Carbon fiber composite material for in-situ generation of radiation refrigeration particles and preparation method thereof

Abstract

The invention discloses a carbon fiber composite material for in-situ generation of radiation refrigeration particles and a preparation method thereof. The preparation method comprises the following steps: firstly, adding a coupling agent and a silicate ester precursor solution into epoxy resin, and carrying out hydrolytic condensation to generate silicon dioxide particles in situ; preparing a metal chelate from an organic metal compound, a chelating agent and organic acid, adding the metal chelate into an anhydride curing agent solution, and reacting to generate oxidized metal particles in situ; the two components are mixed with a curing accelerator, the mixture and carbon fiber cloth are prepared into prepreg, and the prepreg is laid and subjected to hot press molding. Through a step-by-step bi-component in-situ generation strategy, the radiation refrigeration functional particles are integrated in a carbon fiber composite material matrix in a high-dispersion and strong-interface combination mode, the problems of poor adhesive force of a traditional coating method and agglomeration of a particle direct adding method are solved, and the obtained composite material is high in sunlight reflectivity and atmospheric window emissivity and good in radiation refrigeration performance. Meanwhile, the interlaminar shear strength is kept at 5969 MPa, and the high-efficiency radiation refrigeration material has an efficient radiation refrigeration function and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber composite materials technology, specifically to carbon fiber composite materials with in-situ generated radiation-cooling particles and their preparation methods. Background Technology

[0002] Carbon fiber reinforced composites have been widely used in building structures, automotive bodies, and other fields due to their excellent specific strength, specific stiffness, and durability. However, carbon fiber composites face significant thermal management challenges in outdoor environments: the dark surface of carbon fibers has a high absorption rate of sunlight, and the surface temperature under sunlight is much higher than the ambient temperature. Sustained high temperatures not only increase the indoor heat load of buildings but also accelerate the thermo-oxidative aging and UV degradation of the resin matrix, causing interfacial debonding and microcracks between the fibers and the matrix due to differences in thermal expansion coefficients, further weakening the mechanical properties and service life of the composite material. Therefore, endowing carbon fiber composites with efficient radiative cooling capabilities, enabling them to reflect sunlight and emit heat into outer space through atmospheric windows, is an effective way to solve these problems.

[0003] In existing technologies, coating the surface of carbon fiber composites with radiation-cooling coatings is a common technical solution. However, coating methods have significant shortcomings: on the one hand, the functional particles in radiation-cooling coatings typically account for as much as 30%–40%, leading to a decrease in coating cohesion. Furthermore, the poor wettability and high chemical inertness of carbon fiber composite surfaces further exacerbate the coating's adhesion, making it highly susceptible to cracking, warping, and detachment under temperature alternation and UV aging conditions, resulting in a short service life. On the other hand, some coating systems rely on metal reflective layers or transparent substrates to achieve high reflectivity, which is unsuitable for dark-colored carbon fiber substrates. Another approach is to directly add radiation-cooling functional particles to the resin matrix. However, micro- and nano-particles, due to their high surface energy, are prone to agglomeration in the matrix. Physical dispersion methods cannot fundamentally solve the agglomeration problem. Agglomerated particles form stress concentration points within the composite material, leading to a significant decrease in interlaminar shear strength and severely impairing the mechanical properties of the composite material. Simultaneously, uneven distribution also reduces the efficiency of the radiation-cooling function.

[0004] Therefore, how to integrate radiation cooling functional particles into carbon fiber composite matrix in a highly dispersed and strongly interfacial manner without relying on surface coatings, while maintaining the mechanical properties of composite materials to achieve efficient solar light reflection and infrared thermal radiation, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a carbon fiber composite material with in-situ generated radiation-cooling particles and its preparation method. Radiation-cooling functional particles are generated in-situ in epoxy resin and curing agent, and mixed to obtain radiation-cooling functional prepreg. The radiation-cooling functional prepreg is laid and cured to obtain a carbon fiber composite material with radiation-cooling capability.

[0006] To achieve the above objectives, the present invention proposes the following technical solution: a method for preparing carbon fiber composite materials with in-situ generated radiation-cooling particles, characterized by comprising the following steps:

[0007] (1) Add coupling agent to epoxy resin and stir evenly, add silicate precursor solution, heat and stir to hydrolyze and condense silicate, generate silica particles in situ in epoxy resin, remove solvent to obtain epoxy resin containing silica particles.

[0008] (2) Mix organometallic compounds, chelating agents and organic acids to obtain metal chelates, dissolve acid anhydride curing agents and organic solvents to obtain acid anhydride solutions, add the metal chelates to the acid anhydride solutions and stir to react, generate metal oxide particles in situ in the curing agent, heat to remove byproducts, and obtain a curing agent containing metal oxide particles.

[0009] (3) The epoxy resin containing silica particles obtained in step (1) is mixed with the curing agent containing metal oxide particles obtained in step (2), a curing accelerator is added and stirred evenly, and the carbon fiber cloth is treated with a roller to make a prepreg. The prepreg is laid up and then hot-pressed to obtain a carbon fiber composite material with in-situ generated radiation cooling particles.

[0010] Furthermore, in this invention, the silicate ester precursor in step (1) is tetraethyl orthosilicate, the coupling agent is silane coupling agent KH-560, and the silicate ester precursor solution is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water.

[0011] Furthermore, in this invention, the mass ratio of tetraethyl orthosilicate, anhydrous ethanol and deionized water in step (1) is 1:0.1:(0.35−0.45); the mass ratio of tetraethyl orthosilicate solution added to epoxy resin to epoxy resin is 1:(1.5−3); and the mass ratio of epoxy resin to KH-560 is 1:(0.1−0.15).

[0012] Furthermore, in this invention, the organometallic compound in step (2) is isopropyl titanate and / or zirconium propoxide, and the metal oxide particles correspond to titanium dioxide particles and / or zirconium dioxide particles.

[0013] Furthermore, in this invention, the chelating agent in step (2) is ethylene glycol or acetylacetone, and the organic acid is glacial acetic acid; the molar ratio of the organometallic compound, the chelating agent and glacial acetic acid is 1:(0.5−1.2):0.1.

[0014] Furthermore, in this invention, the anhydride curing agent in step (2) is HK-021 anhydride, the organic solvent is acetone, the mass ratio of the anhydride curing agent to acetone is 10:1, and the mass ratio of the anhydride solution to the metal chelate is 1:(0.4−1).

[0015] Furthermore, in this invention, when the organometallic compound contains zirconium propoxide, deionized water is added when the anhydride solution is mixed with the metal chelate, and the mass ratio of the anhydride solution to the deionized water is 1:0.005.

[0016] Furthermore, in this invention, the size of the silicon dioxide particles generated in situ in step (1) is 300-600 nm; the size of the metal oxide particles generated in situ in step (2) is 300-600 nm.

[0017] Furthermore, in this invention, the mass ratio of the epoxy resin containing silica particles to the curing agent containing metal oxide particles in step (3) is 1:(0.9−1.2); the curing accelerator is DMP-30, and its amount accounts for 1%−3% of the total mass of the epoxy resin and the curing agent.

[0018] The carbon fiber composite material with in-situ generated radiation-cooling particles was prepared using the above-described preparation method.

