Modified pet film and method for hydrophilic modification thereof

Abstract

The application provides a modified PET film, which is grafted with PET hydrophilic groups on the surface, so that the hydrophilicity of the PET film surface is greatly improved, and the water contact angle is at least 25 degrees. The application also provides a hydrophilic modification method of the modified PET film, which comprises the following steps: cleaning the PET film, soaking the PET film in a heated first immersion liquid and a second immersion liquid, and cleaning and drying the PET film, so that the PET film surface is grafted with PEI hydrophilic groups, and the grafting treatment frequency can be adjusted according to the required water contact angle. The modified PET film obtained by the hydrophilic modification method has obvious hydrophilic effect and good stability, and the morphology of the original PET film is maintained.

Description

Technical Field

[0001] This invention relates to the technical field of polymer membranes, and in particular to a modified PET membrane and its hydrophilic modification method. Background Technology

[0002] Nuclear-pore membranes are a novel type of sieve-like filtration membrane. They are typically prepared by irradiating a polymer film with heavy ions to create columnar damage zones with diameters of several nanometers within the polymer, followed by chemical etching to form pores. Nuclear-pore membranes offer controllable pore density and adjustable pore size, making them valuable for applications in filtration, ion transport, and battery separators.

[0003] PET is an abbreviation for polyethylene terephthalate, which is a condensation polymer of terephthalic acid and ethylene glycol. Due to its excellent physical and mechanical strength, chemical stability, dimensional stability, transparency, and thermal stability, PET film is one of the excellent candidate raw materials for core-pore membranes.

[0004] However, PET film's molecular chain lacks hydrophilic groups, exhibiting natural hydrophobicity. Tests show that the water contact angle of raw PET film is approximately 79°, indicating low hydrophilicity. This limits the application of PET core-porous membranes in filtration, and also restricts their application due to the tendency for organic pollutants to adsorb onto the membrane surface. Therefore, surface modification of PET membranes is necessary to improve their hydrophilicity. Common hydrophilic treatment methods include: 1. Surface irradiation treatment: Plasma irradiation is used to activate the membrane surface under different gas atmospheres to generate free radicals, which are then grafted with hydrophilic substances. This method is costly, requires vacuum mode, and cannot achieve continuous production. Moreover, the hydrophilicity of the modified membrane obtained by plasma irradiation treatment decays rapidly. 2. Surface coating treatment: The PET membrane surface is treated by alkaline hydrolysis modification and oxidation modification methods. For example, N-methacrylamide, a dopamine derivative, undergoes oxidative self-polymerization in an alkaline environment to form a hydrophilic coating on the PET membrane surface. However, the synthesis of dopamine derivatives is time-consuming and not suitable for mass production. Furthermore, surface coating treatment may cause uneven membrane surface morphology and pore blockage. 3. Surface chemical grafting treatment: Hydrophilic groups are grafted onto the PET membrane surface through pretreatment or the use of initiators. This method is relatively inexpensive, easy to operate, and suitable for industrialization. However, the existing PET film surface is chemically grafted with groups such as acrylic acid, 4-vinylpyridine, hydroxyethyl methacrylate, and 2-acrylamide-methylpropanesulfonic acid, which limits its application range.

[0005] Therefore, in order to improve the hydrophilicity of PET core-pore membranes and increase their application efficiency, it is necessary to develop a hydrophilic PET membrane that is effective and stable and does not damage the original morphology of the membrane material. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a modified PET film. By grafting polyethyleneimine (PEI) onto the surface of the PET film, the hydrophilicity of the PET film surface is significantly improved, with a minimum water contact angle of 25°. This invention also provides a method for hydrophilic modification of this PET film, allowing the number of grafting treatments to be adjusted according to the desired water contact angle. The modified PET film obtained through this method exhibits significant hydrophilicity, good stability, and retains the morphology of the original PET film.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A modified PET film, wherein hydrophilic groups are grafted onto the surface of the modified PET film, and the modified PET film has the following structural formula:

[0009]

[0010] The number of grafting steps is m = 2; the average value of n is 12.6.

[0011] n is the number of ethyleneimine repeating units in polyethyleneimine. For the PEI molecule with a molecular weight of 600 Da used in this application, the average value of the repeating unit n is 12.6.

[0012] Furthermore, the modified PET film is grafted with PEI groups, and the water contact angle of the modified PET film can be as low as 25°.

[0013] The present invention also provides a method for hydrophilic modification of the above-mentioned modified PET film, comprising the following steps:

[0014] S1. Immerse the PET film in acetonitrile to wash away surface stains;

[0015] S2. Immerse the PET film treated in S1 in the heated first impregnation solution, maintain the temperature, remove the PET film, and then immerse it in acetonitrile stored at room temperature for cleaning.

