CN106731900A - In-situ sol-gel high-strength polyvinylidene fluoride milipore filter and preparation method - Google Patents

Abstract

The invention provides an in-situ-sol-gel method polyvinylidene fluoride ultrafiltration membrane and a preparation method thereof. The nano-silica-reinforced polyvinylidene fluoride ultrafiltration membrane is prepared by using the in-situ sol-gel technology, and the prepared ultrafiltration The pore size of the membrane is 0.3-0.8 μm. Compared with the conventional ultrafiltration membrane, the prepared ultrafiltration membrane accelerates the phase separation process in situ-sol-gel, promotes the formation of honeycomb pores, limits the growth of finger-shaped pores, and has a more uniform pore size distribution. The present invention combines in-situ sol-gel with non-solvent-induced phase separation membrane-making method, which simplifies the reaction process. The crystallization of polyvinylidene fluoride is accelerated during the film forming process, the content of β-crystal form of the film is increased, and the mechanical properties of the polyvinylidene fluoride film are further improved.

Description

In-situ-sol-gel method high-strength polyvinylidene fluoride ultrafiltration membrane and preparation method

technical field

The invention belongs to the technical field of membrane separation, and relates to a preparation method of a high-strength polyvinylidene fluoride ultrafiltration membrane by an in-situ-sol-gel method.

Background technique

Polyvinylidene fluoride is a homopolymer of vinylidene fluoride. It is a hydrophobic linear semi-crystalline polymer with a crystallinity of 50%-80%. It has good weather resistance and chemical stability. It is a comprehensive Membrane material with excellent performance. At present, PVDF membranes are widely used in membrane distillation, water treatment, gas purification, and wine filtration, and have a good application prospect in the field of membrane separation. Due to the excellent oxidation resistance of polyvinylidene fluoride, chemical cleaning can be carried out in the application of its membrane process, and the oxidant used will not corrode the membrane product, so the polyvinylidene fluoride membrane is better applied in the membrane bioreactor ( Utility model patent CN205099452U, an ultrafiltration membrane bioreactor). Membrane bioreactors have high requirements on the performance of the membrane. The prepared ultrafiltration membrane needs to ensure high strength while having high flux, so as to avoid deformation, perforation or even broken wire due to long-term pressure in sewage treatment. The nonsolvent-induced phase separation (NIPS) method is a common method for preparing PVDF ultrafiltration membranes, however, the formation of finger-like pores greatly reduces the membrane strength. In order to solve the problem of film strength reduction caused by finger-shaped holes, researchers at home and abroad have done a lot of research on the NIPS process. The main improvement process is to introduce additives, change the types of casting solution solvent and coagulation bath non-solvent, and adjust the coagulation process. bath temperature.

At present, the doping of nano-inorganic particles is an effective method to solve the above problems, especially metal oxide and silicon oxide materials. Chinese patent CN1724586A "Nano-Alumina Modified Polyvinylidene Fluoride Membrane and Its Preparation Method and Application" obtains a casting membrane solution through physical blending, and prepares a PVDF ultrafiltration membrane through a non-solvent-induced phase separation (NIPS) method. This method can inhibit the formation of macropores and improve the strength of the membrane. Chinese patent CN103861476A "Preparation Method of Polyvinylidene Fluoride Composite Mesoporous Membrane" directly adds mesoporous silica into the casting liquid, and prepares PVDF blend membrane by non-solvent-induced phase separation (NIPS) method. But the biggest problem with the method of directly introducing inorganic nanoparticles is the agglomeration of nanoparticles, which will inhibit the reinforcing effect of nanoparticles in the membrane matrix.

Therefore, the method of preparing polyvinylidene fluoride ultrafiltration membrane by in-situ-sol-gel method can effectively solve the above problems.

Contents of the invention

The patent of the present invention provides an in-situ-sol-gel polyvinylidene fluoride ultrafiltration membrane and its preparation method. The in-situ sol-gel technology is used to prepare nano-silica reinforced polyvinylidene fluoride ultrafiltration membrane. The prepared ultrafiltration The pore size of the filter membrane is 0.3-0.81 μm.

For completing above invention, carry out as follows:

(1) Preparation of sol: Mix solvent 1 and monomer according to the volume ratio, then add deionized water, stir until uniform, and titrate with acid to obtain a stable and transparent sol, that is, the sol.

