Modified aramid nanofiber aqueous dispersion, cellophane and preparation method of modified aramid nanofiber aqueous dispersion

Abstract

The invention relates to a modified aramid nanofiber aqueous dispersion, cellophane and a preparation method of the modified aramid nanofiber aqueous dispersion. The preparation method comprises the following steps: dispersing para-aramid fiber in a DMSO / KOH system to obtain DMSO dispersion liquid of aramid fiber; adding acid anhydride for esterification modification, putting the modified dispersion liquid into a dialysis bag, dialyzing in deionized water, taking out, and carrying out mechanical treatment, so as to obtain the modified aramid nanofiber aqueous dispersion liquid. Carboxylate ions are introduced to the surface of the aramid fiber by adopting an esterification modification method for the first time, so that the aramid fiber is stably dispersed in water for a long time under the action of electrostatic repulsion, the preparation method is simple, the cost is low, and the diameter of the aramid nanofiber can be controlled by regulating and controlling the charge ratio of anhydride. The modified aramid nanofiber cellophane prepared from the aqueous dispersion through vacuum filtration and hot pressing has high strength and high transparency, the tensile strength can reach 257 MPa, the maximum visible light transmittance can reach 83%, and the modified aramid nanofiber cellophane has good application prospects in the field of high-performance transparent materials.

Description

A modified aramid nanofiber aqueous dispersion, cellophane, and preparation method thereof. Technical Field

[0001] This invention relates to the field of polymer nanomaterials, and more particularly to a modified aramid nanofiber aqueous dispersion, cellophane, and a method for preparing the same. Background Technology

[0002] Aramid cellophane is a high-performance paper-based functional material generally prepared from meta- or para-aramid fibers through wet forming and hot pressing densification. This material possesses high strength, high modulus, low density, intrinsic flame retardancy, and excellent electrical insulation and thermal stability, making it promising for applications in electronics, communications, aerospace, and defense. However, the extremely high physicochemical stability of aramid fibers makes them difficult to disperse stably in solvents, posing significant challenges in processing.

[0003] Kotov's team (ACS Nano. 2011, 5, 6945-6954) previously reported a DMSO / KOH system for preparing aramid nanofiber dispersions. They also used this method to prepare aramid cellophane with excellent chemical and thermal stability. However, its mechanical strength was weak, with a tensile strength of only 92 MPa, which is 3% of that of Kevlar fibers. This is because in this system, aramid can only be sealed and stored in DMSO; once it comes into contact with water or other proton donors, it easily aggregates, resulting in a large number of inhomogeneous microstructures in the aramid cellophane. To address this, Zhao's team (ACS Appl. Mater. Interfaces 2024, 16, 20896-20907) utilized the hydrogen bonds formed between the phenolic hydroxyl groups of tannic acid and the amide groups of ANF, as well as the π-π stacking interaction between benzene rings, to adsorb tannic acid (TA) onto the aramid surface. This effectively prevented the self-aggregation of ANF in the aqueous phase, resulting in aramid nanofibers that can be stably dispersed in water. This method greatly expands the compatibility of aramid nanofibers with water-soluble polymers and hydrophilic materials, and the prepared TA / ANF membrane has a tensile strength of 393.8 MPa. However, as an oligomer, TA's adsorption with ANF is not stable, which makes it difficult for the prepared aramid aqueous dispersion to maintain stable dispersion over a long period of time.

[0004] Hu's team (patent application number: 201410833596.3) obtained water-dispersible aramid nanofibers by surface modification of aramid nanofibers and grafting water-soluble polymer m-PEG onto the surface of ANF. However, the preparation process is complex, requiring steps such as exfoliation, modification, dialysis, drying, grafting, and re-dialysis; it is also costly, requiring a large amount of expensive organic substances; and it has stringent reaction conditions. Furthermore, the introduction of numerous other substances severely damages the aramid's structure, resulting in low strength of the prepared aramid cellophane. In addition, the visible light transmittance of the prepared aramid cellophane in the above work is difficult to exceed 80%, limiting the application of aramid in the field of high-strength, flexible, and transparent materials.

