CN106731883B - Polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane and preparation method thereof - Google Patents
Polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane and preparation method thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/14—Ultrafiltration; Microfiltration
- B01D61/145—Ultrafiltration
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/30—Polyalkenyl halides
- B01D71/32—Polyalkenyl halides containing fluorine atoms
- B01D71/34—Polyvinylidene fluoride
Abstract
The invention relates to a polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane and a preparation method thereof, wherein the preparation method comprises the following steps: 1) preparing nano lignocellulose by an acid hydrolysis-high pressure homogenization method; 2) preparing a nano lignocellulose polyvinylidene fluoride blending ultrafiltration membrane by using an immersion precipitation phase inversion method; 3) preparing the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane by using an immersion surface coating method. According to the invention, the nano-cellulose containing lignin and polyvinylidene fluoride are compounded for the first time to form the strength of the hydrogen bond reinforced composite membrane, the hydrophilicity of the polyvinylidene fluoride-based ultrafiltration membrane is improved, the pollution resistance is strong, the problem of low mechanical property caused by poor compatibility of the nano-cellulose and the polyvinylidene fluoride-based membrane is solved by introducing the lignin, and the adhesion effect of a phase interface is improved.
Description
Technical Field
the invention belongs to the field of organic polymer compounds, and particularly relates to a polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane and a preparation method thereof.
Background
the polyvinylidene fluoride is a semi-crystalline polymer in normal state, and the molecular chain of the polyvinylidene fluoride contains three elements of fluorine, carbon and hydrogen. Because the ultrafiltration membrane has the characteristics of excellent membrane forming property, heat resistance, hydrolysis resistance, creep resistance, no toxicity, physical and mechanical properties, chemical stability, heat resistance and the like, the ultrafiltration membrane becomes an ultrafiltration membrane material with wide application, but because the ultrafiltration membrane has certain hydrophobicity, membrane pollution is easy to cause, the application field of the ultrafiltration membrane is limited to a certain extent, and therefore, the improvement of the hydrophilicity of the ultrafiltration membrane and the pollution resistance of the ultrafiltration membrane become an important field for the research of the current membrane material.
Nano-lignocellulose is the main component of the natural pulp sheet, a relatively high molecular mass substance made of lignin and cellulose linked together by LCC (lignin carbohydrate). Lignin has three basic structures, namely a guaiacyl structure, a syringyl structure and a p-hydroxyphenyl structure. Meanwhile, the compound contains various active functional groups, such as hydroxyl, carbonyl, carboxyl, methyl and side chain structures, and is the second most abundant organic matter in the world. Cellulose is mainly synthesized by plants through photosynthesis, is a natural renewable organic high-molecular polymer with the most abundant content on the earth, has the advantages of low price, easy obtainment, reproducibility, biocompatibility, simple preparation and the like, and is concerned by researchers in various fields.
The nano lignocellulose has higher specific surface energy and good hydrophilic property, so that the hydrophilicity of the composite membrane material can be effectively increased, and the anti-pollution capability of the composite membrane material is improved; the nano lignocellulose crystal structure shows strong nano effect, so that the mechanical strength of the composite film is improved. The nano-lignocellulose has high mechanical strength, the interface compatibility between the pure hydrophilic nano-cellulose and the hydrophobic high molecular polymer is poor, the nano-lignocellulose can partially improve the interface combination effect of polyvinylidene fluoride and the nano-cellulose through the existence of lignin, and the performance of the composite material is improved. The interface compatibility of polyvinylidene fluoride and nanocellulose is improved by the existence of lignin, but the interface combination effect of the lignin and the polyvinylidene fluoride cannot bring about great improvement of the performance of the composite material. Therefore, the comprehensive performance of the nano lignocellulose/polyvinylidene fluoride composite material can be further improved by adding the interfacial compatibilizer of polyvinylidene fluoride and nano lignocellulose.
