CN103143273B - Preparation method of aromatic polymer porous membrane - Google Patents

Abstract

The invention discloses a preparation method of an aromatic polymer porous membrane. The porous membrane comprises a flat membrane and a hollow fibrous membrane. The preparation method adopts the following porous membrane casting solution and solution-phase conversion membrane preparation technique. The membrane casting solution comprises the following components in percentage by mass: 1.5-15 wt% of PPTA (poly(p-phenylene terephthalamide)), 4.5-10 wt% of pore-forming agent and 86.5-94 wt% of solvent. The pore-forming agent is a soluble high polymer selected from at least one of PEGs (polyethylene glycols) with the average molecular weight of 600-20000 and PVPs (polyvinyl pyrrolidones) with the average molecular weight of 10000-100000; and the solvent is 98-100 wt% concentrated sulfuric acid. The porous membrane preparation technique comprises the following steps: 1) preparing the membrane casting solution; and 2) preparing the flat porous membrane by a wet process, or preparing the hollow fiber porous membrane by dry-wet spinning formation.

Description

A kind of preparation method of aromatic polymer porous film

technical field

The invention relates to membrane material technology, in particular to a preparation method of an aromatic polymer porous membrane. The aromatic polymer refers to polyparaphenylene terephthalamide [Poly(para-PhenyleneTerephthalamide), PPTA], and the porous membrane includes a flat membrane and a hollow fiber membrane.

Background technique

The meta-aromatic polyamide, polym-phenylene isophthalamide (PMIA), has strong flexibility and good physical-mechanical properties. It can be dissolved in some organic solvents to form an isotropic solution. Good processing performance, PMIA porous membrane material can be made by solution phase inversion method. At present, there have been relevant reports on PMIA membranes with porous structures at home and abroad. For example: Chinese patent CN1681875A [Sasaki Yi, etc., Teijin Co., Ltd.] has introduced a kind of manufacturing method that contains PMIA porous film, and it will contain the polymer solution of PMIA and amide solvent casting on the support body, then impregnated into containing and PMIA Solidify in the amide coagulation bath of immiscible material, make porous membrane; The film-making solution of salt is sprayed from double annular nozzles at or above 70°C, and then subjected to moisture-retention treatment after dry-wet spinning to form a PMIA hollow fiber porous membrane; US Patent U.S.Patent6103862 Nematic liquid crystal thin film material and its preparation method (Alignment film material for a liquid crystal cell and a method for preparing the same)] introduced a novel thin film material for liquid crystal battery, which is mainly through PMIA and carbanion reaction, the halogenated functional group is substituted on the PMIA, and a battery separator with good heat and humidity resistance is obtained.

Para-aromatic polyamide, PPTA, is the most representative aromatic polyamide. The macromolecules are rigid, have lyotropic liquid crystallinity, excellent heat resistance and chemical resistance, and are ideal for preparing high-performance aromatic polyamides. important raw material for fiber. Compared with PMIA, PPTA has more excellent physical-mechanical properties, but because the decomposition temperature of PPTA is low, and only concentrated sulfuric acid can dissolve it, it is difficult to make a film. So far, although there are patent literature reports about PPTA fiber , but not yet seen the patent literature report on the aromatic polymer PPTA porous membrane material.

Contents of the invention

Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing an aromatic polymer porous membrane. The preparation method uses the aromatic polymer PPTA as the film-forming material, and adopts the solution phase inversion method (wet method or dry-wet method) to form the film technology. It has the advantages of simple preparation process, short process, easy control and high efficiency, and is suitable for industrial implementation. and other characteristics; the obtained PPTA porous membrane has the characteristics of high porosity, uniform pore size distribution, good permeability, fibrillation structure, strong filtration retention capacity, and strong compaction resistance, etc., and can be used in acid-base media and organic solvents , oil-water separation and other membrane separation systems under harsh environmental conditions.