[0019] Beneficial effects: The technical solution of this application has the following technical effects:

[0020] This invention utilizes a coupling agent to assist in the in-situ hydrolysis and condensation of a silicate precursor in epoxy resin to generate silica particles, and then uses chelation coordination in an anhydride curing agent to control the slow in-situ hydrolysis of an organometallic compound to generate metal oxide particles. By generating these two types of functional particles separately in two components of the resin system before mixing, carbon fiber composite materials are prepared, fundamentally avoiding the agglomeration problem of added particles. The particles generated in-situ are surrounded by matrix molecules from the nucleation stage, naturally and uniformly dispersed in the matrix. Simultaneously, the particle surfaces form covalent bonds with the matrix through coupling agents or direct chemical reactions, resulting in strong interfacial bonding. Experimental results show that the interlaminar shear strength of the carbon fiber composite material prepared using this method can reach 59-69 MPa, approaching the level of pure carbon fiber composite materials without added particles, and significantly superior to the 27 MPa achieved by the direct physical addition of particles method.

[0021] The carbon fiber composite material prepared by this invention integrates radiative cooling directly into the matrix, eliminating the need for a separate surface coating and completely eliminating the defects of insufficient adhesion between the coating and the carbon fiber substrate, and easy peeling and failure after long-term use. The in-situ generated silica and metal oxide particles have a particle size in the range of 300-600 nm, which precisely matches the wavelength of sunlight in the visible to near-infrared band. They form a multiple scattering network through Mie scattering, effectively reflecting sunlight. At the same time, the silica and metal oxide particles have strong infrared emission characteristics in the 8-13 μm atmospheric window band, which can dissipate heat into space in the form of infrared radiation. Experimental results show that the carbon fiber composite material obtained by this invention has a reflectivity of up to 86.1% in the 0.5-2.5 μm band and an emissivity of over 92% in the 8-13 μm band, with a maximum daytime cooling effect of 4.3°C. In addition, the in-situ generated titanium dioxide and zirconium dioxide particles have an absorption and shielding effect on ultraviolet light, which can delay the ultraviolet aging and degradation of the resin matrix and improve the weather resistance of the carbon fiber composite material in outdoor environments.

[0022] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below can be considered part of the inventive subject matter of this disclosure, provided that such concepts do not contradict each other.

[0023] The foregoing and other aspects, embodiments, and features of the teachings of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the invention, such as features and / or beneficial effects of exemplary embodiments, will become apparent from the following description or may be learned through practice of specific embodiments according to the teachings of the present invention. Attached Figure Description

[0024] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0025] Figure 1 Example 2 shows its high reflectance in the spectral reflectance range of 0.5-2.5 μm in the visible and near-infrared bands.

[0026] Figure 2 Example 2 shows its high emissivity in the visible and near-infrared bands based on the spectral reflectance curves at 8-13 μm.

[0027] Figure 3 Surface SEM image of Example 2;

[0028] Figure 4Comparative Example 1: Surface SEM image. Detailed Implementation

[0029] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0030] The preparation method provided by this invention is generally divided into three steps: Step (1) in-situ generation of silica particles in epoxy resin via sol-gel method; Step (2) in-situ generation of metal oxide particles in an anhydride curing agent via chelation coordination-controlled hydrolysis; Step (3) mixing the two components and then preparing a prepreg with carbon fiber cloth, followed by hot pressing and curing. Each of the three steps performs a specific function in the overall scheme, while also working synergistically to achieve the goal of loading radiation-cooling functional particles with high dispersion and strong interfacial bonding in a carbon fiber composite matrix. The purpose, functional principle, and technical advantages of each step are explained in detail below, followed by specific embodiments and comparative examples.

[0031] Step (1): In-situ generation of silica particles in epoxy resin

[0032] The purpose of this step is to generate uniformly dispersed submicron-sized silica particles in situ within the epoxy resin component, making the epoxy resin the primary carrier for the radiative cooling functional particles.

[0033] The specific procedure is as follows: First, tetraethyl orthosilicate (TEOS), anhydrous ethanol, and deionized water are mixed in a certain mass ratio to prepare a tetraethyl orthosilicate solution. Anhydrous ethanol is used as a co-solvent to improve the miscibility of tetraethyl orthosilicate with water, allowing the hydrolysis reaction to proceed in a homogeneous system. Deionized water provides the water source required for the hydrolysis reaction. Then, silane coupling agent KH-560 is added to the epoxy resin, and after stirring evenly, the above tetraethyl orthosilicate solution is added. The reaction is carried out under vigorous stirring at 80°C for 2 hours. After the reaction is completed, the resin is dried at 80°C for 30 minutes to remove residual ethanol and water, etc., to obtain an epoxy resin with in-situ generated silica particles.

[0034] The functional principle of this step is as follows: Tetraethyl orthosilicate undergoes hydrolysis in the presence of water, with siloxyethyl groups (Si-OC2H5) gradually being replaced by silanol groups (Si-OH). The hydrolysis products further undergo condensation reactions, and dehydration occurs between the silanol groups to form Si-O-Si bonds, resulting in silica gel particles with a three-dimensional network structure. Because the reaction takes place in an epoxy resin matrix, the generated silica particles are surrounded by epoxy resin molecules from the nucleation stage. Further growth and aggregation of the particles are limited by the matrix viscosity and steric hindrance, thus maintaining a uniformly dispersed state in the matrix, with the particle size controlled within the range of 300-600 nm.

[0035] KH-560 coupling agent plays a dual role in this step: one end of its molecule contains a hydrolyzable siloxane group (-Si(OCH3)3), which can undergo a condensation reaction with the silanol groups on the surface of silica particles to form Si-O-Si covalent bonds, thereby anchoring them to the particle surface; the other end contains an epoxy group, which can participate in the subsequent curing and crosslinking reaction of epoxy resin, bridging the silica particles to the epoxy resin crosslinking network through covalent bonds. This covalent connection structure of "particle-coupling agent-matrix" results in an interfacial bonding force between the in-situ generated particles and the matrix that is far superior to that of physical coating, fundamentally different from the method of directly adding particles physically.

[0036] The reason for choosing to generate silica in the epoxy resin component rather than the curing agent component is that the hydrolysis and condensation of tetraethyl orthosilicate is relatively mild and controllable under neutral to weakly alkaline conditions, and the epoxy resin system provides a suitable chemical environment; at the same time, the epoxy groups of KH-560 have good compatibility with epoxy resin, and their pre-addition to the epoxy resin is beneficial to the full expansion and uniform distribution of coupling agent molecules.

[0037] Step (2): In-situ generation of metal oxide particles in the acid anhydride curing agent

[0038] The purpose of this step is to generate uniformly dispersed submicron-sized titanium dioxide and / or zirconium dioxide particles in situ within the anhydride curing agent component, making the curing agent a second carrier for the radiation cooling functional particles.

[0039] The specific operation is as follows: First, an organometallic compound (isopropyl titanate and / or zirconium propoxide), a chelating agent (ethylene glycol or acetylacetone), and glacial acetic acid are mixed at a certain molar ratio to obtain a metal chelate. Then, HK-021 acid anhydride and acetone are dissolved and mixed at a mass ratio of 10:1 to obtain an acid anhydride solution. The metal chelate is added to the acid anhydride solution, and the mixture is stirred and reacted at approximately 30°C for 6-24 hours. After the reaction is completed, the temperature is raised to 80°C, and acetone and reaction byproducts (alcohols, etc.) are removed by stirring and evaporation under vacuum conditions to obtain a curing agent that generates in-situ metal oxide particles. When the organometallic compound is zirconium propoxide, a trace amount of deionized water can be optionally added when mixing the acid anhydride solution and the metal chelate, with a mass ratio of acid anhydride solution to deionized water of 1:0.005, to provide the trace water source required for the hydrolysis of zirconium propoxide.