[0005] Therefore, it is necessary to develop an aramid nanofiber that can be uniformly dispersed in water, has a simple preparation method, and is environmentally friendly in the preparation process, as well as an aramid cellophane with high strength and high transparency. Summary of the Invention

[0006] Therefore, this invention provides a modified aramid nanofiber aqueous dispersion that can be uniformly dispersed in water, has a simple preparation method, and is environmentally friendly in the preparation process, as well as aramid cellophane with high strength and high transparency. At the same time, it also provides a method for preparing the modified aramid nanofiber aqueous dispersion and the modified aramid nanofiber cellophane.

[0007] To achieve the above objectives, the inventors provide a method for preparing a modified aramid nanofiber aqueous dispersion, which includes the following steps:

[0008] Step 1: Disperse para-aramid fibers in a DMSO / KOH system, stir and disperse evenly to obtain a DMSO dispersion of aramid with a mass concentration of 0.2%-4%;

[0009] Step 2: Add the acid anhydride to the DMSO dispersion of the aramid obtained in Step 1 for esterification modification. The molar ratio of the acid anhydride to the aramid structural units in the para-aramid fiber is 0.2-1:1, to obtain the modified aramid DMSO dispersion.

[0010] Step 3: Place the modified aramid DMSO dispersion obtained in Step 2 into a dialysis bag, then dialyze it in deionized water for 36-54 h. After taking it out, perform mechanical treatment to obtain the modified aramid nanofiber aqueous dispersion.

[0011] This invention employs the above-described method. In step 1, para-aramid fibers are directly dispersed in a DMSO / KOH system. In step 2, acid anhydrides are directly used to esterify and modify the para-aramid fibers, thereby improving the hydrophilicity of the aramid nanofibers. By introducing negatively charged carboxylate ions onto the aramid surface, the aramid nanofibers maintain a negatively charged state even after dialysis with deionized water, which helps them to be stably dispersed in water under the action of electrostatic repulsion.

[0012] Further, in step 1, the para-aramid fiber is one of the following: para-aramid yarn, para-aramid chopped fiber, para-aramid pulp fiber, or para-aramid precipitated fiber.

[0013] Furthermore, in step 1, the mass of KOH in the DMSO dispersion of the aramid is 1.5 times that of the aramid. At this ratio, the aramid nanofibers are fully deprotonated, which can expose more esterification modification sites.

[0014] Further, in step 2, the acid anhydride is one of the following: biphenyl anhydride, hexadecyl succinic anhydride, dodecyl succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, octyl succinic anhydride, succinic anhydride, 1,2,4-phenyltriacrylic anhydride, phenylmaleic anhydride, 2,3-naphthalenedicarboxylic anhydride, hexahydrophthalic anhydride, and butyl succinic anhydride.

[0015] Preferably, the anhydride is biphenyl anhydride. The aramid cellophane prepared by modification with biphenyl anhydride has the highest transparency because the addition of biphenyl enhances the π-π conjugation effect between the modified aramid nanofibers, strengthens the interaction between the aramid nanofibers, and results in a higher density of the prepared aramid cellophane. When light passes through, it tends to pass through a homogeneous medium, with a low scattering ratio, thus exhibiting high transparency.

[0016] Further, step 2 specifically involves adding acid anhydride to the aramid DMSO dispersion obtained in step 1, and continuing the reaction at room temperature for 1-2 hours to obtain the modified aramid DMSO dispersion.

[0017] Further, step 3 specifically involves: placing the modified aramid DMSO dispersion from step 2 into a WM 14000 dialysis bag, then dialyzing it in deionized water for 36-48 hours, changing the water every 6 hours to remove unreacted anhydrides from the solution and simultaneously completing solvent replacement from the DMSO system to the water system; after removal, mechanical treatment for 25-35 minutes is performed to redisperse the small amount of aggregated aramid nanofibers, resulting in a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.1%-2%.

