Preparation method of polymer porous membrane with high pollution resistance and good inorganic dirt removal effect and product

Abstract

The invention discloses a method for preparing a polymer anti-pollution membrane, which is characterized in that a'fluorine-containing polymer / styrene-maleic anhydride 'porous membrane is prepared by taking a styrene-maleic anhydride copolymer and a fluorine-containing polymer as base materials and adopting a thermally induced phase separation technology. And loading chitosan on the surface of the porous membrane by utilizing a chemical reaction between anhydride on the surface of the membrane and a small part of amino groups in a chitosan chain. The chitosan molecular chain with pH responsiveness not only improves the hydrophilicity of the membrane and slows down the deposition of inorganic scales on the surface of the membrane, but also has the conformation subjected to'curl-stretch 'reversible transformation (similar to'curl-stretch' motion of earthworms in soil so as to soften the soil) in the'acid washing-alkali washing 'cleaning process of the membrane; hardened inorganic scale deposited on the surface of the membrane becomes loose, the binding force between the inorganic scale and the surface of the membrane becomes weak, and the inorganic scale can be effectively removed through surface water cleaning in the follow-up process. The prepared cleaning agent has the advantages of being high in pollution resistance, good in inorganic dirt removal effect after cleaning and the like.

Description

Technical Field

[0001] The invention relates to a method for preparing a polymer porous membrane, in particular to a method for preparing a polymer porous membrane with strong anti-pollution performance and good inorganic dirt removal effect. Background Art

[0002] Membrane separation technology has been developed in recent years as a separation technology that can achieve high precision. Among them, fluorinated polymers represented by polyvinylidene fluoride are currently widely used as materials for the preparation of porous membranes and are widely used in the fields of water treatment, biological separation and purification, as well as membrane absorption, membrane extraction and other membrane contactor fields. The membrane has good anti-pollution properties and good pollutant removal effects after cleaning, which are prerequisites for whether the water treatment membrane can have practical value. The membrane surface is hydrophilic, the scale layer formed by the pollutants is loose and the binding force with the membrane surface is weak, the pollutants are less likely to adhere to the membrane surface. Grafting suitable hydrophilic groups on the membrane surface is a convenient means to achieve the above goals. Non-solvent phase separation technology and thermal phase separation technology are currently commonly used technologies for preparing polymer porous membranes. Compared with non-solvent phase separation technology, thermal phase separation technology has the advantages of easy control of pore structure, high membrane mechanical properties, and convenient preparation process. It is especially suitable for the preparation of polymer porous membranes without solvents at room temperature. At present, this method has been used to prepare polyvinylidene fluoride porous membranes.

[0003] Thermally induced phase separation technology was invented by Castro in 1981 (US Patent, 4247498, 1981). The film-forming principle of this technology is: polymer and specific diluent are formed into polymer solution at high temperature. When the temperature drops to a certain level, the polymer solution undergoes solid-liquid or liquid-liquid phase separation. After the diluent is extracted, the space occupied by the diluent in the system forms micropores. On this basis, the difference in the solubility of the co-polymer in the diluent is utilized so that one of the polymers solidifies and precipitates from the diluent during the cooling process, while the other polymer is still dissolved in the diluent (the diluent is a solvent for the other polymer). In the subsequent ethanol extraction of the diluent, the other polymer solidifies and precipitates and is deposited on the membrane surface. Fluorine-containing polymers that meet the above conditions include polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and the diluent mainly includes alcohol-soluble triacetin, tributyrin, triethyl acetylcitrate, etc. The co-polymer is styrene-maleic anhydride copolymer (SMA), polymethyl methacrylate, etc.

