A polytetrafluoroethylene hollow fiber membrane for membrane distillation and its preparation method

Abstract

This application relates to the field of water treatment technology, specifically to a polytetrafluoroethylene hollow fiber membrane for membrane distillation and its preparation method. The PTFE hollow fiber membrane provided herein significantly improves the flux, mechanical strength, anti-fouling properties, and antibacterial capabilities of the PTFE hollow fiber membrane by introducing hydroxyethyl methacrylate oligomers, silica sol, and titanium sol, and has promising applications in the membrane distillation field.

Description

Technical Field

[0001] The present application relates to the field of water treatment technology, 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 gives it 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 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 exhibits many advantages in membrane distillation technology, it also has some disadvantages. For example, due to its high melting point and poor thermoplasticity, PTFE has poor processing performance. PTFE's low elasticity and mechanical strength make it unsuitable for applications that need to withstand high-intensity loads. In addition, although PTFE's non-stickiness is an advantage in many cases, it can 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, while it can bring good anti-fouling properties, 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 issues of PTFE hollow fiber membranes are improved. However, existing PTFE distillation molds still have mechanical strength issues, which also limits the application of PTFE membranes. In view of this, the present application provides a PTFE distillation mold with high strength, high stain resistance, high flux, and antibacterial properties. Summary of the Invention

[0005] The present invention aims to provide a polytetrafluoroethylene hollow fiber membrane for membrane distillation and a method for preparing the same, thereby addressing the problems of mechanical strength and low flux mentioned in the aforementioned background art. By employing the above-described technical solution, the high strength, high stain resistance, and high flux properties of the PTFE distillation membrane are achieved. The specific technical solutions of this application are 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, preparing hydroxyethyl methacrylate oligomer under an inert atmosphere using hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator as raw materials;

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

[0009] Step 3: extruding polytetrafluoroethylene (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;

[0010] Step 4: mixing the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer to react, thereby obtaining 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, the mass ratio of hydroxyethyl methacrylate, ethylene glycol dimethacrylate and initiator added in step 1 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 the hydroxyethyl methacrylate oligomer within the range of 250-800, thereby ensuring that the hydroxyethyl methacrylate oligomer has good processability and economy while maintaining sufficient activity, so as to facilitate effective grafting reaction on the 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] The addition of titanium sol can improve the antibacterial ability and enhance the mechanical properties. The amount of addition is controlled in order to control the cross-linking strength and the inorganic material composition within an appropriate 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 amounts of the active PTFE hollow fiber membrane with free radicals and the modified hydroxyethyl methacrylate oligomer added in step 4 are such that the active PTFE hollow fiber membrane with free radicals is 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] By controlling the monomer addition ratio and the initiator dosage, the polymerization degree of the obtained hydroxyethyl methacrylate oligomer is made to be between 250 and 800. The hydroxyethyl methacrylate oligomer contains many unreacted active groups, such as carbon-carbon double bonds (C=C), carboxyl groups (-COOH), and hydroxyl groups (-OH).

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

[0023] Adding silica sol to hydroxyethyl methacrylate oligomer and stirring for 5-20 minutes, then adding titanium sol and mixing and reacting for 1-5 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0024] Furthermore, step 2 further 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, thus ensuring a better grafting effect. Moreover, the introduction of hydroxyl and carboxyl groups can enhance the thermal stability of the PTFE hollow fiber membrane, enabling it to maintain good performance in a high temperature environment and 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 as follows:

[0030] A certain amount of PTFE powder is ground to 0.08-0.4 μm, then extruded at a temperature of 220-250°C and 4-5 kPa, and the extruded hollow fiber membrane is sintered at 370-400°C for 5-40 minutes to obtain a high-strength PTFE hollow fiber membrane; the high-strength PTFE hollow fiber membrane is then 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 0.5-5 wt %;

[0033] Furthermore, 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 above-mentioned method.

