A method for preparing a polyacrylonitrile-based janus film and use thereof

Abstract

The application discloses a preparation method and application of a polyacrylonitrile-based Janus film, and the method adopts a free radical polymerization method, acrylonitrile monomers are used as main raw materials, and hydrophilic and hydrophobic monomers are copolymerized, hydrophilic or hydrophobic polyacrylonitrile copolymers are obtained through precipitation in water and vacuum drying; the polyacrylonitrile copolymers are dissolved in an organic solvent to prepare a spinning stock solution with a certain concentration, a composite film is prepared by adopting a sequential spinning (electrospinning / airflow spinning) method, and a Janus film with double-sided asymmetric wettability is obtained through heat treatment. The film prepared by the method has the characteristics of firm interface layer, controllable wettability, adjustable thickness, efficient separation of oil-water emulsion and the like, and the method is simple in operation, and has industrial application prospects in the fields of liquid collection, liquid single-channel transportation and seawater desalination.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and use of a polyacrylonitrile-based Janus film, and belongs to the field of functional materials and engineering technology. BACKGROUND

[0002] With the development of social economy and the continuous advancement of modern industrialization, the demand for oil and chemicals has increased dramatically, which has promoted the rapid development of the global oil industry. However, various types of oil-water mixtures are produced in the process of oil production and transportation and chemical development, and their arbitrary discharge not only causes waste of oil resources, but also causes serious harm to the ecological system, and even causes corrosion of equipment and safety accidents. Therefore, exploring a safe, simple, economical and efficient oil-water mixture treatment method has become one of the focuses of scientific research in recent years. The super-wettability (super-hydrophobic, super-hydrophilic) film can realize high selectivity in the oil-water mixture separation process due to its unique surface wettability, and has the advantages of low energy consumption, low cost and high efficiency, and gradually becomes the main development direction of the oil-water separation technology field in the future. Compared with the single-wet film, the Janus film with double-sided asymmetric wettability can bring double-function utility or functional synergistic effect, and the Janus film has the characteristics of liquid collection and lossless transportation, which can effectively solve the problem of in-situ treatment of oil-water mixtures.

[0003] There are two strategies for preparing the existing Janus oil-water separation film. One strategy is to physically combine two films with different wettability, for example, CN110039863B discloses a Janus type micro-nano composite fiber film with single-side super-hydrophobic and single-side hydrophilic and a preparation method thereof, which discloses that a hydrophilic micro-nano cellulose acetate fiber film and a hydrophobic modified micro-nano polyvinylidene fluoride fiber film are compounded by a hot pressing method or a bonding method to prepare a Janus type film for industrial oil-water separation. CN113774559A discloses a Janus film and a preparation method thereof, which adopts a sequential stacking method to sequentially perform three times of electrospinning stacking to form a film by using polyurethane spinning solution, cellulose acetate / polyurethane spinning solution and cellulose acetate spinning solution, and uses the cellulose acetate / polyurethane fiber film as an intermediate process layer to improve the interface compatibility between different materials. Since the above preparation method only physically combines two polymer films with different properties, the interface strength is weak and the film is prone to delamination.

[0004] Another strategy is to modify the two sides / single side of the film with different wetting properties, for example, authorized disclosure No. CN111871001B discloses "a Janus material with one-way water transport and its preparation method and application", first immerse the substrate in an aqueous solution containing acid organic matter and water-soluble iron salt for modification treatment, under the protection of water, then spray polydimethylsiloxane on the other side of the substrate to realize double-sided asymmetric wettability, which can complete water directional transport in air and oil. CN111604032B "Janus nitrogen-doped carbon nanofiber film and preparation method and application", first nitrogen-doped hydrophobic carbon nanofiber film to realize the outside hydrophilic, then remove the nitrogen-doped layer to obtain Janus carbon nanofiber film, which can simultaneously realize the absorption of oil on the water surface and the adsorption of fuel dissolved in water. The thickness of the skin layer is not easy to control, the performance is difficult to stabilize, and it is not easy to industrialize. In addition, due to the difference in properties between the modifier and the substrate, the weak binding force will reduce the stability of the material during use.

[0005] In view of the above problems and status, the present application discloses a preparation method and application of polyacrylonitrile-based Janus film. Specifically, an intrinsic wetting polyacrylonitrile copolymer is obtained by in-situ polymerization, effectively avoiding the loss of material functional groups, the thickness of the hydrophilic and hydrophobic layers is controlled by sequential spinning to obtain a composite film with stable performance, and under heating conditions, the cyano group in the polymer is cyclized to enhance the binding force between the hydrophilic and hydrophobic layers for efficient separation of oil-water emulsion. SUMMARY

[0006] The present application aims to provide a preparation method and application of polyacrylonitrile-based Janus film, which uses radical polymerization method, acrylonitrile monomer as main raw material, and hydrophilic and hydrophobic monomers are copolymerized respectively, and then hydrophilic or hydrophobic polyacrylonitrile copolymer is obtained by precipitation in water and vacuum drying; dissolve it in an organic solvent to prepare a spinning solution with a certain concentration, and prepare a composite film by sequential spinning (electrospinning / airflow spinning) method, and obtain a double-sided asymmetric wetting Janus film after heat treatment. The film prepared by this method has the characteristics of firm interface layer, controllable wettability, adjustable thickness, efficient separation of oil-water emulsion, etc., and the operation is simple, which has industrial application prospect in the fields of liquid collection, liquid single-channel transportation and seawater desalination.

