Vitrimer epoxy resin composite material and preparation method thereof

Abstract

The invention discloses a modified aramid fiber reinforced Vitrimer epoxy resin composite material and a preparation method thereof, the composite material realizes dynamic combination through modified aramid fiber and Vitrimer epoxy resin, the surface of the modified aramid fiber has dynamic covalent bonds, and the Vitrimer epoxy resin has a double dynamic crosslinking characteristic. The composite material has the advantages of being high in interface bonding strength and excellent in material mechanical property, the interface of the composite material has the exchange characteristic of dynamic bonds, the interface is endowed with excellent dynamic performance and adaptability, new possibilities are provided for damage repair and reprocessing of the material, and the composite material has good application prospects. The method has important significance for improving the durability and the maintenance efficiency of the material, and develops a new possibility for the application of high-performance composite materials.

Description

Technical Field

[0001] This invention belongs to the field of fiber-reinforced polymer matrix composites technology, and particularly relates to a Vitrimer epoxy resin composite material and its preparation method. Background Technology

[0002] Aramid fibers are used as reinforcements for epoxy resin composites due to their excellent mechanical properties and chemical stability. However, there are obvious limitations in the interfacial bonding between them and epoxy resins. Due to the smoothness and chemical inertness of the aramid fiber surface, there is a lack of sufficient chemical and physical bonding between them and epoxy resins. This causes the composite material to easily debond at the interface when under stress, affecting the overall performance of the material. Therefore, in order to improve the interfacial strength of the material, it is necessary to modify the surface of the aramid fiber to give it surface chemical activity.

[0003] Meanwhile, in the design of traditional aramid fiber reinforced composites, epoxy resin and aramid fibers are impregnated and then thermosetting. Not only is there residual thermal stress at the interface, but the interface is also typically static. This means that once formed, these interfaces cannot adapt to changes in external conditions and cannot self-adjust or repair under external stimuli. This design ignores the importance of dynamic conformal properties of the interface. The introduction of vitrimer-like epoxy resins offers a solution to this problem. Vitrimer-like polymers are polymer networks with dynamic covalent bonds that can exchange under specific conditions such as thermal stimulation. This allows the material to change its network topology while maintaining a constant crosslinking density, giving it the ability to be thermoreshaped and repaired.

[0004] Although vitrimer-like epoxy resins are used in casting and electronic device packaging, their application in fiber-reinforced composites is limited by interfacial properties. This is because traditional interfacial designs do not consider the synergistic matching between the chemical bonds of the modified aramid fibers and the dynamic covalent bonds of the epoxy resin matrix. In other words, the epoxy resin and aramid fibers cannot form exchangeable covalent bonds, which limits the dynamic conformability of the interface and restricts the adaptability, thermoforming and reuse capabilities, and damage repair capabilities of the composite material. Summary of the Invention

[0005] To overcome the aforementioned problems, this invention proposes a Vitrimer epoxy resin composite material and its preparation method. The composite material achieves dynamic bonding through modified aramid fibers and Vitrimer epoxy resin. The modified aramid fibers have dynamic covalent bonds on their surface, and the Vitrimer epoxy resin exhibits dual dynamic crosslinking characteristics. The composite material possesses advantages such as high interfacial bonding strength and excellent mechanical properties. Furthermore, the dynamic bond exchange characteristics at the composite material interface endow it with excellent dynamic performance and adaptability, providing new possibilities for material damage repair and reprocessing. This is of great significance for improving material durability and repair efficiency, opening up new possibilities for the application of high-performance composite materials, thus completing this invention.

[0006] Specifically, the object of the present invention is to provide the following aspects: In a first aspect, a Vitrimer epoxy resin composite material is provided, wherein the composite material is dynamically bonded by modified aramid fibers and Vitrimer epoxy resin, wherein the surface of the modified aramid fibers has dynamic covalent bonds, and the Vitrimer epoxy resin has dual dynamic crosslinking characteristics.

[0007] In a second aspect, a method for preparing the composite material described in the first aspect is provided, the method comprising: Prepare Vitrimer epoxy resin with dual dynamic crosslinking properties; Dynamic covalent bonds are introduced on the surface of aramid fiber matrix to obtain modified aramid fibers; The modified aramid fiber and Vitrimer epoxy resin were cured to prepare the composite material.

[0008] The beneficial effects of this invention include: (1) The Vitrimer epoxy resin composite material provided by the present invention has a cross-linked network with dual dynamic covalent bonds constructed in the epoxy resin matrix, which makes the Vitrimer epoxy resin have excellent dynamic properties, can be damaged and self-repaired, has high toughness and fracture strength, and its viscous flow characteristics meet the requirements of aramid fiber impregnation.

[0009] (2) The Vitrimer epoxy resin composite material provided by the present invention introduces covalent bonds in the interface between the aramid fiber matrix and the epoxy resin matrix. The prepared composite material has the advantages of high interfacial bonding strength and excellent mechanical properties.

