Preparation method of flexible bulletproof composite material based on shear thickening liquid composite negative Poisson's ratio structure and body armor

Abstract

The invention relates to the technical field of bulletproof materials, in particular to a flexible bulletproof composite material based on a shear thickening fluid composite negative Poisson's ratio structure and a body armor. The method comprises the following steps: preparing a functional reinforcing agent with a micro-nano porous structure and a negative Poisson's ratio characteristic, introducing the functional reinforcing agent into a shear thickening liquid system, compounding the functional reinforcing agent with ultra-high molecular weight polyethylene fibers to form multi-element gel fibers, and weaving and dipping in a glue solution to prepare the flexible composite material. The material has the dynamic response characteristic of shear thickening fluid and the densification energy absorption mechanism of a negative Poisson's ratio structure, and the energy dissipation efficiency and the multiple impact resistance are remarkably improved; the bulletproof vest adopts a three-layer synergistic structure of the bullet facing surface layer, the energy dissipation layer and the backing layer, light weight and flexibility are kept while a good bulletproof effect and a high protection level are achieved, and the bulletproof vest is suitable for individual protection in a complex threat scene.

Description

Technical Field

[0001] This invention relates to the field of bulletproof materials technology, specifically to a method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure and a bulletproof vest. Background Technology

[0002] With the increasing demands of modern security, flexible bulletproof equipment is being used more and more widely in military, police, and civilian fields. Traditional flexible bulletproof materials mainly rely on high-strength fibers (such as ultra-high molecular weight polyethylene and aramid) to absorb impact energy through a layered structure. Although they have a certain bulletproof capability, they have significant shortcomings when facing high-speed projectiles: First, the fiber layers mainly dissipate energy through tensile deformation, and have poor strain rate sensitivity, making it difficult to rapidly increase impact resistance in a very short time; second, conventional materials lack dynamic response capabilities, and after repeated impacts, fiber slippage and interlayer separation are prone to occur, leading to a decrease in protective performance; third, existing bulletproof vests mostly use rigid or semi-rigid backings, which are not comfortable enough and have a high density.

[0003] In recent years, shear-thickening fluids (STFs) have been introduced into the field of flexible bulletproofing due to their characteristic of rapidly increasing viscosity under high-speed shear ("liquid-solid transition"), which can lock kinetic energy at the moment of impact. However, pure STF systems suffer from problems such as poor dispersion stability, weak bonding with fiber interfaces, and easy leakage, which restricts their practical application. In addition, single STFs rely on viscosity abrupt changes to dissipate energy and lack auxiliary structures to enhance energy dissipation pathways, resulting in a still relatively high risk of blunt force damage.

[0004] Negative Poisson's ratio structural materials exhibit a "tensile expansion" effect, where they expand laterally under tension and contract laterally under compression. This allows them to densify upon impact, enhancing the overall toughness and energy absorption efficiency of the material. However, current research primarily focuses on negative Poisson's ratio structures in the form of metals or foams, making it difficult to form stable composites with flexible fibers and STFs.

[0005] Based on the above, the present invention provides a flexible bulletproof composite material and bulletproof vest based on a shear thickening liquid composite negative Poisson's ratio structure to solve the technical problems mentioned above. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a flexible bulletproof composite material that is lightweight, flexible, has good bulletproof effect, high protection level, and has a synergistic energy absorption mechanism, and to construct a multi-layer synergistic protection bulletproof vest based on this, thereby solving the technical problems of poor bulletproof effect, low protection level, heavy weight, and poor flexibility of existing bulletproof vests.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite with a negative Poisson's ratio structure includes the following steps: Step 1: Add the functional enhancer to the white oil at a mass ratio of 1:2-10. After high-speed shear dispersion, heating, circulation reflux and filtration, filter out the large particles. After evaporation to remove water from the remaining mixed components, store the resulting shear thickening liquid for later use. Step 2: Mix ultra-high molecular weight polyethylene with white oil and heat to 190-230℃ to prepare a mixture with a polyethylene concentration of 0.5-2.5wt%; in addition, mix the shear thickening liquid with white oil at a volume ratio of 1:0.5-2, and store the resulting mixture for later use. Step 3: Add the mixed components to the mixture at a mass ratio of 1:3-15, and after extrusion molding, obtain multi-component gel fiber with a solid content of 5-20 wt%; then, after organic solvent extraction and drying, obtain mixed fiber with a functional reinforcing agent content of 0.5-4 wt%. Step 4: The obtained mixed fibers are knitted by warp knitting, weft knitting, and woven into fabric; then the fabric is impregnated in adhesive solution to make a flexible bulletproof composite material; wherein the content of shear thickening adhesive in the flexible bulletproof composite material is 25-35wt%.