[0016] S3. Immerse the PET film treated in S2 in the heated second impregnation solution, maintain the temperature, remove the PET film, and quickly and completely immerse it in ultrapure water for cleaning.

[0017] S4. Remove the PET membrane from the ultrapure water and dry it in the air to obtain a modified PET membrane with a grafting step number m = 1.

[0018] As a further description of the hydrophilic modification method of the present invention, steps S1-S4 are repeated, and after each complete treatment by steps S1-S4, the grafting step count m of the PET film is incremented by 1.

[0019] The grafting step number m represents the number of grafting steps and corresponds to m layers of PEI. For example, after two steps S1-S4, the grafting step number m is 2, meaning that 2 layers of PEI have been grafted.

[0020] The reaction formula is as follows:

[0021]

[0022] As a further description of the hydrophilic modification method of the present invention, the first impregnation solution, by weight, comprises the following components: 0.46-0.92 parts phosphorus oxychloride, 24 parts acetonitrile, Molecular sieve 0.10-0.50 parts.

[0023] As a further description of the hydrophilic modification method of the present invention, the second impregnation solution, by weight, comprises the following components: 1.8-3.6 parts polyethyleneimine, 24 parts acetonitrile, 0.10-0.50 parts of molecular sieve; the molecular weight of the polyethyleneimine is 600 Da.

[0024] As a further description of the hydrophilic modification method of the present invention, both the first impregnation solution and the second impregnation solution are heated to 20-60°C. Preferably, in step S2, the PET film is immersed in the first impregnation solution heated to 50°C; in step S3, the PET film is immersed in the second impregnation solution heated to 50°C.

[0025] As a further description of the hydrophilic modification method of the present invention, in S1, the immersion time of the PET film in acetonitrile is 0.5-1.5 min; preferably, the immersion time is 1 min.

[0026] As a further description of the hydrophilic modification method of the present invention, in step S2, the PET film is immersed in the first impregnation solution for a constant temperature immersion time of 3-7 minutes. Preferably, the constant temperature immersion time in the first impregnation solution is 5 minutes.

[0027] As a further description of the hydrophilic modification method of the present invention, in step S3, the PET film is immersed in the second impregnation solution for a constant temperature immersion time of 5-30 minutes. Preferably, the constant temperature immersion time in the second impregnation solution is 15 minutes.

[0028] Based on the above technical solution, compared with the prior art, the technical effects achieved by the present invention are as follows:

[0029] (1) The modified PET membrane provided by the present invention improves the hydrophilicity of the PET membrane surface by performing PEI grafting modification treatment on the surface of the PET membrane. While maintaining the morphology of the PET prokaryotic membrane, its water contact angle can reach as low as 25°, and the water flux is increased by 24-35% compared with the unmodified PET prokaryotic membrane.

[0030] (2) The hydrophilic modification method for modified PET film provided by this invention allows for adjustment of the number of grafting steps according to the required water contact angle. The process is quick, simple, and inexpensive. After treatment with this hydrophilic modification method, the hydrophilicity of PET film is significantly improved, and the contact angle of the PET film decreases with increasing number of treatment steps. Compared with hydrolysis modification, oxidation modification, and plasma treatment methods, this method exhibits significant hydrophilic modification effects and good stability, maintaining the morphology of the PET film during the hydrophilic modification process. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the contact angle of an unmodified PET film.

[0032] Figure 2 This is a schematic diagram of the contact angle of the modified PET film in Example 1 of the present invention.

[0033] Figure 3 This is a comparison of the water flux of a single-step grafted modified PET membrane (m=1) and an unmodified PET core-pore membrane.

[0034] Figure 4 The graph shows the relationship between the contact angle of the modified PET film and the number of PEI grafting steps (m).

[0035] Figure 5 The graph shows the relationship between the water flux of the modified PET membrane and the number of PEI grafting steps (m). Detailed Implementation

[0036] To facilitate understanding of the present invention, a more comprehensive description will be given below in conjunction with the accompanying drawings and specific embodiments. The drawings illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0038] A modified PET film, wherein the surface of the modified PET film is grafted with hydrophilic PEI groups, and the modified PET film has the following structural formula:

[0039]

[0040] The number of grafting steps is m = 2; the average value of n is 12.6.

[0041] The modified PET film was prepared by the following hydrophilic modification method, specifically including the following steps:

[0042] S1. Immerse the PET film in acetonitrile to wash away surface stains;

[0043] S2. Immerse the PET film treated in S1 in the heated first impregnation solution. After constant temperature immersion treatment, remove the PET film and immerse it in acetonitrile stored at room temperature for cleaning.