[0010] (3) The method for preparing the Vitrimer epoxy resin composite material provided by the present invention involves covalently grafting a silane coupling agent containing disulfide bonds onto the surface of an aramid fiber matrix, and forming a double dynamic crosslinking network in the epoxy resin matrix through dynamic covalent bonds of ester exchange and disulfide exchange. This method achieves dynamic conformal capability at the interface between the aramid fiber and the epoxy resin, and damage repair capability of the composite material, through the exchange reaction between the disulfide bonds on the surface of the modified aramid fiber and the disulfide bonds in the Vitrimer epoxy resin, as well as the dynamic crosslinking characteristics within the Vitrimer epoxy resin.

[0011] (4) The method for preparing Vitrimer epoxy resin composite material provided by this invention introduces the same type of dynamic covalent bonds simultaneously on the surface of the aramid fiber matrix and inside the epoxy resin matrix, enabling dynamic bond exchange at the composite material interface. This endows the interface with excellent dynamic properties and adaptability, providing a pathway for material damage repair and thermal remodeling. This innovative design not only improves the bonding strength of the interface but also endows the material with excellent dynamic properties and adaptability, providing new possibilities for material damage repair and reprocessing. This is of great significance for improving the durability and repair efficiency of materials and opens up new possibilities for the application of high-performance composite materials. Attached Figure Description

[0012] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0013] In the attached diagram: Figure 1 The spectrum comparison diagram of the modified aramid fiber in Example 3 and the unmodified aramid fiber in Comparative Example 1 is shown. Figure 2 A schematic diagram illustrating the reaction principle for preparing Vitrimer epoxy resin in a preferred embodiment is shown. Figure 3(a) shows a schematic diagram of the interfacial reaction principle between modified aramid fiber and Vitrimer epoxy resin. Figure 3(b) shows a schematic diagram of the interface reaction principle between modified aramid fiber and Vitrimer epoxy resin. Figure 4(a) shows the viscosity-temperature curves of modified aramid fiber and Vitrimer epoxy resin during vacuum pressure impregnation in Example 1. Figure 4(b) shows the viscosity-temperature curves of modified aramid fibers and Vitrimer epoxy resin during vacuum pressure impregnation in Example 2. Figure 4(c) shows the viscosity-temperature curves of modified aramid fiber and Vitrimer epoxy resin during vacuum pressure impregnation in Example 3. Figure 4(d) shows the viscosity-temperature curves of modified aramid fibers and Vitrimer epoxy resin during vacuum pressure impregnation in Example 4. Figure 5 A comparison graph showing the interfacial normal strength measurement curves of the composite materials prepared in Comparative Example 1 and Example 3 is presented. Figure 6 The diagram shows a comparison of the interfacial bonding properties of the composite materials prepared in Comparative Example 1 and Examples 1-4. Detailed Implementation

[0014] The following will refer to the appendix. Figures 1 to 6 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0015] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0016] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0017] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0018] On the one hand, according to the present invention, a vitrimer-like epoxy resin composite material is provided, wherein the composite material is dynamically bonded by modified aramid fibers and vitrimer-like epoxy resin, wherein the modified aramid fibers have dynamic covalent bonds on their surface and the vitrimer-like epoxy resin has dual dynamic crosslinking characteristics.

[0019] Furthermore, the vitrimer-like epoxy resin possesses ester bond exchange and disulfide bond exchange properties; the dynamic covalent bonds on the surface of the modified aramid fiber are disulfide bonds, which are located at 1045 cm⁻¹. -1 A -Si-OC- peak exists at this location.

[0020] According to the present invention, dynamic crosslinking is achieved by introducing disulfide exchange within a vitrimer-like epoxy resin, thereby introducing dynamic covalent bonds onto the surface of an aramid fiber matrix, resulting in modified aramid fibers. This allows the modified aramid fiber surface to not only form covalent bonds with the vitrimer-like epoxy resin, but also for these bonds to be dynamically exchangeable. This means that even under external stimuli such as temperature changes, if the vitrimer-like epoxy resin moves relative to the aramid fiber matrix, the dynamic covalent bonds at the interface can recombine through exchangeable reactions, thus maintaining effective chemical bonding. Consequently, even when the material is damaged or requires reshaping, the interface can maintain its dynamic conformability, improving the material's repair capabilities and adaptability, and enhancing the performance of the composite material.

[0021] In this invention, when the molar content of the curing agent containing disulfide bonds is 10% to 20% of the epoxy groups in the epoxy resin, the interfacial shear strength retention rate of the composite material after rebonding is between 78% and 96%.

