Polydimethylsiloxane (PDMS) / polyvinylidene fluoride (PVDF) composite membrane based on chemically modified PVDF base material

Abstract

The invention relates to a PDMS (Polydimethylsiloxane) / PVDF (Polyvinylidene Fluoride) composite membrane based on a chemically modified PVDF substrate. The PDMS / PVDF composite membrane is formed by sequentially modifying the PVDF substrate by NaOH, HClO and GMA (Glycidyl Methacrylate) and grafting vinyl functionalized PDMS. The invention also relates to a preparation method of the PDMS / PVDF composite film, and the preparation method comprises the following steps: sequentially carrying out NaOH, HClO and GMA three-step GMA modification on the PVDF base material, introducing methacrylate double bonds to the surface of the PVDF base material, further carrying out thermal crosslinking and grafting on the PDMS selection layer, and preparing the PDMS / PVDF composite film, so that the adhesive force of the PDMS selection layer is improved; the cracking and layering phenomena of the PDMS / PVDF composite membrane in practical application can be effectively relieved; meanwhile, the pervaporation ethanol separation performance of the membrane is also greatly improved, and the application prospect of the PDMS membrane in the actual pervaporation process is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate grafted with a PDMS selective layer, and a preparation method and application thereof. Background Art

[0002] As a new type of biofuel, bioethanol has an energy content similar to gasoline and emits less toxic pollutants than fossil fuels, and is expected to alleviate the energy crisis caused by the shortage of fossil fuels. In recent decades, membrane technology has attracted extensive attention in high-selectivity separation operations. Among them, pervaporation technology has broad prospects in the separation of bioethanol due to its high selectivity, low energy consumption, and non-toxicity to microorganisms. Polydimethylsiloxane (PDMS) has the characteristics of low raw material cost and good processing performance, and is widely used in the separation of ethanol, and is known as the benchmark for alcohol-selective separation membranes. Polyvinylidene fluoride (PVDF) has characteristics such as thermal stability and mechanical stability, and is widely used in the preparation of pervaporation membrane materials.

[0003] During the separation operation process, the firmness of the bond between the PDMS selective layer and the base membrane directly determines the service life of the composite membrane. However, when actually using a PDMS membrane for pervaporation separation of ethanol, problems such as weak adhesion of the selective layer are often faced, and the cracking and delamination of the selective layer seriously restrict the wide application of the PDMS membrane in the pervaporation process and the stability of the pervaporation process.

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

[0005] The technical problem to be solved by the present invention is to provide a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate for the problems of weak adhesion of the selective layer, cracking and delamination of the selective layer, etc. when actually using a PDMS membrane for pervaporation separation of ethanol. The PDMS / PVDF composite membrane has strong adhesion of the PDMS selective layer and excellent pervaporation performance, and can be used in the actual pervaporation process.

[0006] To this end, the first aspect of the present invention provides a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, and its molecular structure is shown in formula (IX):

[0007]

[0008] In formula (IX), x is the number of -Si-O- groups.

[0009] In some embodiments of the present invention, the L of the PDMS / PVDF composite membraneC1 The critical load of C2 is 24.89 mN; and / or, the permeation flux of the PDMS / PVDF composite membrane is -2 ·h -1 975 - 1152 g·m

[0010] The second aspect of the present invention provides a method for preparing a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, which is prepared by thermally cross-linking and grafting PDMS to the GMA-modified substrate obtained by sequentially modifying the PVDF substrate with NaOH, HClO, and GMA.

[0011] According to the present invention, the preparation method includes:

[0012] Step A: After rinsing the PVDF substrate with deionized water, soak it in an aqueous NaOH solution, and then rinse it with deionized water to obtain the NaOH-modified PVDF substrate;

[0013] Step B: Soak the NaOH-modified PVDF substrate in an aqueous HClO solution, and then rinse it with deionized water to obtain the HClO-modified PVDF substrate;

[0014] Step C: Soak the HClO-modified PVDF substrate in a GMA methanol solution, and then rinse it with deionized water to obtain the GMA-modified PVDF substrate;

[0015] Step D: After vacuum degassing the PDMS casting solution, pour it onto the GMA-modified PVDF substrate, perform film scraping, and immediately transfer the coating to an oven for heating and curing to prepare a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate.

