Preparation method of high-strength, high-toughness and high-transparency aramid nanofiber film

Abstract

The application relates to a preparation method of a high-strength high-toughness high-transparency aramid nanofiber film, which is prepared through non-proton solvent replacement, so that the combination between aramid nanofibers is more compact, the defects in the film are reduced, and the prepared film is high in strength, good in toughness and high in transparency. The method provided by the application is simple in preparation process and high in preparation efficiency, and is beneficial to batch production and large-scale application of the aramid nanofiber film.

Description

Technical Field

[0001] This invention belongs to the field of polymer nanomaterials, and specifically relates to a method for preparing a high-strength, high-toughness, and high-transparency aramid nanofiber film. Background Technology

[0002] Para-aramid fibers, due to their superior properties such as high strength, high modulus, high flame retardancy, and high heat resistance, have been widely researched and applied in aerospace, fire retardancy, and electronics. By processing para-aramid fibers through certain methods, aramid nanofibers with diameters of tens of nanometers and lengths of several to tens of micrometers can be obtained. As a novel nanomaterial, aramid nanofibers retain the good thermal stability and excellent insulation properties of macroscopic aramid fibers, and are therefore widely used in the fabrication of films for adsorption filtration, battery separators, and electrical insulation.

[0003] Common methods for preparing aramid nanofiber films include vacuum-assisted filtration molding and the sol-gel method, which differ in preparation efficiency and film performance. Vacuum-assisted filtration molding facilitates composite reinforcement with other materials, requires lower concentrations of the aramid nanofiber dispersion, and produces a denser, stronger film after hot pressing. Therefore, many researchers use this method for film preparation. For example, Chinese patent CN201810424080 uses vacuum-assisted filtration to composite aramid nanofibers with graphene oxide, achieving a film strength of up to 441.48 MPa; Chinese patent CN202211458626 composites aramid nanofibers with fluorinated graphite and prepares a thermally conductive composite paper using vacuum-assisted filtration, achieving a maximum strength of 183.6 MPa.

[0004] Although existing patents employ vacuum-assisted filtration to prepare aramid nanofiber films / papers, this method requires a long filtration time, and due to the vacuum effect, there is a significant difference between the two sides of the film. Furthermore, the film size is limited by the filtration equipment, making large-scale preparation difficult. While the traditional sol-gel method offers high preparation efficiency, the resulting films have numerous defects, low strength, and poor toughness, making them unsuitable for practical applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing high-strength, high-toughness, and high-transparency aramid nanofiber films. This method has high preparation efficiency and is expected to promote the mass production and large-scale application of aramid nanofiber films.

[0006] This invention provides a method for preparing a high-strength, high-toughness, and high-transparency aramid nanofiber film, comprising the following steps:

[0007] (1) A strong base, organic solvent, proton donor and para-aramid are mixed and stirred to obtain an aramid nanofiber dispersion.

[0008] (2) The aramid nanofiber dispersion was allowed to stand and aged, and then degassed under vacuum to prepare a sol layer;

[0009] (3) The sol layer is immersed in a non-protic solvent for solvent replacement to obtain a pre-formed aramid nanofiber film I; the non-protic solvent is removed by drying to obtain a pre-formed aramid nanofiber film II; the sol layer is then immersed in a protic solvent for proton reduction to obtain a pre-formed aramid nanofiber film III; finally, the protic solvent is removed by drying to obtain a high-strength, high-toughness, and high-transparency aramid nanofiber film.

[0010] The strong alkali in step (1) is at least one of potassium hydroxide, sodium hydroxide, potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, potassium tert-butoxide, and sodium tert-butoxide; the molar ratio of the strong alkali to para-aramid is 0.5 to 1.5:1, more preferably, the molar ratio of the strong alkali to para-aramid polymer powder is 0.7 to 1.1:1.

[0011] The proton donor in step (1) is at least one of water, methanol, ethanol, ethylene glycol, isopropanol, and tert-butanol; the organic solvent is dimethyl sulfoxide (DMSO); the volume ratio of the proton donor to DMSO is 1:5 to 100, more preferably, the volume ratio of the proton donor to DMSO is 1:10 to 50.

[0012] The para-aramid in step (1) includes at least one of poly(p-phenylene terephthalamide) polymer, para-aramid filament, para-aramid staple fiber, and para-aramid product; the mass concentration of the aramid nanofiber dispersion is 2% to 15%, more preferably, the mass concentration of the aramid nanofiber dispersion is 3% to 7%.