[0022] According to the present invention, the vitrimer-like epoxy resin with dual dynamic crosslinking properties comprises the following molar proportions of raw materials: epoxy groups in the epoxy resin: curing agent containing disulfide bonds: acid anhydride curing agent: transesterification catalyst = 1: (0.1~0.2): (0.3~0.4): (0.04~0.05), for example 1:0.2:0.3:0.05.

[0023] In this invention, the modified aramid fiber with dynamic covalent bonds comprises the following raw materials: aramid fiber matrix and coupling agent, wherein the coupling agent contains disulfide bonds, preferably a silane coupling agent containing disulfide bonds, such as a disulfide silane coupling agent.

[0024] On the other hand, according to the present invention, a method for preparing the composite material described in the first aspect is provided, the method comprising: Step 1: Prepare a glass-like polymer (Vitrimer) epoxy resin with dual dynamic crosslinking properties; Step 2: Introduce dynamic covalent bonds on the surface of the aramid fiber matrix to obtain modified aramid fibers; Step 3: Curing the modified aramid fiber and vitrimer epoxy resin to prepare the composite material.

[0025] The preparation method of the above composite material is described in detail below.

[0026] Step 1: Prepare a glass-like polymer (Vitrimer) epoxy resin with dual dynamic crosslinking properties.

[0027] According to a preferred embodiment, step 1 includes: Step 1-1: Mix the epoxy resin matrix with a curing agent containing disulfide bonds to obtain the first solution; Steps 1-2: Add an anhydride curing agent and transesterification catalyst to the first solution to obtain the Vitrimer-like epoxy resin.

[0028] According to the present invention, the epoxy resin matrix is ​​endowed with dual dynamic crosslinking properties, enabling the disulfide bonds to undergo exchange reactions even at low concentrations. The curing agent containing disulfide bonds introduces disulfide functional groups into the epoxy resin matrix. To avoid excessively high system viscosity and excessively rapid system reaction rates due to excessive addition of the curing agent containing disulfide bonds, which would affect the system's process window time, an anhydride curing agent is blended with the disulfide bond-containing curing agent to ensure reliable crosslinking while maintaining good processability. Furthermore, since the ester bond network of anhydride-cured epoxy resin is a permanent network and cannot undergo exchange reactions without a catalyst, and the system is difficult to achieve dynamic crosslinking properties at low disulfide bond concentrations, an ester exchange catalyst is selected to enable ester bond exchange, endowing the material with dual dynamic crosslinking properties, allowing disulfide bonds to meet and undergo exchange reactions even at low concentrations.

[0029] In step 1-1, the epoxy resin matrix is ​​bisphenol A epoxy resin, such as E51 type epoxy resin, E44 type epoxy resin and E39 type epoxy resin.

[0030] Among them, E51 type epoxy resin has a small molecular weight and low viscosity, which is beneficial to improving the impregnation effect between the mixed epoxy resin system and the fiber. Therefore, E51 type epoxy resin is preferred.

[0031] In step 1-1, the curing agent containing disulfide bonds is preferably selected from any one or more of 2,2-dithiodiacetic acid, 3,3-dithiodipropionic acid (DTDPA), and 4,4-dithiodibutyric acid, more preferably 3,3-dithiodipropionic acid (DTDPA).

[0032] In this particular curing agent containing disulfide bonds, the product obtained by the crosslinking reaction of the carboxylic acid with the epoxy resin is the same as that of the anhydride curing agent, both of which generate ester bonds in the network, which is beneficial for transesterification and disulfide exchange in the network. Due to the economic efficiency and convenient availability of 3,3-dithiodipropionic acid (DTDPA), 3,3-dithiodipropionic acid (DTDPA) is preferred.

[0033] In the first solution, as the content of the curing agent containing disulfide bonds increases, the viscosity of the vitrimer epoxy resin increases. When the molar ratio of epoxy groups to the curing agent containing disulfide bonds in the epoxy resin matrix is ​​greater than 1:0.3, the viscosity of the vitrimer epoxy resin is too high to cure with the modified aramid fibers. Typically, the molar ratio of epoxy groups to the curing agent containing disulfide bonds in the epoxy resin matrix is ​​1:(0.1~0.2). At this ratio, the disulfide bond content meets the requirements for achieving an exchangeable reaction, and the system viscosity remains below 800 mPa during impregnation with the modified aramid fibers, ensuring effective impregnation. For example, using E51 type bisphenol A epoxy resin and 3,3-dithiodipropionic acid (DTDPA) as an example, a ratio of 1:0.2 is optimal.

[0034] In step 1-1, preferably, a curing agent containing disulfide bonds is added to an epoxy resin matrix at 140-160°C until the curing agent containing disulfide bonds is completely dissolved to obtain a first solution. More preferably, a curing agent containing disulfide bonds is added to an epoxy resin matrix at 145-155°C until the curing agent containing disulfide bonds is completely dissolved to obtain a first solution. For example, a curing agent containing disulfide bonds is added to an epoxy resin matrix at 155°C until the curing agent containing disulfide bonds is completely dissolved to obtain a first solution.

