阅读说明：本技术 一种海岛结构的聚偏氟乙烯多级孔薄膜及其制备方法 (Polyvinylidene fluoride hierarchical pore film with sea-island structure and preparation method thereof ) 是由 李勇进 由吉春 王佳耀 于 2019-09-26 设计创作，主要内容包括：本发明公开一种海岛结构的聚偏氟乙烯多级孔薄膜及其制备方法。该薄膜具有岛状微米级圆孔及纳米级狭缝孔的多级孔结构,材质为聚偏氟乙烯。方法是将聚偏氟乙烯、聚甲基丙烯酸甲酯、聚乳酸和增容剂干燥,然后加入熔融混炼设备熔融混炼5～10min出料冷却至常温,接着熔融压片制备得到厚度为1～150μm的薄膜,将薄膜用索氏特抽提法抽提。聚偏氟乙烯与聚甲基丙烯酸甲酯形成海相,聚乳酸独立形成岛相,聚偏氟乙烯在薄膜的海相中自身结晶,形成纳米级三维互穿的网络,使独立的岛相相连接,两级可调；获得的薄膜与单级孔薄膜相比具有2.1倍通量的提高,并且保持了截留的效率,同时具有良好的延展性与机械强度。(The invention discloses a polyvinylidene fluoride hierarchical pore film with a sea-island structure and a preparation method thereof. The film has a hierarchical pore structure with island-shaped micron-scale round holes and nanometer-scale slit holes, and is made of polyvinylidene fluoride. The method comprises the steps of drying polyvinylidene fluoride, polymethyl methacrylate, polylactic acid and a compatibilizer, adding the dried polyvinylidene fluoride, polymethyl methacrylate, polylactic acid and compatibilizer into a melting and mixing device, melting and mixing for 5-10 min, discharging, cooling to normal temperature, melting and tabletting to obtain a film with the thickness of 1-150 mu m, and extracting the film by a Soxhlet extraction method. Polyvinylidene fluoride and polymethyl methacrylate form a sea phase, polylactic acid independently forms an island phase, polyvinylidene fluoride is crystallized in the sea phase of the film to form a nano-scale three-dimensional interpenetrating network, so that the independent island phases are connected, and the two-stage adjustment is realized; the resulting membrane has a 2.1 times flux enhancement compared to a single stage pore membrane and retains the efficiency of entrapment while having good ductility and mechanical strength.)

1. A polyvinylidene fluoride hierarchical pore film with a sea-island structure is a film with the thickness of 1-150 mu m, and is characterized in that the film has a hierarchical pore structure and is made of polyvinylidene fluoride;

the multistage hole structure is composed of a plurality of micron-sized round holes and a plurality of nanoscale through holes which are distributed around the micron-sized round holes and penetrate through the micron-sized round holes, and the micron-sized round holes and the nanoscale through holes are connected through the polyvinylidene fluoride substrate; the nanoscale interpenetrating continuous through holes are slit holes which are formed by etching polymethyl methacrylate in a polyvinylidene fluoride matrix, wherein the length of the slit holes is 100-200 nm, and the width of the slit holes is 1-100 nm; the micron-sized round hole is specifically an island-shaped round hole with the size of 1-5 mu m formed by etching polylactic acid in the polyvinylidene fluoride substrate.

2. The method for preparing polyvinylidene fluoride hierarchical pore membrane of sea-island structure of claim 1, which comprises the steps of:

drying polyvinylidene fluoride, polymethyl methacrylate, polylactic acid and a compatibilizer;

step (2), stirring and premixing the dried polyvinylidene fluoride, polymethyl methacrylate, polylactic acid and compatibilizer, adding the mixture into a melting and mixing device, and melting and mixing for 5-10 min at 180-210 ℃;

the polylactic acid accounts for 5-20% of the total mass of the ternary blend of polyvinylidene fluoride, polylactic acid and polymethyl methacrylate, and the mass content of the polyvinylidene fluoride in the polyvinylidene fluoride and the polymethyl methacrylate is 20-90%;

discharging the mixture subjected to melt mixing from a melt mixing device, and cooling to normal temperature;

step (4), melting and tabletting the cooled mixture to prepare a film with the thickness of 1-150 mu m;

and (5) extracting the film in the step (4) by a Soxhlet extraction method, wherein the extraction liquid is a good solvent of polylactic acid and polymethyl methacrylate, the heating temperature is controlled to enable the extraction liquid to flow back once every 6-8 min, the extraction time is 6-12 h, the film is taken out after the extraction is finished, the film is placed in ethanol for 2h, and then the film is transferred to deionized water to be placed for 2h, so that the polyvinylidene fluoride hierarchical pore film in a wet state is obtained.

