Bonding fiber for separation membrane supporting body, preparation method and application

Abstract

The invention provides a viscose fiber for a separation membrane support, a preparation method and an application. Polymeric monomers of the adhesive fibers comprise terephthalic acid, ethylene glycol, maleimide and carbon nanotubes; pET short fibers are bonded and linked through dynamic covalent bonds to form polyester fibers with larger molecular weight; in a heating processing state, dynamic covalent bonds are broken, and the bonded fibers become a plurality of short fibers, so that the flowability is improved, and plasticity and processing are facilitated; during cooling forming, the dynamic covalent bonds are restored again, the short fibers and the carbon nanotubes are bonded through the covalent bonds again, a compact cross-linked network is formed, and the mechanical performance of the overall structure is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membrane supports, and particularly relates to a bonding fiber for a separation membrane support, a preparation method and an application thereof. Background Art

[0002] With the rapid development of membrane separation technology, separation membranes are widely used in various fields such as seawater desalination, wastewater treatment, biomedical, petrochemical, food and beverage processing, etc. Higher requirements are put forward for the structure and performance of the separation membrane support in various fields such as biomedical, petrochemical, food and beverage processing. Higher requirements are put forward for the structure and performance of the separation membrane support in various fields such as biomedical, petrochemical, food and beverage processing. Higher requirements are put forward for the structure and performance of the separation membrane support in various fields such as biomedical, petrochemical, food and beverage processing.

[0003] In the existing preparation technologies of separation membrane supports, low-melting-point polyester (PET) fibers or other low-melting-point bonding substances are usually used as binders, which can be melted at a lower temperature, facilitating the formation of a uniform bonding layer between fibers or particles, penetrating into the microporous structure of the matrix material, and forming a solid fiber network after cooling, thereby enhancing the overall thermal stability and mechanical strength.

[0004] However, the low-melting-point bonding components are prone to thermal deformation during the drying process and in the later high-temperature use environment, thus affecting the use effect of the entire separation membrane. For example, its low-melting-point characteristic still makes it prone to local melting, shrinkage or morphological changes in a high-temperature environment, thereby affecting the stability and pore structure of the separation membrane support; during the drying or curing process of the bonding fiber, the control of the melting and cooling rates is also very crucial, too fast or too slow may lead to uneven bonding between fibers, forming weak connection points; under some high-temperature operating conditions, such as being exposed to high-temperature media for a long time during the separation process, the bonding fiber may gradually degrade due to repeated thermal cycles, reducing the mechanical properties and separation effect of the overall structure, etc.

[0005] Especially in some high-temperature filtration fields (such as textile and printing wastewater treatment, fruit juice purification, boiler water treatment, etc.), separation membranes with high temperature resistance are required, while most of the separation membrane supports on the market at present can only be used at lower temperatures. Therefore, the development of separation membrane supports with high temperature resistance is of crucial significance. Summary of the Invention

[0006] The purpose of the present invention is to provide a bonding fiber for a separation membrane support, a preparation method and an application thereof, to improve the crystallinity of the bonding fiber after processing, and ensure 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, and the polymerization monomers of the bonding fiber include terephthalic acid, ethylene glycol, maleimide, and carbon nanotubes.

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

[0010]

[0011] Wherein, * is the site where the main chain is dynamically covalently bonded to the carbon nanotube; a is any positive integer selected from 50 - 140.

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

[0013] Further 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] The sp 2 hybrid carbon skeleton of the carbon nanotube contains conjugated double bonds and can undergo a D - A reaction with the double bond on maleimide as a dienophile or a diene to form a dynamic covalent bond. The breaking temperature of this dynamic covalent bond is 100°C - 150°C. When the temperature is 150°C or higher, all DA bonds can break, the molecular weight and adhesiveness of the bonding fiber decrease, and the fluidity increases. When the processing is completed, after stretching and cooling, with the crystallization optimization of the carbon nanotube and the orientation effect of stretching, the reaction equilibrium will shift towards the addition direction during cooling, so that the broken bonds are partially or completely restored, improving the molecular weight and crystallinity and ensuring the mechanical properties of the overall structure.

[0016] In some embodiments, the mass ratio of the carbon nanotubes to maleimide added is 0.5 - 1:1. The commonly used temperature for textile printing and dyeing wastewater treatment is 30 - 50°C, the commonly used temperature for fruit juice purification is 50 - 90°C, and the commonly used temperature for boiler water treatment is 80 - 110°C. When the above-mentioned bonding fiber is used in these process environments, the breaking temperature of the dynamic covalent bond is not reached, and the mechanical properties of the bonding fiber can still be maintained; when the use environment is more severe, such as a higher temperature of 200 - 300°C, due to the addition of carbon nanotubes, the crystallinity of the bonding fiber is improved, and as a rigid filler, it can bear stress, directly enhancing the rigidity and strength of the composite material and maintaining the integrity of the overall structure.