[0016] Preferably, in Step A, the concentration of the aqueous NaOH solution is 0.05 mol / L; and / or, the soaking time is 0.5 h.

[0017] Preferably, in Step B, the concentration of the aqueous HClO solution is 0.05 mol / L; and / or, the soaking time is 0.5 h.

[0018] Preferably, in Step C, the concentration of the GMA methanol solution is 0.1 mol / L; and / or, the soaking time is 0.5 h.

[0019] Preferably, in Step D, the temperature of the heating and curing is 80 °C.

[0020] According to the present invention, the PDMS casting solution is prepared by mixing vinyl-terminated PDMS with hydrogen-containing silicone oil, n-heptane, and a catalyst to form a PDMS casting reaction solution, and then stirring and reacting at room temperature.

[0021] Preferably, in the PDMS casting reaction solution, the mass ratio of vinyl-terminated PDMS to hydrogen-containing silicone oil is 1:1, the mass ratio of vinyl-terminated PDMS to n-heptane is 1:1, and the mass ratio of vinyl-terminated PDMS to the catalyst is 10:1; and / or, the stirring reaction time is 24 h.

[0022] Preferably, the molecular weight of the vinyl-terminated PDMS is 50000.

[0023] Preferably, the catalyst is a platinum catalyst.

[0024] 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 as described in the second aspect of the present invention in the separation process.

[0025] In some embodiments of the present invention, the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

[0026] The present invention uses a PVDF substrate as the bottom membrane and PDMS as the selective layer, and prepares a PDMS / PVDF composite membrane by modifying the PVDF substrate with GMA in three steps and grafting PDMS, effectively improving the problem of weak adhesion of the selective layer during the pervaporation process. The interface of the modified PDMS / PVDF composite membrane shows excellent adhesion between the PVDF layer and the PDMS layer, which helps to prevent cracking and delamination of the PDMS selective layer. With the increase in the adhesion of the PDMS selective layer, the cracking and delamination phenomena of the PDMS / PVDF composite membrane in practical applications can be effectively alleviated, and at the same time, the performance of pervaporation separation of ethanol is also greatly improved, greatly enhancing the application prospect of the PDMS membrane in the actual pervaporation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To make the present invention easy to understand, the present invention will be described in detail below with reference to the drawings.

[0028] Figure 1 Shows the NaOH modification path of PVDF.

[0029] Figure 2 Shows the HClO modification path of PVDF.

[0030] Figure 3 Shows the GMA modification path of PVDF.

[0031] Figure 4Shows the preparation route of vinyl-functionalized PDMS.

[0032] Figure 5 Shows the preparation route of the PDMS / PVDF composite membrane by thermal cross-linking grafting of PDMS onto the modified PVDF substrate.

[0033] Figure 6 Shows the comparison results of Fourier transform infrared spectra of the PVDF substrate surface before and after NaOH modification.

[0034] Figure 7 Shows the comparison results of Fourier transform infrared spectra of the PVDF substrate surface before and after HClO modification.

[0035] Figure 8 Shows the comparison results of Fourier transform infrared spectra of the PVDF substrate surface before and after GMA modification.

[0036] Figure 9 Shows the typical results of nano-scratch tests on the PDMS / PVDF composite membrane before and after modification; where a is the scratch profile of the unmodified PDMS / PVDF composite membrane, and b is the scratch profile of the modified PDMS / PVDF composite membrane.

[0037] Figure 10 Is a schematic diagram of a pervaporation device. Detailed implementation manners

[0038] To make the present invention easy to understand, the present invention 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 described specific implementation manners. It should also be understood that the terms used herein are only for describing the specific implementation manners and do not represent restrictive.

[0039] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention, the preferred methods and materials are now described.

[0040] In the present invention, the so-called range of dosage concentration, temperature or other physical or chemical properties or characteristics covers or includes the upper and lower limits of the range without special description.

[0041] Ⅰ. Terms

[0042] The term "GMA" as used in the present invention refers to glycidyl methacrylate.

[0043] The term "PDMS" in the present invention refers to polydimethylsiloxane, with the chemical formula (C2H6OSi). n Correspondingly, the "PDMS membrane" refers to a polydimethylsiloxane membrane.

