PVC ultrafiltration membrane and modification method thereof

Abstract

The invention discloses a PVC ultrafiltration membrane and a modification method thereof.The modification method is obviously different from traditional blending modification, body modification, surface modification and other methods, specifically, a PVC ultrafiltration membrane matrix is impacted through high-pressure liquid, the high-pressure liquid is one of an acid solution, an alkaline solution and deionized water, and the PVC ultrafiltration membrane matrix is impacted through the high-pressure liquid; and the included angle between the nozzle for spraying the high-pressure liquid and the PVC ultrafiltration membrane substrate is 45-50 degrees, so that the hydrophilicity, the surface potential, the water flux and the dye retention rate of the PVC ultrafiltration membrane are remarkably improved on the basis of not changing the raw material components for preparing the PVC membrane. The invention also provides the PVC ultrafiltration membrane prepared by the preparation method.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a PVC ultrafiltration membrane and a modification method thereof. Background Art

[0002] Polyvinyl chloride (PVC) is the second largest general-purpose plastic in the world. It has good processing performance, flame retardancy, chemical stability, and certain acid and alkali resistance, and is inexpensive, so it is widely used in the preparation of separation membranes. Due to the low surface tension of the PVC material, the prepared PVC membrane has strong hydrophobicity and extremely low flux. Therefore, specific methods are required to modify the PVC membrane material.

[0003] Currently, the modification methods for PVC membrane materials mainly include blending modification, bulk modification, and surface modification. Blending modification is to mix PVC with other polymers, plasticizers (phthalates, phosphates), rubbers (nitrile rubber, chloroprene rubber), or elastomers, etc. to improve the performance of PVC. Bulk modification is to change the PVC molecular chain through chemical methods to improve its performance. For example, vinyl chloride monomer is copolymerized with other monomers to introduce new functional groups, or through chemical crosslinking or radiation crosslinking methods to form a crosslinked structure between PVC molecular chains. Common surface modification methods include coating modification, plasma treatment, and surface grafting modification. Coating modification is to coat a layer of other materials on the surface of the PVC membrane, such as coatings, resins, etc.; plasma treatment is to use plasma to treat the surface of the PVC membrane to introduce polar groups; surface grafting modification is to graft other functional monomers on the surface of the PVC membrane through chemical reactions. The above modification methods have achieved good results, but each method requires the introduction of other chemical components except polymers, which will increase the preparation cost and process difficulty of the membrane material to a certain extent. Therefore, it is necessary to develop a new modification method for PVC membrane materials. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides a modification method for a PVC ultrafiltration membrane, specifically by impacting the PVC ultrafiltration membrane matrix with high-pressure liquid; the high-pressure liquid is one of an acidic solution, an alkaline solution, and deionized water. The distance between the nozzle of the high-pressure liquid and the PVC ultrafiltration membrane matrix is 2 cm. There is relative movement between the PVC ultrafiltration membrane matrix and the nozzle ejecting the high-pressure liquid, and the speed of the relative movement is 1.0 m / min. The angle between the nozzle of the high-pressure liquid and the PVC membrane sheet is 45° - 50°. The modification method provided by the present invention improves its hydrophilicity, surface potential, water flux, and dye rejection rate without changing the composition of the raw materials for preparing the PVC ultrafiltration membrane.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] The first aspect of the present invention discloses a method for modifying a PVC ultrafiltration membrane, including:

[0007] Using high-pressure liquid to impact the PVC ultrafiltration membrane matrix.

[0008] In the modification method, the liquid is pressurized by a high-pressure pump and sent to a fine-pore nozzle, where it contacts low-pressure air to form high-speed micro-droplets (i.e., the high-pressure liquid), which impact on the PVC ultrafiltration membrane matrix.

[0009] According to some embodiments of the present invention, the preparation method of the PVC ultrafiltration membrane matrix includes the following steps:

[0010] Step 1: Prepare a casting solution from the preparation raw materials according to the following mass percentages:

[0011]

[0012] Prepare the casting solution and let it stand to eliminate air bubbles;

[0013] Step 2: Use the non-solvent induced phase separation method to prepare the PVC ultrafiltration membrane matrix, and soak the PVC ultrafiltration membrane matrix in deionized water for 10 - 12 h and then take it out for standby.

[0014] According to some embodiments of the present invention, in Step 1, the mass percentages of the preparation raw materials of the casting solution are:

[0015]

[0016] According to some embodiments of the present invention, in Step 1, during the preparation process of the casting solution, the temperature is 65°C - 75°C. For example, it can be specifically about 68°C, 70°C or about 72°C.

[0017] According to some embodiments of the present invention, in Step 1, the preparation process of the casting solution is carried out under stirring, and the stirring duration is 6 - 8 h; for example, it can be specifically about 6.5 h, 7 h or about 7.5 h.

