Multifunctional flexible composite protective structure and preparation method thereof

Abstract

The present application provides a kind of multifunctional flexible composite protective structure and preparation method thereof, the composite protective structure is from outer layer to inner layer in turn nanofiber aerogel phase change composite film (KNA / PEG), nanofiber aerogel film (KNA), silica aerogel composite fiber felt, shear hardening / kevlar (SSE / Kevlar) protective main structure, the shear hardening / kevlar protective main structure is the shear hardening precursor Kevlar prepreg stack after heat treatment obtained.The multifunctional flexible composite protective structure of the present application has very low thermal conductivity, low density, flame retardancy, low infrared emissivity, flexibility and impact protection, can block the heat of soldier human body and limit the emission of infrared thermal radiation.

Description

Technical Field

[0001] This invention belongs to the field of human protective equipment technology, specifically relating to a multifunctional flexible composite protective structure and its preparation method. Background Technology

[0002] In the modern battlefield, large-scale firepower clashes between soldiers are no longer the primary mode of combat. Instead, reconnaissance and surprise attacks by small numbers of soldiers are the main methods. This places higher demands on the camouflage and stealth functions of individual soldier protective equipment, especially during nighttime penetration operations. Soldiers' heat radiation signals are the most prominent feature, easily revealing their location. Therefore, reducing infrared radiation emissions from equipment and employing infrared stealth technologies to confuse enemy infrared detection are crucial in modern warfare. Furthermore, rigid protective gear is typically heavy and poorly designed for long-term wear and long-distance marches, making the development of lightweight, flexible individual soldier equipment essential. Therefore, achieving lightweight flexibility and stealth camouflage while maintaining protective performance is of great significance for future battlefield surprise attacks.

[0003] Shear-hardening materials (SSEs) are strain-rate-sensitive adaptive materials. Their energy storage properties, such as viscosity, storage modulus, loss modulus, and damping loss factor, are closely related to the external strain rate environment. Under static or low strain rate loads, they behave as viscous fluids or elastomers. When subjected to high strain rate loads, the material undergoes a phase transition to a solid state, thereby absorbing a large amount of impact energy and improving protective performance. Aramid fiber fabrics have advantages such as high strength, high modulus, good stability, and certain flame-retardant properties, and are commonly used in protective applications. Due to the strain rate adaptive advantage of SSE materials, their combination with ballistic woven fabrics can significantly enhance the interfacial friction, impact energy absorption, and ballistic limits of the fabric. Moreover, compared with pure fabric protective structures of the same areal density, the impact deformation is smaller, providing significant advantages in impact protection.

[0004] According to the Stefan-Boltzmann law, the intensity of infrared thermal radiation per unit area of ​​an object is proportional to the fourth power of its surface infrared emissivity and temperature. Therefore, infrared radiation can be reduced by controlling infrared emissivity and lowering temperature, and cooling measures are more effective. Aerogel materials are lightweight, sparse, and porous materials, with their internal volume almost entirely filled with air. They are the lightest known materials. The extremely low thermal conductivity of air gives aerogel materials excellent thermal insulation properties. However, the excessively low mechanical properties of aerogel materials severely limit their applicability, making them prone to breakage, detachment, and other failures, resulting in a significant decline in performance. Summary of the Invention

[0005] To address the problem that existing individual protective equipment cannot simultaneously achieve protective performance, flexibility, and stealth camouflage, this invention provides a multifunctional flexible composite protective structure and its preparation method. This structure features extremely low thermal conductivity, low density, flame retardancy, low infrared emissivity, flexibility, and impact protection. It can block heat from the soldier's body, limiting infrared heat radiation dissipation, and under infrared thermal imaging, ensure the target's temperature matches the ambient background, effectively integrating the target's thermal appearance into the background. Maintaining a certain degree of flexibility, the composite protective structure can adapt to the bending movements of the human body during wear. Upon impact with a bullet, it rapidly hardens, significantly enhancing impact energy absorption and limiting impact deformation, thereby achieving the purpose of protecting the human body.

[0006] The technical problem solved by this invention is achieved by the following technical solution:

[0007] The first objective of this invention is to provide a multifunctional flexible composite protective structure, which consists of, from the outer layer to the inner layer, a nanofiber aerogel phase change composite membrane (KNA / PEG), a nanofiber aerogel membrane (KNA), a silica aerogel composite fiber mat, and a shear-hardened / aramid (SSE / Kevlar) protective main body structure. The shear-hardened / aramid protective main body structure is obtained by heat treatment after stacking multiple layers of shear-hardened precursor Kevlar prepreg.

[0008] The second objective of this invention is to provide a method for preparing a multifunctional flexible composite protective structure, comprising the following steps: arranging a nanofiber aerogel phase change composite membrane, a nanofiber aerogel membrane, a silica aerogel composite fiber felt, and a shear-hardened / aramid protective main body structure in sequence, and spraying the layers between them with a fluorocarbon resin mixed with B1540 curing agent, and then curing and molding the structure to obtain the final product.

