CN114534525A

CN114534525A - Amination modified anti-pollution porous membrane and preparation method thereof

Info

Publication number: CN114534525A
Application number: CN202111663434.6A
Authority: CN
Inventors: 王军; 汤超; 孟圆圆; 唐妮; 杜延华; 李玲; 陈鲁昌; 张镇
Original assignee: Shandong Huaxia Shenzhou New Material Co Ltd
Current assignee: Shandong Huaxia Shenzhou New Material Co Ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-05-27
Anticipated expiration: 2041-12-31
Also published as: CN114534525B

Abstract

The invention belongs to the technical field of membrane separation, and particularly relates to an amination modified anti-pollution porous membrane and a preparation method thereof. Dissolving a polymer, a hydrophilic diamine monomer compound and polyethylene glycol in dimethylacetamide, and stirring at 60-80 ℃ until the mixture is uniformly mixed to form a uniform casting solution; pouring the casting solution at 25 ℃ of room temperature to one end of a clean glass plate, uniformly scraping the casting solution to the other end by using a coating scraper, and forming a nascent state membrane on the glass plate or pouring the casting solution into a spinning machine to extrude the nascent state membrane; pre-evaporating the nascent-state membrane in the air for 5-30s, quickly placing the nascent-state membrane in a coagulating bath at 20-30 ℃ for phase conversion, and curing to obtain the asymmetric ultrafiltration membrane. The method has the advantages of simple operation and mild conditions, and the prepared hydrophilic ultrafiltration membrane has good pollution resistance, high mechanical strength and good separation performance, and can be used in the fields of wastewater treatment and the like.

Description

Amination modified anti-pollution porous membrane and preparation method thereof

Technical Field

The invention belongs to the technical field of membrane separation, and particularly relates to an amination modified anti-pollution porous membrane and a preparation method thereof.

Background

At present, polymers commonly used for water treatment membranes are polyvinylidene fluoride, polyvinyl chloride, polysulfone, polyethersulfone, cellulose acetate, polyethylene, polypropylene and the like, and the common problems exist at present, namely the pollution resistance of the surface of a membrane material needs to be further improved, the surface is not easy to be subjected to chemical grafting modification, and polyvinylidene fluoride has good thermal stability, chemical stability and mechanical strength, so that the polyvinylidene fluoride is widely applied to the water treatment membranes. In recent years, with the expansion of the application of membrane separation technology, the problem of membrane fouling has also been receiving more and more attention. Introducing hydrophilic groups on the surface of the membrane is an effective strategy for improving the antifouling capacity of the membrane. The surface charge modification of the membrane is combined with the modification with negative charge, but there is a great market demand for high pollution resistance in the field of ultrafiltration membranes applying positive charge.

Surface modification is a common method for preparing electropositive membranes. The surface of the membrane is introduced with the group with positive charge, so that the hydrophilicity can be improved, the anti-pollution performance of the membrane is obviously improved, and the contact angle of the surface of the membrane can be reduced and the adhesion of pollutants is reduced due to the electrostatic repulsion between the hydrophilic polar group and the pollutants. PVDF has been widely used and studied in the membrane field as a membrane-forming material having excellent overall properties. However, polyvinylidene fluoride (PVDF) as a film-forming material has problems of poor alkali resistance, difficulty in generating active sites when hydrophilization modification is performed by a grafting method, and the like. And polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE) is used as a film making material, and the copolymer introduces C-Cl active sites which are easy to react on the basis of keeping the excellent performances of the PVDF such as thermal stability, chemical stability and the like, so that the grafting modification is easy.

At present, researchers at home and abroad do much work on modification of polyvinylidene fluoride-chlorotrifluoroethylene, and related patents mainly include:

patent CN 110066415 a discloses a method for preparing a porous membrane with a functionalized surface, which uses vinylidene fluoride-chlorotrifluoroethylene copolymer as a base membrane, and utilizes the chlorine group in the molecular structure of the copolymer to react with amine compounds to prepare the vinylidene fluoride-chlorotrifluoroethylene copolymer porous membrane with a positively charged surface. However, the base membrane formed by PVDF-CTFE is a grafting point, so that amino groups are not easy to introduce into the molecular chain of the polymer, and grafting is difficult.

Patent CN 111659267 a discloses a method for preparing a pollution-resistant modified porous membrane, which comprises the step of carrying out a reaction of removing HCl on a C-Cl bond in a polymer molecular chain and a small-molecule monoamino hydrophilic compound to prepare a surface-modified negatively-charged or electrically neutral pollution-resistant and highly blood-compatible polymer porous membrane, wherein the small-molecule monoamino compound is easily lost during the use process, and the stability of the membrane product is affected.

