Water-dispersible aramid nanofiber composite dispersion liquid, composite membrane and preparation method of water-dispersible aramid nanofiber composite dispersion liquid

Abstract

The invention relates to a preparation method of a water-dispersible aramid nanofiber composite dispersion liquid, which comprises the following steps: stirring and dispersing para-aramid fibers in a KOH / DMSO system to obtain an aramid nanofiber dispersion liquid; the preparation method comprises the following steps: swelling a chitin raw material, adding anhydride for esterification modification to obtain a modified intermediate, and stirring and dispersing the modified intermediate in DMSO to obtain a chitin nanofiber dispersion liquid; and uniformly mixing the chitin nanofiber dispersion liquid and the aramid nanofiber dispersion liquid, adding deionized water, carrying out centrifugal operation, adding a centrifugal precipitate into a NaOH solution, and carrying out mechanical treatment, so as to obtain the water-dispersible aramid nanofiber composite dispersion liquid. The water-dispersible aramid nanofiber composite dispersion liquid has excellent water dispersibility, the preparation method is simple, and no flocculation phenomenon occurs after the water-dispersible aramid nanofiber composite dispersion liquid is placed for more than 3 months.

Description

Technical Field

[0001] The invention relates to the field of polymer nanomaterials, and in particular to a water-dispersible aramid nanofiber composite dispersion liquid, a composite membrane and a preparation method thereof. Background Art

[0002] Aramid fiber is the full name of poly(p-phenylene terephthalamide) (PPTA). It has excellent properties such as ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, and light weight. It is widely used in aerospace, national defense, electronic communications, petrochemicals and other fields. The rigid chain structure formed by the π-π conjugation inside the molecular chain, the intermolecular hydrogen bonds and the van der Waals force make it difficult for the molecular chain segments to rotate internally, thus presenting a linear chain rigid structure. This structural feature leads to defects such as smooth surface, few active groups, and strong chemical inertness of aramid fibers, which in turn leads to poor interfacial bonding between aramid fibers and matrixes such as resins, limiting their application in high-performance composite reinforcement materials, nanomaterials, filtration materials, biomedicine and other fields.

[0003] Aramid nanofibers were first prepared by the DMSO / KOH system proposed by Professor Kotov of the United States (Dispersions of Aramid Nanofibers: A New Nanoscale Building Block, M. Yang, KQ Cao, L. Sui, et al. Acs Nano. 2011, 5, 6945-6954). A homogeneous, dispersed and stable ANFs / DMSO dispersion was obtained by mixing aramid fibers with KOH and DMSO and stirring continuously for 7-10 days at room temperature. The KOH / DMSO strong base system can effectively and directionally destroy the hydrogen bond cross-linking between the macroscopic aramid fiber molecular chains, and at the same time break the NH bond on the amide bond to deprotonate and form nitrogen anions. The negatively charged molecular chains are dispersed and stably exist under the action of electrostatic repulsion, the π-π conjugated force generated by the benzene ring and the amide bond, and the intermolecular van der Waals force, showing nanoscale size, high aspect ratio and high specific surface area. In recent years, aramid nanofibers have become a new type of functional polymer fiber, comparable to carbon nanotubes and cellulose nanofibers. However, the literature reports that using dimethyl sulfoxide (DMSO) as a solvent and potassium hydroxide to remove hydrogen atoms on the amide bonds of aramid to dissolve macroscopic aramid into nanoscale fibers, the prepared nano-aramid fibers can only exist in a strong alkaline DMSO dispersion system. When the dispersion system contains a proton donor, the PPTA polyanion will immediately obtain hydrogen atoms and protonate, resulting in the regeneration of hydrogen bonds between ANFs molecular chains and the fibers coagulating again. Especially when the dispersion system is water, a large number of aramid nanofibers are protonated and aggregated to form agglomerated precipitates. Therefore, the PPTA polyanion in the ANFs / DMSO solution is highly sensitive to moisture in the air, and the dispersion system easily induces the protonation of ANFs and generates a thin fragment film, which cannot be stored for a long time and needs to be sealed.

