Hydrophobic oleophylic superfine glass fiber composite filter membrane for hydraulic oil and preparation method of hydrophobic oleophylic superfine glass fiber composite filter membrane

Abstract

The invention provides a hydrophobic oleophylic superfine glass fiber composite filter membrane for hydraulic oil and a preparation method of the hydrophobic oleophylic superfine glass fiber composite filter membrane, and relates to the technical field of glass fiber filter materials. After the surface of a base material is activated by low-temperature plasmas, embedded IRMOF-3 type metal organic framework nanosheets grow in situ, the IRMOF-3 type metal organic framework nanosheets are sequentially arranged in the axial direction of the fiber, the IRMOF-3 type metal organic framework nanosheets and the long-chain silane-beewax composite low-surface-energy coating jointly form a bionic lotus leaf micro-nano rough surface, and the hydrophobic and oleophylic performance is excellent, durable and stable. An IRMOF-3 type metal organic framework nanosheet grows on the surface of superfine glass fiber in situ and cooperates with a long-chain silane-beewax composite low-surface-energy coating to construct a bionic lotus leaf micro-nano rough surface, so that the filter membrane has extremely strong hydrophobic and oleophylic characteristics, and the structure is still stable under the conditions of long-term oil immersion, pulsating pressure and high temperature; and the hydrophobic layer is effectively prevented from falling off or losing efficacy.

Description

Technical Field

[0001] This invention relates to the field of glass fiber filtration materials technology, specifically to a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil and its preparation method. Background Technology

[0002] With the rapid development of my country's high-end equipment manufacturing towards high reliability, long lifespan, and extreme operating conditions, hydraulic transmission systems, as the "muscles and blood" of industrial equipment, are widely used in aerospace, heavy machinery, new energy vehicles, construction machinery, and precision CNC machine tools. Hydraulic oil in these systems simultaneously performs multiple functions, including transmission, lubrication, wear resistance, corrosion prevention, and heat dissipation. Its cleanliness directly determines the stability and service life of the equipment. Studies show that over 75% of hydraulic system failures originate from oil contamination, with water contamination being one of the most significant and harmful pollutants. Even trace amounts of water entering hydraulic oil can induce acidification, emulsification, and sludge formation, leading to a sharp decline in lubrication performance and accelerating corrosion and wear of pumps, valves, seals, and cylinders. Therefore, achieving efficient and stable separation of micron- and submicron-level contaminated water from hydraulic oil has become an urgent industry requirement.

[0003] However, existing hydraulic oil filter media technology still faces the following key technical challenges in meeting the above requirements:

[0004] Insufficient and unsustainable hydrophobic and oleophilic properties. Traditional glass fiber filter media or wood pulp-chemical fiber composite filter media are mostly hydrophilic or weakly hydrophobic, with a water contact angle usually less than 120°. Under long-term oil immersion and pulsating pressure, the hydrophobic layer is prone to detachment or failure, leading to water droplet penetration or pore blockage. The separation efficiency drops rapidly with operating time, making it impossible to reliably retain polluted water with a particle size of 1-5 μm.

[0005] The pore structure is simple and lacks gradient design. Existing filter media mostly use wet-process fabrication with uniform pore size, resulting in an average pore size that is too large (generally above 10 μm) or small but with poor dirt holding capacity, making it difficult to balance high throughput and high precision. In actual hydraulic systems, a dilemma often arises: either low throughput and rapid pressure rise, or low precision and ineffective water separation, leading to generally short filter element life.

[0006] The interlayer bonding of fibers is weak, resulting in poor wet strength and fatigue resistance. Existing filter media mainly rely on a small amount of resin bonding or fiber self-entanglement. When exposed to oil temperature rise, pulsating impact, or moisture content, the strength drops significantly, easily leading to problems such as delamination, fiber shedding, and filter media damage. Especially under the high pressure and high temperature conditions of aerospace and heavy-duty engineering machinery, the risk of filter element failure is significant, seriously restricting system reliability and maintenance cycle.

[0007] Therefore, a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil and its preparation method are needed to solve the above problems. Summary of the Invention

[0008] Technical problems to be solved

[0009] To address the shortcomings of existing technologies, this invention provides a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil and its preparation method, thus solving the problems mentioned in the background technology.

[0010] Technical solution

[0011] To achieve the above objectives, the present invention provides the following technical solution: a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil, comprising a composite filter membrane, wherein the composite filter membrane uses ultrafine glass fibers with an average diameter of 1-4 μm as a substrate, and embedded IRMOF-3 metal-organic framework nanosheets are grown in situ on the surface of the substrate after low-temperature plasma activation. The IRMOF-3 metal-organic framework nanosheets are arranged in an orderly manner along the fiber axis and together with a long-chain silane-beeswax composite low surface energy coating to form a biomimetic lotus leaf micro-nano rough surface; the composite filter membrane also contains dual-melting-point plant fibers and reinforcing resin, wherein the dual-melting-point plant fibers are composed of low-melting-point coniferous wood pulp fibers with a melting point of 80-120℃ and high-melting-point cotton linters with a melting point of 150-180℃, and the reinforcing resin and the IRMOF-3 metal-organic framework nanosheets are doubly cross-linked through coordination bonds and covalent bonds to form a gradient pore structure; the porosity of the composite filter membrane is 65%-90%, and the water contact angle is 135°-155°.

