Organic tubular membrane with strong interfacial bonding force and preparation method thereof

Abstract

The application discloses a kind of strong interface bonding force organic tubular membrane and preparation method thereof, belong to separation membrane technical field.The strong interface bonding force organic tubular membrane, including membrane separation layer and non-woven fabric support layer, the non-woven fabric support layer is formed by non-woven fabric inner support band surface layer inward, spiral lap joint is wound into tubular and is welded at lap joint, the non-woven fabric inner support band includes bottom layer and surface layer, surface layer includes part skin-core type composite fiber, skin-core type composite fiber skin layer component is consistent with high molecular polymer material in casting solution, the linear density of surface layer fiber is greater than the linear density of bottom layer fiber, surface layer aperture is greater than bottom layer aperture;The membrane separation layer is formed by casting solution coated on the inner surface of non-woven fabric support layer by phase inversion method, and the casting solution penetrates through the surface layer of non-woven fabric inner support band and enters but does not penetrate the bottom layer.The organic tubular membrane prepared by the method has high interface bonding strength, and the membrane separation layer is not easy to fall off and peel off after being pressed;Mechanical strength is high, coating quality is good, and the yield is high.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to an organic tubular membrane with strong interfacial bonding and its preparation method. Background Technology

[0002] Currently, organic tubular membranes are prepared using an integrated tubular membrane forming machine. Nonwoven fabric strips are welded into nonwoven tubes using ultrasonic waves, and a casting solution is simultaneously coated onto the tubes. The nonwoven fabric, as a support layer, not only provides mechanical support for the membrane separation layer, but its structural characteristics, such as pore size and surface roughness, are also important factors affecting membrane separation performance. Existing nonwoven support layers are generally single-layer structures, with uneven thickness, making it easy for the casting solution to penetrate to the reverse side of the nonwoven fabric during coating, resulting in defective products. Chinese patent CN 115463553 A discloses a double-layer nonwoven support layer, which solves the problem of casting solution penetration to the reverse side of the nonwoven fabric by setting bottom and top layers with different linear densities. However, this patent has the problem of low bonding strength between the top and bottom layers, making them prone to separation under pressure; and the membrane layer and top layer also have technical problems of low bonding strength, making the membrane separation layer prone to detachment and peeling under pressure. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides an organic tubular membrane with strong interfacial bonding and its preparation method.

[0004] The technical solution adopted in this invention is:

[0005] A strong interfacial bonding organic tubular membrane includes a membrane separation layer and a nonwoven fabric support layer. The nonwoven fabric support layer is formed by spirally winding a nonwoven inner support strip with the outer layer facing inward and welding it at the overlap. The nonwoven inner support strip includes a bottom layer and a top layer. The top layer includes a portion of core-sheath composite fibers. The sheath composition of the core-sheath composite fibers is consistent with the polymer material in the casting solution. The membrane separation layer is formed by a phase inversion method using a casting solution coated on the inner surface of the nonwoven fabric support layer. The casting solution permeates through the top layer of the nonwoven inner support strip but does not penetrate the bottom layer.

[0006] Furthermore, it also includes a nonwoven fabric reinforcement layer, which is formed by spirally overlapping and winding a nonwoven fabric outer support strip around the outer surface of the nonwoven fabric support layer and welding it at the overlap. The spiral direction of the nonwoven fabric outer support strip is opposite to that of the nonwoven fabric inner support strip.

[0007] By adopting the above technical solution, the mechanical strength of nonwoven tubes can be further improved.

[0008] Furthermore, the polymer materials include polysulfone, polyethersulfone, polyvinyl chloride, polyvinylidene fluoride, cellulose acetate or polyacrylonitrile and their copolymers; the surface layer of the nonwoven inner support strip is composed of 2-30 wt% of a core-sheath composite fiber and polyester or polypropylene fiber, and the bottom layer of the nonwoven inner support strip is made of polyester or polypropylene fiber.

[0009] Furthermore, the linear density of the surface layer fibers is 0.5–5 dtex, and the surface layer pore size is 25–100 μm; the linear density of the bottom layer fibers is 0.1–1 dtex, and the bottom layer pore size is 5–10 μm.

