Thermoplastic aramid fiber composite material and preparation method thereof

Abstract

The invention relates to the technical field of fiber reinforced composite materials, in particular to a thermoplastic aramid fiber composite material and a preparation method thereof. The thermoplastic aramid fiber composite material comprises a modified aramid fiber fabric, the outer surface of the modified aramid fiber fabric is coated with a skin layer material, the skin layer material is a thermoplastic elastomer, and the skin layer material accounts for 30-50 wt% of the thermoplastic aramid fiber composite material; the thermoplastic elastomer is a thermoplastic polyurethane elastomer. Wherein the modified aramid fiber fabric is subjected to free radical graft copolymerization through 3-methacryloxypropyltriethoxysilane, itaconic acid and acrylic acid under the action of an initiator, and a stable active grafting layer is constructed on the surface of the aramid fiber fabric through covalent bond combination; and a continuous extrusion dipping hot press molding process is combined with multiple surface grafting modification of the aramid fibers, so that the prepared thermoplastic aramid composite material is high in tensile strength and peeling strength, and is resistant to solvents and damp-heat aging.

Description

Technical Field

[0001] This invention relates to the field of fiber-reinforced composite materials technology, specifically to a thermoplastic aramid composite material and its preparation method. Background Technology

[0002] Aramid fibers, especially para-aramid fibers, have become key reinforcing materials for high-end composite materials due to their excellent specific strength, specific modulus, impact resistance, and heat resistance. Traditional aramid composites typically use thermosetting resins (such as epoxy and phenolic resins) as the matrix. While these composites possess high stiffness and heat resistance, their components have some inherent drawbacks: long molding cycles, insufficient toughness, demanding prepreg storage conditions, and the products are not recyclable or reprocessable. These shortcomings limit their further promotion in applications requiring high efficiency, repairability, or environmentally friendly recyclability.

[0003] With the increasing demands for lightweight, impact-resistant, and green manufacturing in modern aerospace, transportation, and defense equipment, the development of aramid composites with excellent mechanical properties, high damage tolerance, rapid prototyping capabilities, and recyclability has become an urgent need. Thermoplastic resin matrices, such as polyetheretherketone (PEEK), polyphenylene sulfide (PPS), and polyamide (PA), offer an ideal way to overcome the shortcomings of thermosetting matrices due to their inherent toughness, melt processability, and potential recyclability. However, due to the obstruction of the large benzene rings in the aramid fiber molecular chain, amide groups are difficult to react with other atoms or groups, resulting in the chemical inertness of aramid fibers. Therefore, in aramid fiber-reinforced composites, the adhesion between the fiber and the matrix is ​​poor, leading to ineffective stress transfer and severely restricting the overall performance of the composite. To optimize the mechanical properties of fiber-reinforced polymer matrix composites, it is essential to effectively transfer stress from the matrix to the fiber through the adhesion between the matrix and the fiber. Therefore, it is usually necessary to modify the fiber surface to reduce the orientation degree or add a certain number of active groups to improve the interfacial compatibility of the composite. The core challenge in realizing the industrialization of high-performance thermoplastic aramid composite materials is to construct a robust interfacial layer between aramid fibers and thermoplastic resins through effective preparation processes. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of existing technologies, the present invention aims to provide a thermoplastic aramid composite material. This thermoplastic aramid composite material is produced by free radical graft copolymerization of 3-methacryloyloxypropyltriethoxysilane, itaconic acid, and acrylic acid under the action of an initiator. A stable active graft layer is constructed on the surface of aramid fiber fabric through covalent bonding. Then, a thermoplastic elastomer matrix is ​​attached to the surface of the active graft layer. The resulting thermoplastic aramid composite material has high tensile strength, high peel strength, solvent resistance, and resistance to damp heat aging, making it highly practical.

[0005] The preparation method of the thermoplastic aramid composite material of the present invention is simple, easy to operate and control, which is conducive to large-scale industrial production. The thermoplastic aramid composite material obtained has stable quality and excellent comprehensive performance.