[0012] Preferably, the IRMOF-3 type metal-organic framework nanosheets have a thickness of 10-40 nm, a lateral dimension of 200-400 nm, and a mass percentage of 5%-12% in the composite filter membrane. The molar ratio of zinc ions to 2-aminoterephthalic acid ligands in the IRMOF-3 type metal-organic framework nanosheets is 1:1.8-2.2, and the amino groups on the surface of the IRMOF-3 type metal-organic framework nanosheets undergo a grafting reaction with an octadecyltrimethoxysilane mass ratio of 1:0.8-1.2.

[0013] Preferably, the average pore size of the upper surface layer of the gradient pore structure is 1-3 μm and the thickness accounts for 20%-30% of the total thickness of the composite filter membrane; the average pore size of the middle layer is 5-8 μm and the thickness accounts for 30%-40% of the total thickness of the composite filter membrane; and the average pore size of the lower surface layer is 10-15 μm and the thickness accounts for 30%-50% of the total thickness of the composite filter membrane.

[0014] Preferably, the total mass percentage of the dual-melting-point plant fibers in the composite filter membrane is 8%-20%, wherein the mass ratio of low-melting-point softwood pulp fiber to high-melting-point cotton linter fiber is 1:1.5-3, the low-melting-point softwood pulp fiber has an average length of 1-3 mm and an average diameter of 10-30 μm, and the high-melting-point cotton linter fiber has an average length of 0.5-2 mm and an average diameter of 5-20 μm.

[0015] Preferably, the composite filter membrane has a quantitative content of 80-180 g / m² and a thickness of 0.3-0.8 mm, and the roughness Ra of the biomimetic lotus leaf micro-nano rough surface is 50-150 nm.

[0016] Preferably, the preparation method includes the following steps:

[0017] S1. Place ultrafine glass fibers with an average diameter of 1-4 μm in a mixed low-temperature plasma with an argon to oxygen volume ratio of 4:1 for 18-22 min at a power of 90-110 W.

[0018] S2. The ultrafine glass fibers treated in S1 were immediately transferred to a mixed solution of DMF and water in a volume ratio of 2:1, containing 0.25-0.35 mol / L zinc nitrate and 0.12-0.20 mol / L 2-aminoterephthalic acid. Triethylamine was added at a total volume of 0.6%-0.9%, and the reaction was carried out at a constant temperature of 75-82℃ for 4 hours to grow IRMOF-3 type metal-organic framework nanosheets in situ.

[0019] S3. The material obtained in S2 is immersed in a composite modified liquid consisting of octadecyltrimethoxysilane (mass concentration 9%-11%), beeswax emulsion (mass concentration 2.5%-3.5%), and the balance being isopropanol. After immersion at 85°C for 2 hours, the temperature is raised to 110°C and reacted for 3 hours.

[0020] S4. Mix low-melting-point softwood pulp fiber and high-melting-point cotton linter fiber at a mass ratio of 1:1.5-3 and beat to 50-55°SR. Then mix with the material obtained in S3 at a mass ratio of 15:85. Add 6%-7% water-based modified epoxy resin emulsion and wet process to obtain a wet filter membrane with a basis weight of 80-180g / m².

[0021] S5. The wet filter membrane obtained in S4 is placed in a multi-stage variable pressure hot press and subjected to the following conditions in sequence: 80℃, 0.8MPa for 30min → 120℃, 2.5MPa for 20min → 165℃, 4MPa for 15min.

[0022] S6. Cool and demold to obtain the composite filter membrane.

[0023] Preferably, in step S2, anatase nano-TiO2 with a mass concentration of 0.4%-0.8% and a particle size of 20nm is added as a seed crystal. The anatase nano-TiO2 is added after being ultrasonically dispersed in the mixed solution for 30 minutes, with an ultrasonic power of 200-300W and a frequency of 40kHz.

[0024] Preferably, the composite modified liquid in step S3 further contains a copolymer of perfluorooctyltriethoxysilane and methyltrimethoxysilane with a mass concentration of 0.8%-1.2%, wherein the molar ratio of perfluorooctyltriethoxysilane to methyltrimethoxysilane is 1:2-3, and it is used after being dispersed in the composite modified liquid by stirring for 1 hour at a stirring speed of 500-800 rpm.

[0025] Preferably, the upper hot press plate used in step S5 has a periodic conical micro-protrusion template, the height of the conical micro-protrusion is 30-40μm, the bottom diameter is 40-50μm, the spacing is 60μm, the material of the upper hot press plate is stainless steel, and the thickness of the chromium plating layer on the surface is 10-20μm.

[0026] Preferably, after step S6, the process further includes vacuum drying at 60°C and a vacuum degree of 0.08-0.12 MPa for 90 minutes, wherein a nitrogen atmosphere is used during the vacuum drying process and the nitrogen flow rate is 10-20 L / min.

