A high-performance polytetrafluoroethylene composite liquid filter material and its preparation method

Abstract

This invention relates to the field of filtration materials technology and discloses a high-performance polytetrafluoroethylene (PTFE) composite liquid filtration material and its preparation method, comprising the following steps: PTFE fibers are plasma-treated, then mixed and reacted with a silane coupling agent, ethanol, and deionized water; the mixture is then removed, dried, and carded into a web to obtain a surface layer; PTFE fibers, polyimide fibers, sodium polyacrylate, reinforcing materials, and deionized water are mixed and dispersed under high shear to obtain a slurry; the slurry is then wet-formed and heat-cured to obtain an intermediate layer; PTFE vinyl fabric is used as the bottom layer, and the intermediate and surface layers are sequentially laid, followed by hot pressing and biaxial stretching to obtain the filtration material. Through an innovative gradient structure design, the problems of weak interlayer bonding and insufficient mechanical strength in traditional PTFE filter media are solved. The prepared composite material possesses excellent chemical stability, high filtration accuracy, high mechanical strength, and long service life.

Description

Technical Field

[0001] This invention relates to the field of filtration materials technology, specifically to a high-performance polytetrafluoroethylene composite liquid filtration material and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) materials are widely used in liquid filtration due to their excellent chemical stability, high temperature resistance, and low surface energy. However, traditional PTFE filter materials suffer from weak interlayer bonding and insufficient mechanical strength, which limits their performance and service life in harsh environments.

[0003] In existing technologies, PTFE filter materials typically employ a single material or a simple composite structure, making it difficult to simultaneously meet the requirements of high filtration accuracy, high mechanical strength, and long service life. Especially in liquid filtration applications, where materials need to withstand significant pressure and chemical corrosion, traditional PTFE filter media are prone to delamination and breakage. Therefore, developing a high-performance PTFE composite liquid filter material with excellent interlayer bonding, high mechanical strength, and a long service life is of great significance. Summary of the Invention

[0004] This invention provides a high-performance polytetrafluoroethylene composite liquid filter material and its preparation method, which solves the problems of poor mechanical properties and poor filtration performance of filter materials.

[0005] The technical solution of the present invention:

[0006] A method for preparing a high-performance polytetrafluoroethylene composite liquid filter material includes the following preparation steps:

[0007] S1. After plasma treatment of polytetrafluoroethylene fibers, they are mixed and reacted with silane coupling agent, ethanol and deionized water, then removed, dried, combed and laid into a web to obtain the surface layer.

[0008] S2. Polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heated to cure to obtain an intermediate layer.

[0009] The process involves mixing polytetrafluoroethylene (PTFE) fibers, polyimide fibers, sodium polyacrylate, reinforcing materials, and deionized water to form a slurry, which is then wet-molded to create a fiber fabric. The polyimide fibers serve as the skeleton, while the sodium polyacrylate can evenly disperse the powdered PTFE fibers into the polyimide fiber skeleton. After heating and curing, the PTFE fibers first melt at the intersections of the polyimide fibers to form strong "weld points," thus solidifying the originally loose polyimide fiber network into a robust cross-linked network fiber fabric, which then serves as the intermediate layer.

[0010] S3. Using polytetrafluoroethylene vinyl cloth as the bottom layer, the intermediate layer and the surface layer are laid in sequence, and then hot pressing and biaxial stretching are performed to obtain the filter material.

[0011] Furthermore, in step S1, the plasma processing power is 300-800W, the processing time is 1-10min, and the processing gas is oxygen.

[0012] Further, in step S1, the surface layer has a unit area weight of 15-25 g / m². 2 .

[0013] Further, in step S1, the silane coupling agent is γ-aminopropyltriethoxysilane;

[0014] Further, in step S1, the mass ratio of the polytetrafluoroethylene fiber, silane coupling agent, ethanol and deionized water is 10:(0.5-1):(80-100):(20-30);

[0015] Furthermore, in step S1, the reaction temperature is 60-80℃ and the time is 1-2 hours.

[0016] Further, in step S2, the mass ratio of the polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material and deionized water is 10:(3-5):(0.3-0.5):(1-1.5):(80-100).

[0017] Furthermore, in step S2, the high-shear dispersion speed is 2000-8000 rpm, and the high-shear dispersion time is 5-30 min.

[0018] Furthermore, in step S2, the heating and curing temperature is 330-350℃, and the heating and curing time is 2-10 minutes.