The technical solution of the present invention to solve the technical problem is to design a method for preparing an aromatic polymer porous membrane, the porous membrane includes a flat plate membrane and a hollow fiber membrane, and the preparation method adopts the following porous membrane casting solution and solution phase Conversion method membrane process, the mass fraction of the casting solution consists of:

PPTA 1.5～15wt%,

Porogen 4.5～10wt%,

Solvent 86.5～94wt%, the sum of each component is 100%,

The porogen is a soluble polymer, at least one selected from PEG with an average molecular weight of 600 to 20,000 and PVP with an average molecular weight of 10,000 to 100,000; the solvent is concentrated sulfuric acid with a mass concentration of 98 to 100 wt %;

The membrane-making process of described porous membrane is:

1) Configure casting solution

Mix the PPTA resin and the solvent concentrated sulfuric acid solution according to the stated ratio, stir and swell at 30-40°C to form a transparent viscous mixture, then add the porogen in the stated proportion, heat up to 80-85°C, and mix thoroughly Finally, vacuum defoaming to form a uniform casting solution;

2) Preparation of flat porous membrane or hollow fiber porous membrane

(1) Preparation of flat porous membrane

Scrape-coat the obtained casting solution on a clean glass plate at room temperature to make a flat porous membrane, and immediately immerse it in a 15-18°C ultrafiltration water coagulation bath, keep it for 24 hours to solidify and form, and then put it in 50-60°C hot water Soak for 3 to 4 hours; or put into an aqueous solution with a small amount of sulfuric acid, soak for 3 to 4 hours at 50 to 60°C, then soak in absolute ethanol for 1 to 2 hours, and then wash with deionized water to remove the residues in the membrane acid and dehydrated alcohol to obtain the aromatic polymer flat porous membrane;

(2) Preparation of hollow fiber porous membrane

The casting solution is metered by a metering pump, extruded from a hollow spinning spinneret, immersed in a coagulation bath at 15-18°C after passing through an appropriate air gap, to obtain a porous primary hollow fiber porous membrane, and then undergoes extraction, washing, After the winding step, the aromatic polymer hollow fiber porous membrane is obtained.

Compared with the prior art, the preparation method of the aromatic polymer porous membrane of the present invention adopts the solution phase inversion method (wet method or dry-wet method), which has the advantages of simple membrane making process, short process, high efficiency, and can effectively adjust the pore size of the membrane Size and other characteristics. Adopt the aromatic polymer PPTA porous membrane that the preparation method of the present invention gains, owing to add a large amount of water-soluble low molecular weight polymer porogens, can make gained membrane have larger pure water flux, simultaneously different molecular weight porogens also can make The separation accuracy of the membrane is increased, and the rejection rate of the obtained membrane can be increased by adding a porogen with a small average molecular weight, and because the aromatic polymer PPTA porous membrane has corrosion resistance, it can replace the inorganic membrane and be used under certain harsh environmental conditions , greatly saving the production cost, and easy to implement and popularize in industrialization.

Description of drawings

Fig. 1 is the photogram of the surface network-like pore structure of the aromatic polymer porous film obtained by the preparation method of the present invention;

Fig. 2 is a photograph of the cross-sectional shape and structure of the aromatic polymer porous membrane obtained by the preparation method of the present invention. The finger-like hole structure in the longitudinal section is clearly visible in the white box in Figure 2.

Specific implementation method

Further describe the present invention below in conjunction with embodiment and accompanying drawing thereof.

The preparation method of the aromatic polymer PPTA porous membrane designed by the present invention (referred to as the preparation method), the porous membrane includes a flat membrane and a hollow fiber membrane, and the preparation method adopts the following porous membrane casting solution and solution phase inversion method (wet method or dry-wet) membrane process,

The mass fraction of described casting liquid consists of:

PPTA 1.5～15wt%,

Porogen 4.5～10wt%,

Solvent 86.5～94wt%, the sum of each component is 100%,

The porogen is a soluble polymer, at least one selected from PEG with an average molecular weight of 600-20,000 and PVP with an average molecular weight of 10,000-100,000; when two or more porogens are selected, the mixing ratio is arbitrary; The solvent is concentrated sulfuric acid with a mass concentration of 98-100 wt%.