[0009] The nanofiber aerogel phase change composite membrane is obtained by adsorbing the thermal phase change material PEG through the micro-capillary force of the KNA film under high temperature melting.

[0010] The shear-hardening / aramid protective main structure is obtained by uniformly mixing the prepared shear-hardening rubber with methyl vinyl silicone rubber and vulcanizing agent, adding fumed silica and pressing at 60°C, laying the resulting film flat on the surface of Kevlar woven fabric and compounding it with double pressure rollers to obtain the shear-hardening precursor Kevlar prepreg, and then obtaining it after interlayer variable angle laying and stacking, and hot pressing.

[0011] Furthermore, the preparation method of the nanofiber aerogel membrane is as follows: aramid short fibers are dispersed in a dimethyl sulfoxide solution, then a strong alkali is added to form an alkaline environment, and after a thorough sol-gel process, a nanofiber dispersion is obtained. Then, after deionized hydrogel, anhydrous ethanol and tert-butanol replacement, a nanofiber hydrogel is obtained, and then freeze-dried to obtain a nanofiber aerogel membrane.

[0012] Furthermore, the mass ratio of added aramid short fibers to dimethyl sulfoxide is 1.5–2.5: 97.5–98.5.

[0013] Furthermore, the mass of the strong base added is 1% of the mass of the mixed solution.

[0014] Furthermore, the nanofiber dispersion is scraped to form a sol film, then immersed in deionized water for displacement to form a gel film, and residual dimethyl sulfoxide and proton salts are removed. Then, it is immersed in a mixed solution of anhydrous ethanol and tert-butanol for solvent displacement to obtain nanofiber hydrogel.

[0015] Furthermore, the freeze-drying time is 48–72 hours.

[0016] Furthermore, the preparation method of the silica aerogel composite fiber felt is as follows: a silicon source, anhydrous ethanol, and deionized water are mixed in proportion and the pH value is adjusted to 3-4 to carry out a hydrolysis reaction. After the hydrolysis is completed, the pH value of the solution is adjusted to 6-7 to carry out a condensation reaction. Before gelation, aluminum silicate ceramic fiber felt is added and placed in a sealed container to form a gel. The gel is aged, replaced, modified, and dried to obtain silica aerogel composite fiber felt.

[0017] Furthermore, the molar ratio of the silicon source to anhydrous ethanol and deionized water is 1:6 to 10:2 to 6.

[0018] Furthermore, dilute hydrochloric acid is selected as the acid used to adjust the acidic environment, and ammonia water is selected as the alkali used to adjust the alkaline environment.

[0019] Furthermore, the volume ratio of ammonia water to anhydrous ethanol is 1:30.

[0020] Furthermore, the silicon source is selected from tetraethyl orthosilicate, methyl orthosilicate, butyl orthosilicate, isopropyl orthosilicate, methyltriethoxysilane, or ethyltrimethoxysilane.

[0021] Furthermore, the hydrolysis and condensation reactions occur at temperatures of 25–35°C.

[0022] Furthermore, the gel aging process involves immersing the formed gel in a sufficient volume of a mixed solution of silicon source and anhydrous ethanol, wherein the volume ratio of silicon source to anhydrous ethanol during aging is 1:5.

[0023] Furthermore, the replacement involves immersing the aged gel in anhydrous ethanol, and the modification involves immersing the replaced gel in a sufficient amount of modifying solution for 8–24 hours. The modifying solution is a mixture of a modifier and anhydrous ethanol, and the modifier is hexamethyldisilazane, trimethylchlorosilane, dimethyldichlorosilane, or methyltrichlorosilane.

[0024] Furthermore, the preparation method of the shear hardening adhesive is as follows: after fully dissolving boric acid in isopropanol, hydroxyl silicone oil is added and stirred evenly. Then, the isopropanol is heated at 150-200°C to volatilize. After volatilization, the mixture is placed in a vacuum kneader for polymerization reaction. After the mixture becomes a viscous polymer with a silky luster, the shear hardening adhesive is obtained.

[0025] Furthermore, the ratio of boric acid to hydroxy silicone oil is 1 ml: 50 mg.

[0026] Furthermore, the polymerization reaction conditions are 200–250°C for 1.5–2.5 h.

[0027] Furthermore, the mass ratio of the shear-hardening rubber, methyl vinyl silicone rubber, and vulcanizing agent is 70:30:1.

[0028] Furthermore, the vulcanizing agent is benzoyl peroxide.

[0029] Furthermore, the amount of silica added is 15% of the total mass of the colloid.

[0030] Furthermore, the thickness of the film obtained by lamination is 0.5 mm.