[0040] The functional principle of this step is as follows: Organometallic compounds (such as isopropyl titanate Ti(OC3H7)4 or zirconium propoxide Zr(OC3H7)4) are metal alkoxides. Their metal-oxygen bonds are extremely sensitive to moisture. When they come into direct contact with water, a violent and uncontrollable hydrolysis reaction occurs, forming a large number of coarse and unevenly distributed precipitate particles in a very short time. To solve this problem, this invention employs a strategy of first coordinating a chelating agent with the metal alkoxide. The chelating agent (ethylene glycol or acetylacetone), as a multidentate ligand, forms a stable chelate ring structure with the metal center, occupying some coordination positions and reducing the hydrophilic activity of the metal center, thereby significantly reducing the hydrolysis rate. Glacial acetic acid, as a weak acid, provides proton catalysis for the hydrolysis of the metal alkoxide. Furthermore, due to its weak acid nature, the rate of proton release is limited, further regulating the hydrolysis rate. Under the combined regulation of chelating agent and glacial acetic acid, metal alkoxides undergo a slow and uniform hydrolysis-condensation reaction in acid anhydride solution, nucleating and growing in a controlled manner, and finally generating metal oxide particles with a particle size of 300-600 nm in situ in the curing agent.

[0041] Acetone is added to the acid anhydride as an organic solvent to reduce the viscosity of the anhydride system, allowing the metal chelate to mix and disperse quickly and uniformly within the anhydride, thus preventing uneven hydrolysis due to excessively high local concentrations. After the reaction is complete, the acetone is completely removed by heating and vacuuming, leaving no residue in the final product.

[0042] The reason for choosing to generate metal oxide particles in the anhydride curing agent rather than the epoxy resin component is as follows: the hydrolysis of metal alkoxides requires an acidic environment to regulate the rate, and anhydrides themselves are weakly acidic, providing a suitable pH environment when combined with glacial acetic acid. Furthermore, if the hydrolysis reaction of metal alkoxides were carried out in the epoxy resin, the alcohols and water produced during hydrolysis might prematurely initiate ring-opening side reactions of the epoxy groups, affecting the subsequent curing effect. In contrast, the anhydride curing agent does not react significantly with alcohols at room temperature, exhibiting better chemical compatibility. Simultaneously, the residual hydroxyl groups on the surface of the in-situ generated metal oxide particles can react with the anhydride groups during subsequent curing to form ester bonds, achieving chemical bonding between the particles and the curing agent matrix and enhancing interfacial adhesion.

[0043] Step (3): Mixing and preparing prepreg and hot pressing

[0044] The purpose of this step is to combine the two components containing functional particles prepared in steps (1) and (2) respectively, and then composite them with carbon fiber cloth to obtain the final radiation-cooled carbon fiber composite material.

[0045] The specific operation is as follows: Epoxy resin containing silica particles and curing agent containing metal oxide particles are mixed at a mass ratio of 1:(0.9-1.2). A curing accelerator, DMP-30, accounting for 1%-3% of the total mass of the epoxy resin and curing agent, is added and stirred until homogeneous to obtain a resin system that generates in-situ radiative cooling particles. This resin system is then mixed with carbon fiber cloth and processed into prepreg sheets using roller clamping at 80°C. The prepreg sheets are then alternately laid according to a predetermined layering scheme and placed in a hot press for hot pressing and curing to obtain a carbon fiber composite material that generates in-situ radiative cooling particles.

[0046] DMP-30 is 2,4,6-tris(dimethylaminomethyl)phenol. As a tertiary amine curing accelerator, it catalyzes the ring-opening of acid anhydrides and promotes the cross-linking reaction between acid anhydrides and epoxy groups, shortening the curing time and increasing the cross-linking density. The purpose of the 80°C roller clamping treatment is to reduce the viscosity of the resin system, allowing the resin containing functional particles to fully wet the surface of the carbon fiber bundles and the interfiber gaps, ensuring the wetting quality of the prepreg.

[0047] The three steps of this invention have a close synergistic relationship and are not simply a series combination. First, steps (1) and (2) adopt a "step-by-step, two-component" strategy, in which the two types of functional particles are generated separately in epoxy resin and curing agent. This design stems from the incompatibility of chemical conditions for the in-situ generation reaction of silica and metal oxide particles: the silica precursor TEOS is suitable for mild hydrolysis under neutral to weakly alkaline conditions, while metal alkoxides require acidic conditions to regulate the hydrolysis rate. If the two reactions are carried out simultaneously in the same component, the conflict of acid and base conditions will lead to one reaction going out of control or the other reaction not proceeding sufficiently. The step-by-step strategy allows each particle to be generated in a controlled manner in the most suitable chemical environment, ensuring the uniformity of particle size and dispersion quality of the two types of particles.

[0048] Secondly, the introduction of KH-560 coupling agent in step (1) not only enhances the interfacial bonding between silica and epoxy resin, but also has a positive impact on the overall system after the two components are mixed in step (3). The epoxy groups of KH-560 can participate in the epoxy-anhydride curing and crosslinking reaction in step (3), "anchoring" the silica particles to the overall crosslinking network. At the same time, the hydroxyl groups on the surface of the metal oxide particles in step (2) react with the anhydride or epoxy groups during the curing process in step (3) to form ester bonds or ether bonds, achieving chemical anchoring. The two types of particles bond to the crosslinking network through different chemical pathways, forming a "dual-particle-dual-path" interfacial reinforcement structure.

[0049] Furthermore, the particles generated in situ in steps (1) and (2) achieve functional complementarity and optical synergy in the overall matrix after being mixed in step (3): the refractive index of silica particles (approximately 1.46) is similar to that of epoxy resin (approximately 1.55), resulting in limited scattering efficiency when used alone. However, silica particles exhibit strong Si-O-Si stretching vibration absorption in the 9-11 μm band, making them excellent infrared emitting materials. Titanium dioxide particles have a high refractive index (approximately 2.5-2.7), which differs greatly from the refractive index of the matrix, making them excellent solar scattering materials. However, their infrared emission performance is not as good as that of silica. Zirconia particles possess both a high refractive index (approximately 2.15) and good mid- and far-infrared emission performance. The combined use of multiple particles achieves both high reflectivity and high emission in the 0.3-2.5 μm solar radiation band and the 8-13 μm atmospheric window band, which is more efficient than using a single type of particle.

[0050] Example 1

[0051] Step (1): Preparation of tetraethyl orthosilicate solution: Take 100 g of tetraethyl orthosilicate, add 10 g of anhydrous ethanol and 35 g of deionized water, and stir to mix evenly. Add 13 g of silane coupling agent KH-560 to 100 g of bisphenol A type epoxy resin E-51, and mechanically stir at room temperature for 15 minutes until completely homogeneous. Then add 40 g of tetraethyl orthosilicate solution to the above mixture, and stir vigorously at 1500 rpm for 2 hours under 80°C water bath conditions. After the reaction is complete, dry at 80°C for 30 minutes to remove residual ethanol and water, and obtain epoxy resin with in-situ generated silica particles.

