CN115888425A - Preparation method of hydrophilic polytetrafluoroethylene hollow fiber membrane - Google Patents
Preparation method of hydrophilic polytetrafluoroethylene hollow fiber membrane Download PDFInfo
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Abstract
The invention belongs to the technical field of hollow fiber membrane preparation, and particularly relates to a preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane, which comprises the following steps: (1) Putting the polytetrafluoroethylene hollow fiber membrane into absolute ethyl alcohol, soaking the polytetrafluoroethylene hollow fiber membrane until the polytetrafluoroethylene hollow fiber membrane is transparent, taking out the polytetrafluoroethylene hollow fiber membrane, and soaking the polytetrafluoroethylene hollow fiber membrane into PVA hydrophilic mixed solution to obtain a modified polytetrafluoroethylene hollow fiber membrane; (2) Selecting a cross-linking agent, preparing a cross-linking agent aqueous solution, adjusting the pH value, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 1) in the cross-linking agent aqueous solution; (3) And (3) taking out the polytetrafluoroethylene hollow fiber membrane treated in the step (2), cleaning and airing to obtain the hydrophilic polytetrafluoroethylene hollow fiber membrane. The polytetrafluoroethylene hollow fiber membrane modified by the method has the advantages of small damage to the membrane structure, lasting modification effect, simple and easy process, convenience and high efficiency.
Description
Technical Field
The invention belongs to the technical field of hollow fiber membrane preparation, and particularly relates to a preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane.
Background
Polytetrafluoroethylene is known under the english name polytetrafluoroethene, abbreviated as PTFE. Polytetrafluoroethylene is a linear crystal thermoplastic material with white waxy feeling, the surface of the polytetrafluoroethylene is smooth, the appearance of the polytetrafluoroethylene is in a transparent or opaque state according to the crystallinity of the polytetrafluoroethylene, and the transparency is generally poorer as the crystallinity is higher. The polytetrafluoroethylene has the characteristics of good chemical stability, high temperature resistance, electrical insulation and the like, so that the polytetrafluoroethylene becomes an ideal material in the technical field of films. In recent years, with the development of membrane separation technology, polytetrafluoroethylene hollow fiber membranes and flat membranes are widely used in the fields of membrane distillation, fuel cells, environmental protection, and the like. However, due to the symmetrical molecular structure of PTFE, the surface tension and friction coefficient of PTFE are very low, and the surface hydrophobicity is high, so that the PTFE membrane is limited in the application field of water treatment. Therefore, modification of PTFE hollow fiber membranes to compensate for the performance deficiencies of PTFE has become an important research and development direction.
At present, the main methods for modifying the surface of the PTFE hollow fiber membrane include a physical modification method, a chemical modification method, a plasma treatment method, a high-energy radiation grafting method and the like. The modification methods have the defects of more or less damage to the membrane body structure, non-lasting and stable modification effect, complicated operation steps, complex instruments and equipment and the like.
Disclosure of Invention
The invention aims to solve the technical problems and provides a preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane, and the modified polytetrafluoroethylene hollow fiber membrane has the advantages of small damage to the membrane structure, lasting modification effect, simple and feasible process, convenience and high efficiency.
The technical scheme of the invention is as follows:
a preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Putting the polytetrafluoroethylene hollow fiber membrane into absolute ethyl alcohol, soaking the polytetrafluoroethylene hollow fiber membrane until the polytetrafluoroethylene hollow fiber membrane is transparent, taking out the polytetrafluoroethylene hollow fiber membrane, and soaking the polytetrafluoroethylene hollow fiber membrane into PVA hydrophilic mixed solution to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(2) Selecting a cross-linking agent, preparing a cross-linking agent aqueous solution, adjusting the pH value to 2.8-3.3, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 1) in the cross-linking agent aqueous solution;
(3) And (3) taking out the polytetrafluoroethylene hollow fiber membrane treated in the step (2), cleaning and airing to obtain the hydrophilic polytetrafluoroethylene hollow fiber membrane.
