Pdms / pvdf composite membrane based on chemically modified pvdf substrate

Abstract

This invention relates to a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, comprising a PVDF substrate sequentially modified with NaOH, Na2SO4, and methacrylic acid, grafted with methacrylate-functionalized PDMS. The invention also relates to a method for preparing the above-mentioned membrane, which involves sequentially chemically modifying the PVDF substrate with NaOH, Na2SO4, and methacrylic acid in three steps, introducing acrylate double bonds onto the surface of the PVDF substrate, followed by further photopolymerization grafting of a PDMS selective layer to prepare the PDMS / PVDF composite membrane. This improves the adhesion of the PDMS selective layer, effectively mitigating cracking and delamination phenomena in practical applications of the PDMS / PVDF composite membrane. Simultaneously, the membrane's performance in pervaporation separation of phenol is significantly enhanced, greatly improving the application prospects of PDMS membranes in actual pervaporation processes.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing and applying a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate and grafted with a PDMS selective layer. Background Technology

[0002] Phenolic wastewater is widely generated and discharged in industries such as coatings, plastics, and petroleum. Due to its high toxicity and carcinogenicity, it has serious adverse effects on the ecological environment and human health. Separating phenol from aqueous solutions has become a top priority for environmental and food safety. Traditional phenol separation methods include adsorption, advanced oxidation, and liquid-liquid extraction. To facilitate mass transfer, these separation processes are typically carried out at high temperatures in industry, requiring considerable energy. In recent decades, membrane technology has attracted widespread attention for highly selective separation operations. Among them, pervaporation technology, with its high selectivity, low energy consumption, and non-toxicity to microorganisms, shows great promise in phenol separation. Polydimethylsiloxane (PDMS) has advantages such as low raw material cost and good processing performance, demonstrating broad prospects in the separation of phenolic wastewater. Polyvinylidene fluoride (PVDF), with its thermal stability and mechanical stability, is widely used in the preparation of pervaporation membrane materials.

[0003] During the separation process, the strength of the bond between the PDMS selective layer and the substrate directly determines the membrane's lifespan. However, in practical applications of PDMS membranes for pervaporation separation of phenol, the problem of weak selective layer adhesion is frequently encountered. Cracks and delamination of the selective layer severely restrict the widespread application of PDMS membranes in pervaporation processes and the stability of the pervaporation process.

[0004] Therefore, it is crucial to prepare a PDMS / PVDF composite membrane with high PDMS selective layer adhesion and excellent pervaporation performance. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, which addresses the problems of weak selective layer adhesion, selective layer cracking and delamination encountered when using PDMS membranes for pervaporation separation of phenol. This PDMS / PVDF composite membrane has strong PDMS selective layer adhesion and excellent pervaporation performance, and can be used in actual pervaporation processes.

[0006] Therefore, the first aspect of the present invention provides a PDMS / PVDF composite film based on a chemically modified PVDF substrate, which is composed of a PVDF substrate modified sequentially with NaOH and Na2SO4 and grafted with methacrylate-functionalized PDMS, and its molecular structure is shown in formula (IX):

[0007]

[0008] In formula (IX), m is the number of -CH2-CF2- groups; n is the number of -CH2CFO- groups; and x is the number of -Si-O- groups.

[0009] In some embodiments of the present invention, the L of the PDMS / PVDF composite membrane C1 The critical load is 50.2 mN; and / or, the L of the PDMS / PVDF composite membrane is... C2 The critical load is 57.5 mN; and / or, the permeation flux of the PDMS / PVDF composite membrane is 2256.2-2332.8 g·m³. -2 ·h -1 The separation factor was 8.11-8.53.

[0010] A second aspect of this invention provides a method for preparing a PDMS / PVDF composite film based on a chemically modified PVDF substrate, comprising:

[0011] Step A: After rinsing the PVDF substrate with dewatering water, immerse it in NaOH aqueous solution, and then rinse it with dewatering water to obtain the sodium hydroxide modified PVDF substrate.

[0012] Step B: Immerse the sodium hydroxide-modified PVDF substrate in a Na2SO4 aqueous solution, then rinse it with dewatering water to obtain the Na2SO4-modified PVDF substrate.

[0013] Step C: Immerse the Na2SO4-modified PVDF substrate in an aqueous methacrylic acid solution, and then rinse it clean with dewatering water to obtain the Na2SO4-modified PVDF substrate.