[0007] The preparation method of the polyacrylonitrile-based Janus film according to the present application is carried out according to the following steps:

[0008] Preparation of hydrophilic polyacrylonitrile copolymer:

[0009] a. Acrylonitrile and hydrophilic monomer, which is one or two of acrylic acid, acrylamide, itaconic acid, hydroxyethyl acrylate or N-hydroxymethyl acrylamide, and 0.1-0.25 g of ammonium persulfate are added to a mixed solvent of dimethylformamide: water at a mass ratio of 1:1 at a molar ratio of 95:5-75:25, and stirring is continued at a temperature of 50-70°C for 4-8 h to obtain a mixture;

[0010] b. The mixture obtained in step a is washed with water and ethanol for 3-5 times in sequence, filtered, and then dried in a vacuum drying oven to obtain a polymer powder;

[0011] Preparation of hydrophobic polyacrylonitrile copolymer:

[0012] c. Acrylonitrile and hydrophobic monomer, which is one or two of fluorine-containing monomer and long-chain alkane monomer, and 0.1-0.20 g of azobisisobutyronitrile are added to dimethylformamide at a molar ratio of 99:1-60:40, and stirring is continued at a temperature of 50-70°C under inert gas protection for 12-48 h to obtain a polymer solution; wherein the fluorine-containing monomer is one or two of hexafluorobutyl acrylate, perfluorobutyl ethylene, hexafluorobutyl methacrylate, dodecafluoroheptyl methacrylate, perfluorodecyl ethylene, perfluorobutyl ethyl acrylate, perfluorobutyl ethyl methacrylate, perfluorooctanol acrylate, and perfluorooctyl ethyl acrylate; and the long-chain alkane monomer is one or two of styrene, dodecene, hexadecene, n-heptene, and pentene;

[0013] d. The polymer solution obtained in step c is precipitated with water, and the polymer powder is obtained after drying in a vacuum drying oven at a temperature of 70°C;

[0014] Preparation of spinning solution:

[0015] e. The hydrophilic polymer powder obtained in step b and the hydrophobic polymer powder obtained in step d are respectively dissolved in a benign solvent to prepare a spinning solution, and the mass fraction of the hydrophilic and hydrophobic copolymers is 5-30% and 5-30% respectively, and stirring is continued at a temperature of 50-80°C for 4-6 h, and then the solution is left to stand for 0.5-2 h to remove bubbles; wherein the benign solvent is trifluoroacetic acid, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl pyrrolidone, tetrahydrofuran, sulfolane, or ethylene nitrate;

[0016] Janus film is spun by sequential spinning method:

[0017] f、using two syringes to suck the hydrophilic and hydrophobic copolymer solutions obtained in step e, and then performing sequential spinning, selecting a 18-24 gauge needle, installing the syringes in a syringe pump, the polymer injection rate being 0.3-3 mL / h, the spinning distance being 8-20 cm, using a drum as a receiver, the rotation speed of the drum being 40-300 rpm, the spinning time being 5-120 min, the spinning mode being one or both of electrospinning and airflow spinning, wherein the electrospinning voltage is 8-25 kV, the airflow pressure of the airflow spinning is 0.05-0.5 MPa, the main body layer spinning time is 45-120 min, the skin layer spinning time is 5-25 min, and after the spinning is completed, the sample is placed in an oven at 150-210 ℃ for heat treatment for 30-180 min, to obtain the Janus film.

[0018] The polyacrylonitrile-based Janus film obtained by the method is used for preparing an oil-water emulsion.

[0019] Compared with the prior art, the preparation method and the use of the polyacrylonitrile-based Janus film have the following innovations:

[0020] The polyacrylonitrile copolymer with intrinsic hydrophobicity or hydrophilicity is directly synthesized by using an in-situ synthesis modification method, the two-side asymmetric wettability film is obtained by using a sequential spinning method, the interface strength of the hydrophilic and hydrophobic film is enhanced by promoting the cyclization chemical reaction between the cyano groups through heat treatment, the defects of the traditional Janus film, such as easy loss of wettability and easy separation of the hydrophilic and hydrophobic layers, are overcome, and the preparation process is simple and easy for industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a diagram of the single-channel transportation of water droplets on the Janus film prepared in Example 1 of the present application;

[0022] Figure 2 FIG. 3 is a diagram of the single-channel transportation of water droplets under oil on the Janus film prepared in Example 3 of the present application;

[0023] Figure 3 FIG. 5 is a diagram of the single-channel transportation of oil droplets under water on the Janus film prepared in Example 5 of the present application;

[0024] Figure 4 FIG. 6 is a diagram of the separation efficiency of oil-in-water emulsion and the optical microscope photos of the emulsion before and after separation by Example 2 (A, B) and the separation efficiency of water-in-oil emulsion and the optical microscope photos of the emulsion before and after separation by Example 7 (C, D). DETAILED DESCRIPTION

[0025] The present application will be further described in conjunction with the specific embodiments, but it should not be understood that the scope of the above-mentioned subject matter of the present application is limited to the following embodiments.