[0006] The objective of this invention is achieved through the following technical solution: a thermoplastic aramid composite material, comprising a modified aramid fiber fabric, wherein the outer surface of the modified aramid fiber fabric is covered with a skin material, wherein the skin material is a thermoplastic elastomer.

[0007] Furthermore, the skin material accounts for 30-50 wt% of the thermoplastic aramid composite material; the thermoplastic elastomer is a thermoplastic polyurethane elastomer. Preferably, the thermoplastic polyurethane elastomer is at least one of polyester-type thermoplastic polyurethane elastomer or polyether-type thermoplastic polyurethane elastomer.

[0008] Furthermore, the preparation method of the modified aramid fiber layer includes the following steps: A1. Ultrasonically clean the aramid fiber fabric with acetone for 15-20 minutes to remove oil and dust from the fabric surface, and then dry it in a 55-65℃ forced-air drying oven for 1-2 hours for later use. A2. Immerse the aramid fiber fabric pretreated in step A1 completely in the surface etching agent and heat it to 80-90℃ for 30-60 minutes. Then wash it with water until the pH of the washing solution is 7. Place the aramid fiber fabric in a 55-65℃ forced-air drying oven for 1-2 hours and then transfer it to a 90-110℃ vacuum drying oven for 0.8-1.2 hours until constant weight is obtained to obtain the roughened aramid fabric. A3. At a temperature of 25-30℃, the roughened aramid fiber fabric is completely immersed in 3-methacryloxypropyltriethoxysilane hydrolysate for 2-4 hours. Then, the aramid fiber fabric is removed and placed in a 55-65℃ forced-air drying oven for 0.8-1.2 hours. Then, it is transferred to a 110-120℃ oven for 1-2 hours. Finally, the grafted aramid fiber fabric is ultrasonically cleaned with anhydrous ethanol for 8-12 minutes to remove the ungrafted free 3-methacryloxypropyltriethoxysilane from the surface. It is then dried at 55-65℃ to constant weight to obtain silane-grafted aramid fiber fabric. A4. Immerse the silane-grafted aramid fiber fabric in the monomer polymerization solution, purge with nitrogen to remove oxygen for 8-12 minutes, and then place it in a constant temperature water bath at 60-70℃ for 2-3 hours to initiate free radical grafting polymerization of monomers on the aramid surface; remove the fabric, rinse repeatedly with deionized water to remove unpolymerized monomers and homopolymers from the surface, dry in a forced-air dryer at 55-60℃ for 1-2 hours, and then vacuum dry at 90-110℃ to constant weight to obtain the modified aramid fiber fabric.

[0009] Furthermore, in step A1, the areal density of the aramid fiber fabric is 50-200 g / m³. 2 The thickness is 0.07-0.15 mm, wherein the aramid fiber fabric is woven from aramid fibers with a fineness of 150-300D. Preferably, the aramid fiber fabric is an aramid 1414 plain / twill fabric.

[0010] Furthermore, in step A2, the surface etchant is a 5-10 wt% NaOH aqueous solution. The strong alkali is used to perform limited hydrolysis of the amide bonds on the surface of the aramid fiber, etching out micro- and nano-scale grooves and micropores, increasing the surface area, and simultaneously exposing active functional groups (-NH2, -COOH).

[0011] Further, in step A3, the preparation method of the 3-methacryloxypropyltriethoxysilane hydrolysate includes the following steps: preparing a solvent by mixing anhydrous ethanol and deionized water at a volume ratio of 9:1, adding 3-methacryloxypropyltriethoxysilane, and controlling the mass concentration of the coupling agent to be 1-3wt%; adjusting the pH of the hydrolysate to 4-5 with glacial acetic acid to promote the hydrolysis of silaneoxy groups, and stirring magnetically for 30 min to obtain a transparent 3-methacryloxypropyltriethoxysilane hydrolysate.

