Filtering membrane based on high-density polyethylene non-woven fabric supporting layer and preparation method of filtering membrane

Abstract

The invention discloses a filtering membrane based on a high-density polyethylene non-woven fabric supporting layer and a preparation method thereof, the filtering membrane comprises the supporting layer and a polymeric membrane layer formed on the supporting layer through a phase inversion method, the supporting layer is made of high-density polyethylene non-woven fabric and is formed by high-pressure thermal bonding of HDPE superfine fibers prepared through a flash evaporation method, and the polymeric membrane layer is made of high-density polyethylene non-woven fabric. The diameter of the fiber is 3-15 [mu] m, the aperture is less than 0.2 [mu] m, the gram weight is 70-150 g / m < 2 >, the thickness is 70-250 [mu] m, and the longitudinal breaking strength is 40-100 N / cm. The manufacturing cost of the filtering membrane is remarkably reduced, the bonding strength of the supporting layer and the polymeric membrane layer is good, and the obtained filtering membrane has good mechanical performance and filtering performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of filter membranes, and particularly relates to a filter membrane based on a high-density polyethylene non-woven fabric support layer and a preparation method thereof. Background Art

[0002] In the field of industrial applications, filter membranes are widely used in pressure-driven filtration processes and are usually made of polymer materials. However, the filter membranes prepared solely from polymer materials have low strength and are difficult to meet the requirements for mechanical properties and pressure resistance in actual use. Therefore, the commonly used filter membranes in the market mostly adopt a composite structure, that is, a polymer material is coated on a support layer to improve the overall strength and stability. The support layer is usually composed of non-woven fabric materials, and its main function is to provide mechanical support for the polymer filter membrane and ensure the structural integrity of the filter membrane under high-pressure environments.

[0003] In the prior art, the commonly used non-woven fabric materials for the support layer include polyethylene terephthalate (PET), polyethylene (PE), and polypropylene-polyethylene blend (PP / PE). For example, CN103551054A discloses a solution using non-woven fabrics made of materials such as PET, PE, or PP / PE as the support layer of the filter membrane. Among them, PET non-woven fabric is the most widely used in domestic filter membrane products due to its mature preparation process and stable performance; while foreign products, such as MICRODYN-NADIR, tend to use PP / PE blend non-woven fabric as the support layer to obtain better chemical resistance. However, due to process limitations and differences in application scenarios, PE non-woven fabric is less used in the support layer of filter membranes.

[0004] Although the above non-woven fabric materials meet the support requirements of the filter membrane to a certain extent, they still have significant defects. First, although the preparation technology of PET non-woven fabric is mature, its acid and alkali resistance is poor, and its performance is prone to degradation in acidic or alkaline environments, resulting in a shortened service life of the filter membrane. Second, although the acid and alkali resistance of PP / PE blend non-woven fabric has been improved, its preparation process is complex and the production cost is high, making it difficult to reduce the overall manufacturing cost of the filter membrane. According to statistics, the non-woven fabric support layer accounts for nearly 50% of the cost of organic filter membranes, becoming a key factor restricting the cost reduction of filter membranes. In addition, the binding force between PET and PP / PE non-woven fabrics and hydrophilic polymer materials (such as cellulose acetate membranes) is poor, and delamination or peeling is prone to occur under pressure driving, which further limits their application in hydrophilic filter membranes.

[0005] In the prior art, reducing costs and improving the bonding strength between the film layer and the support layer have always been difficult problems in the filtration membrane preparation industry. Although existing research has attempted to optimize performance by improving the coating process or adjusting the formulation of polymer materials, these methods often only target specific problems and fail to propose a systematic solution starting from the support layer material itself. Therefore, there is an urgent need for a new non-woven fabric material that can significantly reduce costs, improve the bonding strength with the polymer film layer, and meet the usage requirements of the filtration membrane in different chemical environments. Summary of the Invention

[0006] The object of the present invention is to overcome the defects of the prior art and provide a filtration membrane based on a high-density polyethylene non-woven fabric support layer.