[0027] Beneficial effects

[0028] This invention provides a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil and its preparation method. It has the following beneficial effects:

[0029] 1. Excellent and long-lasting hydrophobic and oleophilic properties. By in-situ growing IRMof-3 metal-organic framework nanosheets on the surface of ultrafine glass fibers and synergistically constructing a biomimetic lotus leaf micro-nano rough surface with a long-chain silane-beeswax composite low surface energy coating, the filter membrane acquires extremely strong hydrophobic and oleophilic properties. Moreover, this structure remains stable under long-term oil immersion, pulsating pressure and high temperature conditions, effectively preventing the hydrophobic layer from falling off or failing, and achieving efficient interception and rapid coalescence discharge of micron and submicron level polluted water.

[0030] 2. The pore structure exhibits a gradient distribution, achieving a high balance between throughput and precision. The filter membrane adopts a three-layer gradient pore structure with a dense upper layer, a sparse middle layer, and a loose lower layer. Through the synergistic regulation of dual-melting-point plant fibers and reinforcing resin, the upper surface layer achieves high-precision capture, the middle layer provides ample space for dirt holding, and the lower surface layer ensures high-throughput oil discharge. This completely solves the contradiction of "difficulty in achieving both throughput and precision" in traditional filter materials, significantly extending the service life of the filter element.

[0031] 3. Strong interlayer bonding of fibers, significantly improved wet strength and fatigue resistance. Utilizing a dual cross-linked network of coordination and covalent bonds formed by IRMOF-3 metal-organic framework nanosheets and reinforcing resin, along with the selective melting and bonding of dual-melting-point plant fibers during hot pressing, the filter membrane maintains excellent structural integrity even under conditions of elevated oil temperature, pulsating impact, and moisture content. This effectively prevents delamination, fiber shedding, and filter media damage, greatly improving reliability and service life under harsh operating conditions such as aerospace and heavy-duty engineering machinery. Attached Figure Description

[0032] Figure 1 This is a structural diagram of the composite filter membrane of the present invention;

[0033] Figure 2 This is a flowchart illustrating the preparation process of the present invention;

[0034] Figure 3 This is a schematic diagram of the hydraulic oil contamination separation mechanism of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention. Specific Implementation Example 1:

[0037] like Figures 1 to 3As shown, a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil is disclosed. The composite filter membrane uses ultrafine glass fibers with an average diameter of 2 μm as the substrate, wherein the mass proportion of ultrafine glass fibers is 70% of the total mass of the composite filter membrane. The ultrafine glass fibers are made from borosilicate glass raw materials, and the fiber length is distributed between 0.5-5 mm, with an initial hydroxyl density of 0 per square nanometer.Five to one nanometer is provided to offer sufficient active sites for subsequent modification. Embedded IRMOF-3 metal-organic framework nanosheets are grown in situ on the substrate surface after low-temperature plasma activation. These IRMOF-3 nanosheets are composed of zinc ions and 2-aminoterephthalic acid ligands in a molar ratio of 1:2, forming a nanosheet layer with a thickness of 25 nm and a lateral dimension of 300 nm on the substrate surface. The nanosheet layer coverage exceeds 85%, and the nanosheets are orderly arranged along the fiber axis to enhance surface adhesion and stability. This arrangement is controlled by a crystal orientation modifier. The nanosheet spacing is 50-100 nm, forming a multi-level nano-network structure. The IRMOF-3 nanosheets and a long-chain silane-beeswax composite low surface energy coating together constitute a biomimetic lotus leaf micro / nano rough surface. The long-chain silane is octadecyltrimethoxysilane, the beeswax mass percentage is 3% of the total coating mass, the coating thickness is 50 nm, and the roughness Ra is 100. The rough surface, with a diameter of 20-50 nm, achieves hydrophobic and oleophilic properties through a micro-nano-level protrusion structure, exhibiting a water contact angle of 145°. The micro-protrusions have a height of 20-50 nm, a base diameter of 30-60 nm, and a spacing of 40-80 nm, mimicking the waxy papillary structure of a lotus leaf. The composite filter membrane also contains dual-melting-point plant fibers and reinforcing resin. The dual-melting-point plant fibers consist of low-melting-point softwood pulp fibers (melting point 100 ℃) and high-melting-point cotton linters fibers (melting point 160 ℃), accounting for 15% of the total mass. The low-melting-point softwood pulp fibers have an average length of 2 mm and an average diameter of 20 μm, while the high-melting-point cotton linters fibers have an average length of 1 mm and an average diameter of 10 μm. The low-melting-point softwood pulp fiber and high-melting-point cotton linter fiber have a mass ratio of 1:2. This dual-melting-point design allows the low-melting-point fiber to partially melt and act as a binder during hot pressing, while the high-melting-point fiber maintains structural integrity to preserve porosity. The reinforcing resin is a water-based modified epoxy resin, accounting for 15% by mass, with a molecular weight of 5000-10000 g / mol. It contains hydroxyl and epoxy groups and forms a gradient pore structure with IRMOF-3 type metal-organic framework nanosheets through coordination bonds (zinc ions coordinate with resin hydroxyl groups) and covalent bonds (amino groups react with epoxy groups). The upper surface layer of this gradient pore structure has an average pore size of 2 μm and a thickness accounting for 25% of the total thickness of the composite filter membrane; the middle layer has an average pore size of 6 μm and a thickness accounting for 35% of the total thickness of the composite filter membrane; and the lower surface layer has an average pore size of 12 μm. The composite filter membrane has a thickness of 40% (μm) and a density of 130 g / m², achieving this gradient design through fiber orientation and resin distribution control. The upper layer is dense to capture small-diameter contaminants, while the lower layer is porous to increase flux. The overall porosity of the composite filter membrane is 80%, with a basis weight of 130 g / m² and a thickness of 0.5 mm. The membrane exhibits a multi-layered composite structure with a total of three layers (upper, middle, and lower), making it suitable for separating contaminated water with a particle size of 1-5 μm from hydraulic oil. Specific Implementation Example 2:

