CN116808851B - Polyvinylidene fluoride hierarchical porous film based on volume rejection effect and preparation method and application thereof - Google Patents
Polyvinylidene fluoride hierarchical porous film based on volume rejection effect and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a polyvinylidene fluoride hierarchical porous film based on a volume rejection effect and a preparation method thereof. The film has a multistage pore structure with continuous micron-sized columnar pores and nanometer-sized slits Kong Guli, and the specific method is that polyvinylidene fluoride and dimethyl sulfone are magnetically stirred for 2 hours at the temperature of 180 ℃ to form transparent uniform solution by a solution blending method; pouring the blending solution into a custom mold rapidly, controlling the temperature by using a polarized light heat table to perform isothermal crystallization, and cooling to obtain a film with the thickness of 100-500 mu m; and immersing the film into deionized water for etching to remove the dimethyl sulfone phase. The micron-sized columnar macropores formed by the dimethyl sulfone form sea phase, the island phase formed by nano-sized micropores formed by connecting polyvinylidene fluoride self-crystallization is formed, two stages are adjustable, the advantages of the obtained film combined film and the volume rejection effect are expected to realize the aim of large-scale, low-cost and universal separation in the industrial field through the volume rejection porous film.
Description
Technical Field
The invention relates to the field of high polymer materials, in particular to a polyvinylidene fluoride hierarchical porous film based on a volume rejection effect, a preparation method and application thereof, and specifically relates to a preparation method for preparing a polyvinylidene fluoride film with a hierarchical pore structure of sea-like macropores and island-like micropores by crystallization-induced phase separation of the hierarchical porous film based on the volume rejection effect.
Background
Porous polymer films combine many of the excellent properties of both "high molecular" and "porous", such as good mechanical properties and ease of processing, making porous polymer film technology attractive for use in these fields. The performance of the porous membrane serves as a core component of the membrane separation technology, determining the final performance of the membrane technology. Among them, the size and structure of the membrane pores have a relatively large influence on the performance thereof, and the regulation of the pore size has been considered as one of the most important problems. Secondly, the membrane separation technology is used as a water resource purification technology with low energy consumption and high efficiency, has the characteristics of high separation efficiency and amplification, and is widely paid attention to and paid attention to. The method has attractive application prospect in the fields of drinking water purification, sewage treatment, petrochemical industry, hemodialysis, lithium battery diaphragms, solar batteries and the like. Although membrane separation has many advantages, conventional membranes do not allow for volume-exclusion separations, which are often aided by Gel Permeation Chromatography (GPC), which is the most widely used method of separating high molecular homologs. Numerous commercial GPC products have been developed and successfully applied to molecular weight and distribution determination of macromolecules.
However, these commercial GPCs are only suitable for analytical testing and are difficult to apply directly to the bulk separation of high molecular homologs. In addition to the high cost, existing methods for separating high molecular homologs (including GPC) cannot achieve both "high separation efficiency" and "high separation purity". Therefore, how to combine the advantages of membrane separation and volume exclusion, and finally, it is worth researching to eliminate the problems in the original GPC technology by using the high throughput and simple operation of the membrane separation technology, and based on this, it is necessary to develop a preparation method of a special hierarchical porous membrane of "sea-like macropores and island-like micropores" based on the volume exclusion effect.
The hierarchical porous material (HIERARCHICALLY POROUS MATERIALS) refers to a porous material with macropores, mesopores or/and micropores distributed on a pore structure. Because the hierarchical porous material has a unique gradient porous structure, compared with a continuous medium material and a single pore structure material, the hierarchical porous material has a co-continuous macroporous structure which plays a role of a transportation channel for other substances, and mesopores and micropores on a framework can provide a quite high specific surface area, and the size and the shape of the hierarchical porous material also have certain selectivity for other substances. Therefore, the hierarchical porous material is hopeful to overcome the problems of unsmooth substance transmission, low separation efficiency and the like of the existing single porous material, has wider application prospect in the important fields of adsorption, separation, catalysis, filtration and the like, and has been paid more attention to the research field of porous materials.
Polyvinylidene fluoride has good chemical stability, oxidation resistance and high temperature resistance, and meanwhile, has good flexibility and processability, so that the polyvinylidene fluoride is commonly applied to the preparation of polymer separation membranes. Starting from the preparation of the polyvinylidene fluoride porous film with micron-sized columnar holes and nanometer-sized slits Kong Guli, the invention provides a method for preparing a hierarchical porous separation film with volume rejection effect by utilizing a crystallization-induced phase separation mode, and the obtained film combines the advantages of the film and the volume rejection effect, thereby being expected to realize the targets of large-scale, low-cost and universal separation in the industrial field.