3. The method for preparing polyvinylidene fluoride hierarchical pore membrane with sea-island structure according to claim 2, wherein the mass ratio of polyvinylidene fluoride, polymethyl methacrylate and polylactic acid in step (2) is 2: 2: 1.

4. the method for preparing polyvinylidene fluoride multistage pore membrane of sea-island structure according to any one of claims 2-3, wherein the compatibilizer is added in step (2) in the amount of 0.01-0.5% by mass of the total amount of polyvinylidene fluoride, polymethyl methacrylate and polylactic acid.

5. The method for preparing polyvinylidene fluoride hierarchical pore membrane of sea-island structure according to claim 4, wherein the bulking agent in step (2) is 0.5% by mass of total mass of polyvinylidene fluoride, polymethyl methacrylate and polylactic acid.

6. The method for preparing polyvinylidene fluoride hierarchical pore membrane of sea-island structure according to any one of claims 2-5, characterized in that good solvent of polylactic acid and polymethyl methacrylate in step (5) is chloroform, dichloromethane or carbon tetrachloride.

7. The method for preparing a sea-island structure polyvinylidene fluoride multistage pore membrane according to any one of claims 2 to 6, wherein the melt-kneading temperature in the step (2) is 200 ℃ and the kneading time is 10 min.

8. The method for preparing polyvinylidene fluoride multistage pore membrane with sea-island structure according to any one of claims 2-7, wherein the melt tabletting method in step (4) is to use hot pressing at 180-210 ℃ for 1-3 min, then rapidly transfer to 140-150 ℃ for annealing treatment for 3-12 h, and the nano-pores of the membrane obtained after etching are orderly arranged and micron-sized round holes.

Technical Field

The invention relates to the field of high polymer materials, in particular to a preparation method for obtaining a polyvinylidene fluoride film with a hierarchical pore structure by combining incompatible system phase separation and crystallization-induced phase separation.

Background

The polymer porous membrane has great application potential in the fields of separation membranes, battery diaphragms and the like, and the preparation method thereof is widely concerned. The design of the membrane structure is an important point for the preparation of the polymer porous membrane according to the application field of the polymer porous membrane. In the practical use of the polymer porous separation membrane, the retention efficiency and the separation flux thereof become important indexes for evaluating the separation efficiency thereof. Generally, the interception efficiency comes from controlling the aperture, and the separation flux also decreases with the decrease of the aperture, so that the increase of the interception efficiency and the increase of the separation flux cannot be considered. In addition, the structure and performance of the membrane are closely related, and therefore the design of the membrane structure is one of the main strategies to solve the contradiction, wherein the design of the hierarchical pore structure can effectively solve the above problems. The hierarchical porous material has two or more pore structures, and is usually designed by combining two or more templates with different sizes, however, the hierarchical regulation of the two-level templates and the consideration of the mechanical properties and the separation properties of the obtained hierarchical porous material still remain problems to be solved in the field.

Therefore, it is necessary to develop a method of preparing a hierarchical porous membrane having a sea-island structure.

Polyvinylidene fluoride has excellent chemical resistance, high temperature resistance, excellent flexibility and good processability, and is often used as a material of choice for polymer separation membranes. Starting from the preparation of the hierarchical porous polyvinylidene fluoride with the sea-island structure, the invention provides a method for preparing a separation membrane with the hierarchical porous structure by combining incompatible system phase separation and crystallization-induced phase separation, and is expected to be applied to multiple industries such as water treatment, battery diaphragm and the like.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a hierarchical porous polyvinylidene fluoride film with an island structure.

