Preparation method of hydrophilic PVDF (Polyvinylidene Fluoride) membrane
By modifying PVDF with starch-grafted monomers through melt grafting, a hydrophilic functional PVDF film was prepared, which solved the problem of insufficient hydrophilicity of PVDF film, improved hydrophilicity and stability, enhanced outdoor antifouling performance, and reduced modification costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG YUMA SUN SHADING TECH CORP LTD
- Filing Date
- 2026-03-16
- Publication Date
- 2026-05-19
AI Technical Summary
Existing PVDF membranes lack sufficient hydrophilicity for outdoor applications, making it difficult to meet the high requirements for self-cleaning and environmental protection performance. Existing modification methods suffer from problems such as short-lasting hydrophilicity, high cost, or complex operation.
A starch-grafted monomer and PVDF melt grafting modification method was adopted. The starch chains were refined by acid hydrolysis, and after the grafting reaction, they were blended with PVDF to prepare a PVDF hydrophilic functional film. The high hydrophilicity and small molecular chain structure of starch were utilized to improve the grafting rate and the durability of hydrophilicity.
It significantly improves the hydrophilicity and stability of PVDF membranes, enhances outdoor antifouling performance, reduces modification costs, and simplifies the operation process.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of outdoor materials, and more specifically to a method for preparing a hydrophilic PVDF membrane. Background Technology
[0002] Polyvinylidene fluoride (PVDF), as a high-performance polymer material, is widely used in microfiltration and separation technologies due to its excellent hydrophobicity, chemical stability, and biocompatibility. However, PVDF decorative membranes for outdoor applications typically have strong hydrophobicity. While this property effectively cleans inorganic substances such as dust and sand through its high hydrophobic self-cleaning ability, it is less effective at removing oily stains. This limitation makes it difficult for outdoor PVDF membranes to meet the higher requirements for self-cleaning and environmental performance in practical applications.
[0003] Currently, common methods for improving the hydrophilicity of PVDF membranes include surface coating modification, blending with hydrophilic polymers, irradiation crosslinking, and grafting modification. However, these methods have some drawbacks: while surface coating and blending modification are simple and feasible, the hydrophilicity is not durable and is prone to peeling and phase separation; irradiation crosslinking, although highly efficient and with controllable hydrophilicity, requires significant equipment investment, and irradiation may affect the weather resistance of PVDF; traditional grafting methods suffer from low grafting rates and insufficient hydrophilicity of grafted monomers. Therefore, developing a novel preparation method that can effectively improve the hydrophilicity and stability of PVDF membranes has become a current research hotspot.
[0004] Patent CN111286068A discloses a method for preparing a hydrophilic-hydrophobic composite membrane by surface grafting of zwitterions. This method includes hydroxylation of the PVDF membrane surface, preparation of the grafting solution, and preparation of the hydrophilic-hydrophobic composite membrane. This method can form a nanoscale superhydrophilic surface on a PVDF base membrane, with the hydrophilic coating causing no damage to the base membrane, and the static contact angle of the coating surface decreasing from 98° to 46°. However, this method suffers from problems such as long post-processing time, a long overall production cycle, and potential environmental pollution.
[0005] Patent CN112961293A discloses a two-step method for preparing highly surface-active amphiphilic grafted starch slurry. This method uses a modification process of copolymerizing starch with hydrophilic and lipophilic grafted monomers respectively. The reaction process is complicated, the conditions are stringent, and the equipment and operation precision requirements are high. Summary of the Invention
[0006] The purpose of this invention is to provide a method for preparing a hydrophilic PVDF membrane to address the above-mentioned problems and solve the problem of insufficient hydrophilicity of PVDF membranes in the prior art.
[0007] To achieve the above objectives, this invention discloses a method for preparing a hydrophilic PVDF membrane, specifically comprising the following steps: S1. The original starch is acid-hydrolyzed to break down and refine into small starch molecules, and then grafted with graft monomers to obtain starch graft monomers. S2. Starch grafting monomers are melt-grafted with PVDF to obtain PVDF grafted modified masterbatch. S3, PVDF, PMMA, and PVDF graft-modified masterbatch are granulated and modified with various additives, and then cast into PVDF hydrophilic functional films.
[0008] Preferably, in step S1, the acid hydrolysis process involves mixing the original starch and pure water at a mass ratio of 2:3~8, then adding acid and stirring the mixture for 4~6 hours at a temperature of 20℃~40℃; then neutralizing with alkali and adjusting the pH to 8; then centrifuging to separate the precipitate, washing the precipitate and adding pure water to obtain a small molecule chain starch suspension.
