High-concentration aramid nanofiber dispersion liquid, preparation method and application thereof

Abstract

This invention discloses a high-concentration aramid nanofiber dispersion, its preparation method, and its applications, belonging to the field of nanofiber technology. The method uses potassium hydroxide as a dispersion solvent, deprotonates the aramid fibers in an alkaline environment, and successfully increases the concentration of the aramid nanofiber dispersion to 10 wt% through mechanical stirring and gradient temperature control. This method is simple and easy to implement. Furthermore, it significantly shortens the preparation time of the high-concentration aramid nanofiber dispersion, significantly improves preparation efficiency, and reduces preparation costs. The aramid nanofiber-based hydrogel prepared using this method exhibits good mechanical strength, with a tensile strength reaching 4.45 MPa and an elastic modulus reaching 3.6 MPa, thus solving the problem of poor mechanical properties in hydrogel materials.

Description

Technical Field

[0001] This invention belongs to the field of nanofiber technology, specifically relating to a high-concentration aramid nanofiber dispersion, its preparation method, and its application. Background Technology

[0002] Hydrogels are three-dimensional network polymer materials capable of absorbing large amounts of water. Due to their excellent biocompatibility and stimuli-responsiveness, they hold great promise for applications in biomedicine, flexible electronics, and soft robotics. However, most hydrogels exhibit low mechanical strength and poor fracture toughness, making them prone to permanent fracture under tension, indicating significant drawbacks in tensile mechanical properties. Although highly tensile hydrogels have been developed using techniques such as dual-network systems, they often suffer from low modulus, weak load-bearing capacity, and are susceptible to stress relaxation and fatigue damage under cyclic loading, resulting in insufficient mechanical stability. This unsatisfactory mechanical strength contradicts their broad application prospects, representing a key challenge in current scientific research.

[0003] Aramid nanofibers (ANFs) are fibrous materials with nanoscale diameters prepared from aramid (aromatic polyamide). As a representative system of synthetic polymer nanomaterials, they exhibit mechanical properties comparable to carbon nanotubes due to their molecular structure derived from high-strength poly(p-phenylene terephthalamide), making them ideal nanostructural units. However, the concentration (solid content) of aramid nanofiber dispersions is relatively low. For example, in Chinese invention patent CN115160636A, the mass concentration of the aramid nanofiber dispersion is 0.45~1.75%; in Chinese invention patent CN119286043A, the mass concentration of the aramid nanofiber aqueous dispersion is 0.5%. 2.5wt%. Low solids content dispersions still pose a fundamental bottleneck to subsequent material manufacturing: low-concentration dispersions cannot construct dense three-dimensional network structures, and the resulting hydrogels, aerogels, and other fiber network structures are unstable, with macroscopic mechanical properties still lower than those required for practical applications.

[0004] The development of high-concentration dispersions has become one of the effective ways to solve the above-mentioned dilemmas, and has breakthrough significance for the field of nanocomposite materials. In Chinese invention patent with publication number CN115368625A, a dispersion of aramid nanofibers of 0.1wt% to 15wt% is disclosed. However, the applicant found in his research that the aramid nanofibers in this dispersion could no longer form a stable structure. Summary of the Invention

[0005] 1. The problem to be solved

[0006] This invention addresses the technical problem of low aramid nanofiber concentration in aramid nanofiber dispersions by providing a high-concentration aramid nanofiber dispersion, its preparation method, and its applications. The method uses potassium hydroxide as a dispersion solvent, deprotonates the aramid fibers in an alkaline environment, and successfully increases the concentration of the aramid nanofiber dispersion to 10 wt% through mechanical stirring and gradient temperature control. This method is simple and easy to implement. Furthermore, it significantly shortens the preparation time of the high-concentration aramid nanofiber dispersion, significantly improves preparation efficiency, and reduces preparation costs. The aramid nanofiber-based hydrogel prepared using this method exhibits good mechanical strength, with a tensile strength reaching 4.45 MPa and an elastic modulus reaching 3.6 MPa, thus solving the problem of poor mechanical properties in hydrogel materials.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a method for preparing a high-concentration aramid nanofiber dispersion, the method comprising the following steps:

