Method for producing a nonwoven support for reverse osmosis membranes with a high-liquid wetting coating

Abstract

This invention relates to a method for preparing a nonwoven fabric support for reverse osmosis membranes with a highly hydrophilic coating, belonging to the technical field of reverse osmosis membrane supports. This invention employs low-temperature plasma vapor-phase grafting modification technology to perform hydrophilic modification treatment on the fiber layer after hot rolling and light setting. The purpose of this invention is to solve the problems of slippage between the uncoated surface and the light roller, weak bonding between the coated surface of the support and the casting solution, and poor hydrophilicity of the coated surface. The support preparation method proposed in this invention ensures non-slippage at the contact surface with the light roller, while maintaining high hydrophilicity and high smoothness of the coated surface, thus guaranteeing both flux performance and strong bonding with the coating.

Description

Technical Field

[0001] This invention relates to a method for preparing a nonwoven fabric support for a reverse osmosis membrane with a highly hydrophilic coating surface, belonging to the technical field of reverse osmosis membrane support. Background Technology

[0002] A reverse osmosis membrane is an artificial semi-permeable membrane with specific characteristics, designed to mimic biological semi-permeable membranes. When pressure is applied to the feed solution on one side of the membrane, and this pressure exceeds the osmotic pressure of the feed solution, the solvent will permeate in the reverse direction of natural osmosis. The solvent obtained on the low-pressure side of the membrane is the permeate; the solution obtained on the high-pressure side is the concentrate. Therefore, reverse osmosis membranes can effectively remove soluble salts, colloids, microorganisms, and organic matter from water.

[0003] Reverse osmosis membrane separation technology, as a novel, efficient, and precise separation technology, has become an indispensable separation method in industrial and agricultural production, science and technology, and daily life. Its application in the chemical industry is becoming increasingly widespread, and it also finds applications in environmental protection, food, medicine, electronics, power, metallurgy, textiles, and seawater desalination. This technology holds significant strategic importance for promoting socio-economic development, building a resource-saving society, protecting the environment, and even constructing an ecological civilization.

[0004] Currently, the most widely used type of reverse osmosis membrane is the composite membrane. Composite membranes are characterized by being made primarily of two or more materials, consisting of a very thin dense layer and a porous support layer. The porous support layer, also known as the base membrane, enhances mechanical strength; the dense layer, also known as the skin layer, performs the separation function. Composite membranes allow for the selection of materials with good separation performance and high mechanical strength for both the dense layer and the support layer, depending on their requirements. Therefore, the dense layer of a composite membrane can be made very thin, which helps reduce drag pressure and ensures both the separation rate and water permeability of the composite membrane.

[0005] The aforementioned porous support layer is generally prepared by applying a casting solution to one side of the support using methods such as slit coating. The side of the support covered by the coating is the coated surface, and the side not covered by the coating is the uncoated surface. To further enhance the strength of the porous support layer, polyester nonwoven fabric is commonly used as the support. Nonwoven fabric has good chemical stability and, except for acid corrosion, exhibits good corrosion resistance to various other chemical reagents. Nonwoven fabric has high crystallinity and a regular structure, possessing excellent mechanical properties, as well as high strength, hardness, and elasticity. A prominent feature is its resistance to bending fatigue; it shows no damage after repeated bending. Nonwoven fabric also has good heat resistance; its products can be sterilized at temperatures above 100°C and do not deform at 150°C without external force.

[0006] CN112681001A discloses a wet-laid nonwoven fabric for a reverse osmosis membrane support substrate and its preparation method. The raw material fibers include main fibers, hot-melt fibers, and multifidus fibers. The main fibers are made of PET; the hot-melt fibers include a surface layer and an inner core; the surface layer is made of modified COPET, and the inner core is made of PET; the multifidus fibers are made of polyolefin. A single-layer support is prepared through pretreatment, molding, drying, and hot rolling. The nonwoven fabric disclosed in this patent uses fibers with a linear density of [insert density here]. For coating surfaces, coarser fibers (0.5-2 dtex) result in lower fiber layer porosity and smoothness, negatively impacting casting performance. Insufficient hydrophilicity of the coating surface leads to poor bonding strength with the coating and increases the likelihood of dead pores (pores not connected to other pores in the support). Increasing the number of dead pores in the support layer does not contribute to increased water flux. A single-layer support structure ensures uniform smoothness on both sides. However, excessive smoothness on the uncoated surface can cause slippage on the calender rolls during production. Therefore, a single-layer structure with uniform smoothness on both sides cannot simultaneously guarantee strong bonding with the casting solution and prevent slippage on the rolls. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of slippage when the uncoated surface contacts the light roller, and poor hydrophilicity of the coated surface, resulting in weak bonding between the coating and the casting solution. The support proposed in this invention has high hydrophilicity, high smoothness and excellent porosity on the coated surface, provided that the uncoated surface does not slip when it contacts the light roller, thus ensuring both throughput performance and strong bonding with the coating.

