Polytetrafluoroethylene hollow fiber membrane for membrane distillation and preparation method thereof

Abstract

The invention relates to the technical field of water treatment, in particular to a polytetrafluoroethylene hollow fiber membrane for membrane distillation and a preparation method thereof. According to the PTFE hollow fiber membrane provided by the invention, the hydroxyethyl methylacrylate oligomer, the silica sol and the titanium sol are introduced, so that the flux, the mechanical strength, the anti-pollution performance and the antibacterial ability of the PTFE hollow fiber membrane are remarkably improved, and the PTFE hollow fiber membrane has a relatively good prospect when being applied to the field of membrane distillation.

Description

Technical Field

[0001] The present application relates to the technical field of water treatment, and in particular to a polytetrafluoroethylene hollow fiber membrane for membrane distillation and a preparation method thereof. Background Art

[0002] PTFE is often used as a membrane distillation material for the following reasons: 1. Hydrophobicity: PTFE has excellent hydrophobicity, which is a very important characteristic in membrane distillation technology. 1. Hydrophobicity ensures that water vapor can pass through the membrane pores smoothly without being blocked by the wetting effect of liquid water; 2. Chemical stability: PTFE shows extremely high stability to most chemicals, including strong acids and strong bases, which makes it have great advantages in treating various industrial wastewaters; 3. Heat resistance: PTFE can maintain its physical and chemical properties unchanged at higher temperatures, which is an important consideration for the high temperature environment that may be encountered during membrane distillation; 4. Mechanical strength: PTFE membrane has high mechanical strength and can withstand certain pressure and stretching, which helps to maintain the structural integrity of the membrane and ensure long-term stable operation; 5. Air permeability: PTFE membrane has good air permeability, which is very beneficial for water vapor transfer during membrane distillation; 6. Pollution resistance: PTFE membrane has a smooth surface and is not easy to adhere to pollutants, which helps to reduce membrane pollution and maintenance costs; 7. Superhydrophobic modification: By superhydrophobic modification of PTFE flat microporous membrane, its hydrophobicity can be further improved, which is of great significance for improving the efficiency of membrane distillation and reducing energy consumption.

[0003] However, although PTFE has shown many advantages in membrane distillation technology, it also has some disadvantages. For example, due to the high melting point and poor thermoplasticity of PTFE, the processing performance is poor. The low elasticity and mechanical strength of PTFE make it unsuitable for occasions that need to withstand high-intensity loads. In addition, although the non-stickiness of PTFE is an advantage in many cases, it may become a disadvantage in applications that require good adhesion between materials. For example, during the assembly process of membrane distillation equipment, the non-stickiness may cause the membrane to be loosely bonded to other components, affecting the overall performance of the equipment. In addition, PTFE is generally hydrophobic, which can bring better anti-fouling performance, but it will limit the flux of the membrane.

[0004] Patent CN106659985B discloses a high-toughness hollow fiber membrane based on vinylidene fluoride polymer. By using a component containing vinylidene fluoride polymer with relatively low crystallinity, the toughness and durability of PTFE hollow fiber membrane are improved. However, the existing PTFE distillation mold still has mechanical strength problems. This will also limit the application of PTFE membrane. In view of this, the present application provides a PTFE distillation mold with high strength, high stain resistance, high flux and antibacterial. Summary of the invention

[0005] The purpose of the present invention is to provide a polytetrafluoroethylene hollow fiber membrane for membrane distillation and a preparation method thereof, so as to solve the problems of mechanical strength, low flux, etc. raised in the above background technology. By adopting the above technical scheme, the high strength, high stain resistance, high flux and other properties of the PTFE distillation membrane are achieved. The specific technical scheme of this application is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation, comprising the following steps:

[0007] Step 1, using hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator as raw materials to prepare hydroxyethyl methacrylate oligomer under an inert atmosphere;

[0008] Step 2, adding silica sol and titanium sol in sequence to the hydroxyethyl methacrylate oligomer for modification to obtain modified hydroxyethyl methacrylate oligomer;

[0009] Step 3, extruding polytetrafluoroethylene (PTFE) powder to obtain a PTFE hollow fiber membrane, then sintering to obtain a high-strength PTFE hollow fiber membrane, and then irradiating with low-pressure plasma to obtain an active PTFE hollow fiber membrane with free radicals;

[0010] Step 4: Mix the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer to react, so as to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0011] Furthermore, the initiator in step 1 is at least one of dibenzoyl peroxide (BPO) and azobisisobutyronitrile (AIBN).

