability, with a water permeability of approximately 2 to 10% compared to when no non-solvent is used.
increase twice. At this time, it is assumed that the electrolyte influences the spread of the polymer chains and has some influence on the membrane structure.

When an electrolyte exists, the state of aromatic polysulfone in a mixed solution of a polar organic solvent and a non-solvent becomes unstable, and even a small amount of coagulation solution tends to cause precipitation. A layer without cavities is probably formed on the surface.

As polar organic solvents, N-methylbiplJton, dimethylformamide, dimethylacetamide, etc. are used, and so-called non-solvents that are miscible with polar organic solvents but do not dissolve aromatic polysulfone include dimethyl sulfoxide, propylene glycol, etc. is used. The ratio of the non-solvent to the polar organic solvent may be within any range as long as the mixed liquid can maintain a homogeneous state.
% is preferred. Examples of electrolytes include common salt, metal salts of inorganic acids such as sodium nitrate, potassium nitrate, sodium nitrate, and zinc chloride, metal salts of organic acids such as sodium acetate and sodium formate, sodium polystine sulfonate, polyvinylbenzyltrimethylammonium chloride, etc. Polyelectrolyte, sodium dioctyl sulfoconolinate,
Ionic surfactants such as sodium alkylmethyltaurate are used. Although these electrolytes exhibit some effects when added alone to an aromatic polysulfone solution, they exhibit particularly remarkable effects when added as an aqueous solution. The amount of the electrolyte aqueous solution to be added is as long as the addition does not cause loss of uniformity of the solution.
There is no particular limit, but usually O5 volume % to 10
It is capacity %. Further, there is no particular restriction on the concentration of the electrolyte aqueous solution, and the higher the concentration, the greater the effect, but the concentration usually used is 7% by weight to 60% by weight.

The concentration of the polymer solution as a membrane forming stock solution is 5 to 35% by weight.
, preferably 70 to 303% by weight. If it exceeds 35% by weight, the water permeability of the resulting semipermeable membrane becomes so small that it has no practical meaning, and if the concentration is lower than S weight it%, a hollow fiber semipermeable membrane with sufficient strength cannot be obtained. I can't get it.

Water is most commonly used as the coagulating liquid, but organic solvents that do not dissolve the polymer may also be used, or a mixture of two or more of these non-solvents may be used. It is also possible to use different liquids as the inner and outer coagulating liquids or coagulating liquids with different liquid compositions.

The aromatic polysulfone hollow fiber semipermeable membrane obtained by this manufacturing method has pores on both the inner and outer surfaces of the hollow fibers, and has a layer with no cavities, and these intermediate layers are also different from the surface layer. Forms a continuous polymer phase. The diameter of the pores gradually increases from both surfaces of the hollow fiber toward the inside of the membrane.
It is maximum inside the membrane, which is approximately the stopping distance from both surfaces. The pore size changes continuously from the membrane surface to the inside, forming a tapered structure. The diameters of the pores on the inner and outer surfaces are in the range /θ to 10oX. Its diameter is estimated by measuring the transmission rejection rate when aqueous dextran solutions with different average molecular weights and aqueous protein solutions of various types are passed through it, and by observing the vicinity of the surface using a transmission electron microscope.

There are no cavities near both surfaces of the hollow fiber over a thickness of approximately Sμ from the surface toward the inside, although there are differences depending on the spinning conditions. Cavities may be present in layers within the membrane that form a continuous polymeric phase with layers near the surface that are void-free. Cavities are missing portions of the membrane-forming polymer and have a diameter of more than 10 microns. Therefore, in the present invention, pores with a diameter of 10 μm or less are referred to as pores.

In general, the number of cavities decreases when the film thickness is reduced;
When the thickness is 0μ or less, hollow fibers with few cavities can be easily produced.

Hollow fibers with few cavities have excellent consolidation resistance and mechanical strength.
It also has good water permeability.

The thickness of the hollow fiber semipermeable membrane of the present invention is preferably 10 to 1 Isoμ. If it is thinner than 70μ, the mechanical strength will be low. Film thicknesses exceeding 1 isoμ are neither necessary nor desirable. Both in the absence of cavities and in the presence of cavities, there are many pores in the inner layer of the membrane, and their diameters gradually increase continuously as they move away from the membrane surface toward the inside. The maximum diameter is reached at a portion approximately equidistant from the surface, and the average diameter thereof is 70 μm when observed using an electron microscope. The reason why the diameter of the pores increases as it moves away from the membrane surface toward the inside of the membrane is thought to be because coagulation occurs from the surface toward the inside, and solidification occurs quickly at the surface and slowly toward the inside.

