A modified polytetrafluoroethylene membrane for adsorbing metal ions and its preparation method and application

Abstract

The invention discloses a method for preparing a modified polytetrafluoroethylene membrane for adsorbing metal ions, comprising the following steps: weighing a monomer: acrylic acid, a crosslinking agent: di(methacryloyloxyethyl) hydrogen phosphate, thionyl chloride, a photoinitiator and an antioxidant in a certain proportion and completely dissolving them in a solvent for standby use; transferring the polytetrafluoroethylene flat membrane to the above solution system and soaking it for a certain period of time; using a plasma surface treatment machine to treat the soaked polytetrafluoroethylene flat membrane, and then photocuring it by ultraviolet light for a period of time to obtain a modified polytetrafluoroethylene flat membrane. The invention uses a hydrophilic monomer and a hydrophilic crosslinking agent, and in the cooperation of a solvent, obtains a modified polytetrafluoroethylene membrane with good water wetting effect, and after being subjected to external friction, the grafted hydrophilic polymer is not easy to fall off, and is easy to industrialize.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a modified polytetrafluoroethylene membrane for adsorbing metal ions and a preparation method and application thereof. Background Art

[0002] Conventional plasma grafting polymerization often involves first subjecting the polytetrafluoroethylene membrane to plasma treatment to fill its surface with polar groups, and then grafting hydrophilic polymers onto the surface. The disadvantages of this method are: 1. The number of polar groups on the surface of the plasma-treated polytetrafluoroethylene membrane is limited, so the number of hydrophilic polymer chains grafted onto it is also limited. 2. The introduction of hydrophilic groups improves the water wetting performance of the polytetrafluoroethylene membrane, but the hydrophilic groups can only be grafted onto the surface, and the degree of improvement is not large. 3. When subjected to external friction or when subjected to excessive water pressure during filtration, the surface-grafted hydrophilic polymers are not sufficiently bonded to the polytetrafluoroethylene, and are prone to fall off. 4. Although some people have added crosslinking agents to increase hydrophilic segments, the crosslinking agents used are usually bonded to the hydrophilic polymers through polar groups, but this polar chemical bond is very easy to break under acidic or alkaline conditions. Summary of the invention

[0003] The object of the present invention is to provide a method for preparing a modified polytetrafluoroethylene membrane for adsorbing metal ions, which has simple reaction conditions and equipment, is easy to realize automated operation, and is suitable for industrial automated mass production.

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a modified polytetrafluoroethylene membrane for adsorbing metal ions, comprising the following steps:

[0005] The monomer: acrylic acid, the cross-linking agent: di(methacryloyloxyethyl) hydrogen phosphate, thionyl chloride, the photoinitiator and the antioxidant are weighed in a certain proportion and completely dissolved in the solvent for later use;

[0006] The polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for a certain period of time;

[0007] The impregnated polytetrafluoroethylene flat membrane is treated by using a plasma surface treatment machine, and then photocured by ultraviolet light for a period of time to obtain a modified polytetrafluoroethylene flat membrane.

[0008] The polytetrafluoroethylene flat membrane was immersed in the solution system for 7 hours and photocured by 20W ultraviolet light for 1 minute.

[0009] The amount of acrylic acid used is 12-22 wt%.

[0010] The usage of di(methacryloyloxyethyl) hydrogen phosphate is 0.3-1.9wt%.

[0011] The amount of the photoinitiator used is 1-3wt%, and the photoinitiator is one of 1-hydroxycyclohexyl phenyl ketone, benzoyl acetone, diisopropyl dimethyl pyrrolidone, dimethylaminobenzoate, benzothiazolinethione, and N-phenyl-N-(4-methylphenyl)amine.

[0012] The amount of the antioxidant used is 0.1-2wt%, and the antioxidant is one of bis(2-hydroxy-3,5-di-tert-butyl-4-methylphenyl)propane, p-xylene diphenol, triphenylphosphonic acid, 2,6-di-tert-butyl-4-methylbenzoquinone, and dibutyl dithiodibenzoate.

[0013] The usage amount of the solvent is 75-85wt%; the solvent is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran, dichloromethane and acetone.

[0014] The treatment conditions of the plasma surface treatment machine are: gas Ar or He, power 100W and treatment time 90s-180s.