[0052] Step (2): Preparation of titanate chelate: Take 100 g of isopropyl titanate, add 23 g of ethylene glycol and 2 g of glacial acetic acid, stir and mix evenly to obtain titanate chelate. Preparation of acid anhydride solution: Take 100 g of HK-021 methyltetrahydrophthalic anhydride, add 10 g of acetone, and stir until completely dissolved. Add 40 g of titanate chelate to 100 g of acid anhydride solution, and stir at 500 rpm for 12 hours at 30°C. After the reaction is complete, raise the temperature to 80°C, and stir and evaporate under a vacuum of -0.09 MPa for 30 minutes to remove acetone and byproducts such as isopropanol generated in the reaction, to obtain a curing agent for in-situ generation of titanium dioxide particles.

[0053] Step (3): Take 100 g of epoxy resin containing silica particles obtained in step (1), 110 g of curing agent containing titanium dioxide particles obtained in step (2), and 4 g of DMP-30, and mechanically stir and mix them evenly at room temperature to obtain a resin system that generates radiation cooling functional particles in situ. The resin system and T300 carbon fiber plain weave fabric are treated with rollers at 80°C to make a prepreg sheet with a resin mass fraction of about 45%. The prepreg sheet is alternately laid in a [0° / 90°] 4s layup scheme for a total of 16 layers, placed in a flat hot press, and cured according to the curing regime of 80°C for 1 hour → 120°C for 2 hours → 150°C for 4 hours. It is hot-pressed and cured under a pressure of 0.5 MPa, and demolded after natural cooling to room temperature to obtain a carbon fiber composite material with radiation cooling function.

[0054] Example 2

[0055] Step (1): Preparation of tetraethyl orthosilicate solution: Take 100 g of tetraethyl orthosilicate, add 10 g of anhydrous ethanol and 40 g of deionized water, and stir to mix evenly. Add 15 g of silane coupling agent KH-560 to 100 g of bisphenol A type epoxy resin E-51, and mechanically stir at room temperature for 15 minutes until completely homogeneous. Then add 60 g of tetraethyl orthosilicate solution to the above mixture, and stir vigorously at 1500 rpm for 2 hours under 80°C water bath conditions. After the reaction is complete, dry at 80°C for 30 minutes to remove residual ethanol and water, and obtain epoxy resin with in-situ generated silica particles.

[0056] Step (2): Preparation of titanate chelate: Take 100 g of isopropyl titanate, add 23 g of ethylene glycol and 2 g of glacial acetic acid, stir and mix evenly to obtain titanate chelate. Preparation of acid anhydride solution: Take 100 g of HK-021 methyltetrahydrophthalic anhydride, add 10 g of acetone, and stir until completely dissolved. Add 60 g of titanate chelate to 100 g of acid anhydride solution, and stir at 500 rpm for 12 hours at 30°C. After the reaction is complete, raise the temperature to 80°C, and stir and evaporate under a vacuum of -0.09 MPa for 30 minutes to remove acetone and byproducts such as isopropanol generated in the reaction, to obtain a curing agent for in-situ generation of titanium dioxide particles.

[0057] Step (3): Take 100 g of epoxy resin containing silica particles obtained in step (1), 100 g of curing agent containing titanium dioxide particles obtained in step (2), and 3 g of DMP-30, and mechanically stir and mix them evenly at room temperature to obtain a resin system that generates radiation cooling functional particles in situ. The resin system and T300 carbon fiber plain weave fabric are treated with rollers at 80°C to make a prepreg sheet with a resin mass fraction of about 45%. The prepreg sheet is alternately laid in a [0° / 90°] 4s layup scheme for a total of 16 layers, placed in a flat hot press, and cured according to the curing regime of 80°C for 1 hour → 120°C for 2 hours → 150°C for 4 hours. It is hot-pressed and cured under a pressure of 0.5 MPa, and demolded after natural cooling to room temperature to obtain a carbon fiber composite material with radiation cooling function.

[0058] Figure 1 The figure shows the spectral reflectance curve of the carbon fiber composite material obtained in Example 2 in the 0.5-2.5 μm band. It can be seen from the figure that the composite material has high reflectance in the visible and near-infrared bands. Figure 2 The spectral emissivity curve of the carbon fiber composite material obtained in Example 2 in the 8-13 μm band shows that it has high emissivity in the atmospheric window band. Figure 3The image shows a surface SEM image of the carbon fiber composite material obtained in Example 2. It can be seen from the image that the functional particles generated in situ are uniformly dispersed in the resin matrix without obvious agglomeration. The particle size is about 300-600 nm.

[0059] Example 3

[0060] Step (1): Preparation of tetraethyl orthosilicate solution: Take 100 g of tetraethyl orthosilicate, add 10 g of anhydrous ethanol and 40 g of deionized water, and stir to mix evenly. Add 13 g of silane coupling agent KH-560 to 100 g of bisphenol A type epoxy resin E-51, and mechanically stir at room temperature for 15 minutes until completely homogeneous. Then add 40 g of tetraethyl orthosilicate solution to the above mixture, and stir vigorously at 1500 rpm for 2 hours under 80°C water bath conditions. After the reaction is complete, dry at 80°C for 30 minutes to remove residual ethanol and water, and obtain epoxy resin with in-situ generated silica particles.

[0061] Step (2): Preparation of zirconium propoxide chelate: Take 100 g of zirconium propoxide, add 18 g of acetylacetone and 2 g of glacial acetic acid, stir and mix evenly to obtain zirconium propoxide chelate. Preparation of acid anhydride solution: Take 100 g of HK-021 methyltetrahydrophthalic anhydride, add 10 g of acetone, and stir until completely dissolved. Add 60 g of zirconium propoxide chelate to 100 g of acid anhydride solution, and add 0.55 g of deionized water (the mass ratio of acid anhydride solution to deionized water is 1:0.005). Stir and react at 500 rpm for 12 hours at 30°C. After the reaction is completed, raise the temperature to 80°C, stir and evaporate under a vacuum of -0.09 MPa for 30 minutes to remove acetone and byproducts such as n-propanol generated in the reaction, and obtain a curing agent for in-situ generation of zirconium dioxide particles.

[0062] Step (3): Take 100 g of epoxy resin containing silica particles obtained in step (1), 110 g of curing agent containing zirconium dioxide particles obtained in step (2), and 4 g of DMP-30, and mechanically stir and mix them evenly at room temperature to obtain a resin system that generates radiation-cooling functional particles in situ. The resin system and T300 carbon fiber plain weave fabric are treated with rollers at 80°C to make a prepreg sheet with a resin mass fraction of about 45%. The prepreg sheet is alternately laid in a [0° / 90°] 4s layup scheme for a total of 16 layers, placed in a flat hot press, and cured according to the curing regime of 80°C for 1 hour → 120°C for 2 hours → 150°C for 4 hours. It is hot-pressed and cured under a pressure of 0.5 MPa, and demolded after natural cooling to room temperature to obtain a carbon fiber composite material with radiation-cooling function.

[0063] Example 4

[0064] Step (1): Preparation of tetraethyl orthosilicate solution: Take 100 g of tetraethyl orthosilicate, add 10 g of anhydrous ethanol and 45 g of deionized water, and stir to mix evenly. Add 13 g of silane coupling agent KH-560 to 100 g of bisphenol A type epoxy resin E-51, and mechanically stir at room temperature for 15 minutes until completely homogeneous. Then add 60 g of tetraethyl orthosilicate solution to the above mixture, and stir vigorously at 1500 rpm for 2 hours under 80°C water bath conditions. After the reaction is complete, dry at 80°C for 30 minutes to remove residual ethanol and water, and obtain epoxy resin with in-situ generated silica particles.