[0008] Furthermore, the organic solvent is either dichloromethane or xylene.

[0009] Furthermore, the functional enhancer is prepared by the following method: Step 1: Mix 4,4'-diaminodiphenyl ether, N,N-dimethylformamide, and pyromellitic dianhydride evenly at a ratio of 3-5g:120-150mL:5-6g. React in an ice-water bath under nitrogen protection for 2-4 hours. While stirring, pour the product into deionized water until the solid precipitates completely. Wash the precipitated solid with deionized water and ethanol 3-5 times each, then freeze-dry it. Mix the resulting solid powder with deionized water and triethylamine at a mass ratio of 1:30-50:0.25-0.5 and stir for 3-5 hours. The second step involves transferring the product components obtained in step one into a circular mold, while simultaneously applying a constant annular gradient temperature field around the mold to directionally freeze the product components. After freeze-drying and gradient heating heat treatment, the resulting gel is then subjected to pulverization, solvent replacement, and drying to obtain the functional enhancer.

[0010] Furthermore, the specific conditions for freeze-drying in the first step are as follows: temperature gradient from -20 to 40℃, pressure of 10-20 Pa; heating rate of 3-5℃ / 10 min, and holding at 5℃ for 50-70 min.

[0011] Furthermore, in the second step, liquid nitrogen is used as the cryocooler for directional freezing, and the freezing time is set to 40-60 minutes.

[0012] Furthermore, in the second step, the freeze-drying temperature is -30 to -50°C, the pressure is 10-20 Pa, and the freeze-drying time is 50-80 hours.

[0013] Furthermore, the specific steps of the gradient heating heat treatment in the second step are as follows: raise the temperature from room temperature to 70-80℃ and hold for 30-40 minutes; raise the temperature to 100-110℃ and hold for 20-30 minutes; raise the temperature to 120-130℃ and hold for 20-30 minutes; raise the temperature to 150-160℃ and hold for 50-60 minutes; raise the temperature to 180-190℃ and hold for 20-30 minutes; raise the temperature to 200-210℃ and hold for 20-30 minutes; raise the temperature to 240-250℃ and hold for 60-70 minutes.

[0014] Furthermore, the specific operation of the pulverization process in the second step is as follows: first, extrude the material for 2-5 hours at a temperature of 30-50℃ and a pressure of 0.5-3MPa, and then stir it at a speed of 1000-3000r / min for 2-4 hours; and during solvent replacement, replace the pulverized gel with methanol 3-5 times.

[0015] Furthermore, in the second step, the drying method uses carbon dioxide, ethanol, or methanol as a supercritical fluid, and supercritical drying is carried out at a temperature of 80-200℃ and a pressure of 8-12MPa for a drying time of 3-8 hours.

[0016] A bulletproof vest includes: a projectile-facing layer, an energy-dissipating layer, and a backing layer; wherein, The impact-resistant surface layer is made of ultra-high molecular weight polyethylene fabric with a tensile strength higher than 30 cN / dtex and a modulus higher than 800 cN / dtex and aramid non-woven fabric, with the ultra-high molecular weight polyethylene fabric located on the outermost layer. The thickness of the impact-resistant surface layer is 5-10 mm. The energy dissipation layer is composed of the above-mentioned flexible bulletproof composite material based on a shear thickening liquid composite negative Poisson's ratio structure, and the layers are fixed together by a spot bonding process; the thickness of the energy dissipation layer is 15-25mm. The backing layer has a density of 0.04-0.06 g / cm³. 3 It is made of polyurethane foam material, and the thickness of the backing layer is 10-15mm.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. The functional reinforcing agent in this invention is prepared from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride through a special process, resulting in a functional reinforcing agent with a special micro / nano structure, low density, and negative Poisson's ratio. The use of this functional reinforcing agent not only significantly improves the strain rate sensitivity of the shear thickening liquid system, enabling it to undergo a more rapid viscosity change under high-speed impact, thus efficiently dissipating energy, but also effectively improves the interfacial bonding between the system and ultra-high molecular weight polyethylene fibers, enhancing the overall integrity of the composite material. Furthermore, the lateral shrinkage densification effect of the negative Poisson's ratio structure and the liquid-solid phase transition of the shear thickening liquid form a synergistic energy absorption mechanism, significantly improving energy dissipation efficiency and effectively reducing the risk of blunt force trauma to internal organs. In addition, the synergistic effect between the shear thickening liquid and the fiber raw materials significantly improves the stab resistance of the prepared flexible bulletproof composite material and bulletproof vest, enabling it to cope with more complex threat scenarios.