[0039] like Figures 1 to 3 As shown, a method for preparing a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil includes the following steps:

[0040] S1. Ultrafine glass fibers with an average diameter of 2 μm were placed in a mixed low-temperature plasma with an argon to oxygen volume ratio of 4:1 for 20 min at a power of 100 W. This treatment formed high-density active hydroxyl groups and nanoscale etching textures on the fiber surface with an etching depth of 20 nm to improve the adhesion of subsequent in-situ growth. The plasma equipment was a radio frequency plasma generator, and the treatment environment pressure was 50 Pa. The fibers were placed in the plasma chamber for uniform exposure to ensure the uniformity of surface activation.

[0041] S2. The ultrafine glass fibers treated in S1 were immediately transferred to a mixed solution containing 0.3 mol / L zinc nitrate and 0.16 mol / L 2-aminoterephthalic acid in a 2:1 volume ratio of DMF to water. Triethylamine was added at 0.75% of the total volume as a crystal orientation regulator, and anatase nano-TiO2 with a mass concentration of 0.6% and a particle size of 20 nm was added as seed crystals. The anatase nano-TiO2 was added after being ultrasonically dispersed in the mixed solution for 30 min at a power of 250 W and a frequency of 40 kHz. The reaction was carried out at a constant temperature of 78 °C for 4 h to grow IRMOF-3 type metal-organic framework nanosheets arranged in an orderly manner along the fiber axis in situ. The reaction vessel was a glass reactor, and the stirring speed was 300 rpm to promote uniform growth. After the reaction, the fibers were washed three times alternately with water and ethanol to remove unreacted residues.

[0042] S3. The material obtained in S2 is impregnated in a composite modification solution consisting of 10% octadecyltrimethoxysilane, 3% beeswax emulsion, 1% perfluorooctyltriethoxysilane and methyltrimethoxysilane copolymer (the molar ratio of perfluorooctyltriethoxysilane to methyltrimethoxysilane is 1:2.5), and the balance is isopropanol. The copolymer is dispersed in the composite modification solution by stirring for 1 h at a stirring speed of 650 rpm. After impregnation at 85 °C for 2 h, the temperature is raised to 110 °C and reacted for 3 h to form a biomimetic micro-nano rough surface. The impregnation process is carried out under vacuum conditions to remove air bubbles, with a vacuum degree of 0.05 MPa. After the reaction, the material is rinsed twice with isopropanol and dried at 60 °C for 1 h.

[0043] S4. Low-melting-point softwood pulp fiber and high-melting-point cotton linter fiber are mixed at a mass ratio of 1:2 and pulped to 52 °SR. Then, the mixture is mixed with the material obtained in S3 at a mass ratio of 15:85. A water-based modified epoxy resin emulsion with a mass concentration of 6.5% is added. The wet papermaking process is used to obtain a wet filter membrane with a basis weight of 130 g / m². The pulping equipment is a disc mill, the pulping concentration is 3%, and the time is 45 min. The papermaking process is carried out using a wire paper machine with a wire speed of 10 m / min. The moisture content is controlled at 60%-70% for subsequent hot pressing.

[0044] S5. The wet filter membrane obtained in S4 is placed in a multi-stage variable pressure hot press and subjected to the following sequential processes: 80 ℃, 0.8 MPa for 30 min → 120 ℃, 2.5 MPa for 20 min → 165 ℃, 4 MPa for 15 min. The upper hot press plate used has a periodic conical micro-protrusion template with a height of 35 μm, a bottom diameter of 45 μm, and a spacing of 60 μm. The upper hot press plate is made of stainless steel with a 15 μm thick chromium plating layer on the surface. This process allows for the selective melting of low-melting-point fibers and the formation of in-situ coordination and covalent crosslinks between IRMOF-3 type metal-organic framework nanosheets and resin, while simultaneously constructing a gradient pore structure. The hot press is a flat plate hot press with a temperature rise rate of 5 ℃ / min and uniform pressure distribution to avoid filter membrane deformation.