[0031] Furthermore, the shear-hardening precursor Kevlar prepreg is laid in 25 to 75 layers.

[0032] Furthermore, the hot pressing conditions are 120°C, 20MPa, and pressing time of 20min.

[0033] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0034] This invention creates a lightweight, flexible, bulletproof, and infrared heat radiation blocking multifunctional flexible composite protective structure. A layer of fluorocarbon resin is sprayed onto the surface of the composite protective structure to enhance its weather resistance. The KNA / PEG film, with its ultra-low infrared transmittance, acts as an infrared heat radiation blocker; the KNA film isolates external heat and reduces internal and external heat transfer; the silica aerogel composite fiber felt blocks internal heat; and the shear-hardened / aramid composite fabric provides bulletproof and impact-resistant properties. This flexible composite protective structure ultimately blocks heat transfer from the human body and limits infrared heat radiation dissipation, ensuring the target's temperature matches the ambient temperature under infrared thermal imaging, thus improving the stealth and safety of individual soldiers.

[0035] Aramid nanofiber aerogel membranes are prepared using a sol-gel-drying process with high-performance aramid fibers. This process overcomes the shortcomings of traditional aerogel materials, which suffer from low strength. Furthermore, it is easily combined with temperature phase change materials to prepare nanofiber aerogel phase change composite membranes (KNA / PEG) with excellent heat storage performance and low infrared emissivity. Silica aerogel composite fiber felts contain diverse silicon sources and are prepared using a sol-gel process under normal pressure, resulting in low production costs. When combined with fiber felts, they exhibit excellent thermal insulation properties. When applied to individual soldier infrared stealth equipment, they effectively block body heat. The surface infrared thermal radiation is limited by the KNA / PEG composite membrane and kept consistent with the ambient background temperature, achieving infrared stealth for the human body. The shear-hardening / aramid protective main structure behaves as a viscous fluid or elastomer under static or low strain rate loads. When subjected to high strain rate loads, the material undergoes a phase change to a solid state, thereby absorbing a large amount of impact energy and improving protective performance. By uniformly dispersing shear-hardening adhesive in aramid fibers, the hardness of the aramid fibers interacts with the shear-hardening adhesive, improving both impact resistance and energy dissipation levels, resulting in better impact resistance than shear-hardening adhesive alone.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a multifunctional flexible composite protective structure according to the present invention.

[0038] Figure 2 This is a schematic diagram of the structure of the nanofiber aerogel membrane of the present invention.

[0039] Figure 3 This is a schematic diagram of the structure of the nanofiber aerogel phase change composite membrane of the present invention.

[0040] Figure 4 This is a schematic diagram of the structure of the silica aerogel composite fiber felt of the present invention.

[0041] Figure 5 This is a schematic diagram of the shear-hardening / aramid protective main structure of the present invention (Figure a is the overall structure, and Figure b is a partially enlarged structure).

[0042] Figure 6 This is a schematic diagram of the stacked shear-hardening / aramid protective main structure of the present invention.

[0043] Figure 7 This is a diagram illustrating the infrared thermal radiation blocking mechanism of the multifunctional flexible composite protective structure of the present invention.

[0044] Figure 8 This is a diagram illustrating the infrared thermal radiation blocking mechanism of the nanofiber aerogel phase change composite membrane of the present invention.

[0045] Figure 9 This is a diagram illustrating the aerogel thermal insulation mechanism of the present invention. Detailed Implementation

[0046] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0047] In addition, unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be obtained by purchasing them from the market or prepared by existing methods.

[0048] Example 1

[0049] A method for preparing a multifunctional flexible composite protective structure includes the following steps:

[0050] 1) Preparation method of nanofiber aerogel membrane (KNA):

[0051] Aramid short fibers were dispersed in a dimethyl sulfoxide solution at a mass ratio of 2:98. Then, 1% potassium hydroxide (by mass) of the mixed solution was added to create an alkaline environment, making the solution strongly alkaline. This strong alkalinity caused the removal of hydrogen atoms from the aromatic amide bonds, leading to the formation of polyanions in the aramid fibers. The gradual reduction of intermolecular hydrogen bonds and the weakening of π-π bond accumulation resulted in a further increase in repulsive forces. The aramid fibers gradually dissociated, forming nanofibers, which increased the reaction area and promoted the decomposition of the protofibers. Ultimately, the decomposition products were dispersed in DMSO solvent. The mixed solution was stirred for 5–9 days, and after a thorough sol-gel process, a deep red nanofiber dispersion was obtained. The nanofiber dispersion was then coated to form a sol film, which was then immersed in deionized water for displacement to form a gel film, removing residual dimethyl sulfoxide and proton salts. The gel was then immersed in a mixture of deionized water and tert-butanol for solvent displacement to obtain a nanofiber hydrogel. Finally, the hydrogel was freeze-dried for 48–72 hours to obtain a nanofiber aerogel membrane.

