A hydrophobic polytetrafluoroethylene nanocomposite film and its preparation method

Abstract

This invention discloses a hydrophobic polytetrafluoroethylene (PTFE) nanocomposite membrane and its preparation method, belonging to the field of PTFE membrane processing and manufacturing technology. The invention uses dimethylformamide and dimethylacetamide as polar solvents and acetone as a non-polar solvent, adding inorganic ionic additive LiCl to electrospin a PTFE membrane. Then, using the PTFE membrane as a base membrane, multi-walled carbon nanotubes (mCNTs-PTFE membrane) are loaded onto the base membrane through vacuum filtration. Finally, the mCNTs-PTFE membrane is immersed in a silver-silica nanoparticle suspension, washed, and dried to obtain the PTFE nanocomposite hydrophobic membrane. The PTFE nanocomposite hydrophobic membrane of this invention expands the range of preparation conditions while reducing the toxicity and corrosiveness of the mixed solvent. Furthermore, by loading silver nanoparticles and mCNTs, the multi-level roughness structure of the membrane surface is altered, forming a fiber morphology with a uniform fiber structure and small pore diameter, thus improving the hydrophobic and antifouling properties of the composite membrane.

Description

Technical Field

[0001] This invention belongs to the field of polytetrafluoroethylene membrane processing and manufacturing technology, specifically relating to a polytetrafluoroethylene nanocomposite membrane with enhanced hydrophobic properties and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) microporous membranes are thin films with micropores and excellent filtration performance, formed by mixing and curing PTFE resin particles with additives such as oil, followed by expansion, stretching, and heat setting at temperatures below their melting point. PTFE microporous membranes have a microporous structure with interwoven fibers, exhibiting outstanding chemical stability, excellent high and low temperature resistance, and good corrosion resistance. Therefore, PTFE filter materials can be widely used in separation processes under harsh conditions. Simultaneously, due to its strong hydrophobicity, PTFE is also an ideal membrane material for membrane contactor processes. It can be made into microporous membranes with microporous structures and is widely used for removing acidic components from mixed gases, removing trace gases from water, and membrane distillation processes.

[0003] Currently, almost all commercially available polytetrafluoroethylene (PTFE) microporous membranes are produced using the extrusion molding-stretching method. The core process of each method involves mixing PTFE dispersion resin with additives, followed by extrusion molding, additive removal, stretching, and shaping to obtain the PTFE microporous membrane. The membrane micropore morphology is a dotted-line structure composed of "microfibers" and "nodes." However, due to process limitations, the membranes prepared by these methods have a wide micropore size distribution and poor uniformity. Reducing the pore size leads to a simultaneous decrease in membrane porosity, and the membrane feels soft and thin, resulting in low mechanical strength and hindering subsequent processing. Furthermore, because the "microfibers" constituting the membrane micropore structure are too fine and weak, they are prone to deformation or breakage during use, causing an increase in micropore size and a decrease in separation performance.

[0004] Currently, the most widely used method for modifying polytetrafluoroethylene (PTFE) is surface modification. For example, Chinese Patent No. CN101190975A discloses dissolving a fluorinated surfactant in a solvent and mixing it with a crosslinking agent and a catalyst to obtain a fluorinated surfactant mixture; then, PTFE films are impregnated with the fluorinated surfactant mixture, pre-dried at 80-150°C for 1-10 minutes, and then baked at 110-200°C for 1-10 minutes to obtain a surface-modified superhydrophobic PTFE film. US Patent No. US20120058016A1 discloses dissolving a fluorinated polymer in a solvent to form a solution, or using an emulsion, and attaching the solution or emulsion to the fibrillary microstructure of a PTFE microporous membrane by means of impregnation, spraying, etc., and then drying at 40-140°C to obtain a surface-modified superhydrophobic PTFE film.

[0005] The patent documents described above all describe surface modification methods, which significantly improve the hydrophobicity of polytetrafluoroethylene (PTFE) films by forming surface-modified films on the PTFE film structure. However, these processes involve extrusion operations to manufacture the PTFE film and the formation of surface coatings, which complicates the manufacturing process, significantly reduces production efficiency, and increases production costs. Furthermore, the formed hydrophobic coating is prone to damage and peeling during long-term operation, making it impossible to guarantee the high hydrophobicity of the film over a long period.