Described film-making process is specifically as follows:

1) Configure casting solution

Mix the PPTA resin and concentrated sulfuric acid solution according to the stated ratio, stir and swell at 30-40°C to form a transparent viscous mixture, then add porogen, raise the temperature to 80-85°C, mix thoroughly, and vacuum Bubbles to form a uniform casting solution;

2) Preparation of flat porous membrane or hollow fiber porous membrane

(1) Preparation of flat porous membrane

Preparation of PPTA flat porous membrane by solution phase inversion method (wet method): scrape-coat the obtained casting solution on a clean glass plate at room temperature to make a flat membrane, and immediately immerse it in an ultrafiltration water coagulation bath at 15-18°C to keep After curing for 24 hours, soak in hot water at 50-60°C for 3-4 hours, or put it into an aqueous solution with a small amount of sulfuric acid, soak at 50-60°C for 3-4 hours, and then soak in absolute ethanol for 1-4 hours 2h, and then washed with deionized water to remove the residual acid and absolute ethanol in the membrane, to obtain the aromatic polymer PPTA flat porous membrane of the present invention.

(2) Preparation of hollow fiber porous membrane

The PPTA hollow fiber porous membrane is made by the solution phase inversion method (dry-wet spinning forming): the casting liquid is metered by a metering pump, extruded from the hollow spinning spinneret, and immersed in the In a coagulation bath at 15-18°C, a porous nascent hollow fiber membrane is obtained, and after processes such as extraction, washing, and winding, the aromatic polymer PPTA hollow fiber porous membrane is obtained. The proper air gap is a known technique.

By adopting the method for preparing the aromatic polymer porous membrane of the present invention, both the PPTA hollow fiber porous membrane and the PPTA flat porous membrane can be prepared. The preparation method of the aromatic polymer hollow fiber membrane is an important innovation point of the present invention. Due to the high extrusion speed in the dry-wet spinning process, the flow orientation effect of the casting liquid in the spinneret is significant, and the rigidity of the PPTA macromolecule is strong, and the de-orientation effect at the moment when the spinning fine flow leaves the spinneret is weak , under the action of winding tension, the nascent hollow fiber membrane maintains a higher macromolecular orientation state structure, showing better mechanical properties, so there is no need for post-stretching treatment.

The soluble porogen in the present invention is a mixture of one or more of PEG with an average molecular weight of 600-20,000, and PVP with an average molecular weight of 10,000-100,000 in any proportion. As far as the present invention is concerned, after the film-forming system forms a film, the porogen is dissolved and washed out after extraction and washing, forming many interpenetrating dissolution micropores in the film (see Figures 1 and 2). At the same time, after adding a large amount of porogen to the system, the viscosity of the system can be significantly reduced, which is conducive to the full mixing of the system and ensures the uniformity of the obtained membrane material.

What is not mentioned in the present invention is applicable to the prior art.

The present invention will be further described below in conjunction with specific embodiments, but specific embodiments are only used as specific examples of the technical solutions described in the present invention, and do not limit the protection scope of the claims of the present invention.

Example 1

Dissolve PPTA resin with a mass fraction (the same below) of 3.5wt% in 86.5wt% concentrated sulfuric acid with a concentration of 98wt%, then add porogen PEG6000, heat up to 80°C to completely dissolve, and defoam in a vacuum oven to obtain casting solution required. Scrape-coat the casting liquid at room temperature to form a flat film, and immediately immerse it in ultrafiltered water at 16°C, and solidify and form it for 24 hours. The obtained membranes were placed in ice water at 5°C, room temperature at 25°C and hot water at 50°C for 24 hours of extraction and washing. Then perform a performance test: wash the residual liquid on the membrane with deionized water, and then filter the pure water at 0.1Mpa to measure its water flux. The water fluxes of the obtained membranes were 132.70 (L/m ² h), 149.28 (L/m ² h) and 165.87 (L/m ² h), respectively.

Example 2

As described in Example 1, with other conditions unchanged, the porogen was changed to PEG with molecular weights of 2,000, 10,000, or 20,000, and placed in ice water at 5°C for extraction and washing for 24 hours. Then perform a performance test: wash the residual liquid on the membrane with deionized water, and then filter the pure water at 0.1Mpa to measure its water flux; the water flux of the obtained membrane is 79.62 (L/m ² h), 82.94 (L /m ² h) and 99.52 (L/m ² h).