[0065] Step (2): Preparation of zirconium propoxide chelate: Take 100 g of zirconium propoxide, add 20 g of acetylacetone and 2 g of glacial acetic acid, stir and mix evenly to obtain zirconium propoxide chelate. Preparation of acid anhydride solution: Take 100 g of HK-021 methyltetrahydrophthalic anhydride, add 10 g of acetone, and stir until completely dissolved. Add 80 g of zirconium propoxide chelate to 100 g of acid anhydride solution, and add 0.55 g of deionized water (the mass ratio of acid anhydride solution to deionized water is 1:0.005). Stir and react at 500 rpm for 12 hours at 30°C. After the reaction is completed, raise the temperature to 80°C, stir and evaporate under a vacuum of -0.09 MPa for 30 minutes to remove acetone and byproducts such as n-propanol generated in the reaction, and obtain a curing agent for in-situ generation of zirconium dioxide particles.

[0066] Step (3): Take 100 g of epoxy resin containing silica particles obtained in step (1), 110 g of curing agent containing zirconium dioxide particles obtained in step (2), and 4 g of DMP-30, and mechanically stir and mix them evenly at room temperature to obtain a resin system that generates radiation-cooling functional particles in situ. The resin system and T300 carbon fiber plain weave fabric are treated with rollers at 80°C to make a prepreg sheet with a resin mass fraction of about 45%. The prepreg sheet is alternately laid in a [0° / 90°] 4s layup scheme for a total of 16 layers, placed in a flat hot press, and cured according to the curing regime of 80°C for 1 hour → 120°C for 2 hours → 150°C for 4 hours. It is hot-pressed and cured under a pressure of 0.5 MPa, and demolded after natural cooling to room temperature to obtain a carbon fiber composite material with radiation-cooling function.

[0067] Example 5.

[0068] Step (1): Preparation of tetraethyl orthosilicate solution: Take 100 g of tetraethyl orthosilicate, add 10 g of anhydrous ethanol and 45 g of deionized water, and stir to mix evenly. Add 13 g of silane coupling agent KH-560 to 100 g of bisphenol A type epoxy resin E-51, and mechanically stir at room temperature for 15 minutes until completely homogeneous. Then add 60 g of tetraethyl orthosilicate solution to the above mixture, and stir vigorously at 1500 rpm for 2 hours under 80°C water bath conditions. After the reaction is complete, dry at 80°C for 30 minutes to remove residual ethanol and water, and obtain epoxy resin with in-situ generated silica particles.

[0069] Step (2): Preparation of zirconium propoxide and isopropyl titanate chelate: Take 50 g of zirconium propoxide and 50 g of isopropyl titanate, add 20 g of acetylacetone and 2 g of glacial acetic acid, stir and mix evenly to obtain the zirconium propoxide and isopropyl titanate chelate. Preparation of acid anhydride solution: Take 100 g of HK-021 methyltetrahydrophthalic anhydride, add 10 g of acetone, and stir until completely dissolved. Add 80 g of the zirconium propoxide and isopropyl titanate chelate to 100 g of acid anhydride solution, and simultaneously add 0.55 g of deionized water (the mass ratio of acid anhydride solution to deionized water is 1:0.005), and stir and react at 500 rpm for 12 hours at 30°C. After the reaction is completed, raise the temperature to 80°C, and stir and evaporate for 30 minutes under a vacuum of -0.09 MPa to remove acetone and byproducts such as n-propanol generated in the reaction, to obtain a curing agent that generates zirconium dioxide and titanium dioxide particles in situ.

[0070] Step (3): Take 100 g of epoxy resin containing silica particles obtained in step (1), 110 g of curing agent containing zirconium dioxide and titanium dioxide particles obtained in step (2), and 4 g of DMP-30, and mechanically stir and mix them evenly at room temperature to obtain a resin system that generates radiation cooling functional particles in situ. The resin system and T300 carbon fiber plain weave fabric are treated with rollers at 80°C to make a prepreg sheet with a resin mass fraction of about 45%. The prepreg sheet is alternately laid in a [0° / 90°] 4s layup scheme for a total of 16 layers, placed in a flat hot press, and cured according to the curing regime of 80°C for 1 hour → 120°C for 2 hours → 150°C for 4 hours. It is hot-pressed and cured under a pressure of 0.5 MPa, and demolded after natural cooling to room temperature to obtain a carbon fiber composite material with radiation cooling function.

[0071] Comparative Example 1 (Direct Physical Addition of Particles Method)

[0072] Step (1): Take 100 g of bisphenol A type epoxy resin E-51, 100 g of HK-021 methyltetrahydrophthalic anhydride and 4 g of DMP-30, and mix them evenly by mechanical stirring at room temperature. Then add 10 g of commercial silica nanoparticles (particle size 300-600 nm) and 10 g of commercial titanium dioxide nanoparticles (particle size 300-600 nm) to the above mixture, and stir at 1500 rpm for 30 minutes to obtain an epoxy resin system filled with radiation cooling functional particles.

[0073] Step (2): The resin system filled with radiation-cooling functional particles and T300 carbon fiber plain weave fabric were processed by roller clamping at 80°C to form a prepreg sheet with a resin mass fraction of approximately 45%. The prepreg sheet was alternately laid up in a [0° / 90°] 4s layup scheme for a total of 16 layers, and then hot-pressed and cured according to the same curing regime as in the example to obtain the carbon fiber composite material filled with radiation-cooling functional particles.

[0074] The purpose of Comparative Example 1 is to verify the differences between the direct physical addition of pre-formed particles and the in-situ generation method of the present invention in terms of particle dispersibility, mechanical properties and radiative cooling performance.

[0075] Comparative Example 2 (pure carbon fiber composite material, without functional particles)

[0076] Step (1): Take 100 g of bisphenol A type epoxy resin E-51, 100 g of HK-021 methyltetrahydrophthalic anhydride and 4 g of DMP-30, and mix them evenly by mechanical stirring at room temperature to obtain a pure epoxy resin system.

[0077] Step (2): The above-mentioned pure epoxy resin system and T300 carbon fiber plain weave fabric are processed by roller clamping at 80°C to form a prepreg sheet with a resin mass fraction of approximately 45%. The prepreg sheet is alternately laid up in a [0° / 90°] 4s layup scheme for a total of 16 layers, and then hot-pressed and cured according to the same curing regime as in the example to obtain a pure carbon fiber composite material without functional particles.

[0078] Comparative Example 2 served as a baseline control group to evaluate the radiative cooling effect of each embodiment and the impact of the introduction of functional particles on mechanical properties.

[0079] Comparative Example 3

[0080] Step (1): Take 100 g of bisphenol A type epoxy resin E-51, 100 g of HK-021 methyltetrahydrophthalic anhydride and 4 g of DMP-30, and mix them evenly by mechanical stirring at room temperature to obtain a pure epoxy resin system.

[0081] Step (2): The above-mentioned pure epoxy resin system and T300 carbon fiber plain weave cloth are treated with rollers at 80°C to form a prepreg sheet with a resin mass fraction of approximately 45%. The prepreg sheet is alternately laid up in a [0° / 90°] 4s layup scheme for a total of 16 layers, and then hot-pressed and cured according to the same curing regime as in the example to obtain: pure carbon fiber composite material.