[0015] Another object of the present invention is to provide a modified polytetrafluoroethylene membrane that is not easy to fall off and has a better adsorption effect, which is prepared by the above method.

[0016] The modified polytetrafluoroethylene membrane prepared by the present invention is used in adsorbing iron ions.

[0017] The modified polytetrafluoroethylene membrane prepared by conventional plasma grafting polymerization is not hydrophilic enough and has an unsatisfactory wetting effect on aqueous solutions. In addition, hydrophilic polymers are generally grafted on the surface of the polytetrafluoroethylene membrane through polar bonds. When subjected to external friction or too much water pressure during filtration, the binding force between the hydrophilic polymer and the polytetrafluoroethylene is not strong enough, resulting in easy falling off. The present invention uses hydrophilic monomers and hydrophilic crosslinking agents in combination with solvents to obtain a modified polytetrafluoroethylene membrane for adsorbing metal ions and a preparation method thereof, which has good water wetting effect, is not easy to fall off after being subjected to external friction, and is easy to industrialize.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The reaction conditions and equipment are simple, easy to realize automated operation, and suitable for industrial automated mass production;

[0020] 2. The present invention uses a hydrophilic cross-linking agent, which can increase the number of acrylic acid and polytetrafluoroethylene flat membranes, thereby introducing a large number of carboxyl groups into the membrane, thereby improving the membrane's wetting effect on water;

[0021] 3. During the preparation process, the cross-linking agent and acrylic acid monomer are dissolved in the solvent. After the solvent soaks the polytetrafluoroethylene flat membrane, the cross-linking agent and acrylic acid monomer enter the interior of the membrane, and then a carbon-carbon double bond cross-linking reaction is carried out inside the membrane, so that a large amount of polyacrylic acid is physically entangled with the molecular weight of the membrane, thereby improving the bonding force between polyacrylic acid and the polytetrafluoroethylene flat membrane, making it difficult for the grafted polymer to fall off. In addition, because the chemical activity of the carbon-carbon bond is low, it is not easy to break in acid or alkali. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with specific embodiments.

[0023] The invention relates to water infiltration, ultraviolet curing reaction of carbon-carbon double bonds, and complexation of trivalent iron ions by carboxyl groups. An olefin monomer having a hydrophilic group and a carboxyl group having the function of adsorbing trivalent iron ions is polymerized on a polytetrafluoroethylene flat membrane, and the membrane complexes with the trivalent iron ions through the carboxyl groups on the surface, thereby realizing the function of adsorbing trivalent iron ions.

[0024] Specifically, the monomer and polymer thereof adopted by the present invention all have hydrophilic groups, such as acrylic acid with carboxyl, di(methacryloyloxyethyl) ester of hydrogen phosphate with phosphate group. Acrylic acid can provide a large amount of carboxyl groups and ferric ion complexation after polymerization, and simultaneously due to the hydrophilic effect of the carboxyl group, the wetting effect of polytetrafluoroethylene flat membrane on water can be improved. Di(methacryloyloxyethyl) ester of hydrogen phosphate has two double bonds and a phosphate group, and the two double bonds can play the cross-linking effect on acrylic acid monomer, and cross-linking can make more acrylic acid be bonded to polytetrafluoroethylene flat membrane on the one hand, and can improve the bonding force of polyacrylic acid and membrane by increasing the physical winding of the molecular chain inside polyacrylic acid and polytetrafluoroethylene flat membrane on the other hand, so that the polyacrylic acid on bonding is not easy to fall off.

[0025] Plasma surface treatment can introduce polar groups, especially hydroxyl groups that can react with acyl chloride, into the polytetrafluoroethylene flat membrane.

[0026] The role of thionyl chloride is to convert the carboxyl groups of acrylic acid into acyl chloride groups, which then react with the hydroxyl groups on the plasma-treated polytetrafluoroethylene flat membrane.

[0027] The role of the solvent is to infiltrate the polytetrafluoroethylene flat membrane, so that the monomer acrylic acid and the cross-linking agent di(methacryloyloxyethyl) hydrogen phosphate enter the interior of the membrane to carry out a cross-linking reaction.