The above solvent 1 is: N,N dimethylformamide, N,N dimethylacetamide, acetone, γ-butyrolactone, ethyl acetate, dibutyl phthalate, dimethyl sulfoxide, tetrahydrofuran , N-methylpyrrolidone, one or two mixed solvents in triethyl phosphate (wherein the volume ratio of the mixed solvent is any ratio); the above-mentioned monomers are: tetraethoxysilane, ethylene glycol, trimethoxy One or two monomers in base silane, isocyanate and triethoxy silane are mixed (wherein the volume ratio of the mixed monomers is in any proportion).

(2) Preparation of casting solution: Add the sol prepared in step (1) dropwise into the polyvinylidene fluoride solution, put it into the reagent bottle, equip the stirring device, put the reagent bottle into the oil bath Inside, heat up to 60-90°C, fully stir for 24-36 hours, keep the temperature constant, stir at a rate of 800-1000r/min, slow down the rate of stirring to 50-100r/min at the end of the stirring, to facilitate the discharge of air bubbles.

The solvent 2 used in the polyvinylidene fluoride solution is: N,N dimethylformamide, N,N dimethylacetamide, acetone, γ-butyrolactone, ethyl acetate, dibutyl phthalate, dimethyl One or two solvents in sulfoxide, tetrahydrofuran, N-methylpyrrolidone, and triethyl phosphate are mixed (wherein the volume ratio of the mixed solvent is in any proportion).

(3) leave the casting solution prepared in step (2) at a temperature of 60-90° C. until there are no bubbles in the casting solution, and scrape a layer of liquid film with a thickness of 0.2 to 0.3 mm on a clean glass plate. Quickly immerse the liquid membrane together with the glass plate in deionized water at a temperature of 10-30°C, the film solidifies and automatically peels off the glass plate, and fully replaces it with water to obtain a polyvinylidene fluoride ultrafiltration membrane.

Wherein in step (1), the acid used is hydrochloric acid or dilute sulfuric acid; pH=1.0～1.5.

Wherein in step (1), the volume ratio of solvent 1 and monomer used is 1:0.8-1:1.5.

Wherein in step (1), the volume ratio of the mixed solution to deionized water is: 100:1-5.

Wherein in step (1), stirring refers to high-speed stirring at 20-45° C. for 1-3 hours.

The amount of the sol used in the step (2) is 1-5 wt.% of the mass of the polyvinylidene fluoride solution.

Wherein the concentration of the polyvinylidene fluoride solution used in the step (2) is 10-25wt.%.

Compared with the polyvinylidene fluoride microporous membrane disclosed in current patents and articles, the patent of the present invention has the following technical advantages:

(1) The present invention utilizes the in-situ-sol-gel method to prepare high-strength polyvinylidene fluoride ultrafiltration membranes. Compared with conventional ultrafiltration membranes, the in-situ-sol-gel accelerated phase separation process of the prepared ultrafiltration membranes promotes The formation of honeycomb pores limits the growth of finger-shaped pores, and the pore size distribution is more uniform.

(2) In-situ-sol-gel method, the reaction conditions are mild (room temperature or slightly higher than room temperature and normal pressure), the system starts from a solution, the ratio of various components is easy to control, and nano-silica with good dispersion performance can be prepared. Polyvinylidene fluoride ultrafiltration membrane.

(3) The present invention combines the in-situ-sol-gel and non-solvent-induced phase separation membrane-making method, which simplifies the reaction process. The crystallization of polyvinylidene fluoride is accelerated during the film forming process, the content of β-crystal form of the film is increased, and the mechanical properties of the polyvinylidene fluoride film are further improved.

Description of drawings

Fig. 1 is the Fourier transform attenuated total reflection infrared spectrogram of the ultrafiltration membrane prepared in Example 3 and the polyvinylidene fluoride ultrafiltration membrane comparison sample.

Fig. 2 is the upper surface structure scanning electron microscope picture (10000 times) of the ultrafiltration membrane that embodiment 3 prepares

Fig. 3 is the cross-sectional structure scanning electron microscope picture (5000 times) of the ultrafiltration membrane that embodiment 3 prepares

Fig. 4 is the cross-section pore size distribution diagram of the ultrafiltration membrane prepared in embodiment 3

Table 1 is the pore size, pore size distribution and mechanical property data of concrete implementation 1-5 and comparative sample

detailed description

The terms used in the present invention, unless otherwise stated, generally have the meanings commonly understood by those skilled in the art.