[0010] S1, prepare a solution of dimethyl sulfoxide and potassium hydroxide, and heat and stir under sealed conditions until the potassium hydroxide is completely dissolved to obtain a dispersion solvent;

[0011] S2, add aramid fibers to the dispersion solvent, heat and stir at 25~35℃ for 8~10 h to obtain the first aramid nanofiber dispersion;

[0012] S3, add aramid fibers to the first aramid nanofiber dispersion, heat and stir at 50~60℃ for 2~4 h to obtain the second aramid nanofiber dispersion;

[0013] S4, add aramid fibers to the second aramid nanofiber dispersion, heat and stir at 50~60℃ for 2~4 h to obtain a high-concentration nanofiber dispersion;

[0014] in:

[0015] The mass of aramid fiber added in step S2 is greater than the mass of aramid fiber added in step S3, and the mass of aramid fiber added in step S3 is greater than the mass of aramid fiber added in step S4.

[0016] Furthermore, the mass of aramid fiber added in step S2 is equal to the sum of the masses of aramid fiber added in steps S3 and S4.

[0017] Furthermore, the ratio of the total mass of the added aramid fibers to the total mass of dimethyl sulfoxide and potassium hydroxide is 1:49 to 1:9, thus obtaining a 2%wt to 10%wt aramid nanofiber dispersion.

[0018] Furthermore, the ratio of the total mass of the added aramid fibers to the total mass of dimethyl sulfoxide and potassium hydroxide is 1:9, thus obtaining a 10%wt aramid nanofiber dispersion.

[0019] Furthermore, in step S1 above, the mass ratio of potassium hydroxide to dimethyl sulfoxide is 1:(17~19).

[0020] Furthermore, in step S1 above, the heating and stirring conditions include: a temperature of 30°C and a rotation speed of 70 r / min.

[0021] Furthermore, in step S2 above, the heating and stirring conditions include: 30°C, a rotation speed of 70 r / min, and a time of 10 h.

[0022] Furthermore, in step S3 above, the heating and stirring conditions include: 55°C; a rotation speed of 70 r / min; and a time of 3 h.

[0023] Furthermore, in step S4 above, the heating and stirring conditions include: 55°C; a rotation speed of 70 r / min; and a time of 2 h.

[0024] Furthermore, in the above-mentioned high-concentration aramid nanofiber dispersion, the diameter of the aramid nanofibers is 16~30 nm.

[0025] Furthermore, in the above-mentioned high-concentration aramid nanofiber dispersion, the diameter of the aramid nanofibers is 20~28 nm.

[0026] Furthermore, in the above-mentioned high-concentration aramid nanofiber dispersion, the diameter of the aramid nanofibers is 22~24 nm.

[0027] Furthermore, the above-mentioned high-concentration aramid nanofiber dispersion has a viscosity of 800~1200 Pa·s at 85℃.

[0028] Furthermore, the viscosity of the above-mentioned high-concentration aramid nanofiber dispersion can be maintained for 2-5 hours at 85°C and for 4-7 hours at 65°C.

[0029] The present invention also provides the application of the high-concentration aramid nanofiber dispersion prepared by the above-mentioned method in the preparation of hydrogels.

[0030] This invention also provides a method for preparing aramid nanofiber-based hydrogels. The method involves mixing a high-concentration aramid nanofiber dispersion prepared by the above-mentioned method with a polyvinyl alcohol solution to prepare the aramid nanofiber-based hydrogel. Specifically, the method includes:

[0031] Prepare a 15% wt~25% wt polyvinyl alcohol solution;

[0032] A high-concentration aramid nanofiber dispersion was mixed with a polyvinyl alcohol solution and stirred at 50-70°C to obtain a mixture.

[0033] The mixture was transferred to a mold, and the mold was placed in deionized water for 10-15 h to obtain aramid nanofiber-based hydrogel.