[0052] Freeze-drying ensures that the internal solvent of the gel material is sublimated in a frozen state. During the drying process, the solvent freezes into ice to maintain the spatial structure of the gel. The ice crystals in the hydrogel are sublimated by vacuum to obtain aramid nanofiber aerogel material. Freeze-drying is more convenient and efficient than typical supercritical drying.

[0053] See appendix Figure 2The diagram shows a nanofiber aerogel membrane. The nanofiber aerogel membrane prepared by the method of the present invention has smaller crystal size and more uniform morphology.

[0054] 2) Preparation method of nanofiber aerogel phase change composite membrane (KNA / PEG):

[0055] The nanofiber aerogel membrane obtained in step 1) was placed in PEG 10k thermal phase change material in a high-temperature molten state. PEG was fully adsorbed by the micro-capillary force of the KNA film. After cooling, a nanofiber aerogel phase change composite membrane was obtained.

[0056] Due to its good flexibility, high porosity, excellent thermal insulation properties, and remarkable capillary force, aramid nanofiber aerogel film can more fully adsorb PEG, giving the nanofiber aerogel phase change composite film better thermal insulation performance.

[0057] 3) Preparation method of silica aerogel composite fiber felt:

[0058] Tetraethyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a molar ratio of 1:8:4, and dilute hydrochloric acid was added to adjust the pH to 3-4. The mixture was then subjected to hydrolysis at 30°C for 4 hours. After hydrolysis, diluted ammonia was added at a volume ratio of 1:30 to adjust the pH to 6-7 to carry out polycondensation. Before gelation, a 1-3 mm thick layer of aluminosilicate ceramic fiber felt was added until it was completely soaked. The mixture was stirred for 15 minutes and then sealed in a container to form a gel.

[0059] The formed gel was immersed in a sufficient volume of a mixed solution of tetraethyl orthosilicate and anhydrous ethanol at 30℃ for aging. The volume ratio of tetraethyl orthosilicate to anhydrous ethanol during aging was 1:5. The aged gel was then immersed in anhydrous ethanol for 30 hours for displacement, and then the displaced gel was immersed in a sufficient volume of a modifying solution for 20 hours. The modifying solution was a mixture of hexamethyldisilazane and anhydrous ethanol at a volume ratio of 1:5. During the modification process, hydrophobic groups continuously replaced hydrophilic groups in the gel, thereby enhancing the gel's network structure. The modified gel was then immersed in anhydrous ethanol again for 30 hours for displacement, and then the displaced gel was placed in an atmospheric pressure drying oven and dried using a temperature gradient method. The temperature was gradually increased and then kept constant for slow drying to reduce the destructive force on the wet gel during drying, resulting in silica aerogel composite fiber felt.

[0060] See appendix Figure 4 The diagram shows the structure of silica aerogel composite fiber felt, where the aerogel tightly coats the fiber felt, forming a good overall structure.

[0061] 4) Preparation method of shear-hardened / aramid protective main body structure (SSE / Kevlar):

[0062] After fully dissolving boric acid in isopropanol, hydroxyl silicone oil was added to the boric acid solution at a ratio of 50 mg / ml and stirred until homogeneous. Then, the solution was heated at 180°C for 30 min to evaporate the isopropanol. During this process, the solution was stirred every 5 min to maintain the uniformity of the reaction. After evaporation, the solution was placed in a vacuum kneader and polymerized at 220°C for 2 h. Once the mixture became a viscous polymer with a silky luster, shear hardening gel (SSG) was obtained.

[0063] The prepared shear-hardening rubber was mixed with methyl vinyl silicone rubber and benzoyl peroxide in a mass ratio of 70:30:1 in an open mixing mill until homogeneous. During the mixing process, 15% by weight of silica was added. After homogeneous mixing, a film was formed by pressing at 60°C using a film press to form a film with a thickness of 0.5 mm.

[0064] The obtained film is laid flat on the surface of Kevlar woven fabric and pressed and laminated by double pressure rollers to obtain shear-hardening precursor Kevlar prepreg. Then, through interlayer variable angle laying and stacking, the number of layers is 50. The shear-hardening / aramid protective main structure is obtained by hot pressing at 120℃ and 20MPa for 20 minutes.

[0065] See appendix Figure 6 (a) During stacking, the shear-hardening precursor Kevlar prepreg is stacked at an angle offset of 15° to form a shear-hardening / aramid protective main structure. Specifically, 50 layers of shear-hardening adhesive-reinforced flexible fabric composite are stacked at an angle offset of 15° to form the shear-hardening / aramid protective main structure. Because orthogonal weaves have a distinct directionality, to enhance the protective performance of the main structure, multiple layers of shear-hardening precursor Kevlar prepreg are stacked at a certain angle. The angle offset between adjacent prepreg layers during stacking forms a flexible protective layer, dispersing and transferring stress.

