A twisted interlocking structure stretchable carbon nanofiber aerogel and its preparation method

Abstract

This invention discloses a twisted interlocking structure stretchable carbon nanofiber aerogel and its preparation method. The aerogel uses spring-like helical coiled fibers as structural units, formed by the continuous twisting and interlocking of multiple helical coiled fibers along their length. The method includes the following steps: first, mixing a polymer, solvent, and moisture content regulator to prepare a spinning solution sensitive to the moisture content of the spinning environment; then, controlling the temperature and humidity of the electrospinning environment to create a humidity gradient between the high moisture content in the environment and the low moisture content of the spinning solution, inducing rapid and premature solidification of the electrospinning jet to obtain a twisted interlocking structure stretchable carbon nanofiber aerogel precursor; and finally, obtaining the final product through pre-oxidation and carbonization. This invention solves the problem of insufficient stretchability of carbon nanofiber aerogels; moreover, the preparation method of this invention is simple, easy to implement, and continuous, and can be carried out on existing electrospinning production equipment.

Description

Technical Field

[0001] This invention relates to a twisted interlocking structure stretchable carbon nanofiber aerogel and its preparation method, belonging to the field of nanomaterials technology. Background Technology

[0002] Carbon aerogels possess a three-dimensional network porous structure, exhibiting excellent properties such as high porosity, large specific surface area, low density, high electrical conductivity, and low thermal conductivity. They also possess chemical inertness and selective adsorption, making them ideal materials for energy storage, electromagnetic shielding, electrocatalysis, high-temperature insulation, and separation filtration. Traditional carbon aerogels consist of a three-dimensional network of interconnected nanoparticles, but the lack of effective interparticle connections results in significant brittleness, making them difficult to use alone. Introducing reinforcing / toughening components such as whiskers and fibers can improve the mechanical strength of particulate aerogels, but the composites still suffer from problems such as easy powder detachment and poor deformation capacity, seriously affecting their safety and reliability during use. In recent years, elastic carbon aerogels based on fine microstructure design have been extensively studied. Using carbon nanotubes and graphene as building blocks, a series of self-supporting carbon aerogels have been developed, transforming their internal structure from fragile particle connections to continuous self-assembled networks or face-to-face stacked structures, endowing the materials with a certain degree of compressive resilience. However, this structure contains a large number of fixed connection points or non-stretchable sheet structures, which can lead to transient structural damage or failure even under very small tensile strains, limiting its practical application prospects. Using flexible nanofibers with high aspect ratio and good continuity as building blocks, intertwined and relatively sliding connection structures can be formed inside the aerogel, which is expected to solve the bottleneck problem of poor tensile properties of carbon aerogels.

[0003] Common methods for preparing carbon nanofiber aerogels include biomass carbonization and freeze-drying. Chinese invention patent application CN201410227565.3 discloses a method for preparing carbon nanofiber aerogel oil-absorbing materials using bacterial cellulose. Cultured bacterial cellulose is prepared into a hydrogel, dried to obtain a bacterial cellulose aerogel, and then subjected to thermal pyrolysis under an argon atmosphere to obtain the carbon nanofiber aerogel. Chinese invention patent application CN202211050959.7 discloses a carbon nanofiber aerogel and its application in fire-resistant and heat-insulating materials. Modified phenolic resin is dissolved in ethanol to obtain a spinning solution, which is then subjected to a series of treatments including electrospinning, carbonization, homogenization, and freeze-drying to prepare the carbon nanofiber aerogel. The above preparation methods are complex and cumbersome, and the preparation process is discontinuous. Chinese invention patent application CN202011386739.2 discloses a method for rapidly preparing graphene fiber aerogels. This method utilizes an airflow-blown spinning process to form a self-supporting carbon nanofiber aerogel precursor in one step, followed by vacuum high-temperature setting to obtain the final product. However, this method suffers from insufficient tensile strength, resulting in a loose and random structure in the prepared fiber aerogel. The material exhibits poor overall uniformity and is prone to localized stress unevenness under tensile stress, leading to structural damage.

[0004] Therefore, there is a need to develop a simple, easy-to-implement, and continuous process to prepare carbon nanofiber aerogels with excellent tensile properties to meet the application needs of various fields. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a twisted interlocking structure stretchable carbon nanofiber aerogel and its preparation method.