[0034] Furthermore, the mass ratio of the above-mentioned high-concentration aramid nanofiber dispersion to the polyvinyl alcohol solution is 1:(2~3). Even further, the mass ratio of the above-mentioned high-concentration aramid nanofiber dispersion to the polyvinyl alcohol solution is 1:2.5.

[0035] Furthermore, the above-mentioned polyvinyl alcohol solution is a 20% wt polyvinyl alcohol solution.

[0036] Furthermore, the solvent for the above polyvinyl alcohol solution is dimethyl sulfoxide.

[0037] Furthermore, the above stirring includes stirring at 60°C for 1 min.

[0038] Furthermore, the mold was placed in deionized water for 12 hours.

[0039] The present invention also provides an aramid nanofiber-based hydrogel prepared by the above-mentioned method, which has good mechanical strength, with a tensile strength of up to 4.45 MPa and an elastic modulus of up to 3.6 MPa.

[0040] 3. Beneficial effects

[0041] Compared with the prior art, the advantages of this invention are as follows:

[0042] (1) The high-concentration aramid nanofiber dispersion, its preparation method, and its application provided by this invention have the advantages of good stability, uniform fiber diameter, and high aspect ratio. The leap from low to high concentration of aramid nanofiber dispersion essentially opens up a key pathway for the transformation of nano-building units into macroscopic high-performance materials, and promotes nanocomposite materials into a new stage of synergistic design of toughness and functionality.

[0043] (2) The high-concentration aramid nanofiber dispersion, its preparation method, and its application provided by this invention are based on the deprotonation of aramid fibers under alkaline conditions. Through mechanical stirring and gradient temperature, the concentration of the aramid nanofiber dispersion was successfully increased to 10 wt%. This method does not introduce other reagents and is simple and easy to implement. At the same time, it can significantly shorten the preparation time of the high-concentration aramid nanofiber dispersion, significantly improve the preparation efficiency, and reduce the preparation cost.

[0044] (3) The high-concentration aramid nanofiber dispersion and its preparation method and application provided by the present invention are used to prepare hydrogels. A aramid nanofiber-based hydrogel material with excellent mechanical strength is successfully prepared through a simple solvent exchange process. Attached Figure Description

[0045] Figure 1 This is an electron microscope image of a 10% aramid nanofiber dispersion.

[0046] Figure 2 These are the statistical results of fiber diameter in a 10% aramid nanofiber dispersion.

[0047] Figure 3 Electron micrographs of the aramid nanofiber dispersions in Example 2 and Comparative Example 1, where A is the aramid nanofiber dispersion of Example 2 with an average diameter of 23 nm; and B is the aramid nanofiber dispersion of Comparative Example 1 with an average diameter of 18 nm.

[0048] Figure 4 This is an electron microscope image of the 2wt% aramid nanofiber dispersion prepared in Comparative Example 1.

[0049] Figure 5 This is a macroscopic photograph of the prepared aramid nanofiber-based hydrogel.

[0050] Figure 6 It refers to the tensile properties of aramid nanofiber-based hydrogels. Detailed Implementation

[0051] The present invention will be further described below with reference to specific embodiments.

[0052] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0053] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0054] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0055] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0056] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0057] As used in this article, fiber refers to a thin (micrometer or nanometer diameter) and long material with a certain degree of flexibility.

[0058] As used in this article, aramid, or aromatic polyamide, is a polymer material whose main chain is composed of alternating aromatic rings (such as benzene rings) and amide bonds (-CONH-).

[0059] As used in this article, aramid nanofibers (ANFs) are fiber materials with nanoscale diameters prepared from aramid (aromatic polyamide) through a special method.

[0060] As used in this article, aramid nanofiber dispersion is a liquid system formed by uniformly dispersing aramid nanofibers in a specific solvent.

[0061] As used in this article, hydrogel is a three-dimensional cross-linked network structure material formed by high molecular polymers. It has the characteristics of high water absorption and retention, biocompatibility, etc., and is widely used in medical, agricultural, and daily life fields.