[0010] The surface and bottom layers of the nonwoven support substrate are made of fibers with different linear densities. The linear density of the surface layer fibers is greater than that of the bottom layer fibers, resulting in a smaller surface roughness of the bottom layer. This facilitates improved ultrasonic welding quality during the rolling process, thereby enhancing the mechanical strength of the nonwoven support tube. The surface layer has a larger pore size than the bottom layer. During the penetration of the casting solution, the larger pore size of the surface layer, coupled with the resistance provided by the smaller pores in the bottom layer, allows the casting solution made of polymer to penetrate evenly through the surface layer to the bottom layer. This improves coating quality, increases yield, and enhances the interfacial bonding strength of the membrane.

[0011] Furthermore, the surface layer weight is 40–80 g / m². 2 The surface layer thickness is 0.02–0.1 mm, and the surface layer air permeability is 15–75 dm³. 3 / m 2 •s; the base weight is 80-140 g / m² 2 The bottom layer thickness is 0.1–0.15 mm, and the bottom layer air permeability is 1–10 dm³. 3 / m 2 •s. By controlling the basis weight, air permeability, and thickness, the penetration effect and mechanical strength of the casting solution can be further guaranteed.

[0012] Furthermore, the thickness of the nonwoven outer support strip is 0.12–0.25 mm, and the basis weight is 120–220 g / m². 2 The fiber linear density is 0.1–1 dtex. The fiber linear density of the nonwoven outer support strip is consistent with that of the bottom layer, making it easy to weld and providing good mechanical strength.

[0013] Furthermore, the thickness of the membrane separation layer is 30–150 μm, and the penetration thickness of the casting solution is 20–110 μm. This allows the casting solution to penetrate at least through the surface layer to reach the bottom layer, thereby further improving the bonding strength between the surface layer and the bottom layer, while ensuring the bonding strength between the membrane separation layer and the nonwoven fabric support layer.

[0014] The preparation method of any of the above-mentioned organic tubular membranes with strong interfacial adhesion includes the following steps:

[0015] (1) The non-woven inner support belt and the casting liquid are placed together on the tubular coating machine. The non-woven inner support belt is spirally wound on the mandrel at a set angle and rolled into a tubular non-woven support layer by ultrasonic welding. At the same time, the casting liquid is pumped into the coating head at a certain rate and uniformly coated on the inner surface of the non-woven support layer through the coating head to form a membrane separation layer and make a tubular membrane element.

[0016] (2) The prepared tubular membrane element is immersed in a coagulation bath to complete the phase transformation and obtain an organic tubular membrane with strong interfacial bonding.

[0017] Preferably, the viscosity of the casting solution is 20,000 to 70,000 cp.

[0018] More preferably, the extrusion speed of the casting solution and the winding speed of the nonwoven support tube satisfy the following relationship:

[0019] Dt = 3.95Vs + 2.3;

[0020] Where: Vs is the winding speed, meters per minute; Dt is the casting solution extrusion speed, milliliters per minute.

[0021] By using the above-mentioned viscosity of the casting solution and the extrusion speed of the casting solution, the penetration effect of the casting solution can be effectively controlled.

[0022] Preferably, the ultrasonic welding frequency is 15–40 kHz, the amplitude is 8–50 micrometers, and the welding pressure is 3.0–8.5 bar.

[0023] The beneficial effects of this invention are:

[0024] The surface layer of the nonwoven inner support belt contains a mixture of core-sheath composite fibers. Since the sheath composition of the core-sheath composite fibers is consistent with the polymer material in the casting solution, the sheath fibers have a high affinity for the casting solution. During coating, the casting solution penetrates into the nonwoven fabric along the sheath fibers. During the phase transformation process, the casting solution that has penetrated into the nonwoven fabric can be better anchored within the nonwoven support structure, greatly enhancing the bonding strength between the membrane and the nonwoven fabric. In addition, during the coating process, the solvent component in the casting solution partially dissolves the sheath of the core-sheath composite fibers, so that during the phase transformation process, the partially dissolved sheath undergoes a cross-linking reaction with the polymer casting solution, further enhancing the bonding strength between the membrane and the nonwoven fabric. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of an organic tubular membrane with strong interfacial bonding according to the present invention. Detailed Implementation

[0026] The present invention will be further illustrated below with specific examples to facilitate understanding of the invention, but this does not limit the invention.