[0082] Step (3): Apply ZS-411 type radiation cooling coating to the surface of pure carbon fiber composite material, control the film thickness to 100 μm, and obtain carbon fiber composite material with surface coated radiation cooling layer.

[0083] The coating adhesion was rated as Grade 1 in the cross-cut adhesion test. According to the temperature resistance test in GB / T9755-2014, after three cycles, two of the three test panels showed obvious cracking.

[0084] IV. Performance Testing Methods and Results

[0085] The following performance tests were conducted on the carbon fiber composite materials obtained in each embodiment and comparative example: the solar spectral weighted reflectance R of the samples in the 0.5-2.5 μm band was measured using a UV-Vis-NIR spectrophotometer (with integrating sphere accessory); the spectral weighted emissivity E of the samples in the 8-13 μm atmospheric window band was measured using a Fourier transform infrared spectrometer (with integrating sphere accessory); the interlaminar shear strength of the samples was determined using the short beam method according to GB / T 1450.1 standard; the daytime cooling effect test was conducted under sunny conditions (solar irradiance of approximately 800-900 W / m²), with each sample (10 cm × 10 cm) placed horizontally on a polystyrene foam insulation platform, using Comparative Example 2 as the control group, and the temperature difference between the steady-state surface temperature of the sample and that of Comparative Example 2 was recorded using thermocouples. The test results are summarized in Table 1.

[0086] Table 1 Performance test results of carbon fiber composites

[0087] sample Reflectivity R / % Emittance E / % Interlaminar shear strength / MPa Daytime cooling effect / °C Example 1 73.4 93.1 61 2.1 Example 2 82.9 92.4 59 3.4 Example 3 78.6 93.4 69 2.8 Example 4 85.5 92.8 62 4.1 Example 5 86.1 93.6 64 4.3 Comparative Example 1 63.3 92.2 27 1.2 Comparative Example 2 40.4 91.7 70 — Comparative Example 3 95.1 96.3 21 6.8

[0088] Sample (after 1000 hours of aging) Interlaminar shear strength / MPa Reflectivity R / % Emittance E / % Example 1 51 69.8 92.3 Example 2 58 76.6 92.9 Example 3 53 72.3 91.8 Example 4 55 80.1 93.0 Example 5 61 82.3 91.4 Comparative Example 1 43 50.8 90.8 Comparative Example 2 44 39.9 90.1 Comparative Example 3 18 77.9 93.8

[0089] Analysis of the experiment yields the following conclusions:

[0090] (i) In-situ generation method is significantly superior to direct physical addition method – mechanical properties are preserved.

[0091] As shown in Table 1, the interlaminar shear strength of Examples 1-5, which used the in-situ generation method, was 59-69 MPa, while that of Comparative Example 1, which used the direct physical addition method, was only 27 MPa, a significant difference. Using Comparative Example 2 (pure carbon fiber composite material, ILSS=70 MPa) as the baseline, the interlaminar shear strength retention rate of Examples 1-5 reached 84%-99%, while that of Comparative Example 1 was only 39%.

[0092] From the perspective of underlying mechanisms, the fundamental reason for the significant differences mentioned above lies in the dispersion state of the particles and the interfacial bonding mode. In Comparative Example 1, commercial silica and titanium dioxide nanoparticles, due to their high surface energy and strong van der Waals forces between particles, are prone to agglomeration in epoxy resin, forming micron-sized or even tens of micron-sized particle clusters. Figure 4 The image shows a surface SEM image for Comparative Example 1. It is evident from the image that the functional particles exhibit a large-scale aggregated state, with the equivalent size of the particle clusters being much larger than the 300-600 nm diameter range of individual particles. Figure 4 and Figure 3 (The SEM image of Example 2 shows uniform particle dispersion with no obvious agglomeration.) A comparison visually verifies the fundamental difference in particle dispersion between the in-situ generation method and the direct physical addition method. In Comparative Example 1, agglomerates form enriched regions in the fiber bundle gaps of the carbon fiber prepreg. On the one hand, this hinders the effective wetting of the fibers by the resin, resulting in dry spots and defects at the fiber-matrix interface. On the other hand, the agglomerates themselves, as rigid inclusions, become stress concentration sources under stress, causing cracks to preferentially initiate at the agglomerate-matrix interface and propagate along the interlaminar layer, significantly reducing the interlaminar shear strength.

[0093] In Examples 1-5, the functional particles were uniformly dispersed in the matrix during the liquid precursor stage through in-situ reaction. From nucleation onwards, the particles were surrounded by matrix molecules, eliminating the conditions for direct contact and aggregation of solid particles. Simultaneously, the silica particles were covalently bonded to the epoxy resin crosslinking network via KH-560 coupling agent, and the hydroxyl groups on the surface of the metal oxide particles reacted with acid anhydride groups to form ester bonds. Both types of particles were chemically embedded in the crosslinking network, with no weak bonding regions at the interface. Therefore, the in-situ generated particles not only do not become mechanically weak points but also play a role in nano-toughening and interface reinforcement to a certain extent. It is particularly noteworthy that the interlaminar shear strength of Example 3 reached 69 MPa, only 1 MPa lower than that of the pure carbon fiber composite, indicating that under suitable in-situ generation conditions, the introduction of functional particles has almost no negative impact on the mechanical properties of the composite material.

[0094] (II) In-situ generation method to achieve efficient radiation cooling of carbon fiber composite materials - significantly improved reflectivity and emissivity

[0095] As shown in Table 1, the solar reflectance of Comparative Example 2 (pure carbon fiber composite material) is only 40.4%, because carbon fiber itself is black and strongly absorbs sunlight. The reflectance of Examples 1-5 ranges from 73.4% to 86.1%, with Example 5 being the highest (86.1%), an improvement of over 45 percentage points compared to Comparative Example 2. In the atmospheric window band, the emissivity of all examples reaches over 92%, with Example 5 being the highest (93.6%), an improvement of approximately 2 percentage points compared to Comparative Example 2's 91.7%. Example 5 achieves a daytime cooling effect of 4.3°C, the best among all examples.

[0096] From a fundamental mechanism perspective, the significant increase in reflectivity is due to the efficient multi-scattering network formed by the in-situ generated functional particles within the matrix. Silica particles (refractive index approximately 1.46), titanium dioxide particles (refractive index approximately 2.5-2.7), and zirconium dioxide particles (refractive index approximately 2.15) all exhibit refractive index differences compared to the epoxy resin matrix (refractive index approximately 1.55). When the particle size (300-600 nm) is on the same order of magnitude as the visible-near-infrared wavelength of sunlight (400-2500 nm), the scattering cross-section of the particles reaches its maximum according to Mie scattering theory. When incident sunlight passes through the surface of the composite material, it is repeatedly scattered by the uniformly dispersed functional particles, causing a large number of photons to deflect in their propagation direction. A significant portion of the light is scattered back into the space above the surface, thus macroscopically manifesting as high reflectivity. The in-situ generation method ensures highly uniform dispersion of particles and avoids the reduction of effective scattering cross section caused by agglomeration. Therefore, the reflectivity of Examples 1-5 is significantly higher than that of Comparative Example 1 (63.3%), which was directly added but had severe particle agglomeration.