[0008] This invention proposes a nonwoven fabric support for reverse osmosis membranes with a highly hydrophilic coating and its preparation method: It includes a two-layer structure, layer A and layer B; The A layer is composed of PET fine fibers with a diameter of 5μm-7μm and PET bonding fibers with a diameter of 5μm-8μm, and the B layer is composed of PET fine fibers with a diameter of 7μm-10μm and PET bonding fibers with a diameter of 10μm-12μm. The nonwoven fabric support for the reverse osmosis membrane is prepared according to the following method: S1. Prepare slurries with a mass concentration of 0.25%-0.30% using water as a medium from the PET fibers constituting layer A and layer B respectively; S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration at the wire is controlled at 0.008%-0.02%, and the ratio of longitudinal to transverse fibers is controlled at (1-2):1. S3. After wet forming, the fiber layer is attached to a steam cylinder for drying and shaping. The surface temperature of the steam cylinder is 110℃-140℃, and the steam pressure is 0.30MPa-0.55MPa. S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 180℃-230℃, the hydraulic cylinder pressure is controlled at 2.0MPa-5.5MPa, the calender running speed is controlled at 10m / min-30m / min, and the crystallinity of the PET fiber is controlled at 48%-55%. S5. Low-temperature plasma vapor-phase grafting modification technology is used to perform hydrophilic modification on the hot-rolled and light-set fiber layer. The vapor-phase grafting gas is acrylic acid, the grafting time is controlled between 3 min and 20 min, the grafting temperature is between 60℃ and 80℃, and the grafting rate is 0.1% to 0.5%.

[0009] Furthermore, the basis weight of layer A is 30g / m2-40g / m2, and the basis weight of layer B is 35g / m2-45g / m2.

[0010] Furthermore, the A layer contains 60%-70% PET fine fibers and 30%-40% PET binder fibers, while the B layer contains 60%-70% PET fine fibers and 30%-40% PET binder fibers.

[0011] Furthermore, the fiber lengths of the A and B layers are 3mm-5mm.

[0012] Furthermore, the smoothness of the surface of layer A is 12S-20S, and the smoothness of the surface of layer B is 5S-10S.

[0013] Furthermore, the thickness of the nonwoven fabric support is 85μm-100μm.

[0014] Furthermore, one side of layer A is the coated surface of the nonwoven fabric support, and one side of layer B is the uncoated surface of the nonwoven fabric support.

[0015] Furthermore, the bonding temperature of the PET bonding fiber is 150℃-200℃.

[0016] Furthermore, the water contact angle of layer A is 0 degrees to 5 degrees.

[0017] The beneficial effects of this invention are: 1. The reverse osmosis membrane nonwoven support with a highly hydrophilic coating surface provided by the present invention, wherein layer A is composed of PET fine fibers with a diameter of 5μm-7μm and PET bonding fibers with a diameter of 5μm-8μm. Generally speaking, the finer the fiber, the larger the specific surface area of ​​the fiber and the better the compactness. The present invention uses layer A as the coating surface, and the compactness between PET fine fibers is improved due to the finer diameter of the fibers, reducing the penetration of coating liquid into the uncoated surface.

[0018] 2. Using layer A, which incorporates PET fine fibers with a diameter of 5μm-7μm, as the coating surface improves the coating performance of the nonwoven fabric support. The porosity of the coating layer ensures that the coating surface of the nonwoven fabric support forms uniformly distributed small pores, reducing the appearance of larger pores on the coating surface. The probability of this can improve the air permeability of the nonwoven fabric support, while avoiding dead pores caused by large pores on the coating surface, thereby increasing the flux of the reverse osmosis membrane.

[0019] 3. During the high-temperature calendering process, the crystallinity of the nonwoven fabric support is controlled within the range of 48%-55%. Crystallinity affects the mechanical properties of the nonwoven fabric support. If it is too high, the water production of the reverse osmosis membrane product will decrease and the separation rate will increase. If it is too low, the mechanical properties of the nonwoven fabric support will decrease. The crystallinity range provided by this invention enables the nonwoven fabric support to have both excellent stiffness and reasonable water production and separation rate.