[0012] Furthermore, in step 1, the mass ratio of hydroxyethyl methacrylate, ethylene glycol dimethacrylate and initiator is 80-95:5-10:1;

[0013] The purpose of controlling the added mass ratio of hydroxyethyl methacrylate, ethylene glycol dimethacrylate and initiator is to control the molecular weight of hydroxyethyl methacrylate oligomer within the range of 250-800, so as to ensure that hydroxyethyl methacrylate oligomer has good processability and economy while maintaining sufficient activity, so as to facilitate effective grafting reaction on PTFE hollow fiber membrane; when the molecular weight is too large, it will not only affect the grafting effect, but also affect the uniformity of the obtained product.

[0014] Furthermore, the mass ratio of the silica sol to the titanium sol added in step 2 is 1:4-9;

[0015] Silica sol acts as a cross-linking agent and should not be added in excessive amounts, because the added silica sol will eventually form silica gel, which has a network structure and is relatively brittle. Too much of this structure will affect the mechanical strength.

[0016] Furthermore, the mass ratio of the hydroxyethyl methacrylate oligomer to the titanium sol in step 2 is 100:4-9;

[0017] Adding titanium sol can improve the antibacterial ability and enhance the mechanical properties. The amount of addition is controlled in order to control the crosslinking strength and the inorganic substance composition within a suitable range. At the same time, the addition of titanium sol is beneficial to improving the high temperature resistance of the prepared PTFE.

[0018] Furthermore, the amount of the active PTFE hollow fiber membrane with free radicals and the modified hydroxyethyl methacrylate oligomer added in step 4 is such that the active PTFE hollow fiber membrane with free radicals can be fully immersed in the alcohol solution of the modified hydroxyethyl methacrylate oligomer.

[0019] Furthermore, the specific process of preparing hydroxyethyl methacrylate oligomer in step 1 is:

[0020] Mixing hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator, and adding an appropriate amount of ethyl acetate, heating the resulting mixture to 80-160° C. under an inert atmosphere for polymerization, and then freeze-drying at -20 to -10° C. to obtain the hydroxyethyl methacrylate oligomer;

[0021] The polymerization degree of the obtained hydroxyethyl methacrylate oligomer is 250-800 by controlling the monomer addition ratio and the initiator dosage; the hydroxyethyl methacrylate oligomer contains many unreacted active groups, such as carbon-carbon double bonds (C=C), carboxyl groups (-COOH), hydroxyl groups (-OH), etc.

[0022] Furthermore, the specific process of adding silica sol and titanium sol for modification in step 2 is:

[0023] Add silica sol to hydroxyethyl methacrylate oligomer and stir for 5-20 minutes, then add titanium sol and mix well to react for 1-5 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0024] Furthermore, step 2 also includes a step of further performing hydrophilic modification;

[0025] Furthermore, the hydrophilic modification uses a hydroxy acid as a hydrophilic modifier; the hydroxy acid is selected from at least one of α-hydroxypropionic acid, hydroxysuccinic acid and 2-hydroxypropane-1,2,3-tricarboxylic acid;

[0026] This type of substance is a small molecule hydroxy acid with good environmental protection and hydrophilic modification effect; in addition, the introduction of this type of small molecule carboxyl acid on the PTFE surface can form a denser cross-linked network structure, further enhancing the mechanical strength of the membrane while having little effect on the molecular weight of the resulting hydroxyethyl methacrylate oligomer, thereby ensuring a better grafting effect; and the introduction of hydroxyl and carboxyl groups can enhance the thermal stability of the PTFE hollow fiber membrane, so that it can still maintain good performance in a high temperature environment and can be suitable for high temperature conditions.

[0027] Furthermore, the specific process of the hydrophilic modification is:

[0028] Add hydroxy acid to react while adding titanium sol;

[0029] Furthermore, the specific preparation process of the active PTFE hollow fiber membrane with free radicals in step 3 is:

[0030] A certain amount of PTFE powder is ground to 0.08-0.4 μm, and then extruded at a temperature of 220-250°C and 4-5 kPa, and then the extruded hollow fiber membrane is sintered at 370-400°C for 5-40 minutes to obtain a high-strength PTFE hollow fiber membrane; then the high-strength PTFE hollow fiber membrane is introduced into low-pressure plasma and irradiated with plasma for 30-300 seconds to generate free radicals, hydrophilic groups and active groups;

[0031] Furthermore, the hydrophilic groups are hydroxyl groups and amino groups; the active groups are C=O and C=C groups;

[0032] Furthermore, the content of the modified hydroxyethyl methacrylate oligomer in the alcohol solution of the modified hydroxyethyl methacrylate oligomer is 0.5-5wt%;

