CN115073775A - Preparation method of aramid fiber-based pH response film - Google Patents
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Abstract
The invention discloses a preparation method of an aramid fiber-based pH response film. Adding Kevlar fiber into a mixed solution mixed with alkali, an organic solvent and a green catalyst, and deprotonating to obtain a dark red solution; then adding water to separate out the aramid nano-fiber from the solution, and washing away the organic solvent and other small molecules by using a large amount of water; then heating and hydrolyzing the precipitated aramid nano-fiber in the presence of mixed acid to obtain acidified aramid fiber with a pH response functional group; and mixing the acidified aramid fiber and the aramid fiber, and preparing the film by a vacuum filtration method. According to the invention, the aramid nano-fiber is acidified, so that the amino-and carboxyl-acidified aramid nano-fiber with pH response is obtained, and then the amino-and carboxyl-acidified aramid nano-fiber is compounded with the aramid fiber to obtain the pH response film with high strength, high temperature resistance and chemical corrosion resistance, so that the application range of the aramid nano-fiber is further expanded.
Description
Technical Field
The invention belongs to the field of nano materials and films, and particularly relates to a preparation method for preparing a pH response film by utilizing aramid nano fibers.
Background
The aromatic polyamide organic fiber, namely aramid fiber, is composed of liquid crystal rodlike amido bond and linear molecules connected by two aromatic rings. As a warp in aramid fibers, Kevlar was first developed in the 60's of the 20 th century by the american dupont company and was modernized in 1973. The chemical structure is formed by repeated arrangement of para-amido bonds linked on a benzene ring. In the molecule, the amide group is positioned between two benzene rings, and forms large pi bond conjugation with the benzene rings, the internal steric hindrance is high, the macromolecular chain is highly oriented along the length direction, and the strong inter-chain binding force is provided, so that the composite material has the advantages of high strength, high modulus, high temperature resistance, chemical corrosion resistance, low density, impact resistance, fatigue resistance, low expansion and the like.
In the molecule, an amide group is positioned between two benzene rings, and forms large pi bond conjugation with the benzene rings, the internal rotation steric hindrance is high, the large molecular chain is highly oriented along the length direction, and the strong inter-chain binding force is provided, so that the fiber has the excellent performances of high strength, high modulus, high temperature resistance, acid and alkali resistance, low density, impact resistance, fatigue resistance, low expansion, heat conductivity, non-combustibility, non-melting property and the like in the unprecedented field, and is often used in the fields of industrial protection, protective equipment, high-strength structural part manufacturing, electronics and electricity, automobile traffic, chemical industry, aerospace, military and emergency rescue, and has irreplaceable functions.
According to current articles and patent reports, the aramid nanofiber inherits the aramid crystal structure and excellent mechanical properties and has the small-size effect of a nano material. In recent years, the research heat of aramid nanofibers is gradually improved, various synthetic methods including electrostatic spinning, electro-blowing, deprotonation and the like are proposed, and particularly, significant progress is made on battery separators and sewage filtration membrane products. However, no pH-responsive films based on aramid fibers have been reported.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the invention provides a preparation method of an aramid fiber-based pH response film. The method is a rapid, simple and efficient preparation method for preparing the high-strength pH response membrane. According to the invention, the aramid nano-fiber is acidified to obtain the acidified aramid nano-fiber with amino and carboxyl with pH response, and then the acidified aramid nano-fiber is compounded with the aramid fiber to obtain the pH response film with high strength, high temperature resistance and chemical corrosion resistance, so that the application range of the aramid nano-fiber is further expanded.
The purpose of the invention is realized by the following technical scheme:
a preparation method of an aramid-based pH response film comprises the following steps:
(1) firstly, pretreating Kevlar fibers, then adding the treated Kevlar fibers into an organic solvent in which alkali and a catalyst are dissolved, introducing nitrogen at normal temperature to remove oxygen, and stirring to obtain an aramid nanofiber solution for later use;
(2) taking an aramid nano-fiber solution, adding water to separate out, and washing the aramid nano-fiber solution to be neutral by using a large amount of water with the help of vacuum filtration; then heating and acidifying the aramid fiber in the presence of mixed acid to obtain acidified aramid fiber nano-fiber with amino and carboxyl;
(3) taking an aramid nano-fiber solution, dispersing acidified aramid fibers in water to obtain an acidified aramid fiber dispersion liquid, and mixing the dispersion liquid with the aramid nano-fiber solution; then, the membrane is filtered by vacuum filtration, and is washed to be neutral by a large amount of water; putting the membrane and the filter paper into acetone, demoulding, and sequentially soaking the membrane in ethanol and n-hexane for a certain time to replace the former solvent; and finally, carrying out vacuum drying to obtain the aramid fiber-based pH response film.