[0035] Furthermore, epoxy resin at 140~160℃ has low viscosity without decomposing, thus yielding a homogeneous first solution.

[0036] In steps 1-2, the anhydride curing agent is preferably selected from any one or more of methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 4-methyltetrahydrophthalic anhydride (MeTHPA), more preferably 4-methyltetrahydrophthalic anhydride (MeTHPA). Because 4-methyltetrahydrophthalic anhydride (MeTHPA) has lower viscosity, the mixed epoxy resin system has low viscosity, making it suitable for impregnation with modified aramid fibers. In steps 1-2, the transesterification catalyst is preferably selected from one of zinc acetate, organotin compounds, zinc acetylacetone, and triethanolamine (TEOA), more preferably triethanolamine (TEOA). This is because triethanolamine has lower viscosity, and adding it to the epoxy resin matrix can effectively reduce the overall viscosity of the system. Furthermore, compared to organometallic catalysts, it is safer to use and has less environmental impact.

[0037] In steps 1-2, the molar ratio of epoxy groups, anhydride curing agent, and transesterification catalyst in the epoxy resin is 1:(0.3~0.4):(0.04~0.05), for example, 1:0.3:0.05. This molar ratio is chosen to achieve the dynamic properties of disulfide and transesterification while ensuring sufficient curing reaction of the epoxy resin matrix. This ratio balances the number of epoxy groups, disulfide bonds, and exchangeable ester bonds. Simultaneously, the amount of transesterification catalyst, such as triethanolamine, added ensures the efficiency of transesterification catalysis while avoiding excessive amounts that could lead to other side reactions and an excessively rapid curing reaction rate, thus ensuring good impregnation properties and dynamic reversibility of the material.

[0038] In steps 1-2, after the temperature of the first solution drops to 90-100°C, an anhydride curing agent is added; then, when the temperature drops to 70-80°C, an ester exchange catalyst is added to obtain the vitrimer-like epoxy resin. For example, after the temperature of the first solution drops to 90°C, an anhydride curing agent is added; then, when the temperature drops to 80°C, an ester exchange catalyst is added to obtain the vitrimer-like epoxy resin.

[0039] Furthermore, since the addition of the transesterification catalyst will accelerate the crosslinking reaction of the epoxy resin system and gradually increase the viscosity of the system, it should be added to the system last to ensure sufficient impregnation time.

[0040] In one implementation, Figure 2 The diagram illustrates the reaction principle for preparing vitrimer-like epoxy resins, using E51 type bisphenol A epoxy resin (DGEBA), 4-methyltetrahydrophthalic anhydride (MeTHPA), 3,3-dithiodipropionic acid (DTDPA), and triethanolamine (TEOA) as examples.

[0041] Step 2: Introduce dynamic covalent bonds on the surface of the aramid fiber matrix to obtain modified aramid fibers.

[0042] In step 2, the dynamic covalent bonds introduced on the surface of the aramid fiber matrix are disulfide bonds, which enable it to dynamically bond with the vitrimer epoxy resin.

[0043] Furthermore, in order to graft functional groups containing disulfide bonds onto the surface of the aramid fiber matrix, a silane coupling agent containing disulfide bonds needs to be selected for grafting. The silane coupling agent needs to undergo hydrolysis to make the end rich in hydroxyl groups so that it can be grafted onto the surface of the aramid fiber.

[0044] In step 2, a silane coupling agent containing disulfide bonds is selected to introduce disulfide bonds on the surface of the aramid fiber matrix. Specifically, the silane coupling agent containing disulfide bonds is hydrolyzed, and then the aramid fiber matrix is ​​modified to introduce disulfide bonds on the surface of the aramid fiber matrix, thereby obtaining modified aramid fibers.

[0045] In step 2, the silane coupling agent containing disulfide bonds is preferably a disulfide silane coupling agent (Si-75).

[0046] In step 2, the aramid fiber matrix is ​​para-aramid fiber.

[0047] The inventors have discovered that para-aramid fibers have superior tensile strength and modulus compared to heterocyclic aramids and meta-aramids. In composite materials, they can significantly improve the overall strength and stiffness of the composite material, while having a relatively low density, which helps to reduce the overall density of the composite material and improve the specific strength and specific stiffness of the material.

[0048] In a preferred embodiment, the hydrolysis includes: dissolving a silane coupling agent containing disulfide bonds in a dispersant, adjusting the pH to 3-5 with an acidic solvent, and then sonicating at 30-45°C for 8-14 hours to obtain a coupling agent hydrolysate. For example, dissolving a silane coupling agent containing disulfide bonds in a dispersant, adjusting the pH to 4 with an acidic solvent, and then sonicating at 35°C for 12 hours to obtain a coupling agent hydrolysate.