Because the polytetrafluoroethylene hollow fiber membrane has low surface energy and poor wettability of a dry membrane, the dry membrane needs to be wetted in advance in order to ensure the smooth modification, before the modification, the unmodified polytetrafluoroethylene hollow fiber membrane is soaked in absolute ethyl alcohol, when the ethyl alcohol is soaked, the ethyl alcohol only needs to be soaked in the polytetrafluoroethylene hollow fiber membrane, and the material-liquid ratio of the polytetrafluoroethylene hollow fiber membrane does not influence the result.
Since most of small molecular alcohols react with the monoaldehyde reversibly, the conversion rate is low. The polyvinyl alcohol is influenced by the molecular chain structure, the configuration and the intramolecular and intramolecular hydrogen bonds, so that the reaction activity of the polyvinyl alcohol is higher than that of small molecular alcohol, therefore, the polyvinyl alcohol and the additive are adopted to prepare the PVA hydrophilic mixed solution, namely, the PVA hydrophilic mixed solution is a mixture of the PVA aqueous solution and the additive, preferably, the volume ratio of the PVA aqueous solution to the additive in the PVA hydrophilic mixed solution is 1. The material-liquid ratio of the polytetrafluoroethylene hollow fiber membrane to the PVA hydrophilic mixed solution is not required, and the PVA hydrophilic mixed solution is just submerged in the polytetrafluoroethylene hollow fiber membrane.
Preferably, the concentration of the PVA aqueous solution is 2-40 g/L, and the impregnation in the step (1) is 0.25-4 h. The invention can increase the surface adsorption quantity of PVA on the surface of the membrane by adjusting the concentration of the hydrophilic mixed solution for soaking the PVA and the soaking time, and lays a foundation for the subsequent modified polytetrafluoroethylene hollow fiber membrane. In addition, the soaking concentration and the soaking time cannot be too long, the soaking concentration is too high or the soaking time is too long, the PVA hydrophilic mixed solution is deposited on the surface to block membrane pores, and the water flux is reduced.
In general, any hydrophilic organic molecule containing carboxylic acid, sulfonic acid, sulfuric acid, amino group or amine group and its salt, hydroxyl group, amide group, ether bond or other groups can be used as the additive, but preferably, the additive of the present invention is a surfactant, specifically, one or more selected from sodium dodecylbenzene sulfonate, sodium dodecylsulfonate, sodium dodecylsulfate, stearic acid, alkyl glucoside, ethyl cellulose, carbomer, chitosan, carboxymethyl chitosan, polyvinylpyrrolidone, poly (sodium 4-styrenesulfonate), span, and tween, and preferably, the concentration of the additive of the present invention is 5 to 20g/L. If the concentration of the additive is too high, the viscosity of the solution is high, so that a large amount of granular substances appear on the surface of the hollow fiber membrane, and the membrane pores are also covered, thereby affecting the water flux.
The PVA hydrophilic mixed solution prepared by the invention directly impregnates the surface of the PTFE hollow fiber membrane pre-infiltrated by ethanol, the PTFE hollow fiber membrane is taken out and put into an aldehyde solution, in a reaction solution, the hydroxyl in PVA molecules and the aldehyde group in aldehyde molecules carry out acetalization reaction to generate hemiacetal or acetal, and meanwhile, active groups (carboxylic acid, sulfonic acid, sulfuric acid, amino or amino and salts thereof, hydroxyl, amide, ether bond and the like) in additive molecules and the aldehyde group carry out Schiff base reaction. Therefore, the PVA and the surfactant are crosslinked under the bridge action of aldehyde to form three-dimensional network hydrogel which is wrapped on the fiber surface of the PTFE microporous membrane, so that the hydrophilicity of the PTFE microporous membrane is improved, and the hydrophilic polytetrafluoroethylene hollow fiber membrane is obtained.
Preferably, in step (2) of the present invention, the cross-linking agent is selected from one or more of formaldehyde, chloroacetaldehyde, acetaldehyde, butyraldehyde, and glutaraldehyde.