Disclosure of Invention
A first object of the present invention is to provide a polyvinylidene fluoride hierarchical porous membrane based on the volume exclusion effect, which aims at overcoming the drawbacks of the prior art.
The polyvinylidene fluoride hierarchical porous film based on the volume repulsive effect has the thickness of 100-500 mu m, and has hierarchical porous structure and is made of polyvinylidene fluoride;
The hierarchical porous structure is composed of a plurality of nanoscale slit holes and a plurality of microscale interpenetrating continuous through holes distributed around the nanoscale slit holes, wherein the nanoscale slit holes form island phases, and the microscale interpenetrating continuous through holes form sea phases with bicontinuous networks and are connected with the island phases; the micron-sized interpenetrating continuous through holes are columnar holes with the length of 100-300 mu m and the aperture of 500 nm-5 mu m between polyvinylidene fluoride spherulites; the nanoscale slit holes are holes with the aperture of 1-100 nm between polyvinylidene fluoride platelets and stacks.
A second object of the present invention is to provide a method for preparing the polyvinylidene fluoride hierarchical porous film based on the volume exclusion effect.
The method comprises the following specific steps:
step (1), drying polyvinylidene fluoride and dimethyl sulfone, mixing, magnetically stirring for 2-3 hours at 180-210 ℃ until melting and mixing, and preparing transparent uniform 30-80 wt% polymer solution;
Preferably, the mass ratio of polyvinylidene fluoride to dimethyl sulfone is 1:1, a step of;
preferably, the solution blending temperature is 180℃and the time is 2 hours.
Pouring the blending solution obtained in the step (1) into a mould rapidly, sealing the periphery of the mould, controlling the temperature to be 110-150 ℃, crystallizing at constant temperature for 90-360 min, and cooling to obtain a film with the thickness of 100-500 mu m;
Preferably, the temperature is controlled to 115 ℃ in the step (2), and the isothermal crystallization is carried out for 180 minutes.
And (3) immersing the film prepared in the step (2) into deionized water, placing for 40-50 h, etching to remove a dimethyl sulfone phase, placing for 10-12 h in ethanol, then placing for 10-12 h in normal hexane, and drying to remove water to obtain the polyvinylidene fluoride hierarchical porous film based on the volume rejection effect.
It is a third object of the present invention to provide the use of the polyvinylidene fluoride hierarchical porous membrane described above for separating homologs in a volume exclusion effect.
Compared with the prior art, the invention has the beneficial effects that:
In the invention, unlike the structure of sea-like small holes and island-like large holes, polyvinylidene fluoride is crystallized to form nano-scale small holes to form island phases, micron-scale columnar large holes formed by dimethyl sulfone form sea phases to form a mutually penetrating bicontinuous network and are connected with the island phases, and the obtained film combines the advantages of the film and the volume repulsive effect, and has the multi-level hole characteristics of sea-like large holes and island-like small holes;
In addition, the invention obtains a special multistage pore structure by researching the melting point phase diagrams of polyvinylidene fluoride and dimethyl sulfone and adjusting the corresponding crystallization temperature and crystallization time under specific composition so as to control the proportion of columnar macropores and slit pinholes, and the sizes of the columnar macropores and the nanoscale slit holes in sea phase can be regulated and controlled through components and thermal history.
The invention adopts dimethyl sulfone as a pore-forming agent, and simultaneously, the dimethyl sulfone is a good solvent of polyvinylidene fluoride after the dimethyl sulfone is melted; and the dimethyl sulfone has a higher melting point (about 110 ℃), and when the crystallization temperature is lower than the melting point, crystals start to precipitate, thereby being beneficial to subsequent separation.
The polyvinylidene fluoride hierarchical pore film has a volume exclusion effect, can separate homologs, and has a good separation effect in separating 996,000 and polymethyl methacrylate (PMMA) with a molecular weight of 15,000. When the blending solution is separated, the PMMA with large molecular weight has larger radius of gyration and can only pass through columnar macropores at the same flow rate, the number of the passed apertures is small, the diffusion path is short, the retention time is short, and the PVDF film is firstly passed through; and PMMA with small molecular weight has smaller radius of gyration than that of the small pore, and flows through the large pore and the small pore simultaneously, corresponding to longer diffusion path and leaching time.