[0018] 2. The flexible bulletproof composite material prepared in this invention combines the intelligent rheological properties of shear-thickening fluid with the mechanical properties of a negative Poisson's ratio structure, achieving a balance between high energy absorption efficiency and excellent resistance to repeated impacts. Furthermore, the flexible bulletproof composite material uses ultra-high molecular weight polyethylene fiber as its skeleton, maintaining lightweight and inherent flexibility while possessing excellent bulletproof performance, resulting in high wearing comfort and mobility. The interfacial bonding and mechanical anchoring effect of the functional reinforcing agent inhibits fiber slippage, preventing fiber fatigue fracture caused by long-term compression or repeated impacts.

[0019] 3. In this invention, the bulletproof vest effectively constructs a protective mechanism with synergistic protection through the coordinated operation of its various layers. Specifically, the high-strength fiber cloth surface layer is primarily responsible for the initial impact of the bullet; the core energy dissipation layer utilizes the properties of flexible bulletproof composite materials to significantly absorb and disperse impact kinetic energy; and the polyurethane foam backing provides final cushioning, reducing the risk of blunt force trauma. This structural design enables the bulletproof vest to achieve overall lightweighting while ensuring the necessary protection level. Furthermore, the spot bonding process provides a certain degree of relative movement space between the layers, optimizing its resistance to multiple impacts. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] The adhesive solutions used in the following examples and comparative examples were prepared as follows: polyethylene glycol 200, polyethylene glycol 400 and nano-silica with an average particle size of 550 nm were mixed and stirred at a rate of 400-600 r / min in a mass ratio of 1:1-3:0.2-0.6, while being ultrasonically treated in a water bath environment at 50-70℃, and finally allowed to stand in a vacuum chamber at room temperature for 6-8 hours to remove air bubbles.

[0022] Example 1 A method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite with a negative Poisson's ratio structure includes the following steps: Step 1: Add the functional enhancer to the white oil at a mass ratio of 1:2. After high-speed shear dispersion, heating, circulation reflux and filtration, filter out the large particles. After evaporation to remove water from the remaining mixed components, store the resulting shear thickening liquid for later use. Step 2: Mix ultra-high molecular weight polyethylene with white oil and heat to 190°C to prepare a mixture with a polyethylene concentration of 0.5 wt%. Separately, mix shear thickening liquid and white oil at a volume ratio of 1:0.5 and store the resulting mixture for later use. Step 3: Add the mixed components to the mixture at a mass ratio of 1:3, and after extrusion molding, obtain multi-component gel fiber with a solid content of 5wt%; then, after dichloromethane extraction and drying, obtain mixed fiber with a functional reinforcing agent content of 0.5wt%. Step 4: The obtained mixed fibers are knitted by warp knitting, weft knitting, and woven into fabric; then the fabric is impregnated in adhesive solution to make a flexible bulletproof composite material; wherein the content of shear thickening adhesive in the flexible bulletproof composite material is 25-35wt%.