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

[0018] S1: Add terephthalic acid and ethylene glycol into a reactor, add a catalyst, and heat for reaction;

[0019] S2: Adjust the reaction temperature to 160 - 200 °C, add maleimide, and keep the temperature for stirring reaction;

[0020] S3: Acidify the carbon nanotubes, add the treated carbon nanotubes into a solvent, and ultrasonically disperse to obtain a dispersion; add the dispersion into the reaction product of step S2, keep the temperature for stirring reaction, slowly cool to room temperature after the reaction, precipitate the polymer in methanol, vacuum dry, and melt spin to obtain the bonding fiber.

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

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

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

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

[0025] In a third aspect, the present invention also provides an application of the bonding fiber on a separation membrane support.

[0026] Beneficial effects:

[0027] 1. By bonding and linking PET short fibers through dynamic covalent bonds to form polyester bonding fibers with a larger molecular weight; under the heating and processing state, the dynamic covalent bonds break, and the bonding fibers become multiple PET short fibers, with the molecular weight decreasing and the fluidity increasing, facilitating plasticity and bonding; when cooling and forming, 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, enhancing the mechanical properties of the overall structure.

[0028] 2. When the temperature is lower than the dynamic covalent bond breaking temperature, the formed product can maintain its original state; when the temperature is higher than the dynamic covalent bond breaking temperature, the carbon nanotubes, as rigid fillers, can bear stress, directly improving the rigidity and strength of the composite material, playing a role in maintaining the integrity of the overall structure, and overall improving the service performance of the composite material at high temperatures. Description of the drawings

[0029] Figure 1This is the infrared spectrum of the bonded fiber prepared in Example 1 of the present invention. Detailed implementation mode

[0030] The present invention will be described below in conjunction with specific implementation schemes. It should be noted that the following examples are examples of the present invention, only for explaining the present invention, and not for limiting the present invention. Without departing from the gist or scope of the present invention, other combinations and various improvements within the concept of the present invention can be made.

[0031] Unless otherwise specified, the chemical reagents used in the present invention are all ordinary commercially available analytical pure. The multi-walled carbon nanotubes and single-walled carbon nanotubes are all purchased from Shandong Dazhan Nano Materials Co., Ltd.

[0032] Example 1

[0033] S1: Take 10 mol of terephthalic acid and 12 mol of ethylene glycol and add them to the reactor. Add 0.02 mol of tetrabutyl titanate, heat to 240 °C and react for 4 h, while introducing slow-flowing nitrogen to remove moisture; ensure that the degree of polymerization (DP) is 100 through GPC testing;

[0034] S2: Adjust the reaction temperature to 200 °C, add 4 g of maleimide, keep warm and stir for 2 h; through preparation, press the product with KBr tablets and conduct infrared spectrum analysis to detect the signal changes of C=O (1714 cm-1) and C=C (1635 cm-1) to ensure the successful grafting of maleimide;

[0035] S3: Weigh 2 g of multi-walled carbon nanotubes, stir them in 10 mL of dilute sulfuric acid at a speed of 550 rpm for 10 min for activation, wash the activated carbon nanotubes to neutrality, add them to 10 ml of xylene, and ultrasonically disperse to obtain a stable dispersion; add the dispersion to the reaction product in step S2, keep warm and stir at 200 °C for 4 h, after the reaction, slowly cool to room temperature, add it to methanol to precipitate the polymer, evaporate the solvent, wash, vacuum dry, and melt spin to obtain the bonded fiber. The infrared spectrum is as Figure 1 shown.

[0036] Example 2

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

[0038] Example 3

[0039] Except that the DP is controlled to be 50, it is made in the same way as in Example 1.

[0040] Example 4

[0041] Except that the DP is controlled to be 140, it is made in the same way as in Example 1.

[0042] Example 5

[0043] It was prepared in the same manner as in Example 1 except that multi-walled carbon nanotubes were replaced with single-walled carbon nanotubes.

[0044] Comparative Example 1

[0045] It was prepared in the same manner as in Example 1 except that the addition amount of multi-walled carbon nanotubes was changed to 1 g.

[0046] Comparative Example 2

[0047] It was prepared in the same manner as in Example 1 except that the addition amount of multi-walled carbon nanotubes was changed to 6 g.

[0048] Comparative Example 3

[0049] It was prepared in the same manner as in Example 1 except that S3 was adjusted to the following steps.

[0050] S3: Weigh 2 g of multi-walled carbon nanotubes, activate them by fully stirring in 10 mL of dilute sulfuric acid at a rotation speed of 550 rpm for 10 min, wash the activated carbon nanotubes to neutrality, add them to the reaction product in step S2, and perform melt spinning to obtain the binder fiber.

[0051] Comparative Example 4

[0052] It was prepared in the same manner as in Example 1 except that DP was controlled to be 40.

[0053] Comparative Example 5

[0054] It was prepared in the same manner as in Example 1 except that DP was controlled to be 200.