[0066] 5) Fabrication of a multifunctional flexible composite protective structure:

[0067] The nanofiber aerogel membrane, nanofiber aerogel phase change composite membrane, silica aerogel composite fiber mat, and shear-hardening / aramid protective main body structure obtained in steps 1), 2), 3), and 4) are coated with fluorocarbon resin mixed with B1540 curing agent between adjacent layers in the following order: shear-hardening / aramid protective main body structure, silica aerogel composite fiber mat, nanofiber aerogel membrane, and nanofiber aerogel phase change composite membrane. After curing, a multifunctional flexible composite protective structure is obtained.

[0068] Fluorocarbon resin, with its strong CF bond as a backbone, has advantages such as weather resistance, heat resistance, cold resistance, and chemical resistance. When mixed with B1540 curing agent and sprayed, it forms a composite protective structure that is lightweight, flexible, bulletproof, and blocks infrared heat radiation.

[0069] Example 2

[0070] A method for preparing a multifunctional flexible composite protective structure includes the following steps:

[0071] 1) Preparation method of nanofiber aerogel membrane (KNA):

[0072] Aramid short fibers were dispersed in a dimethyl sulfoxide solution at a mass ratio of 1.5:98.5. Then, 1% potassium hydroxide (by mass of the mixed solution) was added to create an alkaline environment, making the solution strongly alkaline and promoting the decomposition of the fibrils. This ultimately led to the dispersion of the decomposition products in DMSO solvent. The mixed solution was stirred for 5–9 days, and after a thorough sol-gel process, a deep red nanofiber dispersion was obtained. The nanofiber dispersion was then coated to form a sol film, which was then immersed in deionized water for displacement to form a gel film, removing residual dimethyl sulfoxide and protonate. Next, it was immersed in a mixed solution of deionized water and tert-butanol for solvent displacement to obtain a nanofiber hydrogel. Finally, it was freeze-dried for 48–72 hours to obtain a nanofiber aerogel membrane.

[0073] 2) Preparation method of nanofiber aerogel phase change composite membrane (KNA / PEG):

[0074] The nanofiber aerogel membrane obtained in step 1) was placed in PEG 10k thermal phase change material in a high-temperature molten state. PEG was fully adsorbed by the micro-capillary force of the KNA film. After cooling, a nanofiber aerogel phase change composite membrane was obtained.

[0075] 3) Preparation method of silica aerogel composite fiber felt:

[0076] Isopropyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a molar ratio of 1:10:3, and dilute hydrochloric acid was added to adjust the pH to 3-4. The mixture was then subjected to hydrolysis at 35°C for 4 hours. After hydrolysis, diluted ammonia was added at a volume ratio of 1:30 to adjust the pH to 6-7 to carry out polycondensation. Before gelation, a 1-3 mm thick layer of aluminosilicate ceramic fiber felt was added until it was completely soaked. The mixture was stirred for 15 minutes and then sealed in a container to form a gel.

[0077] The formed gel was immersed in a sufficient mixture of isopropyl orthosilicate and anhydrous ethanol at 35℃ for aging. The volume ratio of isopropyl orthosilicate to anhydrous ethanol during aging was 1:5. The aged gel was then immersed in anhydrous ethanol for 30 hours for displacement, and then the displaced gel was immersed in a sufficient amount of modifying solution for 24 hours. The modifying solution was a mixture of dimethyldichlorosilane and anhydrous ethanol at a volume ratio of 1:5. During the modification process, hydrophobic groups continuously replaced hydrophilic groups in the gel, thereby enhancing the network structure of the gel. The modified gel was immersed in anhydrous ethanol again for 30 hours for displacement, and then the gel after displacement was placed in an atmospheric pressure drying oven and dried using a temperature gradient method. The temperature was gradually increased and then kept constant for slow drying to reduce the destructive force on the wet gel during drying, resulting in silica aerogel composite fiber felt.

[0078] 4) Preparation method of shear-hardened / aramid protective main body structure (SSE / Kevlar):

[0079] After fully dissolving boric acid in isopropanol, hydroxyl silicone oil was added to the boric acid solution at a ratio of 50 mg / ml and stirred until homogeneous. Then, the solution was heated at 200°C for 30 minutes to evaporate the isopropanol. During this process, the solution was stirred every 5 minutes to maintain the uniformity of the reaction. After evaporation, the solution was placed in a vacuum kneader and polymerized at 220°C for 2 hours. Once the mixture became a viscous polymer with a silky luster, shear hardening gel (SSG) was obtained.

[0080] The prepared shear-hardening rubber was mixed with methyl vinyl silicone rubber and benzoyl peroxide in a mass ratio of 70:30:1 in an open mixing mill until homogeneous. During the mixing process, 15% by weight of silica was added. After homogeneous mixing, a film was formed by pressing at 60°C using a film press to form a film with a thickness of 0.5 mm.