In order to increase the content of hydrophilic groups, the concentration of the aqueous solution of the crosslinking agent of the present invention is preferably 1 to 200g/L. Preferably, in the step (2) of the present invention, the impregnation is performed for 0.25 to 4 hours. Under the acidic condition, the proper concentration and immersion time of the cross-linking agent aqueous solution have the best catalytic effect, and a cross-linked product with the highest hydroformylation rate and the highest strength can be obtained. After the PTFE hollow fiber membrane is soaked by PVA hydrophilic mixed solution, a large number of hydrophilic layers are attached to the surface and an inner hole of the PTFE hollow fiber membrane, and crosslinking is enhanced in aldehyde liquid, so that the acting force between the PVA crosslinking layer and the PTFE hollow fiber membrane is enhanced, and the hydrophilic performance of the modified PTFE hollow fiber membrane is kept for a long time. The material-liquid ratio of the polytetrafluoroethylene hollow fiber membrane to the cross-linking agent aqueous solution is not required, and the cross-linking agent aqueous solution only needs to be submerged in the polytetrafluoroethylene hollow fiber membrane.
Due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. according to the invention, the polytetrafluoroethylene hollow fiber membrane is impregnated by the PVA hydrophilic mixed solution, so that the hydrophilicity of the polytetrafluoroethylene hollow fiber membrane can be improved, and then the polytetrafluoroethylene hollow fiber membrane is impregnated by the cross-linking agent, so that the acting force between the PVA cross-linking layer and the PTFE hollow fiber membrane is enhanced, the hydrophilic performance of the modified PTFE hollow fiber membrane is kept for a long time, and the modified PTFE hollow fiber membrane has excellent anti-aging performance.
2. The PVA aqueous solution and the additive in the PVA hydrophilic mixed solution are compounded and mixed, so that the hydrophilicity of the polytetrafluoroethylene hollow fiber membrane can be obviously improved, the acting force between the PVA cross-linking layer and the PTFE hollow fiber membrane is enhanced, and the hydrophilic durability of the polytetrafluoroethylene hollow fiber membrane is improved.
3. The method effectively improves the hydrophilic performance of the PTFE hollow fiber membrane, and has simple and easy preparation process and easy industrial production.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 1g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare the PVA aqueous solution with the concentration of 2 g/L;
2) Preparing an additive: 2g of Tween and 2g of span are added into 500mL of pure water and stirred uniformly to prepare the additive with the concentration of 8 g/L;
3) Uniformly stirring a PVA aqueous solution and an additive according to a volume ratio of 1;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 4 hours to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting formaldehyde as a cross-linking agent, dissolving 200g of formaldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 200g/L, adjusting the pH to 2.8 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step (2) in the cross-linking agent aqueous solution for 0.75h;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 2
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 3g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare 6g/L PVA aqueous solution;
2) Preparing an additive: adding 4.5g of sodium dodecyl sulfate and 4.5g of carbomer into 500mL of pure water, and uniformly stirring to prepare an additive with the concentration of 18 g/L;
3) Mixing the PVA aqueous solution and the additive according to the volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 3 hours to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting formaldehyde as a cross-linking agent, dissolving 20g of formaldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 20g/L, adjusting the pH value to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) into the cross-linking agent aqueous solution for 1.5 hours;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 3
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 5g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare 10g/L PVA aqueous solution;
2) Preparing an additive: adding 1.5g of stearic acid and 1g of alkyl glucoside into 500mL of pure water, and uniformly stirring to prepare an additive with the concentration of 5 g/L;
3) Mixing PVA aqueous solution and an additive according to a volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 2 hours to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting glutaraldehyde as a cross-linking agent, dissolving 100g of glutaraldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 100g/L, adjusting the pH to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) in the cross-linking agent aqueous solution for 1h;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 4
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 7g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare 14g/L PVA aqueous solution;
2) Preparing an additive: adding 10g of ethyl cellulose into 500mL of pure water, and uniformly stirring to prepare an additive with the concentration of 20 g/L;
3) Mixing the PVA aqueous solution and the additive according to the volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 2.5 hours to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting butyraldehyde as a cross-linking agent, dissolving 150g of butyraldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 150g/L, adjusting the pH value to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) into the cross-linking agent aqueous solution for 2 hours;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 5