[0007] Another object of the present invention is to provide a preparation method for the above-mentioned filtration membrane based on a high-density polyethylene non-woven fabric support layer.

[0008] Another object of the present invention is to provide the use of the above-mentioned high-density polyethylene non-woven fabric in the preparation of a support layer for a filtration membrane.

[0009] The technical solution of the present invention is as follows:

[0010] A filtration membrane based on a high-density polyethylene non-woven fabric support layer, comprising a support layer and a polymer film layer formed on the support layer by the phase inversion method. The material of the support layer is high-density polyethylene (HDPE) non-woven fabric, which is formed by high-pressure thermal bonding of HDPE ultra-fine fibers prepared by the flash evaporation method. Its fiber diameter is 3-15 μm, the pore size is less than 0.2 μm, the gram weight is 70-150 g / m2, the thickness is 70-250 μm, and the longitudinal breaking strength is 40-100 N / cm.

[0011] In a preferred embodiment of the present invention, the fiber diameter of the high-density polyethylene non-woven fabric is 3-9 μm, the pore size is 0.1 μm, the gram weight is 70-80 g / m2, the thickness is 170-200 μm, and the longitudinal breaking strength is 58-62 N / cm.

[0012] In a preferred embodiment of the present invention, the high-density polyethylene non-woven fabric is subjected to corona treatment, and the treatment time is 2-10 s.

[0013] In a preferred embodiment of the present invention, the material of the polymer film layer is a hydrophilic polymer material, and the hydrophilic polymer material is cellulose acetate.

[0014] More preferably, the formulation of the casting solution for forming the polymer film layer includes: 20 wt% of cellulose acetate, 10 wt% of polyvinylpyrrolidone, 5 wt% of polyethylene glycol 400, and 65 wt% of N,N-dimethylacetamide (DMAC).

[0015] In a preferred embodiment of the present invention, the material of the polymer film layer is a hydrophobic polymer material, and the hydrophobic polymer material is polyethersulfone.

[0016] More preferably, the polymer film layer is prepared by the phase inversion method, and the casting solution formulation includes: 20 wt% of polyethersulfone, 8 wt% of polyvinylpyrrolidone, 7 wt% of polyethylene glycol 400, and 65 wt% of N,N-dimethylacetamide (DMAC).

[0017] The preparation method of the above-mentioned filter membrane includes the following steps:

[0018] (1) Prepare high-density polyethylene non-woven fabric: The polymer ethylene hydrocarbon is hot-melt processed into continuous filaments by the flash evaporation method and formed into high-density polyethylene non-woven fabric through high-pressure thermal bonding;

[0019] (2) Coating the polymer film layer: The prepared casting solution is coated on the surface of the high-density polyethylene non-woven fabric obtained in step (1), and a polymer film layer is formed by the phase inversion method;

[0020] (3) Post-treatment: The material obtained in step (2) is soaked in a 10% glycerol solution and dried to obtain the product;

[0021] Before step (2), when the material of the polymer film layer is a hydrophilic polymer material, the high-density polyethylene non-woven fabric is subjected to corona treatment for 2 - 10 s; when the material of the polymer film layer is a hydrophobic polymer material, the corona treatment is omitted.

[0022] The use of high-density polyethylene non-woven fabric in the preparation of the filter membrane support layer, the high-density polyethylene non-woven fabric is formed by hot-melting 100% polymer ethylene hydrocarbon into continuous filaments and then through high-pressure thermal bonding, its fiber diameter is 3 - 15 μm, the pore size is less than 0.2 μm, the gram weight is 70 - 150 g / m2, and the thickness is 70 - 250 μm, and the longitudinal breaking strength is 50 - 100 N / cm.