According to the polyvinylidene fluoride film, the structures of micro-level macropores and nano-level micropores can be regulated and controlled by changing the mass ratio of polyvinylidene fluoride to dimethyl sulfone or different crystallization time and cooling rate, the columnar macropores are 500-5 mu m in size, and the slit micropores are 1-100 nm in size. The membrane pore structure has a size sieving effect.
Meanwhile, the polyvinylidene fluoride porous film is prepared by only using common solution blending equipment, is simple in preparation and strong in processability, and can be obtained after being soaked in deionized water and dried. And the dimethyl sulfone obtained by etching is very convenient to recycle in a recrystallization or sublimation mode, is beneficial to reducing the pollution of the diluent to the environment, and is an environment-friendly material.
The polyvinylidene fluoride porous film prepared by the invention has the advantages of the film combined film and the volume rejection effect, and is expected to realize the targets of large-scale, low-cost and universal separation in the industrial field.
Drawings
FIG. 1 is a photograph of a multi-stage pore film scanning electron microscope of polyvinylidene fluoride prepared in example 1, wherein the scale is 20 μm (each of the inset scales is 5 μm).
FIG. 2 is a photograph of a polyvinylidene fluoride multi-stage pore film scanning electron microscope prepared in example 2, wherein the scale is 50. Mu.m.
FIG. 3 is a scanning electron micrograph of a single-stage polyvinylidene fluoride film prepared in comparative example, wherein the scale is 10. Mu.m.
FIG. 4 is an etching principle, A is a schematic diagram of crystallization behavior of the polyvinylidene fluoride porous membrane, and B is a separation route 1 and a separation route 2 of PMMA with different molecular weights during separation; wherein, the high molecular PMMA flows out through the columnar macropores (route 1), and the low molecular PMMA flows out through the slit micropores (route 2).
Fig. 5 (a) shows GPC curves corresponding to two molecular weight PMMA and a mixed solution (stock solution) thereof, and (b) shows GPC curves corresponding to the obtained GPC curves obtained by separating polyvinylidene fluoride multi-stage pore films prepared in comparative examples, example 1, and example 2, collecting liquids for 0 to 2 minutes, and performing GPC testing.
Fig. 6 shows the data of the high molecular PMMA content (Area (a)) and the low molecular PMMA content (Area (B)) obtained from the stock solutions, the comparative examples, and the GPC curves obtained under the above conditions.
Detailed Description
The present invention will be described in detail below with reference to the drawings and the detailed description, but the invention is not limited to the scope of the described detailed description.
Polyvinylidene fluoride (PVDF) used below was purchased from Kureha Chemical, japan under the model KF850; dimethyl sulfone DMSO2 (99%) was supplied by chinese saen chemical technology (Shanghai); two different molecular weight polymethyl methacrylates (PMMA) were purchased from Sigma-Aldrich, U.S. and the parameters are shown in Table 1.
Table 1 different molecular weights PMMA used in this study
Example 1
Respectively drying polyvinylidene fluoride, dimethyl sulfone and polymethyl methacrylate in a vacuum drying oven at 80 ℃ overnight;
sequentially adding 10g of polyvinylidene fluoride and 10g of dimethyl sulfone into a glass bottle, taking dimethyl sulfone as a solvent of the polyvinylidene fluoride, and preparing transparent uniform 50wt% polymer solution by stirring for 2 hours at the magnetic stirring speed of 500rpm/min at the solution blending temperature of 180 ℃;
pouring the obtained blending solution into a custom mold rapidly, sealing the periphery with silicone grease, controlling the temperature to 115 ℃ by using a polarized light heat table, performing isothermal crystallization for 180min, and cooling to room temperature;
Immersing the prepared film into deionized water, placing for 24-48 h, etching to remove dimethyl sulfone phase, then sequentially transferring into de-ethanol and n-hexane, and placing for 2-4 h to obtain the polyvinylidene fluoride hierarchical pore film in a wet state. The etching process is as shown in fig. 4.
Example 2.
The isothermal crystallization time in example 1 was adjusted to 90min, and other experimental conditions were the same as in example 1, to finally obtain a polyvinylidene fluoride hierarchical pore film.
Example 3.
The isothermal crystallization time in example 1 was adjusted to 360min, and other experimental conditions were the same as in example 1, to finally obtain a polyvinylidene fluoride hierarchical pore film.
Example 4.
Sequentially adding 6g of polyvinylidene fluoride and 14g of dimethyl sulfone into a glass bottle, taking dimethyl sulfone as a solvent of the polyvinylidene fluoride, and preparing transparent uniform 30wt% polymer solution by stirring for 2 hours at the magnetic stirring speed of 500rpm/min at the solution blending temperature of 180 ℃; other experimental conditions were the same as in example 1, and finally a polyvinylidene fluoride multi-stage pore film was obtained.