In order to further enhance the number of hydrophilic groups on the surface of the membrane by a blending modification method and enhance the anti-pollution capability of the ultrafiltration membrane, dopamine DOPA molecules contain catechol and amino functional groups, can be self-polymerized and compounded on the surface of a base material in an oxidation environment to form a polydopamine layer with high adhesiveness, and more hydrophilic groups are introduced on the surface of the ultrafiltration membrane by coating and modifying the polydopamine surface, so that the composite membrane material is improved in the aspects of anti-pollution performance, mechanical performance and the like, and has a good application prospect and an important theoretical value.
The method comprises the steps of preparing nano lignocellulose by adopting an acid hydrolysis-high pressure homogenization method, preparing a nano lignocellulose/polyvinylidene fluoride blended membrane material by adopting an immersion precipitation phase inversion method, and preparing a polydopamine/nano lignocellulose/polyvinylidene fluoride composite ultrafiltration membrane by coating and modifying the surface of polydopamine.
Disclosure of Invention
Aiming at the defects in the field, the invention aims to provide a polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane and a preparation method thereof.
The technical scheme for realizing the above purpose of the invention is as follows:
A polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane is prepared from raw materials comprising polyvinylidene fluoride, nano lignocellulose, dopamine and an organic solvent; wherein the weight ratio of the polyvinylidene fluoride to the nano lignocellulose to the dopamine is (16-18): (0.06-0.4): 1.8-2.2); the weight-volume ratio of the polyvinylidene fluoride to the organic solvent is (16-18) to (70-85) in g/mL; the organic solvent is N, N-dimethylacetamide.
Preferably, the weight ratio of the polyvinylidene fluoride to the nano lignocellulose to the dopamine is 16 (0.1-0.4) to (1.8-2.2).
Preferably, the weight-volume ratio of the polyvinylidene fluoride to the organic solvent is 16 (83-84) in g/mL.
Further, the raw material of the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane also comprises deionized water.
Further, the thickness of the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane is 100-200 μm.
The lignocellulose of the invention can be prepared by adopting a conventional method in the prior art, such as an acid hydrolysis-high pressure homogenization method (for example, the acid is dilute sulfuric acid) by taking a natural color pulp board or a natural pulp board as a raw material.
the invention also provides a preparation method of the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane, which comprises the following steps:
1) Preparing nano lignocellulose by an acid hydrolysis-high pressure homogenization method: hydrolyzing the natural color pulp board by using dilute sulfuric acid, centrifuging at a high speed, washing the precipitate to be neutral by using deionized water, and obtaining solid matter, namely lignocellulose; transferring the obtained solid into an organic solvent, namely N, N-dimethylacetamide according to a ratio, and homogenizing under high pressure to obtain a nano lignocellulose solution;
2) preparing a nano lignocellulose polyvinylidene fluoride blending ultrafiltration membrane by using an immersion precipitation phase inversion method: mixing the nano lignocellulose solution obtained in the step 1) and polyvinylidene fluoride according to the proportion to prepare a casting film stock solution; carrying out vacuum defoaming treatment on the casting film stock solution, and then preparing a film, namely the nano lignocellulose polyvinylidene fluoride blended ultrafiltration film;
3) Preparing a polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane by using an immersion surface coating method: fixing the blended ultrafiltration membrane prepared in the step 2) in a reaction tank, adding a polydopamine solution with the concentration of 2g/L, performing coating modification under the conditions of shaking (or vibration), room temperature and oxygen, then washing the residual polydopamine solution on the surface of the obtained membrane with deionized water, soaking the obtained membrane in absolute ethyl alcohol (for at least 20min), and removing the polydopamine with weak adhesion to obtain the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane. It may be stored in deionized water.
Preferably, the concentration of the dilute sulfuric acid in the step 1) is 30-35 wt%.
preferably, the unbleached pulp sheet of step 1) is crushed by a crusher before being hydrolyzed by acid. Preferably, the weight-to-volume ratio of the unbleached pulp sheet to 30-35 wt% dilute sulfuric acid solution is 1:18 in g/mL.
Preferably, the hydrolysis temperature in the step 1) is 60-70 ℃, and the hydrolysis time is 6-9 hours.