[0019] Furthermore, in step S2, the weight per unit area of ​​the intermediate layer is 10-25 g / m². 2 .

[0020] Further, in step S2, the reinforcing material is specifically prepared by the following steps:

[0021] A1. Add tannic acid to ethanol and stir until completely dissolved. Add calcium carbonate granules and continue stirring. Then, dry in an oven at 80-90℃ until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules.

[0022] A2. Add zinc nitrate hexahydrate, 2-aminobenzothiazole and 2-methylimidazole to methanol, stir until uniform, add sodium formate and tannic acid modified calcium carbonate particles, stir until uniform, purge with nitrogen gas, after the reaction is complete, centrifuge, wash and dry to obtain modified calcium carbonate particles.

[0023] A3. Add carboxymethyl cellulose and modified calcium carbonate particles to deionized water, stir evenly, add tea polyphenols and ferric chloride, stir until gel-like, wash the gel, freeze-dry to obtain the reinforcing material.

[0024] Furthermore, in the A1 reaction process described above, tannic acid contains a large number of phenolic hydroxyl groups, which have good adhesive properties and can adhere to the surface of calcium carbonate particles to obtain tannic acid-modified calcium carbonate particles.

[0025] Furthermore, in the A2 reaction process described above, zinc ions in zinc nitrate hexahydrate can combine with oxygen-containing functional groups on the surface of tannic acid-modified calcium carbonate particles, causing zinc ions to deposit on the surface of tannic acid-modified calcium carbonate particles. 2-Methylimidazole and 2-aminobenzothiazole serve as organic ligands, and zinc ions react with the organic ligands to form a three-dimensional network structure of zinc-based metal-organic framework, thereby achieving the synthesis of zinc-based metal-organic framework on the surface of calcium carbonate particles and obtaining modified calcium carbonate particles.

[0026] Furthermore, in the A3 reaction process described above, ferric chloride acts as a crosslinking agent, which can bind with the oxygen-containing functional groups of carboxymethyl cellulose through strong hydrogen bonds, and can also form a hydrogen bond network with the phenolic hydroxyl groups of tea polyphenols, thereby forming a three-dimensional network aerogel structure. Modified calcium carbonate particles can be embedded into the aerogel structure to obtain a reinforcing material.

[0027] Further, in step A1, the mass ratio of tannic acid, ethanol and calcium carbonate particles is (0.5-0.8):(20-30):(3-5).

[0028] Further, in step A2, the mass ratio of the calcium carbonate particles modified with zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and tannic acid is (1.6-2):(1-2):(2-3):(75-80):(1-1.4):(3-5).

[0029] Further, in step A3, the mass ratio of carboxymethyl cellulose, modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride is (2-3):(1-2):(120-150):(1-1.5):(0.3-0.5).

[0030] Further, in step S3, the hot pressing temperature is 320-340℃, the hot pressing pressure is 10-15MPa, and the hot pressing time is 10-30min.

[0031] Furthermore, in step S3, the bidirectional stretching includes longitudinal stretching and transverse stretching.

[0032] Furthermore, the longitudinal stretching temperature is 250-300℃, and the stretching ratio is (2-4):1.

[0033] Furthermore, the transverse stretching temperature is 280-320℃, and the stretching ratio is (3-5):1.

[0034] Furthermore, the thickness of the filter material is 1-2 mm.

[0035] The present invention has the following beneficial effects:

[0036] (1) In the technical solution of the present invention, a zinc-based metal-organic framework is synthesized on the surface of calcium carbonate particles. On the one hand, calcium carbonate particles, as an inorganic toughening agent, have good mechanical strength and can enhance the mechanical properties of the filter material. The synthesized zinc-based metal-organic framework has a large specific surface area and a highly ordered and adjustable pore structure, which can adsorb toxic and harmful molecules in sewage and complete the filtration of sewage. On the other hand, the coordination bonds in the zinc-based metal-organic framework can absorb and weaken the impact force generated by sewage, and avoid the filter material being subjected to the impact force of sewage flow for a long time, which would cause the polytetrafluoroethylene filter material to crack and break, affecting the filtration performance.