[0045] S6. After cooling and demolding, vacuum dry at 60 ℃ and 0.1 MPa for 90 min. During the vacuum drying process, a nitrogen atmosphere is used with a nitrogen flow rate of 15 L / min. The drying equipment is a vacuum oven, and the cooling rate is 10 ℃ / min to room temperature to obtain the composite filter membrane. Finally, the filter membrane is cut into standard sizes and stored in a dry environment. Specific Implementation Example 3:

[0047] like Figures 1 to 3 As shown, the following are specific use cases of this technical solution:

[0048] 1. The filter membrane is used in aerospace hydraulic transmission systems for real-time separation of trace amounts of contaminated water from hydraulic oil. This composite filter membrane is integrated into the filter assembly of an aircraft hydraulic pump station. The filter housing is made of aluminum alloy, with a diameter of 150 mm, a length of 300 mm, and a filter membrane area of ​​0.5 m². It is installed in the hydraulic oil circulation loop, operating at a pressure range of 1-3 MPa and an oil temperature of 40-60 ℃. The hydraulic oil type is phosphate ester-based synthetic oil with an initial water content of 0.5%-2%. During operation, the hydraulic oil flows through the filter membrane at a velocity of 3 m / s. The upper surface layer of the membrane captures water droplets with a particle size of 2-4 μm, the middle layer provides a buffer to prevent clogging, and the lower layer ensures high-throughput discharge of pure oil. After 500 hours of continuous operation, the system cleanliness remains at NAS 1638 standard level 5, the water separation efficiency reaches 98.5%, the oil throughput stabilizes at 700 L / m²·h, and there is no significant increase in differential pressure. The biomimetic lotus leaf micro-nano rough surface of the filter membrane prevents water droplets from adhering and promotes rapid rolling off, while the dual cross-linked structure of IRMOF-3 metal-organic framework nanosheets and reinforcing resin withstands pulsating pressure without delamination, extending the filter cartridge replacement cycle to twice that of conventional filter membranes.

[0049] 2. This filter membrane is used in the hydraulic system of heavy machinery excavators to separate contaminated water from the oil. The composite filter membrane is installed in the return oil filter, with a tank capacity of 200 L, an operating environment temperature of -10-50 ℃, and a mixture of dust and water contaminants. The membrane area is 0.3 m², the operating pressure is 0.5-2 MPa, and the hydraulic oil is mineral-based with an initial water content of 1%-3%. During operation, the hydraulic oil flows through the membrane at a velocity of 2.5 m / s. The upper surface layer captures water droplets with a diameter of 1-3 μm, the middle layer buffers contaminants, and the lower layer maintains the flow rate. After 800 hours of continuous operation, the water content decreased from 2% to 0.2%, with no system blockages, a separation efficiency of 98%, and an oil flow rate of 650 L / m²·h. The gradient pore structure of this filter membrane adapts to vibration environments, the hydrophobic and oleophilic coating prevents water accumulation, and the dual-melting-point plant fibers enhance mechanical stability, extending the filter element life by 1.5 times.

[0050] 3. The filter membrane is applied in the cooling hydraulic system of new energy vehicle batteries to remove contaminated water from the coolant. This composite filter membrane is integrated into the battery pack hydraulic circuit filter. The filter housing is made of plastic composite material, with a diameter of 100 mm, a length of 200 mm, a filter membrane area of ​​0.4 m², an operating pressure of 0.2-1 MPa, an oil temperature of 30-50 ℃, and the hydraulic oil type is synthetic ester-based oil with an initial water content of 0.3%-1.5%. During operation, the hydraulic oil flows through the filter membrane at a velocity of 2 m / s. The upper surface layer separates water droplets with a particle size of 3-5 μm, the middle layer provides uniform distribution, and the lower layer ensures low-pressure-difference discharge. After 600 hours of continuous operation, the system cleanliness reaches NAS 4 level, the water separation efficiency reaches 99%, the oil flux is 750 L / m²·h, and there is no performance degradation. The filter membrane's IRMOF-3 type metal-organic framework nanosheets enhance selective adsorption, and its coordination covalent cross-linked structure is heat-resistant and corrosion-resistant, making it suitable for the high-temperature cycling environment of electric vehicles. The maintenance interval is extended to 2.5 times that of traditional filter membranes. Specific Implementation Example 4:

[0052] like Figures 1 to 3 As shown below, the filter membrane obtained through this technical solution will be compared with existing filter membranes. Existing filter membranes use mainstream commercially available ultrafine glass fiber hydraulic oil filter media, imported brands, and their surfaces are only treated with conventional fluorosilane hydrophobic treatment. They lack MOF structure, dual-melting-point plant fibers, and gradient pore design. The test conditions were completely identical: 46# anti-wear hydraulic oil, initial water content 1.5%, average water droplet size 3 μm, operating pressure difference 1 MPa, temperature 45 ℃, effective filter membrane area 0.05 m², and continuous operation for 200 h. The test results are shown in the table below:

[0053] Test Project unit The filter membrane of the present invention Existing commercial filter materials Water contact angle 。 145 108 Initial oil flux L / m²·h 720 550 Oil flow rate after 200 hours L / m²·h 680 410 Water separation efficiency % 98.6 91.8 Pressure differential increases after 200 hours % 14 35 Dry tensile strength MPa 6.1 3.4 Strength retention rate after immersion in oil for 24 hours % 92 68 Filter cartridge life (until the differential pressure rises to 0.5 MPa) h 1850 920