[0006] This invention controls the degree of phase separation in the spinning solution before and after electrospinning by adjusting the water content. First, a polymer insoluble in water and a solvent miscible with water are selected. By adding a water content regulator, the spinning solution is transformed from a stable state of homogeneous coexistence to a metastable limit stage. Then, the temperature and humidity of the spinning environment are controlled to create a humidity gradient between the high water vapor content in the environment and the low water content of the spinning solution. During the spinning process, when water vapor enters the jet, its water content exceeds the critical value, and the spinning solution instantly breaks through the metastable limit stage of homogeneous coexistence and enters an unstable state. The solvent and polymer spontaneously separate, ensuring rapid jet solidification in advance. This allows the jet to undergo sufficient whipping and stretching while flying in the spinning area, while retaining its spring-like helical coil shape during the intense whipping process. This forms spring-like helical coiled fibers that can be stretched and torsional deformed. Multiple strands of helical coiled fibers continuously twist each other along the length direction to form a stretchable interlocking network connection structure, thereby obtaining a stretchable carbon nanofiber aerogel precursor with a twisted interlocking structure. Finally, the final product is obtained through pre-oxidation and carbonization. This invention solves the problem of insufficient stretchability of carbon nanofiber aerogels; moreover, the preparation method of this invention is simple and easy to implement, and the process is continuous, and can be carried out on existing electrospinning production equipment.

[0007] To solve the above problems, the present invention is achieved through the following technical solution:

[0008] This invention provides a twisted interlocking structure of stretchable carbon nanofiber aerogel. The carbon nanofiber aerogel uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0009] Preferably, the carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio ≥1000 and a diameter of 50–1000 nm, wherein the coiling rate of the helical coiled fibers is 10–40%, and the density of the twisted interlocking structure is 100–1000 fibers / cm². 3 .

[0010] Preferably, the carbon nanofiber aerogel has a pore size of 1–5 μm and a bulk density of 5–100 mg / cm³. 3 The thickness ranges from 2 to 50 mm.

[0011] Preferably, the carbon nanofiber aerogel has a tensile modulus of 2-20 kPa, a tensile breaking strength of 10-50 kPa, can fully recover when stretched to 50-150% of its own length, has a plastic deformation of ≤10% after 1000 load-unload tensile cycles at 50% strain, and can be cyclically stretched 10-1000 times in the range of -100℃ to 500℃ without breaking.

[0012] This invention also provides a method for preparing the above-mentioned twisted interlocking structure stretchable carbon nanofiber aerogel, comprising the following steps:

[0013] Step 1): Dissolve the polymer in a solvent, and prepare a homogeneous and stable polymer base liquid after heating and stirring;

[0014] Step 2): Add the water content regulator to the polymer base liquid obtained in step 1), and prepare a metastable limiting stage spinning solution with homogeneous coexistence by heating and stirring;

[0015] Step 3): Electrospin the spinning solution obtained in step 2). Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, the solvent and polymer spontaneously separate, the jet is fast and solidifies in advance, forming spiral coiled fibers and twisting and interlocking to form carbon nanofiber aerogel precursor.

[0016] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0017] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from step 4) is placed in a vacuum tube furnace for carbonization to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0018] Preferably, in step 1), the polymer includes any one or more of polyacrylonitrile, polyvinyl butyral, polymethyl methacrylate, polyvinylidene fluoride, asphalt, polystyrene, and polyethylene; the solvent includes any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, tetrahydrofuran, N-methylpyrrolidone, and methanol; the polymer base liquid has a mass fraction of 5-20%; the heating and stirring temperature is 40-90°C; the stirring speed is 120-1000 rpm; and the stirring time is 2-10 h.

[0019] Preferably, in step 2), the water content regulator is a hydrate, including any one or more of barium chloride dihydrate, copper sulfate pentahydrate, aluminum chloride hexahydrate, chromium trichloride hexahydrate, ferrous sulfate heptahydrate, zinc sulfate heptahydrate, and potassium aluminum sulfate dodecahydrate; the amount of water content regulator added is 1-10% of the mass of the spinning solution; the heating and stirring temperature is 40-90℃, the stirring speed is 120-1000 rpm, and the stirring time is 2-10 h.

[0020] Preferably, in step 3), the electrospinning environment temperature is 20-35℃ and the environment humidity is 30-60%; the electrospinning process parameters are: voltage 10-100kV, receiving distance 10-50cm, and injection speed 1-100mL / h.

[0021] Preferably, in step 4), the pre-oxidation temperature is 180–300°C, and the holding time is 60–120 min.