[0037] (2) In the technical solution of the present invention, modified calcium carbonate particles, carboxymethyl cellulose, tea polyphenols and ferric chloride are mixed and reacted to form a three-dimensional network structure aerogel with carboxymethyl cellulose as the skeleton. This aerogel can absorb and weaken external stress, further enhance the mechanical properties of polytetrafluoroethylene filter material, and the formed aerogel has a porous structure, which can also improve the filtration efficiency of polytetrafluoroethylene filter material for sewage. In addition, the modified calcium carbonate particles are embedded in the aerogel, which improves the dispersion of modified calcium carbonate particles in the intermediate layer, improves the mechanical properties of the intermediate layer and the filtration performance for sewage, thereby improving the filtration efficiency of polytetrafluoroethylene filter material for sewage.

[0038] (3) In the technical solution of the present invention, the filter material specifically includes a three-layer gradient structure of polytetrafluoroethylene vinyl cloth bottom layer, middle layer and surface layer. Through the design of the three-layer gradient structure and the precise control of the bidirectional stretching process, the internal structure of the material is optimized, and the filtration accuracy and mechanical strength are improved.

[0039] Among them, the surface layer is formed by plasma treatment and silane coupling agent treatment of polytetrafluoroethylene fibers, followed by carding and web laying to improve the surface activity of the surface layer and enhance the interfacial bonding ability between the surface layer and the intermediate layer.

[0040] Intermediate layer: Polyimide fiber serves as the skeleton, and polytetrafluoroethylene fiber is melted at the intersection of the polyimide fiber to form strong weld points, thus consolidating the originally loose polyimide fiber network into a strong porous cross-linked fiber fabric as the intermediate layer. This intermediate layer acts as a supporting skeleton in the polytetrafluoroethylene filter material, enhancing the mechanical properties of the polytetrafluoroethylene filter material. Furthermore, the porous structure of the intermediate layer can enhance the filtration performance of the polytetrafluoroethylene filter material.

[0041] In addition, the addition of dispersant sodium polyacrylate and high shear treatment to the mixture of polyimide fibers, polyimide fibers and reinforcing materials ensures the uniform distribution of polyimide fibers, polyimide fibers and reinforcing materials, and eliminates defects such as structural inhomogeneity and cloudiness caused by fiber agglomeration or filler flocculation, which affect the mechanical properties and filtration performance of the filter material.

[0042] The added reinforcing material is uniformly dispersed in the intermediate layer. When the filter material is under stress, it can effectively induce crazes and deflect the propagation path of microcracks. It can also absorb a large amount of fracture energy through processes such as interface debonding and reinforcing material pull-out, thereby significantly improving the mechanical properties of the filter material. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] The raw materials used in the embodiments of this invention are shown below, and all reagents used are analytical grade.

[0045] The polytetrafluoroethylene fiber and polyimide fiber have a fineness of 5D and a length of 10mm.

[0046] The surface layer has a unit area weight of 20g / m² 2 ;

[0047] The intermediate layer has a unit area weight of 20g / m² 2 ;

[0048] The dimensions of the polytetrafluoroethylene vinyl fabric are 60cm × 60cm × 0.5mm.

[0049] The silane coupling agent is γ-aminopropyltriethoxysilane.

[0050] The calcium carbonate particles have a diameter of 3 micrometers.

[0051] The carboxymethyl cellulose, product number C804618, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0052] Example 1

[0053] A method for preparing a high-performance polytetrafluoroethylene composite liquid filter material includes the following preparation steps:

[0054] S1. Polytetrafluoroethylene (PTFE) fibers are subjected to plasma treatment, then mixed with γ-aminopropyltriethoxysilane, ethanol, and deionized water, reacted at 60°C for 1 hour, removed, dried, and combed into a web to obtain a surface layer; the plasma treatment power is 300W, the treatment time is 1 minute, and the treatment gas is oxygen; the mass ratio of PTFE fibers, γ-aminopropyltriethoxysilane, ethanol, and deionized water is 10:0.5:80:20.

[0055] S2. Polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heat-cured to obtain an intermediate layer. The mass ratio of polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water is 10:3:0.3:1:80. The high-shear dispersion speed is 2000 rpm, and the high-shear dispersion time is 5 min. The heat curing temperature is 330℃, and the heat curing time is 2 min.

[0056] S3. Using polytetrafluoroethylene vinyl cloth as the bottom layer, the intermediate layer and the surface layer are laid in sequence, and then hot-pressed and biaxially stretched to obtain the filter material; the hot-pressing temperature is 320℃, the hot-pressing pressure is 10MPa, and the hot-pressing time is 10min.