[0023] In a preferred embodiment of the present invention, the high-density polyethylene non-woven fabric is subjected to corona treatment for 2 - 10 s.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention uses HDPE non-woven fabric as the support layer of the filter membrane. Its raw materials are widely sourced, and the preparation process is mature and efficient. Compared with the PET non-woven fabric and PP / PE blended non-woven fabric commonly used in the support layer of traditional filter membranes, the price of HDPE non-woven fabric is only 10% to 50% of theirs. Since the support layer accounts for nearly 50% of the cost of the organic filter membrane, the material replacement in the present invention significantly reduces the overall membrane production cost, providing an economic guarantee for the large-scale production and market promotion of the filter membrane.

[0026] 2. By corona treating the surface of the HDPE non-woven fabric in the present invention, its contact angle is reduced from 110° to 98°, the hydrophobicity is weakened, and the surface energy is significantly increased, thereby enhancing the adhesion to hydrophilic polymer materials (such as cellulose acetate). Experimental data shows that when the HDPE non-woven fabric without corona treatment is combined with the cellulose acetate membrane, the peeling grid number in the cross-cut test is as high as 24 grids (total 25 grids), indicating poor bonding strength; while after corona treatment, the peeling grid number is reduced to 4 grids, and the bonding strength far exceeds that of PET non-woven fabric (peeling 21 grids). This improvement effectively solves the problem of insufficient bonding strength between PET and PP / PE non-woven fabrics and hydrophilic membranes in the prior art, and avoids the risk of delamination between the membrane layer and the support layer under pressure drive.

[0027] 3. The HDPE non-woven fabric in the present invention is prepared by the flash evaporation method and the high-pressure thermal bonding process, and has characteristics such as a fiber diameter of 3 - 15 μm, a pore size less than 0.2 μm, and a longitudinal breaking strength of 50 - 100 N / cm. Its breaking strength is higher than 40 N / cm, meeting the strength requirements of the equipment for the support layer. At the same time, compared with PET and PP / PE non-woven fabrics, HDPE non-woven fabric is not easy to shed chips, and it is not easy to tear along the rupture, ensuring the structural stability of the filter membrane during use. The flux and rejection rate tests show that for the filter membrane using HDPE non-woven fabric in the application of hydrophilic polymers (such as cellulose acetate), the flux is nearly doubled compared with that of PET non-woven fabric, and the rejection rate remains above 95%, taking into account both high-efficiency filtration and cost control.

[0028] 4. The present invention first introduces the HDPE non-woven fabric commonly used in the textile industry into the field of the support layer of the filter membrane, breaking through the limitations of traditional PET and PP / PE materials. The HDPE non-woven fabric is not only applicable to hydrophobic polymer (such as polyethersulfone, polyvinylidene fluoride) membrane layers, showing the same bonding strength as in the prior art, but also adapts to hydrophilic membrane layers through corona treatment, significantly broadening the selection range of filter membrane support layer materials and providing a flexible solution for different application scenarios. Description of the Drawings

[0029] Figure 1 Showing the comparison results of the electron microscope structures of HDPE-1, corona-treated HDPE-1, and PET-1 in Example 1 of the present invention.

[0030] Figure 2 Show the comparison results of the cross-sectional electron microscope structures of the polymer film layers on HDPE-1, corona-treated HDPE-1, and PET-1 in Example 1 of the present invention.

[0031] Figure 3 Show the comparison results of the surface electron microscope structures of the polymer film layers on HDPE-1, corona-treated HDPE-1, and PET-1 in Example 1 of the present invention.

[0032] Figure 4 Show the comparison results of the bonding strengths of HDPE-1, corona-treated HDPE-1, and PET-1 in Example 1 of the present invention.

[0033] Figure 5 Show the comparison results of the fluxes and rejection rates of HDPE-1, corona-treated HDPE-1, and PET-1 in Example 1 of the present invention.

[0034] Figure 6 Show the comparison results of the mechanical strengths of HDPE-2, corona-treated HDPE-1, and PET-1 in Example 1 of the present invention.