[0097] Within the 8-13 μm atmospheric window band, the Si-O-Si stretching vibration mode of silica exhibits strong infrared absorption / emission characteristics at approximately 9-11 μm. According to Kirchhoff's law, under thermal equilibrium conditions, the emissivity of a material at a certain wavelength equals its absorptivity; therefore, silica particles are strong infrared emitters in this band. The metal-oxygen vibration modes of titanium dioxide and zirconium dioxide also show good infrared activity in the 8-13 μm band. The emissivity of all embodiments exceeds 92%, indicating that the in-situ generated particles effectively enhance the infrared radiation capability of the composite material within the atmospheric window band. The net cooling effect of radiative cooling depends on a comprehensive balance between "reducing solar absorption" and "enhancing infrared thermal radiation." The daytime cooling effect is positively correlated with the combined performance of reflectivity and emissivity. Example 5 achieved the highest daytime cooling effect (4.3°C) with the highest reflectivity (86.1%) combined with the highest emissivity (93.6%), verifying the advantages of the synergistic effect of multiple functional particles.

[0098] (III) Synergistic effect of the combined use of titanium dioxide and zirconium dioxide – outstanding performance of Example 5

[0099] Example 5 uses both isopropyl titanate and zirconium propoxide as organometallic compound precursors to generate mixed particles of titanium dioxide and zirconium dioxide in situ within an anhydride curing agent. All performance indicators are the best values ​​among all examples: reflectivity 86.1%, emissivity 93.6%, interlaminar shear strength 64 MPa, and daytime cooling rate 4.3°C.

[0100] From a fundamental mechanistic perspective, the synergistic effect of using titanium dioxide and zirconium dioxide together lies in the complementary optical properties of the two particles. Titanium dioxide has the highest refractive index (approximately 2.5-2.7), resulting in the largest refractive index difference with the epoxy resin matrix. It exhibits the strongest scattering efficiency in the visible to near-infrared band, making it the main contributor to improved solar reflectivity. Although zirconium dioxide has a lower refractive index (approximately 2.15), its Zr-O vibrational mode exhibits superior infrared activity in the 8-13 μm atmospheric window band compared to titanium dioxide's Ti-O vibrational mode, thus contributing more to infrared emissivity. When the two particles coexist in the matrix, titanium dioxide dominates the solar scattering and reflection function, while zirconium dioxide enhances the infrared thermal radiation function. Both particles maximize their effectiveness in their respective advantageous wavelength bands, achieving an optimal combination of "high reflectivity + high emissivity." Compared to Example 2 (82.9% reflectivity, 92.4% emissivity) using titanium dioxide alone and Example 4 (85.5% reflectivity, 92.8% emissivity) using zirconium dioxide alone, Example 5 shows improvements in both reflectivity and emissivity. This is not a simple compromise or average, but rather exhibits a synergistic effect exceeding the individual effects of each component alone. In terms of mechanical properties, Example 5 has an interlaminar shear strength of 64 MPa, which is also superior to the 59-61 MPa of Examples 1-2 containing TiO2, indicating that the dispersion and interfacial bonding of the TiO2 and ZrO2 mixed particles in the matrix are equally excellent.

[0101] (iv) In-situ generation method is significantly superior to coating method - Structural durability defects in Comparative Example 3

[0102] Comparative Example 3 involved coating a pure carbon fiber composite material surface with a 100 μm thick ZS-411 type radiation-cooling coating. Its initial optical performance was excellent: reflectivity of 95.1%, emissivity of 96.3%, and daytime cooling of 6.8°C, all higher than those of the embodiments of this invention. This result is as expected because the coating method concentrates a high concentration of radiation-cooling functional particles in a thin surface layer. The density of scattering centers and infrared emitters per unit area is much higher than that of the scheme that disperses the particles throughout the thickness of the substrate, naturally resulting in stronger optical performance in the initial state.

[0103] However, Comparative Example 3 exhibits serious deficiencies in structural durability. While the coating adhesion in the cross-cut adhesion test is rated at level 1, which is considered good, two out of the three test panels showed significant cracking after only three temperature cycles in the temperature resistance test conducted according to GB / T 9755-2014. This indicates that in actual outdoor use environments, the surface radiation-cooling coating of carbon fiber composites is highly susceptible to macroscopic cracks after experiencing alternating day-night temperature differences and seasonal temperature variations. These cracks not only disrupt the optical continuity of the coating and reduce reflectivity and emissivity, but also become channels for moisture and ultraviolet radiation to penetrate the substrate, accelerating the aging and degradation of the carbon fiber composite material itself.

[0104] From a fundamental mechanistic perspective, the poor durability of coatings on carbon fiber composites stems from interfacial mismatch. Carbon fiber composites have an extremely low coefficient of thermal expansion (approaching zero or even negative in the fiber direction), while radiation-cooled coatings, typically based on organic resins or inorganic silicates, have a significantly higher coefficient of thermal expansion than the carbon fiber composite substrate. During temperature cycling, the inconsistent thermal expansion / contraction between the coating and substrate generates repeated shear and tensile stresses at the interface. When the accumulated stress exceeds the bonding strength of the coating-substrate interface or the tensile strength of the coating itself, cracking and peeling occur. Furthermore, carbon fiber composites have high surface chemical inertness and low surface energy; the adhesion between the coating and substrate relies primarily on physical bonding (van der Waals forces and mechanical anchoring), lacking chemical bonding, resulting in inherently weak interfacial adhesion.

[0105] In contrast, in embodiments 1-5 of this invention, the radiative cooling functional particles are chemically bonded within the matrix and integrally formed with the carbon fiber composite material, eliminating the weak point of the coating-substrate interface. The covalent bonds (Si-O-Si bonds, ester bonds) between the functional particles and the matrix will not break due to temperature cycling, and the particle dispersion remains stable during use. Although the initial optical performance of each embodiment of this invention is slightly lower than that of the coating method, its structural reliability and long-term stability are far superior to the coating method, and it can continuously and stably provide radiative cooling functionality throughout the entire lifespan of the carbon fiber composite material.

[0106] (V) Long-term weather resistance advantages of in-situ generation method – verified by 1000-hour aging test

[0107] To further verify the performance stability of the carbon fiber composite material of the present invention under long-term outdoor use conditions, a 1000-hour accelerated aging test was conducted on all examples and comparative examples. The test results of interlaminar shear strength, reflectivity, and emissivity of each sample after aging are summarized in Table 2.

[0108] As shown in Table 2, in terms of mechanical properties, the interlaminar shear strength (ILSS) of Examples 1-5 after 1000 hours of aging was 51-61 MPa, with a retention rate of 77%-98% (relative to their initial values). Among them, Example 5 had the highest ILSS after aging (61 MPa) and a retention rate of 95%, while Example 2 achieved a retention rate of 98% (58 / 59 MPa). In stark contrast, the ILSS of Comparative Example 2 (pure carbon fiber composite material without any functional particles) dropped sharply from 70 MPa to 44 MPa after aging, with a retention rate of only 63%, a decrease of 37%. This comparison reveals a key fact: without any UV shielding and thermal management protection, the resin matrix of the pure carbon fiber composite material underwent severe photo-oxidative degradation and thermo-oxidative aging during the 1000-hour aging process, leading to the destruction of the matrix crosslinking network, damage to the fiber-matrix interface, and a sharp decline in mechanical properties. Examples 1-5, containing in-situ generated functional particles, showed significantly higher absolute interlaminar shear strengths (51-61 MPa) after aging compared to the unprotected pure carbon fiber composite material (44 MPa), with a retention rate 14-35 percentage points higher. Comparative Example 1 (direct physical addition method) had an ILSS of 43 MPa after aging, comparable to Comparative Example 2 but far lower than the other examples, indicating that the physically added agglomerated particles failed to provide effective UV shielding protection to the matrix. Comparative Example 3 (coating method) saw its ILSS drop to 18 MPa after aging, the lowest among all samples. This was because the coating cracked during aging, allowing moisture and UV radiation to penetrate the substrate through the cracks, accelerating the aging and degradation of the carbon fiber composite material, even more severely than the uncoated Comparative Example 2.