[0044] S3. Immerse the PET film treated in S2 in the heated second impregnation solution. After constant temperature immersion treatment, remove the PET film and quickly and completely immerse it in ultrapure water for cleaning.

[0045] S4. Remove the PET membrane from the ultrapure water and dry it in the air to obtain a single-step modified PET membrane.

[0046] Repeat steps S1-S4. After each complete processing through steps S1-S4, increment the PET film grafting step count m by 1.

[0047] In step S1, the immersion time of the PET film in acetonitrile is 0.5-1.5 min, preferably 1 min.

[0048] In S2, the first impregnation solution consists of the following components by weight: 0.46-0.92 parts phosphorus oxychloride, 24 parts acetonitrile, 0.10-0.50 parts of molecular sieve. The first impregnation solution has been heated to 50°C, and the PET film is immersed in the first impregnation solution for constant temperature treatment for 3-7 minutes, preferably 5 minutes.

[0049] In S3, the second impregnation solution consists of the following components by weight: 1.8-3.6 parts polyethyleneimine, 24 parts acetonitrile, 0.10-0.50 parts of molecular sieve. The second impregnation solution has been heated to 50°C, and the PET film is immersed in the second impregnation solution for constant temperature treatment for 5-30 minutes, preferably 15 minutes.

[0050] The following is the complete reaction equation for PEI grafting modification on the surface of PET film:

[0051]

[0052] The reaction equation is explained below:

[0053] In each grafting step, the terminal PEI group is NH2. Due to space limitations, the NH2 terminal groups in plots with m ≥ 2 are omitted. All individual PEI molecules in each layer have a molecular weight of 600 Da.

[0054] When the grafting step number m = 1, the modified PET film and PEI are connected by amide bonds (-C(O)-NH-); when the grafting step number m ≥ 2, the PEI molecules in adjacent layers are connected by phosphatamide bonds (-NH-P(O)-NH-). Due to the limited drawing space, some phosphatamide bonds in the figures with grafting steps m = 4 and m = 5 are simplified to wavy lines.

[0055] Comparative Example 1

[0056] Unmodified PET film.

[0057] Figure 1 This is a schematic diagram of the contact angle of an unmodified PET film. Tests show that... Figure 1 As shown, the contact angle of the unmodified PET film is 79.2°.

[0058] Example 1

[0059] A modified PET film is prepared by the following hydrophilic modification method, the specific steps of which are as follows:

[0060] Immerse the PET core-pore membrane in acetonitrile for 1 minute to wash away surface stains.

[0061] The PET core-pore membrane was immersed in a first impregnation solution heated to 50°C; the first impregnation solution contained phosphorus oxychloride, acetonitrile, and... Molecular sieve ratio: 0.46:24:0.1; After immersion treatment at constant temperature for 5 minutes, the PET film was removed and immersed in acetonitrile stored at room temperature for cleaning.

[0062] The PET film is immersed in a second impregnation solution heated to 50°C; in the second impregnation solution, the ratio of polyethyleneimine to acetonitrile is: Molecular sieve ratio: 3.6:24:0.5; immersion treatment at constant temperature for 15 minutes, then remove the PET membrane and quickly and completely immerse it in ultrapure water for cleaning, followed by air drying. Repeat the above steps 4 times.

[0063] Figure 2 This is a schematic diagram of the contact angle of the modified PET film in Example 1. After testing, as shown... Figure 2As shown, the PET film in this embodiment achieved maximum hydrophilicity after undergoing five hydrophilic modification treatments, and the contact angle of the PET film after hydrophilic modification treatment decreased from 79.2° to 25.0°.

[0064] contrast Figure 1 and Figure 2 As shown in the contact angle diagram, the water contact angle of the PET film after 5 grafting steps decreased from 79.2° to 25.0°. This result is better than common surface modification methods, such as hydrolysis modification and oxidation modification, and also better than most other grafting methods. Moreover, its hydrophilic stability is higher than that of plasma treatment modification methods.

[0065] Example 2

[0066] A modified PET film is prepared by the following hydrophilic modification method, the specific steps of which are as follows:

[0067] Immerse the PET core-pore membrane in acetonitrile for 1 minute to wash away surface stains.

[0068] The PET core-pore membrane was immersed in a first impregnation solution heated to 50°C; the first impregnation solution contained phosphorus oxychloride, acetonitrile, and... Molecular sieve ratio: 0.92:24:0.25; After immersion treatment at constant temperature for 5 minutes, the PET film was removed and immersed in acetonitrile stored at room temperature for cleaning.