[0049] The dispersant is preferably an ethanol solution, such as an 80% ethanol solution. Ethanol solutions are not only non-toxic, but also exhibit excellent dispersibility of silane coupling agents containing disulfide bonds in ethanol solutions.

[0050] Furthermore, the mass fraction of the silane coupling agent containing disulfide bonds in the dispersant is 6-8%, for example 7.5%.

[0051] In step 2, the acidic solution is not limited to strong or weak acids, but is preferably a weak acid, such as acetic acid, which is more conducive to the hydrolysis reaction.

[0052] In step 2, ultrasound helps break the chemical bonds of the coupling agent, thereby accelerating the hydrolysis reaction. The longer the ultrasound treatment time, the more complete the hydrolysis reaction; ultrasound for 8–14 hours is more suitable. Ultrasound at 30–45°C further accelerates the hydrolysis reaction rate.

[0053] In step 2, during modification, the para-aramid fiber is placed in a coupling agent hydrolysate, and then the para-aramid fiber is removed, washed, and dried to obtain the modified aramid fiber.

[0054] Furthermore, during modification, the temperature of the coupling agent hydrolysis solution is 40℃~70℃, and the duration is 5~10 hours, for example, treatment at 60℃ for 8 hours. The above hydrolysis temperature and time are suitable hydrolysis conditions for silane coupling agents containing disulfide bonds. Within the above time and temperature range, the silane coupling agent containing disulfide bonds will gradually hydrolyze to generate silanol groups, which are convenient for subsequent grafting onto the surface of the aramid fiber matrix.

[0055] In this invention, the modified material can be cleaned with water and ethanol.

[0056] In this invention, after modification, the drying temperature is 80~110℃ and the time is 1~3h, for example, the drying temperature is 100℃ and the time is 2h.

[0057] In one embodiment, the infrared spectrum of the modified aramid fiber is as follows: Figure 1 As shown, the modified aramid fiber 1635 cm −1 The stretching vibration peak of the -C=O group (amide I band) is present at 3317 cm⁻¹, and the stretching vibration peak of the -NH bond on the amide group is present at 3317 cm⁻¹. −1 At 1045cm -1 The presence of the -Si-OC- peak indicates that the coupling agent was successfully grafted onto the surface of the aramid fiber matrix through a chemical reaction.

[0058] Step 3: Curing the modified aramid fiber and vitrimer epoxy resin to prepare the composite material.

[0059] In step 3, before curing, the modified aramid fiber and the glass-like polymer (Vitrimer) epoxy resin are vacuum pressure impregnated to make the aramid fiber and the glass-like polymer (Vitrimer) epoxy resin bond more tightly, resulting in a composite material with a high fiber volume fraction.

[0060] Furthermore, during impregnation, the viscosity is less than 800 mpas and the temperature is between 50 and 60°C; preferably, the viscosity is 300 to 580 mpas and the temperature is between 55 and 60°C; for example, the viscosity is 580 mpas and the temperature is 55°C.

[0061] In step 3, the curing temperature is 120℃~180℃, and the curing time is 6~14 hours.

[0062] According to a preferred embodiment, the curing process involves measuring heat flow curves at different heating rates using a non-isothermal DSC method to obtain curing reaction kinetics. A suitable curing kinetic model is then selected for optimization to ensure an appropriate reaction rate and a degree of curing greater than 0.999. During this process, the inventors discovered that a stepwise heating curing method can reduce residual stress in the composite material during curing. This is because a slow temperature increase reduces the accumulation of internal stress caused by thermal stress during curing, which is beneficial to the mechanical properties and durability of the composite material. Stepwise heating avoids structural damage caused by excessively rapid temperature changes. Furthermore, through stepwise heating, the vitrimer epoxy resin gradually softens and flows, ensuring that the vitrimer epoxy resin penetrates the modified aramid fibers uniformly and more easily during curing, resulting in a bubble-free and defect-free cured body. This effectively enhances the bond between the fiber and the matrix, improves interfacial adhesion strength, and optimizes the crosslinking density and mechanical properties of the composite material. Excessive heating may lead to uneven curing.

[0063] In step 3, as shown in Figure 3(a), which illustrates the first principle of the interfacial reaction between modified aramid fiber and vitrimer epoxy resin, and Figure 3(b), which illustrates the second principle of the interfacial reaction between modified aramid fiber and vitrimer epoxy resin, during curing, because vitrimer epoxy resin has the property of ester bond exchange, even if the disulfide bond content in vitrimer epoxy resin is low, it can still exchange with the disulfide bonds on the surface of modified aramid fiber, that is, disulfide exchange occurs between the two.

[0064] In this invention, the dynamic conformal capability of the interface between aramid fiber and epoxy resin and the damage repair capability of the composite material are achieved through the exchange reaction between the disulfide bonds on the surface of modified aramid fiber and the disulfide bonds in the vitrimer epoxy resin, as well as the dynamic crosslinking characteristics within the vitrimer epoxy resin.