[0057] Biaxial stretching includes longitudinal stretching and transverse stretching; the longitudinal stretching temperature is 250℃ and the stretching ratio is 2:1; the transverse stretching temperature is 280℃ and the stretching ratio is 3:1.

[0058] The filter material is 1mm thick.

[0059] The reinforcing material is prepared by the following steps:

[0060] A1. Add tannic acid to ethanol and stir at 60°C until completely dissolved. Add calcium carbonate granules and continue stirring for 30 minutes. Place in an oven at 80°C and dry until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules. The mass ratio of tannic acid, ethanol and calcium carbonate granules is 0.5:20:3.

[0061] A2. Zinc nitrate hexahydrate, 2-aminobenzothiazole, and 2-methylimidazole were added to methanol and stirred until homogeneous. Sodium formate and tannic acid-modified calcium carbonate particles were then added and stirred until homogeneous. Nitrogen gas was introduced, and the mixture was reacted at 60°C for 4 hours. The mixture was centrifuged at 8000 r / min, washed three times with methanol, washed three times with deionized water, and dried in a 60°C oven for 10 minutes to obtain modified calcium carbonate particles. The mass ratio of zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and tannic acid-modified calcium carbonate particles was 1.6:1:2:75:1:3.

[0062] A3. Add carboxymethyl cellulose and modified calcium carbonate particles to deionized water, stir evenly, add tea polyphenols and ferric chloride, stir at 300 r / min for 1 h until gel-like, wash the gel three times with deionized water, freeze-dry at -20℃ for 24 h to obtain the reinforcing material; the mass ratio of carboxymethyl cellulose, modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride is 2:1:120:1:0.3.

[0063] Example 2

[0064] A method for preparing a high-performance polytetrafluoroethylene composite liquid filter material includes the following preparation steps:

[0065] S1. Polytetrafluoroethylene (PTFE) fibers were plasma-treated, then mixed with γ-aminopropyltriethoxysilane, ethanol, and deionized water, and reacted at 70°C for 1.5 h. The mixture was then removed, dried, and combed into a web to obtain a surface layer. The plasma treatment power was 600 W, the treatment time was 5 min, and the treatment gas was oxygen. The mass ratio of PTFE fibers, γ-aminopropyltriethoxysilane, ethanol, and deionized water was 10:0.8:90:25.

[0066] S2. Polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heat-cured to obtain an intermediate layer. The mass ratio of polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water is 10:4:0.4:1.3:90. The high shear dispersion speed is 6000 rpm, and the high shear dispersion time is 15 min. The heat curing temperature is 340℃, and the heat curing time is 6 min.

[0067] S3. Using polytetrafluoroethylene vinyl cloth as the bottom layer, the intermediate layer and the surface layer are laid in sequence, and then hot-pressed and biaxially stretched to obtain the filter material; the hot-pressing temperature is 330℃, the hot-pressing pressure is 13MPa, and the hot-pressing time is 20min.

[0068] Biaxial stretching includes longitudinal stretching and transverse stretching; the longitudinal stretching temperature is 280℃ and the stretching ratio is 3:1; the transverse stretching temperature is 300℃ and the stretching ratio is 4:1.

[0069] The filter material is 1.5mm thick.

[0070] The reinforcing material is prepared by the following steps:

[0071] A1. Add tannic acid to ethanol and stir at 60°C until completely dissolved. Add calcium carbonate granules and continue stirring for 30 minutes. Place in an oven at 85°C and dry until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules. The mass ratio of tannic acid, ethanol and calcium carbonate granules is 0.7:25:4.

[0072] A2. Zinc nitrate hexahydrate, 2-aminobenzothiazole, and 2-methylimidazole were added to methanol and stirred until homogeneous. Sodium formate and tannic acid-modified calcium carbonate particles were then added and stirred until homogeneous. Nitrogen gas was introduced, and the mixture was reacted at 60°C for 4 hours. The mixture was centrifuged at 8000 r / min, washed three times with methanol, and three times with deionized water. The mixture was then dried in a 60°C oven for 10 minutes to obtain modified calcium carbonate particles. The mass ratio of zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and tannic acid-modified calcium carbonate particles was 1.8:1.5:2.5:78:1.2:4.

[0073] A3. Add carboxymethyl cellulose and modified calcium carbonate particles to deionized water, stir evenly, add tea polyphenols and ferric chloride, stir at 300 r / min for 1 h until gel-like, wash the gel three times with deionized water, freeze-dry at -20℃ for 24 h to obtain the reinforcing material; the mass ratio of carboxymethyl cellulose, modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride is 2.5:1.5:130:1.3:0.4.