Patent CN108579474B discloses a negatively charged fluoropolymer-based composite membrane based on interlayer covalent interaction enhancement. The support layer and the functional layer in the composite membrane are combined under the action of a C-O and/or C-N covalent bond, and the composite membrane is a negatively charged microfiltration membrane or ultrafiltration membrane and has carboxyl and/or sulfonic group on the surface. The composite membrane has the characteristics of high flux, good flux stability, excellent interception and anti-pollution performance, stable combination among layers in the membrane and the like. Due to the negative charge property of the membrane, the composite membrane has better selectivity and contamination resistance to certain charged pollutants. But the grafting process tends to block the pores of the membrane.

In a word, the modification research of the polyvinylidene fluoride-chlorotrifluoroethylene is mainly developed by copolymerization with other functional monomers or blending with other substances, and the aim of the modification research is mainly to improve the hydrophilicity and the surface charge property, solve the problems of easy pollution caused by PVDF and the like.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide an amination modified anti-pollution porous membrane, wherein an amination mode is adopted to graft a modified polymer, and a prepared hydrophilic ultrafiltration membrane has good anti-pollution performance, high mechanical strength and better separation performance, and can be used in the fields of wastewater treatment and the like; the invention also provides a preparation method of the compound, which is simple to operate and mild in condition.

The invention adopts amination mode to modify polymer, and amine radicals in amine compound molecules directly generate in-situ substitution reaction at C-Cl active sites under alkaline environment to generate free Cl^-The process does not involve bond formation or bond breaking, and the required activation energy is low, and therefore, the reaction is relatively easy to occur in an aprotic polar solvent. And (3) performing elimination reaction on PVDF-CTFE at a C-Cl active site to remove HCl to form a C ═ C double bond, and carrying amine radicals by a rear amine compound to attack the C ═ C double bond so as to open the double bond and further perform addition reaction. The reaction selects diamine monomer with hydrophilic polar groups such as hydroxyl, carboxyl and the like as graft copolymer, and the diamine monomer and PVDF-CTFE are subjected to graft copolymerization in the membrane casting solution, and the graft copolymerization modification is completed by a one-step method, so that the method is simple and easy to implement.

According to the invention, polyvinylidene fluoride-chlorotrifluoroethylene is modified in an amine compound graft copolymerization mode with hydrophilic polar groups, the hydrophilicity and the membrane surface charge of the polyvinylidene fluoride-chlorotrifluoroethylene are improved, and the adsorption of pollutants is reduced and the pollution resistance of the pollutants is improved by adding a hydrophilic amine compound.

The invention is realized by the following technical scheme:

the preparation method of the amination modified anti-pollution porous membrane adopts a non-solvent induced phase separation method to introduce hydrophilic diamine monomer compound into a polymer membrane material body to prepare the ultrafiltration membrane.

The hydrophilic diamine monomer compound contains a benzene ring structure, the benzene ring contains a hydrophilic group, and the hydrophilic group is one of hydroxyl, carboxyl, sulfonic group or sulfhydryl.

Preferably, the preparation method of the aminated modified anti-pollution porous membrane comprises the following steps:

1) dissolving the polymer, hydrophilic diamine monomer compound and polyethylene glycol after vacuum drying in dimethylacetamide, and stirring at constant temperature of 60-80 ℃ until the mixture is uniformly mixed to form a uniform casting solution;

pouring the casting solution at room temperature to one end of a clean and undamaged glass plate, and scraping the casting solution to the other end at a constant speed by using a coating scraper to form a nascent state film on the glass plate; or pouring the casting solution into a spinning machine to be extruded into a nascent-state membrane; pre-evaporating the nascent-state membrane in the air, and then placing the nascent-state membrane in a coagulating bath for phase inversion;

3) curing to form an asymmetric ultrafiltration membrane, transferring to deionized water, and soaking for 24h for later use.

In the present invention, the polymer is preferably one or a mixture of two or more of polyvinyl chloride, polychlorotrifluoroethylene, a copolymer of polyvinylidene fluoride and vinyl chloride or a copolymer of polyvinylidene fluoride and chlorotrifluoroethylene.

In the present invention, the hydrophilic diamine monomer compound is preferably one or a mixture of two or more of 3, 3-dihydroxybenzidine, 3, 4-diaminodiphenyl sulfone, 3, 5-diaminobenzoic acid, and 2-aminophenol.

