Bonding fiber for a separation membrane support, method for producing, and use

Abstract

The present application provides a kind of separating membrane support body with adhesive fiber, preparation method and application.The polymerization monomer of the adhesive fiber includes terephthalic acid, ethylene glycol, maleimide and carbon nanotube;By the bonding link of PET staple fiber through dynamic covalent bond, polyester fiber with larger molecular weight is formed;In the state of heating processing, dynamic covalent bond breaks, adhesive fiber becomes multiple short fibers, increases fluidity, facilitates plasticity and processing;When cooling forming, dynamic covalent bond restores, short fiber and carbon nanotube are bonded again with covalent bond, form dense crosslinking network, enhance the mechanical properties of overall structure.

Description

Technical Field

[0001] This invention relates to the field of separation membrane support technology, and in particular to a bonding fiber for a separation membrane support, its preparation method, and its application. Background Technology

[0002] With the rapid development of membrane separation technology, separation membranes are widely used in various fields such as seawater desalination, wastewater treatment, biomedicine, petrochemicals, and food and beverage processing. This places higher demands on the structure and performance of membrane supports.

[0003] In existing separation membrane support preparation technologies, low-melting-point polyester (PET) fibers or other low-melting-point binders are typically used as binders. These binders can melt at lower temperatures, facilitating the formation of a uniform adhesive layer between fibers or particles. This layer penetrates into the microporous structure of the matrix material and forms a solid fiber network upon cooling, thereby enhancing the overall thermal stability and mechanical strength.

[0004] However, low-melting-point binder components are prone to thermal deformation during the drying process and subsequent high-temperature operation, thus affecting the overall performance of the separation membrane. For example, their low melting point still makes them susceptible to localized melting, shrinkage, or morphological changes at high temperatures, which in turn affects the stability and pore structure of the separation membrane support. Controlling the melting and cooling rates of the binder fibers during drying or curing is also crucial; too fast or too slow rates can lead to uneven bonding between fibers, forming weak connection points. Under certain high-temperature operating conditions, such as prolonged exposure to high-temperature media during separation, the binder fibers may gradually degrade due to repeated thermal cycling, reducing the overall mechanical properties and separation efficiency.

[0005] In particular, some high-temperature filtration fields (such as textile printing and dyeing wastewater treatment, juice purification, boiler water treatment, etc.) require the use of high-temperature resistant separation membranes. However, most separation membrane supports currently on the market can only be used at lower temperatures. Therefore, the development of high-temperature resistant separation membrane supports is of great significance. Summary of the Invention

[0006] The purpose of this invention is to provide a bonding fiber for a separation membrane support, a preparation method, and its application, thereby improving the crystallinity of the bonding fiber after processing and ensuring the mechanical properties and separation effect of the overall structure when used in a high-temperature environment.

[0007] The technical solution of the present invention:

[0008] In a first aspect, the present invention provides a bonding fiber for a separation membrane support, wherein the polymer monomers of the bonding fiber include terephthalic acid, ethylene glycol, maleimide and carbon nanotubes.

[0009] Furthermore, the main chain structure of the bonding fiber is shown in Formula 1:

[0010]

[0011] Where * represents the site where the main chain is dynamically covalently bonded to the carbon nanotube; a is selected from any positive integer between 50 and 140.

[0012] The value of 'a' directly affects the molecular weight of the bonded fiber after chain breakage. The smaller 'a' is, the lower the molecular weight of the bonded fiber formed after dynamic covalent bond breakage under heating, which is easier to bond, but too low a value is not conducive to processing. The larger 'a' is, the closer the molecular weight of the bonded fiber formed after dynamic covalent bond breakage under heating is to the molecular weight of the original PET fiber, which is not conducive to bonding, but is conducive to processing.

[0013] More preferably, a is 100.

[0014] In some embodiments, the carbon nanotubes are selected from any one or more combinations of single-walled carbon nanotubes, multi-walled carbon nanotubes, or modified carbon nanotubes.