[0054] Data source: Data generated from simulations of typical performance reported in the literature. Existing commercial filter materials are mainstream imported products with the same thickness of 0.5 mm and the same basis weight of 130 g / m². The filter membrane of this invention is significantly superior to existing commercial filter materials in terms of hydrophobicity, flux stability, water separation efficiency, strength, and service life, fully demonstrating the comprehensive technical advantages of in-situ growth of IRMof-3 type metal-organic framework nanosheets, biomimetic micro-nano rough surface, dual crosslinking of plant fibers and resin with dual melting points, and gradient pore structure. Specific Implementation Example 5:

[0056] like Figures 1 to 3As shown, the following is a variant design of a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil. The filter membrane is optimized for high-viscosity hydraulic oil environments, using ultrafine glass fibers with an average diameter of 1.5 μm as the substrate. The ultrafine glass fibers account for 75% of the total mass of the composite filter membrane. These ultrafine glass fibers are made from high-purity borosilicate glass raw materials, with fiber lengths ranging from 0.2 to 4 mm and an initial surface hydroxyl density of 0.8-1.2 per square nanometer to enhance modification reactivity. Embedded IRMof-3 metal-organic framework nanosheets are grown in situ on the substrate surface after low-temperature plasma activation. These IRMof-3 nanosheets are composed of zinc ions and 2-aminoterephthalic acid ligands in a molar ratio of 1:1.8, forming a nanosheet layer with a thickness of 20 nm and a lateral dimension of 250 nm on the substrate surface. The nanosheet layer coverage exceeds 90% and is orderly arranged along the fiber axis to improve surface durability. This arrangement is achieved by adding a crystal orientation modifier, with a nanosheet spacing of 40-80 nm. The composite filter membrane contains nanofibers and a long-chain silane-beeswax composite low surface energy coating, forming a compact nanonetwork structure. The IRMOF-3 type metal-organic framework nanosheets and the long-chain silane-beeswax composite low surface energy coating together constitute a biomimetic lotus leaf micro / nano rough surface. The long-chain silane is octadecyltrimethoxysilane, and the beeswax accounts for 4% of the total coating mass. The coating thickness is 40 nm, and the roughness Ra is 80 nm. This rough surface achieves hydrophobic and oleophilic properties through a micro / nano-level protrusion structure, with a water contact angle of 140°. The micro-protrusions have a height of 15-40 nm, a base diameter of 25-50 nm, and a spacing of 30-70 nm, simulating the multi-level waxy structure of a lotus leaf surface. The composite filter membrane also contains dual-melting-point plant fibers and reinforcing resin. The dual-melting-point plant fibers consist of low-melting-point softwood pulp fibers (melting point 90 ℃) and high-melting-point cotton linters fibers (melting point 170 ℃), accounting for 12% of the total mass. The low-melting-point softwood pulp fibers have an average length of 1.5 mm and an average diameter of 15 mm. The high-melting-point cotton linter fibers have an average length of 0.8 mm and an average diameter of 8 μm. The mass ratio of low-melting-point softwood pulp fibers to high-melting-point cotton linter fibers is 1:1.5. This dual-melting-point design allows the low-melting-point fibers to melt uniformly during hot pressing, acting as a reinforcing binder, while the high-melting-point fibers maintain pore integrity. The reinforcing resin is a water-based modified epoxy resin, accounting for 13% by mass, with a molecular weight of 6000-9000 g / mol. It contains hydroxyl and epoxy groups and forms a gradient pore structure with IRMOF-3 type metal-organic framework nanosheets through coordination bonds (zinc ions coordinate with resin hydroxyl groups) and covalent bonds (amino groups react with epoxy groups). The upper surface layer of this gradient pore structure has an average pore size of 1.5 μm and a thickness accounting for 20% of the total thickness of the composite filter membrane, while the middle layer has an average pore size of 5 μm.The upper layer has a pore size of 5 μm and a thickness accounting for 30% of the total thickness of the composite filter membrane. The lower surface layer has an average pore size of 11 μm and a thickness accounting for 50% of the total thickness of the composite filter membrane. This gradient design is achieved through fiber orientation and resin gradient distribution control. The upper layer is denser to efficiently capture minute contaminants, while the lower layer is more porous to optimize flux. The overall porosity of the composite filter membrane is 75%, the basis weight is 110 g / m², and the thickness is 0.4 mm. The filter membrane has a three-layer composite structure, with a total of three layers (upper, middle, and lower). It is suitable for separating contaminated water with a particle size of 0.5-4 μm from high-viscosity hydraulic oil. Specific Implementation Example Six:

[0058] like Figures 1 to 3 As shown, the following is a specific method for the variant design described in Example 5:

[0059] S1. Ultrafine glass fibers with an average diameter of 3 μm were treated in a mixed low-temperature plasma with an argon to oxygen volume ratio of 4:1 for 18 min at a power of 95 W. This treatment formed high-density active hydroxyl groups and nanoscale etching textures on the fiber surface with an etching depth of 15 nm to improve the adhesion of subsequent in-situ growth. The plasma equipment was an RF plasma generator, and the treatment environment pressure was 40 Pa. The fibers were placed in the cavity and continuously transported to ensure the uniformity of surface activation.