[0013] The stirring reaction temperature in step (1) is from room temperature to 80°C, the stirring reaction rate is from 50 rpm to 1000 rpm, and the stirring reaction time is from 2 h to 48 h.

[0014] The static aging time in step (2) is 12h to 48h; the vacuum degassing temperature is room temperature to 80℃, the vacuum degree is -0.1MPa, and the vacuum degassing time is 0.5h to 2h.

[0015] The thickness of the sol layer in step (2) is 0.3 mm to 2 mm, more preferably, the thickness of the sol layer is 0.5 mm to 1.5 mm.

[0016] The method for preparing the sol layer in step (2) is as follows: it is formed by scraping it onto a dry, clean and flat glass plate or by pouring it into other containers.

[0017] The aprotic solvent in step (3) is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, ethyl acetate, acetonitrile, dichloromethane, and chloroform.

[0018] The proton solvent in step (3) is at least one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, water, methanol, ethanol, ethylene glycol, and isopropanol.

[0019] The solvent replacement time in step (3) is 15 min to 1 h; the proton reduction time is 5 to 30 min.

[0020] The drying temperature in step (3) is 60℃~80℃.

[0021] Beneficial effects

[0022] (1) This invention uses non-protic solvent replacement to make the aramid nanofibers bond more tightly, reducing defects inside the film. The prepared film is smooth and flat, with high strength and toughness and high transparency.

[0023] (2) The preparation process of this invention is simple, without the need for time-consuming vacuum filtration and hot pressing processes. The preparation time is short and the efficiency is high. By adjusting the thickness of the sol layer and changing the size of the glass plate or container carrying the sol layer, films of different thicknesses and sizes can be prepared, which can meet a wider range of practical application needs. Attached Figure Description

[0024] Figure 1 This is a SEM image of the surface of the aramid nanofiber film prepared in Example 1.

[0025] Figure 2 The image shows the stress-strain curve of the aramid nanofiber film prepared in Example 1.

[0026] Figure 3 The image shows the UV-Vis spectrum of the aramid nanofiber film prepared in Example 1.

[0027] Figure 4 The image shows the surface SEM image of the aramid nanofiber film prepared in Comparative Example 1.

[0028] Figure 5 The stress-strain curve of the aramid nanofiber film prepared for Comparative Example 1 is shown. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0030] Test methods

[0031] 1. Surface morphology

[0032] SEM tests were performed using a high-resolution cold field emission scanning electron microscope (Hitachi, Regulus 8230) with an accelerating voltage of 5 kV. The sample was attached to the sample stage with conductive adhesive, and gold was sprayed onto it for 90 seconds before testing.

[0033] 2. Tensile strength and elongation at break

[0034] According to the test conditions of GB / T 1040.3-2006 Thin Films and Sheets, the film was cut into strips 10 mm wide and 150 mm long, and tensile tests were performed on an electronic universal testing machine (Shenzhen Sansi Zongheng Technology Co., Ltd., UTM6202 model). The tensile speed was 5 mm / min, the initial distance between the fixtures was 100 mm, and each sample was tested 5 times, and the average value was taken.

[0035] 3. Visible light transmittance

[0036] UV-Vis spectrophotometer (PerkinElmer, lambda950) was used for UV-Vis spectroscopy measurements, with a scanning range of 250-800 nm. The transmittance of the sample in visible light was measured using the transmittance value at 500 nm in the spectral curve. Each sample was measured five times, and the average value was taken.

[0037] Example 1

[0038] (1) Mix 1.77g potassium methoxide, 100ml dimethyl sulfoxide, 4ml tert-butanol and 3g PPTA polymer powder, and stir continuously at 200rpm for 8h at 60℃ to prepare an aramid nanofiber dispersion with a mass concentration of 3%.

[0039] (2) The aramid nanofiber dispersion was allowed to stand for 24 hours and then degassed under vacuum for 1 hour at 60°C and a vacuum degree of -0.1MPa.

[0040] (3) The vacuum-degassed aramid nanofiber dispersion was scraped onto a dry, clean and flat 10cm×10cm glass plate, with a sol layer thickness of 0.7mm.