[0027] In the following examples and comparative examples, the method for testing the tensile strength at break of the organic tubular membrane is as follows: A dry film sample of the organic tubular membrane is selected and a specimen with a length of 240 mm is prepared. The tensile strength at break and elongation of the specimen are tested using a tensile testing machine.

[0028] The method for testing bubble point pressure is as follows: Immerse the organic tubular membrane in water, seal one end, and introduce gas into the other end. Slowly increase the pressure until the first bubble appears, and record the pressure value at this time, which is the bubble point pressure.

[0029] The method for testing peel strength is as follows: Cut five samples each of 15mm wide and 200mm long from the organic tubular membrane along both the transverse and longitudinal directions; at one end of the sample, manually pre-peel the membrane separation layer from the nonwoven support layer by 50mm along the length direction; clamp both ends of the peeled portion of the sample with the upper and lower clamps of the universal testing machine, so that the long axis of the sample coincides with the center line of the two clamps; set the test parameters such as test speed and sample width; click the test start option, the test begins, the equipment automatically tests the force value during the peeling process of the sample, and reports the final test results.

[0030] Example 1

[0031] S1: Preparation of nonwoven inner support strip:

[0032] A. PET fiber and core-sheath composite fiber are mixed at a mass ratio of 98:2 to prepare the surface sizing; the core component of the core-sheath composite fiber is PET, and the surface component is polysulfone; the linear density of PET fiber and core-sheath composite fiber is 5 dtex; PP fiber with a fiber length of 6 mm and a linear density of 1 dtex is used to prepare the bottom sizing.

[0033] B. The dispersed surface slurry and bottom slurry are fed to a double-layer forming mesh for forming to prepare double-layer wet fibers; then the prepared double-layer wet fibers are successively pressed, dried, and hot rolled and calendered for bonding and shaping to obtain a non-woven fabric support substrate.

[0034] C. Cut the obtained nonwoven fabric support substrate into strips to obtain nonwoven fabric inner support strips.

[0035] S2: Coating for rolled tubes:

[0036] Using an organic tubular membrane production equipment, the nonwoven inner support strip obtained in step S1 is spirally wound onto a central shaft with the surface layer facing inward at a set angle. During winding, the overlapping parts are ultrasonically welded to form a tubular nonwoven support layer. The ultrasonic welding frequency is 20kHz, the amplitude is 30 micrometers, and the welding pressure is 5.5 bar. Simultaneously, a polysulfone casting solution with a viscosity of 70000cp is pumped into a coating head at a certain rate and uniformly coated onto the inner surface of the nonwoven support layer to form a membrane separation layer, thus producing a tubular membrane element. The winding speed of the nonwoven support tube is controlled at 3 meters / minute, and the extrusion speed of the casting solution is 14 milliliters / minute.

[0037] S3: Immerse the prepared tubular membrane element in a coagulation bath to complete the phase transformation and obtain an organic tubular membrane A with strong interfacial bonding.

[0038] The wet forming of double-layer forming mesh is an existing technology. The surface layer pore size and the bottom layer pore size can be controlled by controlling the concentration of the surface layer slurry and the bottom layer slurry; the surface layer thickness and the bottom layer thickness can be controlled by controlling the mesh laying thickness of the surface layer slurry and the bottom layer slurry; and finally, the total thickness can be controlled by hot rolling.

[0039] See Figure 1 The resulting organic tubular membrane A includes a membrane separation layer 10 and a nonwoven fabric support layer 20. The nonwoven fabric support layer 20 includes a bottom layer 22 and a top layer 21. The thickness of the separation layer 10 is 70 μm, the thickness of the top layer 21 is 50 μm, the thickness of the bottom layer is 130 μm, and the permeation thickness of the casting solution is 52 μm. The basis weight of the top layer is 60 g / m³. 2 The surface layer has an air permeability of 35 dm. 3 / m 2 •s; the base weight is 120g / m² 2 The bottom layer has a breathability of 10dm. 3 / m 2 ·s.