[0012] Furthermore, in step A4, the method for preparing the monomer polymerization solution includes the following steps: adding 8-12 wt% itaconic acid, 5-10 wt% acrylic acid and 0.5-1 wt% initiator to deionized water, stirring magnetically until completely dissolved, and finally adjusting the pH of the monomer polymerization solution to 6-7 with NaOH.

[0013] The thermoplastic aramid composite material of the present invention forms a large number of active sites such as hydroxyl and amide bonds on the surface of aramid fiber fabric roughened by etching with NaOH aqueous solution. When the fabric is immersed in 3-methacryloyloxypropyltriethoxysilane hydrolysate, the ethoxy group in the silane coupling agent molecule hydrolyzes to generate silanol (-Si-OH). The silanol forms hydrogen bonds with the hydroxyl and amide bonds on the aramid surface, and undergoes dehydration condensation during subsequent drying and baking to form stable Si-OC chemical bonds, thereby firmly anchoring the silane coupling agent to the surface of the aramid fiber. The carbon-carbon double bond (C=C) at the other end of the silane molecule is retained on the fiber surface, becoming the grafting active site for subsequent free radical polymerization. The silane-grafted aramid fabric is immersed in a monomer polymerization solution containing itaconic acid, acrylic acid, and an initiator. After nitrogen deoxygenation, under constant temperature water bath conditions, the initiator simultaneously initiates the free radical graft copolymerization of the terminal double bonds of silane, itaconic acid, and acrylic acid. The itaconic acid molecules, possessing dicarboxyl groups and bireactive double bonds, can moderately branch the grafted polymer chains, improving the cohesive strength and stability of the grafted layer. Ultimately, a continuous, uniform, and non-detachable graft-modified layer is formed on the aramid surface. This grafted layer is tightly bonded to the aramid fiber through Si-OC chemical bonds and is rich in polar carboxyl groups on its surface. It can form excellent interfacial bonding and compatibility with the subsequent thermoplastic polyurethane elastomer skin layer, improving the problems of surface inertness, weak interfacial bonding, and easy delamination of traditional aramid fibers. This significantly enhances the interfacial strength, toughness, moisture and heat resistance, and processability of the composite material.

[0014] Furthermore, the initiator is ammonium persulfate.

[0015] This invention also provides a method for preparing a thermoplastic aramid composite material, comprising the following steps: S1. Place the thermoplastic elastomer granules in a vacuum drying oven and dry at 80-100℃ for 4-6 hours until the moisture content is ≤0.05% to prevent bubbles and pinholes from forming during melt molding. S2. The modified aramid fiber fabric is fed into the impregnation die of the extruder through the unwinding device. A guide roller is installed in the die to ensure that the fabric passes through smoothly. S3. Add the dried thermoplastic elastomer granules to the extruder hopper, turn on the screw, and after the thermoplastic elastomer granules are melted and plasticized in the barrel, they are accurately delivered to the impregnation die by the melt metering pump. The thermoplastic elastomer melt fully covers and impregnates the fiber gaps of the aramid fiber fabric in the die, realizing melt impregnation. S4. The impregnated thermoplastic elastomer / aramid fabric composite preform is fed into a continuous hot press through a traction device, and passes through the preheating section, forming section and cooling section of the hot press in sequence to obtain a thermoplastic aramid composite material. The formed composite material is then wound up by a winding device.

[0016] Furthermore, in step S3, the temperature of the extruder zone 1 is 140-160℃, the temperature of zone 2 is 160-180℃, the temperature of zone 3 is 170-190℃, the temperature of zone 4 is 170-190℃, and the temperature of the die head is 170-185℃; the screw speed is 100-300 r / min, and the melt metering pump speed is 5-20 r / min.

[0017] Furthermore, in step S4, the temperature of the preheating section is 160-180℃, the temperature of the forming section is 170-185℃, and the temperature of the cooling section is 30-50℃; the pressure of the hot press roller is 10-20MPa. The rotation speed of the hot press roller is synchronized with the traction speed of the fabric, both being 1-5m / min.