[0026] Example 1

[0027] Preparation of hydrophilic polyacrylonitrile copolymers:

[0028] a. 20g of acrylonitrile and itaconic acid monomers and 0.1g of ammonium persulfate were added to 100g of dimethylformamide:water mixed solvent in a mass ratio of 1:1 at a molar ratio of 90:10. The mixture was stirred continuously at 50℃ for 4 hours to obtain a mixture.

[0029] b. Wash the mixture obtained in step a with water and ethanol three times in sequence, filter it, and then dry it in a vacuum drying oven to obtain polymer powder.

[0030] Preparation of hydrophobic polyacrylonitrile copolymers:

[0031] c. Add 40g of acrylonitrile and perfluorobutylethylene monomers and 0.20g of azobisisobutyronitrile to dimethylformamide at a molar ratio of 95:5. Stir and react for 12h at 50℃ under inert gas protection to obtain a polymer solution.

[0032] d. The polymer solution obtained in step c is precipitated with water and dried in a vacuum drying oven at 70°C to obtain polymer powder.

[0033] Preparation of spinning solution:

[0034] e. Dissolve the hydrophilic polymer powder obtained in step b and the hydrophobic polymer powder obtained in step d in N,N-dimethylacetamide solvent to prepare spinning solution. The mass fraction of the copolymer is 5%. Stir at 50°C for 4 hours and then let stand for 0.5 hours to degas, to obtain hydrophilic and hydrophobic copolymer solution.

[0035] Janus film spinning using sequential spinning method:

[0036] f. Using two syringes, respectively, draw in the hydrophilic and hydrophobic copolymer solutions obtained in step e, and perform sequential spinning. Select an 18-gauge needle, install the syringe in the injection pump, and inject the hydrophilic polymer at a rate of 1 mL / h and the hydrophobic polymer at a rate of 0.5 mL / h. The spinning distance is 15 cm, and a roller is used as the receiver with a rotation speed of 120 rpm. First, electrospin the hydrophilic host layer at 17 kV for 45 min, and then electrospin the hydrophobic skin layer at 14 kV for 5 min. After spinning, place the sample in a 160℃ oven for heat treatment for 180 min to obtain the Janus film.

[0037] The resulting membrane can collect the aqueous phase in water-in-oil emulsions and separate oil-in-water emulsions with a separation efficiency of 99.3%.

[0038] Example 2

[0039] Preparation of hydrophilic polyacrylonitrile copolymer:

[0040] a, 30 g of acrylonitrile, N-hydroxymethyl acrylamide and itaconic acid monomers in a molar ratio of 95:2.5:2.5, and 0.15 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide:water in a mass ratio of 1:1, and stirring was continued at a temperature of 55°C, and after 5 h of reaction, a mixture was obtained;

[0041] b, the mixture obtained in step a was washed with water and ethanol 5 times in turn, and after filtration, it was placed in a vacuum drying oven to obtain a polymer powder;

[0042] Preparation of hydrophobic polyacrylonitrile copolymer:

[0043] c, 40 g of acrylonitrile and styrene monomers in a molar ratio of 99:1, and 0.20 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 70°C for 32 h to obtain a polymer solution;

[0044] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70°C, a polymer powder was obtained;

[0045] Preparation of spinning solution:

[0046] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in N,N-dimethylformamide solvent to prepare a spinning solution, and the mass fraction of the copolymer was 30%, and under the condition of heating at a temperature of 60°C, stirring was continued for 5 h, and then it was left to stand for 1 h to remove bubbles;

[0047] Janus film was spun by sequential spinning method:

[0048] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e for sequential spinning, a 24-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 1 mL / h, and the injection rate of the hydrophobic polymer was 2 mL / h, the spinning distance was 20 cm, a drum was used as a receiver, and the rotation speed was 80 rpm, the hydrophilic main layer was spun by air spinning at a pressure of 0.05 MPa for 120 min, and then the hydrophobic skin layer was spun by air spinning at a pressure of 0.4 MPa for 25 min, after spinning, the sample was placed in an oven at a temperature of 180°C for heat treatment for 120 min to obtain a Janus film.

[0049] The obtained film can collect the water phase in the water-in-oil emulsion, and separate the oil-in-water emulsion, and the separation efficiency is 99.2%.