The pretreatment in the step (1) comprises the following steps: cutting Kevlar fiber into 1-2cm short fiber, extracting with acetone and water for 12h, and drying in an oven at 40-70 deg.C for 12-48 h.
In the step (1), the organic solvent is dimethyl sulfoxide, the alkali is at least one of potassium hydroxide, potassium tert-butoxide and sodium hydroxide, and the catalyst is water or methanol.
The dosage of the alkali in the step (1) is 2-6 times of the dosage of amido bond substances in the Kevlar fibers, the dosage of the catalyst is 2-6 times of the dosage of amido bond substances in the Kevlar chopped fibers, the dispersion temperature of the catalyst and the alkali in the organic solvent is 50-70 ℃, and the dispersion time is 3-6 hours.
And (2) stirring for 12-48 hours in the step (1) until the system is a dark red stable solution.
And (3) adding water for precipitating the aramid nano-fiber in the step (2) in the same volume as the volume of the obtained aramid nano-fiber solution, dropwise adding the water, and continuously stirring for 12-24 hours after dropwise adding is finished to obtain a uniform colloidal dispersion.
In the step (2), the mixed acid used for acidifying the aramid nano-fiber is mixed acid of sulfuric acid and nitric acid. Wherein the concentration of sulfuric acid is 37.5 wt% and the concentration of nitric acid is 8.75 wt%. The acidification time is 1-2 h, and the acidification temperature is 85-95 ℃.
In the step (3), the mass ratio of the acidified aramid fiber to the aramid fiber in the aramid nanofiber solution obtained in the step is 1: 9-1: 1.
In the step (3), the volume of the acidified aramid fiber dispersion liquid is the same as that of the aramid nano-fiber taking solution obtained in the step (3);
and (3) dropwise adding the acidified aramid fiber dispersion liquid into the aramid nano-fiber solution, and continuously stirring for 12-24 hours to obtain a uniform colloidal dispersion.
And (3) peeling the membrane and the filter paper by using acetone, soaking the membrane in ethanol and normal hexane for 8-12 h, and drying the membrane at the temperature of 40-60 ℃ for 24-48 h under vacuum.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the Kevlar fiber can be completely dissolved within 7-10 days, and the dissolving time of the Kevlar fiber is greatly shortened by adding the green solvent; 2. according to the invention, the acidified aramid fiber is added into the aramid fiber for the first time, so that a certain pH correspondence is given to the film by virtue of amino and carboxyl formed in the acidification process, and the problem that the compatibility of the aramid fiber with a pH response material is poor due to too strong intermolecular hydrogen bond is solved; 3. in the invention, the aramid nano-fiber and the acidified aramid nano-fiber are prepared into a film by means of a vacuum filtration method in the process of preparing the film, and the wet film is separated from the filter paper by means of acetone for the first time.
Drawings
Fig. 1 is a graph showing the water flux (a) and bovine serum albumin rejection (b) of the aramid-based pH-responsive membrane prepared in example 1 as a function of pH.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. The raw materials related to the invention can be directly purchased from the market. For process parameters not specifically noted, reference may be made to conventional techniques.
Example 1
(1) Cutting Kevlar-49 fiber into 1-2cm short fiber, extracting with acetone and distilled water for 12h, and oven drying in a vacuum oven at 60 deg.C for 24 h.
(2) 0.0378g of deionized water and 0.075g of potassium hydroxide were weighed into a 100ml round bottom flask containing 25ml of dimethyl sulfoxide, and magnetically stirred at 50 ℃ for 4h to give a pale yellow liquid which was cooled to room temperature.
0.05g of Kevlar fiber treated in step (1) was weighed and added to the above solution. Introducing nitrogen to remove oxygen for half an hour, and magnetically stirring for 48 hours at normal temperature to obtain a uniform and stable dark red aramid nanofiber solution.