[0035] Figure 7 Show the comparison results of the electron microscope structures of HDPE-2, PP / PE, and PET-2 in Example 2 of the present invention.

[0036] Figure 8 Show the comparison results of the cross-sectional electron microscope structures of the polymer film layers on HDPE-2, PP / PE, and PET-2 in Example 2 of the present invention.

[0037] Figure 9 Show the comparison results of the surface electron microscope structures of the polymer film layers on HDPE-2, PP / PE, and PET-2 in Example 2 of the present invention.

[0038] Figure 10 Show the comparison results of the bonding strengths of HDPE-2, PP / PE, and PET-2 in Example 2 of the present invention.

[0039] Figure 11 Show the comparison results of the fluxes and rejection rates of HDPE-2, PP / PE, and PET-2 in Example 2 of the present invention.

[0040] Figure 12 Show the comparison results of the mechanical strengths of HDPE-2, PP / PE, and PET-2 in Example 2 of the present invention. Detailed implementation manners

[0041] The technical solutions of the present invention will be further described and illustrated below through specific implementation manners in conjunction with the accompanying drawings.

[0042] Example 1

[0043] (1) Preparation of high-density polyethylene non-woven fabric: Prepared by the flash evaporation method, specifically including: After softening high-density polyethylene HDPE chips with a density of 0.95 g / cm 3 , they are mixed with dichloromethane in a mixing kettle, and a spinning solution with a concentration of 15 wt% is prepared under the conditions of a temperature of 200 °C and a pressure of 20 MPa; The spinning solution is sprayed through a decompression nozzle into a room-temperature environment, and dichloromethane instantly volatilizes to form HDPE ultrafine fibers; The HDPE ultrafine fibers are divided and redirected under the action of a baffle and then deposited on a receiving net to form a fiber web; The fiber web is conveyed to a metal light roller hot rolling machine and thermally bonded under the conditions of a temperature of 230 °C and a linear pressure of 15 MPa to form a non-woven fabric HDPE-1 with a thickness of 170 μm, a gram weight of 70 g / m 2 , a fiber diameter of 3 - 6 μm, a pore diameter of 0.1 μm, and a longitudinal breaking strength of 58 N / cm;

[0044] Corona treatment of HDPE-1: Using a single-sheet corona treatment machine, adjusting the power to 2 kW and the treatment time to 5 s; The comparison of the pure water contact angles before and after corona treatment is shown in Table 1 below:

[0045] Table 1

[0046] Initial water contact angle Spreading condition HDPE-1 110° No change in 2 min HDPE-1 corona 98° No change in 2 min PET-1 59° 20s

[0047] The comparison of the microstructures before and after corona treatment is as Figure 1 shown. Under the same magnification, the number of pores on the surface of the HDPE non-woven fabric is significantly more than that on the PET surface. The main reason is that the HDPE fibers are finer. Theoretically, the more pores in the non-woven fabric, the better the bonding force between the polymer film layer and the non-woven fabric;

[0048] (2) Coating the polymer film layer: The prepared casting solution is coated on the surface of HDPE-1 obtained in step (1), and then immersed in a pure water coagulation solution to form the polymer film layer of the filter membrane through phase inversion; The formula of the casting solution is as follows:

[0049]

[0050] (3) Post-treatment: The material obtained in step (2) is soaked in a 10% glycerol solution and dried in an oven at 70 °C to obtain the filter membrane;

[0051] As Figure 2 can be seen, under the same magnification, the number of pores on the surface of the HDPE non-woven fabric is significantly more than that on the PET surface. The main reason is that the HDPE fibers are finer. Theoretically, the more pores in the non-woven fabric, the better the bonding force between the polymer film layer and the non-woven fabric;

[0052] As Figure 3It can be seen that the surface structure is consistent with the surface of the PET non-woven fabric filter membrane after corona treatment, showing a smooth surface. The surface of the HDPE filter membrane without corona treatment forms bubble-like protrusions, so it is proved that the hydrophilic polymer coating material, cellulose acetate, must undergo corona treatment.