[0050] Example 3

[0051] Preparation of hydrophilic polyacrylonitrile copolymer:

[0052] a, 20 g of monomers of acrylonitrile: itaconic acid: acrylic acid in a molar ratio of 80:10:10, and 0.1 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, and stirring was continued at a temperature of 60°C, and after 6 h of reaction, a mixture was obtained;

[0053] b, the mixture obtained in step a was washed with water and ethanol four times in sequence, and after filtration, it was placed in a vacuum drying oven to be dried, and a polymer powder was obtained;

[0054] Preparation of hydrophobic polyacrylonitrile copolymer:

[0055] c, 20 g of monomers of acrylonitrile: hexafluorobutyl acrylate: hexadecene in a molar ratio of 80:10:10, and 0.1 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 60°C for 48 h, and a polymer solution was obtained;

[0056] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70°C, a polymer powder was obtained;

[0057] Preparation of spinning solution:

[0058] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in trifluoroacetic acid solvent to prepare a spinning solution, and the mass fraction of the hydrophilic and hydrophobic copolymers was 25% and 10% respectively, and after stirring at a temperature of 50°C for 6 h, it was left to stand for 2 h to be defoamed;

[0059] Spinning of Janus film by sequential spinning method:

[0060] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, a 22-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 1.5 mL / h, the injection rate of the hydrophobic polymer was 0.5 mL / h, the spinning distance was 8 cm, a drum was used as a receiver, and the rotation speed was 180 rpm, the hydrophilic main layer was first electrospun at 20 kV for 100 min, and then the hydrophobic skin layer was airflow spun at 0.5 MPa for 15 min, after the spinning was completed, the sample was placed in an oven at 160°C for heat treatment for 120 min, and a Janus film was obtained.

[0061] The obtained film can collect the water phase in the water-in-oil, and separate the oil-in-water emulsion, and the separation efficiency is 98.5%.

[0062] Example 4

[0063] Preparation of hydrophilic polyacrylonitrile copolymer:

[0064] a, 50 g of monomers of acrylonitrile and hydroxyethyl acrylate in a molar ratio of 75:25, and 0.25 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, and stirring was continued at a temperature of 70 °C, and after 7 h of reaction, a mixture was obtained;

[0065] b, the mixture obtained in step a was washed with water and ethanol three times in turn, and after filtration, it was placed in a vacuum drying oven to dry, and a polymer powder was obtained;

[0066] Preparation of hydrophobic polyacrylonitrile copolymer:

[0067] c, 30 g of monomers of acrylonitrile: hexafluorobutyl methacrylate: pentene in a molar ratio of 85:10:5, and 0.150 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 60 °C for 24 h, and a polymer solution was obtained;

[0068] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0069] Preparation of spinning solution:

[0070] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in dimethyl sulfoxide solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 20% and 25% respectively, and under the condition of heating at a temperature of 70 °C, stirring was continued for 5 h, and then it was left to stand for 1 h to remove bubbles;

[0071] Spinning of Janus film by sequential spinning method:

[0072] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, an 18-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 2 mL / h, and the injection rate of the hydrophobic polymer was 1 mL / h, the spinning distance was 12 cm, a drum was used as a receiver, and the rotation speed was 100 rpm, the hydrophilic main layer was spun by air-jet spinning at 0.1 MPa for 80 min, and then the hydrophobic skin layer was spun by electrospinning at 25 kV for 10 min, after the spinning was completed, the sample was placed in an oven at 200 °C for heat treatment for 50 min, and a Janus film was obtained.

[0073] The obtained film can collect the water phase in water-in-oil, and separate the oil-in-water emulsion, and the separation efficiency is 98.3%.

[0074] Example 5

[0075] Preparation of hydrophilic polyacrylonitrile copolymer:

[0076] a, 40 g monomers of acrylonitrile: acrylic acid in a molar ratio of 85:15, and 0.2 g of ammonium persulfate were added to a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, 100 g, at a temperature of 70 °C, and continuously stirred for 8 h, to obtain a mixture;

[0077] b, the mixture obtained in step a was washed with water and ethanol four times in turn, filtered, and dried in a vacuum drying oven to obtain a polymer powder;

[0078] Preparation of hydrophobic polyacrylonitrile copolymer:

[0079] c, 40 g monomers of acrylonitrile: hexadecene: perfluorodecyl ethylene in a molar ratio of 60:30:10, and 0.20 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and continuously stirred at a temperature of 50 °C under inert gas protection for 20 h to obtain a polymer solution;

[0080] d, the polymer solution obtained in step c was precipitated with water, and the polymer powder was obtained after drying in a vacuum drying oven at a temperature of 70 °C;

[0081] Preparation of spinning solution:

[0082] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were dissolved in N-methyl pyrrolidone solvent respectively to prepare a spinning solution, and the mass fraction of the hydrophilic and hydrophobic copolymers was 5% and 30% respectively, and stirred at a temperature of 80 °C for 5 h, and then left to stand for 1.5 h to remove bubbles;

[0083] Sequential spinning method for spinning Janus film:

[0084] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e for sequential spinning, a 20-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 3 mL / h, the injection rate of the hydrophobic polymer was 3 mL / h, the spinning distance was 20 cm, a drum was used as a receiver, the rotation speed of the drum was 250 rpm, the hydrophobic main layer was first electrospun at 18 kV for 60 min, and then the hydrophilic skin layer was electrospun at 10 kV for 15 min, after the spinning was completed, the sample was placed in an oven at 170 °C for heat treatment for 150 min to obtain a Janus film.