[0022] Preferably, in step 5), the high-temperature carbonization atmosphere in the vacuum tube furnace is nitrogen or argon, and the temperature is raised to a high temperature of 400-1300°C at a heating rate of 1-10°C / min, and the holding time at the high temperature is 60-120 min.

[0023] The principle of this invention is as follows:

[0024] This invention prepares a spinning solution sensitive to the moisture content of the spinning environment by controlling the types and proportions of polymers, solvents, and water content regulators. First, selecting a water-insoluble polymer and a water-miscible solvent is a prerequisite for phase separation between the polymer and solvent during the subsequent spinning process. Simultaneously, in preparing a homogeneous and stable spinning solution, increasing the proportion of the water content regulator promotes the binodal line and swirl line in the ternary phase diagram of the polymer-solvent-water system to approach the polymer-solvent axis as closely as possible. This reduces the homogeneous coexistence stable region to the left of the binodal line and the metastable region between the binodal line and the swirl line, while increasing the homogeneous coexistence unstable region to the right of the swirl line. Ultimately, this adjusts the spinning solution from a homogeneous stable state to the limit stage of the metastable-to-unstable transition. At this point, no phase separation effect occurs between the solvent and polymer, but a slight increase in the water content within the system will cause the spinning solution to break through the metastable limit and become unstable, resulting in transient phase separation. Therefore, in the subsequent electrospinning stage, after the water vapor in the environment enters the jet, the water content of the spinning solution quickly exceeds the critical value, and the spinning solution system then changes from the metastable limit stage to the unstable state. At this time, the solvent and polymer spontaneously separate, the solvent evaporates rapidly, and the polymer is enriched and precipitated, thereby enabling the jet to solidify into helical crimped fibers quickly and in advance.

[0025] The spirally coiled fibers and their twisted interlocking structure obtained in this invention are key to the stretchability of carbon nanofiber aerogels. When the proportion of water content regulator in the spinning solution is low, the solvent in the jet evaporates slowly, and the polymer accumulates slowly, thus slowing down the curing rate and delaying the curing sites. The jet is continuously subjected to an electric field force in the axial direction, causing the coiled structure to be slowly stretched, reducing its degree of coiling, and thus obtaining straight fibers. The carbon nanofiber aerogel precursor, constructed from straight fibers, exhibits an interlocking and stacked structure, leading to poor uniformity and easy delamination, which affects its tensile properties. When the water content regulator in the spinning solution increases to a critical value, the solvent in the jet evaporates rapidly, the polymer accumulates quickly, the curing rate accelerates, and the curing sites are advanced. This allows the jet to undergo sufficient whipping and stretching during its flight in the spinning region, while retaining its spring-like helical coiled shape during the intense whipping process. Multiple helical coiled jets continuously twist and intertwine with each other along the length direction of the curing front, ultimately resulting in a stretchable, interlocking network connection structure for the carbon nanofiber aerogel precursor. When the water content regulator in the spinning solution is too high, it will affect the fiber morphology and mechanical properties. Therefore, the spinning solution preparation and spinning process control method of this invention can ensure good spinning results.

[0026] Compared to traditional aerogels, helical coiled fibers and their interlocking twisted structures impart excellent stretchability to the material at the same bulk density. The structural units of carbon nanofiber aerogels possess a highly elastic morphology, capable of withstanding external stress through elongation and torsional deformation via their spring-like helical coiled structures, and returning to their original shape after stress removal. Simultaneously, the continuous interlocking twisted network between fibers allows for fiber slippage but restricts fiber detachment. This elastic fiber structure and abundant inter-fiber elastic connection sites reduce plastic deformation and fracture caused by tensile stress concentration, resulting in excellent tensile modulus, tensile fracture strength, tensile recovery, fatigue resistance, and mechanical stability in extreme temperature environments. This self-supporting, interlocking twisted structure of helical coiled fibers enhances the performance of carbon nanofiber aerogels in complex mechanical environments.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention provides a twisted interlocking structure stretchable carbon nanofiber aerogel and its preparation method, which is simple, easy to implement and has a continuous process. It can be obtained by using the corresponding spinning solution and adjusting the spinning process on existing electrospinning production equipment.

[0029] (2) The twisted interlocking structure stretchable carbon nanofiber aerogel prepared by the present invention has excellent tensile modulus, tensile fracture strength, tensile recovery, fatigue resistance and mechanical stability in extreme temperature environment, which can meet the application needs of carbon nanofiber aerogel in various fields. Detailed Implementation

[0030] To make the present invention more apparent and understandable, preferred embodiments are described in detail below.