[0065] According to a preferred embodiment, the curing includes: First stage: Curing at 100~130℃ for 1~3 hours; Second stage: Curing at 135~150℃ for 2~4 hours; Third stage: Curing at 155~175℃ for 2~4 hours.

[0066] More preferably, the curing includes: First stage: Curing at 110~120℃ for 1.5~2 hours; Second stage: Curing at 135~145℃ for 2~3 hours; Third stage: Curing at 160~170℃ for 3~4 hours.

[0067] More preferably, the curing includes: First stage: Curing at 120℃ for 2 hours; Second stage: Curing at 140℃ for 3 hours; Third stage: Curing at 160℃ for 3 hours.

[0068] In a preferred embodiment, the original interfacial shear strength of the aramid-reinforced vitrimer epoxy resin composite material based on dynamic covalent bonds is 16.5 MPa, the shear strength after secondary interfacial repair is 15.9 MPa, the interfacial shear strength retention rate after rebonding reaches 96.4%, and the interfacial normal strength reaches 32.04 MPa, which is 52.9% higher than that of the unmodified fiber epoxy resin system (20.95 MPa).

[0069] The present invention is further described below through specific examples; however, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention.

[0070] Example 1

[0071] (1) 6 g of disulfide silane coupling agent (Si-75) was added to 64 g of anhydrous ethanol and 16 g of deionized water. The pH was adjusted to 4 with acetic acid and then ultrasonically treated at 35 °C for 12 h to obtain the coupling agent hydrolysate. Para-aramid fiber (Kevlar29) was washed with acetone and dried, and then placed in the coupling agent hydrolysate. It was reacted in a water bath at 60 °C for 8 h. The para-aramid fiber (Kevlar29) was taken out, washed with water and ethanol, and dried at 100 °C for 2 h to obtain the modified aramid fiber.

[0072] (2) The epoxy groups of E51 type bisphenol A epoxy resin (DGEBA), 4-methyltetrahydrophthalic anhydride (MeTHPA) and triethanolamine (TEOA) are mixed in a molar ratio of 1:0.5:0.05 and the following steps are performed: 4-Methyltetrahydrophthalic anhydride (MeTHPA) was added to E51 type bisphenol A epoxy resin (DGEBA) at 90℃, and then triethanolamine (TEOA) was added when the temperature was lowered to 80℃. Vacuum degassing was then performed to obtain a single transesterification glass polymer (Vitrimer) epoxy resin. (3) Vacuum pressure impregnation of modified aramid fiber and single transesterification glass polymer (Vitrimer) epoxy resin is performed. The impregnation viscosity is 300 MPa and the temperature is 55°C. Then, it is cured as follows: cured at 120°C for 2 hours, then cured at 140°C for 3 hours, and then cured at 160°C for 3 hours to obtain a glass polymer (Vitrimer) epoxy resin composite material.

[0073] An interfacial re-bonding experiment was conducted on the composite material. The original interfacial bond strength was 16.1 MPa, and the interfacial strength after secondary bonding was 1.92 MPa, with an interfacial re-bonding efficiency of 11.9%.

[0074] Example 2

[0075] (1) 6 g of disulfide silane coupling agent (Si-75) was added to 64 g of anhydrous ethanol and 16 g of deionized water. The pH was adjusted to 4 with acetic acid and then ultrasonically treated at 35 °C for 12 h to obtain the coupling agent hydrolysate. Para-aramid fiber (Kevlar29) was washed with acetone and dried, and then placed in the coupling agent hydrolysate. It was reacted in a water bath at 60 °C for 8 h. The para-aramid fiber (Kevlar29) was taken out, washed with water and ethanol, and dried at 100 °C for 2 h to obtain the modified aramid fiber.

[0076] (2) The epoxy groups of E51 type bisphenol A epoxy resin (DGEBA), 3,3-dithiodipropionic acid (DTDPA), 4-methyltetrahydrophthalic anhydride (MeTHPA) and triethanolamine (TEOA) are mixed in a molar ratio of 1:0.1:0.4:0.05 and the following steps are performed: 3,3-Dithiodipropionic acid (DTDPA) was added to E51 type bisphenol A epoxy resin (DGEBA) at 155℃ until the 3,3-dithiodipropionic acid (DTDPA) was completely dissolved to obtain a first solution; when the first solution was cooled to 90℃, 4-methyltetrahydrophthalic anhydride (MeTHPA) was added, and then when the temperature was cooled to 80℃, triethanolamine (TEOA) was added. Vacuum degassing was performed to obtain a vitrimer-like epoxy resin.