[0004] Calcium sulfate (CaSO 4 ), silicates, barium sulfate (BaSO 4), carbonates and other small water-insoluble inorganic particles. These substances will be adsorbed, deposited, and hardened on the membrane surface during the long-term operation of the membrane process, turning into inorganic fouling, which will lead to a decrease in flux and a reduction in membrane life. Scaling caused by calcium carbonate can be removed by acid washing, while CaSO 4 , silicate, BaSO 4 Inorganic dirt such as iodine and iodine are insoluble in acids and alkalis, and have strong binding force with the membrane surface, so the membrane pollution problem caused by them is particularly prominent. The polymer porous membrane with strong anti-pollution performance and good inorganic dirt removal effect shows that the membrane surface not only has strong hydrophilicity to slow down the adsorption, deposition and hardening process of pollutants on the membrane surface, but also the inorganic dirt structure becomes loose and the force with the membrane surface becomes weaker during the cleaning process. Smart membranes have the characteristics of reversible and sensitive response to environmental stimuli (pH, light, pressure, temperature, electric field, magnetic field, etc.). They not only retain the advantages of traditional separation membranes, but also make corresponding feedback adjustments when stimulated by the external environment, broadening the application range of membrane separation technology. Among them, pH-responsive membranes are grafted with acid and base groups that are easily hydrolyzed or protonated, such as amino groups (chitosan), carboxyl groups (polyacrylic acid), phosphoric acid and other long-chain groups that are responsive to pH. For example, if a positively charged polyelectrolyte is grafted, when the solution pH is less than pK a When the pH of the environment is greater than pK a When the functional groups of the polyelectrolyte are deprotonated and charged, the chain segments are in a curled and contracted state. If a negatively charged polyelectrolyte is grafted, the change process is the opposite. This reversible change process of "curling = stretching" of the polymer long chain in an acid-base environment will make the inorganic dirt structure loose and the binding force with the membrane surface weaker, and it will easily fall off the membrane surface after washing with clean water. Since "acid washing-alkali washing" is a necessary step for membrane cleaning, it is possible to achieve strong membrane anti-fouling and good inorganic dirt removal effect by grafting hydrophilic long-chain groups with pH response on the membrane surface. Summary of the invention

[0005] The purpose of the present invention is to provide a method and product for preparing a polymer porous membrane with strong anti-pollution properties and good inorganic dirt removal effect. It has low requirements for membrane preparation, and the grafted polymer has strong hydrophilicity and significant pH responsiveness, so as to overcome the shortcomings of the prior art.

[0006] The present invention is implemented as follows: SMA copolymer and fluorine-containing polymer are used as substrates, hot nitrogen is used as core liquid, and a "fluorine-containing polymer / SMA" porous membrane is prepared by thermally induced phase separation technology. The different solubility of SMA and fluorine-containing polymer in diluent is utilized to make the fluorine-containing polymer solidify and precipitate from the diluent during the cooling process, while SMA is still dissolved in the diluent. In the subsequent ethanol extraction process of the diluent, SMA solidifies and precipitates and deposits on the surface of the fluorine-containing polymer membrane. Then, the MA on the membrane surface and the amine group in the chitosan chain are used to undergo an amination reaction to load chitosan on the porous membrane surface to form a hydrophilic pH-responsive porous polymer membrane. The following steps are included:

[0007] 1) Mixing and granulation: Calculated by mass, 20-25 parts of a fluorine-containing polymer with a weight average molecular weight of 500-700 kDa, 5-10 parts of SMA and 0.1-0.5 parts of an antioxidant are dried separately and then mixed with 64.5-69.9 parts of a single diluent; the mixture is extruded and granulated, and the obtained pellets are dried and stored for standby use; the single diluent is one of tributyrin, tributyl citrate and triacetin, which are soluble in ethanol but insoluble in water at room temperature;

[0008] 2) Extrusion membrane formation: the pellets obtained in step 1) are spun at a spinning temperature of 160-170°C and a flow rate of 1.5-2.5 L / h; hot nitrogen is used as the cavity fluid at a temperature of 80-100°C and a flow rate of 0.8-8 L / h; the polymer solution passes through an air gap of 1-5 cm in length and enters a coagulation bath composed of deionized water, and is cooled with deionized water and wound into filaments. The resulting primary membrane filaments are extracted with ethanol with a purity of not less than 99% at 30-40°C to remove the diluent. After two extractions, a hollow fiber-based membrane with an outer diameter of 1.2-1.4 mm and an inner diameter of 0.6-0.7 mm is obtained.

[0009] 3) Graft modification: The hollow fiber-based membrane prepared in step 2) is immersed in an aqueous solution with a formic acid concentration of 2%wt and a chitosan concentration of 2-6wt%, reacted at 55-65°C for 4-6h, taken out, washed with deionized water and stored.