Therefore, the radius r of a pore located a distance l inward from the membrane surface is a function of l, and as an example (same as used in the example) is N
- Regarding hollow fibers with a membrane thickness of 100μ spun in a system of -methylbi-ridone-dimethylsulfoxide-sodium nitrate
The relationship between and r is shown in Figure 1.

In this hollow fiber, /S~30n? It shows a high water permeability of /m'·day·short, and especially a thin hollow fiber spun with a low concentration polymer shows a high water permeability. In general, the water permeability of aromatic polysulfone hollow fibers spun under the same conditions is inversely proportional to the membrane thickness, as shown in Figure 2 for the same hollow fiber as shown in Figure 1, and increases as the membrane thickness becomes thinner. The fact that Polyacrylonitrile, sulfonated polysulfone, polycarbonate, cellulose acetate-1
In anisotropic semipermeable membranes such as -, it is said that the water permeability is determined by the surface layer (also called the skin layer), but the semipermeable membrane of the present invention has water permeability from the surface regardless of whether there is a cavity or not. It is thought that all layers up to the inside of the membrane have resistance to water permeability, and the entire membrane thickness determines water permeability. Furthermore, in aromatic polysulfone hollow fibers with different film thicknesses spun under the same conditions, the diameters of the pores on the surface are almost the same, and the thickness of the layer near the surface where there are no cavities is also constant regardless of the film thickness. However, the fact that water permeability is inversely proportional to membrane thickness indicates that the resistance to hydraulic flow through the membrane is It is shown that this is caused by the entire film thickness, and is not determined only by the surface layer, as in the case of anisotropic semipermeable membranes. Furthermore, this is supported by the fact that it has high water permeability despite having void-free layers on both surfaces.

The hollow fibers obtained in this way can have extremely high water permeability by making them thinner, and because they have a structure with layers without cavities on both surfaces, they can be backwashed and are not compacted. There are fewer changes during various operations, making it easier to use and providing excellent mechanical strength.

Furthermore, since the thin film thin circular diameter hollow fiber has a small priming volume and can increase the surface area, it can be used for various medical p-filtrates, such as membranes for transparent artificial kidneys and protein concentration membranes for ascites. It can also be used as a membrane.

Hereinafter, it will be explained in detail using examples.

Example/ Two grams of a 20% sodium acetate aqueous solution is added to a 20/2 mixed solution of N-methylpyrrolidone 3732 and dimethyl sulfoxide to form a homogeneous solution. In this solution, 10 g of polysulfone having a repeating unit represented by the formula (hereinafter referred to as polysulfone) and Ri2 were dissolved to obtain a polymer solution. The viscosity of this polymer solution is 70 g0 centipoise (20° C.). This polymer solution is extruded through an annular nozzle for manufacturing hollow fibers, and is coagulated from the inside and outside of the hollow fibers using water as a coagulating liquid.
A hollow fiber-like semipermeable membrane was obtained. The water permeability of the obtained hollow fiber semipermeable membrane in pure water is /jt, Om''/nI+・day・1
,Met. The water permeability of hollow fibers of the same shape when spinning using water instead of aqueous sodium acetate solution is Q, j; m7
m-day, and the water permeability of the one using an aqueous solution of sodium acetate is much higher. In addition, the cut rates for dextrans with molecular weights of 70,000 and 70,000 are A, 3%, and 2%, respectively.
It was gross.

Example 50% by weight aqueous sodium nitrate solution gomt was mixed with dimethylacetamitom-O- and dimethyl sulfoxide/30θ
The same polysulfone 7 as described in Examples was added to the mixed solvent of 艷 to make a homogeneous solution. ;0? was added to prepare a polymer solution. A hollow fiber semipermeable membrane was obtained from this polymer solution in the same manner as in Example.

The inner diameter of the hollow fiber is θ2 tu and the outer diameter is 0. It was lIm.

The water permeability of a semipermeable membrane with pure water is /0. j m'／m'condolence・
The water permeability for hollow fibers of the same shape when water is used instead of an aqueous sodium nitrate solution is 0. gm In
' 1 day, significantly larger than ~. The cut rate for dextran with a molecular weight of 10,000 was 17 g%. The cut rates for bovine serum albumin and cytochrome C from horse heart were 99 and 5, respectively.