[0006] Therefore, in order to overcome the shortcomings of the above-mentioned surface modification method and the defects of the superhydrophobic polytetrafluoroethylene membrane obtained by the surface modification method, it is urgent to find a simple, rapid and effective method to prepare polytetrafluoroethylene nanocomposite membranes with both controllable nanofiber pore size and high hydrophobic properties. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention utilizes the combination of polar and non-polar solvents, along with electrospinning technology and the combined use of inorganic ionic additive LiCl, to expand the preparation conditions of polytetrafluoroethylene nanocomposite membranes while reducing the toxicity and corrosiveness of the mixed solvents. This results in the formation of a fiber morphology with a uniform fiber structure and small pore diameter, thereby improving the hydrophobic properties of the nanocomposite membrane.

[0008] The technical solution of the present invention is as follows:

[0009] One objective of this invention is to provide a method for preparing a polytetrafluoroethylene nanocomposite film with enhanced hydrophobic properties, comprising the following steps:

[0010] (1) Dissolve polytetrafluoroethylene (PTFE) and inorganic ionic additive LiCl solution in a mixed solution of dimethylformamide (DMF), dimethylacetamide (DMAC), and acetone to obtain a PTFE polymer mixed solution;

[0011] (2) The PTFE polymer mixture solution obtained in step (1) is spun by electrospinning to obtain a polytetrafluoroethylene (PTFE) base film.

[0012] (3) Multi-walled carbon nanotubes (mCNTs) are uniformly dispersed in a mixed solvent of water and isopropanol. After ultrasonic dispersion, they are filtered onto the surface of a polytetrafluoroethylene (PTFE) base film. Excess mCNTs are removed by rinsing with deionized water and dried to obtain an mCNTs-PTFE film.

[0013] (4) Dissolve SiO2 nanoparticles in 0.1 mol / L sodium hydroxide solution and stir evenly. Collect the bottom precipitate by centrifugation and wash with deionized water. After drying, obtain hydroxyl-terminated silicon nanoparticles. Then add deionized water and disperse by ultrasonication. Dissolve and disperse AgNO3 in the hydroxyl-terminated nanoparticle solution. At the same time, add ammonia water. After centrifugation again, wash with ethanol and deionized water and dry in an oven again to obtain silver-silica nanoparticles.

[0014] (5) Immerse the mCNTs-PTFE film in the silver-silica nanoparticle suspension prepared in step (4), and after immersion coating, take it out, wash and dry it to obtain a polytetrafluoroethylene nanocomposite film loaded with silver nanoparticles.

[0015] Furthermore, in step (1), the mass ratio of dimethylformamide (DMF) to acetone is 6:4.

[0016] Furthermore, in step (1), the concentration of LiCl is 0.004-0.006 wt.%, and the concentration of PTFE in the mixed solution is 15-25 wt.%.

[0017] Furthermore, the PTFE polymer mixture obtained in step (1) is mechanically stirred at 60°C for at least 1 day, and then the uniformly stirred mixture is placed at room temperature to cool and degas overnight.

[0018] Furthermore, the electrospinning parameters in step (2) are as follows: the spinning voltage is +15.5kV and -1.5kV; the spinning distance is 12-15cm; the feed speed is 0.5ml / h; the inner diameter of the spinning needle is 0.41mm; the diameter of the rotating cylinder of the electrospinning fiber collector is 10cm, the length is 20cm, the rotation speed is 350r / min; and the spinning time is 2h.

[0019] Furthermore, in step (2), after electrospinning, polytetrafluoroethylene (PTFE) base film is obtained by vacuum drying at 60°C for 24 hours.

[0020] Furthermore, in step (3), the mixed solvent consists of water and isopropanol in a volume ratio of 4:7.

[0021] Furthermore, in step (4), the mass ratio of SiO2 to AgNO3 is 5-10:1, and the volume ratio of NaOH to ammonia is 30-300:1.

[0022] Furthermore, the centrifugation speed in step (4) is 8000-10000 rpm.

[0023] The second objective of this invention is to provide a polytetrafluoroethylene nanocomposite membrane with enhanced hydrophobic properties.