[0062] The reagents used in this invention include:

[0063] Potassium hydroxide (KOH): purity ≥99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0064] Dimethyl sulfoxide (DMSO): purity ≥99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0065] Polyvinyl alcohol: purity ≥99%, purchased from Sigma-Aldrich;

[0066] Aramid fiber: Kevlar ® PPTA pulp, purchased from DuPont, USA, is a poly(p-phenylene terephthalamide) pulp (PPTA).

[0067] Example 1

[0068] This embodiment provides a high-concentration aramid nanofiber dispersion and its preparation method.

[0069] In this embodiment, the high-concentration aramid nanofiber dispersion is a dispersion of 10 wt% aramid nanofibers.

[0070] Its preparation method includes the following steps:

[0071] S1, Preparation of dispersion solvent: Add 85 g of dimethyl sulfoxide (DMSO) and 5 g of potassium hydroxide (KOH, ground into powder) to a three-necked reactor in sequence. After sealing the three-necked reactor with a magnetic spindle equipped with a stirring paddle, place the device on a temperature-controlled heating jacket and fix it with an iron stand. Control the temperature at 30°C. Connect the magnetic spindle to the stirring control device and turn on the mechanical stirring device (control the speed at 70 r / min) to fully stir the dispersion solvent.

[0072] S2, add 5 g of Kevlar to the dispersion solvent. ® PPTA pulp (aramid fiber) was stirred for 10 h to disperse the aramid fiber, resulting in a 5.26 wt% aramid nanofiber dispersion.

[0073] S3, add 3 g of aramid fiber to the dispersion, control the temperature of the heating jacket at 55℃, and keep stirring for 3 h to obtain an 8.16 wt% aramid nanofiber dispersion;

[0074] S4. Add 2 g of aramid fiber to the dispersion, maintain the temperature at 55℃, and stir for 2 h to obtain a 10 wt% aramid nanofiber dispersion.

[0075] Electron microscopy was used to observe a 10 wt% aramid nanofiber dispersion, and the electron microscopy image is as follows: Figure 1 As shown, the fiber structure in the dispersion is clearly visible.

[0076] The diameter was statistically analyzed, and the results are as follows: Figure 2 As shown, the obtained nanofibers exhibit a uniform diameter distribution (ranging from 16 to 30 nm), primarily concentrated between 20 and 28 nm, with a high aspect ratio. This dispersion can meet the application requirements of various fiber-based materials and has broad prospects.

[0077] Example 2

[0078] This embodiment provides a high-concentration aramid nanofiber dispersion and its preparation method.

[0079] In this embodiment, the high-concentration aramid nanofiber dispersion is a dispersion of 2wt% aramid nanofibers.

[0080] Its preparation method includes the following steps:

[0081] S1, Preparation of dispersion solvent: 93 g of dimethyl sulfoxide (DMSO) and 5 g of potassium hydroxide (KOH, ground into powder) are added sequentially to a three-necked reactor. After sealing the three-necked reactor with a magnetic spindle equipped with a stirring paddle, the device is placed on a temperature-controlled heating jacket and fixed with an iron stand. The temperature is controlled at 30°C. The magnetic spindle is connected to the stirring control device, and the mechanical stirring device is turned on (the speed is controlled at 70 r / min) to fully stir the dispersion solvent.

[0082] S2, add 1 g of Kevlar to the dispersion solvent. ® PPTA pulp (aramid fiber) was stirred for 10 h to disperse the aramid fiber, resulting in a 1.01 wt% aramid nanofiber dispersion.

[0083] S3, add 0.6 g of aramid fiber to the dispersion, control the temperature of the heating jacket at 55℃, and keep stirring for 3 h to obtain a 1.61 wt% aramid nanofiber dispersion;

[0084] S4. Add 0.4 g of aramid fiber to the dispersion, maintain the temperature at 55℃, and stir for 2 h to obtain a 2wt% aramid nanofiber dispersion.