[0018] According to some embodiments of the present invention, the pressure of the high-pressure liquid is 1 MPa - 3 MPa. For example, it can be specifically about 1.5 MPa, 2.0 MPa or about 2.5 MPa.

[0019] According to some embodiments of the present invention, the high-pressure liquid is at least one of water, acidic solution and alkaline solution.

[0020] According to some embodiments of the present invention, when the high-pressure liquid is water, the conductivity of the water is ≤ 11.7 μs / cm. For example, it can specifically be about 0.06 μs / cm, 0.05 μs / cm, or about 0.04 μs / cm. The types of water actually selected include at least one of deionized water, ultrapure water, and distilled water.

[0021] According to some embodiments of the present invention, when the high-pressure liquid is an acidic solution, the concentration of the acidic solution is 10 -6 ~10 -4 mol / L. For example, it can specifically be about 5×10 -6 mol / L or about 5×10 -5 mol / L.

[0022] According to some embodiments of the present invention, when the high-pressure liquid is an acidic solution, the concentration of the acidic solution is 10 -5 mol / L.

[0023] According to some embodiments of the present invention, when the high-pressure liquid is an acidic solution, the concentration of the acidic solution is 10 -6 mol / L.

[0024] According to some embodiments of the present invention, when the high-pressure liquid is an acidic solution, the solute of the acidic solution is HCl.

[0025] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the concentration of the alkaline solution is 10 -6 ~10 -4 mol / L. For example, it can specifically be about 5×10 -6 mol / L or about 5×10 -5 mol / L.

[0026] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the concentration of the alkaline solution is 10 -4 mol / L.

[0027] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the concentration of the alkaline solution is 10 -5 mol / L.

[0028] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the concentration of the alkaline solution is 10 -6 mol / L.

[0029] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the solute of the alkaline solution is at least one of NaOH, KOH, and LiOH.

[0030] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the solute of the alkaline solution is NaOH.

[0031] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the solute of the alkaline solution is KOH.

[0032] According to some embodiments of the present invention, when the high-pressure liquid is an alkaline solution, the solute of the alkaline solution is LiOH.

[0033] According to some embodiments of the present invention, the distance between the nozzle ejecting the high-pressure liquid and the PVC ultrafiltration membrane substrate is 1.5 cm to 3 cm, for example, about 2 cm or about 2.5 cm.

[0034] According to some embodiments of the present invention, in the modification method, there is relative motion between the PVC ultrafiltration membrane substrate and the nozzle ejecting the high-pressure liquid; the speed of the relative motion is 0.8 to 1.2 m / min.

[0035] According to some embodiments of the present invention, during the relative movement, the PVC ultrafiltration membrane substrate moves while the nozzle remains stationary. In this case, the PVC ultrafiltration membrane substrate moves by relying on the support plate.

[0036] According to some embodiments of the present invention, the angle formed between the nozzle and the ultrafiltration membrane substrate is 45°-50°, for example, about 48°.

[0037] The second aspect of the present invention discloses a PVC ultrafiltration membrane, which is prepared by the modification method provided in the embodiment of the first aspect of the present invention.

[0038] Preferably, the PVC ultrafiltration membrane is analyzed and evaluated using a nanofiltration membrane analyzer at a temperature of 25°C, an operating pressure of 1 bar, and an effective test area of 22.06 cm 2 The water flux of the PVC ultrafiltration membrane is 450-530 L / (m 2 ·h·bar), for example, it can be about 460L / (m 2 ·h·bar)、470L / (m 2 ·h·bar)、480L / (m 2 ·h·bar)、490L / (m 2 ·h·bar)、500L / (m 2 ·h·bar)、510L / (m 2 ·h·bar) or about 520L / (m 2 ·h·bar).

[0039] Preferably, for the PVC ultrafiltration membrane described above, a nanofiltration membrane analyzer is used for analysis and evaluation at a temperature of 25 °C, an operating pressure of 1 bar, and an effective test area of 22.06 cm 2 , and the Congo red rejection rate of the PVC ultrafiltration membrane is 95.8%-97%. For example, it can specifically be about 96% or about 96.5%.

[0040] Unless otherwise specified, the "about" in the present invention actually means that the allowable error is within the range of ±2%. For example, about 100 is actually 100 ± 2% × 100.