[0040] The obtained organic tubular membrane A has a tensile strength at break of 450 N and a bubble point pressure of 1.5 bar. The membrane layer cannot be completely peeled off from the nonwoven support layer, and a standard peel strength test cannot be performed.

[0041] Example 2

[0042] S1: Preparation of nonwoven inner support strip:

[0043] A. PET fiber and core-sheath composite fiber are mixed at a mass ratio of 70:30 to prepare the surface slurry; the core component of the core-sheath composite fiber is PET, and the surface component is polyvinylidene fluoride; the fiber length of PET fiber and core-sheath composite fiber is 5mm, and the linear density is 5dtex; PP fiber with a fiber length of 6mm and a linear density of 1dtex is used to prepare the bottom slurry.

[0044] B. The dispersed surface slurry and bottom slurry are fed to a double-layer forming mesh for forming to prepare double-layer wet fibers; then the prepared double-layer wet fibers are successively pressed, dried, and hot rolled and calendered for bonding and shaping to obtain a non-woven fabric support substrate.

[0045] C. Cut the obtained nonwoven fabric support substrate into strips to obtain nonwoven fabric inner support strips.

[0046] S2: Preparation of nonwoven fabric outer support strip:

[0047] A. Make PP fibers with a fiber length of 6mm and a linear density of 1dtex into a slurry;

[0048] B. The dispersed slurry is fed onto a single-layer forming mesh to form a single-layer wet fiber; then the obtained single-layer wet fiber is pressed and dried in sequence to obtain a non-woven fabric reinforcing substrate.

[0049] C. Cut the obtained nonwoven fabric reinforcing substrate into strips to obtain the nonwoven fabric outer support strip.

[0050] S3: Coating for rolled tubes:

[0051] Using an organic tubular membrane production equipment, the nonwoven inner support strip obtained in step S1 is spirally wound onto a central shaft with the surface layer facing inward at a set angle. The nonwoven outer support strip obtained in step 2 is wound around the outside of the nonwoven inner support strip at the same angle. During winding, the overlapping parts are ultrasonically welded to form a tubular nonwoven support layer and a nonwoven reinforcement layer. The ultrasonic welding frequency is 40kHz, the amplitude is 50 micrometers, and the welding pressure is 6.5 bar. Simultaneously, a polyvinylidene fluoride casting solution with a viscosity of 50000cp is pumped into the casting head at a certain rate and uniformly coated onto the inner surface of the nonwoven support layer through the casting head to form a membrane separation layer, thus producing a tubular membrane element. The winding speed of the nonwoven support tube is controlled at 3 meters / minute, and the extrusion speed of the casting solution is 14 milliliters / minute.

[0052] S4: Immerse the prepared tubular membrane element in a coagulation bath to complete the phase transformation and obtain an organic tubular membrane B with strong interfacial bonding.

[0053] The resulting organic tubular membrane B comprises a membrane separation layer 10, a nonwoven support layer 20, and a nonwoven reinforcement layer 30. The nonwoven support layer 20 includes a bottom layer 22 and a top layer 21. The separation layer 10 has a thickness of 70 μm, the top layer 21 has a thickness of 50 μm, the bottom layer has a thickness of 130 μm, the reinforcement layer has a thickness of 180 μm, and the permeation thickness of the casting solution is 100 μm. The basis weight of the top layer is 60 g / m³. 2 Air permeability is 35dm 3 / m 2 •s; the base weight is 120g / m² 2 Air permeability is 10dm3 / m 2 •s; reinforcement layer basis weight is 180g / m 2 Air permeability is 10dm 3 / m 2 ·s.

[0054] The obtained organic tubular membrane B has a tensile strength at break of 1018 N and a bubble point pressure of 1.6 bar. The membrane layer cannot be completely peeled off from the nonwoven support layer, and a standard peel strength test cannot be performed.