[0009] Preferably, the grafting reaction process involves adding grafting monomers to the small molecule chain starch suspension at 70℃~90℃ and stirring the mixture; after the stirring reaction is completed, acetone is added to remove excess grafting monomers; then centrifugation is performed, and the resulting precipitate is washed, dried, and crushed to obtain starch grafting monomers.
[0010] Preferably, the native starch is one or more of corn starch, tapioca starch, wheat starch, and ultrafine starch; the acid is one or more of dilute hydrochloric acid, dilute sulfuric acid, acetic acid, citric acid, and tartaric acid; the grafting monomer is one or more of maleic anhydride (MAH), glycidyl methacrylate (GMA), acrylic acid (AA), methacrylic acid (MAA), and acrylamide (AM); and the mass of the grafting monomer is 30% to 50% of the mass of the native starch.
[0011] Preferably, in step S2, the melt grafting modification process involves adding a lubricant to PVDF and starch grafting monomers, mixing them in a high-speed mixer; adding an initiator to the resulting mixture, extruding it in a twin-screw extruder, and then water-cooling and pelletizing the extruded grafted material to obtain PVDF grafted modification masterbatch; wherein the mass ratio of PVDF, starch grafting monomers, lubricant, and initiator is 100~130:30~60:1~3:0.2~1.2; and the PVDF used in step S2 is of a high melt index type.
[0012] Preferably, the lubricant is one of PETS, EBS, and metal stearate; the initiator is one of dicumyl peroxide, benzoyl peroxide, azobisisobutyronitrile, and bis-tert-butyl peroxide.
[0013] Preferably, the temperature of the twin-screw extruder is set to 60℃~185℃, and a counter-rotating screw element for forming material counter-rotating reflux is provided in the middle section and the rear section of the screw arrangement. A side feed port is provided at the counter-rotating reflux position in the middle section. The main speed of the twin-screw extruder is set to 150-200 r / min, and the feeding speed is 20 r / min.
[0014] Preferably, in step S3, the granulation modification process involves mixing PVDF, PMMA, and PVDF grafted modified masterbatch in a high-speed mixer, then adding various additives to the high-speed mixer for further mixing; extruding the mixed material in a twin-screw extruder, and then water-cooling, pelletizing, collecting, and drying the resulting mixture; finally, feeding it into a casting machine to prepare a PVDF hydrophilic self-cleaning film; the additives include titanium dioxide, flow modifier, lubricant, toughening agent, and antioxidant; and the PVDF used in step S3 is selected as a low melt index, high strength type.
[0015] Preferably, PVDF is used as the main component, and the PVDF grafted modified masterbatch is used as the modification main component; the titanium dioxide is selected with a particle size of 200nm-300nm, and the flow modifier is DPGDB; lubricant, toughening agent, and antioxidant constitute other additives; the mass ratio of PVDF, PVDF grafted modified masterbatch, PMMA, titanium dioxide, flow modifier, and other additives is 50~100:20~50:10~30:5~8:2~5:15~30.
[0016] Preferably, the process parameters of the twin-screw extruder are: temperature set to 120℃~210℃, rotation speed to 200~300r / min, and feeding speed to 30r / min; the process parameters of the casting machine are: temperature set to 150℃~240℃, and extrusion speed to 50r / min.
[0017] In summary, the beneficial effects of the present invention are as follows: 1. Although starch can be modified and blended with PVDF, it is prone to retrogradation and aging due to the lack of chemical bonds, which reduces the mechanical properties of the molded PVDF film. This invention modifies starch with grafted monomers first, breaking the hydrogen bonds between starch molecules and fixing the starch onto the grafted monomers. Then, a melt extrusion grafting method is used to graft the starch onto the PVDF backbone, significantly improving the hydrophilicity and stability of PVDF.
[0018] 2. Existing methods for hydrophilic modification of outdoor PVDF generally suffer from the contradiction of insufficient hydrophilicity persistence and complex modification methods. Plasma treatment, blending modification, irradiation, and surface coating methods are simple and low-cost, but the modification effect is not durable, and the hydrophilicity is gradually lost over time. Copolymerization methods have the problems of harsh reaction conditions and high costs. Traditional grafting modification has low grafting rate and limited selection of grafting monomers, resulting in insignificant improvement in hydrophilicity. This invention modifies traditional hydrophilic monomers by utilizing the high hydrophilicity of starch to prepare small-molecule chain starch grafting monomers, thereby improving the hydrophilicity of the grafting monomers and avoiding the self-polymerization problem of traditional grafting monomers at high concentrations. This can significantly improve the hydrophilicity and persistence of PVDF. Detailed Implementation
[0019] The technical solution of the present invention will be clearly and completely described below with reference to embodiments and experimental data. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.