[0053] Performance tests were carried out on the filter membranes and HDPE-1 prepared in this example, as follows:

[0054] A. Adhesion test: The adhesion strength between the polymer film layer and HDPE-1 was tested using the cross-cut method (refer to GB / T9286-98). The results are shown in Table 2 below and Figure 4 as follows:

[0055] Table 2

[0056] HDPE-1 HDPE-1 corona PET-1 (same grammage as HDPE-1) Number of tape peelings: 24 Number of tape peelings: 4 Number of tape peelings: 21

[0057] B. Flux and rejection rate: The results are as Figure 5 shown. HDPE-1 with the same gram weight has better flux performance than PET-1. The flux is almost doubled, and it has the same rejection rate. The rejection rate of bovine serum albumin is higher than 95%.

[0058] C. Mechanical strength test: The results are as Figure 6 shown. After corona treatment, the strength of HDPE-1 remains basically unchanged. The longitudinal breaking strength of non-woven fabrics of different materials is higher than 40 N / cm, which can meet the strength requirements of the equipment for non-woven fabrics.

[0059] Example 2

[0060] (1) Preparation of high-density polyethylene non-woven fabric: Prepared by the flash evaporation method, specifically including: High-density polyethylene HDPE chips with a density of 0.95 g / cm 3 are softened and mixed with dichloromethane in a mixing kettle, and a 15 wt% spinning solution is prepared under the conditions of a temperature of 200 °C and a pressure of 20 MPa; the spinning solution is sprayed through a decompression spray chamber into a room temperature environment, and the solvent instantly volatilizes to form HDPE ultrafine fibers; the HDPE ultrafine fibers are split, turned and redeposited on a receiving net under the action of a baffle to form a fiber web; the fiber web is transported to a metal light roller hot rolling machine and thermally bonded under the conditions of a temperature of 230 °C and a linear pressure of 15 MPa to form a non-woven fabric HDPE-2 with a thickness of 200 μm, a gram weight of 80 g / m 2 , a fiber diameter of 5 - 9 μm, a pore diameter of 0.1 μm, and a longitudinal breaking strength of 62 N / cm. The contact angles of HDPE-2 with respect to DMAC are shown in Table 3 below, and the microstructures of HDPE-2, PET-2 (same gram weight) and PP / PE (same gram weight) are compared as Figure 7 follows:

[0061] Table 3

[0062] Initial DMAC contact angle Spreading condition HDPE-2 0° Spreads in 1 s PET-2 0° Spreads in 1 s PP / PE 0° Spreads in 1 s

[0063] (2) Coating the polymer film layer: Coating the prepared casting solution on the surface of the high-density polyethylene non-woven fabric obtained in step (1), and then immersing the non-woven fabric in pure water coagulant to form the polymer film layer of the filter membrane through phase inversion; the formula of the casting solution is as follows:

[0064]

[0065] (3) Post-treatment: Immerse the material obtained in step (2) in a 10% glycerol solution and dry it in an oven at 70 °C to obtain the filter membrane as shown in Figure 8 and Figure 9 .

[0066] Perform performance tests on the filter membrane prepared in this example, specifically as follows:

[0067] A. Adhesion test: Use the cross-cut method (refer to GB / T9286-98) to test the bonding strength between the polymer film layer and the HDPE non-woven fabric. The results are shown in Table 4 below and Figure 10 as follows:

[0068] Table 4

[0069] HDPE-2 PET-2 PP / PE Number of tape peelings: 1 Number of tape peelings: 0 Number of tape peelings: 3

[0070] B. Flux and rejection rate: The results are as shown in Figure 11 . By comparing the flux and rejection data, the flux of HDP-2 is lower than that of the commonly used PP / PE non-woven fabric and PET non-woven fabric with the same gram weight, but the rejection data of the three are similar, all higher than 95%.