[0018] Furthermore, the mechanical processing equipment in step 3 includes one of the following: a cell disruptor, a juicer, a high-pressure homogenizer, or a microfluidic homogenizer.

[0019] The present invention also discloses a modified aramid nanofiber aqueous dispersion, which is prepared by the above-described preparation method.

[0020] This invention also discloses a simple and low-energy-consumption method for preparing modified aramid nanofiber glass paper, which includes the following steps:

[0021] The modified aramid nanofiber aqueous dispersion was vacuum filtered to form a film and then hot-pressed to obtain the modified aramid nanofiber glass paper.

[0022] Furthermore, the hot pressing conditions are: hot pressing at 60-100 ℃ for 20 min-40 min.

[0023] The present invention also discloses a modified aramid nanofiber glass paper, which is prepared by the above-described preparation method.

[0024] The above technical solution has the following advantages, unlike existing technologies:

[0025] This invention employs a green modification method to improve the hydrophilicity of aramid nanofibers. It innovatively modifies the surface of aramid through esterification, introducing covalently cross-linked carboxyl groups onto the nanofiber surface. This simple, low-cost process allows for the preparation of aramid nanofibers that can be stably dispersed in water. Because the carboxyl groups are grafted onto the aramid nanofiber surface via chemical bonds, they exhibit higher stability compared to physical adsorption, allowing the dispersion to maintain stable dispersion for a long period (over 6 months). Furthermore, by controlling the ratio of anhydride to aramid structural units, the grafting rate of anhydride onto the aramid molecule surface can be increased or decreased, thereby regulating the hydrophilicity of aramid. This allows for the preparation of water-dispersible aramid nanofiber dispersions with varying fiber diameters. Attached Figure Description

[0026] Figure 1 is a picture of the water-dispersed aramid nanofiber dispersion prepared in Example 1;

[0027] Figure 2 is an atomic force microscope image of the water-dispersed aramid nanofiber dispersion prepared in step 3 of Example 2;

[0028] Figure 3 is an atomic force microscope image of the water-dispersed aramid nanofiber dispersion prepared in step 3 of Example 4.

[0029] Figure 4 is a partial comparison of the infrared spectra of the aramid nanofiber glass paper prepared in Example 5 and the unmodified blank aramid nanofiber glass paper. Detailed Implementation

[0030] To explain in detail the technical content, structural features, objectives, and effects of the technical solution, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0031] Example 1

[0032] Step 1: Mix 1 g of para-aramid yarn raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0033] Step 2: Add 188 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.2:1) to the aramid DMSO dispersion prepared in Step 1, and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0034] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0035] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0036] In this embodiment, steps 1-3 prepare a modified aramid nanofiber aqueous dispersion, and step 4 further processes it to obtain modified aramid nanofiber cellophane.

[0037] Figure 1 is a photograph of the modified aramid nanofiber aqueous dispersion prepared in step 3 of this embodiment after bottling. As can be seen from Figure 1, the dispersion has no flocculation or other phenomena and has good dispersibility.

[0038] Example 2

[0039] Step 1: Mix 1 g of para-aramid yarn raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0040] Step 2: Add 376 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.4:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0041] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0042] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0043] The modified aramid nanofiber aqueous dispersion prepared in step 3 was diluted 100 times and then uniformly dropped onto the surface of mica sheets. After air drying, it was photographed using an atomic force microscope. The specific photograph is shown in Figure 2. As can be seen from Figure 2, the modified aramid nanofiber aqueous dispersion prepared in step 3 is uniformly dispersed and does not agglomerate under an atomic force microscope, indicating that the dispersion has good dispersibility.