The present invention will be further described in detail below in conjunction with specific implementation examples. It should be understood that these examples are only for illustration of the present invention, but not to limit the scope of the present invention in any way.

Pore size test: The surface and cross-sectional morphology of the polyvinylidene fluoride microporous membrane were observed with a scanning electron microscope HITACHIS4700 produced in Japan. In order to observe the cross-sectional structure of the membrane, the microporous membrane was frozen and brittle in liquid nitrogen, and the brittle section was fixed vertically upward on the sample stage with double-sided tape. samples in Gold with a thickness of 20-30nm is plated in the E1020 gold plating instrument, and then the morphology and structure of the surface and section of the PVDF hybrid film are observed under the field emission scanning electron microscope S4700.

Infrared test: The mid-infrared spectrometer BRUKER-VerEX70 is used for infrared research. By comparing the infrared spectra of the film and each pure component, the polyvinylidene fluoride film crystal form and content changes are determined.

Mechanical properties test: ISO 527-3:1995 "Test Method for Tensile Properties of Plastic Films" was used to measure the tensile strength and elongation at break of PVDF ultrafiltration membrane. Test conditions: tensile speed is 10mm/min, room temperature.

Example 1

(1) Preparation of sol: N-N dimethylformamide and tetraethoxysilane were prepared into 100ml mixed solution at a volume ratio of 1:0.8, then 1mL of deionized water was added, and stirred at 20°C for 1h at high speed. After fully stirring evenly, titrate with hydrochloric acid with pH=1.0 to obtain a stable and transparent sol, that is, the sol.

(2) Preparation of film-casting solution: Add the sol prepared in step (1) dropwise to a solution with a mass fraction of 10wt.% polyvinylidene fluoride (using phthalate di butyl ester and N-N dimethylformamide), the amount of sol added is 1% of the quality of the polyvinylidene fluoride solution, put it into the reagent bottle, equipped with a stirring device, put the reagent bottle into the oil bath, and heat up to 60°C, stir fully for 24 hours, keep the temperature constant, stir at a rate of 800r/min, and slow down to 100r/min at the end of the stirring to facilitate the discharge of air bubbles.

(3) Put the casting solution prepared in step (2) at a temperature of 60°C until there are no bubbles in the casting solution, scrape a layer of liquid film with a thickness of 0.2mm on a clean glass plate, and place the liquid film together with The glass plate is quickly immersed in deionized water at a temperature of 10°C, the membrane is cured and the glass plate is automatically peeled off, fully replaced with water, and the polyvinylidene fluoride ultrafiltration membrane is obtained.

Example 2

(1) Sol preparation: N-N dimethylacetamide and tetraethoxysilane were prepared into 100ml mixed solution at a volume ratio of 1:1.0, then 2mL of deionized water was added, and stirred at 25°C for 2h at high speed. After fully stirring evenly, titrate with hydrochloric acid with pH=1.0 to obtain a stable and transparent sol, that is, the sol.

(2) Preparation of film-casting solution: Add the sol prepared in step (1) dropwise to a solution with a mass fraction of 10wt.% polyvinylidene fluoride (using phthalate di butyl ester and N-N dimethylformamide), the addition amount is 1% of the N-N dimethylacetamide solution quality of polyvinylidene fluoride, put it into the reagent bottle, equip the stirring device, put the reagent bottle into the oil In the bath, heat up to 70°C, stir fully for 24 hours, keep the temperature constant, and stir at a rate of 800r/min. When the stirring is over, slow down the stirring rate to 100r/min to facilitate the discharge of air bubbles.

(3) Put the casting solution prepared in step (2) at a temperature of 70°C until there are no bubbles in the casting solution, scrape a layer of liquid film with a thickness of 0.2mm on a clean glass plate, and place the liquid film together with The glass plate is quickly immersed in deionized water at a temperature of 20°C, the membrane is cured and the glass plate is automatically peeled off, fully replaced with water, and the polyvinylidene fluoride ultrafiltration membrane is obtained.

Example 3

(1) Preparation of sol: N-N dimethylformamide, tetraethoxysilane and triethoxysilane are prepared in 100ml mixed solution at a volume ratio of 1:1.2:0.3, then 2mL of deionized water is added, and the Stir for 2 hours, and after fully stirring evenly, titrate with pH=1.0 hydrochloric acid to obtain a stable and transparent sol, that is, the sol.