[0024] Furthermore, the hydrophobic membrane has a layered composite structure consisting of a silver nanoparticle layer, an mCNTs layer, and a PTFE layer, arranged sequentially from the outside to the inside.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention innovatively utilizes a method of combining polar and non-polar solvents, electrospinning technology, and the inorganic ion additive LiCl to prepare a polytetrafluoroethylene nanocomposite membrane with enhanced hydrophobic properties. By adding inorganic ions to change the surface tension and polymer chain arrangement in the solution, the pore size of the nanofiber composite membrane is controlled, transforming the fiber morphology from bead-like fibers to a uniform fiber structure with a small pore diameter, thereby improving the hydrophobic properties and stability of the nanocomposite membrane.

[0027] 2. This invention prepares PTFE polymer coating solutions by mixing polar solvents DMF and DMAC with non-polar solvent acetone. This method not only adjusts the polarity of the mixture and expands the temperature range for preparing polytetrafluoroethylene nanocomposite films, which is beneficial to the subsequent electrospinning process and silver nanoparticle loading process, but also reduces the toxicity and corrosiveness of DMF and DMAC in the mixed solvent, thus promoting the safe preparation of this polytetrafluoroethylene nanocomposite film.

[0028] 3. This invention increases the roughness of the membrane by combining mCNTs and a PTFE layer. PTFE and mCNTs are bonded through non-covalent interactions. The π-electron system of carbon nanotubes can interact with the π-electron system in the PTFE membrane, forming π-π interactions. This not only enhances the bonding force of the composite material but also effectively improves the mechanical and hydrophobic properties of the PTFE composite membrane. Furthermore, this invention uniformly disperses and coats the prepared silver-silica nanoparticles onto the mCNTs layer. Silver ions react chemically with the carboxyl groups on the surface of carboxylated multi-walled carbon nanotubes to form silver carboxylate salts, which increases the adsorption and stability of silver ions on the material surface. Silica forms a protective shell, preventing silver particles from directly contacting the external environment, thereby reducing the adhesion of pollutants and helping to extend the service life of the nanoparticles. Together, these factors endow the composite membrane material with excellent antibacterial and antifouling properties.

[0029] Figure Labels

[0030] Figure 1 This is a schematic diagram of the process flow for the polytetrafluoroethylene nanocomposite membrane described in this invention.

[0031] Figure 2 This is a schematic diagram of the electrospinning process of the polytetrafluoroethylene nanocomposite film described in this invention;

[0032] Figure 3This is a contact angle structure diagram of the electrospinning of the polytetrafluoroethylene nanocomposite film described in this invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0034] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0035] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0036] Unless otherwise specified, the experimental methods in the following examples are conventional methods;

[0037] Example 1

[0038] This embodiment provides a polytetrafluoroethylene nanocomposite film with enhanced hydrophobic properties, the preparation method of which includes the following steps:

[0039] S1. PTFE particles and inorganic ionic additive LiCl are added to a mixed solvent of MD / DMF / acetone and stirred at 60°C for 1 day to obtain a mixed solution with a PTFE concentration of 20 wt.% and a LiCl concentration of 0.004 wt.%, wherein the mass ratio of dimethylformamide DMF to acetone in the MD / DMF / acetone mixed solvent is 6:4.

[0040] S2. Add the above mixed solution to a 10ml syringe, and wrap a layer of tin foil around a receiving roller with a diameter of 10cm and a length of 20cm to receive nanofibers. Then, adjust the parameters of the electrospinning machine to perform electrospinning, wherein the needle inner diameter is 0.41mm, the spinning distance is 15cm, the feed speed is 0.5mL / h, the voltage is +15.5kV and 1.5kV, the rotation speed is 350r / min, and the spinning time is 2h. Finally, the electrospinning is completed, the film is peeled off from the tin foil, and dried in an oven at 60℃ for 24h to obtain a PTFE base film.

[0041] S3. Disperse mCNTs uniformly in a mixed solvent of water and isopropanol in a volume ratio of 4:7, ultrasonically disperse for 6 hours, then filter it onto the surface of the PTFE base membrane, rinse the membrane surface with deionized water to remove excess mCNTs, immerse the membrane in deionized water for 1 hour to displace the solvent in the membrane pores, and finally place the membrane in a 60℃ oven to dry for 12 hours for later use.

