JPS62213813A - Method for improving water permeability of micro-porous membrane - Google Patents

Abstract

PURPOSE:To enhance water permeability without loss of heat resistance, chemical resistance and mechanical strength by carrying out oxidation treatment of the surface of micro-porous membrane comprising polyphenylene sulfide as main component. CONSTITUTION:Polymer containing more than 90mol% of p-phenylene sulfide is used as polyohenylene sulfide. Less than 35% of other polymer can be blended with said polymer. Said polyphenylene sulfide is molded in a shape suitable for use. Next, the surface of membrane is treated to turn hydrophilic by oxidizing sulfur of p-phenylene sulfide, main component of polyphenylene sulfide. For oxidizing treatment, hydrogen peroxide, peracetic acid, nitrogen dioxide, permanganate, periodate, chromate and the like are used for oxidization treatment.

Description

[Detailed Description of the Invention] [Industrial Field of Application] Separation using a membrane is an energy-saving type of separation, and its field of application has been expanding more and more in recent years. Applications of microporous V include production of pure water or ultrapure water, dust removal filters for air circuits, recovery of the materials, reduction and recovery of latex and emulsions, wastewater purification such as bacteria removal from gray water, and valves. Oil-water separation, battery separators, electrolytic diaphragms, gas vents, water permeation materials, artificial blood vessels, artificial lungs, plasma separation, juice, cheese protein, etc., which are used in wastewater treatment, cutting oil, rolling wastewater treatment, etc. am1 Separation IP for food products such as clarification of wine, fermentation, steroids, etc.
! It is expected to be used in many fields, such as in the pharmaceutical industry and as a support for gas separation membranes, and has also been put to practical use.

Some polyphenylene sulfide resins (hereinafter abbreviated as PPS) are thermoplastic resins with high heat resistance, mechanical strength, and rigidity, and there is no way to dissolve them at temperatures below 200°C, so acids, alkalis, etc. It has excellent properties that are not attacked by chemicals such as
It is expected that it will be possible to sterilize with steam and chemicals, and to clean with acids and alkalis. Among these fields of application, use in aqueous systems is thought to occupy a large field, and the present invention, which improves the water permeability of a hydrophobic PPS microporous membrane, has an important significance.

[Conventional technology]

Troubles that occur frequently when using #I membranes include smearing and deterioration of water quality caused by concentration polarization due to fapping and scale formation. (b) As a means of reversing such troubles, methods of chemically decomposing, dissolving, or dispersing deposits using chemicals are often used. However, since the deposits on the membrane surface are a mixture of various types, a single chemical can be expected to have a sufficient effect, but in some cases several types of chemicals may be used. Furthermore, in the fields of medicine and foodstuffs, it is necessary to sterilize the armpits before use, and steam sterilization has often been recommended in recent years due to its safety. From this point of view, membranes with excellent heat resistance and chemical resistance are needed (rarely, and PPS microporous membranes are the most suitable for this request. However, since PPS is a hydrophobic polymer, it has low water permeability. The problem was probably due to a lack of sex.

Generally, when hydrophobic polymers are used in aqueous systems, it is possible to use surfactants to impart hydrophilicity to solve the drawbacks of low water permeability and the need for large initial pressure. Although this is usually done, the hydrophilicity gradually decreases as washing is repeated, and it takes a lot of effort to restore performance, making it uneconomical.

[Problem that the invention seeks to solve]

Microporous membranes made mainly of PPS are effectively used for treating organic solvents due to their heat resistance and chemical resistance, but due to their inherent hydrophobicity, conventional techniques are required for use in aqueous systems. There was a limit of 9 kana. Therefore, the present invention provides PPS
The purpose is to provide a microporous membrane that has an improved water permeation rate and can be used for a long period of time while taking advantage of the excellent heat resistance and chemical resistance that it inherently has.

[Means for solving problems]

In view of these problems, the present inventors have developed a method of increasing water overspeed while maintaining heat resistance and chemical resistance by treating the surface of a microporous membrane containing pps as a main component to form a water droplet. We succeeded in obtaining a microporous membrane. That is, the present invention provides P
The present invention provides a hydrophilic microporous membrane by oxidizing the surface of the microporous membrane, including the surface of the pores, of the microporous membrane containing PS as a main component.

PPS in the present invention refers to a polymer containing 90 mol% or more of p-phenylene sulfide as the main structural unit of the polymer. Examples of other structural units that can be contained in an amount of less than 10 mol% include metaphenylene sulfide, trifunctional heptad, diphenylketone sulfide, diphenylsulfone sulfide, biphenyl sulfide, substituted phenylsulfide, nitro, or haloken group.

Less than 35% of the loose polymer particles can be blended with PP5E. If other polymers account for 65% or more, defects will occur in the formation of microporous, heat resistance, chemical resistance, and mechanical properties, resulting in loss of PPS quality. Other polymers that can be blended include polyethylene terephthalate, polybutylene terephthalate, nylon-6, and nylon-6.
66. Crystalline polymers such as polycarbonate, polyoxymethylene, polyphenylene oxide, poly-4-methylpentene-1, polypropylene, polytetrafluoroethylene, polyetheretherketone, and non-quality polymers such as polysulfone and polyethersulfone. can be exemplified. Further, such a raw material resin may contain an appropriate amount of additives such as an antioxidant, an antistatic agent, an antibacterial agent, a lubricant, a surfactant, and the like, if necessary.