[0014] Step D: After vacuum degassing the PDMS casting solution, pour it onto the methacrylic acid-modified PVDF substrate and perform film coating. Immediately after film coating is completed, transfer the coating to a UV lamp for irradiation to prepare a PDMS / PVDF composite film based on a chemically modified PVDF substrate.

[0015] In some embodiments of the present invention, in step A, the concentration of the NaOH aqueous solution is 0.05 mol / L; and / or, the soaking time is 0.5 h.

[0016] In some embodiments of the present invention, in step B, the concentration of the Na2SO4 aqueous solution is 0.07 mol / L; and / or, the soaking time is 0.5 h.

[0017] In some embodiments of the present invention, in step C, the concentration of the aqueous methacrylic acid solution is 0.09 mol / L; and / or, the soaking time is 0.5 h.

[0018] According to the present invention, the PDMS casting solution is prepared by adding a photoinitiator 2-hydroxy-2-methylphenylacetone to a heptane solution of methacrylate-functionalized PDMS and stirring at room temperature.

[0019] In some embodiments of the present invention, during the PDMS casting process, the mass ratio of methacrylate-functionalized PDMS to photoinitiator is 3:1; and / or the stirring time is 24 hours.

[0020] According to the present invention, the preparation method of methacrylate-functionalized PDMS includes: mixing PDMS, silane coupling agent KH570, dibutyltin dilaurate, water and n-heptane, weighing and recording the mixture, stirring at room temperature, weighing again and adding n-heptane to the original weight, stirring again until homogeneous, and preparing methacrylate-functionalized PDMS.

[0021] In some embodiments of the present invention, during the preparation of methacrylate-functionalized PDMS, the mass ratio of 5000 cP PDMS to silane coupling agent KH570 is 11:0.12; and / or, the mass ratio of PDMS to dibutyltin dilaurate is 11:0.1; and / or, the mass ratio of PDMS to water is 11:0.1; and / or, the mass ratio of PDMS to n-heptane is 1:1.

[0022] The third aspect of the present invention provides the application of the PDMS / PVDF composite membrane as described in the first aspect of the present invention or the PDMS / PVDF composite membrane prepared by the method described in the second aspect of the present invention in the separation process.

[0023] In some embodiments of the present invention, the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

[0024] This invention uses PVDF substrate as the base membrane and PDMS as the selective layer. A PDMS / PVDF composite membrane is prepared through a three-step chemical modification of the PVDF substrate and grafting of PDMS. This effectively improves the problem of weak selective layer adhesion during pervaporation. The modified PDMS / PVDF composite membrane exhibits excellent adhesion between the PVDF and PDMS layers, helping to prevent cracking and delamination of the PDMS selective layer. With the increase in PDMS selective layer adhesion, cracking and delamination phenomena in the PDMS / PVDF composite membrane are effectively alleviated in practical applications. Simultaneously, the performance of pervaporation for phenol separation is significantly improved, greatly enhancing the application prospects of PDMS membranes in practical pervaporation processes. Attached Figure Description

[0025] To make the present invention easier to understand, the present invention will be described in detail below with reference to the accompanying drawings.

[0026] Figure 1 The NaOH modification pathway of PVDF is shown.

[0027] Figure 2 The Na2SO4 modification pathway of PVDF is shown.

[0028] Figure 3 The methacrylic acid modification pathway of PVDF is shown.

[0029] Figure 4 The preparation route of methacrylate-functionalized PDMS is shown.

[0030] Figure 5 This paper illustrates the preparation route for PDMS / PVDF composite films by photopolymerization and grafting PDMS onto modified PVDF substrates.

[0031] Figure 6 The results show a comparison of the Fourier transform infrared spectra of the PVDF substrate surface before and after NaOH modification.

[0032] Figure 7 The results show a comparison of the Fourier transform infrared spectra of the PVDF substrate surface before and after Na2SO4 modification.

[0033] Figure 8 The results show a comparison of the Fourier transform infrared spectra of the PVDF substrate surface before and after methacrylic acid modification.

[0034] Figure 9 Typical results of nano-scratch tests on PDMS / PVDF composite films before and after modification are shown: (a) scratch profile, (b) friction profile of unmodified PDMS / PVDF composite film, and (c) scratch profile, (d) friction profile of modified PDMS / PVDF composite film.