[0074] Example 3

[0075] A method for preparing a high-performance polytetrafluoroethylene composite liquid filter material includes the following preparation steps:

[0076] S1. Polytetrafluoroethylene (PTFE) fibers were subjected to plasma treatment, then mixed with γ-aminopropyltriethoxysilane, ethanol, and deionized water, and reacted at 80°C for 2 hours. The mixture was then removed, dried, and combed into a web to obtain a surface layer. The plasma treatment power was 800W, the treatment time was 10 minutes, and the treatment gas was oxygen. The mass ratio of PTFE fibers, γ-aminopropyltriethoxysilane, ethanol, and deionized water was 10:1:100:30.

[0077] S2. Polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heat-cured to obtain an intermediate layer. The mass ratio of polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water is 10:5:0.5:1.5:100. The high-shear dispersion speed is 8000 rpm, and the high-shear dispersion time is 30 min. The heat curing temperature is 350℃, and the heat curing time is 10 min.

[0078] S3. Using polytetrafluoroethylene vinyl cloth as the bottom layer, the intermediate layer and the surface layer are laid in sequence, and then hot-pressed and biaxially stretched to obtain the filter material; the hot-pressing temperature is 340℃, the hot-pressing pressure is 15MPa, and the hot-pressing time is 30min.

[0079] Biaxial stretching includes longitudinal stretching and transverse stretching; the longitudinal stretching temperature is 300℃ and the stretching ratio is 4:1; the transverse stretching temperature is 320℃ and the stretching ratio is 5:1.

[0080] The filter material is 2mm thick.

[0081] The reinforcing material is prepared by the following steps:

[0082] A1. Add tannic acid to ethanol and stir at 60°C until completely dissolved. Add calcium carbonate granules and continue stirring for 30 minutes. Place in a 90°C oven and dry until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules. The mass ratio of tannic acid, ethanol and calcium carbonate granules is 0.8:30:5.

[0083] A2. Zinc nitrate hexahydrate, 2-aminobenzothiazole, and 2-methylimidazole were added to methanol and stirred until homogeneous. Sodium formate and tannic acid-modified calcium carbonate granules were then added and stirred until homogeneous. Nitrogen gas was introduced, and the mixture was reacted at 60°C for 4 hours. The mixture was centrifuged at 8000 r / min, washed three times with methanol, and three times with deionized water. The mixture was then dried in a 60°C oven for 10 minutes to obtain modified calcium carbonate granules. The mass ratio of zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and tannic acid-modified calcium carbonate granules was 2:2:3:80:1.4:5.

[0084] A3. Add carboxymethyl cellulose and modified calcium carbonate particles to deionized water, stir evenly, add tea polyphenols and ferric chloride, stir at 300 r / min for 1 h until gel-like, wash the gel three times with deionized water, freeze-dry at -20℃ for 24 h to obtain the reinforcing material; the mass ratio of carboxymethyl cellulose, modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride is 3:2:150:1.5:0.5.

[0085] Comparative Example 1

[0086] The only difference between this comparative example and Example 3 is the preparation of the reinforcing material, as detailed below:

[0087] The reinforcing material is prepared by the following steps:

[0088] A1. Zinc nitrate hexahydrate, 2-aminobenzothiazole, and 2-methylimidazole were added to methanol and stirred until homogeneous. Sodium formate and calcium carbonate granules were then added and stirred until homogeneous. Nitrogen gas was introduced, and the mixture was reacted at 60°C for 4 hours. The mixture was then centrifuged at 8000 r / min, washed three times with methanol, washed three times with deionized water, and dried in a 60°C oven for 10 minutes to obtain modified calcium carbonate granules. The mass ratio of zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and calcium carbonate granules was 2:2:3:80:1.4:5.

[0089] A2. Add carboxymethyl cellulose and modified calcium carbonate particles to deionized water, stir evenly, add tea polyphenols and ferric chloride, stir at 300 r / min for 1 h until gel-like, wash the gel three times with deionized water, freeze-dry at -20℃ for 24 h to obtain the reinforcing material; the mass ratio of carboxymethyl cellulose, modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride is 3:2:150:1.5:0.5.