[0031] Example 1

[0032] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0033] Step 1): Polyacrylonitrile was dissolved in N,N-dimethylformamide and heated and stirred (heating and stirring temperature 40℃, stirring speed 400rpm, stirring time 5h) to prepare a homogeneous and stable polymer base liquid with a mass fraction of 5%.

[0034] Step 2): Add the water content regulator aluminum chloride hexahydrate to the polymer base liquid obtained in step 1), and prepare a homogeneous metastable limit stage spinning solution by heating and stirring (heating and stirring temperature 40℃, stirring speed 400rpm, stirring time 5h). The amount of water content regulator added is 1% of the mass of the spinning solution.

[0035] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 20℃ and the ambient humidity is 30%. The process parameters of the electrospinning are: voltage 10kV, receiving distance 10cm, and infusion rate 1mL / h.

[0036] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 180℃, holding time 60min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0037] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is nitrogen, the temperature is increased to 400℃ at a heating rate of 1℃ / min, and the holding time at the high temperature is 60min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0038] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0039] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 1000 and a diameter of 50 nm. The coiling rate of the helical coiled fibers is 10%, and the density of the twisted interlocking structure is 100 fibers / cm². 3The carbon nanofiber aerogel has a pore size of 1 μm and a bulk density of 5 mg / cm³. 3 The thickness is 2mm.

[0040] The carbon nanofiber aerogel has a tensile modulus of 2 kPa, a tensile breaking strength of 10 kPa, and can fully recover when stretched to 50% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 10%. It can be cyclically stretched 10 times in the range of -100℃ to 500℃ without breaking.

[0041] Example 2

[0042] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0043] Step 1): Polyacrylonitrile and polyvinyl butyral were dissolved in N,N-dimethylformamide and heated and stirred (heating and stirring temperature 50℃, stirring speed 600rpm, stirring time 5h) to prepare a homogeneous stable polymer base liquid with a mass fraction of 20%.

[0044] Step 2): Add copper sulfate pentahydrate, a water content regulator, to the polymer base solution obtained in Step 1). After heating and stirring (heating and stirring temperature 50℃, stirring speed 600rpm, stirring time 5h), a metastable limiting stage spinning solution with homogeneous coexistence is prepared. The amount of water content regulator added is 10% of the mass of the spinning solution.

[0045] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 25℃ and the ambient humidity is 60%. The process parameters of the electrospinning are: voltage 20kV, receiving distance 20cm, and infusion rate 100mL / h.

[0046] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 230℃, holding time 65min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0047] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is nitrogen, the temperature is increased to 1300℃ at a heating rate of 5℃ / min, and the holding time at the high temperature is 65min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0048] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0049] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 1500 and a diameter of 200 nm. The coiling rate of the helical coiled fibers is 40%, and the density of the twisted interlocking structure is 1000 fibers / cm². 3 The carbon nanofiber aerogel has a pore size of 5 μm and a bulk density of 100 mg / cm³. 3 The thickness is 50mm.

[0050] The carbon nanofiber aerogel has a tensile modulus of 20 kPa, a tensile breaking strength of 50 kPa, and can fully recover when stretched to 150% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 5%. It can be cyclically stretched 1000 times in the range of -100℃ to 500℃ without breaking.

[0051] Example 3

[0052] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0053] Step 1): Polymethyl methacrylate was dissolved in N,N-dimethylformamide and heated and stirred (heating and stirring temperature 65℃, stirring speed 500rpm, stirring time 6h) to prepare a homogeneous and stable polymer base liquid with a mass fraction of 18%.

[0054] Step 2): Add barium chloride dihydrate, a water content regulator, to the polymer base liquid obtained in Step 1). Prepare a metastable spinning solution with homogeneous coexistence by heating and stirring (heating and stirring temperature 65℃, stirring speed 500rpm, stirring time 6h). The amount of water content regulator added is 9% of the mass of the spinning solution.

[0055] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 27℃ and the ambient humidity is 36%. The process parameters of the electrospinning are: voltage 42kV, receiving distance 32cm, and infusion rate 35mL / h.

[0056] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 300℃, holding time 120min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0057] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is nitrogen, the temperature is increased to 900℃ at a heating rate of 7℃ / min, and the holding time at the high temperature is 120min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0058] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0059] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 2500 and a diameter of 500 nm. The coiling rate of the helical coiled fibers is 27%, and the density of the twisted interlocking structure is 450 fibers / cm². 3 The carbon nanofiber aerogel has a pore size of 2.8 μm and a bulk density of 59 mg / cm³. 3 The thickness is 45mm.