[0085] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 97.8%.

[0086] Example 6

[0087] Preparation of hydrophilic polyacrylonitrile copolymer:

[0088] a, 30 g of monomers of acrylonitrile: itaconic acid: acrylamide in a molar ratio of 75:20:5, and 0.15 g of ammonium persulfate were added to a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, 100 g, at a temperature of 65 °C, and continuously stirred, and after 8 h of reaction, a mixture was obtained;

[0089] b, the mixture obtained in step a was washed with water and ethanol four times in turn, filtered, and then placed in a vacuum drying oven to dry to obtain a polymer powder;

[0090] Preparation of hydrophobic polyacrylonitrile copolymer:

[0091] c, 30 g of monomers of acrylonitrile: perfluorodecyl vinyl: hexafluorobutyl acrylate in a molar ratio of 65:20:15, and 0.15 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and continuously stirred at a temperature of 70 °C under inert gas protection for 48 h to obtain a polymer solution;

[0092] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0093] Preparation of spinning solution:

[0094] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were separately dissolved in tetrahydrofuran solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 20% and 20% respectively, and stirred at a temperature of 80 °C for 4 h, and then left to stand for 1.5 h to remove bubbles;

[0095] Sequential spinning method for spinning Janus film:

[0096] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e for sequential spinning, a 24-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 1.5 mL / h, the injection rate of the hydrophobic polymer was 2.5 mL / h, the spinning distance was 18 cm, a drum was used as a receiver, and the rotation speed was 300 rpm, the hydrophobic main layer was first spun by air spinning at 0.4 MPa for 45 min, and then the hydrophilic skin layer was spun by electrospinning at 15 kV for 5 min, after spinning, the sample was placed in an oven at 160 °C for heat treatment for 180 min to obtain a Janus film.

[0097] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 98.2%.

[0098] Example 7

[0099] Preparation of hydrophilic polyacrylonitrile copolymer:

[0100] a, 35 g of monomers of acrylonitrile: acrylamide in a molar ratio of 90:10 and 0.175 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, and stirring was continued at a temperature of 50 °C, and after 4 h of reaction, a mixture was obtained;

[0101] b, the mixture obtained in step a was washed with water and ethanol three times in sequence, and after filtration, it was placed in a vacuum drying oven to be dried, and a polymer powder was obtained;

[0102] Preparation of hydrophobic polyacrylonitrile copolymer:

[0103] c, 25 g of monomers of acrylonitrile: n-heptene in a molar ratio of 90:10 and 0.125 g of azobisisobutyronitrile were added to 100 g of dimethylformamide under inert gas protection, and stirring was continued at a temperature of 70 °C for 30 h, and a polymer solution was obtained;

[0104] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0105] Preparation of spinning solution:

[0106] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in a sulfolane solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 15% and 25% respectively, and stirring was continued at a temperature of 50 °C for 6 h, and then it was left to stand for 2 h to remove bubbles;

[0107] Sequential spinning method for spinning Janus film:

[0108] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, a 22-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 0.3 mL / h, the injection rate of the hydrophobic polymer was 1.5 mL / h, the spinning distance was 10 cm, a drum was used as a receiver, the rotation speed of the drum was 200 rpm, the hydrophobic main layer was first electrospun at 14 kV for 120 min, and then the hydrophilic skin layer was airspun at 0.1 MPa for 25 min, after the spinning was completed, the sample was placed in an oven at 190 °C for heat treatment for 80 min, and a Janus film was obtained.

[0109] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 98.9%.

[0110] Example 8

[0111] Preparation of hydrophilic polyacrylonitrile copolymer:

[0112] a, 20 g of monomers of acrylonitrile:N-hydroxymethyl acrylamide in a molar ratio of 80:20, and 0.1 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide:water in a mass ratio of 1:1, and stirring was continued at a temperature of 70 °C, and after 5 h of reaction, a mixture was obtained;

[0113] b, the mixture obtained in step a was washed with water and ethanol five times in turn, and after filtration, it was placed in a vacuum drying oven to be dried, and a polymer powder was obtained;

[0114] Preparation of hydrophobic polyacrylonitrile copolymer:

[0115] c, 35 g of monomers of acrylonitrile:perfluorobutyl ethyl methacrylate in a molar ratio of 70:30, and 0.175 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 50 °C for 48 h, and a polymer solution was obtained;

[0116] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0117] Preparation of spinning solution:

[0118] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in ethylene nitrite solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 25% and 15% respectively, and after stirring for 5 h under heating at a temperature of 70 °C, it was left to stand for 0.6 h to be defoamed;

[0119] Spinning of Janus film by sequential spinning method:

[0120] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, an 18-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 1 mL / h, the injection rate of the hydrophobic polymer was 3 mL / h, the spinning distance was 16 cm, a drum was used as a receiver, and the rotation speed of the drum was 40 rpm, the hydrophobic main layer was first spun by air-jet spinning at 0.45 MPa for 100 min, and then the hydrophilic skin layer was spun by electrospinning at 19 kV for 20 min, after the spinning was completed, the sample was placed in an oven at 210 °C for heat treatment for 30 min, and a Janus film was obtained.