[0090] Comparative Example 2

[0091] The only difference between this comparative example and Example 3 is the preparation of the reinforcing material, as detailed below:

[0092] The reinforcing material is prepared by the following steps:

[0093] A1. Add tannic acid to ethanol and stir at 60°C until completely dissolved. Add calcium carbonate granules and continue stirring for 30 minutes. Place in a 90°C oven and dry until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules. The mass ratio of tannic acid, ethanol and calcium carbonate granules is 0.8:30:5.

[0094] A2. Carboxymethyl cellulose and tannic acid-modified calcium carbonate particles were added to deionized water and stirred evenly. Tea polyphenols and ferric chloride were added, and the mixture was stirred at 300 r / min for 1 h until it became gel-like. The gel was washed three times with deionized water and freeze-dried at -20℃ for 24 h to obtain the reinforcing material. The mass ratio of carboxymethyl cellulose, tannic acid-modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride was 3:2:150:1.5:0.5.

[0095] Comparative Example 3

[0096] The only difference between this comparative example and Example 3 is the preparation of the reinforcing material, as detailed below:

[0097] The reinforcing material is prepared by the following steps:

[0098] A1. Add tannic acid to ethanol and stir at 60°C until completely dissolved. Add calcium carbonate granules and continue stirring for 30 minutes. Place in a 90°C oven and dry until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules. The mass ratio of tannic acid, ethanol and calcium carbonate granules is 0.8:30:5.

[0099] A2. Zinc nitrate hexahydrate, 2-aminobenzothiazole, and 2-methylimidazole were added to methanol and stirred until homogeneous. Sodium formate and tannic acid-modified calcium carbonate granules were then added and stirred until homogeneous. Nitrogen gas was introduced, and the mixture was reacted at 60°C for 4 hours. The mixture was centrifuged at 8000 r / min, washed three times with methanol, and three times with deionized water. The mixture was then dried in a 60°C oven for 10 minutes to obtain modified calcium carbonate granules. The mass ratio of zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and tannic acid-modified calcium carbonate granules was 2:2:3:80:1.4:5.

[0100] A3. Add modified calcium carbonate granules to deionized water, stir evenly, add tea polyphenols and ferric chloride, and stir again to obtain the reinforcing material; the mass ratio of modified calcium carbonate granules, deionized water, tea polyphenols and ferric chloride is 2:150:1.5:0.5.

[0101] Comparative Example 4

[0102] The only difference between this comparative example and Example 3 is the preparation of the intermediate layer, as detailed below:

[0103] S2. Polytetrafluoroethylene fiber, polyimide fiber, reinforcing material, and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heat-cured to obtain an intermediate layer. The mass ratio of polytetrafluoroethylene fiber, polyimide fiber, reinforcing material, and deionized water is 10:5:1.5:100. The high-shear dispersion speed is 8000 rpm, and the high-shear dispersion time is 30 min. The heat curing temperature is 350℃, and the heat curing time is 10 min.

[0104] Comparative Example 5

[0105] The only difference between this comparative example and Example 3 is the preparation of the intermediate layer, as detailed below:

[0106] S2. Polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heat-cured to obtain an intermediate layer. The mass ratio of polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material, and deionized water is 10:5:0.5:1.5:100. The high shear dispersion speed is 8000 rpm, and the high shear dispersion time is 30 min. The heat curing temperature is 350℃, and the heat curing time is 10 min.

[0107] The performance of the filter materials prepared in Examples 1-3 and Comparative Examples 1-6 was then tested.

[0108] Mechanical performance testing: The filter material prepared above was cut into strips of 50cm×50cm with a thickness of 2mm. The breaking strength and elongation at break of the samples were determined using a UTM-Q422 universal tensile tester according to ASTM standard D882-02. Before testing, the thickness of the sample was accurately measured using a vernier caliper. The test was conducted at a tensile speed of 2mm / min. Each group of samples was tested 3 times, and the average value was taken.

[0109] Wastewater parameters: COD 622 mg / L, chloride ion concentration 150 mg / L, total nitrogen concentration 135 mg / L.

[0110] The concentration of COD (M0) in the wastewater was determined according to the method in GB16171-2012 "Emission Standard of Pollutants from Coking Chemical Industry"; the concentration of total nitrogen (G0) in the wastewater was determined according to the national standard HJ 636-2017.