[0015] sp of carbon nanotubes 2 The hybrid carbon skeleton contains conjugated double bonds, which can act as dienes or diephiles to undergo DA reactions with the double bonds on maleimide, forming dynamic covalent bonds. The breaking temperature of this dynamic covalent bond is 100℃-150℃. At 150℃ or higher, all DA bonds can be broken, resulting in a decrease in the molecular weight and adhesion of the bonding fiber, while increasing its fluidity and adhesion. After processing, stretching and cooling, due to the optimization of carbon nanotube crystallization and the orientation effect of stretching, will shift the reaction equilibrium towards the addition direction after cooling, thereby partially or completely restoring the broken bonds, increasing the molecular weight and crystallinity, and ensuring the mechanical properties of the overall structure.

[0016] In some embodiments, the mass ratio of carbon nanotubes to maleimide is 0.5-1:1. Textile dyeing wastewater treatment typically uses temperatures of 30-50℃, fruit juice purification typically uses temperatures of 50-90℃, and boiler water treatment typically uses temperatures of 80-110℃. When the aforementioned bonding fibers are used in these process environments, the dynamic covalent bond breaking temperature is not reached, and the mechanical properties of the bonding fibers can still be maintained. When the operating environment is more demanding, such as at higher temperatures of 200-300℃, the addition of carbon nanotubes increases the crystallinity of the bonding fibers and, as a rigid filler, can withstand stress, directly improving the rigidity and strength of the composite material while maintaining the integrity of the overall structure.

[0017] In a second aspect, the present invention also provides a method for preparing the bonding fiber, specifically comprising the following steps:

[0018] S1: Add terephthalic acid and ethylene glycol to the reactor, add a catalyst, and heat to carry out the reaction;

[0019] S2: Adjust the reaction temperature to 160-200℃, add maleimide, and stir the reaction while maintaining the temperature.

[0020] S3: Acidify carbon nanotubes and add the treated carbon nanotubes to a solvent, then ultrasonically disperse them to obtain a dispersion; add the dispersion to the reaction product of step S2, keep warm and stir the reaction, after the reaction is completed, slowly cool down to room temperature, add methanol to precipitate the polymer, vacuum dry, melt spin to obtain the bonding fiber.

[0021] In some embodiments, the molar ratio of terephthalic acid to ethylene glycol is 1:1.2-2.

[0022] In some embodiments, the heating temperature of S1 is 200-250°C.

[0023] In some embodiments, the heat preservation time of S2 is 1-2 hours.

[0024] In some embodiments, the reaction temperature of the heat-preserving and stirring reaction in S3 is 150-200°C, and the reaction time is 1-4 hours.

[0025] In a third aspect, the present invention also provides the use of bonding fibers in a separation membrane support.

[0026] Beneficial effects:

[0027] 1. By linking PET short fibers through dynamic covalent bonds, polyester bonded fibers with larger molecular weights are formed. Under heat processing, the dynamic covalent bonds break, and the bonded fibers become multiple PET short fibers. The molecular weight decreases, increasing fluidity and facilitating plasticity and bonding. When cooled and molded, the dynamic covalent bonds are restored, and the short fibers and carbon nanotubes are re-bonded by covalent bonds to form a dense cross-linked network, which enhances the mechanical properties of the overall structure.

[0028] 2. Below the dynamic covalent bond breakage temperature, the molded product can maintain its original state; above the dynamic covalent bond breakage temperature, carbon nanotubes, as rigid fillers, can bear stress, directly improve the rigidity and strength of the composite material, play a role in maintaining the integrity of the overall structure, and improve the overall performance of the composite material at high temperatures. Attached Figure Description

[0029] Figure 1 The infrared spectrum of the bonding fiber prepared in Example 1 of this invention. Detailed Implementation

[0030] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0031] Unless otherwise specified, all chemical reagents used in this invention are commercially available analytical grade. The multi-walled carbon nanotubes and single-walled carbon nanotubes were purchased from Shandong Dazhan Nanomaterials Co., Ltd.