[0069] The PET film is immersed in a second impregnation solution heated to 50°C; in the second impregnation solution, the ratio of polyethyleneimine to acetonitrile is: Molecular sieve ratio = 1.8:24:0.1; constant temperature immersion treatment for 15 minutes, remove the PET membrane and quickly and completely immerse it in ultrapure water for cleaning, and then dry it in the air.

[0070] Repeat the above steps four times. After testing, the contact angle of the hydrophilic modified PET film decreased from 79.2° to 25.6°.

[0071] Example 3

[0072] A modified PET film is prepared by the following hydrophilic modification method, the specific steps of which are as follows:

[0073] Immerse the PET core-pore membrane in acetonitrile for 1 minute to wash away surface stains.

[0074] The PET core-pore membrane was immersed in a first impregnation solution heated to 50°C; the first impregnation solution contained phosphorus oxychloride, acetonitrile, and... Molecular sieve ratio: 0.46:24:0.25; After constant temperature immersion treatment for 5 minutes, the PET film was removed and immersed in acetonitrile stored at room temperature for cleaning.

[0075] The PET film is immersed in a second impregnation solution heated to 50°C; in the second impregnation solution, the ratio of polyethyleneimine to acetonitrile is: Molecular sieve ratio = 1.8:24:0.5; constant temperature immersion treatment for 15 minutes, remove the PET membrane and quickly and completely immerse it in ultrapure water for cleaning, and then dry it in air.

[0076] Repeat the above steps four times. After testing, the contact angle of the hydrophilic modified PET film decreased from 79.2° to 25.2°.

[0077] Example 4

[0078] The unmodified PET pronuclear pore membrane of Comparative Example 1 and the preferred PET membrane (m=1) after single-step grafting hydrophilic modification treatment of Example 1 were installed on a customized nucleopore membrane water flux testing device, with an effective testing area of ​​0.785 cm². 2 The pressure applied by the diaphragm vacuum pump is 0.8 MPa.

[0079] The water flux of the PET membrane is calculated by measuring the permeation rate of ultrapure water per unit time, combining the pressure and the total area of ​​the core pores, and using the following formula:

[0080]

[0081] in,

[0082] J represents water flux, measured in m (Pa·s). -1 ;

[0083] Q represents the total volume of water passing through the membrane within a certain time period, in cubic meters (m³). 3 ;

[0084] P is the pressure applied across the membrane, in Pa.

[0085] t represents the time taken for the measurement, in seconds.

[0086] A represents the total area of ​​nuclear pores, in m². 2 .

[0087] The total area A of the nuclear pores is calculated using the following formula:

[0088]

[0089] in,

[0090] d is the diameter of the nuclear pore; it is obtained by measuring the diameters of 15 different nuclear pores and calculating the average value, in meters (m).

[0091] N is the porosity, in cm³.-2 ;

[0092] S represents the effective test area of ​​the nuclear pore membrane used for water flux testing, which is 0.785 cm². 2 .

[0093] During the testing process, five parallel measurements of water flux were performed on each PET core pore membrane sample, and the average value and standard deviation were calculated to determine the magnitude of the water flux and the experimental error.

[0094] Figure 3 This is a comparison chart of the water flux of a single-step grafted modified PET membrane (m=1) and an unmodified PET membrane, as shown below. Figure 3 As shown, the horizontal axis represents the pore size of the PET core-pore membrane (hereinafter referred to as PET membrane), the vertical axis (left) represents the water flux, and the vertical axis (right) represents the percentage increase in water flux.

[0095] Figure 3 (a) A thickness of 12 μm and a pore density of 1 × 10⁻⁶ were used. 8 cm -2 The water flux of the modified PET film increased by 31±5% compared with that of the unmodified PET film.

[0096] Figure 3 (b) A thickness of 12 μm and a pore density of 3 × 10⁻⁶ were used. 8 cm -2 The water flux of the modified PET film increased by 29±5% compared with that of the unmodified PET film.

[0097] It can be seen that the water flux of the modified PET membrane is increased by 24-35% compared with that of the unmodified PET membrane.

[0098] Example 5

[0099] This embodiment uses a grafting step count of m=2 as an example. The structural formula of the modified PET film is as follows:

[0100]

[0101] The hydrophilic modification process specifically includes the following steps:

[0102] S1. Immerse the PET film in acetonitrile to wash away surface stains;

[0103] S2. Immerse the PET film treated in S1 in the heated first impregnation solution. After constant temperature immersion treatment, remove the PET film and immerse it in acetonitrile stored at room temperature for cleaning.