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA water solution, namely putting 10g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare the PVA water solution with the concentration of 20 g/L;
2) Preparing an additive: adding 1.5g of sodium dodecyl benzene sulfonate and 1g of sodium dodecyl sulfate into 500mL of pure water, and uniformly stirring to prepare an additive with the concentration of 5 g/L;
3) Mixing the PVA aqueous solution and the additive according to the volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 1.5 hours to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting glutaraldehyde as a cross-linking agent, dissolving 100g of glutaraldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 100g/L, adjusting the pH to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) in the cross-linking agent aqueous solution for 1h;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 6
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 12g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare 24g/L PVA aqueous solution;
2) Preparing an additive: 3g of polyvinylpyrrolidone is added into 500mL of pure water and stirred uniformly to prepare an additive with the concentration of 6 g/L;
3) Mixing the PVA aqueous solution and the additive according to the volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 1 hour to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting formaldehyde as a cross-linking agent, dissolving 200g of formaldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 200g/L, adjusting the pH value to 3.3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) into the cross-linking agent aqueous solution for 0.5h;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 7
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 15g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare 30g/L PVA aqueous solution;
2) Preparing an additive: 5g of chitosan is added into 500mL of pure water and stirred uniformly to prepare the additive with the concentration of 10 g/L;
3) Mixing the PVA aqueous solution and the additive according to the volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 0.5 hour to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting glutaraldehyde and chloroacetaldehyde as cross-linking agents, dissolving 5g of glutaraldehyde and 5g of chloroacetaldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 10g/L, adjusting the pH value to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) into the cross-linking agent aqueous solution for 3 hours;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 8
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 17g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare PVA aqueous solution with the concentration of 34 g/L;
2) Preparing an additive: adding 6g of poly (4-styrene sodium sulfonate) into 500mL of pure water, and uniformly stirring to prepare an additive with the concentration of 12 g/L;
3) Mixing the PVA aqueous solution and the additive according to the volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 0.75 hour to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting acetaldehyde as a cross-linking agent, dissolving 5g of acetaldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 5g/L, adjusting the pH value to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) in the cross-linking agent aqueous solution for 4 hours;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Example 9
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Preparing a PVA hydrophilic mixed solution:
1) Preparing PVA aqueous solution, namely putting 20g of polyvinyl alcohol into 500mL of pure water, and uniformly stirring to prepare 40g/L PVA aqueous solution;
2) Preparing an additive: adding 3g of carboxymethyl chitosan into 500mL of pure water, and uniformly stirring to prepare an additive with the concentration of 6 g/L;
3) Mixing PVA aqueous solution and an additive according to a volume ratio of 1:1, uniformly stirring to prepare a PVA hydrophilic mixed solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, then making the PTFE hollow fiber membrane transparent, taking out the PTFE hollow fiber membrane, and soaking the PTFE hollow fiber membrane in a PVA hydrophilic mixed solution at room temperature for 0.25 hour to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(3) Selecting formaldehyde and glutaraldehyde as cross-linking agents, dissolving 0.5g of formaldehyde and 0.5g of glutaraldehyde into 1L of water to prepare a cross-linking agent aqueous solution with the concentration of 1g/L, adjusting the pH value to 3 by using hydrochloric acid, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 2) into the cross-linking agent aqueous solution for 0.25h;
(4) Taking out the PTFE hollow fiber membrane treated in the step 3), cleaning and airing to obtain the hydrophilic PTFE hollow fiber membrane.
Comparative example 1
A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane comprises the following steps:
(1) Uniformly stirring 3g of fluorocarbon surfactant in 1000ml of dichloromethane to obtain a fluorocarbon surfactant solution;
(2) Soaking the PTFE hollow fiber membrane in ethanol (the ethanol amount is higher than that of the PTFE hollow fiber membrane) for 12 hours, and then soaking the soaked PTFE hollow fiber membrane in a fluorocarbon surfactant solution for 4 hours to obtain the hydrophilic PTFE hollow fiber membrane.
Comparative example 2
The difference from example 4 is: the PVA aqueous solution and the additive are mixed according to the volume ratio of 1. The rest is the same as example 4.
Comparative example 3
The difference from example 4 is: the PVA aqueous solution and the additive are mixed according to the volume ratio of 0.5. The rest is the same as example 4.