(2) Preparation of film-casting solution: Add the sol prepared in step (1) dropwise to N-N dimethylacetamide solution with a mass fraction of 15wt.% polyvinylidene fluoride (using a volume ratio of 1:1 In the mixed solvent of dibutyl phthalate and N-N dimethylformamide), the addition amount is 3% of the solution quality of polyvinylidene fluoride, put into the reagent bottle, equipped with stirring device, put the reagent bottle into the oil In the bath, heat up to 70°C, stir fully for 24 hours, keep the temperature constant, and stir at a rate of 800r/min. When the stirring is over, slow down the stirring rate to 100r/min to facilitate the discharge of air bubbles.

(3) Put the casting solution prepared in step (2) at a temperature of 70°C until there are no bubbles in the casting solution, scrape a layer of liquid film with a thickness of 0.2mm on a clean glass plate, and place the liquid film together with The glass plate is quickly immersed in deionized water at a temperature of 20°C, the membrane is cured and the glass plate is automatically peeled off, fully replaced with water, and the polyvinylidene fluoride ultrafiltration membrane is obtained.

Example 4

(1) Preparation of sol: Prepare 100ml mixed solution of N-N dimethylformamide and tetraethoxysilane at a volume ratio of 1:1.3, then add 3mL of deionized water, stir at 35°C for 3 hours at high speed, and stir well, Titrate with sulfuric acid at pH=1.0 to obtain a stable and transparent sol, that is, tetraethoxysilane sol.

(2) Preparation of casting solution: Add the sol prepared in step (1) dropwise to a solution with a mass fraction of 20wt.% polyvinylidene fluoride (using phthalate di butyl ester and N-N dimethylformamide mixed solvent), the addition is 4% of the solution quality of polyvinylidene fluoride, put into the reagent bottle, equipped with a stirring device, put the reagent bottle into the oil bath, and heat up to 80 ℃, fully stirred for 24 hours, kept the temperature constant, and the stirring rate was 800r/min. When the stirring was completed, the stirring rate was slowed down to 100r/min, which was beneficial to the discharge of air bubbles.

(3) Put the casting solution prepared in step (2) at a temperature of 80°C until there are no bubbles in the casting solution, scrape a layer of liquid film with a thickness of 0.2mm on a clean glass plate, and place the liquid film together with The glass plate is quickly immersed in deionized water at a temperature of 25°C, the membrane is cured and the glass plate is automatically peeled off, fully replaced with water, and the polyvinylidene fluoride ultrafiltration membrane is obtained.

Example 5

(1) Preparation of sol: Prepare 100ml mixed solution of N-N dimethylformamide and tetraethoxysilane at a volume ratio of 1:1.5, then add 5mL deionized water, stir at 45°C for 3 hours at high speed, and stir well, Titrate with sulfuric acid at pH=1.0 to obtain a stable and transparent sol, that is, the sol.

(2) Preparation of film-casting solution: Add the sol prepared in step (1) dropwise to a mass fraction of 25wt.% polyvinylidene fluoride solution (dibutyl phthalate with a volume ratio of 1:1 ester and N-N dimethylformamide mixed solvent), the addition amount is 5% of the mass of the polyvinylidene fluoride solution, put it into the reagent bottle, equipped with a stirring device, put the reagent bottle into the oil bath, and heat up to 90 °C, Fully stir for 24 hours, keep the temperature constant, and stir at a rate of 800r/min. When the stirring is completed, slow down the rate of stirring to 100r/min to facilitate the discharge of air bubbles.

(3) Put the casting solution prepared in step (2) at a temperature of 90°C until there are no bubbles in the casting solution, scrape a layer of liquid film with a thickness of 0.2mm on a clean glass plate, and place the liquid film together with The glass plate is quickly immersed in deionized water at a temperature of 30°C, the membrane is cured and the glass plate is automatically peeled off, fully replaced with water, and the polyvinylidene fluoride ultrafiltration membrane is obtained.

comparative example

(1) Preparation of film casting solution: in the reagent bottle, dissolve 25wt.% polyvinylidene fluoride in N-N dimethylformamide, equip a stirring device, put the reagent bottle into the oil bath, and heat up to 60 ℃, fully stirred for 24 hours, kept the temperature constant, and the stirring rate was 800r/min. When the stirring was completed, the stirring rate was slowed down to 100r/min, which was beneficial to the discharge of air bubbles.