[0085] Comparative Example 1

[0086] This comparative example provides a high-concentration aramid nanofiber dispersion and its preparation method.

[0087] Referring to Example 2, the difference is that a gradual dissolution using a temperature gradient is not used, specifically including:

[0088] S1, Preparation of dispersion solvent: 93 g of dimethyl sulfoxide (DMSO) and 5 g of potassium hydroxide (KOH, ground into powder) were added sequentially to a three-necked reactor. After sealing the three-necked reactor with a magnetic spindle equipped with a stirring paddle, the device was placed on a temperature-controlled heating jacket and fixed with an iron stand. The temperature was controlled at 55°C. The magnetic spindle was connected to the stirring control device, and the mechanical stirring device was turned on (the speed was controlled at 70 r / min) to fully stir the dispersion solvent.

[0089] S2, add 2 g of Kevlar to the dispersion. ® PPTA pulp (aramid fiber) was stirred at 55°C for 24 hours to obtain a 2wt% aramid nanofiber dispersion.

[0090] Electron microscopy was used to observe the aramid nanofiber dispersions in Example 2 and Comparative Example 1, and the electron microscopic images are as follows: Figure 3 As shown, statistical analysis of their diameters revealed a significant difference in fiber diameter between the two, with the comparative fiber diameter being noticeably smaller. This demonstrates that prolonged dissolution in a 55°C environment accelerates fiber decomposition and reduces ANF quality.

[0091] Comparative Example 2

[0092] This comparative example provides an aramid nanofiber dispersion prepared using a potassium tert-butoxide solution system.

[0093] The preparation method is referenced from Chinese invention patent publication number CN115368625A, entitled "An Aramid-Assisted Polyvinyl Alcohol Aerogel, Its Preparation Method and Application". Specifically, it includes:

[0094] 2 g of aramid nanofibers and 2 g of potassium tert-butoxide were added to 96 g of dimethyl sulfoxide and mechanically stirred for 2 days to obtain an aramid nanofiber dispersion with a concentration of 2 wt%.

[0095] Results analysis:

[0096] The 2% aramid nanofiber dispersion prepared using the method of this invention and the 2% aramid nanofiber dispersion prepared using the potassium tert-butoxide system in this comparative example show significant differences in color.

[0097] The results, observed using a scanning electron microscope, are as follows: Figure 4 As shown, the structure of nanofibers could no longer be observed in the dispersion prepared by dissolving the system with potassium tert-butoxide. The dissolution level of this method is considered to be from the perspective of molecular structure.

[0098] The above-mentioned appearance characterization and scanning electron microscopy test results fully demonstrate that, compared with the potassium tert-butoxide preparation system, the preparation method of the present invention has significant technical advantages, and can stably prepare a high-concentration and morphologically complete aramid nanofiber dispersion, effectively ensuring the structural integrity of the aramid nanofibers; the potassium tert-butoxide system will cause irreversible damage to the structure of aramid nanofibers, resulting in the complete disappearance of the nanofiber structure, and it is impossible to prepare a qualified aramid nanofiber dispersion.

[0099] Example 3

[0100] This embodiment provides a method for preparing high-performance aramid nanofiber-based hydrogel materials.

[0101] Includes the following steps:

[0102] S1, 20 g of polyvinyl alcohol and 80 g of dimethyl sulfoxide are added to a reagent bottle in sequence, and the mixture is magnetically stirred at 95°C for 24 h to obtain a 20%wt polyvinyl alcohol solution.

[0103] S2, 2 g of the 10%wt aramid nanofiber dispersion from Example 1 and 2 g of the 2%wt aramid nanofiber dispersion from Example 2 were added to a beaker with 5 g of 20%wt polyvinyl alcohol solution, and stirred at 60°C for 1 min to obtain a mixture of the two.