The microporous membrane used in the present invention is disclosed in Japanese Patent Application Laid-Open No. 58-6773.
No. 3, Japanese Patent Application Laid-open No. 57-168446, etc., it is molded into a shape suitable for the purpose of use. For flat membranes, p-phenylene sulfide is 90 mol%.
The pps'l containing the above is melt-extruded to produce a non-porous unstretched film, and the unstretched film is subjected to cold stretching, hot field stretching and heat setting under conditions set in the coaxial direction with the above melt extrusion. Formed into a porous flat membrane. In addition, in hollow fiber membranes, the raw material resin is melt-spun through a hollow fiber spinneret to form undrawn hollow fibers, which are then heat-treated, stretched, and heat-set under certain conditions to form a material next to the microporous hollow fibers. It is formed.

The hydrophilic treatment of the present invention involves chemically treating the surface of PPS to oxidize the sulfur of p-7 22 Lemburghide, which is the main constituent unit of 2, pps, and converting it to -5O7- or -
This is done by noting S〇-. The treatment of the present invention needs to be carried out under mild conditions. If treated under harsh conditions, the structure of the PPS microporous membrane itself may be destroyed, which is not preferable.

The reagent used in the treatment method of the present invention to oxidize -S- in the main chain bone of PPS to 18O- or 15O1- may be an organic peroxide such as hydrogen peroxide or peracetic acid. , nitrogen dioxide, permanganate, periodic acid, and chromium. It is desirable that the treated microporous membrane has a moderate hydrophilicity 2S. If there are too few hydrophilic groups, the water wettability of the membrane will be low and the effect of improving the water transport overrate will be small; if there are too many hydrophilic groups, on the other hand, the physical properties will be adversely affected. The general conditions regarding the concentration of the oxidizing agent used in the treatment, the treatment temperature, and the treatment time are shown below.

(1) When hydrogen peroxide is used as an oxidizing agent, commercially available hydrogen peroxide of about 60% is usually used. Since the oxidation of PPS is very slow with hydrogen peroxide alone, in the present invention it is preferable to carry out the 9-oxidation reaction by using yJ74 acid 1 abacus as a sulfuric acid solution. The method for preparing peroxide Honshu-sulfur modified solution is to cool concentrated sulfuric acid (95%) to about 20°C, and add it to 30°C while stirring.
% hydrogen peroxide aqueous solution dropwise. The hydrogen peroxide concentration is α1~ICLO%, preferably [15~5
%. The degree of oxidation progress when the microporous membrane is immersed in the above solution and subjected to oxidation treatment is as follows:
Varies depending on processing temperature and processing time. Processing temperature #'i
The temperature is 5°C to 50°C, preferably 10°C to 40°C. The treatment time varies depending on the concentration of the oxidizing agent and the treatment temperature, so it cannot be defined unconditionally, but within the above-mentioned preferred temperature and treatment temperature ranges, it is 10 seconds to 300 seconds.

(21 In the case of peracetic acid, the peracetic acid used in the present invention is usually diluted with 40% acetic acid, which is commercially available as an acetic acid bath solution. Any organic solvent can be used, but it is usually preferable to dilute with acetic acid.The concentration of peracetic acid used in the present invention is CL1 to 100%.
, the preferred system is 5 to 5.0%. The oxidation rate of the peracetic acid-butyric acid solution tends to be slightly slower than that of the hydrogen peroxide-sulfuric acid system, so in order to accelerate the oxidation rate, the treatment temperature is 30 to 100°C, preferably 40 to 80°C.
Perform at ℃. Although the treatment time is not constant as in the case of the hydrogen peroxide-#L acid solution, it is 10 seconds to 300 seconds within the above concentration and treatment temperature range.

(3) In the case of 9-dioxide, it is possible to make acid 11S in nitrogen dioxide gas, but it is usually more economical to dilute it with air or nitrogen. In the present invention, 6 to 80%, preferably 5 to 2
Used as a nitrogen stream with a concentration of 0%. Usually, the fermentation temperature is room temperature and the treatment time is 10 to 300 seconds.

The microporous membrane treated under such conditions and subjected to surface oxidation is washed with water, diluted alkali, and water, and then dried to obtain a final product.

[Effects of the present invention]

As is clear from the above description, the hydrophilic microporous membrane according to the present invention has improved water permeability without losing the heat resistance, chemical resistance, and mechanical strength of PPS. Therefore, it can be used in aqueous fields where hydrophobic pps microporous membranes could not be used.