[0004] Therefore, the aramid nanofiber solution prepared by the above-mentioned literature method has the problems of being only dispersed in the KOH / DMSO system, being unable to be uniformly and stably dispersed in the aqueous phase system, and being unable to be stored for a long time, which greatly limits its application in water-soluble polymers and hydrophilic materials, making it impossible for the aramid nanofiber with excellent performance to achieve a significant enhancement effect, limiting its application field. Secondly, the membrane made of aramid nanofibers in the DMSO system has low mechanical strength (about 100MPa), which may be related to the greatly reduced crystallinity of aramid nanofibers in the DMSO system.

[0005] To address the above problems, there are currently three main ways to solve them:

[0006] (1) High-pressure injection: For example, the Chinese invention patent with patent application number 201810142388.7 proposed a "method for preparing water-dispersible aramid nanofibers and aramid nanopaper". The patent discloses the use of high-pressure injection of deionized water and washing with anhydrous ethanol and deionized water to obtain colloidal aramid nanofibers, which are dispersed in deionized water under stirring, wet-formed and pressed to obtain aramid nanopaper with a tensile strength of only 97 MPa.

[0007] (2) High-pressure injection and compounding: For example, the Chinese invention patent with patent application number 201810141732.0 proposed "an aramid nanofiber film composite aramid paper and its preparation method". The patent discloses the use of high-pressure injection of deionized water and washing with anhydrous ethanol and deionized water to obtain colloidal aramid nanofibers, which are dispersed in deionized water under stirring, and the wet-formed aramid nanofiber film is used as the surface layer and the bottom layer, and the para-aramid short fiber and para-aramid pulp / precipitated fiber slurry suspension are used as the core layer. After wet lamination, hot pressing is performed to obtain a composite aramid paper with a tensile strength of only 73.6 MPa.

[0008] (3) Modification: For example, the Chinese invention patent with patent application number 201410833596.3 proposed a "method for preparing water-dispersible aramid nanofibers and their application". The patent discloses that aramid fibers, catalysts and alkali are placed in an organic solvent (such as DMF, DMSO, NMP, DMAC), heated and stirred to disperse them evenly, and then small organic molecules with active functional groups that can undergo nucleophilic reactions with nitrogen anions (bromopropyne, chloropropyne, 5-chloro-1-pentyne and 1-bromo-2-butyne) are added to react to obtain an aramid nanofiber aqueous solution. However, obtaining water-soluble small molecules or functional groups through modification will lead to a decrease in its tensile strength, modulus and heat resistance. In addition, the reaction not only has many steps, but also requires a catalyst, and the preparation process is complicated. In order to obtain aramid nanofibers, freeze-drying is required, which consumes a lot of energy.

[0009] Therefore, it is necessary to develop an aramid nanofiber that has excellent properties such as tensile strength and can be uniformly dispersed in water. Summary of the invention

[0010] To this end, the present invention provides a water-dispersible aramid nanofiber composite dispersion liquid, a composite membrane and a preparation method thereof which are high-strength and can be uniformly dispersed in water.

[0011] To achieve the above object, the inventors provide a method for preparing a water-dispersible aramid nanofiber composite dispersion, which comprises the following steps:

[0012] Step 1: stirring and dispersing the para-aramid fiber in a KOH / DMSO system to obtain an aramid nanofiber dispersion having a mass concentration of 1‰-4‰;

[0013] Step 2: After the chitosan raw material is swollen, an acid anhydride is added for esterification modification to obtain a modified intermediate, wherein the molar ratio of the acid anhydride to the chitosan raw material is 0.1-5:1; the modified intermediate is stirred and dispersed in DMSO to obtain a chitosan nanofiber dispersion with a mass concentration of 0.5‰-1%;

[0014] Step 3: Mix the chitosan nanofiber dispersion obtained in step 2 and the aramid nanofiber dispersion obtained in step 1 to obtain a mixed solution, wherein the mass concentration of the chitosan nanofiber dispersion in the mixed solution is above 5%. After mixing evenly, add deionized water and perform centrifugation. Take the precipitate obtained by centrifugation, add the precipitate into a NaOH solution and perform mechanical treatment to disperse it in the NaOH solution to obtain a chitosan nanofiber / aramid nanofiber composite dispersion with a mass concentration of 0.1‰-2‰, that is, obtain the water-dispersed aramid nanofiber composite dispersion.