[0104] S3, the mixture in S2 is transferred to a polytetrafluoroethylene mold, and the mold is placed in deionized water for 12 h to obtain aramid nanofiber-polyvinyl alcohol composite hydrogel prepared by 10% aramid nanofiber dispersion and aramid nanofiber-polyvinyl alcohol composite hydrogel prepared by 2% aramid nanofiber dispersion, namely aramid nanofiber-based hydrogel.

[0105] The prepared aramid nanofiber-based hydrogel is shown in the figure. Figure 5 As shown in the figure, the first and second from the left are aramid nanofiber-polyvinyl alcohol composite hydrogels (2%ANF) prepared with 2% aramid nanofiber dispersion, and the first and second from the right are aramid nanofiber-polyvinyl alcohol composite hydrogels (10%ANF) prepared with 10% aramid nanofiber dispersion.

[0106] The mechanical tensile properties of this hydrogel material were tested using a material tensile testing machine. The test results are as follows: Figure 6 As shown, the strength of the 10% aramid nanofiber dispersion composite hydrogel (10% ANF) is significantly stronger than that of the 2% aramid nanofiber dispersion composite hydrogel (2% ANF).

Claims

1. A method for preparing a high-concentration aramid nanofiber dispersion, characterized in that, The preparation method includes the following steps: S1, prepare a solution of dimethyl sulfoxide and potassium hydroxide, and heat and stir under sealed conditions until the potassium hydroxide is completely dissolved to obtain a dispersion solvent; S2, add aramid fibers to the dispersion solvent, heat and stir at 25~35℃ for 8~10 h to obtain the first aramid nanofiber dispersion; S3, add aramid fibers to the first aramid nanofiber dispersion, heat and stir at 50~60℃ for 2~4 h to obtain the second aramid nanofiber dispersion; S4, add aramid fibers to the second aramid nanofiber dispersion, heat and stir at 50~60℃ for 2~4 h to obtain a high-concentration nanofiber dispersion; in: The mass of aramid fiber added in step S2 is greater than the mass of aramid fiber added in step S3, and the mass of aramid fiber added in step S3 is greater than the mass of aramid fiber added in step S4. The mass of aramid fiber added in step S2 is equal to the sum of the mass of aramid fiber added in steps S3 and S4. The ratio of the total mass of the added aramid fibers to the total mass of dimethyl sulfoxide and potassium hydroxide is 1:49 to 1:

9.

2. The method for preparing the high-concentration aramid nanofiber dispersion according to claim 1, characterized in that, In the dispersion, the diameter of the aramid nanofibers is 16~30 nm.

3. The method for preparing the high-concentration aramid nanofiber dispersion according to claim 2, characterized in that, The In step S2, the heating and stirring conditions include: 30°C, 70 r / min rotation speed, and 10 h time; In step S3, the heating and stirring conditions include: 55℃; rotation speed of 70 r / min; and time of 3 h. In step S4, the heating and stirring conditions include: 55°C; rotation speed of 70 r / min; and time of 2 h.

4. The application of the high-concentration aramid nanofiber dispersion prepared by the method of any one of claims 1-3 in the preparation of hydrogels.

5. A method for preparing an aramid nanofiber-based hydrogel, characterized in that, The method includes: Prepare a 15% wt~25% wt polyvinyl alcohol solution; The high-concentration aramid nanofiber dispersion prepared by any one of the methods described in claims 1-3 is mixed with a polyvinyl alcohol solution and stirred at 50-70°C to obtain a mixture. The mixture was transferred to a mold, and the mold was placed in deionized water for 10-15 h to obtain aramid nanofiber-based hydrogel.

6. The method for preparing aramid nanofiber-based hydrogel according to claim 5, characterized in that, The mass ratio of the high-concentration aramid nanofiber dispersion to the polyvinyl alcohol solution is 1:(2~3).

7. An aramid nanofiber-based hydrogel, characterized in that, The aramid nanofiber-based hydrogel is prepared by the preparation method described in claim 5 or 6.

8. The aramid nanofiber-based hydrogel according to claim 7, characterized in that, The tensile strength of the aramid nanofiber-based hydrogel reaches 4.45 MPa.

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