[0010] 4) The hollow fiber membrane prepared in step 3) is used for a period of time and then subjected to acid washing and alkali washing steps.

[0011] The fluorine-containing polymer described in step 1) refers to polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0012] The SMA described in step 1) refers to an SMA having a weight average molecular weight of 100 to 120 kDa and a ratio of MA in SMA of 20% to 25%.

[0013] The mixing described in step 1) refers to mixing at 700-800 rpm for 10-20 min.

[0014] The extrusion granulation of the mixture in step 1) refers to adding the mixture into a twin-screw extruder with a length-to-diameter ratio of 40 and extruding and granulating it at 160-170°C.

[0015] The winding speed in the spinning process described in step 1) is 20 to 40 m / min.

[0016] The diluent described in step 1) is one of tributyrin, tributyl citrate and triacetin, which is soluble in ethanol but insoluble in water at room temperature and can dissolve SMA.

[0017] The molecular weight of the chitosan in step 3) is between 30 and 150 kDa.

[0018] The acid described in step 4) is hydrochloric acid, the base is sodium hydroxide, the cleaning range is pH 1 to 12, and the cleaning time is 10 to 30 minutes.

[0019] The principle of the present invention is as follows: (1) When preparing a "fluoropolymer / styrene-maleic anhydride" porous membrane by thermally induced phase separation technology, the different solubility of SMA and fluoropolymer in the diluent is utilized to make the fluoropolymer solidify and precipitate from the diluent during the cooling process, while SMA is still dissolved in the diluent. In the subsequent ethanol extraction process of the diluent, SMA solidifies and precipitates and deposits on the surface of the fluoropolymer membrane. Then, the anhydride on the membrane surface and a small part of the amine groups in the chitosan chain are used to react with each other to load chitosan on the porous membrane surface to form a hydrophilic pH-responsive porous polymer membrane. When the amount of SMA blended is appropriate, due to the certain compatibility between SMA and PVDF, the two polymer long chains are entangled with each other at the interface without SMA falling off. (2) The pH-responsive chitosan molecular chain not only improves the hydrophilicity of the membrane and slows down the deposition of inorganic scale on the membrane surface, but also undergoes a reversible transformation of "curling = stretching" in the membrane "acid washing-alkaline washing" cleaning process (similar to the "curling = stretching" of earthworms crawling in the soil to loosen the soil), making the hardened inorganic scale deposited on the membrane surface loose and the binding force with the membrane surface weaker, which facilitates the subsequent surface water cleaning to effectively remove the inorganic scale. Since "acid cleaning-alkaline cleaning" is a necessary step for membrane cleaning, it is possible to achieve strong membrane anti-pollution and good inorganic scale removal effect by grafting pH-responsive hydrophilic long-chain groups on the membrane surface. In addition, it has the following characteristics: (1) Requirements for polymer content, molecular weight and ratio to ensure that the membrane has good mechanical properties, the MA functional groups on the membrane surface have a suitable density and the SMA does not fall off. The overall polymer content is between 25% and 35%, of which the fluorine-containing polymer with a weight average molecular weight of 500 to 700 kDa is 20 to 25 parts, and the SMA content with a weight average molecular weight of 100 to 120 kDa and a ratio of MA to SMA of 20% to 25% is 5 to 10 parts. (2) Requirements for diluents. The diluent is one of tributyrin, tributyl citrate, and triacetin, which are soluble in ethanol but insoluble in water at room temperature and can dissolve SMA. Experiments have found that common high-boiling point organic solvents such as diethyl sebacate, dibutyl sebacate, tributyl citrate, dibutyl phthalate, methyl salicylate, γ-butyrolactone, propylene carbonate, ethylene carbonate, triethyl phosphate, caprolactam, etc., which have strong interactions with polyvinylidene fluoride, and benzophenone, etc., cannot be used as diluents for the patent application because of their limited ability to dissolve SMA. (3) Requirements for grafting conditions. Although fluoropolymers can undergo grafting reaction with amine groups under alkaline conditions, this will damage the surface of the fluoropolymer membrane. Chitosan can only be dissolved in aqueous formic acid solution under weak acid conditions. Therefore, chitosan cannot be directly grafted on the surface of the fluoropolymer membrane. The reaction between anhydride and amine groups can be carried out in aqueous formic acid solution. Therefore, it is necessary to first introduce anhydride into the surface of the fluoropolymer membrane.(4) The effect of pH responsiveness is related to the grafting degree and the length of the grafted chain. Experiments have shown that the SMA model has a weight average molecular weight of 100-120 kDa, the proportion of MA in SMA is 20%-25%, and the addition amount is 5-10 parts. If the addition amount is too high, the thick SMA deposition layer will fall off. If the addition amount is too small, the surface MA density is low, the amount of grafted chitosan is small, and the pH responsiveness is not obvious. The weight average molecular weight of chitosan is between 30 and 150 kDa. If the weight average molecular weight is too low, the grafted chain is short, and the pH responsiveness is not significant. If the weight average molecular weight is too high, the steric hindrance is too large, and the pH responsiveness is reduced due to the reduced grafting degree. (5) Core liquid. It is hot air at 80°C rather than other liquid organic solvents. (6) The pH range and the order of "acid washing-alkali washing" or "alkali washing-acid washing" have a great influence on the looseness of inorganic dirt. For grafted chitosan, the pH range is 1-12 (within the jump range) and the "acid wash-alkaline wash" sequence is better. For grafted PAA, the pH range is 1-12 and the "alkaline wash-acid wash" sequence is better. (7) The extractant is ethanol at 30-40°C, which further improves the compressive resistance of the membrane fiber and ensures that the membrane fiber can withstand 4 bar pressure without obvious flux attenuation (attenuation rate is less than 8%) after external pressure test.