[0044] The term "PVDF" in the present invention refers to polyvinylidene fluoride, with the chemical formula (C2H2F2). n Correspondingly, the "PVDF substrate" refers to a polyvinylidene fluoride substrate.

[0045] The term "MeOH" in the present invention refers to methanol.

[0046] The term "water" in the present invention, without special limitation and explanation, refers to one or more of deionized water, distilled water, and ultrapure water.

[0047] The term "dehydrated water" in the present invention, without special limitation and explanation, refers to deionized water.

[0048] II. Embodiments

[0049] As described above, during the separation operation, the firmness of the bond between the PDMS selective layer and the substrate directly determines the service life of the membrane. The currently used PDMS / PVDF substrate often faces problems such as weak adhesion of the PDMS selective layer, cracking, and delamination of the selective layer during the actual pervaporation process; in view of this, the inventors of the present invention have conducted extensive research on the PVDF substrate and the PDMS membrane.

[0050] The inventors of the present invention have found that by successively modifying the PVDF substrate with NaOH, HClO, and GMA and thermally cross-linking and grafting PDMS, a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate can be prepared. This composite membrane has strong adhesion of the PDMS selective layer and excellent pervaporation performance, and can be used in the actual pervaporation process to achieve efficient separation of target substances (such as ethanol).

[0051] To achieve the present invention, the present invention uses the following method to prepare a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, which includes:

[0052] (1) NaOH modification of the PVDF substrate: After rinsing the PVDF substrate with dehydrated water, soak it in an aqueous NaOH solution with a concentration of 0.05 mol / L for 0.5 h, and then rinse it with dehydrated water to obtain the PVDF substrate modified with NaOH; the NaOH solution is formed by dissolving NaOH in water.

[0053] (2)HClO modification of PVDF substrate: Immerse the NaOH-modified PVDF substrate in an aqueous HClO solution with a concentration of 0.05 mol / L for 0.5 h, and then rinse it thoroughly with deionized water to obtain the HClO-modified PVDF substrate; the aqueous HClO solution is formed by dissolving HClO in water;

[0054] (3)GMA modification of PVDF substrate: Immerse the HClO-modified PVDF substrate in a GMA methanol solution with a concentration of 0.1 mol / L for 0.5 h, and then rinse it thoroughly with deionized water to obtain the GMA-modified PVDF substrate; the GMA methanol solution is formed by dissolving GMA in MeOH;

[0055] (3)Preparation of PDMS / PVDF composite membrane by thermal cross-linking grafting of PDMS onto the modified PVDF substrate: After vacuum degassing the PDMS casting solution, pour it onto the GMA-modified PVDF substrate, perform blade coating, and then transfer it to an oven for heating at 80 °C. After curing, a PDMS / PVDF composite membrane based on the chemically modified PVDF substrate is prepared.

[0056] According to the present invention, the preparation method of the above PDMS casting solution includes:

[0057] Blend vinyl-terminated PDMS, hydrogen-containing silicone oil, catalyst, and n-heptane, weigh and record, stir at room temperature, weigh again and add n-heptane to the original weight, and stir evenly again to prepare the PDMS casting solution.

[0058] (1)React vinyl-terminated PDMS with hydrogen-containing silicone oil by stirring to obtain vinyl-functionalized PDMS;

[0059] (2)Vinyl-functionalized PDMS forms a n-heptane solution of vinyl-functionalized PDMS in n-heptane;

[0060] (3)The n-heptane solution of vinyl-functionalized PDMS is stirred and reacted at room temperature under the action of a catalyst to prepare the PDMS casting solution.

[0061] (3)Under the action of a catalyst, the n-heptane solution of vinyl-functionalized PDMS is stirred and reacted at room temperature to prepare the PDMS casting solution.

[0062] In some specific preferred examples of the present invention, the preparation method of the PDMS casting solution includes: Blend vinyl-terminated PDMS with a molecular weight of 50,000, hydrogen-containing silicone oil, catalyst, and n-heptane, weigh and record, stir at room temperature, weigh again and add n-heptane to the original weight, and stir evenly again to prepare the PDMS casting solution.