[0077] (3) Vacuum pressure impregnation of modified aramid fiber and vitrimer epoxy resin was carried out. The impregnation viscosity was 450 MPa and the temperature was 55°C. Then, it was cured as follows: cured at 120°C for 2 hours, then cured at 140°C for 3 hours, and then cured at 160°C for 3 hours to obtain vitrimer epoxy resin composite material.

[0078] An interfacial re-bonding experiment was conducted on the composite material. The original interfacial bond strength was 15.8 MPa, and the interfacial strength after secondary bonding was 12.4 MPa, with an interfacial re-bonding efficiency of 78.4%.

[0079] Example 3

[0080] (1) 6 g of disulfide silane coupling agent (Si-75) was added to 64 g of anhydrous ethanol and 16 g of deionized water. The pH was adjusted to 4 with acetic acid and then ultrasonically treated at 35 °C for 12 h to obtain the coupling agent hydrolysate. Para-aramid fiber (Kevlar29) was washed with acetone and dried, and then placed in the coupling agent hydrolysate. It was reacted in a water bath at 60 °C for 8 h. The para-aramid fiber (Kevlar29) was taken out, washed with water and ethanol, and dried at 100 °C for 2 h to obtain the modified aramid fiber.

[0081] (2) The epoxy groups of E51 type bisphenol A epoxy resin (DGEBA), 3,3-dithiodipropionic acid (DTDPA), 4-methyltetrahydrophthalic anhydride (MeTHPA) and triethanolamine (TEOA) are mixed in a molar ratio of 1:0.2:0.3:0.05 and the following steps are performed: 3,3-Dithiodipropionic acid (DTDPA) was added to E51 type bisphenol A epoxy resin (DGEBA) at 155℃ until the 3,3-dithiodipropionic acid (DTDPA) was completely dissolved to obtain a first solution; when the first solution was cooled to 90℃, 4-methyltetrahydrophthalic anhydride (MeTHPA) was added, and then when the temperature was cooled to 80℃, triethanolamine (TEOA) was added. Vacuum degassing was performed to obtain a vitrimer-like epoxy resin.

[0082] (3) Vacuum pressure impregnation of modified aramid fiber and vitrimer epoxy resin was carried out. The impregnation viscosity was 580 MPa and the temperature was 55°C. Then, it was cured as follows: cured at 120°C for 2 hours, then cured at 140°C for 3 hours, and then cured at 160°C for 3 hours to obtain vitrimer epoxy resin composite material.

[0083] The interfacial normal strength of the composite material was tested and found to be 32.04 MPa. An interfacial re-bonding experiment was conducted on the composite material; the initial interfacial bond strength was 16.5 MPa, and the interfacial strength after secondary bonding was 15.9 MPa, with an interfacial re-bonding efficiency of 96.4%.

[0084] Example 4

[0085] (1) 6 g of disulfide silane coupling agent (Si-75) was added to 64 g of anhydrous ethanol and 16 g of deionized water. The pH was adjusted to 4 with acetic acid and then ultrasonically treated at 35 °C for 12 h to obtain the coupling agent hydrolysate. Para-aramid fiber (Kevlar29) was washed with acetone and dried, and then placed in the coupling agent hydrolysate. It was reacted in a water bath at 60 °C for 8 h. The para-aramid fiber (Kevlar29) was taken out, washed with water and ethanol, and dried at 100 °C for 2 h to obtain the modified aramid fiber.

[0086] (2) The epoxy groups of E51 type bisphenol A epoxy resin (DGEBA), 3,3-dithiodipropionic acid (DTDPA), 4-methyltetrahydrophthalic anhydride (MeTHPA) and triethanolamine (TEOA) are mixed in a molar ratio of 1:0.3:0.2:0.05 and the following steps are performed: 3,3-Dithiodipropionic acid (DTDPA) was added to E51 type bisphenol A epoxy resin (DGEBA) at 155℃ until the 3,3-dithiodipropionic acid (DTDPA) was completely dissolved to obtain a first solution; when the first solution was cooled to 90℃, 4-methyltetrahydrophthalic anhydride (MeTHPA) was added, and then when the temperature was cooled to 80℃, triethanolamine (TEOA) was added. Vacuum degassing was performed to obtain a vitrimer-like epoxy resin.

[0087] (3) Vacuum pressure impregnation of modified aramid fibers and vitrimer epoxy resin was carried out at an impregnation temperature of 55°C. It was found that the viscosity of the epoxy resin system was too high at this temperature, exceeding 10. 5 mpas cannot be impregnated and cannot be used to prepare composite materials.