[0033] Further, the temperature of the alcohol solution of the modified hydroxyethyl methacrylate oligomer is 20-80°C;

[0034] Furthermore, the specific preparation process of step 4 is as follows:

[0035] The active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer are mixed and reacted for 10-80 minutes, and then immersed in pure water for cleaning to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0036] In a second aspect, the present invention provides a polytetrafluoroethylene hollow fiber membrane for membrane distillation, which is prepared by the method described above.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present application significantly improves the hydrophilicity of the PTFE hollow fiber membrane by introducing hydroxyethyl methacrylate oligomer, silica sol and titanium sol. The improvement of the hydrophilicity enables the PTFE hollow fiber membrane to have a higher flux, thereby improving work efficiency and reducing the risk of pollution and clogging;

[0039] 2. Due to the introduction of silica sol and titanium sol for modification, the modified PTFE hollow fiber membrane has higher mechanical strength and can withstand greater pressure and tension; and the mechanical strength of hydroxyethyl methacrylate oligomer is improved by adding ethylene glycol dimethacrylate and hydroxyethyl methacrylate copolymers. In addition, the introduction of silica sol allows its active silanol groups to react with hydroxyl groups in ethylene glycol dimethacrylate, hydroxyl groups in titanium sol, and hydroxyl groups on hydroxyethyl methacrylate to form a dense network structure, which further enhances the mechanical strength of hydroxyethyl methacrylate oligomer. Finally, hydroxyethyl methacrylate oligomer is introduced into the PTFE hollow fiber membrane, thereby improving the mechanical strength of the PTFE hollow fiber membrane and increasing the flux.

[0040] 3. The surface of the PTFE hollow fiber membrane of the present application contains a large number of hydrophobic groups such as methyl and fluorine, which makes the PTFE hollow fiber membrane have better anti-pollution performance and reduces the adhesion and accumulation of pollutants. The improvement of this anti-pollution performance prolongs the service life of the membrane and reduces the maintenance cost of the PTFE hollow fiber membrane;

[0041] 4. Due to the introduction of titanium sol in this application, titanium oxide is finally formed, so that the PTFE hollow fiber membrane also has certain antibacterial ability and high temperature resistance, and can be applied to more stringent working scenarios, with good application prospects. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0045] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and BPO are mixed in sequence at a mass ratio of 90:5:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0046] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer at a mass ratio of 1:7 of silica sol to titanium sol and 100:7 of hydroxyethyl methacrylate oligomer to titanium sol, stirring for 15 minutes, and then adding titanium sol to mix and react for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0047] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 4.5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 200 seconds;

[0048] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 50°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 50 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0049] Example 2

[0050] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0051] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and AIBN are mixed in sequence at a mass ratio of 80:10:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 80° C. under an inert atmosphere for polymerization reaction for 30 minutes, and then freeze-dried at -20° C. to obtain the hydroxyethyl methacrylate oligomer;

[0052] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer in a mass ratio of 1:4 and 100:4, stirring for 5 minutes, and then adding titanium sol to mix and react for 5 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0053] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 220° C. and 5 kPa, and then sintering the extruded hollow fiber membrane at 370° C. for 40 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 30 seconds;

[0054] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 0.5wt%, the temperature is 20°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 80 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0055] Example 3

[0056] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0057] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and BPO are mixed in sequence at a mass ratio of 95:5:1, and an appropriate amount of ethyl acetate is added, and the resulting mixture is heated to 80-160° C. under an inert atmosphere for polymerization reaction for 1 hour, and then freeze-dried at -10° C. to obtain the hydroxyethyl methacrylate oligomer;

[0058] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer at a mass ratio of 1:9 of silica sol to titanium sol and 100:9 of hydroxyethyl methacrylate oligomer to titanium sol, stirring for 20 minutes, and then adding titanium sol to mix and react for 1 hour to obtain modified hydroxyethyl methacrylate oligomer;

[0059] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 250° C. and 4 kPa, and then sintering the extruded hollow fiber membrane at 400° C. for 5 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 300 seconds;

[0060] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 5wt%, the temperature is 80°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 10 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0061] Example 4

[0062] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0063] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and BPO are mixed in sequence at a mass ratio of 85:8:1, and an appropriate amount of ethyl acetate is added, and the resulting mixture is heated to 100° C. under an inert atmosphere for polymerization reaction for 1.5 hours, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0064] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer according to the mass ratio of silica sol to titanium sol being 1:6, the mass ratio of hydroxyethyl methacrylate oligomer to titanium sol being 100:6, and the mass ratio of hydroxyethyl methacrylate oligomer to α-hydroxypropionic acid being 95:1, stirring for 10 minutes, and then adding titanium sol and α-hydroxypropionic acid, mixing and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0065] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; and then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma;