[0060] The carbon nanofiber aerogel has a tensile modulus of 10 kPa, a tensile breaking strength of 46 kPa, and can fully recover when stretched to 129% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 7%. It can be cyclically stretched 713 times in the range of -100℃ to 500℃ without breaking.

[0061] Example 4

[0062] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0063] Step 1): Polyvinylidene fluoride was dissolved in N,N-dimethylacetamide, N,N-dimethylformamide and acetone, and heated and stirred (heating and stirring temperature 90℃, stirring speed 400rpm, stirring time 2h) to prepare a homogeneous stable polymer base liquid with a mass fraction of 15%.

[0064] Step 2): Add the water content regulator zinc sulfate heptahydrate to the polymer base liquid obtained in step 1), and prepare a homogeneous metastable limit stage spinning solution by heating and stirring (heating and stirring temperature 90℃, stirring speed 400rpm, stirring time 2h). The amount of water content regulator added is 7% of the mass of the spinning solution.

[0065] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 35℃ and the ambient humidity is 43%. The process parameters of the electrospinning are: voltage 100kV, receiving distance 40cm, and infusion rate 29mL / h.

[0066] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 280℃, holding time 100min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0067] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is argon, the temperature is increased to 960℃ at a heating rate of 10℃ / min, and the holding time at the high temperature is 100min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0068] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0069] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 3500 and a diameter of 700 nm. The coiling rate of the helical coiled fibers is 38%, and the density of the twisted interlocking structure is 900 fibers / cm². 3 The carbon nanofiber aerogel has a pore size of 3.6 μm and a bulk density of 41 mg / cm³. 3 The thickness is 18mm.

[0070] The carbon nanofiber aerogel has a tensile modulus of 18 kPa, a tensile breaking strength of 47 kPa, and can fully recover when stretched to 145% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 6%. It can be cyclically stretched 826 times in the range of -100℃ to 500℃ without breaking.

[0071] Example 5

[0072] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0073] Step 1): Dissolve asphalt in tetrahydrofuran and N,N-dimethylformamide, and prepare a homogeneous stable polymer base liquid by heating and stirring (heating and stirring temperature 45℃, stirring speed 700rpm, stirring time 8h). The mass fraction of the polymer base liquid is 9%.

[0074] Step 2): Add the water content regulator potassium aluminum sulfate dodecahydrate to the polymer base liquid obtained in step 1), and prepare a homogeneous metastable limit stage spinning solution by heating and stirring (heating and stirring temperature 45℃, stirring speed 700rpm, stirring time 8h). The amount of water content regulator added is 9% of the mass of the spinning solution.

[0075] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 27℃ and the ambient humidity is 38%. The process parameters of the electrospinning are: voltage 72kV, receiving distance 50cm, and infusion rate 50mL / h.

[0076] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 195℃, holding time 85min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0077] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is nitrogen, the temperature is increased to 1000℃ at a heating rate of 5℃ / min, and the holding time at the high temperature is 85min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0078] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0079] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 1900 and a diameter of 350 nm. The coiling rate of the helical coiled fibers is 30%, and the density of the twisted interlocking structure is 580 fibers / cm². 3 The carbon nanofiber aerogel has a pore size of 1.8 μm and a bulk density of 50 mg / cm³. 3 The thickness is 33mm.

[0080] The carbon nanofiber aerogel has a tensile modulus of 9 kPa, a tensile breaking strength of 27 kPa, and can fully recover when stretched to 125% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 8%. It can be cyclically stretched 550 times in the range of -100℃ to 500℃ without breaking.

[0081] Example 6

[0082] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0083] Step 1): Polystyrene was dissolved in tetrahydrofuran and N,N-dimethylformamide, and a homogeneous stable polymer base liquid was prepared by heating and stirring (heating and stirring temperature 70℃, stirring speed 120rpm, stirring time 10h). The mass fraction of the polymer base liquid was 20%.

[0084] Step 2): Add the water content regulator chromium trichloride hexahydrate to the polymer base liquid obtained in Step 1), and prepare a homogeneous metastable limit stage spinning solution by heating and stirring (heating and stirring temperature 70℃, stirring speed 120rpm, stirring time 10h). The amount of water content regulator added is 8% of the mass of the spinning solution.