[0063] In the above steps for preparing the PDMS casting solution, the mass ratio of vinyl-terminated PDMS with a molecular weight of 50,000 to hydrogen-containing silicone oil is 1:1; the mass ratio of vinyl-terminated PDMS to the catalyst is 10:1; and / or, the mass ratio of vinyl-terminated PDMS to n-heptane is 1:1.

[0064] As can be seen from the above, the preparation route of the PDMS / PVDF composite membrane based on the chemically modified PVDF substrate according to the present invention is specifically as follows:

[0065] (1) The NaOH modification route of the PVDF substrate (Compound I) is as Figure 1 shown. From Figure 1 it can be seen that after hydrolysis modification with the NaOH solution, the surface of the PVDF substrate is defluorinated to form carbon-carbon double bond functional groups, and the PVDF substrate after NaOH modification (Compound II) is obtained;

[0066] (2) The HClO modification route of the PVDF substrate (Compound II) after NaOH modification is as Figure 2 shown. From Figure 2 it can be seen that after modification with the HClO aqueous solution, the carbon-carbon double bond functional groups on the surface of the PVDF substrate react with HClO, and partial hydroxyl functional groups are grafted onto the surface of the PVDF substrate, and the PVDF substrate after HClO modification (Compound III) is obtained;

[0067] (3) The GMA (Compound IV) modification route of the PVDF substrate (Compound III) after HClO modification is as Figure 3 shown. From Figure 3 it can be seen that after modification with the GMA methanol solution, partial hydroxyl functional groups on the surface of the PVDF substrate are transformed into methacrylate functional groups, and the PVDF substrate after GMA modification (Compound V) is obtained;

[0068] (4) The preparation route of vinyl-functionalized PDMS is as Figure 4 shown. From Figure 4 it can be seen that through the hydrosilylation reaction of vinyl-terminated PDMS (Compound VI) with hydrogen-containing silicone oil (Compound VII), vinyl-functionalized PDMS (Compound VIII) is obtained;

[0069] (5) The preparation route of the PDMS / PVDF composite membrane by thermally cross-linking and grafting PDMS onto the modified PVDF substrate is as Figure 5 shown. From Figure 5 it can be seen that the acrylate double bonds on the surface of the PVDF substrate (Compound V) after GMA modification and the acrylate double bonds in vinyl-functionalized PDMS (Compound VIII) undergo thermal cross-linking under heating conditions, and a PDMS selective layer is grafted onto the surface of the PVDF substrate, and the PDMS / PVDF composite membrane is successfully prepared.

[0070] It is easy to understand that the PDMS / PVDF composite membrane based on the chemically modified PVDF substrate prepared by the above preparation method or route is composed of a PVDF substrate modified by GMA in three steps of sodium hydroxide, HClO and GMA and grafted with a PDMS selective layer, and its molecular structure is shown in Formula (IX):

[0071]

[0072] In Formula (IX), x is the number of -Si-O- groups.

[0073] In the present invention, the PVDF substrate is modified by GMA in three steps, namely, NaOH modification, HClO modification and GMA modification. The methacrylate double bond is introduced onto the surface of the PVDF substrate, and then a PDMS selective layer is grafted by thermal crosslinking to prepare a PDMS / PVDF composite membrane, so as to improve the adhesion and pervaporation performance of the PDMS selective layer. Through nano-scratch testing, it is found that the cracking and delamination phenomena of the PDMS selective layer are effectively alleviated, and the adhesion is significantly enhanced; through pervaporation testing, it is found that the PDMS / PVDF composite membrane prepared by grafting PDMS on the chemically modified PVDF substrate improves the separation factor for ethanol.

[0074] The research results show that in the present invention, the critical load of the L of the PDMS / PVDF composite membrane C1 is 24.89 mN; and / or, the critical load of the L of the PDMS / PVDF composite membrane C2 is 52.15 mN; and / or, the permeation flux of the PDMS / PVDF composite membrane is 975 - 1152 g·m -2 ·h -1 , and the separation factor is 10.6 - 12.6.

[0075] The present invention also provides the application of the above PDMS / PVDF composite membrane or the PDMS / PVDF composite membrane prepared by the above preparation method in the separation process.