Preferably, the high-speed centrifugal rotating speed in the step 1) is 3000r/min-4000 r/min.
Preferably, the high-pressure homogenizing pressure in the step 1) is 80-100MPa, and the homogenizing is carried out for 5-10 times.
Specifically, the step 1) comprises the steps of placing the natural pulp board in a 30-35 wt% dilute sulfuric acid solution, hydrolyzing for 6-9 hours at 60-70 ℃, centrifuging at a high speed, washing the precipitate with deionized water until the eluate is neutral, wherein the obtained solid is lignocellulose, transferring the solid into N, N-dimethylacetamide, and carrying out homogeneous dispersion for 5-10 times under the pressure of 80-100MPa to obtain the nano lignocellulose solution. Preferably, the weight to volume ratio of the lignocellulose or the nano lignocellulose to the N, N-dimethylacetamide in g/mL is (0.06-0.4): (70-85); further preferred are (0.1-0.4): 83-84).
preferably, step 2) prepares the casting film stock solution under ultrasonic stirring conditions.
Preferably, the temperature of the ultrasonic stirring in the step 2) is 80-100 ℃, and the stirring time is 4-6 h; the ultrasonic power is 200w-300 w.
Specifically, the step 2) comprises the steps of adding polyvinylidene fluoride into the N, N-dimethylacetamide solution of the uniformly dispersed nano lignocellulose, and ultrasonically stirring to dissolve the polyvinylidene fluoride to obtain the casting film stock solution.
In the step 2), vacuumizing is performed under the ultrasonic action, and vacuum defoaming treatment is performed on the casting film stock solution, wherein the vacuum degree during defoaming is-0.05 to-0.09 MPa.
Preferably, the time of the vacuum defoaming treatment in the step 2) is 1-2 h.
Wherein, in the step 2), the step of preparing the film comprises: placing the casting film stock solution on a glass plate and scraping to form a film; and immersing the glass plate in deionized water, carrying out immersion precipitation phase transformation at normal temperature, and standing for 1-2h to obtain the blended ultrafiltration membrane material. The thickness of the film may be 100-200 μm.
Preferably, the film coating modification time of the step 3) is 2-6 h.
The shaking (or shaking) in the step 3) can be carried out by placing the reaction tank on a shaker.
The polydopamine solution can be prepared by adopting a conventional method in the field; for example, dopamine is weighed, dissolved in a proper amount of deionized water at normal temperature, and ultrasonically stirred for 3 hours (ultrasonic power 200W) to obtain a polydopamine solution.
The weight to volume ratio described in the present invention may also be other units known to those skilled in the art, such as kilograms per liter.
The invention also discloses the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane prepared by the preparation method.
The invention has the beneficial effects that:
According to the invention, the nano-cellulose containing lignin and polyvinylidene fluoride are compounded for the first time, and the hydroxyl in the nano-lignocellulose and the polyvinylidene fluoride form hydrogen bonds, so that the strength of the composite membrane is enhanced, the hydrophilicity of the ultrafiltration membrane taking the polyvinylidene fluoride as a matrix is improved, and the obtained composite ultrafiltration membrane has strong anti-pollution capacity; meanwhile, the introduction of lignin solves the problem of low mechanical property caused by poor compatibility of the nano-cellulose and the polyvinylidene fluoride matrix, and improves the adhesion effect of a phase interface. In order to further enhance the number of hydrophilic groups on the surface of the membrane by a blending modification method and enhance the anti-pollution capability of the ultrafiltration membrane, dopamine DOPA molecules contain catechol and amino functional groups, can be self-polymerized and compounded on the surface of a base material in an alkaline solution and an oxidation environment to form a polydopamine layer with high adhesion, and more hydrophilic groups are introduced on the surface of the ultrafiltration membrane by coating and modifying the polydopamine surface, so that the composite membrane material is improved in the aspects of anti-pollution performance, mechanical performance and the like, and has a good application prospect and an important theoretical value.
experiments confirm that the key parameters for controlling the mechanical property and the hydrophilic property of the polyvinylidene fluoride composite membrane are the addition amount of the nano lignocellulose, the thickness of the ultrafiltration membrane and the surface coating time.