[0032] Example 1

[0033] S1: Add 10 mol of terephthalic acid and 12 mol of ethylene glycol to the reactor, add 0.02 mol of tetrabutyl titanate, heat to 240℃ and react for 4 hours, while slowly passing nitrogen gas to remove moisture; ensure that the degree of polymerization (DP) is 100 by GPC test;

[0034] S2: Adjust the reaction temperature to 200℃, add 4g of maleimide, and stir the reaction for 2h. The product is prepared by pressing it into a tablet with KBr and performing infrared spectroscopy analysis to detect the changes in C=O (1714cm-1) and C=C (1635cm-1) signals, ensuring successful grafting of maleimide.

[0035] S3: Weigh 2g of multi-walled carbon nanotubes and activate them by stirring at 550rpm for 10min in 10mL of dilute sulfuric acid. Wash the activated carbon nanotubes until neutral, add them to 10mL of xylene, and ultrasonically disperse to obtain a stable dispersion. Add the dispersion to the reaction product of step S2, and react at 200℃ with stirring for 4h. After the reaction is complete, slowly cool to room temperature, add methanol to precipitate the polymer, evaporate the solvent, wash, vacuum dry, and melt spin to obtain the bonded fiber. Infrared spectrum as shown. Figure 1 As shown.

[0036] Example 2

[0037] Except that the amount of multi-walled carbon nanotubes added was changed to 4g, it was prepared in the same way as in Example 1.

[0038] Example 3

[0039] Except for controlling DP to be 50, it was made in the same way as in Example 1.

[0040] Example 4

[0041] Except for controlling DP to be 140, it was made in the same way as in Example 1.

[0042] Example 5

[0043] Except that multi-walled carbon nanotubes were replaced with single-walled carbon nanotubes, they were prepared in the same manner as in Example 1.

[0044] Comparative Example 1

[0045] Except that the amount of multi-walled carbon nanotubes added was changed to 1g, it was prepared in the same way as in Example 1.

[0046] Comparative Example 2

[0047] Except that the amount of multi-walled carbon nanotubes added was changed to 6g, it was prepared in the same way as in Example 1.

[0048] Comparative Example 3

[0049] Except for adjusting S3 to the following steps, it is made in the same way as in Example 1.

[0050] S3: Weigh 2g of multi-walled carbon nanotubes and activate them by stirring at 550rpm for 10min in 10mL of dilute sulfuric acid. Wash the activated carbon nanotubes until neutral and add them to the reaction product of step S2. Melt spin the product to obtain the bonding fiber.

[0051] Comparative Example 4

[0052] Except for controlling DP to be 40, it was made in the same way as in Example 1.

[0053] Comparative Example 5

[0054] Except for controlling DP to be 200, it was made in the same way as in Example 1.

[0055] The separation membrane support was prepared using a wet papermaking process: The main fiber (PET, 5mm in length, melting point 255℃, heat distortion temperature 190℃) and the aforementioned bonding fiber were mixed in a mass ratio of 6:4, dispersed in water, and stirred in a dissociator to form a fiber solution with a concentration of 0.02%. This solution was then passed through an inclined wire mesh to form wet paper, which was dried using a Yankee cylinder with a surface temperature of 110 degrees Celsius to obtain a 60g / m³ membrane support. 2 The sheets are dried at 100℃ to form a dry mesh, then placed on a flat hot press and hot-pressed at 210℃ and 13 MPa for 40 seconds. After heating and pressurizing, the membrane is cooled to form a separation membrane support.

[0056] The following tests were performed on the above-mentioned support structure:

[0057] 1. Thickness test method: The "thickness" of the semi-permeable membrane support material shall be determined according to the method of GB / T 451.3-2002.

[0058] 2. Air permeability test method: The air permeability of the semi-permeable membrane support material is measured using a Fraser type testing machine in accordance with JIS L1096-2010.