[0121] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 98.5%.

[0122] Example 9

[0123] Preparation of hydrophilic polyacrylonitrile copolymer:

[0124] a, 25 g of monomers of acrylonitrile: hydroxyethyl acrylate in a molar ratio of 95:5, and 0.125 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, and stirring was continued at a temperature of 55°C, and after 8 h of reaction, a mixture was obtained;

[0125] b, the mixture obtained in step a was washed with water and ethanol three times in sequence, and after filtration, it was placed in a vacuum drying oven for drying to obtain a powder;

[0126] Preparation of hydrophobic polyacrylonitrile copolymer:

[0127] c, 40 g of monomers of acrylonitrile: perfluorooctyl ethyl acrylate in a molar ratio of 75:25, and 0.20 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 60°C for 40 h to obtain a polymer solution;

[0128] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70°C, a polymer powder was obtained;

[0129] Preparation of spinning solution:

[0130] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in N,N-dimethylformamide solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 5% and 10% respectively, and after stirring for 5 h under heating at a temperature of 60°C, it was left to stand for 1 h to remove bubbles;

[0131] Spinning of Janus film by sequential spinning method:

[0132] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, a 20-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 2 mL / h, the injection rate of the hydrophobic polymer was 0.3 mL / h, the spinning distance was 18 cm, a drum was used as a receiver, and the rotation speed was 150 rpm, the hydrophobic main layer was first electrospun at 21 kV for 80 min, and then the hydrophilic skin layer was electrospun at 19 kV for 10 min, after the spinning was completed, the sample was placed in an oven at 150°C for heat treatment for 100 min to obtain a Janus film.

[0133] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 97.7%.

[0134] Example 10

[0135] Preparation of hydrophilic polyacrylonitrile copolymer:

[0136] a, 25 g of monomers of acrylonitrile: itaconic acid at a molar ratio of 95:5, and 0.125 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water at a mass ratio of 1:1, and stirring was continued at a temperature of 50 °C, and after 8 h of reaction, a mixture was obtained;

[0137] b, the mixture obtained in step a was washed with water and ethanol four times in sequence, and after filtration, it was placed in a vacuum drying oven for drying to obtain a polymer powder;

[0138] Preparation of hydrophobic polyacrylonitrile copolymer:

[0139] c, 40 g of monomers of acrylonitrile: dodecene at a molar ratio of 75:25, and 0.20 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 55 °C for 48 h to obtain a polymer solution;

[0140] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0141] Preparation of spinning solution:

[0142] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in dimethyl sulfoxide solvent for the preparation of spinning solutions, and the mass fractions of the hydrophilic and hydrophobic copolymers were 12% and 20% respectively, and after stirring for 4 h under heating at a temperature of 65 °C, it was left to stand for 1.5 h for defoaming;

[0143] Spinning of Janus film by sequential spinning method:

[0144] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e for sequential spinning, an 18-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 1.8 mL / h, the injection rate of the hydrophobic polymer was 0.8 mL / h, the spinning distance was 15 cm, a drum was used as a receiver, and the rotation speed was 200 rpm, the hydrophobic main layer was first electrospun at a voltage of 25 kV for 90 min, and then the hydrophilic skin layer was electrospun at a voltage of 10 kV for 15 min, after the spinning was completed, the sample was placed in an oven at a temperature of 170 °C for heat treatment for 110 min to obtain a Janus film.

[0145] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 97.3%.

[0146] Example 11

[0147] Preparation of hydrophilic polyacrylonitrile copolymer:

[0148] a, 30 g of monomers of acrylonitrile: hydroxyethyl acrylate: acrylic acid at a molar ratio of 90:5:5, and 0.15 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water at a mass ratio of 1:1, and stirring was continued at a temperature of 65 °C, and after 7 h of reaction, a mixture was obtained;

[0149] b, the mixture obtained in step a was washed with water and ethanol three times in sequence, and after filtration, it was placed in a vacuum drying oven to be dried, and a polymer powder was obtained;

[0150] Preparation of hydrophobic polyacrylonitrile copolymer:

[0151] c, 30 g of monomers of acrylonitrile: perfluorobutyl ethyl acrylate: styrene at a molar ratio of 70:15:15, and 0.15 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 65 °C for 36 h, and a polymer solution was obtained;

[0152] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0153] Preparation of spinning solution:

[0154] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in a good solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 25% and 20% respectively, and after stirring for 4 h under heating at a temperature of 70 °C, it was allowed to stand for 1 h to be defoamed;

[0155] Sequential spinning method for spinning Janus film:

[0156] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, a 20-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 1.5 mL / h, the injection rate of the hydrophobic polymer was 1.0 mL / h, the spinning distance was 18 cm, a drum was used as a receiver, and the rotation speed of the drum was 150 rpm, the hydrophobic main layer was first spun by air-jet spinning at a pressure of 0.35 MPa for 100 min, and then the hydrophilic skin layer was spun by electrospinning at a voltage of 20 kV for 15 min, after the spinning was completed, the sample was placed in an oven at a temperature of 170 °C for heat treatment for 120 min, and a Janus film was obtained.