Drawings
FIG. 1: and (3) a surface scanning electron microscope photo of the vinylidene fluoride ultrafiltration membrane prepared in the comparative example with the magnification of 400 times.
FIG. 2: a surface scanning electron microscope photograph of the polydopamine nano-lignocellulose polyvinylidene fluoride composite ultrafiltration membrane prepared in the example 1 with the magnification of 400 times.
FIG. 3: the surface scanning electron microscope photograph of the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane prepared in the example 2 with the magnification of 400 times.
FIG. 4: a surface scanning electron microscope photograph of the polydopamine nano-lignocellulose polyvinylidene fluoride composite ultrafiltration membrane prepared in the example 3 with the magnification of 400 times.
Detailed Description
The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. The examples do not show the specific techniques or conditions, according to the technical or conditions described in the literature in the field, or according to the product specifications. The reagents or instruments used are conventional products available from regular distributors, not indicated by the manufacturer.
The embodiment of the invention adopts: the natural color pulp sheet is purchased from Shandong spring forest for papermaking; sulfuric acid, N-dimethylacetamide was purchased from beijing chemical plants; dopamine, polyvinylidene fluoride (PVDF) was purchased from shanghai yi ltd.
The vacuum degassing device used below is formed by adopting a simple laboratory instrument and mainly comprises a vacuum pump, a suction flask and an ultrasonic oscillator, wherein the casting film stock solution is poured into the suction flask, the suction flask is placed in the ultrasonic oscillator, and the suction flask is connected with the vacuum pump so as to realize vacuum degassing of the casting film stock solution.
Example 1
1. Preparing materials according to the following mixture ratio:
16g of polyvinylidene fluoride, 0.1g of nano lignocellulose, 83.9mL of N, N-dimethylacetamide, 4g of dopamine and 4L of deionized water.
Dissolving 4g of dopamine into 2L of deionized water at normal temperature, and ultrasonically stirring for 3h (ultrasonic stirring power is 200W) to obtain 2g/L polydopamine solution.
The preparation method of the nano lignocellulose solution comprises the following steps: the method comprises the steps of putting a natural pulp board (firstly crushed by a crusher) into a 30 wt% dilute sulfuric acid solution, hydrolyzing for 8 hours at 60 ℃ at a solid-liquid ratio of 1:18g/mL, carrying out high-speed centrifugal precipitation, washing and precipitating with deionized water until eluate is neutral to obtain a solid substance, namely lignocellulose, transferring 0.1g of the solid substance into 83.9mL of N, N-dimethylacetamide, homogenizing under 100MPa for 10 times, and uniformly dispersing the nano lignocellulose in the N, N-dimethylacetamide to obtain the natural pulp board.
2. Preparation of a casting dope
Adding 16g of polyvinylidene fluoride into the nano lignocellulose solution obtained in the step 1), and carrying out ultrasonic stirring for 5 hours (the ultrasonic stirring power is 200W) at the temperature of 80 ℃ to obtain a nano lignocellulose polyvinylidene fluoride casting film stock solution.
3. Degassing of casting film liquid
and (3) placing the prepared casting film stock solution into a vacuum degassing device, starting a vacuum pump to carry out ultrasonic vacuum-reduction vacuum-pumping degassing (ultrasonic power is 200W) on the casting film stock solution at 90 ℃, wherein the relative vacuum degree is-0.09 MPa, and the degassing time is 4 h.
4. Film scraping formation
1) Casting the defoamed casting solution on a clean glass plate, and adjusting the film scraping thickness of an automatic film scraping machine to 200 mu m;
2) And immersing the glass plate in deionized water, carrying out immersion precipitation phase transformation at normal temperature, and standing for 1-2h to obtain the blended ultrafiltration membrane material. The thickness of the film was 200. mu.m.