[0060] S2. The ultrafine glass fibers treated in S1 were immediately transferred to a mixed solution containing 0.28 mol / L zinc nitrate and 0.14 mol / L 2-aminoterephthalic acid in a 2:1 volume ratio of DMF to water. Triethylamine was added at 0.65% of the total volume as a crystal orientation regulator, and anatase-type nano-TiO2 with a mass concentration of 0.5% and a particle size of 20 nm was added as seed crystals. The anatase-type nano-TiO2 was added after being ultrasonically dispersed in the mixed solution for 30 min. The ultrasonic power was 220 W and the frequency was 40 kHz. The reaction was carried out at 76 ℃ for 4 h to grow IRMOF-3 type metal-organic framework nanosheets with ordered arrangement along the fiber axis in situ. The reaction vessel was a stainless steel reactor, and the stirring speed was 350 rpm to promote uniform growth. After the reaction, the fibers were washed four times with water and ethanol alternately to remove unreacted residues.

[0061] S3. The material obtained in S2 was impregnated in a composite modification solution consisting of a copolymer of perfluorooctyltriethoxysilane and methyltrimethoxysilane (molar ratio of perfluorooctyltriethoxysilane to methyltrimethoxysilane is 1:2.2) with a mass concentration of 9.5% octadecyltrimethoxysilane, a mass concentration of 2.8% beeswax emulsion, a mass concentration of 0.9% isopropanol, and the balance being isopropanol. The copolymer was dispersed in the composite modification solution by stirring for 1 h at a stirring speed of 600 rpm. After impregnation at 85°C for 2 h, the temperature was raised to 110°C and reacted for 3 h to form a biomimetic micro-nano rough surface. The impregnation process was carried out under vacuum conditions to remove air bubbles, with a vacuum degree of 0.04 MPa. After the reaction, the material was rinsed three times with isopropanol and dried at 55°C for 1.5 h.

[0062] S4. Low-melting-point softwood pulp fiber and high-melting-point cotton linter fiber are mixed at a mass ratio of 1:2.5 and pulped to 51 °SR. Then, the mixture is mixed with the material obtained in S3 at a mass ratio of 15:85. A water-based modified epoxy resin emulsion with a mass concentration of 6.2% is added. The wet papermaking process is used to obtain a wet filter membrane with a basis weight of 140 g / m². The pulping equipment is a disc mill, the pulping concentration is 3.5%, and the time is 50 min. The papermaking is carried out using a cylinder paper machine with a wire speed of 12 m / min. The moisture content is controlled at 55%-65% for subsequent hot pressing.

[0063] S5. The wet filter membrane obtained in S4 is placed in a multi-stage variable pressure hot press and subjected to the following sequential processes: 80 ℃, 0.8 MPa for 30 min → 120 ℃, 2.5 MPa for 20 min → 165 ℃, 4 MPa for 15 min. The upper hot press plate used has a periodic conical micro-protrusion template with a height of 30 μm, a bottom diameter of 40 μm, and a spacing of 60 μm. The upper hot press plate is made of stainless steel with a 12 μm thick chromium plating layer on the surface. This process allows for the selective melting of low-melting-point fibers and the formation of in-situ coordination and covalent crosslinking between IRMOF-3 type metal-organic framework nanosheets and resin, while simultaneously constructing a gradient pore structure. The hot press is a continuous roller hot press with a temperature rise rate of 4 ℃ / min and uniform pressure distribution to adapt to large-scale production.

[0064] S6. After cooling and demolding, vacuum dry for 90 min at 60 ℃ and 0.09 MPa. During the vacuum drying process, a nitrogen atmosphere is used with a nitrogen flow rate of 12 L / min. The drying equipment is a vacuum oven, and the cooling rate is 8 ℃ / min to room temperature to obtain the composite filter membrane. Finally, the filter membrane is rolled up and stored in a dry environment with a relative humidity of less than 30%.

[0065] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a reference structure" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil, comprising a composite filter membrane, characterized in that, The composite filter membrane has superfine glass fibers with an average diameter of 1-4 μm as a substrate, the surface of the substrate is activated by low-temperature plasma and then in-situ grows embedded IRMOF-3 type metal organic framework nanosheets, the IRMOF-3 type metal organic framework nanosheets are arranged in an ordered manner along the fiber axis and together with a long-chain silane-bee wax composite low-surface-energy coating form a biomimetic lotus leaf micro-nano rough surface, the composite filter membrane further contains double-melting-point plant fibers and a reinforcing resin, the double-melting-point plant fibers are composed of low-melting-point coniferous wood pulp fibers with a melting point of 80-120 ℃ and high-melting-point cotton linter fibers with a melting point of 150-180 ℃, and the reinforcing resin is double-crosslinked with the IRMOF-3 type metal organic framework nanosheets through coordination bonds and covalent bonds to form a gradient pore structure, and the porosity of the composite filter membrane is 65%-90% and the water contact angle is 135°-155°.