[0081] The obtained film is laid flat on the surface of Kevlar woven fabric and pressed and laminated by double pressure rollers to obtain shear-hardening precursor Kevlar prepreg. Then, through interlayer variable angle laying and stacking, the number of layers is 50. The shear-hardening / aramid protective main structure is obtained by hot pressing at 120℃ and 20MPa for 20 minutes.

[0082] See appendix Figure 6 (b) During stacking, the shear-hardening precursor Kevlar prepreg is stacked at an angle offset of 30° to form a shear-hardening / aramid protective main structure.

[0083] 5) Fabrication of a multifunctional flexible composite protective structure:

[0084] The nanofiber aerogel membrane, nanofiber aerogel phase change composite membrane, silica aerogel composite fiber mat, and shear-hardening / aramid protective main body structure obtained in steps 1), 2), 3), and 4) are coated with fluorocarbon resin mixed with B1540 curing agent between adjacent layers in the following order: shear-hardening / aramid protective main body structure, silica aerogel composite fiber mat, nanofiber aerogel membrane, and nanofiber aerogel phase change composite membrane. After curing, a multifunctional flexible composite protective structure is obtained.

[0085] Example 3

[0086] A method for preparing a multifunctional flexible composite protective structure includes the following steps:

[0087] 1) Preparation method of nanofiber aerogel membrane (KNA):

[0088] Aramid short fibers were dispersed in a dimethyl sulfoxide solution at a mass ratio of 2.5:97.5. Then, 1% potassium hydroxide (by mass of the mixed solution) was added to create an alkaline environment, making the solution strongly alkaline and promoting the decomposition of the fibrils. This ultimately led to the dispersion of the decomposition products in DMSO solvent. The mixed solution was stirred for 5–9 days, and after a thorough sol-gel process, a deep red nanofiber dispersion was obtained. The nanofiber dispersion was then coated to form a sol film, which was then immersed in deionized water for displacement to form a gel film, removing residual dimethyl sulfoxide and protonate. Next, it was immersed in a mixed solution of deionized water and tert-butanol for solvent displacement to obtain a nanofiber hydrogel. Finally, it was freeze-dried for 48–72 hours to obtain a nanofiber aerogel membrane.

[0089] 2) Preparation method of nanofiber aerogel phase change composite membrane (KNA / PEG):

[0090] The nanofiber aerogel membrane obtained in step 1) was placed in PEG 10k thermal phase change material in a high-temperature molten state. PEG was fully adsorbed by the micro-capillary force of the KNA film. After cooling, a nanofiber aerogel phase change composite membrane was obtained.

[0091] 3) Preparation method of silica aerogel composite fiber felt:

[0092] Methyl orthosilicate, anhydrous ethanol, and deionized water were mixed in a molar ratio of 1:6:6, and dilute hydrochloric acid was added to adjust the pH to 3-4. The mixture was then subjected to hydrolysis at 25°C for 4 hours. After hydrolysis, diluted ammonia was added at a volume ratio of 1:30 to adjust the pH to 6-7 to carry out polycondensation. Before gelation, a 1-3 mm thick layer of aluminosilicate ceramic fiber felt was added until it was completely soaked. The mixture was stirred for 15 minutes and then sealed in a container to form a gel.

[0093] The formed gel was immersed in a sufficient volume of a mixed solution of methyl orthosilicate and anhydrous ethanol at 25℃ for aging. The volume ratio of methyl orthosilicate to anhydrous ethanol during aging was 1:5. The aged gel was then immersed in anhydrous ethanol for 30 hours for displacement, and then the displaced gel was immersed in a sufficient volume of a modifying solution for 20 hours. The modifying solution was a mixture of hexamethyldisilazane and anhydrous ethanol at a volume ratio of 1:5. During the modification process, hydrophobic groups continuously replaced hydrophilic groups in the gel, thereby enhancing the gel's network structure. The modified gel was then immersed in anhydrous ethanol again for 30 hours for displacement, and then the displaced gel was placed in an atmospheric pressure drying oven and dried using a temperature gradient method. The temperature was gradually increased and then kept constant for slow drying to reduce the destructive force on the wet gel during drying, resulting in silica aerogel composite fiber felt.

[0094] 4) Preparation method of shear-hardened / aramid protective main body structure (SSE / Kevlar):

[0095] After fully dissolving boric acid in isopropanol, hydroxyl silicone oil was added to the boric acid solution at a ratio of 50 mg / ml and stirred until homogeneous. Then, the solution was heated at 180°C for 30 min to evaporate the isopropanol. During this process, the solution was stirred every 5 min to maintain the uniformity of the reaction. After evaporation, the solution was placed in a vacuum kneader and polymerized at 220°C for 2 h. Once the mixture became a viscous polymer with a silky luster, shear hardening gel (SSG) was obtained.