5. Surface coating
Fixing the blended ultrafiltration membrane in a reaction tank, pouring a dopamine solution into the reaction tank, then placing the splint reaction tank on a shaking table, coating the blended ultrafiltration membrane in an aqueous solution with polydopamine concentration of 2g/L for 3h at room temperature under an aerobic condition, flushing the residual dopamine solution on the surface by using deionized water after the coating modification is finished, and soaking the membrane in absolute ethyl alcohol for 20min to remove the polymeric dopamine which is not firmly adhered, thus obtaining the polydopamine nano-lignocellulose polyvinylidene fluoride composite ultrafiltration membrane. It may be stored in deionized water.
Comparing the weight of the membrane before and after the poly-dopamine coating, 2g of poly-dopamine was coated on the composite ultrafiltration membrane.
A surface scanning electron micrograph at 400 Xmagnification is shown in FIG. 2.
And (3) performing ultrafiltration performance test on the sample, wherein the membrane sample is 100mm multiplied by 0.2mm (length multiplied by width multiplied by thickness), the test times are 10, the result is averaged, the performance index of the composite membrane is obtained, the water flux of the membrane material is 544L/m 2/h, and the rejection rate is 93.1%.
The tensile test of the sample was conducted in accordance with ASTM (ZB-WL300) test standard, and the tensile rate of a film sample was 1mm/min, and the tensile test was conducted 10 times at 100mm X15 mm X0.15 mm (length X width X thickness), and the results were averaged to obtain the performance index of the composite film, and the tensile strength and elongation at break of the film material were 6.7MPa and 7.4%, respectively.
Example 2
1. Preparing materials according to the following mixture ratio:
16g of polyvinylidene fluoride, 0.1g of nano lignocellulose, 83.9mL of N, N-dimethylacetamide, 4g of dopamine and 2L of deionized water.
dissolving 4g of dopamine into 2L of deionized water at normal temperature, and ultrasonically stirring for 3h (ultrasonic stirring power is 200W) to obtain 2g/L polydopamine solution.
The preparation method of the nano lignocellulose solution comprises the following steps: the method comprises the steps of putting a natural pulp board (firstly crushed by a crusher) into a 30 wt% dilute sulfuric acid solution, hydrolyzing for 8 hours at 60 ℃ at a solid-liquid ratio of 1:18g/mL, carrying out high-speed centrifugal precipitation, washing and precipitating with deionized water until eluate is neutral to obtain a solid substance, namely lignocellulose, transferring 0.1g of the solid substance into 83.9mL of N, N-dimethylacetamide, homogenizing under 100MPa for 10 times, and uniformly dispersing the nano lignocellulose in the N, N-dimethylacetamide to obtain the natural pulp board.
2. Preparation of a casting dope
Adding 16g of polyvinylidene fluoride into the nano lignocellulose solution obtained in the step 1), and carrying out ultrasonic stirring for 5 hours (the ultrasonic stirring power is 200W) at the temperature of 80 ℃ to obtain a nano lignocellulose polyvinylidene fluoride casting film stock solution.
3. Degassing of casting film liquid
And (3) placing the prepared casting film stock solution into a vacuum degassing device, starting a vacuum pump to carry out ultrasonic vacuum-reduction vacuum-pumping degassing (ultrasonic power is 200W) on the casting film stock solution at 90 ℃, wherein the relative vacuum degree is-0.09 MPa, and the degassing time is 4 h.
4. film scraping formation
1) Casting the defoamed casting solution on a clean glass plate, and adjusting the film scraping thickness of an automatic film scraping machine to 200 mu m;
2) And immersing the glass plate in deionized water, carrying out immersion precipitation phase transformation at normal temperature, and standing for 1-2h to obtain the blended ultrafiltration membrane material. The thickness of the film was 200. mu.m.
5. Surface coating
fixing the blended ultrafiltration membrane in a reaction tank, pouring a dopamine solution into the reaction tank, then placing the splint reaction tank on a shaking table, coating the blended ultrafiltration membrane in an aqueous solution with polydopamine concentration of 2g/L for 6 hours at room temperature under an aerobic condition, after the coating modification is finished, flushing the residual dopamine solution on the surface by using deionized water, and soaking the membrane in absolute ethyl alcohol for 20 minutes to remove the polymeric dopamine which is not firmly adhered, thus obtaining the polydopamine nano-lignocellulose polyvinylidene fluoride composite ultrafiltration membrane. It may be stored in deionized water.