[0111] The filter material prepared above is tightly attached to the inside of the Buchner funnel. 100 mL of wastewater is taken and filtered under a pressure of 0.4 MPa, so that the wastewater passes through the filter material prepared above and is discharged from the bottom of the funnel. The filtrate is collected. The COD and total nitrogen concentrations in the filtrate are measured again according to the above method and recorded as M1 and N1, respectively. The removal efficiency is calculated.

[0112] Wherein, COD removal efficiency = (M0-M1) / M0×100%; total nitrogen removal efficiency = (N0-N1) / N0×100%;

[0113] The COD concentration in the collected filtrate was determined according to the methods in GB16171-2012 "Emission Standard of Pollutants from Coking Chemical Industry"; the total nitrogen concentration in the collected filtrate was determined according to national standard HJ 636-2017. The chloride ion concentration in the collected filtrate was determined according to GB / T 11896-1989 standard; the industrial wastewater discharge standard stipulates that the chloride ion content shall not exceed 50 mg / L.

[0114] The test results are shown in Table 1 below.

[0115]

[0116] As can be seen from the data in Table 1, the filter materials prepared in Examples 1-3 have good mechanical properties and filtration performance.

[0117] In Comparative Example 1, when the tannic acid-modified calcium carbonate particles were replaced with a reinforcing material prepared from calcium carbonate particles and added to the intermediate layer of the filter material, the mechanical and filtration properties of the filter material decreased. This demonstrates that tannic acid contains a large number of phenolic hydroxyl groups, which have good adhesive properties. By adhering to the surface of calcium carbonate particles and imparting a large number of phenolic hydroxyl groups, it is beneficial to synthesize a zinc-based metal-organic framework on the surface of calcium carbonate particles. When added to the large intermediate layer, the filter material is prepared, thus improving its filtration and mechanical properties.

[0118] Comparative Example 2: When the modified calcium carbonate particles were replaced with tannic acid-modified calcium carbonate particles to prepare a reinforcing material, and this material was added to the middle layer of the filter material, the mechanical and filtration performance of the filter material decreased. This demonstrates that the synthesis of a zinc-based metal-organic framework on the surface of calcium carbonate particles, with calcium carbonate particles acting as an inorganic toughening agent, provides good mechanical strength and enhances the mechanical properties of the filter material. Furthermore, the synthesized zinc-based metal-organic framework has a large specific surface area and a highly ordered, tunable pore structure, enabling it to adsorb toxic and harmful molecules in wastewater and complete the filtration of wastewater. On the other hand, the coordination bonds in the zinc-based metal-organic framework can absorb and weaken the impact force generated by wastewater, preventing the filter material from being subjected to long-term impact from the water flow, which could cause cracks and breakage in the polytetrafluoroethylene filter material and affect its filtration performance.

[0119] In Comparative Example 3, the reinforcing material prepared without carboxymethyl cellulose was added to the intermediate layer of the filter material, resulting in a decrease in the mechanical and filtration performance of the filter material. This demonstrates that the three-dimensional network structure aerogel with carboxymethyl cellulose as the backbone can absorb and weaken external stress, further enhancing the mechanical properties of the polytetrafluoroethylene (PTFE) filter material. Moreover, the porous structure of the formed aerogel can also improve the filtration efficiency of the PTFE filter material for wastewater. In addition, the embedding of modified calcium carbonate particles into the aerogel improves the dispersibility of the modified calcium carbonate particles in the intermediate layer, thereby improving the mechanical properties and filtration performance of the intermediate layer for wastewater, and ultimately enhancing the filtration efficiency of the PTFE filter material for wastewater.

[0120] Comparative Example 4: When the reinforcing material prepared without sodium polyacrylate was added to the middle layer of the filter material, the mechanical properties and filtration performance of the filter material decreased. This proves that adding sodium polyacrylate as a dispersant to the mixture of polyimide fibers, polyimide fibers and reinforcing materials ensures the uniform distribution of polyimide fibers, polyimide fibers and reinforcing materials, and eliminates defects such as structural inhomogeneity and "cloudy spots" caused by fiber agglomeration or filler flocculation, which affect the mechanical properties and filtration performance of the filter material.

[0121] Comparative Example 5, which prepared the intermediate layer of the filter material without heating and curing, showed a decrease in the mechanical and filtration performance of the filter material. This demonstrates that the polyimide fiber acts as the skeleton, and the polytetrafluoroethylene fiber melts at the intersections of the polyimide fiber to form strong "welds," thus solidifying the originally loose polyimide fiber network into a robust porous cross-linked network. This intermediate layer serves as a supporting skeleton in the polytetrafluoroethylene filter material, enhancing its mechanical properties. Furthermore, the porous structure of the intermediate layer enhances the filtration performance of the polytetrafluoroethylene filter material.