[0157] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 95.8%.

[0158] Example 12

[0159] Preparation of hydrophilic polyacrylonitrile copolymer:

[0160] a, 50 g of monomers of acrylonitrile: itaconic acid in a molar ratio of 80:20, and 0.25 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, and stirring was continued at a temperature of 50 °C, and after 8 h of reaction, a mixture was obtained;

[0161] b, the mixture obtained in step a was washed with water and ethanol 5 times in turn, and after filtration, it was placed in a vacuum drying oven to dry, and a polymer powder was obtained;

[0162] Preparation of hydrophobic polyacrylonitrile copolymer:

[0163] c, 40 g of monomers of acrylonitrile: pentene: hexadecene in a molar ratio of 70:20:10, and 0.20 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and under the protection of inert gas, stirring was continued at a temperature of 60 °C for 48 h, and a polymer solution was obtained;

[0164] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70 °C, a polymer powder was obtained;

[0165] Preparation of spinning solution:

[0166] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in tetrahydrofuran solvent to prepare a spinning solution, and the mass fraction of the hydrophilic and hydrophobic copolymers was 25% and 15% respectively, and after stirring for 5 h under heating at a temperature of 60 °C, it was left to stand for 1 h to remove bubbles;

[0167] Spinning of Janus film by sequential spinning method:

[0168] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, a 22-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 2 mL / h, and the injection rate of the hydrophobic polymer was 0.3 mL / h, the spinning distance was 18 cm, a drum was used as a receiver, and the rotation speed was 150 rpm, the hydrophilic main layer was first electrospun at 10 kV for 70 min, and then the hydrophobic skin layer was airflow spun at 0.15 MPa for 15 min, after spinning, the sample was placed in an oven at 180 °C for heat treatment for 110 min, and a Janus film was obtained.

[0169] The obtained film can collect the water phase in the water-in-oil, and separate the oil-in-water emulsion, and the separation efficiency is 98.2%.

[0170] Example 13

[0171] Preparation of hydrophilic polyacrylonitrile copolymer:

[0172] a, 20 g of monomers of acrylonitrile:acrylamide in a molar ratio of 92:8 and 0.1 g of ammonium persulfate were added to 100 g of a mixed solvent of dimethylformamide:water in a mass ratio of 1:1, and stirring was continued at a temperature of 55°C, and after 4.5 h of reaction, a mixture was obtained;

[0173] b, the mixture obtained in step a was washed with water and ethanol four times in turn, and after filtration, the product was placed in a vacuum drying oven to obtain a polymer powder;

[0174] Preparation of hydrophobic polyacrylonitrile copolymer:

[0175] c, 35 g of monomers of acrylonitrile:perfluorooctanol acrylate in a molar ratio of 65:35 and 0.175 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and stirring was continued at a temperature of 55°C under inert gas protection, and after 44 h of reaction, a polymer solution was obtained;

[0176] d, the polymer solution obtained in step c was precipitated with water, and after drying in a vacuum drying oven at a temperature of 70°C, a polymer powder was obtained;

[0177] Preparation of spinning solution:

[0178] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were respectively dissolved in N,N-dimethylformamide solvent to prepare a spinning solution, and the mass fraction of the hydrophilic and hydrophobic copolymers was 10% and 25% respectively, and stirring was continued at a temperature of 55°C for 4.5 h, and then the product was left to stand for 1.5 h to remove bubbles;

[0179] Janus film prepared by sequential spinning method:

[0180] f, two syringes were used to suck in the hydrophilic and hydrophobic copolymer solutions obtained in step e to perform sequential spinning, a 24-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 2 mL / h, the injection rate of the hydrophobic polymer was 0.3 mL / h, the spinning distance was 18 cm, a drum was used as a receiver, and the rotation speed was 150 rpm. The hydrophobic main layer was first spun by air-jet spinning at 0.35 MPa for 110 min, and then the hydrophilic skin layer was spun by air-jet spinning at 0.3 MPa for 15 min, and after spinning, the sample was placed in an oven at 160°C for heat treatment for 90 min to obtain a Janus film.

[0181] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 96.8%.