[0042] S4. Dissolve SiO2 nanoparticles in 0.1 mol / L NaOH solution and stir evenly to obtain a mixed solution. Centrifuge the mixed solution at 9000 rpm at room temperature, collect the precipitate at the bottom of the centrifuge tube, wash with deionized water, and then dry in an oven to obtain hydroxyl-terminated silicon nanoparticles. Add the hydroxyl-terminated silicon nanoparticles to deionized water and disperse ultrasonically. Dissolve and disperse AgNO3 in the hydroxyl-terminated nanoparticle solution, and add ammonia water. After magnetic stirring, centrifuge again at 9000 rpm, collect the precipitate at the bottom of the centrifuge tube, wash with ethanol and deionized water respectively, and then dry in an oven to obtain silver-silica nanoparticles, wherein the mass ratio of SiO2 to AgNO3 is 7:1, and the volume ratio of NaOH to ammonia water is 165:1.

[0043] S5. Immerse the mCNTs-PTFE film in a silver-silica nanoparticle suspension, remove it after immersion coating, wash and dry it to obtain the mCNTs-PTFE film loaded with silver nanoparticles.

[0044] The method can also be adjusted according to the actual preparation process, with the PTFE concentration set to 15 wt.% or 25 wt.%, the LiCl concentration set to 0.005 wt.% or 0.006 wt.%, the spinning distance set to 12 cm or 14 cm, and the centrifugation speed set to 8000 rpm or 100000 rpm. The mass ratio of SiO2 to AgNO3 can also be selected as 5:1 or 10:1, and the volume ratio of NaOH to ammonia water can also be 30:1 or 300:1.

[0045] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film, characterized in that, Includes the following steps: (1) Dissolve polytetrafluoroethylene (PTFE) and inorganic ionic additive LiCl solution in a mixed solution of dimethylformamide (DMF), dimethylacetamide (DMAC), and acetone to obtain a PTFE polymer mixed solution; (2) The PTFE polymer mixture solution obtained in step (1) is spun by electrospinning to obtain a polytetrafluoroethylene (PTFE) base film. (3) Carboxylated multi-walled carbon nanotubes (mCNTs) are uniformly dispersed in a mixed solvent of water and isopropanol. After ultrasonic dispersion, they are filtered onto the surface of a polytetrafluoroethylene (PTFE) base film. Excess carboxylated multi-walled carbon nanotubes (mCNTs) are removed by rinsing with deionized water. After drying, mCNTs-PTFE film is obtained. (4) Dissolve SiO2 nanoparticles in 0.1 mol / L sodium hydroxide solution and stir evenly. Collect the bottom precipitate by centrifugation and wash with deionized water. After drying, obtain hydroxyl-terminated silicon nanoparticles. Then add deionized water and disperse by ultrasonication. Dissolve and disperse AgNO3 in the hydroxyl-terminated nanoparticle solution. At the same time, add ammonia water. After centrifugation again, wash with ethanol and deionized water and dry in an oven again to obtain silver-silica nanoparticles. (5) Immerse the mCNTs-PTFE film in the silver-silica nanoparticle suspension prepared in step (4), and after immersion coating, take it out, wash and dry it to obtain a polytetrafluoroethylene nanocomposite film loaded with silver nanoparticles.

2. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, In step (1), the mass ratio of dimethylformamide (DMF) to acetone is 6:

4.

3. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, In step (1), the concentration of LiCl in the mixed solution is 0.004-0.006 wt.%, and the concentration of PTFE in the mixed solution is 15-25 wt.%.

4. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, The PTFE polymer mixture obtained in step (1) is mechanically stirred at 60°C for at least 1 day, and then the well-stirred mixture is placed at room temperature to cool and degas overnight.

5. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, The electrospinning parameters in step (2) are as follows: spinning voltage is +15.5kV and -1.5kV; spinning distance is 12-15cm; and feed speed is 0.5ml / h.

6. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, In step (2), the inner diameter of the electrospinning needle is 0.41 mm; the diameter of the rotating cylinder of the electrospinning fiber collector is 10 cm, the length is 20 cm, the rotation speed is 350 r / min, and the spinning time is 2 h.

7. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, In step (2), polytetrafluoroethylene (PTFE) base film is obtained by electrospinning and then vacuum drying at 60°C for 24 h.

8. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, In step (3), the mixed solvent consists of water and isopropanol in a volume ratio of 4:

7.

9. The method for preparing a hydrophobic polytetrafluoroethylene nanocomposite film as described in claim 1, characterized in that, In step (4), the mass ratio of SiO2 to AgNO3 is 5-10:1, and the volume ratio of NaOH to ammonia is 30-300:

1.

10. A hydrophobic polytetrafluoroethylene nanocomposite membrane prepared by the method according to any one of claims 1 to 9.

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