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

[0038] 1. This application significantly improves the hydrophilicity of the PTFE hollow fiber membrane by introducing hydroxyethyl methacrylate oligomers, silica sol, and titanium sol. The increased hydrophilicity enables the PTFE hollow fiber membrane to have a higher flux, thereby improving work efficiency and reducing the risk of contamination 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. In addition, the mechanical strength of the 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 simultaneously with the hydroxyl groups in ethylene glycol dimethacrylate, the hydroxyl groups in titanium sol, and the hydroxyl groups on hydroxyethyl methacrylate to cross-link and form a dense network structure, further enhancing the mechanical strength of the hydroxyethyl methacrylate oligomer. Ultimately, the introduction of hydroxyethyl methacrylate oligomers into the PTFE hollow fiber membrane improves the mechanical strength of the PTFE hollow fiber membrane and increases the flux.

[0040] 3. The surface of the PTFE hollow fiber membrane of this 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. This improvement in anti-pollution performance extends 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 eventually formed, so that the PTFE hollow fiber membrane also has certain antibacterial ability and high temperature resistance, which can be used in more stringent working scenarios and has good application prospects. DETAILED DESCRIPTION

[0042] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described 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 making creative efforts 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 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, mixing and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0047] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 4.5 kPa, and then sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 50 minutes, and then immersed in pure water for cleaning 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 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 at a mass ratio of 1:4 for silica sol and 100:4 for hydroxyethyl methacrylate oligomer, stirring for 5 minutes, and then adding titanium sol, mixing, and reacting for 5 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0053] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 220°C and 5 kPa, and sinter the extruded hollow fiber membrane at 370°C for 40 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 80 minutes, and then immersed in pure water for cleaning 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 a mass ratio of 95:5:1, and an appropriate amount of ethyl acetate is added. 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 for silica sol and 100:9 for hydroxyethyl methacrylate oligomer and stirring for 20 minutes, then adding titanium sol, mixing, and reacting for 1 hour to obtain modified hydroxyethyl methacrylate oligomer;

[0059] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 250°C and 4 kPa, and sinter the extruded hollow fiber membrane at 400°C for 5 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 10 minutes, and then immersed in pure water for cleaning 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 a mass ratio of 85:8:1, and an appropriate amount of ethyl acetate is added. The resulting mixture is heated to 100° C. under an inert atmosphere for polymerization 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 at a mass ratio of 1:6 for silica sol to titanium sol, 100:6 for hydroxyethyl methacrylate oligomer to titanium sol, and 95:1 for hydroxyethyl methacrylate oligomer to α-hydroxypropionic acid, stirring for 10 minutes, then adding titanium sol and α-hydroxypropionic acid, mixing, and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0065] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 5 kPa, and sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce 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 and reacted for 40 minutes, and then immersed in pure water for cleaning 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 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 at a mass ratio of 1:5 for silica sol to titanium sol, 100:5 for hydroxyethyl methacrylate oligomer to titanium sol, and 85:1 for hydroxyethyl methacrylate oligomer to hydroxysuccinic acid, stirring for 15 minutes, then adding titanium sol and hydroxysuccinic acid, mixing, and reacting for 1 hour to obtain modified hydroxyethyl methacrylate oligomer;

[0071] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 240°C and 4 kPa, and sinter the extruded hollow fiber membrane at 370°C for 40 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 60 minutes, and then immersed in pure water for cleaning 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 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, 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, mixing and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0077] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 4.5 kPa, and then sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 50 minutes, and then immersed in pure water for cleaning 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 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 the titanium sol to the hydroxyethyl methacrylate oligomer at a mass ratio of 100:6, mixing and reacting for 3 hours to obtain a modified hydroxyethyl methacrylate oligomer;