[0122] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0123] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance polytetrafluoroethylene composite liquid filter material, characterized in that, It is prepared by the following steps: S1. After plasma treatment of polytetrafluoroethylene fibers, they are mixed and reacted with silane coupling agent, ethanol and deionized water, then removed, dried, combed and laid into a web to obtain the surface layer. S2. Polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material and deionized water are mixed and dispersed under high shear to obtain a slurry. The slurry is then wet-formed and heated to cure to obtain an intermediate layer. S3. Using polytetrafluoroethylene vinyl cloth as the bottom layer, the intermediate layer and the surface layer are laid in sequence, and then hot pressing and biaxial stretching are performed to obtain the filter material. The reinforcing material is obtained by mixing and reacting modified calcium carbonate particles, carboxymethyl cellulose, tea polyphenols and ferric chloride. The modified calcium carbonate particles are obtained by surface-treating calcium carbonate particles with tannic acid, followed by a reaction with zinc nitrate hexahydrate, 2-aminobenzothiazole, and 2-methylimidazole.

2. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S1, the plasma processing power is 300-800W, the processing time is 1-10min, and the processing gas is oxygen. In step S1, the surface layer has a unit area weight of 15-25 g / m². 2 .

3. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S1, the silane coupling agent is γ-aminopropyltriethoxysilane; The mass ratio of the polytetrafluoroethylene fiber, silane coupling agent, ethanol and deionized water is 10:(0.5-1):(80-100):(20-30); The reaction is carried out at a temperature of 60-80℃ for 1-2 hours.

4. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S2, the mass ratio of polytetrafluoroethylene fiber, polyimide fiber, sodium polyacrylate, reinforcing material and deionized water is 10:(3-5):(0.3-0.5):(1-1.5):(80-100).

5. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S2, the high-shear dispersion speed is 2000-8000 rpm, and the high-shear dispersion time is 5-30 min; The heating and curing temperature is 330-350℃, and the heating and curing time is 2-10 minutes; The intermediate layer has a unit area weight of 10-25 g / m² 2 .

6. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S2, the reinforcing material is specifically prepared by the following steps: A1. Add tannic acid to ethanol and stir until completely dissolved. Add calcium carbonate granules, continue stirring, and then dry in an oven at 80-90℃ until the ethanol evaporates to obtain tannic acid-modified calcium carbonate granules. A2. Add zinc nitrate hexahydrate, 2-aminobenzothiazole and 2-methylimidazole to methanol, stir until uniform, add sodium formate and tannic acid modified calcium carbonate particles, stir until uniform, purge with nitrogen gas, after the reaction is complete, centrifuge, wash and dry to obtain modified calcium carbonate particles. A3. Add carboxymethyl cellulose and modified calcium carbonate particles to deionized water, stir evenly, add tea polyphenols and ferric chloride, stir until gel-like, wash the gel, freeze-dry to obtain the reinforcing material.

7. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 6, characterized in that, In step A1, the mass ratio of tannic acid, ethanol and calcium carbonate particles is (0.5-0.8):(20-30):(3-5); In step A2, the mass ratio of the calcium carbonate particles modified with zinc nitrate hexahydrate, 2-aminobenzothiazole, 2-methylimidazole, methanol, sodium formate, and tannic acid is (1.6-2):(1-2):(2-3):(75-80):(1-1.4):(3-5); In step A3, the mass ratio of carboxymethyl cellulose, modified calcium carbonate particles, deionized water, tea polyphenols and ferric chloride is (2-3):(1-2):(120-150):(1-1.5):(0.3-0.5).

8. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S3, the hot pressing temperature is 320-340℃, the hot pressing pressure is 10-15MPa, and the hot pressing time is 10-30min.

9. The method for preparing a high-performance polytetrafluoroethylene composite liquid filter material according to claim 1, characterized in that, In step S3, the bidirectional stretching includes longitudinal stretching and transverse stretching; The longitudinal stretching temperature is 250-300℃, and the stretching ratio is (2-4):1; The transverse stretching temperature is 280-320℃, and the stretching ratio is (3-5):

1.

10. A filter material prepared by the method of any one of claims 1-9 for preparing a high-performance polytetrafluoroethylene composite liquid filter material.

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