[0020] The benefits of the present invention are as follows: (1) Compared with the prior art, the present invention grafts chitosan on the membrane surface not directly under alkaline conditions but in a weakly acidic aqueous solution of formic acid, thereby avoiding the damage of the alkaline conditions to the surface of the fluorine-containing polymer membrane. (2) The cleaning of inorganic dirt from the membrane can only be achieved in combination with the "acid-base cleaning" step, and "acid-base cleaning" is a necessary step for membrane cleaning. Therefore, it has good adaptability, does not require equipment to be updated, is easy to promote, and has good industrial prospects. The present invention is simple and easy to implement, has a wide range of material sources, is low in cost, and has good use effects. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0022] Embodiment 1:

[0023] 1) 25 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 10 parts of SMA with a weight average molecular weight of 120 kDa and an MA content of 25%, and 0.1 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate are dried separately by mass, and then fully mixed with 64.9 parts of triacetin in a mixer (700 rpm, time 10 min), extruded through an extruder (twin-screw extruder with a length-to-diameter ratio of 40, temperature 170° C.), and cooled and granulated in air to obtain mixture particles;

[0024] 2) Use hot nitrogen at a temperature of 80°C as the cavity fluid with a flow rate of 2.5L / h. The obtained material particles are spun by an extruder at 170°C with a flow rate of 8L / h; after passing through an air gap of 5cm in length, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into filaments (winding speed is 30m / min). The obtained primary membrane filaments are extracted with ethanol with a purity of not less than 99% at 40°C for 1h to remove the diluent. After extraction twice, a hollow fiber-based membrane with an outer diameter of 1.3mm and an inner diameter of 0.7mm is obtained.

[0025] 3) The hollow fiber-based membrane was immersed in an aqueous solution with a formic acid concentration of 2%wt and a chitosan concentration of 6wt% with a molecular weight of 150 kDa, and reacted at 65°C for 6 hours before being taken out to obtain a pH-responsive membrane with surface grafted chitosan.

[0026] Use 200 ppm CaSO 4 The solution was contaminated as a model pollutant for 1 hour, and was cleaned with a hydrochloric acid solution of pH = 1 and a sodium hydroxide aqueous solution of pH-12 for 30 minutes respectively, and then with deionized water for 10 minutes. PVDF / SMA (reference 1) and a hydrophilic non-pH responsive membrane grafted with PEG20000 (reference 2) were used as references for comparison with the chitosan grafted membrane. The results showed that the flux recovery rate of reference 1 was 40.5%, the flux recovery rate of reference 2 was 55.6%, and the flux recovery rate of the grafted chitosan membrane was 98.9%.