[0015] The present invention adopts the above preparation method. In the dispersion treatment in step 1, the para-aramid fiber is cracked in DMSO and dispersed into a dark red, clear and transparent dispersion. The aramid nanofiber dispersion flocculates when it meets water.

[0016] There is no order of precedence for the above steps 1 and 2 of the present invention.

[0017] In the step 2, the chitosan nanofibers are modified by acid anhydride esterification. The modified chitosan nanofibers have amphiphilicity and excellent mechanical properties. The modified chitosan nanofibers contain hydrophilic component carboxyl groups and lipophilic component acid anhydrides, which can be used as surfactants, have amphiphilic properties, and can be well dispersed in NaOH solutions and DMSO.

[0018] In step 3, the chitosan nanofiber dispersion and the aramid nanofiber dispersion can be uniformly mixed, and after adding deionized water, the aramid nanofibers will precipitate when they come into contact with water, and the chitosan nanofibers can be precipitated together with the chitosan nanofibers. At the same time, due to the uniform presence of chitosan nanofibers, the aramid nanofibers will not be tightly combined. When adding NaOH solution for mechanical treatment, the chitosan nanofibers have hydrophilic carboxyl groups after modification and tend to be dispersed in the NaOH solution, so the aramid nanofibers can be dispersed in the NaOH solution together with the modified chitosan nanofibers under mechanical treatment.

[0019] In step 3, the mass concentration of the chitosan nano-dispersion is controlled to be above 5%, because too little chitosan nanofiber content will not be able to prevent the aramid nanofiber from self-aggregating after contacting water.

[0020] Preferably, in step 1, the para-aramid fiber is one of the following: para-aramid yarn aramid, para-aramid short fiber, para-aramid pulp fiber or para-aramid fibrid.

[0021] Preferably, 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-trimethylbenzene anhydride, succinic anhydride, phenylmaleic anhydride, 2,3-naphthalene dicarboxylic anhydride, hexahydrophthalic anhydride, butyl succinic anhydride.

[0022] Preferably, in step 2, the chitosan raw material swelling treatment is: adding the purified chitosan raw material into a KOH / DMSO system, stirring and swelling at room temperature for 4-72 hours, so as to facilitate further modification of the chitosan.

[0023] Preferably, step 2 is specifically as follows: after swelling the chitosan raw material, add anhydride, continue stirring the reaction at room temperature for 0.5-2h to obtain a modified intermediate, stir and disperse the modified intermediate in DMSO, stir for 1-4h and then centrifuge to obtain a DMSO-dispersed chitosan nanofiber dispersion.

[0024] Preferably, in step 3, the mechanical treatment equipment is one of the following: a cell disruptor, a juicer, a high-pressure homogenizer, or a microfluidizer.

[0025] Preferably, in step 3, the pH of the NaOH solution is 10-12.

[0026] The invention also discloses a water-dispersible aramid nanofiber composite dispersion liquid, which is prepared by the above-mentioned preparation method.

[0027] The present invention also discloses a method for preparing a water-dispersible aramid nanofiber composite membrane, which comprises the following steps:

[0028] The water-dispersible aramid nanofiber composite dispersion is firstly centrifuged, then vacuum filtered to form a membrane and hot pressed to obtain the water-dispersible aramid nanofiber composite membrane.

[0029] Preferably, the filter membrane used in the vacuum filtration is a nylon filter membrane with a pore size of 0.1 μm-0.5 μm.

[0030] Preferably, the hot pressing condition is: hot pressing at 60-100° C. for 20 min-40 min, thereby improving the strength of the composite film.

[0031] The invention also discloses a water-dispersible aramid nanofiber composite membrane, which is prepared by the above-mentioned preparation method.

[0032] The present invention controls the performance of the composite membrane by controlling the dosage ratio of the chitin nanofiber dispersion and the aramid nanofiber dispersion. Since the mass concentration of the aramid nanofiber in the composite membrane can be controlled to be up to 95%, the strength of the composite membrane is greatly improved.

[0033] Different from the prior art, the above technical solution has the following advantages:

[0034] 1. The water-dispersible aramid nanofiber composite dispersion prepared by the present invention has excellent water dispersibility, and the preparation method is simple, and it remains stable at a rotation speed of 9800 rpm, and no flocculation occurs when placed at room temperature for more than 3 months.