[0055] A separator membrane support was prepared by a wet papermaking process: The main fiber (PET, length 5 mm, melting point 255 °C, heat distortion temperature 190 °C) and the above binder fiber were mixed in a mass ratio of 6:4, dispersed in water, stirred and dispersed by a disintegrator into a fiber solution with a concentration of 0.02%, formed a wet paper through a inclined screen, dried it with a Yankee cylinder with a surface of 110 degrees to obtain a sheet with a basis weight of 60 g / m 2 After drying at 100 °C to form a dry web, it was placed on a flat hot press, hot pressed at 210 °C and 13 Mpa for 40 s, and cooled after heat pressing treatment to form a separator membrane support.

[0056] The following tests were carried out on the above support:

[0057] 1. Thickness test method: The "thickness" of the semipermeable membrane support material was measured 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 Frazier-type testing machine in accordance with JIS L1096-2010.

[0059] 3. Curling condition test method: When coating the semi-permeable membrane on the coated surface of the semi-permeable membrane support material, observe whether it curls towards the coated surface side. The curling property of the semi-permeable membrane support material is observed by the naked eye. If no curling is found, it is marked as "×", and if curling occurs, it is marked as "√".

[0060] 4. Tensile strength test method: The "tensile strength" of the semi-permeable membrane support material is measured in accordance with the method of GB / T 12914-2008.

[0061] 5. Thermal deformation test method: Immerse the material in 100 °C hot water and dimethyl silicone oil at 180 °C for 30 min respectively, and observe the thermal deformation situation.

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

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

[0064] Table 1

[0065]

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

[0067] It can be seen from Table 1 that the support body made by mixing the bonding fiber and PET fiber provided by the present invention has excellent support performance at high temperature, and can achieve the improvement of mechanical properties under the conditions of smaller unit area weight and thinner thickness.

[0068] It can be seen from the comparison between the examples and Comparative Examples 1-2 that by adjusting the ratio of carbon nanotubes to maleimide, the crosslinking density can be controlled, which is beneficial to regulating the structure of the porous membrane, effectively preventing excessive leakage of the casting solution, and reducing the occurrence of pinholes and printing through phenomena; at the same time, the mechanical properties of the support body are adjusted.

[0069] It can be seen from the comparison between the examples and Comparative Examples 4-5 that the molecular weight of the bonding fiber should not be too large or too small. If it is too small, although the fluidity is good and the bonding property is strong, it is not easy to process, and it is easy to adhere during hot pressing, resulting in uneven and non-smooth surface of the support body; if it is too large, the bonding performance is average, but it is easy to peel off as a whole.

[0070] The present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention. However, these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A bonding fiber for a separation membrane support, characterized in that, The polymerization monomers of the bonding fiber include terephthalic acid, ethylene glycol, maleimide, and carbon nanotubes.

2. The bonded fiber according to claim 1, wherein The main chain structure of the bonding fiber is shown in Formula 1: Wherein, * is the site for dynamic covalent bond connection between the main chain and the carbon nanotubes; a is any positive integer selected from 50 - 140.

3. The bonded fiber according to claim 1, wherein The carbon nanotubes are selected from any one or more combinations of single-walled carbon nanotubes, multi-walled carbon nanotubes, or modified carbon nanotubes.

4. The bonded fiber according to claim 1, characterized in that, The mass ratio of the addition of carbon nanotubes to maleimide is 0.5 - 1:

1.

5. The preparation method of the bonded fiber according to any one of claims 1-4, characterized in that, It includes the following steps: S1: Take terephthalic acid and ethylene glycol and add them into a reactor, add a catalyst, and heat for reaction; S2: Adjust the reaction temperature to 160 - 200 °C, add maleimide, and keep the temperature and stir for reaction; S3: Acidify the carbon nanotubes, add the treated carbon nanotubes into a solvent, and ultrasonically disperse to obtain a dispersion; add the dispersion into the reaction product of step S2, keep the temperature and stir for reaction, slowly cool to room temperature after the reaction, precipitate the polymer in methanol, vacuum dry, and melt spin to obtain the bonding fiber.

6. The preparation method of the bonded fiber according to claim 5, wherein The molar ratio of the addition of terephthalic acid to ethylene glycol is 1:1.2 - 2.

7. The preparation method of the bonded fiber according to claim 5, characterized in that, The heating temperature in step S1 is 200 - 250 °C.

8. The method for preparing the bonded fiber according to claim 5, characterized in that, The heat preservation time in step S2 is 1 - 2 h.

9. The method for preparing the bonded fiber according to claim 5, wherein The reaction temperature of the heat preservation and stirring reaction in step S3 is 150 - 200 °C, and the reaction time is 1 - 4 h.

10. Application of the bonding fiber according to any one of claims 1 - 4 or the bonding fiber prepared by the preparation method according to any one of claims 5 - 9 on a separation membrane support.

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