[0027] Embodiment 2:

[0028] 1) 25 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 10 parts of SMA with a weight average molecular weight of 120 kDa and an MA content of 25%, and 0.1 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate are dried separately, and then fully mixed with 64.9 parts of tributyrin in a mixer (700 rpm, time 10 min), extruded through an extruder (twin-screw extruder with a length-to-diameter ratio of 40, temperature 170° C.), and cooled and granulated in air to obtain mixture particles;

[0029] 2) Use hot nitrogen at a temperature of 80°C as the cavity fluid with a flow rate of 2.5L / h. The obtained material particles are spun by an extruder at 170°C with a flow rate of 8L / h; after passing through an air gap of 5cm in length, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into filaments (winding speed is 30m / min). The obtained primary membrane filaments are extracted with ethanol with a purity of not less than 99% at 40°C for 1h to remove the diluent. After extraction twice, a hollow fiber-based membrane with an outer diameter of 1.3mm and an inner diameter of 0.7mm is obtained.

[0030] 3) The hollow fiber-based membrane was immersed in an aqueous solution of 2%wt formic acid and 6wt% chitosan with a molecular weight of 150 kDa, reacted at 65°C for 6 hours, and then taken out to obtain a pH-responsive membrane with surface grafted chitosan.

[0031] Use 200 ppm CaSO 4 The solution was contaminated as a model pollutant for 1 hour, and was cleaned with a sodium hydroxide aqueous solution of pH-12 and a hydrochloric acid solution of pH=1 for 30 minutes respectively, and then with deionized water for 10 minutes. PVDF / SMA (reference 1) and a hydrophilic non-pH responsive membrane grafted with PEG20000 (reference 2) were used as references for comparison with the chitosan grafted membrane. The results showed that the flux recovery rate of reference 1 was 40.1%, the flux recovery rate of reference 2 was 54.7%, and the flux recovery rate of the chitosan grafted membrane was 93.8%.

[0032] Embodiment 3:

[0033] 1) 25 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 10 parts of SMA with a weight average molecular weight of 120 kDa and an MA content of 25%, and 0.1 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate are dried separately by mass, and then fully mixed with 64.9 parts of acetyl tributyl citrate in a mixer (700 rpm, time 10 min), extruded through an extruder (twin-screw extruder with a length-to-diameter ratio of 40, temperature 170° C.), and cooled and granulated in air to obtain mixture particles;

[0034] 2) Use hot nitrogen at a temperature of 80°C as the cavity fluid with a flow rate of 2.5L / h. The obtained material particles are spun by an extruder at 170°C with a flow rate of 8L / h; after passing through an air gap of 5cm in length, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into filaments (winding speed is 30m / min). The obtained primary membrane filaments are extracted with ethanol with a purity of not less than 99% at 40°C for 1h to remove the diluent. After extraction twice, a hollow fiber-based membrane with an outer diameter of 1.3mm and an inner diameter of 0.7mm is obtained.

[0035] 3) The hollow fiber-based membrane was immersed in an aqueous solution with a formic acid concentration of 2%wt and a chitosan concentration of 6wt% with a molecular weight of 30 kDa, and reacted at 65°C for 6 hours before being taken out to obtain a pH-responsive membrane with surface grafted chitosan.

[0036] Use 200 ppm CaSO 4The solution was contaminated as a model pollutant for 1 hour, and was cleaned with hydrochloric acid solution with pH = 1 and sodium hydroxide aqueous solution with pH -12 for 30 minutes respectively, and then with deionized water for 10 minutes. PVDF / SMA (reference 1) and hydrophilic non-pH responsive membrane grafted with PEG20000 (reference 2) were used as references for comparison with the membrane grafted with chitosan. The flux recovery rate of reference 1 was 40.5%, the flux recovery rate of reference 2 was 55.6%, and the flux recovery rate of the grafted chitosan membrane was 92.4%.