(3) And (3) putting 5ml of the dark red aramid nano fiber solution prepared in the step (2) into a 50ml round-bottom flask, dropwise adding 5ml of distilled water into the flask, continuously stirring the mixture by magnetic force for 12 hours, and washing the mixture to be neutral by the aid of vacuum filtration by using the distilled water.
And then adding the obtained neutral nano aramid fiber into mixed acid containing 37.5 wt% of sulfuric acid and 8.75 wt% of nitric acid, stirring for 1h at 90 ℃, quickly cooling to room temperature, washing with distilled water by vacuum filtration with the aid of distilled water to be neutral, and dispersing the neutral nano aramid fiber into 15ml of distilled water to obtain an acidified aramid fiber dispersion liquid.
(4) Dropwise adding the acidified aramid fiber dispersion liquid obtained in the step (3) into 15ml of the dark red aramid fiber nano-solution obtained in the step (2), and continuously stirring for 12h to obtain an orange colloidal dispersion.
Taking 10ml of orange colloidal dispersion, carrying out vacuum filtration to form a membrane, washing the membrane to be neutral by using a large amount of water, putting the membrane into acetone to separate the membrane from filter paper, then sequentially putting the membrane into ethanol and N-hexane to soak for 8h, taking out the membrane to be fixed by using the filter paper, putting the membrane into a vacuum oven at 60 ℃, and drying for 36h to obtain the aramid fiber-based pH response membrane with the breaking strength of 67MPa and the thermal decomposition temperature of 470 ℃, wherein the pH response of the obtained membrane is hardly changed after the obtained membrane is respectively soaked in organic solvents of dimethyl sulfoxide, N-methylpyrrolidone, N-dimethylformamide, dimethylacetamide, tetrahydrofuran, dichloromethane, toluene and methanol for 7 days.
Fig. 1 is a graph showing the water flux (a) and bovine serum albumin rejection (b) of the aramid-based pH-responsive membrane prepared in example 1 as a function of pH.
The experimental process of the change rule of water flux along with the pH value is as follows: the water flux of the membrane was measured at room temperature using a stirred ultrafiltration cup. The transmembrane pressure was 0.1 MPa. Adjusting the pH value to 2.0-13.0 by using hydrochloric acid (0.1M) and sodium hydroxide (0.1M). The ionic concentration of the above solution was adjusted with 0.005M sodium chloride solution. To obtain an average, at least five water flux measurements were made for each membrane and averaged.
The experimental process of the bovine serum albumin retention rate along with the change rule of the pH value: the method for measuring the retention of bovine serum albumin is similar to the method for measuring the water flux. Bovine Serum Albumin (BSA) solutions of different concentrations (50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900 and 1000mg/L) and different pH values were first prepared and their absorbances were recorded at 280nm with a uv-vis spectrophotometer. A standard curve of the relationship between the absorbance and the concentration of the bovine serum albumin is obtained. The retention of Bovine Serum Albumin (BSA) was then measured using a stirred ultrafiltration cup. Bovine serum albumin solution (1000mg/L) was used for the test, operating at 0.1 MPa. Then 5mL of the filtrate was collected and the absorbance at 280nm was recorded with a UV-Vis spectrophotometer. BSA retention (R,%) was obtained from formula (1):
wherein C is p And C 0 The BSA concentrations in the filtrate and feed solution were measured, respectively. Each membrane was tested at least five times at different pH values and averaged. After each test, the films were washed with ethanol and deionized water, respectively.
Example 2
(1) Cutting Kevlar-49 fiber into 1-2cm short fiber, extracting with acetone and distilled water for 12h, and oven drying in a vacuum oven at 60 deg.C for 24 h.
(2) 0.0538g of methanol and 0.0622g of potassium tert-butoxide are weighed into a 100ml round-bottomed flask containing 25ml of dimethyl sulfoxide, and the mixture is magnetically stirred at 50 ℃ for 4 hours to obtain a colorless transparent liquid which is cooled to room temperature.
0.05g of Kevlar fiber treated in step (1) was weighed and added to the above solution. Introducing nitrogen to remove oxygen for half an hour, and magnetically stirring for 24 hours at normal temperature to obtain a uniform and stable dark red aramid nanofiber solution.