[0035] Figure 10 This is a schematic diagram of a pervaporation device. Detailed Implementation

[0036] To facilitate understanding of the present invention, it will be described in detail below with reference to the accompanying drawings. However, before describing the present invention in detail, it should be understood that the present invention is not limited to the specific embodiments described. It should also be understood that the terminology used herein is for describing specific embodiments only and is not intended to be restrictive.

[0037] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While any methods and materials similar to or equivalent to those described herein may be used in the practice or testing of this invention, preferred methods and materials are now described.

[0038] In this invention, the range of dosage concentration, temperature or other physical or chemical properties or characteristics, unless otherwise specified, covers or includes the upper and lower limits of that range.

[0039] I. Terminology

[0040] In this invention, the term "1173" refers to 1173 photoinitiator, namely 2-hydroxy-2-methylphenylacetone photoinitiator.

[0041] In this invention, the term "PDMS" refers to polydimethylsiloxane, with the chemical formula (C2H6OSi). n Accordingly, the “PDMS membrane” refers to a polydimethylsiloxane membrane.

[0042] In this invention, the term "PVDF" refers to polyacrylonitrile (Polyvinylidene fluoride), with the chemical formula (C2H2F2). n Accordingly, the “PVDF substrate” refers to polyvinylidene fluoride vinyl material.

[0043] Unless otherwise specified, the term "water" in this invention refers to one or more of deionized water, distilled water, and ultrapure water.

[0044] II. Implementation Plan

[0045] As mentioned earlier, the strength of the bond between the PDMS selective layer and the substrate directly determines the membrane's lifespan during the separation process. Currently used PDMS / PVDF substrates often face problems such as weak adhesion of the PDMS selective layer, selective layer cracking, and delamination during actual pervaporation. In view of this, the inventors have conducted extensive research on PVDF substrates and PDMS membranes.

[0046] The inventors have discovered that by performing a three-step chemical modification of a PVDF substrate with NaOH, Na2SO4, and methacrylic acid, followed by photopolymerization and grafting of PDMS, a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate can be prepared. This composite membrane exhibits strong PDMS selective layer adhesion and excellent pervaporation performance, making it suitable for use in actual pervaporation processes.

[0047] To achieve the present invention, the present invention uses the following method to prepare a PDMS / PVDF composite film based on a chemically modified PVDF substrate, which includes the following steps:

[0048] (1) NaOH modification of PVDF substrate: After rinsing the PVDF substrate with dewatering water, it is soaked in a 0.05mol / L NaOH aqueous solution for 0.5h, and then rinsed with dewatering water to obtain the sodium hydroxide modified PVDF substrate; the NaOH solution is formed by dissolving NaOH in water;

[0049] (2) Na2SO4 modification of PVDF substrate: The PVDF substrate modified with sodium hydroxide was immersed in a Na2SO4 aqueous solution with a concentration of 0.07mol / L for 0.5h, and then rinsed with water to obtain the Na2SO4 modified PVDF substrate; the Na2SO4 aqueous solution was formed by dissolving Na2SO4 in water.

[0050] (3) PVDF substrate modified with methacrylic acid: The PVDF substrate modified with Na2SO4 was immersed in an aqueous solution of 0.09 mol / L methacrylic acid for 0.5 h, and then rinsed with water to obtain the PVDF substrate modified with methacrylic acid; the aqueous solution of methacrylic acid was formed by dissolving methacrylic acid in water;

[0051] (3) Photopolymerization of PDMS grafted onto modified PVDF substrate to prepare PDMS / PVDF composite film: After vacuum degassing of PDMS casting solution, it is poured onto methacrylic acid modified PVDF substrate and coated. After coating is completed, the coating is immediately transferred to ultraviolet lamp for irradiation to prepare PDMS / PVDF composite film based on chemically modified PVDF substrate.

[0052] According to the present invention, the preparation method of the above-mentioned PDMS casting solution includes the following steps:

[0053] S1, PDMS, silane coupling agent KH570, dibutyltin dilaurate, water and n-heptane are mixed, weighed and recorded, stirred at room temperature, weighed again and n-heptane is added to the original weight, and stirred again until homogeneous to prepare methacrylate-functionalized PDMS.

[0054] S2, methacrylate-functionalized PDMS was diluted with n-heptane to form a methacrylate-functionalized PDMS diluent, and 2-hydroxy-2-methylphenylacetone was added as a photoinitiator. After stirring at room temperature for 24 hours, a PDMS casting solution was obtained.