[0035] 2. The water-dispersible water-dispersible aramid nanofiber composite dispersion prepared by the present invention is uniformly composed of chitin nanofibers and aramid nanofibers, has high crystallinity, and maintains a good crystalline structure. The water-dispersible aramid nanofiber composite membrane prepared thereby has a maximum breaking strength of 344 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a picture of the water-dispersible aramid nanofiber composite dispersion prepared in Example 1;

[0037] Figure 2 The UV transmittance of the water-dispersible aramid nanofiber composite dispersion prepared in Example 1 at different storage times;

[0038] Figure 3 This is an atomic force microscope photograph of the water-dispersible aramid nanofiber composite dispersion prepared in step 3 of Example 1;

[0039] Figure 4 This is a field emission scanning electron microscope photograph of the cross section of the water-dispersible aramid nanofiber composite membrane prepared in Example 1. DETAILED DESCRIPTION

[0040] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0041] In each embodiment of the present invention, the chitosan raw material is pretreated to obtain chitosan. The treatment operation can be performed by the following method: the chitosan raw material is purified by soaking in an acid solution to remove protein, then soaking in an alkaline solution to remove calcium carbonate, and finally soaking in a bleaching solution to remove pigment.

[0042] The method comprises soaking in an acid solution to remove protein, soaking in an alkaline solution to remove calcium carbonate, and finally soaking in a bleaching solution to remove pigment. Specifically, the chitosan is soaked in a 2 mol / L hydrochloric acid solution for 48 hours to remove calcium carbonate, soaked in a 4% aqueous hydroxide solution for 48 hours to remove protein, soaked in a bleaching solution at 80°C for 3 hours to remove pigment, washed with deionized water, and dried to obtain the purified chitosan. The percentage of each component in the bleaching solution is: 0.38% sodium hypochlorite, 0.55% sodium hydroxide, 1.58% acetic acid, and the remaining component is water.

[0043] Example 1

[0044] Step 1: 1 g of para-aramid yarn aramid raw material was mixed with 1.5 g of KOH and 500 mL (550 g) of DMSO, and stirred at room temperature for 7 days for dispersion treatment to obtain an aramid nanofiber dispersion with a mass concentration of 2‰.

[0045] Step 2: 80 mg of purified chitosan was mixed with 20 mg of KOH and 20 mL (22 g) of DMSO, and stirred and swollen at room temperature for 72 h, then 88.4 mg (the molar ratio of biphenyl anhydride to chitosan structural unit was 1:1) of biphenyl anhydride was added, and the reaction was continued at room temperature with stirring for 1 h. 20 mL of DMSO was added to the obtained product and stirred and diluted for 2 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 2‰.

[0046] Step 3: Take 40 mL of aramid nanofiber dispersion dispersed in the DMSO system and mix it with 10 mL of chitin nanofiber dispersion dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate into 100 mL of pH 11 NaOH solution, mechanically treat it with a cell disruptor for 30 minutes, and then take it out to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 1‰.

[0047] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Put the composite membrane into a hot press and hot press it at an air pressure of 0.04 MPa and 80° C. for 30 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0048] In this embodiment, steps 1-3 prepare a water-dispersible aramid nanofiber composite dispersion, which is further processed in step 4 to obtain a water-dispersible aramid nanofiber composite membrane.

[0049] After testing, the density of the water-dispersible aramid nanofiber composite membrane is 1.02 g / m 3, light transmittance 68%, tensile strength 350MPa, toughness 23.2MJ / m 3 .

[0050] Figure 1 This is a photo of the water-dispersible aramid nanofiber composite dispersion prepared in step 3 of this embodiment after being bottled. Figure 1 It can be seen that the dispersion has no flocculation and other phenomena, and has good dispersibility.

[0051] After the water-dispersible aramid nanofiber composite dispersion prepared in step 3 is bottled, it is placed for 90 days, and the ultraviolet transmittance of the dispersion is observed at different storage days (0 days, 30 days, 50 days, 70 days, and 90 days). The test results are shown in FIG. Figure 2 .Depend on Figure 2 It can be seen that after 90 days of storage, the transmittance of the water-dispersed aramid nanofiber composite dispersion is still very high, indicating that the dispersion has good dispersibility and there is no flocculation or other phenomena.