[0066] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 40°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 40 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0067] Example 5

[0068] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0069] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and AIBN are mixed in sequence at a mass ratio of 92:6:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0070] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer according to the mass ratio of silica sol to titanium sol being 1:5, the mass ratio of hydroxyethyl methacrylate oligomer to titanium sol being 100:5, and the mass ratio of hydroxyethyl methacrylate oligomer to hydroxysuccinic acid being 85:1, stirring for 15 minutes, and then adding titanium sol and hydroxysuccinic acid, mixing and reacting for 1 hour to obtain modified hydroxyethyl methacrylate oligomer;

[0071] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 240° C. and 4 kPa, and then sintering the extruded hollow fiber membrane at 370° C. for 40 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 200 seconds;

[0072] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 2wt%, the temperature is 60°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 60 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0073] Comparative Example 1

[0074] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0075] Step 1, hydroxyethyl methacrylate and BPO are mixed in sequence at a mass ratio of 90:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0076] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer at a mass ratio of 1:7 of silica sol to titanium sol and 100:7 of hydroxyethyl methacrylate oligomer to titanium sol, stirring for 15 minutes, and then adding titanium sol to mix and react for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0077] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 4.5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 200 seconds;

[0078] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 50°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 50 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0079] Comparative Example 2

[0080] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0081] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and BPO are mixed in sequence at a mass ratio of 90:5:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0082] Step 2, adding titanium sol to hydroxyethyl methacrylate oligomer at a mass ratio of 100:6, mixing and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0083] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 4.5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 200 seconds;

[0084] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 50°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 50 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0085] Comparative Example 3

[0086] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0087] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and initiator (BPO) are mixed in sequence at a mass ratio of 90:5:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0088] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer at a mass ratio of 1:100, stirring for 15 minutes, and then reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0089] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 4.5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 200 seconds;

[0090] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 50°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 50 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0091] Comparative Example 4

[0092] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0093] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and BPO are mixed in sequence at a mass ratio of 90:5:1, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0094] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer in a mass ratio of 2:7 and 100:7, stirring for 15 minutes, then adding titanium sol, mixing and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0095] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 4.5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma and receiving plasma irradiation for 200 seconds;

[0096] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 50°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 50 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0097] Comparative Example 5

[0098] A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation:

[0099] Step 1, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, and BPO are mixed in a mass ratio of 90:5:1.5, and an appropriate amount of ethyl acetate is added, the resulting mixture is heated to 120° C. under an inert atmosphere for polymerization reaction, and then freeze-dried at -15° C. to obtain the hydroxyethyl methacrylate oligomer;

[0100] Step 2, adding silica sol to hydroxyethyl methacrylate oligomer at a mass ratio of 1:7 of silica sol to titanium sol and 100:7 of hydroxyethyl methacrylate oligomer to titanium sol, stirring for 15 minutes, and then adding titanium sol to mix and react for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0101] Step 3, grinding a certain amount of PTFE powder to 0.08-0.4 μm, and then extruding it at a temperature of 230° C. and 4.5 kPa, and then sintering the extruded hollow fiber membrane at 380° C. for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; and then introducing the high-strength PTFE hollow fiber membrane into low-pressure plasma;

[0102] Step 4, the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer (the content of modified hydroxyethyl methacrylate oligomer is 3wt%, the temperature is 50°C) are mixed until the active PTFE hollow fiber membrane with free radicals is completely immersed in the alcohol solution of modified hydroxyethyl methacrylate oligomer to react for 50 minutes, and then immersed in pure water for washing to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0103] Performance Testing

[0104] The performance of the polytetrafluoroethylene hollow fiber membrane provided in the examples and comparative examples was tested, and the test method was as follows:

[0105] 1. Penetration performance test method:

[0106] The test liquids were NaCl aqueous solution and MgSO4 aqueous solution, respectively, the concentrations of NaCl aqueous solution and MgSO4 aqueous solution were 0.5% and 0.5%, respectively, the temperature of NaCl aqueous solution and MgSO4 aqueous solution was 75°C, the test was carried out under a vacuum degree of 0.092MPa, the PTFE hollow fiber membrane was operated for 6h per day during the test, and it was continuously operated for three months. The average flux and average retention rate of the PTFE hollow fiber membrane prepared in the embodiment and the comparative example were tested, and the results are shown in Table 1;

[0107] 2.Mechanical properties test method:

[0108] Refer to QB / T 4876-2015 standard, the test results are shown in Table 2;

[0109] 3. Antibacterial test method:

[0110] At room temperature, the PTFE membrane was immersed in water and the time when bacterial plaques were produced was observed;

[0111] 4. Anti-fouling performance test method:

[0112] The anti-fouling performance in this article is expressed by the flux recovery rate under certain conditions. The specific test method is that after the PTFE hollow fiber membrane is used continuously for 20 times, the PTFE hollow fiber membrane prepared in the embodiment and the comparative example is cleaned with 35°C warm water under the same conditions, and then the flux recovery rate is measured.