[0028] Embodiment 1:

[0029] 22wt% monomer acrylic acid, 0.3wt% crosslinking agent di(methacryloyloxyethyl) hydrogen phosphate, 1wt% 1-hydroxycyclohexyl phenyl ketone, 0.1wt% 3-methyl methacrylate, 1.6wt% thionyl chloride are completely dissolved in 75wt% N, N-dimethylacetamide (DMAc) for use. After taking out, the polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for 7h. The immersion process is kept airtight to prevent the solution from volatilizing. A plasma surface treatment machine is used, and the treatment conditions are Ar, power 100W and treatment time 90s-180s, and the impregnated polytetrafluoroethylene flat membrane is treated, and then photocured by 20W ultraviolet light for 1min to obtain a modified polytetrafluoroethylene flat membrane.

[0030] Embodiment 2:

[0031] 18wt% monomer acrylic acid, 0.3wt% crosslinking agent di(methacryloyloxyethyl) hydrogen phosphate, 1wt% 1-hydroxycyclohexyl phenyl ketone, 0.1wt% 3-methyl methacrylate, 1.6wt% thionyl chloride are completely dissolved in 79wt% N, N-dimethylacetamide (DMAc) for use. After taking out, the polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for 7h. The immersion process is kept airtight to prevent the solution from volatilizing. A plasma surface treatment machine is used, and the treatment conditions are He, power 100W and treatment time 90s-180s to treat the impregnated polytetrafluoroethylene flat membrane, and then photocured by 20W ultraviolet light for 1min to obtain a modified polytetrafluoroethylene flat membrane.

[0032] Embodiment 3:

[0033] 16wt% monomer acrylic acid, 0.3wt% crosslinking agent di(methacryloyloxyethyl) hydrogen phosphate, 1wt% 1-hydroxycyclohexyl phenyl ketone, 0.1wt% 3-methyl methacrylate, 1.6wt% thionyl chloride are completely dissolved in 81wt% N, N-dimethylformamide (DMF) for use. After taking out, the polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for 7h. The immersion process is kept airtight to prevent the solution from volatilizing. A plasma surface treatment machine is used, and the treatment conditions are Ar, power 100W and treatment time 90s-180s. The impregnated polytetrafluoroethylene flat membrane is treated, and then photocured by 20W ultraviolet light for 1min to obtain a modified polytetrafluoroethylene flat membrane.

[0034] Embodiment 4:

[0035] 14wt% monomer acrylic acid, 0.3wt% crosslinking agent di(methacryloyloxyethyl) hydrogen phosphate, 1wt% 1-hydroxycyclohexyl phenyl ketone, 0.1wt% 3-methyl methacrylate, 1.6wt% thionyl chloride are completely dissolved in 83wt% N, N-dimethylacetamide (DMAc) for use. After taking out, the polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for 7h. The immersion process is kept airtight to prevent the solution from volatilizing. A plasma surface treatment machine is used, and the treatment conditions are Ar, power 100W and treatment time 90s-180s. The impregnated polytetrafluoroethylene flat membrane is treated, and then photocured by 20W ultraviolet light for 1min to obtain a modified polytetrafluoroethylene flat membrane.

[0036] Embodiment 5:

[0037] 13wt% monomer-acrylic acid, 0.3wt% crosslinking agent di(methacryloyloxyethyl) hydrogen phosphate, 1wt% 1-hydroxycyclohexyl phenyl ketone, 0.1wt% 3-methyl methacrylate, 1.6wt% thionyl chloride are completely dissolved in 84wt% N, N-dimethylacetamide (DMAc) for use. After taking out, the polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for 7h. The immersion process is kept airtight to prevent the solution from volatilizing. A plasma surface treatment machine is used, and the treatment conditions are Ar, power 100W and treatment time 90s-180s, and the impregnated polytetrafluoroethylene flat membrane is treated, and then photocured by 20W ultraviolet light for 1min to obtain a modified polytetrafluoroethylene flat membrane.

[0038] Comparative Example:

[0039] 13wt% monomer-acrylic acid, 1wt% 1-hydroxycyclohexyl phenyl ketone, 0.1wt% 3-methyl methacrylate, 1.6wt% thionyl chloride are completely dissolved in 84.3wt% N, N-dimethylacetamide (DMAc) for standby use. After taking out, the polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for 7h. The immersion process is kept airtight to prevent the solution from volatilizing. A plasma surface treatment machine is used, and the treatment conditions are Ar, power 100W and treatment time 90s-180s, and the impregnated polytetrafluoroethylene flat membrane is treated, and then light-cured for 1min by 20W ultraviolet light to obtain a modified polytetrafluoroethylene flat membrane.