[0104] S3. Immerse the PET film treated in S2 in the heated second impregnation solution. After constant temperature immersion treatment, remove the PET film and quickly and completely immerse it in ultrapure water for cleaning.

[0105] S4. Remove the PET membrane from the ultrapure water and dry it in the air to obtain a single-step modified PET membrane.

[0106] Repeat steps S1-S4. After each complete treatment by steps S1-S4, increment the grafting step count m in the PET film by 1.

[0107] Figure 4 The graph shows the relationship between the contact angle of the modified PET film and the number of PEI grafting steps (m). Figure 4 As shown, the contact angle of the modified PET film decreases as the number of PEI grafting steps (m) increases from 0 to 5: the contact angle of the modified PET film grafted in a single step is 60°, while the contact angle of the modified PET film grafted in 5 steps reaches 25°. This indicates that the more PEI groups grafted onto the surface of the PET film, the better its hydrophilicity. However, the contact angle at PEI grafting step m=7 is not significantly different from that at PEI grafting step m=5. Therefore, it can be determined that repeating steps S1-S4 5 times on the PET film, i.e., when m=5, can achieve a good hydrophilic effect.

[0108] Figure 5 This is a graph showing the relationship between the water flux of the modified PET membrane and the number of PEI grafting steps (m). In this example, the PET membrane used in the test had a thickness of 12 μm and a pore density of 1 × 10⁻⁶. 8 cm -2 The aperture is 473 nm. For example... Figure 5 As shown, compared with the unmodified PET core-pore membrane, the core-pore membrane with a grafting step number m=1 has higher hydrophilicity, and its pore inner walls are more easily wetted by water, thus increasing water flux. However, when the grafting step number continues to increase from 1 to 5, the long-chain hydrophilic molecules formed on the pore inner walls of the core-pore membrane will actually impede water flow due to the swelling effect in water, leading to a decrease in water flux. The longer the length of the long-chain molecules, the more obvious the swelling effect, and the greater the decrease in water flux.

[0109] The above description is merely an example and illustration of the structure of this invention, and while the description is specific and detailed, it should not be construed as limiting the scope of this invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these obvious substitutions all fall within the protection scope of this invention.

Claims

1. A modified PET film, characterized in that, The modified PET film has hydrophilic groups grafted onto its surface, and the modified PET film has the following structural formula: ， The number of grafting steps is m=2; the average value of n is 12.

6.

2. The modified PET film according to claim 1, characterized in that, The modified PET film is grafted with PEI groups, and the water contact angle of the modified PET film can be as low as 25°.

3. A method for hydrophilic modification of a modified PET film, characterized in that, Includes the following steps: S1. Immerse the PET film in acetonitrile to wash away surface stains; S2. The PET film treated in S1 is immersed in the heated first impregnation solution. After constant temperature treatment, the PET film is taken out and immersed in acetonitrile stored at room temperature for cleaning. S3. Immerse the PET film treated in S2 in the heated second impregnation solution, maintain the temperature, remove the PET film, and quickly and completely immerse it in ultrapure water for cleaning. S4. Remove the PET membrane from the ultrapure water and dry it in the air to obtain a modified PET membrane with a grafting step number m=1; The first impregnation solution is composed of the following components by weight: 0.46-0.92 parts phosphorus oxychloride, 24 parts acetonitrile, and 0.10-0.50 parts 3Å molecular sieve; The second impregnation solution is composed of the following components by weight: 1.8-3.6 parts polyethyleneimine, 24 parts acetonitrile, and 0.10-0.50 parts 3Å molecular sieve; wherein the molecular weight of the polyethyleneimine is 600 Da.

4. The method for hydrophilic modification of the modified PET film according to claim 3, characterized in that, Repeat steps S1-S4. After each complete processing through steps S1-S4, increment the PET film grafting step count m by 1.

5. The method for hydrophilic modification of the modified PET film according to claim 3, characterized in that, Both the first and second impregnation solutions are heated to 20-60°C.

6. The method for hydrophilic modification of the modified PET film according to claim 3, characterized in that, In step S1, the immersion time of the PET film in acetonitrile is 0.5-1.5 min.

7. The method for hydrophilic modification of the modified PET film according to claim 3, characterized in that, In step S2, the PET film is immersed in the first impregnation solution for a constant temperature immersion time of 3-7 minutes.

8. The method for hydrophilic modification of the modified PET film according to claim 3, characterized in that, In step S3, the PET film is immersed in the second impregnation solution for a constant temperature immersion time of 5-30 minutes.

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