[0055] Example 3

[0056] S1: Preparation of nonwoven inner support strip:

[0057] A. PP fiber and core-sheath composite fiber are mixed at a mass ratio of 85:15 to prepare the surface slurry; the core component of the core-sheath composite fiber is PP, and the surface component is polyacrylonitrile; the fiber length of PET fiber and core-sheath composite fiber is 8mm and the linear density is 2dtex; PP fiber with a fiber length of 5mm and a linear density of 0.5dtex is used to prepare the bottom slurry.

[0058] B. The dispersed surface slurry and bottom slurry are fed to a double-layer forming mesh for forming to prepare double-layer wet fibers; then the prepared double-layer wet fibers are successively pressed, dried, and hot rolled and calendered for bonding and shaping to obtain a non-woven fabric support substrate.

[0059] C. Cut the obtained nonwoven fabric support substrate into strips to obtain nonwoven fabric inner support strips.

[0060] S2: Coating for rolled tubes:

[0061] Using an organic tubular membrane production equipment, the nonwoven inner support strip obtained in step S1 is spirally wound onto a central shaft with the surface layer facing inward at a set angle. During winding, the overlapping parts are ultrasonically welded to form a tubular nonwoven support layer. The ultrasonic welding frequency is 25kHz, the amplitude is 15 micrometers, and the welding pressure is 5.0 bar. Simultaneously, a polyacrylonitrile casting solution with a viscosity of 50000cp is pumped into the casting head at a certain rate and uniformly coated onto the inner surface of the nonwoven support layer through the casting head to form a membrane separation layer, thus producing a tubular membrane element. The winding speed of the nonwoven support tube is controlled at 2 meters / minute, and the extrusion speed of the casting solution is 10 milliliters / minute.

[0062] S3: Immerse the prepared tubular membrane element in a coagulation bath to complete the phase transformation and obtain an organic tubular membrane C with strong interfacial bonding.

[0063] See Figure 1The resulting organic tubular membrane C includes a membrane separation layer 10 and a nonwoven fabric support layer 20. The nonwoven fabric support layer 20 includes a bottom layer 22 and a top layer 21. The thickness of the separation layer 10 is 150 μm, the thickness of the top layer 21 is 100 μm, the thickness of the bottom layer is 150 μm, and the permeation thickness of the casting solution is 150 μm. The basis weight of the top layer is 80 g / m³. 2 The surface layer has an air permeability of 25 dm. 3 / m 2 •s; the base weight is 140g / m² 2 The bottom layer has a breathability of 5dm. 3 / m 2 ·s.

[0064] The obtained organic tubular membrane C has a tensile strength at break of 650 N and a bubble point pressure of 1.2 bar. The membrane layer cannot be completely peeled off from the nonwoven support layer, and a standard peel strength test cannot be performed.

[0065] Comparative Example 1

[0066] S1: Cut commercially available non-woven fabric support strips into strips of the same size as in Example 1 to obtain non-woven fabric support strips;

[0067] S2: Coating for rolled tubes:

[0068] Using an organic tubular membrane production equipment, a nonwoven fabric support belt is spirally wound onto a central shaft at the same angle and overlap length as in Example 1. During winding, the overlap portion is ultrasonically welded to form a tubular nonwoven fabric support layer. Simultaneously, casting solution is pumped into the casting head at a certain rate and uniformly coated onto the inner surface of the nonwoven fabric support layer through the casting head to form a membrane separation layer, thus producing a tubular membrane element. The ultrasonic welding frequency, amplitude, pressure, as well as the properties and viscosity of the casting solution, the winding speed of the nonwoven fabric support tube, and the extrusion speed of the casting solution are all the same as in Example 1.

[0069] S3: Immerse the prepared tubular membrane element in a coagulation bath to complete the phase transformation and obtain an organic tubular membrane D with strong interfacial bonding.

[0070] The obtained organic tubular membrane D has a tensile strength at break of 300 N, a bubble point pressure of 0.5 bar, and a peel strength of 1.5 N / mm.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also within the protection scope of the present invention.