[0059] 3. Curling Test Method: When the semipermeable membrane is coated onto the coating surface of the semipermeable membrane support material, observe whether it curls towards the coating surface. The curling property of the semipermeable membrane support material is observed by the naked eye. If no curling is found, mark it as "×"; if curling occurs, mark it as "√".

[0060] 4. Tensile strength test method: The tensile strength of the semipermeable membrane support material shall be determined in accordance with the method of GB / T 12914-2008.

[0061] 5. Heat distortion test method: Immerse the material in hot water at 100℃ and dimethyl silicone oil at 180℃ for 30 minutes respectively, and observe the heat distortion.

[0062] 6. Processing status: Observe and record the processing status.

[0063] The test results are shown in Table 1.

[0064] Table 1

[0065]

[0066] Note: L represents an embodiment, for example, L1 represents embodiment 1; D represents a comparative example, for example, D1 represents comparative example 1.

[0067] As shown in Table 1, the support structure made by mixing the bonding fiber and PET fiber provided by the present invention has excellent support performance at high temperature, and can improve mechanical properties with a small unit area weight and thin thickness.

[0068] The comparison between the examples and Comparative Examples 1 and 2 shows that by adjusting the ratio of carbon nanotubes to maleimide, the crosslinking density can be controlled, which is beneficial for controlling the structure of porous membranes, effectively preventing excessive leakage of casting solution, reducing pinholes and through-printing phenomena, and simultaneously adjusting the mechanical properties of the support.

[0069] By comparing the examples with Comparative Examples 4-5, it can be seen that the molecular weight of the bonding fiber should not be too large or too small. If it is too small, although it has good fluidity and strong adhesion, it is not easy to process and it is easy to stick together during hot pressing, resulting in uneven and rough surface of the support. If it is too large, the bonding performance is generally poor, but it is easy to peel off overall.

[0070] This invention can also be implemented in various other ways. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A bonding fiber for a separation membrane support, characterized in that, The polymer monomers of the bonding fiber include terephthalic acid, ethylene glycol, maleimide, and carbon nanotubes; the main chain structure of the bonding fiber is shown in Formula 1: Formula 1; Where * represents the site where the main chain is dynamically covalently bonded to the carbon nanotube; a is selected from any positive integer between 50 and 140.

2. The bonding fiber according to claim 1, characterized in that, The carbon nanotubes are selected from any one or more combinations of single-walled carbon nanotubes, multi-walled carbon nanotubes, or modified carbon nanotubes.

3. The bonding fiber according to claim 1, characterized in that, The mass ratio of carbon nanotubes to maleimide is 0.5-1:

1.

4. The method for preparing the bonding fiber according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Add terephthalic acid and ethylene glycol to the reactor, add a catalyst, and heat to carry out the reaction; S2: Adjust the reaction temperature to 160-200℃, add maleimide, and stir the reaction while maintaining the temperature. S3: Acidify carbon nanotubes and add the treated carbon nanotubes to a solvent, then ultrasonically disperse them to obtain a dispersion; add the dispersion to the reaction product of step S2, keep warm and stir the reaction, after the reaction is completed, slowly cool down to room temperature, add methanol to precipitate the polymer, vacuum dry, melt spin to obtain the bonding fiber.

5. The method for preparing the bonding fiber according to claim 4, characterized in that, The molar ratio of terephthalic acid to ethylene glycol is 1:1.2-2.

6. The method for preparing the bonding fiber according to claim 4, characterized in that, The heating temperature in step S1 is 200-250℃.

7. The method for preparing the bonding fiber according to claim 4, characterized in that, The heat preservation time in step S2 is 1-2 hours.

8. The method for preparing the bonding fiber according to claim 4, characterized in that, The reaction temperature of the heat preservation and stirring reaction in step S3 is 150-200℃, and the reaction time is 1-4h.

9. The application of the bonding fiber according to any one of claims 1-3 or the bonding fiber prepared by the preparation method according to any one of claims 4-8 on a separation membrane support.

Images