[0041] (4) Immerse the glass plate with the sol layer in acetone for 30 min to obtain the preformed aramid nanofiber film I;

[0042] (5) Place the preformed aramid nanofiber film I into an oven and heat it at 60°C to remove acetone, thus obtaining the preformed aramid nanofiber film II.

[0043] (6) Immerse the preformed aramid nanofiber film II in water for 10 min for proton reduction to obtain the preformed aramid nanofiber film III.

[0044] (7) Place the preformed aramid nanofiber film III into an oven and heat it at 60°C to dry it, thereby obtaining the aramid nanofiber film.

[0045] The prepared aramid nanofiber film has an average tensile strength of 401.7 MPa, an average elongation at break of 29.3%, and an average transmittance of 86% at 800 nm in the visible light spectrum.

[0046] Example 2

[0047] (1) Mix 3g potassium tert-butoxide, 100ml dimethyl sulfoxide, 4ml tert-butanol with 3g aramid short fiber, and stir continuously at 200rpm for 24h at 60℃ to prepare an aramid nanofiber dispersion with a mass concentration of 3%.

[0048] (2) The aramid nanofiber dispersion was allowed to stand for 24 hours and then degassed under vacuum for 1 hour at 60°C and a vacuum degree of -0.1MPa.

[0049] (3) The vacuum-degassed aramid nanofiber dispersion was scraped onto a dry, clean and flat 10cm×10cm glass plate, with a sol layer thickness of 1.0mm.

[0050] (4) Immerse the glass plate with the sol layer in acetone for 30 min to obtain the preformed aramid nanofiber film I;

[0051] (5) Place the preformed aramid nanofiber film I into an oven and heat it at 60°C to remove acetone, thus obtaining the preformed aramid nanofiber film II.

[0052] (6) Immerse the preformed aramid nanofiber film II in water for 10 min for proton reduction to obtain the preformed aramid nanofiber film III.

[0053] (7) Place the preformed aramid nanofiber film III into an oven and heat it at 60°C to dry it, thereby obtaining the aramid nanofiber film.

[0054] The prepared aramid nanofiber film has an average tensile strength of 343.0 MPa, an average elongation at break of 28.5%, and an average transmittance of 80% at 800 nm in the visible light spectrum.

[0055] Example 3

[0056] (1) Mix 2.95g potassium methoxide, 100ml dimethyl sulfoxide, 5ml methanol and 5g aramid filament, and stir continuously at 300rpm for 36h at 80℃ to prepare an aramid nanofiber dispersion with a mass concentration of 5%.

[0057] (2) The aramid nanofiber dispersion was allowed to stand for 48 hours and then degassed under vacuum for 1 hour at 60°C and a vacuum degree of -0.1MPa.

[0058] (3) The vacuum-degassed aramid nanofiber dispersion was scraped onto a dry, clean and flat 10cm×10cm glass plate, with a sol layer thickness of 0.7mm.

[0059] (4) Immerse the glass plate with the sol layer in dichloromethane for 45 min to obtain a preformed aramid nanofiber film I.

[0060] (5) Place the preformed aramid nanofiber film I into an oven and heat it at 60°C to remove dichloromethane, thereby obtaining the preformed aramid nanofiber film II.

[0061] (6) Immerse the preformed aramid nanofiber film II in water for 20 min for proton reduction to obtain the preformed aramid nanofiber film III.

[0062] (7) Place the preformed aramid nanofiber film III into an oven and heat it at 60°C to dry it, thereby obtaining the aramid nanofiber film.

[0063] The prepared aramid nanofiber film has an average tensile strength of 338.4 MPa, an average elongation at break of 26.0%, and an average transmittance of 82% at 800 nm in the visible light spectrum.

[0064] Comparative Example 1

[0065] (1) Mix 1.77g potassium methoxide, 100ml dimethyl sulfoxide, 4ml tert-butanol and 3g PPTA polymer powder, and stir continuously at 200rpm for 8h at 60℃ to prepare an aramid nanofiber dispersion with a mass concentration of 3%.

[0066] (2) The aramid nanofiber dispersion was allowed to stand for 24 hours and then degassed under vacuum for 1 hour at 60°C and a vacuum degree of -0.1MPa.

[0067] (3) The vacuum-degassed aramid nanofiber dispersion was scraped onto a dry, clean and flat 10cm×10cm glass plate, with a sol layer thickness of 0.7mm.