[0052] The water-dispersible aramid nanofiber composite dispersion prepared in step 3 was photographed using an atomic force microscope. Figure 3 As shown. Figure 3 It can be seen that the water-dispersible aramid nanofiber composite dispersion prepared in step 3 has fibers that are uniformly dispersed and not agglomerated under an atomic force microscope, indicating that the dispersion has good dispersibility.

[0053] The cross section of the water-dispersible aramid nanofiber composite membrane prepared in step 4 of this embodiment was scanned by field emission scanning electron microscope. The scanning results are shown in Figure 4 .Depend on Figure 4 It can be seen that the cross section of the water-dispersible aramid nanofiber composite membrane has a regular layered structure, and the composite membrane has high strength.

[0054] Example 2

[0055] Step 1: 80 mg of purified chitosan was mixed with 20 mg of KOH and 20 mL (22 g) of DMSO, and stirred and swollen at room temperature for 72 h, then 88.4 mg (the molar ratio of biphenyl anhydride to chitosan structural unit was 1:1) of biphenyl anhydride was added, and the reaction was continued at room temperature with stirring for 1 h. 20 mL of DMSO was added to the obtained product and stirred and diluted for 2 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 2‰.

[0056] Step 2: 1 g of para-aramid yarn aramid raw material was mixed with 1.5 g of KOH and 500 mL (550 g) of DMSO, and stirred at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 2‰.

[0057] Step 3: Take 30 mL of aramid nanofiber dispersion dispersed in the DMSO system and mix it with 20 mL of chitin nanofiber dispersion dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate to 100 mL of pH 11 NaOH solution, mechanically treat it with a cell disruptor for 30 minutes, and then take it out to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 1‰.

[0058] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Put the composite membrane into a hot press and hot press it at an air pressure of 0.04 MPa and 80° C. for 30 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0059] Example 3

[0060] Step 1: 80 mg of purified chitosan was mixed with 20 mg of KOH and 20 mL (22 g) of DMSO, and stirred and swollen at room temperature for 72 h, then 88.4 mg (the molar ratio of biphenyl anhydride to chitosan structural unit was 1:1) of biphenyl anhydride was added, and the reaction was continued at room temperature with stirring for 1 h. 20 mL of DMSO was added to the obtained product and stirred and diluted for 2 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 2‰.

[0061] Step 2: 1 g of para-aramid yarn aramid raw material was mixed with 1.5 g of KOH and 500 mL (550 g) of DMSO, and stirred at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 2‰.

[0062] Step 3: Take 20 mL of aramid nanofibers dispersed in the DMSO system and mix them with 30 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate into 100 mL of NaOH solution with a pH of 11, mechanically treat it with a cell disruptor for 30 minutes, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 1‰.

[0063] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Put the composite membrane into a hot press and hot press it at an air pressure of 0.04 MPa and 80° C. for 30 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0064] Example 4

[0065] Step 1: 80 mg of purified chitosan was mixed with 20 mg of KOH and 20 mL (22 g) of DMSO, and stirred and swollen at room temperature for 72 h, then 88.4 mg (the molar ratio of biphenyl anhydride to chitosan structural unit was 1:1) of biphenyl anhydride was added, and the reaction was continued at room temperature with stirring for 1 h. 20 mL of DMSO was added to the obtained product and stirred and diluted for 2 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 2‰.

[0066] Step 2: 1 g of para-aramid yarn aramid raw material was mixed with 1.5 g of KOH and 500 mL (550 g) of DMSO, and stirred at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 2‰.

[0067] Step 3: Take 10 mL of aramid nanofibers dispersed in the DMSO system and mix them with 40 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate into 100 mL of NaOH solution with a pH of 11, mechanically treat it with a cell disruptor for 30 minutes, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 1‰.