[0041] Other features and advantages of the present invention will be described in the following description of the specification, and part of them will become obvious from the specification or be understood by implementing the present invention. Description of the Drawings

[0042] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0043] Figure 1 is a schematic diagram of the principle of the modification method provided by the embodiment of the present invention;

[0044] Figure 2 is the angle between the nozzle of the high-pressure liquid and the moving direction of the PVC ultrafiltration membrane matrix in the modification method adopted by the embodiment of the present invention. Detailed Embodiments

[0045] The following will clearly and completely describe the concept and technical effects generated by the present invention in conjunction with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0046] Material Preparation Examples

[0047] In this example, a PVC ultrafiltration membrane matrix was prepared. The specific process was as follows:

[0048] Step 1: Prepare a casting solution according to the mass percentages of PVC-14%, PEG800-8%, PEG400-1%, and DMAC-77%, and let it stand to eliminate bubbles; during the preparation process, the temperature was 65 °C, and the preparation process was carried out under stirring, and the stirring duration was 8 h;

[0049] Step 2: Prepare the PVC ultrafiltration membrane matrix by non-solvent induced phase separation method, and soak the PVC ultrafiltration membrane matrix in deionized water for 12 h and then take it out for standby. Among them, the specific preparation process of the PVC ultrafiltration membrane matrix is as follows: First, take a clean glass plate, uniformly cast the casting solution that has removed bubbles in Step 1 at one end of the glass plate, use a self-made scraping rod to scrape a primary membrane with a thickness of about 200 μm evenly on the surface of the glass plate, and then quickly place the glass plate in UP water (ultrapure water) for phase inversion. After the membrane detaches from the glass plate, take it out and soak it in UP water for 12 h for standby.

[0050] Example 1

[0051] Reference Figures 1-2 , this example provides a modification method for PVC ultrafiltration membrane, and the specific modification method includes the following steps:

[0052] Use high-pressure liquid to impact the PVC ultrafiltration membrane matrix;

[0053] The liquid uses ultrapure water;

[0054] The high-pressure liquid, with a pressure of 3 Mbar;

[0055] The distance between the nozzle of the high-pressure liquid and the PVC ultrafiltration membrane matrix is 2 cm;

[0056] There is relative movement between the PVC ultrafiltration membrane matrix and the nozzle spraying the high-pressure liquid, and the speed of the relative movement is 1.0 m / min. Specifically, the PVC ultrafiltration membrane matrix is supported by a support plate and moves with the support plate, and the nozzle remains fixed;

[0057] The included angle between the nozzle of the high-pressure liquid and the PVC membrane sheet is 48°; the pressure of the high-pressure liquid is 3 MPa; the PVC ultrafiltration membrane is obtained through the above steps.

[0058] Example 2

[0059] This example provides a modification method for PVC ultrafiltration membrane, and the difference from Example 1 is:

[0060] The high-pressure liquid uses a NaOH alkaline solution with a concentration of 10 -4 mol / L.

[0061] Example 3

[0062] This example provides a modification method for PVC ultrafiltration membrane, and the difference from Example 1 is:

[0063] The high-pressure liquid uses an HCl acidic solution with a concentration of 10 -4 mol / L.

[0064] Example 4

[0065] This example provides a method for modifying a PVC ultrafiltration membrane, which is different from Example 3 in that:

[0066] The high-pressure liquid is an HCl acidic solution with a concentration of 10 -5 mol / L.

[0067] Example 5

[0068] This example provides a method for modifying a PVC ultrafiltration membrane, which is different from Example 3 in that:

[0069] The pressure of the high-pressure liquid is 2 MPa.

[0070] Test Example 1

[0071] The contact angle and surface potential of the PVC ultrafiltration membranes prepared in Example 1, Example 2, and Example 3 were measured using a KruSS / DSA25 contact angle measuring instrument and a Sur-PASS solid surface Zeta potential instrument.

[0072] The test results are shown in Table 1:

[0073] Table 1 Surface potential and contact angle of the PVC ultrafiltration membranes obtained in the examples and comparative examples

[0074]

[0075] It can be seen from the table results that when the pressure is the same, the modification effects of different high-pressure liquids on the PVC ultrafiltration membrane are ranked as: Example 3 > Example 4 > Example 1 > Example 2, that is, acidic condition > ultrapure water > alkaline condition.

[0076] The reason is that the C-Cl bond in the PVC molecular chain is relatively easy to break under acidic conditions, and dechlorination reaction occurs to form unsaturated double bonds (C=C). Driven by the mechanical force generated by friction, these unsaturated structures are prone to oxidation reaction with water molecules in the solution to generate strongly negatively charged carboxyl groups (-COOH), thereby further enhancing the negative charge on the membrane surface. Compared with deionized water, Na + introduced under alkaline conditions may be adsorbed on the membrane surface, partially shielding the negative charge, so the measured Zeta potential and contact angle decrease the least; the improvement degree of hydrophilicity is also not as good as that under acidic conditions.

[0077] It can be seen from the table results that for the modification effects of HCl solutions with different concentrations on the PVC ultrafiltration membrane, the ranking is: Example 3 > Example 4, that is, the higher the concentration of the HCl solution, the better the modification effect. However, a higher ion concentration will lead to too many free ions in the droplet, generating a shielding effect and interfering with electron transfer; therefore, if it exceeds the concentration range required by the present invention, the modification effect on the PVC ultrafiltration membrane matrix will instead decrease.