[0020] Example 1: A method for preparing a hydrophilic PVDF membrane, comprising the following steps: S1. Preparation of starch grafting monomers: The starch grafting monomer formulation consists of 30 parts corn starch, 0.03 parts 1 mol / L dilute hydrochloric acid, and 15 parts maleic anhydride. The original starch and pure water are added to a reaction vessel at a ratio of 3:7 and stirred to obtain a homogeneous phase. Then, dilute hydrochloric acid is added, and the reaction is maintained at a constant temperature of 20-40℃ for 4 hours. The reaction vessel is then neutralized with alkali, and the pH is titrated to 8 before stopping. The suspension is then centrifuged, washed, and purified water is added to obtain a small-molecule starch suspension. The pH of the suspension is adjusted to 8-9, and the temperature is maintained at 70-90℃. Grafting monomer with a starch content of 50% is added, and the reaction is stirred for 4 hours. After the reaction, acetone is added to remove excess grafting monomer. The mixture is then centrifuged, washed, dried, and crushed to obtain the starch grafting monomer.
[0021] Preparation of S2 and PVDF grafted modified masterbatch: PVDF grafting modified masterbatch formulation: 100 parts PVDF, 50 parts starch grafting monomer, 1 part calcium stearate (CaSt) lubricant, and 0.5 parts dicumyl peroxide (DCP) initiator; weigh and mix according to the proportions, and put into a high-speed mixer, set the speed to 300 r / min, and the mixing time to 10 min; set the twin-screw extrusion temperature to 60℃-185℃, and set one counter-rotating screw element in the middle section and the rear section of the screw to form a reverse swirling flow of material to improve the grafting rate. A side feed port is set at the counter-rotating position in the middle section. Add the initiator according to the proportion. Set the main speed of the twin-screw extruder to 150-200 r / min and the feeding speed to 20 r / min; collect the extruded grafted material by water cooling pelleting, and record it as material A.
[0022] Preparation of S3 and PVDF hydrophilic functional films: PVDF hydrophilic functional film formulation: 60 parts PVDF, 40 parts masterbatch A, 20 parts PMMA, 6 parts titanium dioxide, 2 parts flow modifier DPGDB, and a total of 15 parts lubricant PETS, toughening agent, and antioxidant. First, PVDF, masterbatch A, and PMMA are mixed in a high-speed mixer at 100 rpm for 5 minutes. Then, the remaining material is added to the high-speed mixer at 300 rpm for 10 minutes. The mixed material is then fed into a twin-screw extruder at a temperature of 120℃~210℃, a speed of 200~300 rpm, and a feed rate of 30 rpm. The extruded mixture is water-cooled, pelletized, collected, and dried, and designated as material B. Material B is then fed into an extrusion casting machine at a temperature of 150℃-240℃ and an extrusion rate of 50 rpm to prepare a 35µm PVDF hydrophilic self-cleaning film. Example 2
[0023] The difference from Example 1 is that the starch grafting monomer formulation is: 30 parts corn starch, 0.03 parts 1mol / L dilute hydrochloric acid, and 15 parts AA. Example 3
[0024] The difference from Example 1 is that the PVDF grafted modified masterbatch formulation is as follows: 100 parts PVDF, 50 parts starch graft monomer, 1 part lubricant EBS, and 0.5 parts initiator benzoyl peroxide (BPO). Example 4
[0025] The difference from Example 1 is that the starch grafting monomer formulation and PVDF grafting modified masterbatch formulation are as follows: 30 parts corn starch, 0.03 parts 1mol / L dilute hydrochloric acid, 15 parts AA; 100 parts PVDF, 50 parts starch grafting monomer, 1 part lubricant EBS, and 0.5 parts initiator benzoyl peroxide (BPO). Example 5
[0026] The difference from Example 1 is that the starch grafting monomer formulation and PVDF grafting modified masterbatch formulation are as follows: 30 parts corn starch, 0.03 parts 1mol / L dilute hydrochloric acid, 15 parts AA; 100 parts PVDF, 50 parts starch grafting monomer, 1 part lubricant EBS, and 0.8 parts dicumyl peroxide (DCP). Example 6
[0027] The difference from Example 1 is that the starch grafting monomer formulation and PVDF grafting modified masterbatch formulation are as follows: 30 parts corn starch, 0.03 parts 1mol / L dilute hydrochloric acid, 15 parts AA; 100 parts PVDF, 50 parts starch grafting monomer, 1 part lubricant EBS, and 1.2 parts dicumyl peroxide (DCP). Example 7