That is, the microporous membrane of the present invention can be used in reverse osmosis, ultrafiltration, precision filtration, etc. by incorporating it into a flat membrane or hollow fiber shape. Examples of specific applications include the purification of industrial wastewater in the valve industry, textile industry, atomic crab industry, etc., the production of pure or ultrapure water used in the electronic industry, and the production of fruit juice and protein in food products. Examples include concentration of bonds, production of sterile water in the pharmaceutical and medical fields, recovery of #elements, and diaphragms for electrochemistry.

Because the surface of the porous membrane is made hydrophilic, hollow fibers in particular have new properties such as self-breathing, sweat absorption, and antistatic properties in addition to heat resistance, chemical resistance, and flame retardancy. It can be used as a fiber material for various purposes. Specific examples of such materials include firefighting suits, antistatic clothing, bandages, and the like.

Reference examples related to the production of microporous membranes and implementation PIs of the present invention will be specifically explained below, but the present invention is not limited thereto.

[Reference row 1] Using a PP5t-coat hanger type slit die with logarithmic viscosity (η = CL32), extrude the unstretched sheet onto three chill rolls at a draft rate of 150, and cold stretch it (stretch ratio t3, temperature 20°C), then hot stretching (stretching ratio 2.0, temperature 100°C) and heat setting (stretching ratio α9, temperature 200°C) to a thickness of 25 μm 1 average pore diameter α2
A microporous flat membrane (untreated membrane) 1 with a porosity of 0 μm and 28% was obtained. When the water permeation rate is defined, the pressure difference is 1 kQ/cII
? The order was [1011M/(-).

Further, the contact angle of water with respect to the flat membrane was 73°.

[Reference Example 2] Using a melt extrusion spinning machine, the same pps as used in Reference Example 1 was passed through a hollow #Il conical nozzle at a nozzle temperature of 325°C (5) and a draft rate of 230. A hollow fiber was spun. An electric slit heater at a temperature of 255° C. was placed between the rolls of the resulting hollow fiber set, and heat treatment was performed at the length of the legs. Next, the stretching ratio is t5, the temperature is 110□A, and then the temperature is 240
Heat set at ℃, outer diameter 500μm% thickness 40μm
A microporous hollow fiber having an average pore diameter of 1120 μm and a porosity of 28% was obtained. When the water permeation rate was measured, the pressure difference was 111
．． <//cIF? So a011rttl/ctt?・It was a deception.

Implementation 91J1 The microporous flat membrane obtained in Reference Example 1 was exposed to H, O2 at a predetermined degree of storage.
/H, So, at room temperature for a certain period of time, followed by washing with water [washing with a 15% aqueous sodium hydroxide solution,
After rinsing with water, it was dried under vacuum at 100°C to obtain a microporous flat eyelet suitable for water cultivation.

Table 1 shows the measurement results of the contact angle and water permeation rate of Senkatsu treated with water at different concentrations and treatment times. It can be seen that the contact angle is reduced by the treatment, the wettability to water is improved, and the water permeability is improved. When the surface oil of the flat membrane was inspected using a set electron microscope (SEM), the surface was slightly uneven compared to the reference example 10 membrane, but the pore diameter and condition of the pores were #1. There was even. When the IR spectrum was measured, 10H absorption was observed at 6500α-1, and the absorption increased as the treatment time and treatment concentration increased. Moreover, these absorptions were not observed in the untreated flat membrane, but were oxidized by the treatment.
Immerse Fi in OOOH/CH, COOH for a fixed period of time while maintaining the temperature at 50°C, rinse with water, wash with aqueous solution of sulfur-IJ hydroxide at cL5%°C, and repeat the washing with water at 100°C. The mixture was dried under vacuum to obtain a firewood-water-based microporous flat membrane. Table 2 shows the measurement results of the water contact angle and water permeation rate of the flat membranes treated with varying concentrations and treatment times. IR
Both measurement results and SEMcDBu observation results are based on Example 1.
It was the same aircraft.

Example 6 The microporous hollow fibers obtained in Reference Example 2 were treated with a predetermined concentration of H,
The fibers were immersed in O,/H,So for a certain period of time at room temperature, and then washed and dried in the same manner as in Examples 1 and 2 to obtain hydrophilic microporous hollow fibers. Hollow weaves ## treated with different concentrations and treatment times were bundled into 100 pieces each to a length of 15 cIn.
After making the module into a module, the water permeation rate was measured. The results are shown in Table 3.

Table 3 Example 4 Microporous hollow fibers obtained in Reference Example 2 were held in nitrogen dioxide diluted with total nitrogen to a concentration of 10% for 90 seconds, then taken out, and 100 fibers were bundled to form a module with a length of 15 cyt. After that, when the water permeation rate was measured, the pressure difference was 1 kg/c.
rd' was α030m/(7)2.

Claims (1)

[Scope of Claims] 1. A method for improving water permeability of a microporous membrane, which comprises oxidizing the surface of the microporous membrane containing polyphenylene sulfide as a main component. 2. The oxidation treatment described in claim 1 is performed using one or more of hydrogen peroxide, organic peroxide, nitrogen dioxide, permanganate, periodate, and chromic acid. A method for improving water permeability of microporous membranes.