[0113] Table 1

[0114]

[0115]

[0116] Table 2

[0117]

[0118] It can be seen from Table 1 and Table 2 that the PTFE prepared by the method of the present invention has a higher flux and a better desalination effect; Comparative Example 1 does not add ethylene glycol dimethacrylate, and Comparative Example 2 does not add silica sol, so the crosslinking is reduced and the void structure is reduced, so that the flux is relatively low and the mechanical strength is relatively poor; Comparative Example 3 does not add titanium sol, and titanium oxide cannot be formed for antibacterial and antifouling, so that the antibacterial and antifouling properties are poor, and at the same time, there is no titanium oxide to enhance the structure, which also makes the mechanical strength relatively poor; Comparative Example 4 adds excessive silica sol, resulting in excessive crosslinking, and the excessive silica sol added forms more silicon oxide, which makes the mechanical properties relatively poor, and at the same time reduces the flux and makes the desalination effect worse; Comparative Example 5 adds a large amount of initiator, resulting in a large molecular weight of hydroxyethyl methacrylate oligomer, which makes the grafting effect of modified hydroxyethyl methacrylate oligomer on the PTFE hollow fiber membrane worse, and finally the flux and mechanical properties are relatively worse.

Claims

1. A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation, characterized in that: The following steps are involved: Step 1, using hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator as raw materials to prepare hydroxyethyl methacrylate oligomer under an inert atmosphere; Step 2, adding silica sol and titanium sol in sequence to the hydroxyethyl methacrylate oligomer for modification to obtain modified hydroxyethyl methacrylate oligomer; Step 3, extruding the PTFE powder to obtain a PTFE hollow fiber membrane, then sintering it to obtain a high-strength PTFE hollow fiber membrane, and then irradiating it with low-pressure plasma to obtain an active PTFE hollow fiber membrane with free radicals; Step 4: Mix the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer to react, so as to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

2. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: In step 1, the mass ratio of hydroxyethyl methacrylate, ethylene glycol dimethacrylate and initiator is 80-95:5-10:

1.

3. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: In step 2, the mass ratio of the silica sol to the titanium sol is 1:4-9, and the mass ratio of the hydroxyethyl methacrylate oligomer to the titanium sol is 100:4-9.

4. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: The specific process of preparing hydroxyethyl methacrylate oligomer in step 1 is: Hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator are mixed, and a proper amount of ethyl acetate is added. The obtained mixture is placed in an inert atmosphere and heated to 80-160° C. for polymerization reaction, and then freeze-dried to obtain the hydroxyethyl methacrylate oligomer.

5. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: The specific process of adding silica sol and titanium sol for modification in step 2 is: Silica sol is added to hydroxyethyl methacrylate oligomer and stirred for 5-20 minutes, and then titanium sol is added and mixed to react for 1-5 hours to obtain modified hydroxyethyl methacrylate oligomer.

6. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: Step 2 also includes a step of further performing hydrophilic modification, wherein a hydroxy acid is used as a modifying agent.

7. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: The specific preparation process of the active PTFE hollow fiber membrane with free radicals in step 3 is: A certain amount of PTFE powder is ground to 0.08-0.4μm, then extruded at a temperature of 220-250℃ and 4-5kPa, and then the extruded hollow fiber membrane is sintered at 370-400℃ for 5-40min to obtain a high-strength PTFE hollow fiber membrane; then the high-strength PTFE hollow fiber membrane is introduced into low-pressure plasma and irradiated with plasma for 30-300sec.

8. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: The content of modified hydroxyethyl methacrylate oligomer in the alcohol solution of modified hydroxyethyl methacrylate oligomer in step 4 is 0.5-5wt%.

9. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, characterized in that: The temperature of the alcohol solution of the modified hydroxyethyl methacrylate oligomer is 20-80°C.

10. A polytetrafluoroethylene hollow fiber membrane, characterized in that: Prepared by the method according to any one of claims 1 to 9.

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