[0085] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 25℃ and the ambient humidity is 31%. The process parameters of the electrospinning are: voltage 89kV, receiving distance 19cm, and infusion rate 40mL / h.

[0086] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 200℃, holding time 70min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0087] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is nitrogen, the temperature is increased to 700℃ at a heating rate of 4℃ / min, and the holding time at the high temperature is 70min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0088] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0089] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 1800 and a diameter of 1000 nm. The coiling rate of the helical coiled fibers is 22%, and the density of the twisted interlocking structure is 750 fibers / cm². 3 The carbon nanofiber aerogel has a pore size of 2.6 μm and a bulk density of 37 mg / cm³. 3 The thickness is 28mm.

[0090] The carbon nanofiber aerogel has a tensile modulus of 15 kPa, a tensile breaking strength of 39 kPa, and can fully recover when stretched to 132% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 6%. It can be cyclically stretched 770 times in the range of -100℃ to 500℃ without breaking.

[0091] Example 7

[0092] A method for preparing a twisted interlocking structure stretchable carbon nanofiber aerogel includes the following steps:

[0093] Step 1): Polyethylene was dissolved in N-methylpyrrolidone, tetrahydrofuran, methanol, and N,N-dimethylacetamide. The mixture was heated and stirred (heating and stirring temperature 55℃, stirring speed 1000rpm, stirring time 6h) to prepare a homogeneous and stable polymer base liquid with a mass fraction of 19%.

[0094] Step 2): Add the water content regulator ferrous sulfate heptahydrate to the polymer base liquid obtained in step 1), and prepare a metastable limit stage spinning solution with homogeneous coexistence by heating and stirring (heating and stirring temperature 55℃, stirring speed 1000rpm, stirring time 6h). The amount of water content regulator added is 5% of the mass of the spinning solution.

[0095] Step 3): The spinning solution obtained in Step 2) is subjected to electrospinning. Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, and the solvent and polymer spontaneously separate. The jet is rapid and solidifies in advance, forming helical coiled fibers that twist and interlock to form a carbon nanofiber aerogel precursor. The electrospinning environment temperature is 25℃ and the ambient humidity is 50%. The process parameters of the electrospinning are: voltage 43kV, receiving distance 20cm, and infusion rate 70mL / h.

[0096] Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation (temperature 220℃, holding time 95min) to prepare the pre-oxidized carbon nanofiber aerogel precursor.

[0097] Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization (the high-temperature carbonization atmosphere is argon, the temperature is increased to 600℃ at a heating rate of 7℃ / min, and the holding time at the high temperature is 95min) to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

[0098] The carbon nanofiber aerogel prepared above uses spring-like helical coiled fibers that can be stretched and twisted as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along the length direction to form a stretchable interlocking network connection structure.

[0099] The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio of 2700 and a diameter of 180 nm. The coiling rate of the helical coiled fibers is 35%, and the density of the twisted interlocking structure is 820 fibers / cm². 3 The carbon nanofiber aerogel has a pore size of 2.5 μm and a bulk density of 80 mg / cm³. 3 The thickness is 42mm.

[0100] The carbon nanofiber aerogel has a tensile modulus of 9 kPa, a tensile breaking strength of 26 kPa, and can fully recover when stretched to 110% of its own length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 9%. It can be cyclically stretched 490 times in the range of -100℃ to 500℃ without breaking.

[0101] Comparative Example 1

[0102] Carbon nanofiber aerogels were prepared according to the method in Example 1, except that the amount of water content regulator added was 0.5% of the spinning solution mass, resulting in a densely bonded carbon nanofiber material. The collected densely bonded carbon nanofiber material was then pre-oxidized and carbonized.

[0103] The carbon nanofibers obtained in this example have an aspect ratio of 1000, a diameter of 200 nm, a crimp rate of 0.8%, and a twisted interlocking structure density of 10 nanofibers / cm². 3 The obtained carbon nanofiber material has a pore size of 1 μm and a bulk density of 110 mg / cm³. 3 The aerogel exhibits the following properties: thickness 1 mm, tensile modulus 0.9 kPa, tensile breaking strength 4.8 kPa, complete recovery when stretched to 20% of its length, 11% plastic deformation after 1000 load-unload tensile cycles at 50% strain, and the ability to withstand 4 cyclic stretching cycles within a temperature range of -100℃ to 500℃ without fracture. This comparative example shows that when the water content regulator is added at 0.5% of the spinning solution mass, the polymer and solvent in the spinning solution coexist homogeneously, and sufficient phase separation does not occur during the spinning stage. The fibers exhibit a dense, adhesive structure, failing to form a twisted, interlocking, stretchable network connection structure. Therefore, when the proportion of water content regulator is insufficient, the carbon nanofiber aerogel with the properties required by this invention cannot be obtained.