[0037] Embodiment 4:

[0038] 1) 20 parts of polyvinylidene fluoride with a weight average molecular weight of 700 kDa, 5 parts of SMA with a weight average molecular weight of 120 kDa and an MA content of 25%, and 0.5 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate are dried separately by mass, and then fully mixed with 74.9 parts of triacetin in a mixer (700 rpm, time 10 min), extruded through an extruder (twin-screw extruder with a length-to-diameter ratio of 40, temperature 160° C.), and cooled and granulated in air to obtain mixture particles;

[0039] 2) Use hot nitrogen at a temperature of 80°C as the cavity fluid with a flow rate of 2L / h. The obtained material particles are spun by an extruder at 160°C with a flow rate of 8L / h; after passing through an air gap of 5cm in length, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into filaments (winding speed is 20m / min). The obtained primary membrane filaments are extracted with ethanol with a purity of not less than 99% at 30°C for 1h to remove the diluent. After extraction twice, a hollow fiber-based membrane with an outer diameter of 1.4mm and an inner diameter of 0.7mm is obtained.

[0040] 3) The hollow fiber-based membrane was immersed in an aqueous solution with a formic acid concentration of 2%wt and a chitosan concentration of 4wt% with a molecular weight of 30kDa, and reacted at 55°C for 4h before being taken out to obtain a pH-responsive membrane with surface grafted chitosan.

[0041] Use 200 ppm CaSO 4 The solution was contaminated as a model pollutant for 1 hour, and was cleaned with hydrochloric acid solution with pH = 2 and sodium hydroxide aqueous solution with pH -11 for 30 minutes respectively, and then with deionized water for 10 minutes. PVDF / SMA (reference 1) and hydrophilic non-pH responsive membrane grafted with PEG20000 (reference 2) were used as references for comparison with the membrane grafted with chitosan. The flux recovery rate of reference 1 was 40.7%, the flux recovery rate of reference 2 was 55.6%, and the flux recovery rate of the grafted chitosan membrane was 83.3%.

[0042] Embodiment 5:

[0043] 1) 25 parts of polyvinylidene fluoride-hexafluoropropylene copolymer with a weight average molecular weight of 500 kDa, 10 parts of SMA with a weight average molecular weight of 120 kDa and an MA content of 20%, and 0.5 parts of β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate are dried separately by mass, and then fully mixed with 74.9 parts of triacetin in a mixer (700 rpm, time 10 min), extruded through an extruder (twin-screw extruder with a length-to-diameter ratio of 40, temperature 160° C.), and cooled and granulated in air to obtain mixture particles;

[0044] 2) Use hot nitrogen at a temperature of 80°C as the cavity fluid with a flow rate of 1.5L / h. The obtained material particles are spun by an extruder at 160°C with a flow rate of 6L / h; after passing through an air gap of 5cm in length, they enter a coagulation bath composed of deionized water, are cooled by deionized water, and are wound into filaments (winding speed is 30m / min). The obtained primary membrane filaments are extracted with ethanol with a purity of not less than 99% at 30°C for 1h to remove the diluent. After extraction twice, a hollow fiber-based membrane with an outer diameter of 1.2mm and an inner diameter of 0.6mm is obtained.

[0045] 3) The hollow fiber-based membrane was immersed in an aqueous solution with a formic acid concentration of 2%wt and a chitosan concentration of 4wt% with a molecular weight of 150kDa, and reacted at 55°C for 4h before being taken out to obtain a pH-responsive membrane with surface grafted chitosan.

[0046] Use 200 ppm CaSO 4 The solution was contaminated as a model pollutant for 1 hour, and was cleaned with a hydrochloric acid solution with pH = 1 and a sodium hydroxide aqueous solution with pH -12 for 30 minutes respectively, and then with deionized water for 10 minutes. PVDF / SMA (reference 1) and a hydrophilic non-pH responsive membrane grafted with PEG20000 (reference 2) were used as references for comparison with the chitosan grafted membrane. The results showed that the flux recovery rate of reference 1 was 39.9%, the flux recovery rate of reference 2 was 54.1%, and the flux recovery rate of the chitosan grafted membrane was 96.4%.