[0018] This invention utilizes a twin-screw extruder for melt impregnation, achieving continuous and uniform impregnation of aramid fiber fabrics with thermoplastic elastomer melt. Combined with continuous hot pressing for shaping, it boasts high production efficiency and superior impregnation uniformity and interfacial bonding of the composite material, making it suitable for continuous preparation of roll and sheet materials. The combined process of vacuum drying, extrusion melt impregnation, and continuous hot pressing is simple, easy to control, and conducive to large-scale industrial production, resulting in thermoplastic aramid composite materials of stable quality. The beneficial effects of this invention are as follows: The thermoplastic aramid composite material of this invention is produced by free radical graft copolymerization of 3-methacryloyloxypropyltriethoxysilane, itaconic acid, and acrylic acid under the action of an initiator. A stable active graft layer is constructed on the surface of aramid fiber fabric through covalent bonding. Then, by combining continuous extrusion impregnation hot pressing molding process with multiple surface graft modification of aramid fibers, not only is efficient, stable, and continuous preparation of thermoplastic aramid composite material achieved, but the bonding strength between fiber and elastomer matrix is ​​also greatly improved from the interface mechanism. The resulting thermoplastic aramid composite material has high tensile strength and peel strength, and is resistant to solvent and humid heat aging, making it highly practical.

[0019] Meanwhile, the preparation method of thermoplastic aramid composite materials is simple and easy to control, which is conducive to large-scale industrial production. The thermoplastic aramid composite materials obtained have stable quality and excellent comprehensive performance. Detailed Implementation

[0020] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0021] In some embodiments of the present invention, a thermoplastic aramid composite material includes a modified aramid fiber fabric, the outer surface of which is covered with a skin material, the skin material being a thermoplastic elastomer.

[0022] In some embodiments of the present invention, the skin material accounts for 30-50 wt% of the thermoplastic aramid composite material; the thermoplastic elastomer is a thermoplastic polyurethane elastomer. Preferably, the thermoplastic polyurethane elastomer is at least one of polyester-type thermoplastic polyurethane elastomer or polyether-type thermoplastic polyurethane elastomer.

[0023] In some embodiments of the present invention, the method for preparing the modified aramid fiber layer includes the following steps: A1. Ultrasonically clean the aramid fiber fabric with acetone for 15-20 minutes to remove oil and dust from the fabric surface, and then dry it in a 55-65℃ forced-air drying oven for 1-2 hours for later use. A2. Immerse the aramid fiber fabric pretreated in step A1 completely in the surface etching agent and heat it to 80-90℃ for 30-60 minutes. Then wash it with water until the pH of the washing solution is 7. Place the aramid fiber fabric in a 55-65℃ forced-air drying oven for 1-2 hours and then transfer it to a 90-110℃ vacuum drying oven for 0.8-1.2 hours until constant weight is obtained to obtain the roughened aramid fabric. A3. At a temperature of 25-30℃, the roughened aramid fiber fabric is completely immersed in 3-methacryloxypropyltriethoxysilane hydrolysate for 2-4 hours. Then, the aramid fiber fabric is removed and placed in a 55-65℃ forced-air drying oven for 0.8-1.2 hours. Then, it is transferred to a 110-120℃ oven for 1-2 hours. Finally, the grafted aramid fiber fabric is ultrasonically cleaned with anhydrous ethanol for 8-12 minutes to remove the ungrafted free 3-methacryloxypropyltriethoxysilane from the surface. It is then dried at 55-65℃ to constant weight to obtain silane-grafted aramid fiber fabric. A4. Immerse the silane-grafted aramid fiber fabric in the monomer polymerization solution, purge with nitrogen to remove oxygen for 8-12 minutes, and then place it in a constant temperature water bath at 60-70℃ for 2-3 hours to initiate free radical grafting polymerization of monomers on the aramid surface; remove the fabric, rinse repeatedly with deionized water to remove unpolymerized monomers and homopolymers from the surface, dry in a forced-air dryer at 55-60℃ for 1-2 hours, and then vacuum dry at 90-110℃ to constant weight to obtain the modified aramid fiber fabric.