(3) And (3) putting 5ml of the dark red aramid nano fiber solution prepared in the step (2) into a 50ml round-bottom flask, dropwise adding 5ml of distilled water into the flask, continuously stirring the mixture by magnetic force for 12 hours, and washing the mixture to be neutral by the aid of vacuum filtration by using the distilled water.
And then adding the obtained neutral nano aramid fiber into mixed acid containing 37.5 wt% of sulfuric acid and 8.75 wt% of nitric acid, stirring for 1h at 90 ℃, quickly cooling to room temperature, washing with distilled water by vacuum filtration with the aid of distilled water to be neutral, and dispersing the neutral nano aramid fiber into 15ml of distilled water to obtain an acidified aramid fiber dispersion liquid.
(4) Dropwise adding the acidified aramid fiber dispersion liquid obtained in the step (3) into 15ml of the dark red aramid fiber nano-solution obtained in the step (2), and continuously stirring for 12h to obtain an orange colloidal dispersion.
Taking 10ml of orange colloidal dispersion, carrying out vacuum filtration to form a membrane, washing the membrane to be neutral by using a large amount of water, putting the membrane into acetone to separate the membrane from filter paper, then sequentially putting the membrane into ethanol and N-hexane to soak for 8h, taking out the membrane to be fixed by using the filter paper, putting the membrane into a vacuum oven at 60 ℃, and drying for 24h to obtain the aramid fiber-based pH response membrane with the breaking strength of about 66MPa and the thermal decomposition temperature of about 474 ℃, wherein the pH response of the obtained membrane is hardly changed after the obtained membrane is respectively soaked in organic solvents of dimethyl sulfoxide, N-methylpyrrolidone, N-dimethylformamide, dimethylacetamide, tetrahydrofuran, dichloromethane, toluene and methanol for 7 days.
Example 3
(1) Cutting Kevlar-49 fiber into 1-2cm short fiber, extracting with acetone and distilled water for 12h, and oven drying in a vacuum oven at 60 deg.C for 24 h.
(2) 0.0538g of methanol and 0.0622g of potassium tert-butoxide are weighed into a 100ml round-bottomed flask containing 25ml of dimethyl sulfoxide, and the mixture is magnetically stirred at 50 ℃ for 4 hours to obtain a colorless transparent liquid which is cooled to room temperature.
0.05g of Kevlar fiber treated in step (1) was weighed and added to the above solution. Introducing nitrogen to remove oxygen for half an hour, and magnetically stirring for 24 hours at normal temperature to obtain a uniform and stable dark red aramid nanofiber solution.
(3) And (3) putting 10ml of the dark red aramid nano fiber solution prepared in the step (2) into a 50ml round-bottom flask, dropwise adding 10ml of distilled water into the flask, continuously stirring the mixture for 12 hours by magnetic force, and washing the mixture to be neutral by the aid of vacuum filtration by using the distilled water.
And then adding the obtained neutral nano aramid fiber into mixed acid containing 37.5 wt% of sulfuric acid and 8.75 wt% of nitric acid, stirring for 1h at 90 ℃, quickly cooling to room temperature, washing with distilled water by vacuum filtration with distilled water until the neutral nano aramid fiber is obtained, and dispersing the neutral nano aramid fiber into 10ml of distilled water to obtain an acidified aramid fiber dispersion liquid.
(4) Dropwise adding the acidified aramid fiber dispersion liquid obtained in the step (3) into 10ml of the dark red aramid fiber nano-solution obtained in the step (2), and continuously stirring for 12h to obtain an orange colloidal dispersion.