[0020] 4. The smoothness of the nonwoven fabric support is directly linked to the fiber diameter. The smaller the fiber diameter, the higher the smoothness, and vice versa. The smoothness of the coated and uncoated surfaces of the nonwoven fabric is controlled by controlling the fiber diameter of layers A and B. In this invention, layer A uses finer PET fibers, so the smoothness of layer A is higher than that of layer B. Using layer A as the coating surface, the higher smoothness can improve the leveling and consistency of the coating. At the same time, layer B, as the uncoated surface, uses relatively coarser PET fibers, which gives the nonwoven fabric support better stiffness and mechanical properties, preventing phenomena such as curling or wrinkles. Furthermore, the lower smoothness can suppress the slippage of the nonwoven fabric support when it is driven on the smooth roller, improving the stability of production.

[0021] 5. In this invention, layer A, which serves as the coating surface, is modified using low-temperature plasma vapor-phase grafting technology. When high-energy particles in the plasma bombard the material surface, the energy transferred is generally several to tens of electron volts. This energy exceeds the bond energy of common chemical bonds such as carbon-carbon single bonds and carbon-hydrogen bonds, which can cause these chemical bonds to break, generating a large number of free radicals. When in contact with air, the free radicals quickly combine with oxygen and are converted into peroxy groups, which can exist relatively stably at room temperature for a certain period of time, thus activating the material surface. The peroxy groups on the material surface can release free radicals again when irradiated by ultraviolet light or heated, which can act as initiators for grafting reactions. When in contact with acrylic monomers, they can open the double bonds of the monomers, initiating graft polymerization to generate a hydrophilic polyacrylic acid grafted layer, thereby achieving the functionalization of the polymer material surface. Plasma activation treatment can introduce a large number of polar groups on the surface of nonwoven fabrics. The more of these groups there are, the higher the surface free energy of the nonwoven fabric, and the better its wettability and water absorption. This retains its inherent excellent properties while improving its hydrophilicity. The grafting polymerization of acrylic acid with peroxy groups on the coating surface effectively improves the hydrophilicity consistency of the A layer, thereby improving the uniformity of the casting solution coating. At the same time, it can improve the conversion effect of the coating in the phase separation process and the porosity of the coating, which is conducive to improving the flux and other properties of the reverse osmosis membrane. In addition, the grafting modification treatment on the support coating surface can effectively improve the bonding strength between the fiber layer and the coating, increase the mechanical properties of the support, and thus increase the upper limit of the operating pressure of the reverse osmosis membrane. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] In the description of the embodiments of this application, it should be understood that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship, or the orientation or positional relationship commonly placed when the product of this application is used, or the orientation or positional relationship commonly understood by those skilled in the art. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0024] Example 1 Layer A material preparation: 60 parts by weight of PET fine fibers with a fiber diameter of 5μm-7μm and 40 parts by weight of PET bonded fibers with a fiber diameter of 5μm-8μm; the fiber length is 3mm-5mm. Layer B material preparation: 65 parts by weight of PET fine fibers with a fiber diameter of 7μm-10μm and 35 parts by weight of PET bonded fibers with a fiber diameter of 10μm-12μm; the fiber length is 3mm-5mm.

[0025] The preparation steps adopted in the above technical solution are as follows: S1. The PET fibers constituting layer A and the PET fibers constituting layer B are prepared separately using water as a medium to achieve a mass concentration of [missing information]. 0.25% slurry.

[0026] S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration is controlled at 0.01% and the ratio of longitudinal to transverse fibers is controlled at 1:1.

[0027] S3. After wet forming, the fiber layer is attached to a steam cylinder for drying and shaping. The surface temperature of the steam cylinder is 110℃ and the steam pressure is 0.30MPa.

[0028] S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 180℃, the hydraulic cylinder pressure is controlled at 5MPa, and the running speed of the calender is controlled at 10m / min to achieve semi-crystallization of PET fiber with a crystallinity of 48%.

[0029] S5. Low-temperature plasma vapor-phase grafting modification technology was used to perform hydrophilic modification on the hot-rolled and light-set fiber layer. The vapor-phase grafting gas was acrylic acid, the grafting time was controlled at 3 min, the grafting temperature was 60℃, and the grafting rate was 0.1%.

[0030] Example 2 Layer A material preparation: 70 parts by weight of PET fine fibers with a fiber diameter of 5μm-7μm and 30 parts by weight of PET bonded fibers with a fiber diameter of 5μm-8μm; the fiber length is 3mm-5mm. Layer B material preparation: 70 parts by weight of PET fine fibers with a fiber diameter of 7μm-10μm and 30 parts by weight of PET bonded fibers with a fiber diameter of 10μm-12μm; the fiber length is 3mm-5mm.