[0047] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or any direct or indirect application of other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a polymer porous membrane with strong anti-pollution properties and good inorganic dirt removal effect, characterized in that: Using styrene-maleic anhydride copolymer (SMA) and fluorine-containing polymer as the substrate, a fluorine-containing polymer porous membrane with anhydride (MA) on the surface was prepared by thermally induced phase separation technology. Then, the MA on the membrane surface and the amine groups in the chitosan chain underwent an amination reaction to load chitosan on the porous membrane surface to form a hydrophilic pH-responsive porous polymer membrane.

2. The method for preparing a polymer porous membrane having strong anti-pollution properties and good inorganic dirt removal effect according to claim 1, characterized in that: Taking advantage of the different solubility of SMA and fluoropolymer in diluent, the fluoropolymer solidifies and precipitates from the diluent during the cooling process, while SMA remains dissolved in the diluent. In the subsequent ethanol extraction process of the diluent, SMA solidifies and precipitates and deposits on the surface of the fluoropolymer membrane. Then the MA on the membrane surface undergoes a grafting reaction with the amino groups on the chitosan and is loaded on the membrane surface. The specific steps are as follows: S1. Mix the fluorinated polymer, SMA, diluent and antioxidant in a mixer at a certain mass ratio at 160°C to 170°C, extrude through an extruder, and cool in air to form pellets; S2, melting the obtained mixture particles and forming them into a hollow fiber membrane shape at 160°C to 170°C, first cooling them with air, and then further cooling them into shape in room temperature deionized water; S3, then taking out the membrane and soaking and washing it in an extractant at a certain temperature for a certain period of time to remove the diluent, taking it out and drying it, and then performing grafting modification; S4. Immerse the hollow fiber-based membrane prepared in step S3 in an aqueous solution having a formic acid concentration of 2%wt and a chitosan concentration of 2-6wt%, react at 55-65°C for 4-6h, then take out the membrane with surface grafted chitosan, wash it with deionized water and store it.

3. The method for preparing a polymer porous membrane with strong anti-pollution property and good inorganic dirt removal effect according to claim 2, characterized in that: In step S1, the mass ratio of the fluorine-containing polymer, SMA, diluent and antioxidant is 20-25:5-10:54.5-69.9:0.1-0.

5.

4. The method for preparing a polymer porous membrane having strong anti-pollution properties and good inorganic dirt removal effect according to claim 2, characterized in that: The fluorine-containing polymer in step S1 is a homopolymer or copolymer of polyvinylidene fluoride.

5. The method for preparing a porous membrane with excellent mechanical properties and membrane pore penetration according to claim 2, characterized in that: In step S1, the weight average molecular weight of the fluorine-containing polymer is 500-700 kDa, the weight average molecular weight of SMA is 100-120 kDa, and the proportion of MA in SMA is 20%-25%.

6. The method for preparing a porous membrane with excellent mechanical properties and membrane pore penetration according to claim 2, characterized in that: The diluent in step S1 is one of tributyrin, tributyl citrate and triacetin, which is soluble in ethanol but insoluble in water at room temperature.

7. The method for preparing a porous membrane with excellent mechanical properties and membrane pore penetration according to claim 2, characterized in that: The antioxidant in step S1 is octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

8. The method for preparing a porous membrane with excellent mechanical properties and membrane pore penetration according to claim 2, characterized in that: The extractant in step S3 is anhydrous ethanol, and the washing times are 2 times, each time for 1 hour.

9. The method for preparing a porous membrane with excellent mechanical properties and membrane pore penetration according to claim 2, characterized in that: The temperature of the anhydrous ethanol in step S3 is 30-40°C.

10. The method for preparing a porous membrane with excellent mechanical properties and membrane pore penetration according to claim 2, characterized in that: The molecular weight of the chitosan is between 30 and 150 kDa.

11. The method for preparing a polymer porous membrane having strong anti-pollution property and good inorganic dirt removal effect according to claim 2, characterized in that: The removal effect of inorganic dirt on the membrane surface can only be achieved by combining the cleaning procedures of "acid washing-alkaline washing" or "alkaline washing-acid washing".

12. The method for preparing a polymer porous membrane having strong anti-pollution property and good inorganic dirt removal effect according to claim 11, characterized in that: The acid used for cleaning is hydrochloric acid, the alkali is sodium hydroxide, the concentration range of the cleaning solution is pH 1 to 12, and the cleaning time is 10 to 30 minutes.