Example 3

Dissolve 2.0wt% PPTA resin in concentrated sulfuric acid with a mass fraction of 88wt% and a concentration of 98wt%, then add 10wt% of composite porogens such as PVP60000 and PEG2000, heat up to 80°C to completely dissolve, and defoam in a vacuum oven. That is, the required casting solution is obtained. Scrape-coat the casting solution at room temperature to form a flat film, and put the prepared film in room temperature of 25°C and hot water at 50°C for extraction and washing for 24 hours. Then perform a performance test: wash the residual liquid on the membrane with deionized water, and then filter the pure water at 0.1Mpa to measure its water flux. The water fluxes of the obtained membranes were 265.39 (L/m ² h) and 281.98 (L/m ² h), respectively.

Example 4

According to Example 3, when other conditions remain unchanged, the solid content of PPTA added to the casting solution system is reduced to 1.75wt%, and the performance test of the prepared membrane is performed: the residual liquid on the membrane is cleaned with deionized water , and then filter pure water at 0.1Mpa to measure its water flux. The water fluxes of the obtained membranes were 318.47 (L/m ² h) and 331.74 (L/m ² h), respectively.

Example 5

As described in Example 4, with other conditions unchanged, the extraction and washing conditions were changed to soak in hot water at 50°C, put in absolute ethanol for 2 hours, and then take it out for performance testing: wash the residual liquid on the membrane with deionized water , and then filter the pure water at 0.1Mpa, and measure the water flux to be 364.92 (L/m ² h).

Example 6

Dissolve 1.5wt% of PPTA resin in concentrated sulfuric acid with a mass fraction of 88.5wt% and a concentration of 98wt%, then add 10wt% of a composite porogen of PVP40000 and PEG2000 at a ratio of 1:1, heat up to 80°C to completely dissolve, and Degassing in an oven to obtain the desired casting solution. Scrape-coat the casting solution at room temperature to form a flat film, and place the prepared film at room temperature at 25°C for curing and forming. Put part of the cured and formed film in absolute ethanol for 1 hour and take it out. The other part is soaked in 50°C hot water. Take it out after 1 hour in the water; then perform performance test on the membrane respectively: wash the residual liquid on the membrane with deionized water, and then filter the pure water at 0.1Mpa to measure its water flux. The water fluxes of the obtained membranes were 527.44 (L/m ² h) and 331.74 (L/m ² h), respectively.

Example 7

As described in Example 6, under other conditions unchanged, no PVP was added to the porogen, and the cured and formed membrane was soaked in hot water at 50°C for performance testing after extraction and washing: wash the membrane with deionized water After the residual liquid, the pure water was filtered at 0.1Mpa, and the water flux was measured to be 165.87 (L/m ² h).

Example 8

As described in Example 3, under the condition that other conditions remain unchanged, no porogen is added to the casting solution, and the performance test of the prepared membrane is carried out: the residual liquid on the membrane is cleaned with deionized water, and then the membrane is cleaned at 0.1Mpa. The pure water was filtered under the bottom, and the water flux was determined to be 119.43 (L/m ² h).

Example 9

As described in Example 6, with other conditions unchanged, 2g/L, 0.03wt% 1000ml sodium hydroxide ovalbumin solution (pH=11) was prepared for interception test.

Performance test: wash the residual liquid on the membrane with deionized water, pre-press the PPTA membrane at 0.1Mpa for 20 minutes, then filter the prepared ovalbumin solution, connect the filtrate and protein stock solution every 5 minutes, The absorbance was recorded under the irradiation of a double-beam ultraviolet-visible spectrometer (UV1901), and the filtration flux was determined to be 454.69 (L/m ² h), and the rejection rate was 92.47%.

Example 10

According to Example 3, all conditions remained unchanged, and the casting liquid was processed into a PPTA hollow fiber membrane through a dry-wet spinning process, the air gap height was 10 mm, and the draw ratio of the spinneret was 6.

Performance test: Use the internal pressure method to filter pure water at 0.1Mpa and measure its water flux. The obtained water flux is 521.21 (L/m ² h).

The calculation of the PPTA membrane water flux J of the present invention is according to the following formula:

J=V/(Sⅹt)

Where V is the volume of permeated water (L), S is the membrane area (m ² ), and t is the test time (h).