[0028] The difference from Example 1 lies in the starch grafting monomer formulation and some processes: 30 parts corn starch, 30 parts pure water, 0.03 parts 1mol / L dilute hydrochloric acid, 9 parts maleic anhydride, and a stirring time of 5 hours. The PVDF grafting modification masterbatch formulation in step S2 consists of: 115 parts high melt index PVDF, 30 parts starch grafting monomer, 2 parts calcium stearate (CaSt) lubricant, and 0.2 parts dicumyl peroxide (DCP) initiator. The PVDF hydrophilic functional film formulation in step S3 consists of: 50 parts low melt index high strength PVDF, 20 parts masterbatch A, 10 parts PMMA, 5 parts titanium dioxide, 3 parts flow modifier (DPGDB), and 20 parts other components. Example 8
[0029] The difference from Example 1 lies in the starch grafting monomer formulation and some processes: 30 parts corn starch, 80 parts pure water, 0.03 parts 1mol / L dilute hydrochloric acid, 12 parts maleic anhydride, and a stirring time of 6 hours. The PVDF grafting modification masterbatch formulation in step S2 consists of: 130 parts high melt index PVDF, 60 parts starch grafting monomer, 3 parts calcium stearate (CaSt) lubricant, and 0.2 parts dicumyl peroxide (DCP) initiator. The PVDF hydrophilic functional film formulation in step S3 consists of: 100 parts low melt index high strength PVDF, 50 parts masterbatch A, 30 parts PMMA, 8 parts titanium dioxide, 5 parts flow modifier (DPGDB), and 30 parts other components.
[0030] Comparative Example 1 Purchased from commercially available ordinary PVDF membrane Comparative Example 2 Purchased from commercially available high hydrophobic PVDF membrane Performance testing The prepared membrane is then subjected to subsequent processing and testing, such as hydrophilicity testing and antifouling performance testing, to verify whether it has good outdoor hydrophilic self-cleaning properties.
[0031] (a) Hydrophilicity test: water contact angle on the film surface; (II) The anti-pollution performance test is as follows: 1. Preparation of pollutants: a) Decaying leaves, 50% dust b) Iron oxide, aluminum oxide 30% c) 5% carbon black d) Mineral oil and vegetable oil 15% Place 100 grams of dry sand and 1 gram of the above-prepared contaminant in a sealable container such as a plastic bottle and mix well.
[0032] The membrane sample was adhered to the inside of a cylindrical testing apparatus. The prepared dirt reagent was poured into the apparatus, and the apparatus was rotated for 30 minutes to allow the dirt to adhere to the surface of the sample. The rotation speed was approximately 50 rpm / min. Immediately after the test, the sample surface was rinsed with clean water and placed outdoors in sunlight. After 168 hours, it was rinsed with clean water again, and the color difference value ΔE of the film before and after testing was measured.
[0033] Table 1. Raw material list for PVDF grafted modified masterbatches in Examples 1-8
[0034] The PVDF grafted modified masterbatches A1-A6 prepared in Examples 1-6 were used to prepare PVDF hydrophilic functional materials B1-B6.
[0035] Table 2. Raw material list for PVDF hydrophilic functional films in Examples 1-8
[0036] Materials B1~B6 were cast into films, and their water contact angle and outdoor antifouling performance were tested and compared with commercially available PVDF films. The test results are as follows: Table 3 Performance test results of Examples 1-8 and Comparative Examples 1-2
[0037] From Examples 1 to 4, it can be concluded that Example AA has better hydrophilicity than MAH. The function of MAH is more reflected in interfacial compatibility. Under the same conditions, the grafting efficiency of DCP is greater than that of BPO. Therefore, Example 2 has better hydrophilicity. Compared with Examples 5 and 6, Example 2 shows that appropriately increasing the initiator content can effectively improve the grafting rate, but excessive initiator content will affect the normal grafting reaction. Examples 7 and 8 show low grafting rates due to insufficient initiator content. The better hydrophilicity of Example 2 is due to the higher content of PMMA and starch.
[0038] By comparing the performance test results of Examples 1-8 and Comparative Examples 1-2 in Table 3, it can be seen that the PVDF hydrophilic self-cleaning membranes prepared in Examples 1-8 of the present invention have a significant advantage in outdoor anti-fouling properties compared with commercially available PVDF functional membranes. The significant improvement in the hydrophilicity of PVDF also improves the anti-fouling performance.