Example 5.
8G of polyvinylidene fluoride and 12g of dimethyl sulfone are sequentially added into a glass bottle, and the dimethyl sulfone is used as a solvent of the polyvinylidene fluoride to prepare transparent and uniform 40wt% polymer solution; other experimental conditions were the same as in example 1, and finally a polyvinylidene fluoride multi-stage pore film was obtained.
Example 6.
Sequentially adding 12g of polyvinylidene fluoride and 8g of dimethyl sulfone into a glass bottle, taking dimethyl sulfone as a solvent of the polyvinylidene fluoride, and preparing transparent and uniform 60wt% polymer solution by stirring for 2 hours at the magnetic stirring speed of 500rpm/min at the solution blending temperature of 180 ℃; other experimental conditions were the same as in example 1, and finally a polyvinylidene fluoride multi-stage pore film was obtained.
Example 7.
Sequentially adding 14g of polyvinylidene fluoride and 6g of dimethyl sulfone into a glass bottle, and preparing transparent uniform 70wt% polymer solution by taking the dimethyl sulfone as a solvent of the polyvinylidene fluoride; other experimental conditions were the same as in example 1, and finally a polyvinylidene fluoride multi-stage pore film was obtained.
Example 8.
Sequentially adding 16g of polyvinylidene fluoride and 4g of dimethyl sulfone into a glass bottle, and preparing transparent uniform 80wt% polymer solution by taking dimethyl sulfone as a solvent of the polyvinylidene fluoride; other experimental conditions were the same as in example 1, and finally a polyvinylidene fluoride multi-stage pore film was obtained.
Example 9.
Taking dimethyl sulfoxide as a solvent of polyvinylidene fluoride, sequentially adding 10g of polyvinylidene fluoride and 10g of dimethyl sulfoxide into a glass bottle, and preparing a transparent uniform mixture solution; other experimental conditions were the same as in example 1, and finally a polyvinylidene fluoride multi-stage pore film was obtained.
Comparative example
Respectively drying polyvinylidene fluoride, dimethyl sulfone and polymethyl methacrylate in a vacuum drying oven at 80 ℃ overnight;
sequentially adding 10g of polyvinylidene fluoride and 10g of dimethyl sulfone into a glass bottle, taking dimethyl sulfone as a solvent of the polyvinylidene fluoride, and preparing transparent uniform 50wt% polymer solution by stirring for 2 hours at the magnetic stirring speed of 500rpm/min at the solution blending temperature of 180 ℃;
pouring the obtained blending solution into a custom mold rapidly, sealing the periphery with silicone grease, controlling the temperature to 115 ℃ by using a polarized light heat table, performing isothermal crystallization for 3min, and cooling to room temperature;
Immersing the prepared film into deionized water, placing for 24-48 h, etching to remove dimethyl sulfone phase, then sequentially transferring into de-ethanol and n-hexane, and placing for 2-4 h to obtain the polyvinylidene fluoride hierarchical pore film in a wet state.
The samples obtained in examples 1 to 2 and comparative example were examined by scanning electron microscopy under experimental conditions: the results obtained by metal spraying are shown in FIGS. 1 to 3, respectively.
Samples obtained in examples 1-2 and comparative example were tested for PMMA properties separating two different molecular weights, experimental conditions: the separated liquid was collected for 0 to 2min for GPC measurement, and the results are shown in FIGS. 5 to 6.
As shown in fig. 1, single-stage holes are obtained after dimethyl sulfone is etched by deionized water, and columnar holes with the length of 100-300 μm and the width of 500 nm-5 μm formed by etching dimethyl sulfone exist in a polyvinylidene fluoride matrix; as shown in fig. 2 to 3, after the dimethyl sulfone is etched by deionized water, a multi-level pore structure exists in the polyvinylidene fluoride matrix, specifically, columnar pores with the length of 100 μm to 300 μm and the width of 500nm to 5 μm are formed by etching the dimethyl sulfone between the polyvinylidene fluoride spherulites; etching slit holes with the size of 1-100 nm formed by dimethyl sulfone existing between polyvinylidene fluoride platelets and crystal stacks; and as the crystallization time increases, the size and proportion of the micro-scale columnar pores to the total pores gradually decrease, while the proportion of the nano-scale slit pores to the total pores gradually increases.