(2) Put the casting solution prepared in step (1) at a temperature of 60°C until there are no bubbles in the casting solution, scrape a layer of liquid film with a thickness of 0.2mm on a clean glass plate, and place the liquid film together with The glass plate was quickly immersed in deionized water at a temperature of 30°C, the membrane solidified and the glass plate was automatically peeled off, fully replaced with water, and a polyvinylidene fluoride ultrafiltration membrane comparison sample was prepared.

Table 1 concrete implementation 1-5 and the pore size, pore size distribution and mechanical performance data of comparative sample

Claims (10)

1. The preparation method of high-strength polyvinylidene fluoride ultrafiltration membrane in situ-sol-gel method, is characterized in that, concrete steps are as follows: (1) Preparation of sol: Mix solvent 1 and monomer according to the volume ratio, then add deionized water, stir until uniform, and titrate with acid to obtain a stable and transparent sol, namely the sol; (2) Preparation of casting solution: Add the sol prepared in step (1) dropwise into the polyvinylidene fluoride solution, put it into the reagent bottle, equip the stirring device, put the reagent bottle into the oil bath Inside, heat up to 60-90°C, fully stir for 24-36 hours, keep the temperature constant, stir at a rate of 800-1000r/min, slow down the rate of stirring to 50-100r/min at the end of the stirring, to facilitate the discharge of air bubbles; (3) leave the casting solution prepared in step (2) at a temperature of 60-90° C. until there are no bubbles in the casting solution, and scrape a layer of liquid film with a thickness of 0.2 to 0.3 mm on a clean glass plate. Quickly immerse the liquid membrane together with the glass plate in deionized water at a temperature of 10-30°C, the film solidifies and automatically peels off the glass plate, and fully replaces it with water to obtain a polyvinylidene fluoride ultrafiltration membrane. 2. the preparation method of in-situ-sol-gel method high-strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, in step (1), solvent 1 is: N,N dimethyl formazan Amide, N,N dimethylacetamide, acetone, γ-butyrolactone, ethyl acetate, dibutyl phthalate, dimethyl sulfoxide, tetrahydrofuran, N-methylpyrrolidone, triethyl phosphate One or two mixed solvents, wherein the volume ratio of the mixed solvents is any ratio; the monomer is: one or two of tetraethoxysilane, ethylene glycol, trimethoxysilane, isocyanate, triethoxysilane The monomers are mixed, and the volume ratio of the mixed monomers is any ratio. 3. the preparation method of in-situ-sol-gel method high strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, in step (1), used acid is hydrochloric acid or dilute sulfuric acid; pH= 1.0～1.5. 4. the preparation method of in-situ-sol-gel method high strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, in step (1), the volume ratio of solvent 1 used and monomer is 1:0.8-1:1.5. 5. the preparation method of in-situ-sol-gel method high strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, in step (1), the volume ratio of described mixed solution and deionized water For: 100:1-5. 6. the preparation method of in-situ-sol-gel method high-strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, in step (1), stirring refers to high-speed stirring at 20-45 ℃ for 1 -3h. 7. the preparation method of in-situ-sol-gel method high strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, step (2) wherein the add-on of sol used is polyvinylidene fluoride solution 1-5 wt.% of the mass. 8. the preparation method of in-situ-sol-gel method high strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, the concentration of the polyvinylidene fluoride solution used in step (2) is 10- 25 wt.%. 9. the preparation method of in-situ-sol-gel method high-strength polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, the solvent 2 that polyvinylidene fluoride solution adopts is: N, N dimethyl Formamide, N,N dimethylacetamide, acetone, γ-butyrolactone, ethyl acetate, dibutyl phthalate, dimethyl sulfoxide, tetrahydrofuran, N-methylpyrrolidone, triethyl phosphate One or two solvents are mixed, wherein the volume ratio of the mixed solvent is any ratio. 10. the preparation method of in-situ-sol-gel method high-intensity polyvinylidene fluoride ultrafiltration membrane as claimed in claim 1, is characterized in that, described in-situ-sol-gel method high-intensity polyvinylidene fluoride ultrafiltration The pore size of the membrane is 0.3-0.81 μm.