[0104] Comparative Example 2

[0105] Carbon nanofiber aerogels were prepared according to the method in Example 1, except that the amount of water content regulator added was 15% of the spinning solution mass. After about 5 minutes of spinning, the needle became clogged, preventing continuous material preparation. The collected small amount of carbon nanofiber aerogel precursor was pre-oxidized and carbonized.

[0106] The carbon nanofibers obtained in this example have an aspect ratio of 1000, a diameter of 800 nm, a crimp rate of 6%, and a twisted interlocking structure density of 50 nanofibers / cm². 3 The obtained carbon nanofiber aerogel has a pore size of 6 μm and a bulk density of 100 mg / cm³. 3 The material has a thickness of 0.5 mm, a tensile modulus of 1 kPa, a tensile breaking strength of 5 kPa, and can fully recover when stretched to 21% of its length. After 1000 load-unload tensile cycles at 50% strain, its plastic deformation is 12%. It can be cyclically stretched four times within a temperature range of -100℃ to 500℃ without breaking. This comparative example shows that when the water content regulator is added at 15% of the spinning solution mass, the spinning solution is spinnable. However, because the proportion of water content regulator is too high, phase separation occurs at the spinning needle. The polymer accumulates and precipitates at the needle, causing blockage of the spinning needle and affecting the continuity of spinning and production efficiency.

[0107] Comparative Example 3

[0108] Carbon nanofiber aerogels were prepared according to the method in Example 1, except that the spinning environment humidity was 25%, resulting in a carbon nanofiber aerogel precursor composed of straight fibers. The collected carbon nanofiber aerogel precursor composed of straight fibers was then pre-oxidized and carbonized.

[0109] The carbon nanofibers obtained in this example, composed of straight fibers, have an aspect ratio of 1100, a diameter of 700 nm, a crimp rate of 4%, and a twisted interlocking structure density of 30 fibers / cm². 3 The obtained carbon nanofiber aerogel has a pore size of 3 μm and a bulk density of 70 mg / cm³. 3 The material has a thickness of 1.5 mm, a tensile modulus of 1 kPa, a tensile breaking strength of 6.5 kPa, and can fully recover when stretched to 20% of its length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 11%. It can be cyclically stretched 4 times within a temperature range of -100℃ to 500℃ without breaking. This comparative example shows that under a spinning environment humidity of 25%, the low humidity means insufficient moisture to induce rapid phase separation in the jet, resulting in delayed solidification of the jet. The jet is continuously subjected to an electric field in the axial direction, and its coiled structure is slowly stretched straight, thus obtaining straight fibers. The fibers cannot twist and interlock to form a stretchable network connection structure. The resulting material has poor tensile properties compared to Example 1 and does not meet the requirements of the material developed in this invention.

[0110] Comparative Example 4

[0111] Carbon nanofiber aerogels were prepared according to the method in Example 1, except that the spinning environment humidity was 65%, resulting in a carbon nanofiber aerogel precursor composed of low-curvature fibers. The collected carbon nanofiber aerogel precursor composed of low-curvature fibers was then pre-oxidized and carbonized.

[0112] The carbon nanofibers obtained in this example, composed of low-curvature fibers, have an aspect ratio of 1100, a diameter of 600 nm, a curvature of 5%, and a twisted interlocking structure density of 40 fibers / cm². 3 The obtained carbon nanofiber aerogel has a pore size of 2 μm and a bulk density of 60 mg / cm³. 3 The material has a thickness of 1.8 mm, a tensile modulus of 1.2 kPa, a tensile breaking strength of 7 kPa, and can fully recover when stretched to 29% of its length. After 1000 load-unload tensile cycles at 50% strain, the plastic deformation is 10%. It can be cyclically stretched 5 times within a temperature range of -100℃ to 500℃ without breaking. This comparative example shows that under a spinning environment humidity of 65%, the high humidity reduces the solvent evaporation rate in the spinning solution, inhibiting phase separation. The jet is continuously subjected to an electric field in the axial direction, resulting in reduced crimp and preventing the fibers from twisting and interlocking to form abundant stretchable network connection points. The resulting material has poorer tensile properties than Example 1 and does not meet the requirements of the material developed in this invention.