[0055] In step S2 above, the mass ratio of methacrylate-functionalized PDMS to photoinitiator is 3:1.

[0056] In step S1 above, the mass ratio of 5000 cP PDMS to silane coupling agent KH570 is 11:0.12; and / or, the mass ratio of PDMS to dibutyltin dilaurate is 11:0.1, the mass ratio of PDMS to water is 11:0.1, and the mass ratio of PDMS to n-heptane is 1:1.

[0057] As can be seen from the above, the specific preparation path for preparing PDMS / PVDF composite films based on chemically modified PVDF substrates according to the present invention is as follows:

[0058] (1) NaOH modification pathway for PVDF substrate as follows Figure 1 As shown, from Figure 1 It can be seen that after hydrolysis modification with NaOH solution, carbon-carbon double bond functional groups are formed on the surface of the PVDF substrate after defluorination.

[0059] (2) The Na2SO4 modification pathway of PVDF substrate is as follows: Figure 2 As shown, from Figure 2 It can be seen that after modification with Na2SO4 aqueous solution, the carbon-carbon double bond functional groups on the surface of PVDF substrate react with Na2SO4, and some hydroxyl functional groups are grafted onto the surface of PVDF substrate.

[0060] (3) The methacrylic acid modification pathway of PVDF substrate is as follows: Figure 3 As shown, from Figure 3 It can be seen that after hydrolysis modification with aqueous methacrylic acid, the hydroxyl functional groups on the surface of the PVDF substrate are partially transformed into methacrylate functional groups.

[0061] (4) The preparation route of methacrylate-functionalized PDMS is as follows: Figure 4 As shown, from Figure 4 It can be seen that the acrylate double bond is introduced into PDMS through the reaction of PDMS with silane coupling agent KH570;

[0062] (5) The preparation route for PDMS / PVDF composite films by photopolymerization and grafting of PDMS onto modified PVDF substrate is as follows: Figure 5 As shown, from Figure 5 It can be seen that the acrylate double bonds on the surface of the modified PVDF substrate and the acrylate double bonds in PDMS undergo photopolymerization under ultraviolet light irradiation, and a PDMS selective layer is grafted onto the surface of the PVDF substrate, thus successfully preparing a PDMS / PVDF composite film.

[0063] It is easy to understand that the PDMS / PVDF composite film based on chemically modified PVDF substrate prepared by the above preparation method or route is composed of a PVDF substrate chemically modified in three steps (sodium hydroxide, Na2SO4, and methacrylic acid) and grafted with a PDMS selective layer. Its molecular structure is shown in formula (IX).

[0064]

[0065] In formula (IX), m is the number of -CH2-CF2- groups; n is the number of -CH2CFO- groups; and x is the number of -Si-O- groups.

[0066] This invention involves a three-step chemical modification of a PVDF substrate: NaOH modification, Na2SO4 modification, and methacrylic acid modification. This introduces acrylate double bonds onto the surface of the PVDF substrate. Further photopolymerization grafting of a PDMS selective layer completes the process, resulting in a PDMS / PVDF composite film that improves the adhesion and pervaporation performance of the PDMS selective layer. Nano-scratch testing revealed that cracking and delamination of the PDMS selective layer are effectively mitigated, and adhesion is significantly enhanced. Pervaporation testing showed that the PDMS / PVDF composite film prepared based on a chemically modified PVDF substrate grafted with PDMS improved the separation factor for phenol.

[0067] The research results show that, in this invention, the L of the PDMS / PVDF composite membrane... C1 The critical load is 50.2 mN; and / or, the L of the PDMS / PVDF composite membrane is... C2 The critical load is 57.5 mN; and / or, the permeation flux of the PDMS / PVDF composite membrane is 2256.2-2332.8 g·m³. -2 ·h -1 The separation factor was 8.11-8.53.

[0068] The present invention also provides the application of the above-mentioned PDMS / PVDF composite membrane or the PDMS / PVDF composite membrane prepared by the above-mentioned preparation method in the separation process.

[0069] In some embodiments of the present invention, the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

[0070] Example

[0071] To make the present invention easier to understand, the present invention will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained commercially or by conventional methods.