[0024] In some embodiments of the present invention, in step A1, the areal density of the aramid fiber fabric is 50-200 g / m³. 2 The thickness is 0.07-0.15 mm, wherein the aramid fiber fabric is woven from aramid fibers with a fineness of 150-300D. Preferably, the aramid fiber fabric is an aramid 1414 plain / twill fabric.

[0025] In some embodiments of the present invention, in step A2, the surface etchant is a 5-10 wt% NaOH aqueous solution. A strong alkali is used to perform limited hydrolysis of the amide bonds on the surface of the aramid fiber, etching out micro- and nano-scale grooves and micropores, increasing the surface area, and simultaneously exposing active functional groups (-NH2, -COOH).

[0026] In some embodiments of the present invention, in step A3, the preparation method of the 3-methacryloxypropyltriethoxysilane hydrolysate includes the following steps: preparing a solvent by mixing anhydrous ethanol and deionized water at a volume ratio of 9:1, adding 3-methacryloxypropyltriethoxysilane, and controlling the mass concentration of the coupling agent to be 1-3 wt%; adjusting the pH of the hydrolysate to 4-5 with glacial acetic acid to promote the hydrolysis of silaneoxy groups, and stirring magnetically for 30 min to obtain a transparent 3-methacryloxypropyltriethoxysilane hydrolysate.

[0027] In some embodiments of the present invention, in step A4, the method for preparing the monomer polymerization solution includes the following steps: adding 8-12 wt% itaconic acid, 5-10 wt% acrylic acid and 0.5-1 wt% initiator to deionized water, stirring magnetically until completely dissolved, and finally adjusting the pH of the monomer polymerization solution to 6-7 with NaOH.

[0028] In some embodiments of the present invention, the initiator is ammonium persulfate.

[0029] This invention also provides a method for preparing a thermoplastic aramid composite material, comprising the following steps: S1. Place the thermoplastic elastomer granules in a vacuum drying oven and dry at 80-100℃ for 4-6 hours until the moisture content is ≤0.05% to prevent bubbles and pinholes from forming during melt molding. S2. The modified aramid fiber fabric is fed into the impregnation die of the extruder through the unwinding device. A guide roller is installed in the die to ensure that the fabric passes through smoothly. S3. Add the dried thermoplastic elastomer granules to the extruder hopper, turn on the screw, and after the thermoplastic elastomer granules are melted and plasticized in the barrel, they are accurately delivered to the impregnation die by the melt metering pump. The thermoplastic elastomer melt fully covers and impregnates the fiber gaps of the aramid fiber fabric in the die, realizing melt impregnation. S4. The impregnated thermoplastic elastomer / aramid fabric composite preform is fed into a continuous hot press through a traction device, and passes through the preheating section, forming section and cooling section of the hot press in sequence to obtain a thermoplastic aramid composite material. The formed composite material is then wound up by a winding device.

[0030] In some embodiments of the present invention, in step S3, the temperature of the extruder zone 1 is 140-160℃, the temperature of zone 2 is 160-180℃, the temperature of zone 3 is 170-190℃, the temperature of zone 4 is 170-190℃, and the temperature of the die head is 170-185℃; the screw speed is 100-300 r / min, and the melt metering pump speed is 5-20 r / min.

[0031] In some embodiments of the present invention, in step S4, the temperature of the preheating section is 160-180°C, the temperature of the forming section is 170-185°C, and the temperature of the cooling section is 30-50°C; the pressure of the hot press roller is 10-20 MPa. The rotational speed of the hot press roller is synchronized with the traction speed of the fabric, both being 1-5 m / min.

[0032] Example 1 In this embodiment, a thermoplastic aramid composite material includes a modified aramid fiber fabric, the outer surface of which is covered with a skin material, which is a thermoplastic elastomer.

[0033] Furthermore, the skin material accounts for 40 wt% of the thermoplastic aramid composite material; the thermoplastic elastomer is a thermoplastic polyurethane elastomer. The thermoplastic polyurethane elastomer is selected from polyester-type thermoplastic polyurethane elastomers, specifically BASF 1185A (Shore A 85, melt temperature 160-180℃).