[0023] The functional enhancer is prepared by the following method: Step 1: Mix 4,4'-diaminodiphenyl ether, N,N-dimethylformamide, and pyromellitic dianhydride evenly at a ratio of 3g:120mL:5g. React in an ice-water bath under nitrogen protection for 2 hours. While stirring, pour the product into deionized water until the solid precipitates completely. Wash the precipitated solid three times each with deionized water and ethanol, and then freeze-dry it. Mix the resulting solid powder with deionized water and triethylamine at a mass ratio of 1:30:0.25 and stir for 3 hours. The specific conditions for freeze drying are as follows: temperature gradient from -20 to 40℃, pressure of 10 Pa; heating rate of 3℃ / 10 min, holding at 5℃ for 50 min at intervals of 5℃. The second step involves transferring the product components obtained in step one into a circular mold, while simultaneously applying a constant annular gradient temperature field around the mold to directionally freeze the product components. After freeze-drying and gradient heating heat treatment, the resulting gel is then subjected to pulverization, solvent replacement, and drying to obtain the functional enhancer. Liquid nitrogen was used for directional freezing, and the freezing time was set to 40 minutes. The freeze-drying temperature was -30℃, the pressure was 1Pa, and the freeze-drying time was 50h. The specific steps of the gradient heating heat treatment are as follows: heat from room temperature to 70℃ and hold for 40 minutes; heat to 100℃ and hold for 30 minutes; heat to 120℃ and hold for 30 minutes; heat to 150℃ and hold for 60 minutes; heat to 180℃ and hold for 30 minutes; heat to 200℃ and hold for 30 minutes; heat to 240℃ and hold for 70 minutes. The specific operation of the pulverization process is as follows: first, the material is extruded for 5 hours at a temperature of 30℃ and a pressure of 0.5MPa, and then stirred at a speed of 1000r / min for 4 hours; and during solvent replacement, methanol is used to replace the pulverized gel three times. The drying method uses carbon dioxide as a supercritical fluid and carries out supercritical drying at a temperature of 80℃ and a pressure of 8MPa for 8 hours.

[0024] A bulletproof vest includes: a projectile-facing layer, an energy-dissipating layer, and a backing layer; wherein, The impact-resistant surface layer is made of ultra-high molecular weight polyethylene fabric with a tensile strength higher than 30 cN / dtex and a modulus higher than 800 cN / dtex and aramid non-woven fabric, with the ultra-high molecular weight polyethylene fabric located on the outermost layer. The thickness of the impact-resistant surface layer is 5 mm. The energy dissipation layer is made of the flexible bulletproof composite material prepared above, and the layers are fixed together by a spot bonding process; the thickness of the energy dissipation layer is 15 mm. The backing layer has a density of 0.04 g / cm³. 3 It is made of polyurethane foam material, and the backing layer is 10mm thick.

[0025] Example 2 A method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite with a negative Poisson's ratio structure includes the following steps: Step 1: Add the functional enhancer to the white oil at a mass ratio of 1:5. After high-speed shear dispersion, heating, circulation reflux and filtration, filter out the large particles. After evaporation to remove water from the remaining mixed components, store the resulting shear thickening liquid for later use. Step 2: Mix ultra-high molecular weight polyethylene with white oil and heat to 210°C to prepare a mixture with a polyethylene concentration of 1.5 wt%. In addition, mix the shear thickening liquid and white oil at a volume ratio of 1:1 and store the resulting mixture for later use. Step 3: Add the mixed components to the mixture at a mass ratio of 1:10, and after extrusion molding, obtain multi-component gel fiber with a solid content of 15wt%; then, after dichloromethane extraction and drying, obtain mixed fiber with a functional reinforcing agent content of 2wt%. Step 4: The obtained mixed fibers are knitted by warp knitting, weft knitting, and woven into fabric; then the fabric is impregnated in adhesive solution to make a flexible bulletproof composite material; wherein the content of shear thickening adhesive in the flexible bulletproof composite material is 30wt%.