[0072] Example 1: Preparation of PDMS / PVDF composite film based on chemically modified PVDF substrate

[0073] (1) NaOH modification of PVDF substrate: Weigh 2g of NaOH and dissolve it in 1L of water to prepare a 0.05mol / L NaOH solution. After rinsing the PVDF substrate with deionized water, immerse it in the 0.05mol / L NaOH solution for 0.5h, and then rinse it with deionized water to complete the sodium hydroxide modification of the PVDF substrate.

[0074] (2) Na2SO4 modification of PVDF substrate: Weigh 9.94g of Na2SO4 and dissolve it in 1L of water to prepare a 0.07mol / L Na2SO4 aqueous solution. Stir well and immerse the PVDF substrate modified with 0.05mol / L sodium hydroxide solution for 0.5h in the 0.07mol / L Na2SO4 aqueous solution for 0.5h. Then rinse it with deionized water to complete the Na2SO4 modification of PVDF substrate.

[0075] (3) methacrylic acid modification of PVDF substrate: Weigh 7.74g of methacrylic acid and dissolve it in 1L of water to prepare a 0.09mol / L methacrylic acid aqueous solution. Stir well and immerse the PVDF substrate modified with 0.07mol / L Na2SO4 aqueous solution for 0.5h in the 0.09mol / L methacrylic acid aqueous solution for 0.5h. Then rinse it with deionized water to complete the methacrylic acid modification of PVDF substrate.

[0076] (4) Preparation of methacrylate-functionalized PDMS: 11 g of 5000 cP PDMS, 0.12 g of silane coupling agent KH570, 0.1 g of dibutyltin dilaurate, 0.1 g of deionized water, and 11 g of n-heptane (PDMS:KH570:dibutyltin dilaurate:deionized water:n-heptane = 110:1.2:1:1:110) were mixed in a 50 ml beaker, weighed, and the weight was recorded. The mixture was stirred at 800 rpm for 24 h at room temperature, weighed again, and n-heptane was added to bring the total weight to the original weight. The mixture was stirred again until homogeneous, thus completing the preparation of methacrylate-functionalized PDMS.

[0077] (5) Preparation of PDMS / PVDF substrate: Take 3g of methacrylate-functionalized PDMS, add 0.75g of n-heptane, dilute it to a solvent content of 70%, add 1g of photoinitiator 2-hydroxy-2-methylphenylacetone, and stir at 800rpm for 20min at room temperature; then vacuum degas the stirred PDMS casting solution, the thickness of the scraper is 60μm, then pour the PDMS casting solution onto the modified PVDF substrate, and use an Elcometer-4340 automatic coating machine to scrape the film. After the film is scraped, immediately transfer the coating to a 365nm ultraviolet lamp for irradiation for 3min, with the film 10cm away from the ultraviolet lamp, to complete the preparation of PDMS / PVDF composite film.

[0078] The PVDF substrates modified with NaOH, Na₂SO₄, and methacrylic acid were characterized using Fourier transform infrared spectroscopy (Spectro3, manufacturer: PerkinElmer). The results for NaOH modification are as follows: Figure 6 As shown: Figure 6 The significant enhancement of the C=C peak in the middle proves that hydrolysis modification produced some C=C functional groups; the results after Na2SO4 modification are as follows: Figure 7 As shown: Figure 7 The characteristic peak of C=C in the middle is 1680 cm⁻¹. -1 The decrease in peak area indicates that the PVDF surface modified by Na2SO4 aqueous solution and NaOH solution hydrolysis reacts with the C=C bonds on the surface of the PVDF substrate, successfully grafting hydroxyl groups onto the surface. The results after modification with methacrylic acid are shown below. Figure 8 As shown: Figure 8 The characteristic peak of C=C in the middle is 1680 cm⁻¹. -1 The increase in peak area proves that the PVDF surface modified by NaOH solution hydrolysis with methacrylic acid aqueous solution reacts with the hydroxyl groups on the surface of the PVDF substrate, thus successfully grafting methacrylic acid groups onto the surface of the PVDF substrate.

[0079] Through nano scratch test (model Nst) 3 The test (manufactured by Anton Paar) characterized the adhesion of the PDMS selective layer in the PDMS / PVDF composite film. The test conditions involved gradually increasing the applied load from an initial 3 mN to a maximum load of 60 mN, at a rate of approximately 57 mN / min.