[0034] Furthermore, the preparation method of the modified aramid fiber layer includes the following steps: A1. Clean the aramid fiber fabric with acetone using ultrasonic cleaning for 18 minutes to remove oil and dust from the fabric surface, and then dry it in a 60℃ forced-air drying oven for 1.5 hours for later use. A2. The aramid fiber fabric pretreated in step A1 is completely immersed in the surface etching agent and heated to 70℃ for 45 minutes. Then, it is washed with water until the pH of the washing solution is 7. The aramid fiber fabric is then placed in a 60℃ forced-air drying oven to dry for 1.5 hours, and then transferred to a 100℃ vacuum drying oven to dry for 1 hour until constant weight is obtained, thus obtaining the roughened aramid fabric. A3. At a temperature of 28℃, the roughened aramid fiber fabric is completely immersed in 3-methacryloxypropyltriethoxysilane hydrolysate for 3 hours. Then, the aramid fiber fabric is taken out and placed in a 60℃ forced-air drying oven for 1 hour. Then, it is transferred to a 115℃ oven for 1.5 hours. Finally, the grafted aramid fiber fabric is ultrasonically cleaned with anhydrous ethanol for 10 minutes to remove the ungrafted free 3-methacryloxypropyltriethoxysilane on the surface. It is then dried at 60℃ to constant weight to obtain silane-grafted aramid fiber fabric. A4. Immerse the silane-grafted aramid fiber fabric in the monomer polymerization solution, purge with nitrogen to remove oxygen for 10 min, and then place it in a 65℃ constant temperature water bath for 2.5 h to initiate free radical grafting polymerization of monomers on the aramid surface; remove the fabric, rinse repeatedly with deionized water to remove unpolymerized monomers and homopolymers from the surface, dry in a forced-air dryer at 58℃ for 1.5 h, and then vacuum dry at 100℃ to constant weight to obtain the modified aramid fiber fabric.

[0035] Furthermore, in step A1, the areal density of the aramid fiber fabric is 50-60 g / m². 2 The thickness is 0.09-0.1 mm, wherein the aramid fiber fabric is woven from aramid fibers with a fineness of 200D. The aramid fiber fabric is an aramid 1414 plain weave fabric.

[0036] Furthermore, in step A2, the surface etchant is an 8 wt% NaOH aqueous solution.

[0037] Further, in step A3, the preparation method of the 3-methacryloxypropyltriethoxysilane hydrolysate includes the following steps: preparing a solvent by mixing anhydrous ethanol and deionized water at a volume ratio of 9:1, adding 3-methacryloxypropyltriethoxysilane, and controlling the coupling agent mass concentration to 2wt%; adjusting the pH of the hydrolysate to 4-5 with glacial acetic acid to promote silane hydrolysis, and magnetically stirring for 30 min to obtain a transparent 3-methacryloxypropyltriethoxysilane hydrolysate.

[0038] Furthermore, in step A4, the method for preparing the monomer polymerization solution includes the following steps: adding 10wt% itaconic acid, 8wt% acrylic acid and 1wt% initiator to deionized water, stirring magnetically until completely dissolved, and finally adjusting the pH of the monomer polymerization solution to 6-7 with NaOH.

[0039] Furthermore, the initiator is ammonium persulfate.

[0040] This embodiment also provides a method for preparing a thermoplastic aramid composite material, comprising the following steps: S1. Place the thermoplastic elastomer granules in a vacuum drying oven and dry at 90°C for 5 hours until the moisture content is ≤0.05% to prevent bubbles and pinholes from forming during melt molding. S2. The modified aramid fiber fabric is fed into the impregnation die of the extruder through the unwinding device. A guide roller is installed in the die to ensure that the fabric passes through smoothly. S3. Add the dried thermoplastic elastomer granules to the extruder hopper, turn on the screw, and after the thermoplastic elastomer granules are melted and plasticized in the barrel, they are accurately delivered to the impregnation die by the melt metering pump. The thermoplastic elastomer melt fully covers and impregnates the fiber gaps of the aramid fiber fabric in the die, realizing melt impregnation. S4. The impregnated thermoplastic elastomer / aramid fabric composite preform is fed into a continuous hot press through a traction device, and passes through the preheating section, forming section and cooling section of the hot press in sequence to obtain a thermoplastic aramid composite material. The formed composite material is then wound up by a winding device.