Preferably, in the casting solution, the mass percent of the polymer is 16-20%, the mass percent of the polyethylene glycol is 3-5%, the mass percent of the hydrophilic diamine monomer compound is 1-5%, and the mass percent of the dimethylacetamide is 70-80%.

Adopting a coating scraper to scrape the membrane casting solution to the other end at a constant speed, wherein the thickness of the nascent state membrane formed on the glass plate is 150-250 mu m, and the scraping speed is 55-65mm/s, preferably 60 mm/s; or pouring the casting solution into a spinning machine to extrude the casting solution into a nascent membrane at an extrusion rate of 5-10ml/min, preferably 6 ml/min. The flat membrane is prepared by adopting a coating scraper, and the hollow fiber membrane is prepared by adopting a spinning machine.

The ultrafiltration membrane prepared by the invention is a flat membrane or a hollow fiber membrane.

The amination modified anti-pollution porous membrane is prepared by adopting the preparation method.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention uses diamine compound graft modified polymer containing hydrophilic polar group to prepare water treatment ultrafiltration membrane, the method enhances the charge property of the membrane surface, improves the hydrophilicity of the membrane surface, improves the membrane pore structure, and improves the separation performance, mechanical performance and pollution resistance of the membrane.

2. The preparation method of the invention has simple operation and mild condition

Drawings

FIG. 1-1 is a photograph of the contact angle shown for a sample prepared according to example 1;

FIGS. 1-2 are photographs of the contact angle shown for samples prepared according to comparative example 1;

FIG. 2 is a photograph of the contact angle shown for a sample prepared according to example 2;

FIG. 3 is a photograph of the contact angle shown for the sample prepared according to example 3;

FIG. 4 is a photograph of the contact angle shown for the sample prepared according to example 4;

FIG. 5 is a photograph of the contact angle shown for the sample prepared in example 5.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.

Example 1

1) Stirring 48.0g of dimethylacetamide, 9.6g of polyvinylidene fluoride-chlorotrifluoroethylene, 1.8g of polyethylene glycol and 0.6g of 3, 3-dihydroxybenzidine at a constant temperature of 80 ℃ until the materials are uniformly mixed to form a uniform casting solution;

2) pouring the casting solution at 25 ℃ at room temperature to one end of a clean and undamaged glass plate, and uniformly scraping the casting solution to the other end by using a coating scraper with the thickness of 200 mu m at the speed of 60mm/s to form a nascent state membrane on the glass plate. Pre-evaporating the nascent-state membrane in the air for 10s, quickly placing the nascent-state membrane in a 25 ℃ coagulating bath which is deionized water for phase conversion, and curing to obtain the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water to be soaked for 24 hours for standby. The resulting membrane had a water contact angle of 67.8 °, and the ultrafiltration membrane was subjected to performance testing, the results of which are shown in table 1.

Comparative example 1

1) Stirring 48.6g of dimethylacetamide, 9.6g of polyvinylidene fluoride-chlorotrifluoroethylene and 1.8g of polyethylene glycol at a constant temperature of 80 ℃ until the materials are uniformly mixed to form a uniform casting solution;

2) pouring the casting solution at 25 ℃ at room temperature to one end of a clean and undamaged glass plate, and uniformly scraping the casting solution to the other end by using a coating scraper with the thickness of 200 mu m at the speed of 60mm/s to form a nascent state membrane on the glass plate. Pre-evaporating the nascent-state membrane in the air for 10s, quickly placing the nascent-state membrane in a 25 ℃ coagulating bath which is deionized water for phase conversion, and curing to obtain the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water to be soaked for 24 hours for standby. The resulting membrane had a water contact angle of 105.3 °, and the ultrafiltration membrane was subjected to a performance test, the results of which are shown in table 1.

Example 2

1) Stirring 45g of dimethylacetamide, 10.8g of polychlorotrifluoroethylene, 2.4g of polyethylene glycol and 1.8g of 3, 5-diaminobenzoic acid at a constant temperature of 70 ℃ until the components are uniformly mixed to form a uniform casting solution.

2) Pouring the casting solution into a spinning machine at room temperature of 25 ℃ and extruding at an extrusion rate of 6ml/min to form a nascent membrane. Pre-evaporating the nascent-state membrane for 5s in the air, quickly placing the nascent-state membrane in a 25 ℃ coagulating bath which is deionized water for phase conversion, and curing to obtain the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water at 25 ℃ to be soaked for 24h for standby. The resulting membrane had a water contact angle of 51.5 °, and the ultrafiltration membrane was subjected to a performance test, the results of which are shown in table 1.