[0080] In nano-scratch testing, the critical load of the membrane is determined by observing the friction between the indenter and the membrane during the scratch test loading process. The failure critical load is a quantitative standard for the adhesive strength of composite membranes. C1 The critical load represents the PDMS layer's ability to withstand lateral loads, reflecting its resistance to crack initiation; it is also known as the "lower critical load." C2 The critical load represents the transverse critical load corresponding to the total peeling of the PDMS layer from the PVDF substrate, also known as the "higher critical load".

[0081] Figure 9 Typical scratch results of PDMS / PVDF composite films before and after modification are presented to compare the adhesion of the PDMS selective layer before and after modification. Figure 9 Demonstrates the critical load (L) at the PDMS-PVDF interface. C The determination of ).

[0082] The test results show that the L of the modified PDMS / PVDF composite membrane...C1 and L C2 The modified PDMS / PVDF interface exhibits significantly enhanced adhesion between the PVDF and PDMS layers, which helps prevent cracking and delamination of the film coating. The increased adhesion of the modified PDMS / PVDF composite film is attributed to the photopolymerization grafting of acrylate bonds between the chemically modified PDMS selective layer and the PVDF substrate, which generates partial chemical bonds that significantly enhance the adhesion of the PDMS selective layer.

[0083] Example 2:

[0084] Pervaporation tests were performed on the PDMS / PVDF composite membrane prepared in Example 1.

[0085] Pervaporation test: The separation performance of the obtained cured membrane with 0.1wt% phenol was tested using a pervaporation device under heating conditions of 60℃.

[0086] The pervaporation properties of phenol were tested using a self-made laboratory apparatus at a temperature of 60°C and a phenol concentration of 5 wt%. The specific testing apparatus (pervaporation device) is shown below. Figure 10 As shown.

[0087] Pervaporation results showed that the separation factor of the modified PDMS / PVDF composite membrane was 8.32. After modification with NaOH solution, C=C functional groups were generated on the surface of the PVDF substrate. After reacting with Na2SO4, some hydroxyl groups were grafted onto the surface of the PVDF substrate. After modification with methacrylic acid, some acrylate groups were grafted onto the surface of the PVDF substrate. After photopolymerization, a denser PDMS selective layer was formed, resulting in improved pervaporation performance. The total flux of the NaOH-modified PDMS / PVDF substrate was 2294.5, exhibiting excellent pervaporation performance.

[0088] Comparative Example 1:

[0089] (1) Preparation of methacrylate-functionalized PDMS: 11 g of 5000 cP PDMS, 0.12 g of silane coupling agent KH570, 0.1 g of dibutyltin dilaurate, 0.1 g of deionized water, and 11 g of n-heptane were mixed in a 50 ml beaker, weighed, and the weight was recorded. The mixture was stirred at 800 rpm for 24 h at room temperature, weighed again, and n-heptane was added to bring the weight back to the original level. The mixture was stirred until homogeneous.

[0090] (2) Preparation of PDMS / PVDF substrate: Take 3g of methacrylate-functionalized PDMS, add 0.75g of n-heptane, dilute it to a solvent content of 70%, add 1g of photoinitiator 2-hydroxy-2-methylphenylacetone, and stir at 800rpm for 20min at room temperature; then vacuum degas the stirred PDMS casting solution, the thickness of the scraper is 60μm, then pour the PDMS casting solution onto the unmodified PVDF substrate, and use an Elcometer-4340 automatic coating machine to scrape the film. After the film is scraped, immediately transfer the coating to a 365nm ultraviolet lamp for irradiation for 3min, with the film 10cm away from the ultraviolet lamp, to complete the preparation of PDMS / PVDF substrate.

[0091] (3) Pervaporation test: The separation performance of the obtained PDMS / PVDF composite membrane with 0.1wt% phenol was tested using a pervaporation device under heating conditions of 60℃. The pervaporation test results showed that the separation factor of the unmodified PDMS / PVDF composite membrane with 0.1wt% phenol at 60℃ was 7.05, and the flux was 2122.7 g·m³. -2 h -1 .

[0092] (4) Nanoscratch test: The nanoscratch test results of the unmodified PDMS / PVDF composite film are as follows: Figure 9 As shown, the critical load L C1 =16.1mN, L C2 =35.1mN.