[0068] (4) Immerse the glass plate with the sol layer in water for 15 minutes to obtain a gel film;

[0069] (5) Place the gel membrane in an oven and heat it at 60°C to dry it, thus obtaining an aramid nanofiber film.

[0070] The prepared aramid nanofiber film has an average tensile strength of 127.9 MPa, an average elongation at break of 9.0%, and an average transmittance of 77% at 800 nm in the visible light spectrum.

[0071] Figure 1 and Figure 4 The images show SEM images of the aramid nanofiber films prepared in Example 1 and Comparative Example 1. As can be seen from the images, the aramid nanofibers on the film surface in Comparative Example 1 exhibit a strip-like morphology with a loose and porous arrangement, while the aramid nanofibers on the film surface in Example 1 exhibit an irregularly sized, densely packed state. This indicates that after aprotic solvent replacement, the film structure becomes more compact, and internal defects are reduced. This is beneficial for improving the mechanical properties of the film. Furthermore, the dense structure reduces reflection and scattering of light when it passes through the film, thereby enhancing the visible light transmittance of the film.

[0072] Figure 2 and Figure 5 The figures show the stress-strain curves of the aramid nanofiber films prepared in Example 1 and Comparative Example 1. As can be seen from the figures, the tensile strength of the film in Comparative Example 1 is approximately 118 MPa, and the elongation at break is approximately 8.6%, indicating low strength and poor toughness. In contrast, the tensile strength of the film in Example 1 is approximately 416 MPa, and the elongation at break is approximately 27.8%, demonstrating that the strength and toughness of the film were significantly enhanced after aprotic solvent replacement.

Claims

1. A method for preparing a high-strength, high-toughness, and high-transparency aramid nanofiber film, comprising the following steps: (1) mixing a strong base, an organic solvent, a proton donor, and para-aramid to obtain an aramid nanofiber dispersion by stirring and reacting; (2) allowing the aramid nanofiber dispersion to stand and age, and vacuum degassing to prepare a sol layer; (3) immersing the sol layer in an aprotic solvent to perform solvent replacement, obtaining a preformed aramid nanofiber film I; drying to remove the aprotic solvent, obtaining a preformed aramid nanofiber film II; immersing in a protic solvent to perform proton reduction, obtaining a preformed aramid nanofiber film III; and finally drying to remove the protic solvent, obtaining a high-strength, high-toughness, and high-transparency aramid nanofiber film. The strong base in the step (1) is at least one of potassium hydroxide, sodium hydroxide, potassium methoxide, sodium methoxide, potassium ethoxide, sodium ethoxide, potassium tert-butoxide, and sodium tert-butoxide; and the molar ratio of the strong base to the para-aramid is 0.5-1.5:

1. The proton donor in the step (1) is at least one of water, methanol, ethanol, ethylene glycol, isopropyl alcohol, and tert-butyl alcohol; the organic solvent is dimethyl sulfoxide (DMSO); and the volume ratio of the proton donor to DMSO is 1:5-100. The para-aramid in the step (1) is at least one of poly(para-phenyleneterephthalamide) polymer, para-aramid filament, para-aramid staple, and para-aramid product; and the mass concentration of the aramid nanofiber dispersion is 2%-15%. The standing and aging time in the step (2) is 12-48 hours; the vacuum degassing temperature is room temperature to 80℃, the vacuum degree is -0.1 MPa, and the vacuum degassing time is 0.5-2 hours. The thickness of the sol layer in the step (2) is 0.3-2 mm. The aprotic solvent in the step (3) is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, ethyl acetate, acetonitrile, dichloromethane, and chloroform. The protic solvent in the step (3) is at least one of hydrochloric acid, sulfuric acid, formic acid, acetic acid, water, methanol, ethanol, ethylene glycol, and isopropyl alcohol. The solvent replacement time in the step (3) is 15 minutes-1 hour; and the proton reduction time is 5-30 minutes. The drying temperature in the step (3) is 60-80℃. ​ ​ ​ 2. The method of claim 1, wherein: ​ 3. The method of claim 1, wherein: ​ 4. The method of claim 1, wherein: ​ 5. The method of claim 1, wherein: ​ 6. The method of claim 1, wherein: ​ 7. The method of claim 1, wherein: ​ 8. The method of claim 1, wherein: ​ 9. The method of claim 1, wherein: ​ 10. The method of claim 1, wherein: ​

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