Comparing the weight of the membrane before and after the poly-dopamine coating, 2g of poly-dopamine was coated on the composite ultrafiltration membrane.
A surface scanning electron micrograph at 400 Xmagnification is shown in FIG. 3.
And (3) performing ultrafiltration performance test on the sample, wherein the membrane sample is 100mm multiplied by 0.2mm (length multiplied by width multiplied by thickness), the test times are 10 times, the result is averaged, the performance index of the composite membrane is obtained, the water flux of the membrane material is 597L/m 2/h, and the rejection rate is 92.3%.
The tensile test of the sample was conducted in accordance with ASTM (ZB-WL300) test standard, and the tensile rate of a film sample 100mm × 15mm × 0.15mm (length × width × thickness), the tensile rate 1mm/min, the number of tests 10 times, and the results were averaged to obtain the performance index of the composite film, and the tensile strength and elongation at break of the film material were 6.9MPa and 7.9%, respectively.
Example 3
1. Preparing materials according to the following mixture ratio:
16g of polyvinylidene fluoride, 0.4g of nano lignocellulose, 83.5mL of N, N-dimethylacetamide, 4g of dopamine and 2L of deionized water.
Dissolving 4g of dopamine into 2L of deionized water at normal temperature, and ultrasonically stirring for 3h (ultrasonic stirring power is 200W) to obtain 2g/L polydopamine solution.
The preparation method of the nano lignocellulose solution comprises the following steps: the method comprises the steps of putting a natural pulp board (firstly crushed by a crusher) into a 30 wt% dilute sulfuric acid solution, hydrolyzing for 8 hours at 60 ℃ at a solid-liquid ratio of 1:18g/mL, carrying out high-speed centrifugal precipitation, washing and precipitating with deionized water until eluate is neutral to obtain a solid substance, namely lignocellulose, transferring 0.4g of the solid substance into 83.5mL of N, N-dimethylacetamide, homogenizing under 100MPa for 10 times, and uniformly dispersing the nano lignocellulose in the N, N-dimethylacetamide to obtain the natural pulp board.
2. Preparation of a casting dope
Adding 16g of polyvinylidene fluoride into the nano lignocellulose solution obtained in the step 1), and carrying out ultrasonic stirring for 5 hours (the ultrasonic stirring power is 200W) at the temperature of 80 ℃ to obtain a nano lignocellulose-polyvinylidene fluoride casting film stock solution.
3. Degassing of casting film liquid
And (3) placing the prepared casting film stock solution into a vacuum degassing device, starting a vacuum pump to carry out ultrasonic vacuum-reduction vacuum-pumping degassing (ultrasonic power is 200W) on the casting film stock solution at 90 ℃, wherein the relative vacuum degree is-0.09 MPa, and the degassing time is 4 h.
4. Film scraping formation
1) Casting the defoamed casting solution on a clean glass plate, and adjusting the film scraping thickness of an automatic film scraping machine to 200 mu m;
2) And immersing the glass plate in deionized water, carrying out immersion precipitation phase transformation at normal temperature, and standing for 1-2h to obtain the blended ultrafiltration membrane material. The thickness of the film was 200. mu.m.
5. Surface coating
Fixing the blended ultrafiltration membrane in a reaction tank, pouring a dopamine solution into the reaction tank, then placing the splint reaction tank on a shaking table, coating the blended ultrafiltration membrane in an aqueous solution with polydopamine concentration of 2g/L for 6 hours at room temperature under an aerobic condition, after the coating modification is finished, flushing the dopamine solution remained on the surface with deionized water, and soaking the membrane in absolute ethyl alcohol for 20 minutes to remove the polymeric dopamine with weak adhesion, thus obtaining the polydopamine nano-lignocellulose polyvinylidene fluoride composite ultrafiltration membrane. It may be stored in deionized water.