[0041] Furthermore, in step S3, the temperature of the extruder is 150°C in zone one, 170°C in zone two, 180°C in zone three, 180°C in zone four, and 185°C in the die head; the screw speed is 200 r / min, and the melt metering pump speed is 18 r / min.

[0042] Furthermore, in step S4, the temperature of the preheating section is 170°C, the temperature of the forming section is 185°C, and the temperature of the cooling section is 40°C; the pressure of the hot press roller is 15 MPa. The rotation speed of the hot press roller is synchronized with the traction speed of the fabric, both being 3 m / min.

[0043] Comparative Example 1 The difference between this comparative example and Example 1 is that an equal amount of KH-550 aminosilane is used to replace 3-methacryloyloxypropyltriethoxysilane.

[0044] Comparative Example 2 The difference between this comparative example and Example 1 is that an equal amount of acrylic acid is used instead of itaconic acid.

[0045] Performance testing The thermoplastic aramid composites prepared in Example 1 and Comparative Examples 1-2 were subjected to performance tests. The tensile strength, peel strength, solvent resistance, and damp heat resistance of the thermoplastic aramid composites were tested, and the test data are shown in Table 1 below: Table 1

[0046] Tensile property testing: The tensile strength of thermoplastic aramid composite material was tested according to GB / T 1040.3-2006, with a tensile rate of 5 mm / min.

[0047] Peel strength test: according to GB / T 2790-2014 (Adhesives 180° peel strength test method) Solvent resistance: The sample was immersed in acetone (industrial grade) at 25°C for 24 hours. After removal, the surface was wiped dry, and the tensile strength retention rate of the sample before and after immersion was measured.

[0048] Test of resistance to damp heat: (1) The thermoplastic aramid composite materials prepared in Example 1 and Comparative Examples 1-2 were cut into samples of the same size; (2) The samples were placed in a damp heat test chamber and subjected to continuous damp heat exposure under the set wet and dry cycle conditions. Each cycle included 12 hours of damp heat exposure (set temperature 65℃, humidity 85%RH) and 12 hours of drying (set temperature 25℃, humidity 45%RH); (3) The samples were taken out after 6 cycles and the tensile strength retention rate of the samples before and after damp heat treatment was measured.

[0049] This invention significantly improves the overall performance of thermoplastic aramid composite materials through synergistic grafting modification of 3-methacryloyloxypropyltriethoxysilane and itaconic acid-acrylic acid, combined with an optimized preparation process, and solves the problems of weak interfacial bonding and poor environmental resistance of traditional modification schemes.

[0050] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A thermoplastic aramid composite material, characterized in that: It includes modified aramid fiber fabrics, the outer surface of which is covered with a skin material, the skin material being a thermoplastic elastomer.

2. The thermoplastic aramid composite material according to claim 1, characterized in that: The skin layer material accounts for 30-50 wt% of the thermoplastic aramid composite material; the thermoplastic elastomer is a thermoplastic polyurethane elastomer.