The establishment method comprises the following steps: as shown in fig. 5 (a), two kinds of PMMA with different molecular weights are mixed as a stock solution at a mass ratio of 1:1, two characteristic peaks appear, which correspond to characteristic peaks of elution curves of PMMA with pure 996000 and pure 15000 molecular weights, respectively, and Area (a) is obtained after integration of data obtained according to GPC curves: it is reasonable to say that the relative content is expressed in terms of Area ratio, area (B) ≡1:1.
As shown in fig. 5 (b) and 6, the polyvinylidene fluoride multi-stage pore film prepared in the comparative example was produced with Area (a): area (B) is approximately equal to 1.18, and has no separation effect when being similar to the Area ratio of the stock solution; the polyvinylidene fluoride multi-stage pore film prepared in example 2 had a separation effect, and Area (a): area (B) is approximately equal to 2.96, and the content of the high molecular weight PMMA is 74.78%; the polyvinylidene fluoride multi-stage pore film prepared in example 1 has better separation effect, and the Area (A): area (B) is approximately 4.53, the high molecular weight PMMA content is 81.92%. As shown in table 2, the polyvinylidene fluoride single-stage pore film has the ability to separate homologs, combining the advantages of the film and the volume exclusion effect, as compared to the polyvinylidene fluoride single-stage pore film.
Table 2 comparative table of stock solution parameters and separation efficiency of polyvinylidene fluoride multistage pore films prepared in comparative examples, example 1 and example 2
The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above embodiments, and falls within the scope of the present invention as long as the present invention meets the requirements.
Claims (9)
1. The polyvinylidene fluoride hierarchical porous film based on the volume repulsive effect has the thickness of 100-500 mu m and is characterized by having a hierarchical porous structure and being made of polyvinylidene fluoride;
the hierarchical porous structure is composed of a plurality of nanoscale slit holes and a plurality of microscale interpenetrating continuous through holes distributed around the nanoscale slit holes, wherein the nanoscale slit holes form island phases, and the microscale interpenetrating continuous through holes form sea phases with bicontinuous networks and are connected with the island phases; the micron-sized interpenetrating continuous through holes are columnar holes with the length of 100-300 mu m and the aperture of 500 nm-5 mu m between polyvinylidene fluoride spherulites; the nanoscale slit holes are holes with the aperture of 1-100 nm between polyvinylidene fluoride platelets and platelets.
2. A method for preparing a polyvinylidene fluoride hierarchical porous film based on volume exclusion effect according to claim 1, wherein the preparation method comprises the steps of:
step (1), drying polyvinylidene fluoride and dimethyl sulfone, mixing, and magnetically stirring at 180-210 ℃ for 2-3 h to melt mixing to prepare transparent uniform 30-80-wt% polymer solution;
Pouring the blending solution obtained in the step (1) into a mould, sealing the periphery of the mould, crystallizing at a constant temperature of 110-150 ℃ for 90-360 min ℃, and cooling to obtain a film with the thickness of 100-500 mu m;
And (3) immersing the film prepared in the step (2) into deionized water, etching to remove a dimethyl sulfone phase, placing in ethanol for 10-12 h, then placing in n-hexane for 10-12 h, and drying to remove water to obtain the polyvinylidene fluoride hierarchical porous film based on the volume rejection effect.
3. The preparation method according to claim 2, wherein the mass ratio of polyvinylidene fluoride to dimethyl sulfone in the step (1) is 1: (1-2).
4. The method according to claim 2, wherein the magnetic stirring temperature in the step (1) is 180 ℃.
5. The method of claim 2, wherein the magnetic stirring time in step (1) is 2 h.
6. The process according to claim 2, wherein the temperature of the isothermal crystallization in step (2) is 115 ℃.
7. The process of claim 2, wherein the time for the medium temperature crystallization in step (2) is 180 min.
8. The method according to claim 2, wherein the film in step (3) is immersed in deionized water for 48 to 50 hours.
9. Use of a polyvinylidene fluoride hierarchical porous membrane based on volume exclusion effect according to claim 1 for separating homologs.
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| CN102977524A (en) * | 2012-06-30 | 2013-03-20 | 杭州师范大学 | Polyvinylidene fluoride composite material and preparation method thereof |
| CN107090097A (en) * | 2017-05-02 | 2017-08-25 | 杭州师范大学 | A kind of preparation method of polylactic acid porous thin film shape memory |
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| EP1010457A4 (en) * | 1996-12-10 | 2006-03-22 | Asahi Chemical Ind | Porous polyvinylidene fluoride resin film and process for producing the same |
| WO2010002462A1 (en) * | 2008-07-03 | 2010-01-07 | Millipore Corporation | Porous asymmetric membranes |
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