Comparative example 1

Comparing Examples 1 to 6, it can be shown that with the reduction of PPTA solid content, the flux of PPTA membranes increases significantly, which is due to the increase of membrane porosity.

Comparative example 2

Comparing Examples 1-7 with Example 8, it can be shown that the porogen plays a role in dissolution and pore formation in the system. At the same time, the fibrillation structure characteristic of PPTA also promotes the formation of network-like pore structure and finger-like pore structure in the membrane (see Figures 1 and 2).

Comparative example 3

Through the comparison of the fluxes of the PPTA membrane after extraction and washing at three temperatures in Example 1, it can be seen that as the water temperature increases, the obtained fluxes show an upward trend. This is due to the fact that the high-temperature water bath accelerates the double diffusion rate during the solidification process of the membrane, accelerates the precipitation of the porogen, and increases the internal pores.

Comparative example 4

Comparing the flux results of Examples 4, 5, and 6, it can be seen that the membrane flux of the membrane immersed in absolute ethanol has a significant increase. This is due to the good compatibility of absolute ethanol, which can effectively wash out the substances that are not easy to dissolve in the membrane.

Comparative Example 5

Comparing the flux results of Examples 6 and 7, it can be seen that under the same solid content of PPTA, adding a small amount of PVP to the porogen can greatly increase the porosity. This is mainly because the ketone macromolecules play a role of phase separation in this system, which accelerates the double diffusion speed between the solvent and the coagulant in the wet film, and at the same time, PVP can also promote the formation of fibrillation structure.

Comparative example 6

Through the SEM observation and the test of the rejection rate of the membrane in Example 9, it can be seen that the PPTA membrane of the present invention has a pore size range of about 0.01-0.5 μm, which can effectively intercept ovalbumin.

Claims (3)

1. a preparation method for aromatic polymer perforated membrane, described perforated membrane comprises Flat Membrane and hollow-fibre membrane, this system

Preparation Method adopts following perforated membrane casting solution and solution phase inversion filming technology, and the mass fraction of described casting solution consists of:

PPTA 1.5~15wt%，

Pore-foaming agent 4.5 ~ 10wt%,

Solvent 86.5 ~ 94wt%, each component sum is 100%,

Described pore-foaming agent is soluble high-molecular, be selected from mean molecule quantity be 600 ~ 20000 PEG, mean molecule quantity be at least one in the PVP of 10000 ~ 100000; Described solvent is the concentrated sulfuric acid of mass concentration 98 ~ 100wt%;

The filming technology of described perforated membrane is:

1) casting solution is configured

Described PPTA resin and the solvent concentrated sulfuric acid are mixed by described mass fraction, stirs swelling at 30 ~ 40 DEG C, form clear viscous shape mixture, then add the pore-foaming agent of described mass fraction, be warming up to 80 ~ 85 DEG C, fully after mixing, vacuum defoamation, forms uniform casting solution;

2) plate porous membrane or hollow fiber porous film is prepared

(1) plate porous membrane is prepared

At room temperature gained casting solution blade coating is made plate porous membrane on cleaned glass plate, and immerses immediately in the bath of 15 ~ 18 DEG C of ultrafiltration water condensation, keep 24h curing molding, after put into 50 ~ 60 DEG C of hot water and soak 3 ~ 4h; Or put into and add a small amount of sulphur aqueous acid, at 50 ~ 60 DEG C, soak 3 ~ 4h, then put into absolute ethyl alcohol immersion 1 ~ 2h, and then by washed with de-ionized water, remove acid residual in film and absolute ethyl alcohol, obtain described aromatic polymer plate porous membrane;

(2) hollow fiber porous film is prepared

Described casting solution is measured through measuring pump, is extruded by hollow spinning nozzle, behind suitable the air gap, be immersed in 15 ~ 18 DEG C of coagulating baths, obtain porous to come into being hollow fiber porous film, then wash through extraction, after rolling step, namely obtain described aromatic polymer hollow fiber porous film.

2. the aromatic polymer hollow fiber porous film prepared according to aromatic polymer method for preparing porous film described in claim 1.

3. the aromatic polymer plate porous membrane prepared according to aromatic polymer method for preparing porous film described in claim 1.