Claims
1. A method for preparing a hydrophilic PVDF membrane, characterized in that, Includes the following steps: S1. The original starch is acid-hydrolyzed to break down and refine into small starch molecules, and then grafted with graft monomers to obtain starch graft monomers. S2. Starch grafting monomers are melt-grafted with PVDF to obtain PVDF grafted modified masterbatch. S3, PVDF, PMMA, and PVDF graft-modified masterbatch are granulated and modified with various additives, and then cast into PVDF hydrophilic functional films.
2. The method for preparing the hydrophilic PVDF membrane according to claim 1, characterized in that, In step S1, the acid hydrolysis process involves mixing the original starch and pure water at a mass ratio of 3:3~8, then adding acid and stirring the mixture for 4~6 hours at a temperature of 20℃~40℃. The mixture is then neutralized with alkali and adjusted to pH=8. After centrifugation, the precipitate is washed and then added to pure water to obtain a small molecule chain starch suspension.
3. The method for preparing the hydrophilic PVDF membrane according to claim 2, characterized in that, The grafting reaction process involves adding grafting monomers to the small molecule chain starch suspension at 70℃~90℃ and stirring the mixture. After the stirring reaction is completed, acetone is added to remove excess grafting monomers. The mixture is then centrifuged, and the resulting precipitate is washed, dried, and crushed to obtain starch grafting monomers.
4. The method for preparing the hydrophilic PVDF membrane according to claim 2, characterized in that, The native starch is one or more of corn starch, tapioca starch, wheat starch, and ultrafine starch; the acid is one or more of dilute hydrochloric acid, dilute sulfuric acid, acetic acid, citric acid, and tartaric acid; the grafting monomer is one or more of maleic anhydride, glycidyl methacrylate, acrylic acid, methacrylic acid, and acrylamide; the mass of the grafting monomer is 30% to 50% of the mass of the native starch.
5. The method for preparing the hydrophilic PVDF membrane according to claim 1, characterized in that, In step S2, the melt grafting modification process involves adding a lubricant to PVDF and starch grafting monomers, mixing them in a high-speed mixer, adding an initiator to the resulting mixture, extruding it in a twin-screw extruder, and then water-cooling and pelletizing the extruded grafted material to obtain PVDF grafted modification masterbatch. The mass ratio of PVDF, starch grafting monomers, lubricant, and initiator is 100~130:30~60:1~3:0.2~1.
2. The PVDF used in step S2 is of a high melt index type.
6. The method for preparing the hydrophilic PVDF membrane according to claim 5, characterized in that, The lubricant is one of PTES, EBS, and metal stearate; the initiator is one of dicumyl peroxide, benzoyl peroxide, azobisisobutyronitrile, and bis-tert-butyl peroxide.
7. The method for preparing the hydrophilic PVDF membrane according to claim 5, characterized in that, The temperature of the twin-screw extruder is set to 60℃~185℃. There is a reverse screw element in the middle section and the rear section of the screw to form a reverse swirling flow of material. A side feed port is set at the reverse swirling flow position in the middle section. The main speed of the twin-screw extruder is set to 150-200 r / min, and the feeding speed is 20 r / min.
8. The method for preparing the hydrophilic PVDF membrane according to claim 1, characterized in that, In step S3, the granulation modification process involves mixing PVDF, PMMA, and PVDF grafted modified masterbatch in a high-speed mixer, then adding various additives to the high-speed mixer for further mixing; extruding the mixed material in a twin-screw extruder, and then water-cooling, pelletizing, collecting, and drying the resulting mixture; finally, feeding it into a casting machine to prepare a PVDF hydrophilic self-cleaning film; the additives include titanium dioxide, flow modifier, lubricant, toughening agent, and antioxidant; the PVDF used in step S3 is of the low melt index and high strength type.
9. The method for preparing the hydrophilic PVDF membrane according to claim 8, characterized in that, The PVDF is used as the main component, and the PVDF grafted modified masterbatch is used as the main modification component; the titanium dioxide is selected with a particle size of 200nm~300nm, and the flow modifier is DPGDB; lubricant, toughening agent, and antioxidant constitute other additives; The mass ratio of PVDF, PVDF grafted modified masterbatch, PMMA, titanium dioxide, flow modifier, and other additives is 50~100:20~50:10~30:5~8:2~5:15~30.
10. The method for preparing the hydrophilic PVDF membrane according to claim 8, characterized in that, The process parameters for the twin-screw extruder are: temperature set at 120℃~210℃, rotation speed at 200~300r / min, and feeding speed at 30r / min; the process parameters for the casting machine are: temperature set at 150℃~240℃, and extrusion speed at 50r / min.