Example 3

1) 42g of dimethylacetamide, 12g of polyvinyl chloride, 3g of polyethylene glycol and 3g of 3, 4-diaminodiphenyl sulfone are stirred at a constant temperature of 60 ℃ until the materials are uniformly mixed to form a uniform casting solution.

2) Pouring the casting solution at room temperature of 25 ℃ to one end of a clean and undamaged glass plate, and uniformly scraping the casting solution to the other end by using a coating scraper with the thickness of 200 mu m at the speed of 60mm/s to form a nascent state membrane on the glass plate. Pre-evaporating the nascent-state membrane in the air for 20s, quickly placing the nascent-state membrane in a coagulating bath at 20 ℃ to be deionized water for phase conversion, and curing to obtain the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water to be soaked for 24 hours for standby. The resulting membrane had a water contact angle of 53.2 °, and the ultrafiltration membrane was subjected to a performance test, the results of which are shown in table 1.

Example 4

1) Mixing 47.4g of dimethylacetamide, 9.6g of polyvinylidene fluoride-chloroethylene, 1.8g of polyethylene glycol and 1.2g of 2, 4-aminophenol at a constant temperature of 70 ℃ until the mixture is uniformly mixed to form a uniform casting solution;

2) pouring the casting solution at 25 ℃ into one end of a clean and undamaged glass plate, and uniformly scraping the casting solution to the other end by using a coating scraper with the thickness of 200 mu m at the speed of 60mm/s to form a nascent state membrane on the glass plate. Pre-evaporating the nascent-state membrane in the air for 30s, quickly placing the nascent-state membrane in a coagulating bath at 30 ℃ which is deionized water for phase conversion, and curing the nascent-state membrane into an asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water to be soaked for 24 hours for standby. The resulting membrane had a water contact angle of 52.2 °, and the ultrafiltration membrane was subjected to a performance test, the results of which are shown in table 1.

Example 5

2) pouring the casting solution at 25 ℃ at room temperature to one end of a clean and undamaged glass plate, and uniformly scraping the casting solution to the other end by using a coating scraper with the thickness of 200 mu m at the speed of 60mm/s to form a nascent state membrane on the glass plate. Pre-evaporating the nascent-state membrane for 5s in the air, quickly placing the nascent-state membrane in a 25 ℃ coagulating bath which is deionized water for phase conversion, and curing to obtain the asymmetric ultrafiltration membrane. Then transferring the mixture into deionized water at 25 ℃ to be soaked for 24h for standby. The resulting membrane water contact angle was 71.2 °, and the performance of the ultrafiltration membrane was measured, and the results are shown in table 1.

To illustrate the performance effect of ultrafiltration membranes, the hydrophilicity of the membrane surface was evaluated using the water contact angle, and the lower the contact angle, the better the hydrophilicity. And evaluating the anti-pollution performance of the membrane by adopting the flux recovery rate, wherein the higher the flux recovery rate is, the better the anti-pollution performance is. Evaluating the mechanical property of the film by adopting tensile strength and elongation at break, wherein the higher the tensile strength is, the more difficult the material is to be broken in the deformation process; the larger the elongation at break, the better the material has adaptability to deformation, and the better the mechanical properties indicate that the film has longer service life. The test method is as follows:

the contact angle of the membrane was characterized in this experiment with the aid of a contact angle tester (DSA30S) using water as the probe liquid. After cleaning and vacuum drying, the sample is fixed on a glass slide by using a double-sided adhesive tape, is placed on an instrument on an objective table, 3 mu l of deionized water is dripped on the surface of the film, the figure of the water drop on the surface of the film is captured by a camera and stored, and the contact angle value is automatically obtained by equipment. Each film sample was tested 5 times and the average was taken.

In the experiment, a high-low temperature press (GT-7001-HC6) is adopted to test the tensile property and the elongation at break of the film, and the test comprises the following specific steps: the obtained film from which moisture was completely removed was cut into a 1cm × 15cm long strip, and the strip was placed on an apparatus to conduct a tensile mechanical property test at a tensile speed of 10 mm/min.