[0088] Figure 4(a) shows the viscosity-temperature curve of modified aramid fiber and vitrimer epoxy resin under vacuum pressure impregnation in Example 1; Figure 4(b) shows the viscosity-temperature curve of modified aramid fiber and vitrimer epoxy resin under vacuum pressure impregnation in Example 2; Figure 4(c) shows the viscosity-temperature curve of modified aramid fiber and vitrimer epoxy resin under vacuum pressure impregnation in Example 3; Figure 4(d) shows the viscosity-temperature curve of modified aramid fiber and vitrimer epoxy resin under vacuum pressure impregnation in Example 4. From Figure 4(d), it can be seen that the viscosity of the system is higher than 10 at this time. 5 The mpas cannot meet the process requirements.

[0089] Of the above embodiments 1-4, embodiment 3 is the most effective.

[0090] Comparative Example 1 (1) Add 4-methyltetrahydrophthalic anhydride (MeTHPA) to E51 type bisphenol A epoxy resin (DGEBA) at 90℃ and mix thoroughly. At this time, the molar ratio of epoxy group of E51 type bisphenol A epoxy resin (DGEBA) to 4-methyltetrahydrophthalic anhydride (MeTHPA) is 1:0.5, and a glass-like polymer (Vitrimer) epoxy resin is obtained.

[0091] (2) Para-aramid fiber (Kevlar 29) was cleaned and dried with acetone, and then impregnated with vitrimer epoxy resin under vacuum pressure. The impregnation viscosity was 150 mpas and the temperature was 55℃. Then it was cured as follows: cured at 120℃ for 2h, then cured at 140℃ for 3h, and then cured at 160℃ for 3h to obtain unmodified aramid fiber reinforced epoxy resin composite material.

[0092] The interfacial normal strength of the composite material was tested and found to be 20.95 MPa. An interfacial re-bonding experiment was conducted on the composite material; the initial interfacial bond strength was 13.3 MPa, but the secondary bonding failed, indicating that the composite material does not possess interfacial re-bonding repair properties. Figure 5 The diagram shows a comparison of the interfacial normal strength measurement curves of the composite material prepared in Comparative Example 1 and the composite material prepared in Example 3. It can be seen that the interfacial normal strength of the composite material prepared in Example 3 is higher.

[0093] Figure 1 The image shows a spectral comparison between the modified aramid fiber in Example 3 and the unmodified aramid fiber (para-aramid fiber (Kevlar 29)) in Comparative Example 1. The wavenumber is 1635 cm⁻¹. −1 The absorption peak at 3317 cm⁻¹ is the stretching vibration peak of the -C=O group (amide I band), and the stretching vibration peak of the -NH bond on the amide group is at 3317 cm⁻¹. −1 The figure shows a comparison of the results before and after modification, indicating that the sample grafted with coupling agent (Example 3) can be grown at 1045 cm⁻¹. -1 The observation of the -Si-OC- peak indicates that the Si-75 silane coupling agent was successfully grafted onto the surface of the aramid fiber matrix through a chemical reaction. Figure 6 The diagram shows a comparison of the original interfacial bond strength and the secondary interfacial bond strength of the composite materials prepared in Examples 1-4 and Comparative Example 1. It can be seen that the secondary bonding of the composite material in Comparative Example 1 failed, while the interfacial bond of the composite material in Example 3 was better.

[0094] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A Vitrimer epoxy resin composite material, characterized in that, The composite material is dynamically bonded by modified aramid fibers and Vitrimer epoxy resin. The modified aramid fibers have dynamic covalent bonds on their surface, and the Vitrimer epoxy resin has dual dynamic crosslinking characteristics.

2. The composite material according to claim 1, characterized in that, Preferably, the Vitrimer epoxy resin has disulfide bond exchange properties.

3. The composite material according to claim 1, characterized in that, The dynamic covalent bonds on the surface of the modified aramid fiber are disulfide bonds.

4. The composite material according to claim 1, characterized in that, The modified aramid fiber is at 1045 cm⁻¹ -1 A -Si-OC- peak exists at this location.

5. The composite material according to claim 1, characterized in that, The interfacial shear strength retention rate of the composite material after rebonding is between 78% and 96%.

6. A method for preparing the composite material according to any one of claims 1-5, characterized in that, The method includes: Prepare Vitrimer epoxy resin with dual dynamic crosslinking properties; Dynamic covalent bonds are introduced on the surface of aramid fiber matrix to obtain modified aramid fibers; The modified aramid fiber and Vitrimer epoxy resin were cured to prepare the composite material.

7. The method according to claim 6, characterized in that, The raw materials for preparing Vitrimer epoxy resin with dual dynamic crosslinking properties include an epoxy resin matrix and a curing agent containing disulfide bonds.

8. The method according to claim 7, characterized in that, The molar ratio of epoxy groups to curing agents containing disulfide bonds in the epoxy resin matrix is ​​1:(0.1~0.2).

9. The method according to claim 6, characterized in that, A silane coupling agent containing disulfide bonds is selected to introduce disulfide bonds on the surface of the aramid fiber matrix.

10. The method according to claim 6, characterized in that, The curing temperature is 120℃~180℃.

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