[0093] As can be seen from the above, compared with Comparative Example 1, the modified PDMS / PVDF substrate provided by the present invention exhibits superior adhesion of the PDMS selective layer, and the selective layer demonstrates stronger resistance to cracking and delamination, indicating superior stability during pervaporation. Furthermore, the PDMS membrane permeation flux obtained in the examples at a certain temperature was 2256.2-2332.8 g·m³. -2 ·h -1 The separation factor was 8.11-8.53.

[0094] According to the test results, the PDMS / PVDF composite membrane prepared by chemically modified PVDF substrate showed corresponding improvements in phenol separation factor, phenol concentration in permeate, and phenol selectivity. After chemical modification of the PVDF substrate, the separation factor and permeation flux in the pervaporation test were both improved compared to the unmodified version.

[0095] It should be noted that the embodiments described above are merely preferred embodiments of the present invention, used to explain the present invention, and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the terms used herein are descriptive and explanatory, not limiting. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from its scope and spirit. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications having the same function.

Claims

1. A PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, comprising a PVDF substrate sequentially modified with NaOH, Na2SO4, and methacrylic acid, grafted with methacrylate-functionalized PDMS, the molecular structure of which is shown in formula (IX): In formula (IX), m is the number of -CH2-CF2- groups; n represents the number of -CH2CFO- groups; x represents the number of -Si-O- groups; The L of the PDMS / PVDF composite membrane C1 The critical load is 50.2 mN; and / or, the L of the PDMS / PVDF composite membrane is... C2 The critical load is 57.5 mN.

2. The PDMS / PVDF composite membrane according to claim 1, characterized in that, The permeation flux of the PDMS / PVDF composite membrane is 2256.2-2332.8 g·m³. −2 ·h −1 The separation factor was 8.11-8.

53.

3. A method for preparing a PDMS / PVDF composite film based on a chemically modified PVDF substrate as described in claim 1, comprising: Step A: After rinsing the PVDF substrate with deionized water, immerse it in NaOH aqueous solution, and then rinse it with deionized water to obtain the sodium hydroxide modified PVDF substrate. Step B: Immerse the sodium hydroxide-modified PVDF substrate in a Na2SO4 aqueous solution, and then rinse it with deionized water to obtain the Na2SO4-modified PVDF substrate. Step C: Immerse the Na2SO4-modified PVDF substrate in an aqueous solution of methacrylic acid, and then rinse it with deionized water to obtain the methacrylic acid-modified PVDF substrate. Step D: After vacuum degassing the PDMS casting solution, pour it onto the methacrylic acid modified PVDF substrate and perform film coating. Immediately after film coating is completed, transfer the coating to a UV lamp for irradiation to produce a PDMS / PVDF composite film based on a chemically modified PVDF substrate. In step A, the concentration of the NaOH aqueous solution is 0.05 mol / L; the soaking time is 0.5 h. In step B, the concentration of the Na₂SO₄ aqueous solution is 0.07 mol / L; the soaking time is 0.5 h. In step C, the concentration of the aqueous methacrylic acid solution is 0.09 mol / L; the soaking time is 0.5 h.

4. The preparation method according to claim 3, characterized in that, The PDMS casting solution is prepared by adding a photoinitiator 2-hydroxy-2-methylphenylacetone to a heptane solution of methacrylate-functionalized PDMS and stirring at room temperature.

5. The preparation method according to claim 4, characterized in that, In the preparation of PDMS casting solution, the mass ratio of methacrylate-functionalized PDMS to photoinitiator is 3:1; and / or the stirring time is 24 h.

6. The preparation method according to claim 4, characterized in that, The preparation method of methacrylate-functionalized PDMS includes: mixing PDMS, silane coupling agent KH570, dibutyltin dilaurate, water and n-heptane, weighing and recording the mixture, stirring at room temperature, weighing again, adding n-heptane to the original weight, stirring again until homogeneous, and preparing methacrylate-functionalized PDMS.

7. The preparation method according to claim 6, characterized in that, In the preparation of methacrylate-functionalized PDMS, the mass ratio of 5000 cP PDMS to silane coupling agent KH570 was 11:0.12; the mass ratio of PDMS to dibutyltin dilaurate was 11:0.1; the mass ratio of PDMS to water was 11:0.1; and the mass ratio of PDMS to n-heptane was 1:

1.

8. The application of the PDMS / PVDF composite membrane as described in claim 1 or 2, or the PDMS / PVDF composite membrane prepared by the method described in any one of claims 3-7, in a separation process; the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

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