Test examples
1. Determination of pure Water flux of PTFE hollow fiber membranes of various examples and comparative examples
The hydrophilic PTFE hollow fiber membranes prepared in examples 1 to 9 and comparative examples 1 to 3 were subjected to an external pressure test to test the pure water flux of the membrane filaments. The hydrophilic PTFE hollow fiber membranes prepared in examples 1 to 9 and comparative examples 1 to 3 were subjected to a 5-year equivalent membrane filament aging resistance test according to standard "HJ 2528-2012 hollow fiber membrane bio for environmental protection product requirements", wherein the pure water flux test was performed by pre-pressing for 0.5 hour under an external pressure of 0.02MPa, and then data was taken, and the water yield per unit area of time was obtained, and the results are shown in table 1:
TABLE 1 pure Water flux and flux measurements after sodium hypochlorite immersion
As can be seen from table 1, the PTFE hollow fiber membranes prepared in examples 1 to 9 have excellent hydrophilicity and hydrophilic stability, and have excellent resistance to oxidizing agents. Different from examples 1-9, comparative example 1 adopts a fluorocarbon surfactant with strong acid and alkali resistance, the surfactant comprises a hydrophilic group (hydroxyl, carbonyl, amino, cyano and the like) and a hydrophobic group, according to the Traube rule, the hydrophobic group of the fluorocarbon surfactant is adsorbed on the PTFE surface, the hydrophilic group is exposed outside, the PTFE membrane surface is charged negatively, the fluorocarbon surfactant is charged positively, the membrane is soaked in the fluorocarbon surfactant according to electrostatic adsorption, the surfactant is tightly coated on the membrane surface, and the hydrophilic group is introduced, so that the hydrophilic modification of the PTFE hollow fiber membrane is realized. In the technical scheme of the comparative example 1, a hydrophilic layer is formed on the surface of the PTFE hollow fiber membrane, so that the flux is increased, but the improvement effect on the wettability of the membrane is not obvious. The acid, base and oxidant resistance of the modified membrane depends on the tolerance stability of the hydrophilic layer. Thus, the flux of comparative example 1 and the flux after sodium hypochlorite soaking were much lower than those of examples 1-9.
In contrast, in the examples 1 to 9 of the present patent, the load of the hydrophilic layer is enhanced, first, the additive in the hydrophilic mixed solution is combined with the PVA macromolecules in the PVA aqueous solution to form a composite, and the PVA molecules and the additive molecules have a hydrophobic effect between hydrocarbon chains, and besides, the hydroxyl groups in the PVA macromolecules and each active group (carboxylic acid, sulfonic acid, sulfuric acid, amino group or amino group and salts thereof, hydroxyl group, amide group, ether bond, etc.) in the additive form hydrogen bonds, so that the additive molecules are better combined on the PVA macromolecules. And secondly, the PVA hydrophilic solution is loaded on the surface and the inside of the PTFE hollow fiber membrane, so that the omnibearing hydrophilic modification of the membrane from outside to inside is realized. Therefore, under the same conditions, the tolerance is better than that of comparative example 1. Secondly, in the patent examples 1 to 9 and the comparative example 1, the hydrophilic solution and the PTFE hollow fiber membrane are based on physical surface adsorption, but the comparative example 1 exists in the form of a surface coating, and when the fluorocarbon surfactant hydrophilic layer is broken by the attack of the oxidant, the fluorocarbon surfactant hydrophilic layer is very easy to fall off from the membrane surface, while the patent examples 1 to 9 are hydrophilic cross-linking systems formed by further cross-linking the polymeric active groups in situ, the hydrophilic cross-linking systems are better wound on the PTFE hollow fiber membrane body, and although the molecular chains are broken by the attack of the oxidant, the broken molecules need to be smaller to fall off. In comparative examples 2 and 3, the modification performance of the PTFE hollow fiber membrane is poor due to improper adding proportion of the PVA aqueous solution and the additive.
It can also be known from table 1 that the PTFE hollow fiber membranes prepared in examples 1 to 9 are soaked in 0.5% sodium hypochlorite for 10 days, and the flux increase or attenuation of the pure water membrane under the unit transmembrane pressure difference is within 30%, which meets the 5-year equivalent anti-aging standard, indicating that the hydrophilic polytetrafluoroethylene hollow fiber membranes prepared by the method of the present invention have excellent anti-aging performance and long-lasting hydrophilic performance.