[0078] As can be seen from the tabular results: For the high-pressure liquid impact on the PVC ultrafiltration membrane matrix, under different pressures, the ranking of the modification effects on the PVC ultrafiltration membrane is: Example 3 > Example 5, that is, the greater the pressure, the better the modification effect. However, if the pressure is continuously increased, it will damage the microstructure of the PVC ultrafiltration membrane matrix, and ultimately have an obvious negative impact on the ultrafiltration effect of dyes such as Congo red.

[0079] Test Example 2

[0080] In this example, the Congo red rejection rate and water flux of the PVC ultrafiltration membrane matrix used in the examples and the obtained PVC ultrafiltration membrane were tested; specifically, a nanofiltration membrane analysis and evaluation instrument was used for testing; the test temperature and operating pressure were 25°C and 1 bar respectively, and the effective test area was 22.06 cm 2 ; Before the test, the PVC ultrafiltration membrane / PVC ultrafiltration membrane matrix was pre-pressed at 1.5 bar for 0.5 h to reach a stable state; the dye was Congo red, and an aqueous Congo red solution with a concentration of 0.05 g / L was prepared. Samples were collected every 0.5 h, and the volume of the permeate was recorded; each sample was checked at least three times to prevent any errors.

[0081] The calculation formula for the dye rejection rate is: R = (1 - Cp / Cr) × 100%, where R represents the rejection rate, and Cp and Cr are the concentrations of the liquid passing through the PVC ultrafiltration membrane and the feed aqueous Congo red dye solution respectively.

[0082] The calculation formula for the water flux is: F = V / A × t × p, where F is the permeability (water flux) of the PVC ultrafiltration membrane / PVC ultrafiltration membrane matrix under a given pressure, with the unit of L / (m 2 ·h·bar); V is the volume of the permeate solution (the liquid passing through the PVC ultrafiltration membrane / PVC ultrafiltration membrane matrix) (unit: L), A is the effective area of the PVC ultrafiltration membrane / PVC ultrafiltration membrane matrix (unit: m 2 ), and p is the filtration pressure (unit: bar). The test results are shown in Table 2.

[0083] Table 2 Congo red rejection rate and water flux of the PVC ultrafiltration membrane matrix used in the examples and the obtained PVC ultrafiltration membrane

[0084]

[0085]

[0086] The above results show that a method for modifying a PVC ultrafiltration membrane provided by the present invention can significantly improve the water flux and Congo red rejection rate of the PVC ultrafiltration membrane.

[0087] In summary, the present invention uses a simple modification method to significantly improve its hydrophilicity, surface potential, water flux, and dye rejection rate without changing the matrix / surface material of the PVC membrane and without adding extra chemical reagents, greatly enhancing the practicality of the PVC membrane and making it promising for wide applications in fields such as sewage treatment. Most importantly, the modification method provided by the present invention is simple to operate, low in cost, and easy to carry out large-scale production.

[0088] The above has described the embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments. Within the knowledge scope of those of ordinary skill in the art to which the present invention pertains, various changes can be made without departing from the gist of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A modification method of a PVC ultrafiltration membrane, characterized in that, The modification method includes subjecting the PVC ultrafiltration membrane matrix to high-pressure liquid impact.

2. The modification method according to claim 1, wherein The high-pressure liquid has a pressure of 1 MPa to 3 MPa.

3. The modification method according to claim 1, characterized in that, The high-pressure liquid is at least one of water, acidic solution, and alkaline solution.

4. The modification method according to claim 3, wherein, When the high-pressure liquid is an acidic solution, the concentration of the acidic solution is 10 -6 ~10 -4 mol / L; and / or, the solute of the acidic solution is HCl.

5. The modification method according to claim 3, wherein When the high-pressure liquid is an alkaline solution, the concentration of the alkaline solution is 10 -6 ~10 -4 mol / L; and / or, the solute of the alkaline solution is at least one of NaOH, KOH, and LiOH.

6. The modification method according to claim 1, characterized in that, The distance between the nozzle ejecting the high-pressure liquid and the PVC ultrafiltration membrane matrix is 1.5 cm to 3 cm.

7. According to the modification method described in claim 1, characterized in that, In the modification method, there is relative movement between the PVC ultrafiltration membrane matrix and the nozzle ejecting the high-pressure liquid; the speed of the relative movement is 0.8 to 1.2 m / min.

8. The modification method according to claim 1, wherein The angle between the nozzle ejecting the high-pressure liquid and the PVC ultrafiltration membrane matrix is 45° - 50°.

9. A PVC ultrafiltration membrane, characterized in that, The PVC ultrafiltration membrane is obtained by the modification method according to any one of claims 1 - 8.

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