The polyvinylidene fluoride hierarchical pore film is a film with the thickness of 1-150 mu m, has a hierarchical pore structure and is made of polyvinylidene fluoride. The multistage hole structure is composed of a plurality of micron-sized round holes and a plurality of nanoscale through holes which are distributed around the micron-sized round holes and penetrate through the micron-sized round holes, and the micron-sized round holes and the nanoscale through holes are connected through the polyvinylidene fluoride substrate; the nanoscale interpenetrating continuous through holes are slit holes which are formed by etching polymethyl methacrylate in a polyvinylidene fluoride matrix, wherein the length of the slit holes is 100-200 nm, and the width of the slit holes is 1-100 nm; the micron-sized round hole is specifically an island-shaped round hole with the size of 1-5 mu m formed by etching polylactic acid in the polyvinylidene fluoride substrate.

Another object of the present invention is to provide a method for preparing the polyvinylidene fluoride film having a hierarchical pore (nano-scale continuous through-hole/micro-scale circular hole) structure.

The method comprises the following specific steps:

respectively placing polyvinylidene fluoride, polylactic acid and polymethyl methacrylate in a vacuum drying oven, and drying at 60-100 ℃ until the weight is unchanged;

mixing the dried polyvinylidene fluoride, polylactic acid and polymethyl methacrylate, adding the mixture into a melting and mixing device, and melting and mixing for 5-10 min at 180-210 ℃;

the polylactic acid accounts for 5-20% of the total mass of the ternary blend of polyvinylidene fluoride, polylactic acid and polymethyl methacrylate, and the mass content of the polyvinylidene fluoride in the polyvinylidene fluoride and the polymethyl methacrylate is 20-90%;

preferably, the mass ratio of polyvinylidene fluoride to polymethyl methacrylate to polylactic acid is 2: 2: 1;

preferably, a compatibilizer (a main chain can be polystyrene, polymethyl methacrylate, butyl methacrylate or nanoparticles, a reaction group can be an epoxy group, a maleic anhydride group, and the like) is added in the step (2), and the weight of the compatibilizer is 0.01-0.5%, preferably 0.5% of the total weight of polyvinylidene fluoride, polymethyl methacrylate and polylactic acid.

Preferably, the melt mixing temperature in the step (2) is 200 ℃, and the mixing time is 10 min;

the melting and mixing equipment is various devices commonly used in industry, such as an internal mixer, a single screw extruder, a double screw extruder or an injection machine;

discharging the mixture subjected to melt mixing from a melt mixing device, and cooling to normal temperature;

step (4), melting and tabletting the cooled mixture to prepare a film with the thickness of 1-150 mu m;

in the step (4), if the hot pressing is carried out at 180-210 ℃ for 1-3 min, the film is transferred to 140-150 ℃ within 5 seconds and then is annealed for 3-12 h, and the nano holes of the film obtained after etching are orderly arranged and micron-sized round holes;

extracting the film in the step (4) by a Soxhlet extraction method, wherein the extraction liquid is a good solvent of polylactic acid and polymethyl methacrylate, the heating temperature is controlled to enable the extraction liquid to flow back once every 6-8 min, the extraction time is 6-12 h, the film is taken out after the extraction is finished, the film is placed in ethanol for 2h, and then the film is transferred to deionized water to be placed for 2h, so that the polyvinylidene fluoride hierarchical pore film in a wet state is obtained;

the good solvent of the polylactic acid and the polymethyl methacrylate is chloroform, dichloromethane or carbon tetrachloride;

the invention has the beneficial effects that:

polylactic acid forms an island-shaped phase in a ternary system, polymethyl methacrylate and polyvinylidene fluoride form a sea phase, polyvinylidene fluoride can be crystallized in a melt of the film, a mutually-penetrated bicontinuous network is formed in the sea phase and is connected with the island-shaped phase, two stages of templates are respectively adjustable, graded regulation and control are realized, and in addition, a nano-scale slit hole in the sea phase can be controlled through crystallization;

the polyvinylidene fluoride hierarchical pore film has good ductility and self-supporting performance, the elongation at break of the polyvinylidene fluoride hierarchical pore film formed by etching the film in a wet state can reach more than 40%, the strength at break can reach 4MPa, the elongation at break in a dry state can reach more than 20%, and the strength at break can reach 6.5 MPa;