Example 3 4'ml of a 30% by weight aqueous potassium nitrate solution was added to a mixed solution of 53% dimethylformamide and 291% pulviresogellicol to form a homogeneous solution, and to this was added the same polysulfone/1. Dissolve Of to obtain a polymer solution. The viscosity of this polymer solution is /, r00 centivoise (,2oC). A hollow fiber semipermeable membrane was obtained from this polymer solution in the same manner as in Example. The inner diameter of the hollow fiber was θ2 and the outer diameter was olI. The water permeability of a semipermeable membrane with pure water is guQ m'/m''·day·layer, and the water permeability with respect to a hollow fiber of the same shape when water is used instead of an aqueous potassium nitrate solution is 0.2 m''7 m- It is significantly large compared to day・η. The cut rate for dextran with a molecular cap of 70,000 was about ss. Furthermore, a hollow fiber semipermeable membrane was obtained in exactly the same manner as described above, using dimethylformamide g/f instead of the mixed solvent of dimethylformamide and pulviresogelicol. Its water permeability is l in the salt-added system.
s Il+''/lr?・day・η, and in the salt fish addition system it was 0haυml・day・1.

Example 2: SO% sodium nitrate solution 2-, N-methylpyrrolidone
A homogeneous solution was prepared by adding the mixed solution consisting of Left Group 2, dimethyl sulfoxide, and 29F, and the same polysulfone/Otsu 1 as described in Example 1 was added to this to prepare a polymer solution.

The viscosity of this polymer solution is /30θ centipoise (20
℃). This polymer solution is extruded through an annular nozzle for producing hollow fibers to produce hollow fibers in the same manner as in Example/1. By adjusting the extrusion speed from the nozzle and the winding speed, the film thickness ranges from 30 μm to 350 μm. Hollow fiber semipermeable membranes with various thicknesses were obtained, and the dependence of their water permeability and pore diameter on the membrane thickness was investigated. The results are as shown in FIG. The diameter of the pores on the surface was calculated based on the cutting rate of dextran with a molecular weight of 70,000, assuming that dextran was a spherical molecule.

Incidentally, an electron micrograph (magnification: t'to times) of a cross section of the hollow fiber having a film thickness of 60 μm obtained here is shown in FIG.

Example S One SO heavy accumulation% sodium nitrate solution was added to a mixed solution consisting of 5 lIy of N-methylpyrrolidone and 2 to 2 dimethyl sulfoxide to form a homogeneous solution, and to this was added various amounts of the same polysulfone as described in Example/ A polymer solution of /l17, /&0°/&j, /,Snear% glue seed was prepared by dissolving the polymer in weight percent. The viscosity of these polymer solutions at 20″C is gbO, /θ00.//30, respectively.
．． /300 centiboise.

Hollow fiber semipermeable membranes were produced from these polymer solutions in the same manner as described in Examples. The obtained hollow fibers each had an inner diameter of θ2, an outer diameter of o4tsoi, and a film thickness of 100μ. The water permeability of these hollow fibers to pure water and the diameter of the pores on the surface are as shown in Table 1.

Table l Example 6 From the results of scanning and transmission electron micrographs of the cross section of the hollow fiber produced in Example 5 when the concentration of the polymer was 757% by weight, it was found that the direction from the inner surface of the hollow fiber to the inside of the membrane was The distance l between the two points and the radius r of the pore at that position were measured, and the relationship between the two is shown in FIG.

[Brief explanation of the drawing]

FIG. 7 is a graph showing the relationship between the radius of the pore and the distance from the inner surface of the hollow fiber, and FIG. 2 is a graph showing the relationship between the membrane thickness and the water permeability and the diameter of the surface pore. FIG. 3 is an electron micrograph (magnification: 211Ox) of a cross section of the hollow fiber having a film thickness of 260μ obtained in Example q. Patent applicant Asahi Kasei Industries Co., Ltd. Representative Patent Attorney Toru Hoshino No. 1 ;? "":+, 3, Iy-...-5. /' 1) 0 11" character, iku immanence j1 7.1guso~/-ba begging 7 bodies, 1 no, '7%'\gu$00 /)) one*, li"F7 knowledge “And (1 Cps 2.
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4. o ()11"+"-15 jin ('j1
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Claims (1)

[Claims] (1) An aqueous electrolyte solution is added to a solution in which aromatic polysulfone is dissolved in a mixed solvent of a polar organic solvent that dissolves aromatic polysulfone and a solvent that is miscible with the polar organic solvent but does not dissolve aromatic polysulfone. An aromatic polysulfone hollow fiber-like semipermeable membrane, characterized in that the solution obtained is formed into a hollow fiber shape and then brought into contact with a liquid that is mixed with the mixed solvent but does not dissolve the aromatic polysulfone to remove the solvent. manufacturing method.