[0076] In some embodiments of the present invention, the separation process includes a pervaporation separation process and / or a nanofiltration separation process.

[0077] Ⅲ. Examples

[0078] To make the present invention easier to understand, the present invention will be further described in detail below with reference to examples. These examples are only illustrative and are not limited to the application scope of the present invention. The raw materials or components used in the present invention can be obtained through commercial channels or conventional methods without special instructions.

[0079] Example 1: Preparation of PDMS / PVDF Composite Membrane Based on Chemically Modified PVDF Substrate

[0080] (1) NaOH modification of PVDF substrate: Weigh 2 g of NaOH and dissolve it in 1 L of water to prepare a 0.05 mol / L NaOH solution. After rinsing the PVDF substrate with deionized water, immerse it in the 0.05 mol / L NaOH solution for 0.5 h, and then rinse it with deionized water to complete the NaOH modification of the PVDF substrate.

[0081] (2) HClO modification of PVDF substrate: Weigh 26.25 g of HClO and dissolve it in 1 L of water to prepare a 0.05 mol / L HClO aqueous solution. Stir it evenly. Immerse the PVDF substrate modified with 0.05 mol / L NaOH solution for 0.5 h in the 0.05 mol / L HClO aqueous solution for 0.5 h, and then rinse it with deionized water to complete the HClO modification of the PVDF substrate.

[0082] (3) GMA modification of PVDF substrate: Weigh 14.22 g of GMA and dissolve it in 1 L of MeOH to prepare a 0.1 mol / L GMA methanol solution. Stir it evenly. Immerse the PVDF substrate modified with 0.1 mol / L HClO aqueous solution for 0.5 h in the 0.1 mol / L GMA methanol solution for 0.5 h, and then rinse it with deionized water to complete the GMA modification of the PVDF substrate.

[0083] (4) Preparation of vinyl-functionalized PDMS: Blend 10 g of vinyl-terminated PDMS, 10 g of hydrogen-containing silicone oil, 1 g of catalyst, and 10 g of n-heptane, weigh and record. Stir at room temperature, weigh again and add n-heptane to the original weight, and stir evenly again to prepare vinyl-functionalized PDMS. (vinyl-terminated PDMS: hydrogen-containing silicone oil: catalyst: n-heptane = 10:10:1:10) Blend in a 50 ml beaker, weigh and record. Stir at 800 rpm at room temperature for 24 h, weigh again and add n-heptane to the original weight, and stir evenly again to complete the preparation of vinyl-functionalized PDMS.

[0084] (5) Preparation of PDMS / PVDF composite membrane: Take 3 g of the prepared vinyl-functionalized PDMS and stir it at 800 rpm at room temperature for 20 min; then perform vacuum degassing on the stirred PDMS casting solution, with a blade thickness of 60 μm. Then pour the PDMS casting solution onto the modified PVDF substrate, and use an Elcometer-4340 automatic film coater to coat the film. Immediately transfer the coated film to an 80°C oven and heat it for 30 min to complete the preparation of the PDMS / PVDF composite membrane.

[0085] The above PVDF substrates modified by NaOH, HClO, and GMA were characterized by Fourier transform infrared (model: spectrum3, manufacturer: PerkinElmer). The results of NaOH modification are as Figure 6 shown: Figure 6 The significant enhancement of the C═C peak in Figure 7 proved that partial C═C functional groups were generated by hydrolysis modification. The results of HClO modification are as Figure 7 shown: -1 The decrease in the peak area at 1670 cm Figure 8 of the C═C characteristic peak in Figure 8 proved that by modifying the surface of PVDF hydrolyzed by NaOH solution with HClO aqueous solution, HClO reacted with the C═C on its surface, and hydroxyl groups were successfully grafted onto the surface of the PVDF substrate. The results of GMA modification are as -1 shown:

[0086] The adhesion of the PDMS selective layer of the PDMS / PVDF composite membrane was characterized by nano-scratch testing (model: Nst 3 , manufacturer: Anton Paar). The test conditions were that the applied load gradually increased from an initial 3 mN to a maximum load of 60 mN, with an increase rate of approximately 57 mN / min.