Comparing the weight of the membrane before and after the poly-dopamine coating, 2g of poly-dopamine was coated on the composite ultrafiltration membrane.
a surface scanning electron micrograph at 400 Xmagnification is shown in FIG. 4.
And (3) performing ultrafiltration performance test on the sample, wherein the membrane sample is 100mm multiplied by 0.2mm (length multiplied by width multiplied by thickness), the test times are 10 times, the result is averaged, the performance index of the composite membrane is obtained, the water flux of the membrane material is 658L/m 2/h, and the retention rate is 90.7%.
The tensile test of the sample was conducted in accordance with ASTM (ZB-WL300) test standard, and the tensile rate of a film sample was 1mm/min, and the tensile test was conducted 10 times at 100mm X15 mm X0.15 mm (length X width X thickness), and the results were averaged to obtain the performance index of the composite film, and the tensile strength and elongation at break of the film material were 8.1MPa and 8.3%, respectively.
Comparative example
1. Preparing materials according to the following mixture ratio:
Polyvinylidene fluoride 16g, N, N-dimethylacetamide 84 mL.
2. Preparation of a casting dope
Adding polyvinylidene fluoride into N, N-dimethylacetamide, and carrying out ultrasonic stirring for 5 hours (the ultrasonic stirring power is 200W) at the temperature of 80 ℃ to obtain pure polyvinylidene fluoride casting film stock solution.
3. degassing of casting film liquid
and (3) placing the prepared casting film stock solution into a vacuum degassing device, starting a vacuum pump to carry out ultrasonic vacuum-reduction vacuum-pumping degassing (ultrasonic power is 200W) on the casting film stock solution at 90 ℃, wherein the relative vacuum degree is-0.09 MPa, and the degassing time is 3 h.
4. Film scraping formation
1) Casting the defoamed casting solution on a clean glass plate, and adjusting the film scraping thickness of an automatic film scraping machine to 200 mu m;
2) And immersing the glass plate in deionized water, carrying out immersion precipitation phase transformation at normal temperature, and standing for 1-2h to obtain the composite ultrafiltration membrane material. The thickness of the film may be 200 μm. A surface scanning electron micrograph at 400 Xmagnification is shown in FIG. 1.
And (3) performing ultrafiltration performance test on the sample, wherein the membrane sample is 100mm multiplied by 0.2mm (length multiplied by width multiplied by thickness), the test times are 10 times, the result is averaged, the performance index of the composite membrane is obtained, the water flux of the membrane material is 231L/m 2/h, and the retention rate is 92.1%.
The tensile test of the sample was conducted in accordance with ASTM (ZB-WL300) test standard, and the tensile rate of a film sample was 1mm/min, and the tensile test was conducted 10 times at 100mm X15 mm X0.15 mm (length X width X thickness), and the results were averaged to obtain the performance index of the composite film, and the tensile strength and elongation at break of the film material were 3.2MPa and 4.7%, respectively.
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (11)
1. The polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane is characterized by being prepared from raw materials comprising polyvinylidene fluoride, nano lignocellulose, dopamine and an organic solvent; wherein the weight ratio of the polyvinylidene fluoride to the nano lignocellulose to the dopamine is (16-18): (0.06-0.4): 1.8-2.2); the weight-volume ratio of the polyvinylidene fluoride to the organic solvent is (16-18) to (70-85) in g/mL; the organic solvent is N, N-dimethylacetamide;
The preparation method of the composite ultrafiltration membrane comprises the following steps:
1) Preparing nano lignocellulose by an acid hydrolysis-high pressure homogenization method: hydrolyzing the natural color pulp plate by using dilute sulfuric acid, centrifuging at a high speed, and washing the precipitate to be neutral by using deionized water; transferring the obtained solid into an organic solvent according to the proportion, and homogenizing under high pressure to prepare a nano lignocellulose solution;
2) Preparing a nano lignocellulose polyvinylidene fluoride blending ultrafiltration membrane by using an immersion precipitation phase inversion method: mixing the nano lignocellulose solution obtained in the step 1) and polyvinylidene fluoride according to the proportion to prepare a casting film stock solution; carrying out vacuum defoaming treatment on the casting film stock solution, and then preparing a film, namely the nano lignocellulose polyvinylidene fluoride blended ultrafiltration film;
3) Preparing a polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane by using an immersion surface coating method: fixing the blended ultrafiltration membrane prepared in the step 2) in a reaction tank, adding a polydopamine solution with the concentration of 2g/L, performing coating modification under the conditions of shaking, room temperature and oxygen, then washing off the residual dopamine solution on the surface of the obtained membrane with deionized water, soaking the obtained membrane in absolute ethyl alcohol, and removing polymeric dopamine which is not firmly adhered to obtain the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane.