[0044] Example 3

[0045] Step 1: Mix 1 g of para-aramid yarn raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0046] Step 2: Add 565 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.6:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0047] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0048] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0049] Example 4

[0050] Step 1: Mix 1 g of para-aramid yarn raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0051] Step 2: Add 753 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.8:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0052] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0053] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0054] The modified aramid nanofiber aqueous dispersion prepared in step 3 was diluted 100 times and then uniformly dropped onto the surface of mica sheets. After air drying, it was photographed using an atomic force microscope. The specific photograph is shown in Figure 3. Comparing Figures 2 and 3, it can be seen that the diameter of the aramid nanofibers can be controlled by changing the ratio of acid anhydride to aramid. When the acid anhydride content is increased, there will be greater steric hindrance and electrostatic repulsion between aramid molecular chains, weakening the assembly ability, and therefore the fiber diameter is smaller.

[0055] Example 5

[0056] Step 1: Mix 1 g of para-aramid yarn raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0057] Step 2: Add 941 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0058] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0059] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80°C for 30 min to obtain modified aramid nanofiber cellophane.

[0060] Example 6

[0061] Step 1: Mix 5 g of para-aramid yarn raw material with 500 mL of DMSO and 7.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 1%.

[0062] Step 2: Add 4.7g of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 hour to obtain a modified aramid DMSO dispersion with a mass fraction of 1%.

[0063] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.5%.

[0064] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80°C for 30 min to obtain modified aramid nanofiber cellophane.

[0065] Example 7

[0066] Step 1: Mix 10 g of para-aramid yarn raw material with 500 mL of DMSO and 15 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2%.

[0067] Step 2: Add 9.4g of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 hour to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2%.

[0068] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 30 minutes to obtain a 1% (w / w) modified aramid nanofiber aqueous dispersion.

[0069] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80°C for 30 min to obtain modified aramid nanofiber cellophane.

[0070] Example 8

[0071] Step 1: Mix 15 g of para-aramid yarn raw material with 500 mL of DMSO and 22.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, thereby obtaining a uniformly dispersed aramid DMSO dispersion with a mass fraction of 3%.

[0072] Step 2: Add 14.1g of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 hour to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 3%.

[0073] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1.5%.

[0074] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80°C for 30 min to obtain modified aramid nanofiber cellophane.

[0075] Example 9

[0076] Step 1: Mix 20 g of para-aramid yarn raw material with 500 mL of DMSO and 30 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 4%.

[0077] Step 2: Add 18.8g of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 hour to obtain a modified aramid DMSO dispersion with a mass fraction of 4%.

[0078] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 2%.

[0079] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80°C for 30 min to obtain modified aramid nanofiber cellophane.

[0080] Example 10

[0081] Step 1: Mix 5 g of para-aramid yarn raw material with 500 mL of DMSO and 7.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 1%.

[0082] Step 2: Add 2.1g of maleic anhydride (the molar ratio of maleic anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1h to obtain a modified aramid DMSO dispersion with a mass fraction of 1%.

[0083] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.5%.

[0084] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80°C for 30 min to obtain modified aramid nanofiber cellophane.

[0085] Example 11

[0086] Step 1: Mix 5 g of para-aramid yarn raw material with 500 mL of DMSO and 7.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 1%.

[0087] Step 2: Add 4.46g of octyl succinic anhydride (the molar ratio of octyl succinic anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 1%.

[0088] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 54 hours, changing the water every 6 hours. After removal, mechanically process it with a cell disruptor for 25 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.5%.

[0089] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 70°C for 35 min to obtain modified aramid nanofiber cellophane.

[0090] Example 12

[0091] Step 1: Mix 5 g of para-aramid yarn raw material with 500 mL of DMSO and 7.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 1%.

[0092] Step 2: Add 2.4g of glutaric anhydride (the molar ratio of glutaric anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 1%.

[0093] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 36 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.5%.

[0094] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 60°C for 40 min to obtain modified aramid nanofiber cellophane.

[0095] Example 13

[0096] Step 1: Mix 5 g of para-aramid yarn raw material with 500 mL of DMSO and 7.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 1%.