Claims

1. A twisted interlocking structure stretchable carbon nanofiber aerogel, characterized in that, The carbon nanofiber aerogel uses stretchable and torsional deformable spring-like helical coiled fibers as building blocks. Multiple strands of helical coiled fibers are continuously twisted together along their length to form a stretchable interlocking network structure. The coiled fiber crimp rate is 10-40%, and the density of the torsion interlocking structure is 100-1000 fibers / cm². 3 The carbon nanofiber aerogel has a tensile modulus of 2~20 kPa, a tensile breaking strength of 10~50 kPa, and can fully recover when stretched to 50~150% of its own length. After 1000 loading-unloading tensile cycles at 50% strain, the plastic deformation is ≤10%. It can be cyclically stretched 10~1000 times in the range of -100℃ to 500℃ without breaking.

2. The twisted interlocking structure stretchable carbon nanofiber aerogel according to claim 1, characterized in that, The carbon nanofiber aerogel is composed of helical coiled fibers with an aspect ratio ≥1000 and a diameter of 50~1000nm.

3. The twisted interlocking structure stretchable carbon nanofiber aerogel according to claim 1, characterized in that, The carbon nanofiber aerogel has a pore size of 1~5μm and a bulk density of 5~100mg / cm³. 3 The thickness is 2~50mm.

4. The method for preparing the twisted interlocking structure stretchable carbon nanofiber aerogel according to any one of claims 1-3, characterized in that, The following steps are involved: Step 1): Dissolve the polymer in a solvent, and prepare a stable polymer-based liquid with homogeneous coexistence after heating and stirring; Step 2): Add the water content regulator to the polymer base liquid obtained in Step 1), and prepare a spinning solution in the metastable limit stage with homogeneous coexistence by heating and stirring; Step 3): Electrospinning is performed on the spinning solution obtained in Step 2). Water vapor in the spinning environment diffuses into the interior of the electrospinning jet, the solvent and polymer spontaneously separate, the jet is fast and solidifies in advance, forming spiral coiled fibers and twisting and interlocking to form carbon nanofiber aerogel precursor. Step 4): Place the carbon nanofiber aerogel precursor obtained in step 3) in an oven for pre-oxidation to prepare the pre-oxidized carbon nanofiber aerogel precursor. Step 5): The pre-oxidized carbon nanofiber aerogel precursor from Step 4) is placed in a vacuum tube furnace for carbonization to prepare a stretchable carbon nanofiber aerogel with a twisted interlocking structure.

5. The preparation method according to claim 4, characterized in that, In step 1), the polymer includes any one or more of polyacrylonitrile, polyvinyl butyral, polymethyl methacrylate, polyvinylidene fluoride, asphalt, polystyrene, and polyethylene; the solvent includes any one or more of N,N-dimethylformamide, N,N-dimethylacetamide, acetone, tetrahydrofuran, N-methylpyrrolidone, and methanol; the mass fraction of the polymer base liquid is 5-20%; the heating and stirring temperature is 40-90℃, the stirring speed is 120-1000 rpm, and the stirring time is 2-10 h.

6. The preparation method according to claim 4, characterized in that, In step 2), the water content regulator is a hydrate, including any one or more of barium chloride dihydrate, copper sulfate pentahydrate, aluminum chloride hexahydrate, chromium trichloride hexahydrate, ferrous sulfate heptahydrate, zinc sulfate heptahydrate, and potassium aluminum sulfate dodecahydrate; the amount of water content regulator added is 1-10% of the mass of the spinning solution; the heating and stirring temperature is 40-90℃, the stirring speed is 120-1000 rpm, and the stirring time is 2-10 h.

7. The preparation method according to claim 4, characterized in that, In step 3), the electrospinning environment temperature is 20~35℃ and the ambient humidity is 30~60%; the electrospinning process parameters are: voltage 10~100kV, receiving distance 10~50cm, and injection speed 1~100mL / h.

8. The preparation method according to claim 4, characterized in that, In step 4), the pre-oxidation temperature is 180~300℃ and the holding time is 60~120min.

9. The preparation method according to claim 4, characterized in that, In step 5), the high-temperature carbonization atmosphere in the vacuum tube furnace is nitrogen or argon, and the temperature is raised to a high temperature of 400-1300°C at a heating rate of 1-10°C / min, and held at the high temperature for 60-120 minutes.