[0068] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Put the composite membrane into a hot press and hot press it at an air pressure of 0.04 MPa and 80° C. for 30 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0069] Example 5

[0070] Step 1: 80 mg of purified chitosan was mixed with 20 mg of KOH and 20 mL (22 g) of DMSO, and stirred and swollen at room temperature for 48 h, then 83.6 mg (the molar ratio of octyl succinic anhydride to chitosan structural unit was 1:1) of octyl succinic anhydride was added, and the reaction was continued at room temperature for 30 min. 20 mL of DMSO was added to the obtained product and stirred and diluted for 4 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 2‰.

[0071] Step 2: 1 g of para-aramid yarn aramid raw material was mixed with 1.5 g of KOH and 500 mL (550 g) of DMSO, and stirred at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 2‰.

[0072] Step 3: Take 40 mL of aramid nanofibers dispersed in the DMSO system and mix them with 10 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 min, take out the precipitate, add the precipitate into 100 mL of NaOH solution with a pH of 11, mechanically treat it with a juicer for 60 min, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 1‰.

[0073] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. Put the composite membrane into a hot press and hot press it at an air pressure of 0.04 MPa and 80° C. for 30 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0074] Example 6

[0075] Step 1: 80 mg of purified chitosan was mixed with 20 mg of KOH and 20 mL (22 g) of DMSO, and stirred and swollen at room temperature for 24 h, then 5.8 mg (the molar ratio of phthalic anhydride to chitosan structural unit was 0.1:1) of phthalic anhydride was added, and the reaction was continued at room temperature for 30 min. 140 mL of DMSO was added to the obtained product and stirred and diluted for 1 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 0.5‰.

[0076] Step 2: 0.5 g of para-aramid pulp fiber raw material was mixed with 2.5 g of KOH and 500 mL (550 g) of DMSO, and stirred at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 1‰.

[0077] Step 3: Take 20 mL of aramid nanofibers dispersed in the DMSO system and mix them with 40 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate into 400 mL of NaOH solution with a pH of 11, mechanically treat it with a microjet for 30 minutes, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 0.1‰.

[0078] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.1 μm to obtain a composite membrane. Put the composite membrane into a hot press and perform hot pressing for 40 min at an air pressure of 0.04 MPa and 60° C. to obtain a water-dispersible aramid nanofiber composite membrane.

[0079] Example 7

[0080] Step 1: 80 mg of purified chitosan was mixed with 30 mg of KOH and 40 mL (44 g) of DMSO, and stirred and swollen at room temperature for 24 h, then 197 mg (the molar ratio of succinic anhydride to chitosan structural unit is 5:1) of succinic anhydride was added, and the reaction was continued at room temperature for 2 h. 40 mL of DMSO was added to the obtained product and stirred and diluted for 1 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 1‰.

[0081] Step 2: Mix 1 g of para-aramid fiber precipitate raw material with 2.0 g of KOH and 500 mL (550 g) of DMSO, and stir at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 2‰.

[0082] Step 3: Take 40 mL of aramid nanofibers dispersed in the DMSO system and mix them with 20 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate into 50 mL of NaOH solution with a pH of 12, mechanically treat it with a high-pressure homogenizer for 30 minutes, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 2‰.

[0083] Step 4: Centrifuge the water-dispersible aramid nanofiber composite dispersion at 9800 rpm for 15 min, and perform vacuum filtration with a filter membrane with a pore size of 0.50 μm to obtain a composite membrane. Put the composite membrane into a hot press and hot press it at an air pressure of 0.02 MPa and 80° C. for 40 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0084] Example 8

[0085] Step 1: Mix 80 mg of purified chitosan with 20 mg of KOH and 20 mL (22 g) of DMSO, and stir and swell at room temperature for 24 h. Then add 132.6 mg (the molar ratio of biphenyl anhydride to chitosan structural unit is 1.5:1) of biphenyl anhydride, and continue stirring and reacting at room temperature for 1 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 4‰.

[0086] Step 2: Mix 2 g of para-aramid chopped fiber raw material with 1.0 g of KOH and 500 mL (550 g) of DMSO, and stir at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 4‰.

[0087] Step 3: Take 20 mL of aramid nanofibers dispersed in the DMSO system and mix them with 30 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 min, take out the precipitate, add the precipitate into 250 mL of NaOH solution with a pH of 10, mechanically treat it with a juicer for 60 min, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 0.8‰.