[0040] In order to quantitatively evaluate the adsorption effect of the modified polytetrafluoroethylene flat membrane of the present invention on iron ions. The absorbance of the iron standard solution is measured by using an ultraviolet spectrophotometer and a standard curve of Fe(III) is drawn. Then, the absorbance of Fe(III) in water filtered by the modified polytetrafluoroethylene flat membrane is measured by using an ultraviolet spectrophotometer, thereby calculating the concentration of Fe(III) after adsorption by the polytetrafluoroethylene flat membrane, and calculating the adsorption rate of Fe(III) by the membrane. The calculation results of the adsorption rate of Fe(III) in Examples 1 to 5 and Comparative Example are shown in Table 1.

[0041] Table 1 Adsorption rate of Fe(III) in water samples of Examples 1 to 5 and Comparative Examples

[0042] Adsorption rate of Fe(III) Example 1 61.46％ Example 2 59.32％ Example 3 57.28％ Example 4 55.78％ Example 5 53.61％ Comparative Example 43.26％

[0043] In order to prove that the water wetting effect of the modified polytetrafluoroethylene flat membrane of the present invention is improved after the introduction of the cross-linking agent, contact angle tests were conducted on Examples 1 to 5 and the comparative example. The test results are shown in Table 2.

[0044] Table 2 Water contact angles of Examples 1 to 5 and Comparative Examples

[0045] Contact angle (°) Example 1 23 Example 2 26 Example 3 26 Example 4 29 Example 5 33 Comparative Example 48

[0046] In order to prove that the modified polytetrafluoroethylene flat membrane of the present invention is not easy to fall off after the introduction of the cross-linking agent, a friction test was carried out on the modified 3cm×3cm membrane using a 5cm×5cm sandpaper (1200 mesh). The membrane was rubbed back and forth on the sandpaper 10 times horizontally and 10 times vertically. Then, the contact angle test was carried out on Examples 1 to 5 and the comparative example. The test results are shown in Table 3.

[0047] Table 3 Water contact angles of samples of Examples 1 to 5 and Comparative Examples after rubbing with sandpaper

[0048] Contact angle (°) Example 1 23 Example 2 27 Example 3 28 Example 4 32 Example 5 35 Comparative Example 70

[0049] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a modified polytetrafluoroethylene membrane for adsorbing trivalent iron ions, characterized in that: The following steps are involved: The monomer: acrylic acid, the cross-linking agent: di(methacryloyloxyethyl) hydrogen phosphate, thionyl chloride, the photoinitiator and the antioxidant are weighed in a certain proportion and completely dissolved in the solvent for later use; The polytetrafluoroethylene flat membrane is transferred to the above solution system and soaked for a certain period of time; The impregnated polytetrafluoroethylene flat membrane is treated by a plasma surface treatment machine, and then cured by ultraviolet light for a period of time to obtain a modified polytetrafluoroethylene flat membrane; The amount of acrylic acid used is 12-22wt%; The amount of di(methacryloyloxyethyl) hydrogen phosphate is 0.3-1.9wt%; The amount of photoinitiator is 1-3wt%; The amount of antioxidant is 0.1-2wt%; The amount of solvent used is 75-85wt%.

2. The preparation method according to claim 1, characterized in that: The polytetrafluoroethylene flat membrane was immersed in the solution system for 7 hours and photocured by 20W ultraviolet light for 1 minute.

3. The preparation method according to claim 1, characterized in that: The photoinitiator is one of 1-hydroxycyclohexyl phenyl ketone, benzoyl acetone, diisopropyl dimethyl pyrrolidone, dimethylaminobenzoate, and benzothiazolinethione.

4. The preparation method according to claim 1, characterized in that: The antioxidant is one of p-xylene diphenol and triphenylphosphonic acid.

5. The preparation method according to claim 1, characterized in that: The solvent is one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran, dichloromethane, and acetone.

6. The preparation method according to claim 1, characterized in that: The treatment conditions of the plasma surface treatment machine are: gas Ar or He, power 100 W and treatment time 90 s-180 s.

7. A polytetrafluoroethylene membrane modified by adsorption of metal ions, characterized in that: Prepared according to any one of claims 1 to 6.

8. Use of the modified polytetrafluoroethylene membrane as claimed in claim 7 in adsorbing trivalent iron ions.