[0097] Step 2: Add 3.1g of phthalic anhydride (the molar ratio of phthalic anhydride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 1%.

[0098] Step 3: Place 100 mL of the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 42 hours, changing the water every 6 hours. After dialysis, mechanically process the dispersion using a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.5%.

[0099] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 90°C for 25 min to obtain modified aramid nanofiber cellophane.

[0100] Example 14

[0101] Step 1: Mix 5 g of para-aramid yarn raw material with 500 mL of DMSO and 7.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 1%.

[0102] Step 2: Add 4.0g of 1,2,4-phenyltriglyceride (the molar ratio of 1,2,4-phenyltriglyceride to aramid structural units is 1:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 1%.

[0103] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically process it using a cell disruptor for 35 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.5%.

[0104] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane into a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 100°C for 20 min to obtain modified aramid nanofiber cellophane.

[0105] Example 15

[0106] Step 1: Mix 1 g of para-aramid chopped fiber raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0107] Step 2: Add 565 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.6:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0108] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0109] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0110] Example 16

[0111] Step 1: Mix 1 g of para-aramid pulp fiber raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0112] Step 2: Add 565 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.6:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0113] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0114] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0115] Example 17

[0116] Step 1: Mix 1 g of para-aramid precipitated fiber raw material with 500 mL of DMSO and 1.5 g of KOH, and stir at room temperature for 7 days to disperse the mixture, so as to obtain a uniformly dispersed aramid DMSO dispersion with a mass fraction of 2‰.

[0117] Step 2: Add 565 mg of biphenyl anhydride (the molar ratio of biphenyl anhydride to aramid structural units is 0.6:1) to the aramid DMSO dispersion prepared in Step 1 and continue stirring at room temperature for 1 h to obtain a modified aramid DMSO dispersion with a DMSO dispersion mass fraction of 2‰.

[0118] Step 3: Place the modified aramid DMSO dispersion described in Step 2 into a WM 14000 dialysis bag, and then dialyze it in deionized water for 48 hours, changing the water every 6 hours. After removal, mechanically treat it with a cell disruptor for 30 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 1‰.

[0119] Step 4: Vacuum filter 100 mL of the modified aramid nanofiber aqueous dispersion through a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Place the composite membrane in a hot press and hot press it at a pressure of 0.04 MPa and a temperature of 80 °C for 30 min to obtain modified aramid nanofiber cellophane.

[0120] The modified aramid nanofiber cellophane prepared in Examples 1-17 were tested for tensile strength, elongation at break, modulus, toughness, and film transmittance. The tensile strength and elongation at break were tested using a 68TM-10 high and low temperature materials testing machine (Instron Corporation, USA). Before testing, the cellophane was cut into 5 cm × 1 cm rectangles, and the tensile rate was set to 2 mm / min. Each sample was tested three times. Modulus and toughness were calculated using Origin software. Film transmittance was measured using a UV-5200PC ultraviolet-visible spectrophotometer (Shanghai Yuanxi Instrument Co., Ltd.). The results are shown in Table 1.

[0121] Table 1. Performance test data of the modified aramid nanofiber glasspaper prepared in Examples 1-14

[0122]

[0123] As shown in Table 1, the tensile strength of the modified aramid nanofiber glass paper prepared by this invention is above 190 MPa, and can reach up to 257 MPa.

[0124] Examples 1-5, based on a fixed solution concentration, gradually increased the amount of biphenyl anhydride. Infrared spectroscopy was performed on the modified aramid nanofiber cellophane prepared in Example 5 and the unmodified blank sample. A partial comparison of the resulting infrared spectra is shown in Figure 4. Figure 4 shows that with the addition of biphenyl anhydride, the concentration at 1550 cm⁻¹ increased... -1 The amide II band peak weakens at 1720 cm⁻¹. -1 The enhanced carbonyl peak at the point indicates that biphenyl anhydride was successfully incorporated into the surface of aramid nanofibers.