[0083] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 4.5 kPa, and then sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 50 minutes, and then immersed in pure water for cleaning 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 a mass ratio of 90:5:1, and an appropriate amount of ethyl acetate is added. The resulting mixture is placed in an inert atmosphere and heated to 120° C. 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: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 4.5 kPa, and then sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 50 minutes, and then immersed in pure water for cleaning 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 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 at a mass ratio of 2:7 for silica sol and 100:7 for hydroxyethyl methacrylate oligomer and stirring for 15 minutes, then adding titanium sol and mixing, and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0095] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 4.5 kPa, and then sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce the high-strength PTFE hollow fiber membrane into low-pressure plasma and irradiate it with plasma 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 and reacted for 50 minutes, and then immersed in pure water for cleaning 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, mixing and reacting for 3 hours to obtain modified hydroxyethyl methacrylate oligomer;

[0101] Step 3: Grind a certain amount of PTFE powder to 0.08-0.4 μm, then extrude it at 230°C and 4.5 kPa, and then sinter the extruded hollow fiber membrane at 380°C for 20 minutes to obtain a high-strength PTFE hollow fiber membrane; then introduce 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 and reacted for 50 minutes, and then immersed in pure water for cleaning to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation.

[0103] Performance Testing

[0104] The performance of the polytetrafluoroethylene hollow fiber membranes provided in the examples and comparative examples was tested using the following test methods:

[0105] 1. Penetration performance test method:

[0106] The test solutions were NaCl aqueous solution and MgSO4 aqueous solution, respectively, with concentrations of 0.5% and 0.5% respectively. The temperature of the NaCl aqueous solution and the MgSO4 aqueous solution was 75°C. The test was conducted under a vacuum degree of 0.092 MPa. During the test, the PTFE hollow fiber membrane was operated for 6 hours per day for three consecutive months. The average flux and average retention rate of the PTFE hollow fiber membranes prepared in the examples and comparative examples were tested. 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, PTFE membrane was immersed in water and the time when bacterial plaque was 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 Tables 1 and 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, resulting in a relatively low flux and relatively poor mechanical strength; Comparative Example 3 does not add titanium sol, and titanium oxide cannot be formed for antibacterial and antifouling, resulting in poor antibacterial and antifouling properties. At the same time, there is no titanium oxide to enhance the structure, which also results in relatively poor mechanical strength; Comparative Example 4 adds excessive silica sol, resulting in excessive crosslinking, and the excessive addition of silica sol forms more silica, which in turn makes the mechanical properties relatively poor, while reducing the flux and worsening the desalination effect; Comparative Example 5 adds a large amount of initiator, resulting in a large molecular weight of the hydroxyethyl methacrylate oligomer, which makes the grafting effect of the modified hydroxyethyl methacrylate oligomer on the PTFE hollow fiber membrane poor, and finally the flux and mechanical properties are relatively poor.

Claims

1. A method for preparing a polytetrafluoroethylene hollow fiber membrane for membrane distillation, characterized in that: The following steps are involved: Step 1, preparing hydroxyethyl methacrylate oligomer under an inert atmosphere using hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator as raw materials; Step 2: adding silica sol and titanium sol to the hydroxyethyl methacrylate oligomer in sequence for modification to obtain a 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: mixing the active PTFE hollow fiber membrane with free radicals and the alcohol solution of modified hydroxyethyl methacrylate oligomer to react to obtain the polytetrafluoroethylene hollow fiber membrane for membrane distillation; The mass ratio of hydroxyethyl methacrylate, ethylene glycol dimethacrylate and initiator added in step 1 is 80-95:5-10:1; 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.

2. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein: The specific process of preparing hydroxyethyl methacrylate oligomer in step 1 is: Hydroxyethyl methacrylate, ethylene glycol dimethacrylate and an initiator are mixed, and an appropriate amount of ethyl acetate is added. The resulting 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.

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

4. The method for preparing a polytetrafluoroethylene hollow fiber membrane according to claim 1, wherein: Step 2 also includes a step of further performing hydrophilic modification, wherein the hydrophilic modification uses a hydroxy acid as a modifying agent.

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

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

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

8. A polytetrafluoroethylene hollow fiber membrane, characterized in that: Prepared by the method according to any one of claims 1 to 7.

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