[0096] The prepared shear-hardening rubber was mixed with methyl vinyl silicone rubber and benzoyl peroxide in a mass ratio of 70:30:1 in an open mixing mill until homogeneous. During the mixing process, 15% by weight of silica was added. After homogeneous mixing, a film was formed by pressing at 60°C using a film press to form a film with a thickness of 0.5 mm.

[0097] The obtained film is laid flat on the surface of Kevlar woven fabric and pressed and laminated by double pressure rollers to obtain shear-hardening precursor Kevlar prepreg. Then, through interlayer variable angle laying and stacking, the number of layers is 50. The shear-hardening / aramid protective main structure is obtained by hot pressing at 120℃ and 20MPa for 20 minutes.

[0098] See appendix Figure 6 (a) During stacking, the shear-hardening precursor Kevlar prepreg is stacked at an angle offset of 15° to form a shear-hardening / aramid protective body structure.

[0099] 5) Fabrication of a multifunctional flexible composite protective structure:

[0100] The nanofiber aerogel membrane, nanofiber aerogel phase change composite membrane, silica aerogel composite fiber mat, and shear-hardening / aramid protective main body structure obtained in steps 1), 2), 3), and 4) are coated with fluorocarbon resin mixed with B1540 curing agent between adjacent layers in the following order: shear-hardening / aramid protective main body structure, silica aerogel composite fiber mat, nanofiber aerogel membrane, and nanofiber aerogel phase change composite membrane. After curing, a multifunctional flexible composite protective structure is obtained.

[0101] The present invention discloses the infrared heat radiation blocking principle of a multifunctional flexible composite protective structure:

[0102] See appendix Figure 7 , 8 The silica aerogel composite fiber felt forms a stable fiber network structure, with silica aerogel tightly coating the fiber felt, creating two network structures. This ensures both material structural stability and excellent thermal insulation performance. The complex nanopores effectively reduce gas phase conduction, prevent heat convection, and extend the heat transfer path, providing a certain degree of temperature barrier and resulting in good thermal insulation. The nanofiber aerogel membrane forms a complexly distributed nanoscale porous three-dimensional mesh structure with small pore sizes, further extending the heat transfer path. Aramid nanofibers themselves have strong thermal insulation and antioxidant effects, capable of withstanding external temperatures up to 300 degrees Celsius, and providing good insulation against heat radiation. This invention combines silica aerogel composite fiber felt and nanofiber aerogel membrane for two-stage thermal insulation, resulting in better thermal insulation. The silica aerogel composite fiber felt is mainly used for heat barrier around the human body, while the nanofiber aerogel membrane is mainly used for heat barrier from the external environment.

[0103] After being treated with phase change materials, the nanofiber aerogel phase change composite membrane, specifically PEG 10k, stores heat and softens upon heating, then releases heat to harden again upon solidification. This allows the composite membrane to absorb heat from the environment during use, suppressing temperature rise, and to slowly release stored heat when the environment cools, thus matching the ambient temperature. Therefore, with minimal heat transfer from the human body to the nanofiber aerogel phase change composite membrane, it can achieve infrared stealth by controlling the temperature. It also possesses a certain degree of infrared reflection, enabling stealth under infrared irradiation.

[0104] The impact resistance principle of a multifunctional flexible composite protective structure of the present invention:

[0105] The shear-hardening / aramid protective main structure uniformly disperses shear-hardening adhesive within aramid fibers. Under natural conditions, most BO bonds in the shear-hardening adhesive break (Equation I), and the shear-hardening / aramid protective main structure exhibits a viscoplastic state with typical cold flow characteristics. At the onset of impact, under external impact, BO bonds begin to form in the shear-hardening adhesive, and the number of BO bonds gradually increases (Equation II). The viscosity and modulus of the shear-hardening / aramid protective main structure increase rapidly, strain rate-related parameters are enhanced, and impact resistance is strengthened. As the impact weakens, the BO bonds in the shear-hardening adhesive begin to break, and the number of BO bonds gradually decreases (Equation III). The viscosity and modulus of the shear-hardening / aramid protective main structure gradually decrease, and impact resistance weakens. After the impact is completed and the impact effect is lost, most of the BO bonds in the shear-hardening adhesive break (Equation I), and it returns to a viscoplastic state. This invention uniformly disperses shear-hardening adhesive in aramid fibers. The hardness of the aramid fibers interacts with the shear-hardening adhesive, thereby improving both impact resistance and energy dissipation level, resulting in better impact resistance than shear-hardening adhesive alone.