[0125] As shown in Table 1, with the increase of biphenyl anhydride dosage, the tensile strength of the final modified aramid nanofiber glass paper gradually increased, while the elongation at break gradually decreased. This is because as the grafting rate of biphenyl anhydride onto the aramid increases, the diameter of the aramid nanofibers composing the aramid glass paper becomes smaller, resulting in a denser structure and less deformation. Simultaneously, the transmittance of the glass paper also increases with the decrease in nanofiber size. This is because glass paper is essentially composed of stacked aramid nanofibers; when the fiber size of the film decreases, the film has a denser internal structure, thereby increasing the film's light transmittance.

[0126] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of the present invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of the present invention, or equivalent structural or procedural transformations made using the content of the present invention's specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a modified aramid nanofiber aqueous dispersion, characterized in that: It includes the following steps: Step 1: Disperse para-aramid fibers in a DMSO / KOH system and stir until homogeneous to obtain a DMSO dispersion of aramid with a mass concentration of 0.2%-4%. Step 2: Add acid anhydride to the DMSO dispersion of aramid obtained in Step 1 for esterification modification. The molar ratio of the acid anhydride to the aramid structural units in the para-aramid fibers is 0.2-1:1 to obtain a modified aramid DMSO dispersion. Step 3: Place the modified aramid DMSO dispersion obtained in Step 2 into a dialysis bag and then dialyze it in deionized water for 36-54 h. After removal, perform mechanical treatment to obtain a modified aramid nanofiber aqueous dispersion.

2. The method for preparing the aramid nanofiber aqueous dispersion according to claim 1, characterized in that: In step 1, the para-aramid fiber is one of the following: para-aramid yarn, para-aramid chopped fiber, para-aramid pulp fiber, or para-aramid precipitated fiber.

3. The method for preparing the aramid nanofiber aqueous dispersion according to claim 1, characterized in that: In step 1, the mass of KOH in the DMSO dispersion of the aramid is 1.5 times that of the aramid.

4. The method for preparing the modified aramid nanofiber aqueous dispersion according to claim 1, characterized in that: In step 2, the acid anhydride is one of the following: biphenyl anhydride, hexadecyl succinic anhydride, dodecyl succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, octyl succinic anhydride, succinic anhydride, 1,2,4-phenyltriacid anhydride, phenylmaleic anhydride, 2,3-naphthalenedicarboxylic anhydride, hexahydrophthalic anhydride, and butyl succinic anhydride.

5. The method for preparing the modified aramid nanofiber aqueous dispersion according to claim 1, characterized in that: Step 2 specifically involves adding acid anhydride to the aramid DMSO dispersion obtained in step 1 and continuing the reaction at room temperature for 1-2 hours to obtain the modified aramid DMSO dispersion.

6. The method for preparing the modified aramid nanofiber aqueous dispersion according to claim 1, characterized in that: Step 3 specifically involves: placing the modified aramid DMSO dispersion from step 2 into a WM 14000 dialysis bag, then dialyzing it in deionized water for 36-48 hours, changing the water every 6 hours; after removal, mechanically treating it for 25-35 minutes to obtain a modified aramid nanofiber aqueous dispersion with a mass concentration of 0.1%-2%.

7. A modified aramid nanofiber aqueous dispersion, characterized in that: It is prepared by the preparation method described in any one of claims 1-6.

8. A method for preparing modified aramid nanofiber cellophane, characterized in that: It includes the following steps: The modified aramid nanofiber aqueous dispersion of claim 7 is vacuum filtered to form a film and then hot-pressed to obtain the modified aramid nanofiber glass paper.

9. The method for preparing modified aramid nanofiber cellophane according to claim 8, characterized in that: The hot pressing conditions are: hot pressing at 60-100 ℃ for 20 min-40 min.

10. A modified aramid nanofiber cellophane, characterized in that: It is prepared by the preparation method described in claim 8 or 9.

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