[0087] In the nano-scratch test, the critical load of the membrane was determined by observing the friction between the indenter and the membrane during the scratch test loading process. The failure critical load is a quantitative criterion for the adhesion strength of the composite membrane. The L C1 critical load represents the ability of the PDMS layer to withstand lateral loads, reflects the ability to resist crack initiation, and is also called the "lower critical load". The L C2 critical load represents the lateral critical load corresponding to the total peeling of the PDMS layer from the PVDF substrate, and is also called the "higher critical load".

[0088] Figure 9 Typical scratch results of the PDMS / PVDF composite membrane before and after modification are given to compare the adhesion of the PDMS selective layer before and after modification.

[0089] From the test results, it can be seen that the L C1 and L C2Significantly enhanced, the interface of the modified PDMS / PVDF shows excellent adhesion between the PVDF layer and the PDMS layer, which helps to prevent cracking and delamination of the membrane coating. It is observed that the adhesion of the modified PDMS / PVDF composite membrane increases due to the thermal cross-linking grafting of methacrylate bonds between the PDMS selective layer and the PVDF substrate after GMA modification, and the generation of partial chemical bonds significantly enhances the adhesion of the PDMS selective layer.

[0090] Example 2:

[0091] The pervaporation test was carried out on the PDMS / PVDF composite membrane prepared in Example 1.

[0092] Pervaporation test: The obtained cured membrane was tested for the separation performance of 5wt% ethanol using a pervaporation device under heating conditions at 60°C.

[0093] The pervaporation performance of ethanol was tested using a self-made laboratory device at a test temperature of 60°C and an ethanol feed liquid concentration of 5wt%. The specific pervaporation test device is as Figure 10 shown.

[0094] The pervaporation results show that the separation factor of the modified PDMS / PVDF composite membrane is 12.2. After NaOH solution modification, C=C functional groups are generated on the surface of the PVDF substrate. After reaction with HClO, partial hydroxyl groups are grafted on the surface of the PVDF substrate. After GMA modification, partial acrylate groups are grafted on the surface of the PVDF substrate. After thermal cross-linking, a denser PDMS selective layer is formed, resulting in the improvement of pervaporation performance. The total flux of the PDMS / PVDF substrate after NaOH modification is 1042 g·m -2 ·h -1 , showing excellent pervaporation performance.

[0095] Comparative Example 1:

[0096] (1) Preparation of vinyl-functionalized PDMS: 10 g of vinyl-terminated PDMS, 10 g of hydrogen-containing silicone oil, 1 g of catalyst, and 10 g of n-heptane were blended, weighed and recorded, stirred at room temperature, weighed again and added n-heptane to the original weight, and stirred evenly again to prepare vinyl-functionalized PDMS. (Vinyl-terminated PDMS: hydrogen-containing silicone oil: catalyst: n-heptane = 10:10:1:10) Blended in a 50 ml beaker, weighed and recorded. Stirred at 800 rpm at room temperature for 24 h, weighed again and added n-heptane to the original weight, and stirred evenly again.

[0097] (2) Preparation of PDMS / PVDF composite membrane: 3 g of the prepared vinyl-functionalized PDMS was stirred at 800 rpm for 20 min at room temperature; the stirred PDMS casting solution was then vacuum degassed with a scraper thickness of 60 μm, and then the PDMS casting solution was poured onto an unmodified PVDF substrate and scraped using an Elcometer-4340 automatic coating machine. After scraping, the coating was immediately transferred to an 80°C oven and heated for 30 min to complete the preparation of the PDMS / PVDF composite membrane.

[0098] (3) Pervaporation test: The obtained PDMS / PVDF composite membrane was heated at 60°C and the separation performance of 5 wt% ethanol was tested by a pervaporation device. The pervaporation test results showed that the separation factor of the unmodified PDMS / PVDF composite membrane for separating 5 wt% ethanol at 60°C was 9.5, and the flux was 942 g·m -2 h -1 .

[0099] (4) Nanoscratch test: The nanoscratch test results of the unmodified PDMS / PVDF composite membrane are as follows: Figure 9 As shown, the critical load L C1 =12.59mN, L C2 =19.65mN.