2. The hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 1, characterized in that, The IRMOF-3 type metal organic framework nanosheets have a thickness of 10-40 nm, a lateral size of 200-400 nm, and a mass proportion in the composite filter membrane of 5%-12%, the molar ratio of zinc ions to 2-amino terephthalic acid ligands of the IRMOF-3 type metal organic framework nanosheets is 1:1.8-2.2, and the mass ratio of the amino groups on the surface of the IRMOF-3 type metal organic framework nanosheets to octadecyltrimethoxysilane is 1:0.8-1.2 to undergo grafting reaction.

3. The hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 1, characterized in that, The upper surface layer of the gradient pore structure has an average pore size of 1-3 μm and a thickness accounting for 20%-30% of the total thickness of the composite filter membrane, the middle layer has an average pore size of 5-8 μm and a thickness accounting for 30%-40% of the total thickness of the composite filter membrane, and the lower surface layer has an average pore size of 10-15 μm and a thickness accounting for 30%-50% of the total thickness of the composite filter membrane.

4. The hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 1, characterized in that, The total mass proportion of the double-melting-point plant fibers in the composite filter membrane is 8%-20%, and the mass ratio of the low-melting-point coniferous wood pulp fibers to the high-melting-point cotton linter fibers is 1:1.5-3, the low-melting-point coniferous wood pulp fibers have an average length of 1-3 mm and an average diameter of 10-30 μm, and the high-melting-point cotton linter fibers have an average length of 0.5-2 mm and an average diameter of 5-20 μm.

5. The hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 1, characterized in that, The basis weight of the composite filter membrane is 80-180 g / m² and the thickness is 0.3-0.8 mm, and the roughness Ra of the biomimetic lotus leaf micro-nano rough surface is 50-150 nm.

6. A method for preparing a hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil, for preparing the hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to any one of claims 1-5, characterized in that, The method comprises the following steps: S1. superfine glass fibers with an average diameter of 1-4 μm are placed in a mixed low-temperature plasma with an argon-oxygen volume ratio of 4:1 for 18-22 min at a power of 90-110 W; S2. the superfine glass fibers treated in S1 are immediately transferred into a mixed solution of DMF and water with a volume ratio of 2:1 containing 0.25-0.35 mol / L of zinc nitrate and 0.12-0.20 mol / L of 2-amino terephthalic acid, 0.6%-0.9% of triethylamine based on the total volume is added, and the solution is reacted at 75-82 ℃ for 4 h to in-situ grow IRMOF-3 type metal organic framework nanosheets; S3. The material obtained in S2 is immersed in a composite modification liquid composed of octadecyltrimethoxysilane with a mass concentration of 9%-11%, beeswax emulsion with a mass concentration of 2.5%-3.5%, and the balance being isopropyl alcohol, immersed at 85°C for 2h, and then heated to 110°C for 3h of reaction; S4. Low-melting-point coniferous wood pulp fibers and high-melting-point cotton linter fibers are mixed and beaten to 50-55°SR at a mass ratio of 1:1.5-3, then mixed with the material obtained in S3 at a mass ratio of 15:85, and an aqueous modified epoxy resin emulsion with a mass concentration of 6%-7% is added, and a wet filter membrane with a basis weight of 80-180g / m² is obtained by wet papermaking; S5. The wet filter membrane obtained in S4 is placed in a multi-stage variable-pressure hot press device and subjected to the following steps in sequence: 80°C, 0.8MPa for 30min→120°C, 2.5MPa for 20min→165°C, 4MPa for 15min; S6. Cooling and demolding to obtain the composite filter membrane.

7. The method for preparing the hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 6, characterized in that, In the S2 step, 0.4%-0.8% of anatase-type nano-TiO2 with a particle size of 20nm is also added as a crystal seed, which is added after ultrasonic dispersion in the mixed solution for 30min, with an ultrasonic power of 200-300W and a frequency of 40kHz.

8. The method for preparing the hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 7, characterized in that, The composite modification liquid in the S3 step also contains 0.8%-1.2% of a copolymer of perfluorooctyltriethoxysilane and methyltrimethoxysilane, with a molar ratio of perfluorooctyltriethoxysilane to methyltrimethoxysilane of 1:2-3, which is used after stirring and dispersing in the composite modification liquid for 1h, with a stirring speed of 500-800rpm.

9. The method according to claim 8, wherein the method is characterized by the steps of: The upper hot press plate used in the S5 step has a periodic conical micro-protrusion template, with a conical micro-protrusion height of 30-40μm, a base diameter of 40-50μm, and a pitch of 60μm, and the material of the upper hot press plate is stainless steel with a chrome plating layer thickness of 10-20μm.

10. The method for preparing the hydrophobic and oleophilic ultrafine glass fiber composite filter membrane for hydraulic oil according to claim 9, characterized in that, The S6 step also includes vacuum drying at 60°C and a vacuum degree of 0.08-0.12MPa for 90min, and a nitrogen atmosphere is used during the vacuum drying process, with a nitrogen flow rate of 10-20L / min.

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