3. The thermoplastic aramid composite material according to claim 1, characterized in that: The method for preparing the modified aramid fiber layer includes the following steps: A1. Ultrasonically clean the aramid fiber fabric with acetone for 15-20 minutes to remove oil and dust from the fabric surface, and then dry it in a 55-65℃ forced-air drying oven for 1-2 hours for later use. A2. Immerse the aramid fiber fabric pretreated in step A1 completely in the surface etching agent and heat it to 80-90℃ for 30-60 minutes. Then wash it with water until the pH of the washing solution is 7. Place the aramid fiber fabric in a 55-65℃ forced-air drying oven for 1-2 hours and then transfer it to a 90-110℃ vacuum drying oven for 0.8-1.2 hours until constant weight is obtained to obtain the roughened aramid fabric. A3. At a temperature of 25-30℃, the roughened aramid fiber fabric is completely immersed in 3-methacryloxypropyltriethoxysilane hydrolysate for 2-4 hours. Then, the aramid fiber fabric is removed and placed in a 55-65℃ forced-air drying oven for 0.8-1.2 hours. Then, it is transferred to a 110-120℃ oven for 1-2 hours. Finally, the grafted aramid fiber fabric is ultrasonically cleaned with anhydrous ethanol for 8-12 minutes to remove the ungrafted free 3-methacryloxypropyltriethoxysilane from the surface. It is then dried at 55-65℃ to constant weight to obtain silane-grafted aramid fiber fabric. A4. Immerse the silane-grafted aramid fiber fabric in the monomer polymerization solution, purge with nitrogen to remove oxygen for 8-12 minutes, and then place it in a constant temperature water bath at 60-70℃ for 2-3 hours to initiate free radical grafting polymerization of monomers on the aramid surface; remove the fabric, rinse repeatedly with deionized water to remove unpolymerized monomers and homopolymers from the surface, dry in a forced-air dryer at 55-60℃ for 1-2 hours, and then vacuum dry at 90-110℃ to constant weight to obtain the modified aramid fiber fabric.

4. The thermoplastic aramid composite material according to claim 3, characterized in that: In step A1, the areal density of the aramid fiber fabric is 50-200 g / m³. 2 The thickness is 0.07-0.15mm, wherein the aramid fiber fabric is woven from aramid fibers, and the fineness of the aramid fibers is 150-300D.

5. The thermoplastic aramid composite material according to claim 3, characterized in that: In step A2, the surface etchant is a 5-10 wt% NaOH aqueous solution.

6. The thermoplastic aramid composite material according to claim 3, characterized in that: In step A4, the method for preparing the monomer polymerization solution includes the following steps: adding 8-12 wt% itaconic acid, 5-10 wt% acrylic acid and 0.5-1 wt% initiator to deionized water, stirring magnetically until completely dissolved, and finally adjusting the pH of the monomer polymerization solution to 6-7 with NaOH.

7. The thermoplastic aramid composite material according to claim 6, characterized in that: The initiator is ammonium persulfate.

8. A method for preparing a thermoplastic aramid composite material according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Place the thermoplastic elastomer granules in a vacuum drying oven and dry at 80-100℃ for 4-6 hours until the moisture content is ≤0.05% and set aside for later use. S2. The modified aramid fiber fabric is fed into the impregnation die of the extruder through the unwinding device. A guide roller is installed in the die to ensure that the fabric passes through smoothly. S3. Add the dried thermoplastic elastomer granules to the extruder hopper, turn on the screw, and after the thermoplastic elastomer granules are melted and plasticized in the barrel, they are accurately delivered to the impregnation die by the melt metering pump. The thermoplastic elastomer melt fully covers and impregnates the fiber gaps of the aramid fiber fabric in the die, realizing melt impregnation. S4. The impregnated thermoplastic elastomer / aramid fabric composite preform is fed into a continuous hot press through a traction device, and passes through the preheating section, forming section and cooling section of the hot press in sequence to obtain a thermoplastic aramid composite material. The formed composite material is then wound up by a winding device.

9. The method for preparing a thermoplastic aramid composite material according to claim 8, characterized in that: In step S3, the temperature of the extruder is 140-160℃ in zone one, 160-180℃ in zone two, 170-190℃ in zone three, 170-190℃ in zone four, and 170-185℃ in the die head; the screw speed is 100-300 r / min, and the melt metering pump speed is 5-20 r / min.

10. The method for preparing a thermoplastic aramid composite material according to claim 8, characterized in that: In step S4, the temperature of the preheating section is 160-180℃, the temperature of the forming section is 170-185℃, and the temperature of the cooling section is 30-50℃; the pressure of the hot press roller is 10-20MPa.

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