2. Measurement of contact Angle of PTFE hollow fiber membranes of different examples
(1) The contact angles of the PTFE hydrophobic membranes (unmodified PTFE hollow fiber membranes), the hydrophilic PTFE hollow fiber membranes prepared in examples 1 to 9, and comparative examples 1 to 3 were measured by a contact angle measuring instrument, and the measurement results are shown in table 2. Note: the contact angle measuring instrument used in the contact angle measurement was a JC2000C contact angle measuring instrument manufactured by shanghai midmorning digital technology equipment ltd.
Table 2 contact Angle test
As can be seen from Table 2, in examples 1 to 9, the contact angles of the prepared hydrophilic PTFE hollow fiber membranes are all 50 to 90 degrees, and for the unmodified PTFE hollow fiber membranes, the contact angle is 128 degrees, and the contact angle is reduced by 33 to 58 percent after modification; for the unmodified PTFE hollow fiber membrane, because the surface of the PTFE hollow fiber membrane is super-hydrophobic, water drops dripped on the surface of the PTFE hollow fiber membrane can not penetrate into the PTFE hollow fiber membrane, and because the modified PTFE hollow fiber membrane has hydrophilicity, the water drops dripped on the surface of the PTFE hollow fiber membrane can penetrate into the PTFE hollow fiber membrane. In comparative example 1, the flux of the PTFE hollow fiber membrane modified by the fluorocarbon surfactant is small, the contact angle is 85 degrees, but like the unmodified membrane, water drops dropped on the surface of the PTFE hollow fiber membrane can not deeply penetrate into membrane filaments, and the hydrophilicity of the PTFE hollow fiber membrane is not very strong. Shows that the PTFE hollow fiber membrane has excellent hydrophilic performance after being modified by any surfactant. In comparative examples 2 and 3, due to the inappropriate adding ratio of the PVA aqueous solution to the additive, the PTFE hollow fiber membrane can hardly obtain excellent modification performance. Therefore, the PTFE hollow fiber membrane treated by the method has better hydrophilicity and has strong practical value.
The above description is intended to describe in detail the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the claims of the present invention, and all equivalent changes and modifications made within the technical spirit of the present invention should fall within the scope of the claims of the present invention.
Claims (10)
1. A preparation method of a hydrophilic polytetrafluoroethylene hollow fiber membrane is characterized by comprising the following steps:
(1) Putting the polytetrafluoroethylene hollow fiber membrane into absolute ethyl alcohol, soaking the polytetrafluoroethylene hollow fiber membrane until the polytetrafluoroethylene hollow fiber membrane is transparent, taking out the polytetrafluoroethylene hollow fiber membrane, and soaking the polytetrafluoroethylene hollow fiber membrane into PVA hydrophilic mixed solution to obtain a modified polytetrafluoroethylene hollow fiber membrane;
(2) Selecting a cross-linking agent, preparing a cross-linking agent aqueous solution, adjusting the pH value to 2.8-3.3, and soaking the modified polytetrafluoroethylene hollow fiber membrane obtained in the step 1) in the cross-linking agent aqueous solution;
(3) And (3) taking out the polytetrafluoroethylene hollow fiber membrane treated in the step (2), cleaning and airing to obtain the hydrophilic polytetrafluoroethylene hollow fiber membrane.
2. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: the PVA hydrophilic mixed solution is a mixture of PVA aqueous solution and an additive.
3. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 2, characterized in that: the concentration of the PVA aqueous solution is 2-40 g/L.
4. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 2, characterized in that: the concentration of the additive is 5-20 g/L.
5. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 2, characterized in that: the volume ratio of the PVA aqueous solution to the additive in the PVA hydrophilic mixed solution is 1.
6. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 2, characterized in that: the additive is surfactant or other hydrophilic substances, and is selected from one or more of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, stearic acid, alkyl glucoside, ethyl cellulose, carbomer, chitosan, carboxymethyl chitosan, polyvinylpyrrolidone, poly (4-sodium styrene sulfonate), span, and tween.
7. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein: in the step (1), the impregnation is carried out for 0.25 to 4 hours.
8. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: in the step (2), the cross-linking agent is selected from one or more of formaldehyde, chloroacetaldehyde, acetaldehyde, butyraldehyde and glutaraldehyde.
9. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein: the concentration of the cross-linking agent aqueous solution is 1-200 g/L.
10. The method for preparing a hydrophilic polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein: in the step (2), the dipping is carried out for 0.25 to 4 hours.
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