Taking 10ml of orange colloidal dispersion, carrying out vacuum filtration to form a membrane, washing the membrane to be neutral by using a large amount of water, putting the membrane into acetone to separate the membrane from filter paper, then sequentially putting the membrane into ethanol and N-hexane to soak for 8h, taking out the membrane to be fixed by using the filter paper, putting the membrane into a vacuum oven at 60 ℃, and drying for 24h to obtain the aramid fiber-based pH response membrane with the breaking strength of about 56MPa and the thermal decomposition temperature of about 447 ℃, wherein the pH response of the obtained membrane is hardly changed after the obtained membrane is respectively soaked in organic solvents of dimethyl sulfoxide, N-methylpyrrolidone, N-dimethylformamide, dimethylacetamide, tetrahydrofuran, dichloromethane, toluene and methanol for 7 days.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. The preparation method of the aramid-based pH response film is characterized by comprising the following steps of:
(1) firstly, pretreating Kevlar fibers, then adding the treated Kevlar fibers into an organic solvent in which alkali and a catalyst are dissolved, introducing nitrogen at normal temperature to remove oxygen, and stirring to obtain an aramid nanofiber solution for later use;
(2) taking an aramid nano-fiber solution, adding water to separate out, and washing the aramid nano-fiber solution to be neutral by using a large amount of water with the help of vacuum filtration; then heating and acidifying the aramid fiber in the presence of mixed acid to obtain acidified aramid fiber nano-fiber with amino and carboxyl;
(3) taking an aramid nano-fiber solution, dispersing acidified aramid fibers in water to obtain an acidified aramid fiber dispersion liquid, and mixing the dispersion liquid with the aramid nano-fiber solution; then, the membrane is filtered by vacuum filtration, and is washed to be neutral by a large amount of water; putting the membrane and the filter paper into acetone, demoulding, and sequentially soaking the membrane in ethanol and n-hexane for a certain time to replace the former solvent; and finally, carrying out vacuum drying to obtain the aramid fiber-based pH response film.
2. The preparation method of the aramid-based pH response film according to claim 1, wherein the pretreatment in the step (1) is: cutting Kevlar fiber into 1-2cm short fiber, extracting with acetone and water for 12h, and drying in an oven at 40-70 deg.C for 12-48 h.
3. The preparation method of the aramid-based pH response membrane as claimed in claim 1, wherein the organic solvent in the step (1) is dimethyl sulfoxide, the base is at least one of potassium hydroxide, potassium tert-butoxide and sodium hydroxide, and the catalyst is water or methanol.
4. The preparation method of the aramid-based pH-responsive film according to claim 1, wherein the amount of the alkali in the step (1) is 2-6 times of that of amide bonds in Kevlar fibers, the amount of the catalyst is 2-6 times of that of the amide bonds in Kevlar chopped fibers, the dispersion temperature of the catalyst and the alkali in the organic solvent is 50-70 ℃, and the dispersion time is 3-6 hours.
5. The preparation method of the aramid-based pH response film according to claim 1, wherein the stirring time in the step (1) is 12-48 hours until the system is a dark red stable solution.
6. The preparation method of the aramid-based pH response film according to claim 1, wherein the addition amount of water for precipitating the aramid nanofibers in the step (2) is the same as the volume of the taken aramid-based nanofiber solution, the water is added dropwise, and after the dropwise addition is completed, stirring is continued for 12-24 hours to obtain a uniform colloidal dispersion.
7. The preparation method of the aramid-based pH response film as claimed in claim 1, wherein in the step (2), the mixed acid used for acidifying the aramid nano-fibers is a mixed acid of sulfuric acid and nitric acid, wherein the concentration of the sulfuric acid is 37.5 wt%, and the concentration of the nitric acid is 8.75 wt%; the acidification time is 1-2 h, and the acidification temperature is 85-95 ℃.
8. The preparation method of the aramid-based pH response film according to claim 1, wherein in the step (3), the mass ratio of the acidified aramid fiber to the aramid fiber in the aramid nanofiber taking solution obtained in the step is 1: 9-1: 1.
9. The preparation method of the aramid-based pH-responsive film according to claim 1, wherein in the step (3), the volume of the acidified aramid fiber dispersion liquid is the same as that of the aramid nanofiber solution obtained in the step (3);
and (3) dropwise adding the acidified aramid fiber dispersion liquid into the aramid nano-fiber solution, and continuously stirring for 12-24 hours to obtain a uniform colloidal dispersion.
10. The preparation method of the aramid-based pH response film according to claim 1, wherein in the step (3), after the film and the filter paper are peeled off by using acetone, the film is soaked in ethanol and n-hexane for 8-12 hours, the vacuum drying temperature is 40-60 ℃, and the drying time is 24-48 hours.
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| CN107022094A (en) * | 2017-04-20 | 2017-08-08 | 哈尔滨工业大学 | A kind of preparation method of the transparent flexible film of POSS enhancings aramid nano-fiber |
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| XIAO WANG等: "Composite Aramid Membranes with High Strength and pH-Response", 《POLYMERS》, vol. 13, no. 4, pages 1 - 14 * |
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