2. The composite ultrafiltration membrane of claim 1, wherein the weight ratio of the polyvinylidene fluoride, the nano lignocellulose and the dopamine is 16 (0.1-0.4) to (1.8-2.2).
3. The composite ultrafiltration membrane of claim 2, wherein the weight-to-volume ratio of the polyvinylidene fluoride to the organic solvent in g/mL is 16 (83-84).
4. The composite ultrafiltration membrane of claim 1 or 2, wherein the thickness of the composite ultrafiltration membrane is 100-200 μm.
5. The method for preparing the composite ultrafiltration membrane of any one of claims 1 to 4, which is characterized by comprising the following steps of:
1) preparing nano lignocellulose by an acid hydrolysis-high pressure homogenization method: hydrolyzing the natural color pulp plate by using dilute sulfuric acid, centrifuging at a high speed, and washing the precipitate to be neutral by using deionized water; transferring the obtained solid into an organic solvent according to the proportion, and homogenizing under high pressure to prepare a nano lignocellulose solution;
2) Preparing a nano lignocellulose polyvinylidene fluoride blending ultrafiltration membrane by using an immersion precipitation phase inversion method: mixing the nano lignocellulose solution obtained in the step 1) and polyvinylidene fluoride according to the proportion to prepare a casting film stock solution; carrying out vacuum defoaming treatment on the casting film stock solution, and then preparing a film, namely the nano lignocellulose polyvinylidene fluoride blended ultrafiltration film;
3) preparing a polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane by using an immersion surface coating method: fixing the blended ultrafiltration membrane prepared in the step 2) in a reaction tank, adding a polydopamine solution with the concentration of 2g/L, performing coating modification under the conditions of shaking, room temperature and oxygen, then washing off the residual dopamine solution on the surface of the obtained membrane with deionized water, soaking the obtained membrane in absolute ethyl alcohol, and removing polymeric dopamine which is not firmly adhered to obtain the polydopamine nano lignocellulose polyvinylidene fluoride composite ultrafiltration membrane.
6. The method according to claim 5, wherein the dilute sulfuric acid concentration in the step 1) is 30-35 wt%; the weight-volume ratio of the natural color paste plate to the 30-35 wt% dilute sulfuric acid solution is 1:18 in g/mL.
7. the preparation method according to claim 5 or 6, wherein the step 2) is to prepare a casting film stock solution under ultrasonic stirring conditions; the ultrasonic stirring temperature is 80-100 ℃, and the stirring time is 4-6 h; the ultrasonic power is 200w-300 w.
8. The production method according to claim 5 or 6, wherein a degree of vacuum in the vacuum defoaming treatment is-0.05 to-0.09 MPa.
9. The preparation method according to claim 8, wherein the vacuum defoaming treatment time is 1-2 h.
10. The method according to claim 5 or 6, wherein the step of forming a film in step 2) comprises: placing the casting film stock solution on a glass plate and scraping to form a film; and immersing the glass plate in deionized water, carrying out immersion precipitation phase transformation at normal temperature, and standing for 1-2h to obtain the blended ultrafiltration membrane material.
11. The method according to claim 5 or 6, wherein the film coating modification time of step 3) is 2 to 6 hours.
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