[0106]

[0107] In this invention, the KNA / PEG film, with its ultra-low infrared transmittance, serves to block infrared heat radiation. The KNA film isolates external heat and reduces internal and external heat transfer. The silica aerogel composite fiber felt blocks internal heat, and the shear-hardened / aramid composite fabric provides bulletproof and impact-resistant properties. This flexible composite protective structure ultimately blocks heat transfer from the human body and limits infrared heat radiation, ensuring the target's temperature matches the ambient temperature under infrared thermal imaging, thus improving the stealth and safety of individual soldiers.

[0108] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0109] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing a multifunctional flexible composite protective structure, characterized in that, The process includes the following steps: arranging the nanofiber aerogel phase change composite membrane, nanofiber aerogel membrane, silica aerogel composite fiber felt, and shear-hardened / aramid protective main structure in sequence, and then spraying them between the layers with a fluorocarbon resin mixed with B1540 curing agent, and curing them to obtain the final product. The nanofiber aerogel phase change composite membrane is obtained by adsorbing the thermal phase change material PEG through the microscopic capillary force of the nanofiber aerogel membrane under high temperature melting. The shear-hardening / aramid protective main structure is obtained by uniformly mixing the prepared shear-hardening rubber with methyl vinyl silicone rubber and vulcanizing agent, adding fumed silica, pressing at 60°C, laying the resulting film flat on the surface of Kevlar woven fabric, and compounding with double pressure rollers to obtain the shear-hardening precursor Kevlar prepreg. Then, it is obtained by interlayer variable angle laying and stacking, and hot pressing at 120°C and 20MPa. The mass ratio of the shear-hardening rubber, methyl vinyl silicone rubber, and vulcanizing agent is 70:30:1, and the amount of fumed silica added is 15% of the total mass of the colloid. The shear-hardening precursor Kevlar prepreg is laid in 25 to 75 layers. The shear-hardening adhesive is prepared by dissolving boric acid in isopropanol, adding hydroxyl silicone oil and stirring until homogeneous. The ratio of boric acid to hydroxyl silicone oil is 1 mL: 50 mg. The isopropanol is then heated at 150-200°C to evaporate. After evaporation, the mixture is placed in a vacuum kneader and subjected to a polymerization reaction at 200-250°C for 1.5-2.5 h. The shear-hardening adhesive is obtained when the mixture becomes a viscous polymer with a silky luster.

2. The method for preparing a multifunctional flexible composite protective structure as described in claim 1, characterized in that, The preparation method of the nanofiber aerogel membrane is as follows: aramid short fibers are dispersed in a dimethyl sulfoxide solution, and then a strong alkali is added to form an alkaline environment. After a thorough sol-gel process, a nanofiber dispersion is obtained. Then, a sol film is formed by scraping, and the dispersion is immersed in deionized water to form a gel film. The dispersion is then immersed in a mixed solution of anhydrous ethanol and tert-butanol for solvent replacement to obtain a nanofiber hydrogel. Finally, the dispersion is freeze-dried to obtain a nanofiber aerogel membrane.

3. The method for preparing a multifunctional flexible composite protective structure as described in claim 2, characterized in that: The mass ratio of added aramid short fibers to dimethyl sulfoxide is 1.5~2.5:97.5~98.

5.

4. The method for preparing a multifunctional flexible composite protective structure as described in claim 2, characterized in that: The nanofiber dispersion is scraped to form a sol film, then immersed in deionized water to form a gel film, and residual dimethyl sulfoxide and proton salts are removed. Then, it is immersed in a mixed solution of anhydrous ethanol and tert-butanol for solvent replacement to obtain nanofiber hydrogel.

5. The method for preparing a multifunctional flexible composite protective structure as described in claim 1, characterized in that, The preparation method of the silica aerogel composite fiber felt is as follows: silicon source, anhydrous ethanol and deionized water are mixed in proportion and the pH value is adjusted to 3~4 to carry out hydrolysis reaction. After hydrolysis, the pH value of the solution is adjusted to 6~7 to carry out condensation reaction. Before gelation, aluminum silicate ceramic fiber felt is added and placed in a sealed container to form gel. After aging, displacement, modification, displacement and drying of the gel, silica aerogel composite fiber felt is obtained.

6. The method for preparing a multifunctional flexible composite protective structure as described in claim 5, characterized in that: The molar ratio of the silicon source to anhydrous ethanol and deionized water is 1:6~10:2~6.

7. The method for preparing a multifunctional flexible composite protective structure as described in claim 5, characterized in that: The gel aging process involves immersing the formed gel in a sufficient mixture of silicon source and anhydrous ethanol, with the volume ratio of silicon source to anhydrous ethanol being 1:5 during aging.

8. The method for preparing a multifunctional flexible composite protective structure as described in claim 5, characterized in that: The modification involves placing the replaced gel in a sufficient amount of modifying solution for 8-24 hours. The modifying solution is a mixture of a modifier and anhydrous ethanol. The modifier is hexamethyldisilazane, trimethylchlorosilane, dimethyldichlorosilane, or methyltrichlorosilane.

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