[0088] Step 4: The water-dispersible aramid nanofiber composite dispersion was centrifuged at 9800 rpm for 15 min, and vacuum filtered with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. The composite membrane was placed in a hot press and hot pressed at an air pressure of 0.05 MPa and 100° C. for 20 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0089] Example 9

[0090] Step 1: Mix 80 mg of purified chitosan with 20 mg of KOH and 20 mL (22 g) of DMSO, and stir and swell at room temperature for 24 h. Then add 182.3 mg (the molar ratio of hexahydrophthalic anhydride to chitosan structural unit is 3:1) of hexahydrophthalic anhydride, and continue stirring and reacting at room temperature for 1 h to obtain a chitosan nanofiber dispersion with a DMSO dispersion mass concentration of 4‰.

[0091] Step 2: Mix 2 g of para-aramid chopped fiber raw material with 1.0 g of KOH and 500 mL (550 g) of DMSO, and stir at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 4‰.

[0092] Step 3: Take 20 mL of aramid nanofibers dispersed in the DMSO system and mix them with 30 mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800 rpm for 15 minutes, take out the precipitate, add the precipitate into 133.3 mL of pH 10 NaOH solution, mechanically treat it with a juicer for 60 minutes, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 1.5‰.

[0093] Step 4: The water-dispersible aramid nanofiber composite dispersion was centrifuged at 9800 rpm for 15 min, and vacuum filtered with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. The composite membrane was placed in a hot press and hot pressed at an air pressure of 0.05 MPa and 100° C. for 20 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0094] Example 10

[0095] Step 1: Mix 80 mg of purified chitosan with 20 mg of KOH and 8 mL (8.8 g) of DMSO, and stir and swell at room temperature for 24 h. Then add 132.6 mg (the molar ratio of biphenyl anhydride to chitosan structural unit is 1.5:1) of biphenyl anhydride, and continue stirring and reacting at room temperature for 1 h to obtain a chitosan nanofiber dispersion with a mass concentration of 1% dispersed in DMSO.

[0096] Step 2: Mix 2 g of para-aramid chopped fiber raw material with 1.0 g of KOH and 500 mL (550 g) of DMSO, and stir at room temperature for 7 days to obtain an aramid nanofiber dispersion with a mass concentration of 4‰.

[0097] Step 3: Take 47.5mL of aramid nanofibers dispersed in the DMSO system and mix them with 1mL of chitin nanofibers dispersed in the DMSO system, add deionized water, centrifuge at 9800rpm for 15min, take out the precipitate, add the precipitate into 100mL of NaOH solution with pH 10, mechanically treat it with a juicer for 60min, and then take out the dispersion to obtain a water-dispersed aramid nanofiber composite dispersion with a concentration of 2‰.

[0098] Step 4: The water-dispersible aramid nanofiber composite dispersion was centrifuged at 9800 rpm for 15 min, and vacuum filtered with a filter membrane with a pore size of 0.22 μm to obtain a composite membrane. The composite membrane was placed in a hot press and hot pressed at an air pressure of 0.05 MPa and 100° C. for 20 min to obtain a water-dispersible aramid nanofiber composite membrane.

[0099] The water-dispersible aramid nanofiber composite membranes prepared in Examples 1 to 10 were tested for tensile strength, elongation at break, modulus, and toughness. The tensile strength and elongation at break were tested by using a 68TM-10 high and low temperature material testing machine produced by Instron Corporation of the United States to test the tensile strength and elongation at break of the composite membrane. Before the test, the membrane was cut into 5 cm × 1 cm rectangles, the stretching rate was set to 2 mm / min, and each sample was tested 3 times. The modulus and toughness were calculated using origin software. The test results are shown in Table 1.

[0100] Table 1 Performance test data of water-dispersible aramid nanofiber composite membranes prepared in Examples 1 to 10

[0101]

[0102]

[0103] As can be seen from Table 1, the tensile strength of the water-dispersed aramid nanofiber composite membrane prepared by the present invention is above 170MPa, and can reach up to 344MPa. In Examples 1-4, on the basis of a fixed solution mass concentration, the amount of chitin nanofiber dispersion added is gradually increased, while the amount of aramid nanofiber dispersion added is gradually reduced. From the test data in Table 1, it can be seen that with the reduction in the amount of aramid nanofiber dispersion added, the tensile strength of the composite membrane of the aramid nanofiber finally prepared gradually decreases, and the elongation at break, modulus, and toughness also decrease synchronously. This is because the strength of aramid nanofiber is greater than that of chitin nanofiber, and the proportion of aramid nanofiber is reduced, which has a smaller improvement on strength.