compared with the polyvinylidene fluoride single-stage pore film, the polyvinylidene fluoride multi-stage pore film has higher water flux, and the water flux of the polyvinylidene fluoride multi-stage pore film formed by etching the film can reach 213L/m at the pressure of 1bar when the content of the compatibilizer is 0.5 percent²h, compared with the polyvinylidene fluoride single-stage pore film, the polyvinylidene fluoride single-stage pore film is improved by 2.1 times;

the polyvinylidene fluoride hierarchical pore film has high porosity which reaches 80%;

the pore size of the nano-pores obtained by etching polymethyl methacrylate of the polyvinylidene fluoride hierarchical-pore film cannot change along with the addition amount of the compatibilizer, is slit pores with the length of 100-200 nm and the width of 1-100 nm, and only changes the size of the micro-grade round pores obtained by etching polylactic acid.

Meanwhile, the polyvinylidene fluoride hierarchical pore film is prepared only by using common melting and mixing equipment, and is simple in industrial preparation and strong in processability.

The polyvinylidene fluoride hierarchical pore film prepared by the method can be used in the fields of environmental protection, medical treatment and the like, and the thickness of the film is adjusted according to the application.

Drawings

FIG. 1 is a schematic diagram showing the change of a thin film before and after Soxhlet extraction;

FIG. 2 is a scanning electron micrograph of a comparative example polyvinylidene fluoride single-stage pore film;

FIG. 3 is a scanning electron micrograph of a polyvinylidene fluoride hierarchical porous film prepared in example 1;

FIG. 4(a) shows the etching principle, (b) shows a 100 μm SEM image of the PVDF multi-stage porous film prepared in example 2, and (c) shows a 10 μm SEM image of the PVDF multi-stage porous film prepared in example 2;

FIG. 5 is a scanning electron micrograph of a polyvinylidene fluoride hierarchical porous film prepared in example 3, wherein the ruler is 10 μm;

FIG. 6 is the mechanical diagram of the polyvinylidene fluoride hierarchical pore membrane prepared in example 3;

FIG. 7 is the water flux data of polyvinylidene fluoride hierarchical pore membranes prepared in comparative example and examples 2 and 3;

FIG. 8 is a mercury intrusion plot of polyvinylidene fluoride multi-stage pore membrane prepared in comparative example and example 3;

Detailed Description

The present invention is described in detail below with reference to the attached drawings and the embodiments, but the present invention is not limited to the scope of the embodiments.

Polyvinylidene fluoride (PVDF) used below was produced by wushu chemical industries, japan, and has a model number of KF 850; polylactic acid (PLA) is manufactured by Nature Works, USA, and the model number is 3001D; polymethyl methacrylate (PMMA) is produced by Sigma-Aldrich, USA, compatibilizer SZ-01 (copolymer of methyl methacrylate and glycidyl methacrylate)

FIG. 1 is a schematic diagram showing the change of the film before and after Soxhlet extraction.

Comparative example.

Respectively drying polyvinylidene fluoride and polymethyl methacrylate in a vacuum drying oven at 80 ℃ overnight;

sequentially adding 25g of polyvinylidene fluoride and 25g of polymethyl methacrylate into an internal mixer, wherein the temperature of the internal mixer is 200 ℃, the rotor speed is 20rpm/min, and the internal mixing is carried out for 2 min; then the speed of the rotor is increased to 50rpm/min, banburying is carried out for 10min, and then discharging is carried out, and cooling is carried out to normal temperature.

And (3) hot-pressing the mixture subjected to melting and mixing into a thin film with the thickness of 150 microns in a hot press at 200 ℃, quickly transferring to 140-150 ℃ after hot pressing for 1-3 min, and carrying out annealing treatment for 3-12 h.

Extracting by a Soxhlet extraction method, wherein the extraction liquid is a good solvent of polylactic acid and polymethyl methacrylate, the heating temperature is controlled to enable the extraction liquid to flow back once every 6-8 min, the extraction time is 6-12 h, after the extraction is finished, the extraction liquid is taken out, placed in ethanol for 2h, and then transferred into deionized water for 2h, so that the polyvinylidene fluoride hierarchical pore film in a wet state is obtained.