The flux recovery rate is tested by cutting the ultrafiltration membrane into round pieces with proper size or membrane threads with proper length, loading the round pieces into a filter, filling a feed liquid tank and the filter with deionized water, and prepressing for 30min under the operation pressure of 0.2MPa until the water flux is stable. And after the pre-pressing process is finished, filling the feed liquid tank and the filter with deionized water again, recording the mass of the permeate under the operation pressure of 0.1MPa, calculating the water flux, measuring for 30min to obtain a stable flux A1, and stopping measuring. And after the initial flux measurement is finished, filling the feed liquid tank with BSA solution, filling the filter with BSA solution, recording the mass of the permeate under the operating pressure of 0.1MPa, calculating the flux of the permeate, and measuring for 30min to obtain stable flux. And after the flux of the BSA solution is measured, replacing the filter with deionized water, and carrying out hydraulic cleaning on the surface of the membrane for 30 min. And after the hydraulic cleaning is finished, pouring out the cleaning liquid, filling the buffer tank and the filter with deionized water again, recording the mass of the permeate under the operating pressure, calculating the water flux, measuring for 30min to obtain a stable flux A2, and finishing the measurement. The flux recovery rate FRR is a2/a1 × 100%.

See table 1 for specific results.

Table 1 film test data

Numbering	Water contact Angle (°)	Flux recovery (%)	Tensile Strength (MPa)	Elongation at Break (%)
					Example 1	67.8	82.5	4.3	28.5
Comparative example 1	105.3	46.9	2.9	11.3
					Example 2	51.5	89.8	4.1	22.9
Example 3	53.2	86.5	4.3	27.2
					Example 4	52.2	87.3	4.9	26.9
Example 5	71.2	77.2	4.8	27.6

The content that is not described in the embodiments of the present invention is the prior art, and therefore, the description thereof is omitted.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the inventive concept, and these are all within the scope of the present invention.

Claims

1. A preparation method of an amination modified anti-pollution porous membrane is characterized by comprising the following steps: and introducing a hydrophilic diamine monomer compound into the polymer membrane material body by adopting a non-solvent induced phase separation method to prepare the ultrafiltration membrane.

2. The method for preparing an aminated modified anti-fouling porous film according to claim 1, characterized in that: the hydrophilic diamine monomer compound contains a benzene ring structure, wherein the benzene ring contains a hydrophilic group, and the hydrophilic group is one of hydroxyl, carboxyl, sulfonic group or sulfhydryl.

3. The method for preparing an aminated modified anti-fouling porous film according to claim 1, characterized in that: the method comprises the following steps:

2) pouring the casting solution at room temperature to one end of a clean and undamaged glass plate, and scraping the casting solution to the other end at a constant speed by using a coating scraper to form a nascent state membrane on the glass plate; or pouring the casting solution into a spinning machine to be extruded into a nascent-state membrane; pre-evaporating the nascent-state membrane in the air, and then placing the nascent-state membrane in a coagulating bath for phase inversion;

3) solidifying into asymmetric ultrafiltration membrane, transferring into deionized water, and soaking for use.

4. The method for preparing an aminated modified anti-fouling porous film according to claim 3, characterized in that: the polymer is one or a mixture of more than two of polyvinyl chloride, polychlorotrifluoroethylene, polyvinylidene fluoride and vinyl chloride copolymer or polyvinylidene fluoride and chlorotrifluoroethylene copolymer.

5. The method for preparing an aminated modified anti-fouling porous film according to claim 3, characterized in that: the hydrophilic diamine monomer compound is one or more of 3, 3-dihydroxy benzidine, 3, 4-diaminodiphenyl sulfone, 3, 5-diaminobenzoic acid and 2-aminophenol.

6. The method for preparing an aminated modified anti-fouling porous film according to claim 3, characterized in that: in the casting solution, the mass percentage of the polymer is 16-20%, the mass percentage of the polyethylene glycol is 3-5%, the mass percentage of the hydrophilic diamine monomer compound is 1-5%, and the mass percentage of the dimethylacetamide is 70-80%.

7. The method for preparing an aminated modified anti-fouling porous film according to claim 3, characterized in that: adopting a coating scraper to scrape the membrane casting solution to the other end at a constant speed, and forming a nascent state membrane on the glass plate with the thickness of 150-; or pouring the casting solution into a spinning machine to extrude into a nascent-state membrane at an extrusion rate of 5-10 ml/min.

8. The method for preparing an aminated modified anti-fouling porous film according to claim 3, characterized in that: the pre-evaporation time of the nascent-state membrane in the air is 5-30s, and the temperature of the coagulation bath is 20-30 ℃.

9. The method for preparing an aminated modified anti-fouling porous film according to claim 3, characterized in that: the ultrafiltration membrane is a flat membrane or a hollow fiber membrane.

10. An amination modified anti-pollution porous membrane, which is characterized in that: prepared by the preparation method of any one of claims 1 to 8.