[0104] It should be noted that, although the above embodiments have been described in this article, the patent protection scope of the present invention is not limited thereby. Therefore, based on the innovative concept of the present invention, changes and modifications made to the embodiments described herein, or equivalent structures or equivalent process changes made using the contents of the present invention specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included in the patent protection scope of the present invention.

Claims

1. A method for preparing a water-dispersible aramid nanofiber composite dispersion, characterized in that: It includes the following steps: Step 1: stirring and dispersing the para-aramid fiber in a KOH / DMSO system to obtain an aramid nanofiber dispersion having a mass concentration of 1‰-4‰; Step 2: After the chitosan raw material is swollen, an acid anhydride is added for esterification modification to obtain a modified intermediate, wherein the molar ratio of the acid anhydride to the chitosan raw material is 0.1-5:1; the modified intermediate is stirred and dispersed in DMSO to obtain a chitosan nanofiber dispersion with a mass concentration of 0.5‰-1%; Step 3: The chitosan nanofiber dispersion obtained in step 2 and the aramid nanofiber dispersion obtained in step 1 are mixed to obtain a mixed solution, wherein the mass concentration of the chitosan nanofiber dispersion in the mixed solution is above 5%. After mixing evenly, deionized water is added and centrifuged. The precipitate obtained by centrifugation is taken and the precipitate is added into a NaOH solution for mechanical treatment to disperse it in the NaOH solution to obtain a chitosan nanofiber / aramid nanofiber composite dispersion with a mass concentration of 0.1‰-2‰, i.e., the water-dispersed aramid nanofiber composite dispersion is obtained.

2. The method for preparing the water-dispersible aramid nanofiber composite dispersion according to claim 1, characterized in that: In the step 1, the para-aramid fiber is one of the following: para-aramid yarn aramid, para-aramid short fiber, para-aramid pulp fiber or para-aramid fibrid.

3. The method for preparing the water-dispersible aramid nanofiber composite 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-trimethylbenzene anhydride, phenyl maleic anhydride, 2,3-naphthalene dicarboxylic anhydride, hexahydrophthalic anhydride, butyl succinic anhydride.

4. The method for preparing the water-dispersible aramid nanofiber composite dispersion according to claim 1, characterized in that: In the step 2, the chitosan raw material swelling treatment is as follows: adding the purified chitosan raw material into a KOH / DMSO system, and stirring and swelling at room temperature for 4-72 hours.

5. The method for preparing the water-dispersible aramid nanofiber composite dispersion according to claim 1, characterized in that: The step 2 is specifically as follows: after the chitosan raw material is swollen, anhydride is added, and the reaction is continued under stirring at room temperature for 0.5-2 hours to obtain a modified intermediate, and the modified intermediate is dispersed in DMSO by stirring, and centrifuged after stirring for 1-4 hours to obtain a DMSO-dispersed chitosan nanofiber dispersion.

6. The method for preparing the water-dispersible aramid nanofiber composite dispersion according to claim 1, characterized in that: The mechanical processing equipment in step 3 includes one of the following: a cell disruptor, a juicer, a high-pressure homogenizer, and a microfluidizer.

7. A water-dispersible aramid nanofiber composite dispersion, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 6.

8. A method for preparing a water-dispersible aramid nanofiber composite membrane, characterized in that: It includes the following steps: The water-dispersible aramid nanofiber composite dispersion liquid of claim 7 is first centrifuged, then vacuum filtered to form a membrane and hot pressed to obtain the water-dispersible aramid nanofiber composite membrane.

9. The method for preparing a water-dispersible aramid nanofiber composite membrane according to claim 8, characterized in that: The hot pressing conditions are: hot pressing at 60-100° C. for 20 min-40 min.

10. A water-dispersible aramid nanofiber composite membrane, characterized in that: The compound is prepared by the preparation method described in claim 8 or 9.

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