[0031] The preparation steps adopted in the above technical solution are as follows: S1. The PET fibers constituting layer A and the PET fibers constituting layer B are prepared using water as a medium to achieve a mass concentration of... 0.30% slurry.

[0032] S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration is controlled at 0.02% and the ratio of longitudinal to transverse fibers is controlled at 2:1.

[0033] S3. The fiber layer after wet forming is attached to a steam cylinder for drying and shaping. The surface temperature of the steam cylinder is 140℃ and the steam pressure is 0.55MPa.

[0034] S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 230℃, the pressure is controlled at 5.5MPa, and the running speed of the calender is controlled at 30m / min to achieve semi-crystallization of PET fiber with a crystallinity of 55%.

[0035] S5. Low-temperature plasma vapor-phase grafting modification technology was used to perform hydrophilic modification on the hot-rolled and light-set fiber layer. The vapor-phase grafting gas was acrylic acid, the grafting time was controlled at 20 min, the grafting temperature was 80℃, and the grafting rate was 0.5%.

[0036] Example 3 Layer A material preparation: 65 parts by weight of PET fine fibers with a fiber diameter of 5μm-7μm and 35 parts by weight of PET bonded fibers with a fiber diameter of 5μm-8μm; the fiber length is 3mm-5mm. Layer B material preparation: 60 parts by weight of PET fine fibers with a fiber diameter of 7μm-10μm and 40 parts by weight of PET bonded fibers with a fiber diameter of 10μm-12μm; the fiber length is 3mm-5mm.

[0037] The preparation steps adopted in the above technical solution are as follows: S1. The PET fibers constituting layer A and the PET fibers constituting layer B are prepared using water as a medium to achieve a mass concentration of... 0.27% slurry.

[0038] S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration is controlled at 0.008% and the ratio of longitudinal to transverse fibers is controlled at 1.5:1.

[0039] S3. The fiber layer after wet forming is attached to a steam cylinder for drying and shaping. The surface temperature of the steam cylinder is 130℃ and the steam pressure is 0.48MPa.

[0040] S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 200℃, the pressure is controlled at 2.0MPa, and the running speed of the calender is controlled at 20m / min to achieve semi-crystallization of PET fiber with a crystallinity of 51%.

[0041] S5. Low-temperature plasma vapor-phase grafting modification technology was used to perform hydrophilic modification on the hot-rolled and light-set fiber layer. The vapor-phase grafting gas was acrylic acid, the grafting time was controlled at 10 min, the grafting temperature was 70℃, and the grafting rate was 0.3%.

[0042] Comparative Example 1 Fiber layer preparation: 65 parts by weight of PET fine fibers with a fiber diameter of 5μm and 35 parts by weight of PET bonding fibers with a fiber diameter of 5μm; the fiber length is 5mm.

[0043] The preparation steps adopted in the above technical solution are as follows: S1. The PET fibers constituting layer A and the PET fibers constituting layer B are prepared using water as a medium to achieve a mass concentration of... 0.25% slurry.

[0044] S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration is controlled at 0.008% and the ratio of longitudinal to transverse fibers is controlled at 1:1.

[0045] S3. After wet forming, the fiber layer is attached to a steam cylinder for drying and shaping. The surface temperature of the steam cylinder is 110℃ and the steam pressure is 0.3MPa.

[0046] S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 180℃, the pressure is controlled at 5MPa, and the running speed of the calender is controlled at 15m / min to achieve semi-crystallization of PET fiber with a crystallinity of 48%.

[0047] S5. Low-temperature plasma vapor-phase grafting modification technology was used to perform hydrophilic modification on the hot-rolled and light-set fiber layer. The vapor-phase grafting gas was acrylic acid, the grafting time was controlled at 3 min, the grafting temperature was 60℃, and the grafting rate was 0.1%.

[0048] Comparative Example 2 Fiber layer preparation: 65 parts by weight of PET fine fibers with a fiber diameter of 10μm and 35 parts by weight of PET bonding fibers with a fiber diameter of 12μm; the fiber length is 5mm.

[0049] S1. The PET fibers constituting layer A and the PET fibers constituting layer B are prepared using water as a medium to achieve a mass concentration of... 0.30% slurry.

[0050] S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration is controlled at 0.02% and the ratio of longitudinal to transverse fibers is controlled at 2:1.

[0051] S3. The fiber layer after wet forming is attached to a steam cylinder for drying and shaping. The surface temperature of the steam cylinder is 140℃ and the steam pressure is 0.55MPa.