Claims

1. A strong interfacial bonding organic tubular membrane, characterized in that, The system includes a membrane separation layer and a nonwoven support layer. The nonwoven support layer is formed by spirally winding a nonwoven inner support strip with the outer layer facing inward and welding it at the overlap. The nonwoven inner support strip includes a bottom layer and a top layer. The top layer includes a portion of core-sheath composite fibers. The sheath composition of the core-sheath composite fibers is consistent with the polymer material in the casting solution. The membrane separation layer is formed by a phase inversion method using a casting solution coated on the inner surface of the nonwoven support layer. The casting solution permeates through the top layer of the nonwoven inner support strip but does not penetrate the bottom layer.

2. The organic tubular membrane with strong interfacial bonding according to claim 1, characterized in that, It also includes a nonwoven fabric reinforcement layer, which is formed by spirally overlapping and wrapping a nonwoven fabric outer support strip around the outer surface of the nonwoven fabric support layer and welding it at the overlap. The spiral direction of the nonwoven fabric outer support strip is opposite to that of the nonwoven fabric inner support strip.

3. The organic tubular membrane with strong interfacial bonding according to claim 1, characterized in that, The polymer materials include polysulfone, polyethersulfone, polyvinyl chloride, polyvinylidene fluoride, cellulose acetate, or polyacrylonitrile; the surface layer of the nonwoven inner support strip is made of 2-30 wt% of a core-sheath composite fiber and polyester or polypropylene fiber, and the bottom layer of the nonwoven inner support strip is made of polyester or polypropylene fiber.

4. The organic tubular membrane with strong interfacial bonding according to claim 1 or 2, characterized in that, The linear density of the surface layer fibers is 0.5–5 dtex; the surface layer pore size is 25–100 μm; the linear density of the bottom layer fibers is 0.1–1 dtex; and the bottom layer pore size is 5–10 μm.

5. The organic tubular membrane with strong interfacial bonding according to claim 3, characterized in that, The thickness of the nonwoven fabric outer support strip is 0.12–0.25 mm, and the basis weight is 120–220 g / m². 2 The fiber linear density is 0.1 to 1 dtex.

6. The organic tubular membrane with strong interfacial bonding according to claim 1, characterized in that, The surface layer weight is 40-80 g / m² 2 The surface layer thickness is 0.02–0.1 mm, and the surface layer air permeability is 15–75 dm³. 3 / m 2 •s; the base weight is 80-140 g / m² 2 The bottom layer thickness is 0.1–0.15 mm, and the bottom layer air permeability is 1–10 dm³. 3 / m 2 ·s.

7. The organic tubular membrane with strong interfacial bonding according to claim 5, characterized in that, The thickness of the membrane separation layer is 30–150 μm, and the thickness of the casting solution is 20–110 μm.

8. A method for preparing a strong interfacial bonding organic tubular membrane according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) The non-woven inner support belt and the casting liquid are placed together on the tubular coating machine. The non-woven inner support belt is spirally wound on the mandrel at a set angle and rolled into a tubular non-woven support layer by ultrasonic welding. At the same time, the casting liquid is pumped into the coating head at a certain rate and uniformly coated on the inner surface of the non-woven support layer through the coating head to form a membrane separation layer and make a tubular membrane element. (2) The prepared tubular membrane element is immersed in a coagulation bath to complete the phase transformation and obtain an organic tubular membrane with strong interfacial bonding.

9. The preparation method according to claim 8, characterized in that, The viscosity of the casting solution is 20,000 to 70,000 cp.

10. The preparation method according to claim 8, characterized in that, The extrusion speed of the casting solution and the winding speed of the nonwoven support tube satisfy the following relationship: Dt=3.95Vs+2.3; where: Vs is the winding speed, m / min; Dt is the extrusion speed of the casting solution, ml / min.

11. The preparation method according to claim 8, characterized in that, The ultrasonic welding frequency is 15–40 kHz, the amplitude is 8–50 micrometers, and the welding pressure is 3.0–8.5 bar.

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