[0182] Example 14

[0183] Preparation of hydrophilic polyacrylonitrile copolymer:

[0184] a, 30 g of acrylonitrile: hydroxyethyl acrylate monomers in a molar ratio of 90:10, and 0.15 g of ammonium persulfate were added to a mixed solvent of dimethylformamide: water in a mass ratio of 1:1, 100 g, at a temperature of 55°C, and continuously stirred for 6 h, to obtain a mixture;

[0185] b, the mixture obtained in step a was washed with water and ethanol four times in turn, filtered, and then placed in a vacuum drying oven to dry, to obtain a polymer powder;

[0186] Preparation of hydrophobic polyacrylonitrile copolymer:

[0187] c, 50 g of acrylonitrile: dodecafluoroheptyl methacrylate monomers in a molar ratio of 78:22, and 0.20 g of azobisisobutyronitrile were added to 100 g of dimethylformamide, and continuously stirred at a temperature of 55°C for 24 h under inert gas protection, to obtain a polymer solution;

[0188] d, the polymer solution obtained in step c was precipitated with water, and then dried in a vacuum drying oven at a temperature of 70°C to obtain a polymer powder;

[0189] Preparation of spinning solution:

[0190] e, the hydrophilic polymer powder in step b and the hydrophobic polymer powder obtained in step d were separately dissolved in ethylene nitrite solvent to prepare a spinning solution, and the mass fractions of the hydrophilic and hydrophobic copolymers were 15% and 20% respectively, and the solution was stirred at a temperature of 65°C for 7 h, and then left to stand for 2 h to remove bubbles;

[0191] Spinning of Janus film by sequential spinning method:

[0192] f, the hydrophilic and hydrophobic copolymer solutions obtained in step e were separately sucked into two syringes for sequential spinning, an 18-gauge needle was selected, the syringes were installed in a syringe pump, the injection rate of the hydrophilic polymer was 2 mL / h, and the injection rate of the hydrophobic polymer was 0.3 mL / h, the spinning distance was 18 cm, a drum was used as a receiver, and the rotation speed of the drum was 150 rpm. The hydrophobic main layer was first spun by air spinning at 0.1 MPa for 60 min, and then the hydrophilic skin layer was spun by air spinning at 0.35 MPa for 5 min, and after the spinning was completed, the sample was placed in an oven at a temperature of 170°C for heat treatment for 90 min, to obtain a Janus film.

[0193] The obtained film can collect the oil phase in the oil-in-water emulsion, and separate the water-in-oil emulsion, and the separation efficiency is 97.8%.

Claims

1. A method for preparing a polyacrylonitrile-based Janus film, characterized in that... Follow these steps: Preparation of hydrophilic polyacrylonitrile copolymers: a. Acrylonitrile and one or two of the hydrophilic monomers selected from acrylic acid, acrylamide, itaconic acid, hydroxyethyl acrylate or N-hydroxymethylacrylamide, and 0.1-0.25 g of ammonium persulfate are added to a dimethylformamide:water mixed solvent with a mass ratio of 1:

1. The mixture is stirred continuously at a temperature of 50-70℃ for 4-8 hours to obtain a mixture. b. Wash the mixture obtained in step a with water and ethanol 3-5 times in sequence, filter it, and then dry it in a vacuum drying oven to obtain polymer powder. Preparation of hydrophobic polyacrylonitrile copolymers: c. Acrylonitrile, hydrophobic monomers (fluorinated monomers and long-chain alkane monomers), and 0.1-0.20 g of azobisisobutyronitrile are added to dimethylformamide at a molar ratio of 99:1-60:

40. The reaction is carried out under inert gas protection at a temperature of 50-70℃ with continuous stirring for 12-48 hours to obtain a polymer solution. The fluorinated monomer is one or two of the following: hexafluorobutyl acrylate, perfluorobutylethylene, hexafluorobutyl methacrylate, dodecafluoroheptyl methacrylate, perfluorodecylethylene, perfluorobutyl ethyl acrylate, perfluorobutyl ethyl methacrylate, perfluorooctyl acrylate, and perfluorooctyl ethyl acrylate. The long-chain alkane monomer is one or two of the following: styrene, dodecene, hexadecene, n-heptene, and pentene. d. The polymer solution obtained in step c is precipitated with water and dried in a vacuum drying oven at 70°C to obtain polymer powder. Preparation of spinning solution: e. Dissolve the hydrophilic polymer powder obtained in step b and the hydrophobic polymer powder obtained in step d in a benign solvent to prepare the spinning solution. The mass fractions of the hydrophilic and hydrophobic copolymers are 5-30% and 5-30%, respectively. Stir at a temperature of 50-80℃ for 4-6 hours, and then let stand for 0.5-2 hours to degas. The benign solvent is trifluoroacetic acid, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, sulfolane, or ethyl nitrate. Janus film spinning using sequential spinning method: f. Using two syringes, respectively draw in the hydrophilic and hydrophobic copolymer solutions obtained in step e, and perform sequential spinning. Select needles of size 18-24, install the syringes in the injection pump, the polymer injection rate is 0.3-3 mL / h, the spinning distance is 8-20 cm, the roller is used as the receiver, its rotation speed is 40-300 rpm, the spinning time is 5-120 min, the spinning method is one or both of electrospinning and air-jet spinning, wherein the voltage of electrospinning is 8-25 kV, the air pressure of air-jet spinning is 0.05-0.5 MPa, the spinning time of the main layer is 45-120 min, and the spinning time of the skin layer is 5-25 min. After spinning, place the sample in an oven at 150-210℃ for heat treatment for 30-180 min to obtain polyacrylonitrile-based Janus film.

2. Use of a polyacrylonitrile-based Janus film obtained by the method of claim 1 in the preparation of oil-water emulsions.

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