[0071] C. Mechanical strength test: The results are as shown in Figure 12 . By comparing the data of three different non-woven fabrics, the breaking strength is greater than 40 N / cm, all meeting the requirements of the equipment for the strength of non-woven fabrics.

[0072] The above is only a preferred embodiment of the present invention, and thus the scope of implementation of the present invention cannot be limited thereby. That is, equivalent changes and modifications made according to the scope of the present invention patent and the content of the specification should still fall within the scope covered by the present invention.

Claims

1. A filter membrane based on a high-density polyethylene non-woven fabric support layer, characterized in that: It includes a support layer and a polymer film layer formed on the support layer by a phase inversion method. The support layer is made of high-density polyethylene non-woven fabric, which is made of HDPE ultrafine fibers prepared by a flash evaporation method and bonded under high pressure. The fiber diameter is 3-15μm, the pore size is less than 0.2μm, the gram weight is 70-150g / m2, the thickness is 70-250μm, and the longitudinal breaking strength is 40-100N / cm.

2. The filtration membrane according to claim 1, characterized in that: The fiber diameter of the high-density polyethylene non-woven fabric is 3-9 μm, the pore size is 0.1 μm, the gram weight is 70-80 g / m2, the thickness is 170-200 μm, and the longitudinal breaking strength is 58-62 N / cm.

3. The filtration membrane according to claim 1 or 2, characterized in that: The high-density polyethylene non-woven fabric is subjected to corona treatment for 2-10 seconds.

4. The filtration membrane according to claim 1, characterized in that: The material of the polymer film layer is a hydrophilic polymer material, and the hydrophilic polymer material is cellulose acetate.

5. The filtration membrane according to claim 4, characterized in that: The formula of the casting solution for forming the polymer film layer includes: 20wt% of cellulose acetate, 10wt% of polyvinyl pyrrolidone, 5wt% of polyethylene glycol 400 and 65wt% of NN dimethylacetamide.

6. The filtration membrane according to claim 1, characterized in that: The material of the polymer membrane layer is a hydrophobic polymer material, and the hydrophobic polymer material is polyethersulfone.

7. The filtration membrane according to claim 6, characterized in that: The polymer membrane layer is prepared by a phase conversion method, and the casting solution formula includes: 20wt% of polyethersulfone, 8wt% of polyvinylpyrrolidone, 7wt% of polyethylene glycol 400 and 65wt% of NN dimethylacetamide.

8. The method for preparing a filtration membrane according to any one of claims 1 to 7, characterized in that: The steps include: (1) Preparation of high-density polyethylene non-woven fabric: using flash evaporation to hot-melt polymer ethylene into continuous filaments, and then forming high-density polyethylene non-woven fabric by high-pressure thermal bonding; (2) coating a polymer film layer: coating the prepared casting solution on the surface of the high-density polyethylene non-woven fabric obtained in step (1) to form a polymer film layer by a phase inversion method; (3) Post-treatment: soaking the material obtained in step (2) in a 10% glycerol solution and drying to obtain; Before step (2), when the material of the polymer film layer is a hydrophilic polymer material, the high-density polyethylene non-woven fabric is subjected to a corona treatment for 2-10 seconds; when the material of the polymer film layer is a hydrophobic polymer material, the corona treatment is omitted.

9. Use of high-density polyethylene nonwoven fabric in preparing a filter membrane support layer, characterized in that: The high-density polyethylene non-woven fabric is made of 100% polymer ethylene olefins which are processed into continuous filaments by hot-melt processing and then bonded by high-pressure heat. Its fiber diameter is 3-15μm, pore size is less than 0.2μm, gram weight is 70-150g / m2, thickness is 70-250μm, and longitudinal breaking strength is 50-100N / cm.

10. The use according to claim 9, characterized in that: The high-density polyethylene non-woven fabric is subjected to corona treatment for 2-10 seconds.

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