[0026] The functional enhancer is prepared by the following method: Step 1: Mix 4,4'-diaminodiphenyl ether, N,N-dimethylformamide and pyromellitic dianhydride evenly at a ratio of 4g:130mL:6g. React in an ice-water bath under nitrogen protection for 3 hours. While stirring, pour the product into deionized water until the solid precipitates completely. Wash the precipitated solid with deionized water and ethanol four times each, and then freeze-dry it. Mix the resulting solid powder with deionized water and triethylamine at a mass ratio of 1:40:0.4 and stir for 4 hours. The specific conditions for freeze-drying in the first step are as follows: temperature gradient from -20 to 40℃, pressure of 15 Pa; heating rate of 5℃ / 10 min, and holding at 5℃ for 60 min; The second step involves transferring the product components obtained in step one into a circular mold, while simultaneously applying a constant annular gradient temperature field around the mold to directionally freeze the product components. After freeze-drying and gradient heating heat treatment, the resulting gel is then subjected to pulverization, solvent replacement, and drying to obtain the functional enhancer. Liquid nitrogen was used as the freezing liquid for directional freezing, and the freezing time was set to 50 minutes. The freeze-drying temperature was -40℃, the pressure was 15Pa, and the freeze-drying time was 60h. The specific steps of the gradient heating heat treatment are as follows: heat from room temperature to 75℃ and hold for 35 minutes; heat to 105℃ and hold for 25 minutes; heat to 125℃ and hold for 25 minutes; heat to 155℃ and hold for 55 minutes; heat to 185℃ and hold for 25 minutes; heat to 205℃ and hold for 25 minutes; heat to 245℃ and hold for 65 minutes. The specific operation of the pulverization process is as follows: first, the material is extruded for 4 hours at a temperature of 40℃ and a pressure of 2MPa, and then stirred at a speed of 2000r / min for 3 hours; and during solvent replacement, methanol is used to replace the pulverized gel four times. The drying method uses carbon dioxide, ethanol or methanol as supercritical fluid, and carries out supercritical drying at a temperature of 150℃ and a pressure of 10MPa for 5 hours.

[0027] A bulletproof vest includes: a projectile-facing layer, an energy-dissipating layer, and a backing layer; wherein, The impact-resistant surface layer is made of ultra-high molecular weight polyethylene fabric with a tensile strength higher than 30 cN / dtex and a modulus higher than 800 cN / dtex and aramid non-woven fabric, with the ultra-high molecular weight polyethylene fabric located on the outermost layer. The thickness of the impact-resistant surface layer is 8 mm. The energy dissipation layer is made of the flexible bulletproof composite material prepared above, and the layers are fixed together by a spot bonding process; the thickness of the energy dissipation layer is 20 mm. The backing layer has a density of 0.05 g / cm³. 3 It is made of polyurethane foam material, and the backing layer is 15mm thick.

[0028] Example 3 A method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite with a negative Poisson's ratio structure includes the following steps: Step 1: Add the functional enhancer to the white oil at a mass ratio of 1:10. After high-speed shear dispersion, heating, circulation reflux and filtration, filter out the large particles. After evaporation to remove water from the remaining mixed components, store the resulting shear thickening liquid for later use. Step 2: Mix ultra-high molecular weight polyethylene with white oil and heat to 230°C to prepare a mixture with a polyethylene concentration of 2.5 wt%. Separately, mix the shear thickening liquid and white oil at a volume ratio of 1:2 until homogeneous. Store the resulting mixture for later use. Step 3: Add the mixed components to the mixture at a mass ratio of 1:15, and after extrusion molding, obtain multi-component gel fiber with a solid content of 20wt%; then, after xylene extraction and drying, obtain mixed fiber with a functional reinforcing agent content of 4wt%. Step 4: The obtained mixed fibers are knitted by warp knitting, weft knitting, and woven into fabric; then the fabric is impregnated in adhesive solution to make a flexible bulletproof composite material; wherein the content of shear thickening adhesive in the flexible bulletproof composite material is 35wt%.

[0029] The functional enhancer is prepared by the following method: Step 1: Mix 4,4'-diaminodiphenyl ether, N,N-dimethylformamide and pyromellitic dianhydride evenly at a ratio of 5g:150mL:6g. React in an ice-water bath under nitrogen protection for 4 hours. While stirring, pour the product into deionized water until the solid precipitates completely. Wash the precipitated solid with deionized water and ethanol five times each, and then freeze-dry it. Mix the resulting solid powder with deionized water and triethylamine at a mass ratio of 1:50:0.5 and stir for 5 hours. The specific conditions for freeze drying in the first step are as follows: temperature gradient from -20 to 40℃, pressure of 20Pa; heating rate of 5℃ / 10min, and holding at 5℃ for 70min. The second step involves transferring the product components obtained in step one into a circular mold, while simultaneously applying a constant annular gradient temperature field around the mold to directionally freeze the product components. After freeze-drying and gradient heating heat treatment, the resulting gel is then subjected to pulverization, solvent replacement, and drying to obtain the functional enhancer. In particular, liquid nitrogen was used as the freezing liquid for directional freezing, and the freezing time was set to 60 minutes. The freeze-drying temperature was -50℃, the pressure was 20Pa, and the freeze-drying time was 50h.