[0052] S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 230℃, the pressure is controlled at 5.5MPa, and the running speed of the calender is controlled at 20m / min to achieve semi-crystallization of PET fiber with a crystallinity of 55%.

[0053] S5. Low-temperature plasma vapor-phase grafting modification technology was used to perform hydrophilic modification on the hot-rolled and light-set fiber layer. The vapor-phase grafting gas was acrylic acid, the grafting time was controlled at 20 min, the grafting temperature was 80℃, and the grafting rate was 0.5%.

[0054] Comparative Example 3 Layer A material preparation: 65 parts by weight of PET fine fibers with a fiber diameter of 5μm-7μm and 35 parts by weight of PET bonded fibers with a fiber diameter of 5μm-8μm; the fiber length is 3mm-5mm. Layer B material preparation: 65 parts by weight of PET fine fibers with a fiber diameter of 7μm-10μm and 35 parts by weight of PET bond fibers with a fiber diameter of 10μm-12μm; the fiber length is 3mm-5mm.

[0055] The preparation steps adopted in the above technical solution are as follows: S1. The PET fibers constituting layer A and the PET fibers constituting layer B are prepared using water as a medium to achieve a mass concentration of... 0.27% slurry.

[0056] S2. The paper is formed by wet forming using a double-layer inclined wire paper machine. During forming, the pulp concentration is controlled at 0.01% and the ratio of longitudinal to transverse fibers is controlled at 1.5:1.

[0057] S3. After wet forming, the fiber layer is attached to a steam cylinder for drying and shaping. The steam cylinder temperature is 130℃ and the steam pressure is 0.48MPa.

[0058] S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender. The roller surface temperature of the calender is controlled at 200℃, the pressure is controlled at 5.0MPa, and the running speed of the calender is controlled at 20m / min to achieve semi-crystallization of PET fiber with a crystallinity of 51%.

[0059] The performance test results of the supports obtained in each embodiment and comparative example are shown in Table 1.

[0060] Table 1 Performance Test Results: The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a nonwoven fabric support for a reverse osmosis membrane with a highly hydrophilic coating surface, characterized in that, Includes the following steps: S1. The PET fibers constituting layer A and layer B are respectively prepared into slurries with a mass concentration of 0.25%-0.30% using water as a medium; S2. A double-layer inclined wire paper machine is used for wet forming, and the ratio of longitudinal to transverse fibers is controlled to be (1-2):1 during forming; S3. After wet molding, the fiber layer is pressed tightly against a steam cylinder for drying and shaping; S4. After drying and setting, the fiber layer is calendered and set by a high-temperature calender to control the crystallinity of PET fibers to 48%-55%; S5. The surface of the A layer of the hot-rolled and light-set fiber layer is subjected to hydrophilic modification treatment using low-temperature plasma vapor-phase grafting modification technology, and the vapor-phase grafting gas is acrylic acid.

2. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to claim 1, characterized in that: The A layer is composed of PET fine fibers with a diameter of 5μm-7μm and PET bonding fibers with a diameter of 5μm-8μm, and the basis weight of the A layer is 30g / m²-40g / m².

3. The method for preparing the nonwoven fabric support for the reverse osmosis membrane according to claim 1, characterized in that: The B layer is composed of PET fine fibers with a diameter of 7μm-10μm and PET bonding fibers with a diameter of 10μm-12μm, and the basis weight of the B layer is 35g / m²-45g / m².

4. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to claim 1, characterized in that: The A layer contains 60%-70% PET fine fiber and 30%-40% PET binder fiber.

5. The preparation method according to claim 1, characterized in that: The B layer contains 60%-70% PET fine fibers and 30%-40% PET binder fibers.

6. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to claim 1, characterized in that: The fiber lengths of layers A and B are 3mm-5mm.

7. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to claim 1, characterized in that: The bonding temperature of the PET bonding fiber is 150℃-200℃.

8. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to any one of claims 1-7, characterized in that: One side of layer A is the coated surface of the nonwoven fabric support, with a surface smoothness of 12S-20S and a water contact angle of 0 degrees-5 degrees; one side of layer B is the uncoated surface of the nonwoven fabric support, with a surface smoothness of 5S-10S.

9. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to any one of claims 1-7, characterized in that: In step S5, the surface of layer A is subjected to hydrophilic modification treatment so that its water contact angle is 0-5 degrees.

10. The method for preparing a nonwoven fabric support for a reverse osmosis membrane according to claim 1, characterized in that: The thickness of the nonwoven fabric support is 85μm-100μm.

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