[0100] From the above, it can be seen that compared with Comparative Example 1, the modified PDMS / PVDF substrate provided by the present invention has better adhesion of the PDMS selective layer, and the selective layer has stronger resistance to cracking and delamination, indicating that it has better stability during the pervaporation process. In addition, the permeation flux of the PDMS membrane obtained in the embodiment at a certain temperature is 975-1152 g·m -2 ·h -1 , the separation factor is 10.6-12.6.

[0101] According to the test results, the PDMS / PVDF composite membrane prepared with GMA-modified PVDF substrate has correspondingly improved separation factor for ethanol, ethanol concentration in the permeate and selectivity for ethanol. After the PVDF substrate is modified by GMA, the separation factor and permeation flux of the pervaporation test are improved compared with the unmodified one.

[0102] It should be noted that the above-described embodiments are only preferred embodiments of the present invention for explaining the present invention and do not constitute any limitation to the present invention. The present invention has been described by reference to the exemplary embodiments, but it should be understood that the words used therein are descriptive and explanatory terms rather than limiting terms. Modifications may be made to the present invention within the scope of the claims of the present invention as provided, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, the molecular structure of which is shown in formula (IX): In formula (IX), x is the number of -Si-O- groups.

2. The PDMS / PVDF composite membrane according to claim 1, characterized in that The L of the PDMS / PVDF composite membrane C1 The critical load is 24.89 mN; and / or, the L C2 The critical load is 52.15 mN; and / or the permeation flux of the PDMS / PVDF composite membrane is 975-1152 g·m -2 ·h -1 , the separation factor is 10.6-12.

6.

3. A method for preparing a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate, which is prepared by thermally cross-linking and grafting PDMS onto a GMA-modified PVDF substrate obtained by sequentially modifying the PVDF substrate with NaOH, HClO and GMA.

4. The preparation method according to claim 3, characterized in that: The preparation method comprises: Step A, after rinsing the PVDF substrate with deionized water, immersing it in a NaOH aqueous solution, and then rinsing it with deionized water to obtain a NaOH-modified PVDF substrate; Step B, immersing the NaOH-modified PVDF substrate in an HClO aqueous solution, and then rinsing with deionized water to obtain an HClO-modified PVDF substrate; Step C, immersing the HClO-modified PVDF substrate in a GMA methanol solution, and then rinsing with deionized water to obtain a GMA-modified PVDF substrate; Step D, after vacuum degassing, pour the PDMS casting solution onto the GMA-modified PVDF substrate, perform film scraping, and then transfer to an oven for heating and curing to prepare a PDMS / PVDF composite membrane based on a chemically modified PVDF substrate.

5. The preparation method according to claim 4, characterized in that: In step A, the concentration of the NaOH aqueous solution is 0.05 mol / L; and / or, the soaking time is 0.5 h; and / or, in step B, the concentration of the HClO aqueous solution is 0.05 mol / L; and / or, the soaking time is 0.5 h; and / or, in step C, the concentration of the GMA methanol solution is 0.1 mol / L; and / or, the soaking time is 0.5 h; And / or, in step D, the temperature of heating and curing is 80°C.

6. The preparation method according to claim 4 or 5, characterized in that: The PDMS film casting liquid is prepared by mixing vinyl-terminated PDMS with hydrogen-containing silicone oil, n-heptane and a catalyst to form a PDMS film casting reaction liquid, and then stirring and reacting the mixture at room temperature.

7. The preparation method according to claim 6, characterized in that: In the PDMS film casting reaction solution, the mass ratio of vinyl-terminated PDMS to hydrogen-containing silicone oil is 1:1; and / or, the mass ratio of vinyl-terminated PDMS to n-heptane is 1:1; and / or, the mass ratio of the vinyl-terminated PDMS to the catalyst is 10:1; and / or, the stirring reaction time is 24 hours.

8. The preparation method according to claim 7, characterized in that: The molecular weight of the vinyl terminated PDMS is 30,000-100,000; and / or the catalyst is a platinum catalyst.

9. Use of the PDMS / PVDF composite membrane as claimed in claim 1 or 2 or the PDMS / PVDF composite membrane prepared by the method according to any one of claims 3 to 8 in a separation process.

10. The use according to claim 9, characterized in that: The separation process includes a pervaporation separation process and / or a nanofiltration separation process.

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