[0030] The specific steps of the gradient heating heat treatment are as follows: heat from room temperature to 80℃ and hold for 30 minutes; heat to 110℃ and hold for 20 minutes; heat to 130℃ and hold for 20 minutes; heat to 160℃ and hold for 50 minutes; heat to 190℃ and hold for 20 minutes; heat to 210℃ and hold for 20 minutes; heat to 250℃ and hold for 60 minutes. The specific operation of the pulverization process is as follows: first, the material is extruded for 2 hours at a temperature of 50℃ and a pressure of 3MPa, and then stirred at a speed of 3000r / min for 2 hours; and during solvent replacement, methanol is used to replace the pulverized gel five times. The drying method uses carbon dioxide, ethanol or methanol as supercritical fluid, and carries out supercritical drying at a temperature of 200℃ and a pressure of 12MPa for 3 hours.

[0031] A bulletproof vest includes: a projectile-facing layer, an energy-dissipating layer, and a backing layer; wherein, The impact-resistant surface layer is made of ultra-high molecular weight polyethylene fabric with a tensile strength higher than 30 cN / dtex and a modulus higher than 800 cN / dtex and aramid non-woven fabric, with the ultra-high molecular weight polyethylene fabric located on the outermost layer. The thickness of the impact-resistant surface layer is 10 mm. The energy dissipation layer is made of the flexible bulletproof composite material prepared above, and the layers are fixed together by a spot bonding process; the thickness of the energy dissipation layer is 25 mm. The backing layer has a density of 0.06 g / cm³. 3 It is made of polyurethane foam material, and the backing layer is 15mm thick.

[0032] Comparative Example: The difference between this comparative example and Example 1 is that the shear thickening liquid in this comparative example does not contain a functional enhancer.

[0033] Performance testing: The performance of the functional enhancers prepared in Examples 1-3 and the bulletproof vests prepared in Examples 1-3 and the comparative examples was tested, and the test data are recorded in Tables 1 and 2 respectively. Table 1 Table 2 Note: 1. The V50 bullet velocity test is based on NIJ 0101.06 standard, which uses 9mm pistol bullets to determine the bullet velocity with a 50% probability of penetration.

[0034] 2. Multiple Impact Retention Rate: For V50, three consecutive shots of the same velocity were tested at the same position. The retention rate was calculated as (3rd shot V50 / 1st shot V50) × 100%. The V50 velocity and multiple impact retention rate values ​​in the table have been rounded to the nearest integer.

[0035] 3. Indentation depth: The maximum indentation depth was measured using a tissue-like gel after impact.

[0036] By comparing and analyzing the relevant data in the table, it can be seen that the flexible bulletproof composite material prepared by this invention has the effects of being lightweight and flexible, having good bulletproof performance, high protection level, and synergistic energy absorption mechanism. The prepared bulletproof vest adopts a three-layer synergistic structure of a projectile-facing layer, an energy dissipation layer, and a backing layer, which maintains lightweight and flexibility while achieving good bulletproof performance and high protection level, making it suitable for individual protection in complex threat scenarios. This indicates that the preparation method of the flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure and the bulletproof vest provided by this invention have a broader market prospect and are more suitable for promotion.

[0037] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite with a negative Poisson's ratio structure, characterized in that, Includes the following steps: Step 1: Add the functional enhancer to the white oil at a mass ratio of 1:2-10. After high-speed shear dispersion, heating, circulation reflux and filtration, filter out the large particles. After evaporation to remove water from the remaining mixed components, store the resulting shear thickening liquid for later use. Step 2: Mix ultra-high molecular weight polyethylene with white oil and heat to 190-230℃ to prepare a mixture with a polyethylene concentration of 0.5-2.5wt%; in addition, mix the shear thickening liquid with white oil at a volume ratio of 1:0.5-2, and store the resulting mixture for later use. Step 3: Add the mixed components to the mixture at a mass ratio of 1:3-15, and after extrusion molding, obtain multi-component gel fiber with a solid content of 5-20 wt%; then, after organic solvent extraction and drying, obtain mixed fiber with a functional reinforcing agent content of 0.5-4 wt%. Step 4: The obtained mixed fibers are knitted by warp knitting, weft knitting, and woven into fabric; then the fabric is impregnated in adhesive solution to make a flexible bulletproof composite material; wherein the content of shear thickening adhesive in the flexible bulletproof composite material is 25-35wt%.

2. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 1, characterized in that: The organic solvent is either dichloromethane or xylene.

3. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 1, characterized in that, The functional enhancer is prepared by the following method: Step 1: Mix 4,4'-diaminodiphenyl ether, N,N-dimethylformamide, and pyromellitic dianhydride evenly at a ratio of 3-5g:120-150mL:5-6g. React in an ice-water bath under nitrogen protection for 2-4 hours. While stirring, pour the product into deionized water until the solid precipitates completely. Wash the precipitated solid with deionized water and ethanol 3-5 times each, then freeze-dry it. Mix the resulting solid powder with deionized water and triethylamine at a mass ratio of 1:30-50:0.25-0.5 and stir for 3-5 hours. The second step involves transferring the product components obtained in step one into a circular mold, while simultaneously applying a constant annular gradient temperature field around the mold to directionally freeze the product components. After freeze-drying and gradient heating heat treatment, the resulting gel is then subjected to pulverization, solvent replacement, and drying to obtain the functional enhancer.

4. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 3, characterized in that, The specific conditions for freeze drying in the first step are as follows: temperature gradient from -20 to 40℃, pressure of 10-20 Pa; heating rate of 3-5℃ / 10 min, and holding at 5℃ for 50-70 min.

5. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 3, characterized in that: In the second step, liquid nitrogen is used as the freezing liquid for directional freezing, and the freezing time is set to 40-60 minutes.

6. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 3, characterized in that: In the second step, the freeze-drying temperature is -30 to -50℃, the pressure is 10-20Pa, and the freeze-drying time is 50-80h.

7. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 3, characterized in that, The specific steps of the gradient heating heat treatment in the second step are as follows: raise the temperature from room temperature to 70-80℃ and hold for 30-40 minutes; raise the temperature to 100-110℃ and hold for 20-30 minutes; raise the temperature to 120-130℃ and hold for 20-30 minutes; raise the temperature to 150-160℃ and hold for 50-60 minutes; raise the temperature to 180-190℃ and hold for 20-30 minutes; raise the temperature to 200-210℃ and hold for 20-30 minutes; raise the temperature to 240-250℃ and hold for 60-70 minutes.

8. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 3, characterized in that, The specific operation of the pulverization process in the second step is as follows: first, extrude the material for 2-5 hours at a temperature of 30-50℃ and a pressure of 0.5-3MPa, and then stir it at a speed of 1000-3000r / min for 2-4 hours; and during solvent replacement, replace the pulverized gel with methanol 3-5 times.

9. The method for preparing a flexible bulletproof composite material based on a shear-thickening liquid composite negative Poisson's ratio structure according to claim 3, characterized in that: In the second step, the drying method uses carbon dioxide, ethanol, or methanol as supercritical fluids, and supercritical drying is carried out at a temperature of 80-200℃ and a pressure of 8-12MPa for a drying time of 3-8 hours.

10. A bulletproof vest, characterized in that, include: The structure consists of an attack-resistant surface layer, an energy dissipation layer, and a backing layer; among which... The impact-resistant surface layer is made of ultra-high molecular weight polyethylene fabric with a tensile strength higher than 30 cN / dtex and a modulus higher than 800 cN / dtex and aramid non-woven fabric, with the ultra-high molecular weight polyethylene fabric located on the outermost layer. The thickness of the impact-resistant surface layer is 5-10 mm. The energy dissipation layer is composed of a flexible bulletproof composite material based on a shear thickening liquid composite negative Poisson's ratio structure as described in any one of claims 1-9, and the layers are fixed together by a spot bonding process; the thickness of the energy dissipation layer is 15-25 mm. The backing layer has a density of 0.04-0.06 g / cm³. 3 It is made of polyurethane foam material, and the thickness of the backing layer is 10-15mm.

Images