[0109] From a fundamental mechanistic perspective, Examples 1-5 maintained significantly higher interlaminar shear strength than Comparative Example 2 after aging. The fundamental reason lies in the dual aging protection mechanism provided by the in-situ generated functional particles to the resin matrix. The first mechanism is the ultraviolet shielding effect: the in-situ generated titanium dioxide particles have a band gap of approximately 3.2 eV, capable of absorbing ultraviolet light with wavelengths below approximately 387 nm; the zirconium dioxide particles have a band gap of approximately 5.0 eV, capable of absorbing deep ultraviolet light with wavelengths below approximately 248 nm. These particles, uniformly dispersed in the matrix, form an "ultraviolet filter," intercepting high-energy ultraviolet photons and converting them into harmless heat dissipation, preventing ultraviolet photons from penetrating deep into the resin matrix and causing the breakage of CO and CN bonds in the epoxy resin macromolecular chains, as well as free radical chain degradation reactions. In Comparative Example 2, the pure epoxy resin matrix had no ultraviolet protection; ultraviolet light directly triggered photo-oxidative degradation, which is the main reason for its significant 37% decrease in ILSS. The second mechanism is the thermal management effect: the high reflectivity of the in-situ generated functional particles significantly reduces the surface temperature of the composite material during aging, slowing down the thermo-oxidative aging rate caused by high temperatures. Simultaneously, the lower operating temperature also reduces the interfacial thermal stress between the carbon fiber and the resin matrix due to the difference in their coefficients of thermal expansion, thus reducing the initiation and propagation of interfacial microcracks. The synergistic effect of these two mechanisms results in the functional particle-containing examples exhibiting significantly lower matrix degradation rates and interfacial damage during aging compared to pure carbon fiber composites without particles.

[0110] In terms of optical performance, the reflectance of Examples 1-5 after aging was 69.8%-82.3%, and the emissivity was 91.4%-93.0%, with relatively small attenuation. Among them, the reflectance of Example 5 after aging was 82.3% (attenuation of 3.8 percentage points), and the emissivity was 91.4% (attenuation of 2.2 percentage points), both remaining at a high level and still providing effective radiative cooling function. The reflectance of Comparative Example 2 remained basically unchanged after aging (39.9% vs 40.4%), because the optical properties of the carbon fiber itself did not change much during the aging process, but its emissivity also remained basically stable (90.1% vs 91.7%), indicating that the infrared performance of the pure epoxy resin matrix is ​​not sensitive to aging, further confirming that the excellent retention of mechanical properties in the examples is due to the ultraviolet shielding and thermal management effect of the functional particles, rather than the matrix itself having anti-aging ability. Comparative Example 1 showed a significant decrease in reflectivity to 50.8% after aging (a decrease of 12.5 percentage points). This was because the aggregated particles underwent further debonding and crack propagation due to matrix shrinkage and interface damage during aging. The microcracks around the aggregates became light scattering "dead zones," reducing the effective scattering area and significantly decreasing reflectivity. Comparative Example 3 showed the largest decrease in reflectivity, from 95.1% to 77.9% after aging (a decrease of 17.2 percentage points). This was directly related to the loss of optical continuity of the coating due to cracking and local peeling during aging—the dark carbon fiber substrate was exposed at the cracks in the coating, strongly absorbing sunlight and causing a sharp drop in the macroscopic average reflectivity.

[0111] The above aging test results strongly confirm the significant advantages of the in-situ generation method of this invention in terms of long-term weather resistance. In terms of mechanical properties, the interlaminar shear strength retention rate (77%-98%) of the various embodiments of this invention after aging is much higher than that of pure carbon fiber composites without functional particles (63%), quantitatively demonstrating the UV shielding protection effect of the in-situ generated TiO2 and ZrO2 particles on the resin matrix. In terms of optical properties, although the initial optical performance is not as good as the coating method (Comparative Example 3), after 1000 hours of accelerated aging, the reflectance decay of the various embodiments of this invention is much smaller than that of the coating method (decay of 3.5-5.4 percentage points vs. 17.2 percentage points), and the reflectance of Example 5 after aging (82.3%) has exceeded that of Comparative Example 3 after aging (77.9%), achieving performance reversal. From the perspective of overall life-cycle performance, the in-situ generation method of this invention significantly outperforms the coating method and the direct physical addition method in terms of mechanical reliability and optical performance durability under long-term use conditions.

[0112] (vi) Synergistic effect of particle dispersibility on radiative cooling performance and mechanical properties

[0113] By comprehensively comparing the initial and aging properties of Comparative Example 1 with those of each embodiment, the synergistic effect mechanism of particle dispersion on the multiple properties of composite materials can be revealed.

[0114] Although Comparative Example 1 also added radiation-cooling functional particles (10 g SiO2 + 10 g TiO2), its initial reflectivity was only 63.3%, which was much lower than that of the examples with similar particle content. Figure 4 (SEM image of Comparative Example 1) and Figure 3 The comparison of the SEM images (from Example 2) visually reveals the root cause of the difference: in Comparative Example 1, the particles are severely agglomerated, while in Example 2, the particles are uniformly dispersed. From the perspective of scattering optics principles, particle agglomeration drastically reduces the number of effective scattering centers—assuming n particles agglomerate into a cluster, the number of effective scattering centers drops from n to 1, significantly reducing the total scattering cross-section. Photons pass through the resin layer without being effectively scattered and reach the dark carbon fiber layer where they are absorbed. Furthermore, the equivalent particle size of the agglomerates is much larger than that of individual particles, deviating from the optimal Mie scattering particle size range of 300-600 nm, further reducing the scattering efficiency of individual scattering centers. In contrast, the particles generated in situ in the examples maintain a monodisperse state, with each particle being an independent scattering center. Both scattering efficiency and scattering center density are optimal, thus achieving higher reflectivity with a similar total particle content.

[0115] More importantly, the effects of particle dispersion on mechanical properties and radiative cooling performance show a positively correlated synergistic relationship, rather than an inverse relationship. In the direct physical addition method, while increasing the amount of particles may slightly improve reflectivity, it also exacerbates agglomeration, further deteriorating mechanical properties and creating a seesaw effect between optical and mechanical properties. In the in-situ generation method of this invention, the highly uniform dispersion of particles brings two positive effects: first, each particle acts as an independent scattering center, maximizing optical efficiency; second, the uniformly dispersed particles do not form stress concentrations, thus not impairing mechanical properties. This synergistic effect of "optical and mechanical win-win" is the core advantage of the in-situ generation method, distinguishing it from the direct physical addition method.

[0116] The working principle of the in-situ generated radiation-cooling particle carbon fiber composite material prepared by this invention when used outdoors is as follows: When sunlight shines on the surface of the composite material, the incident light enters the surface resin layer and first encounters submicron particles of silica, titanium dioxide, and / or zirconium dioxide uniformly dispersed in the matrix. These particles have a refractive index difference with the resin matrix, and the particle size is within the optimal range for Mie scattering of sunlight wavelengths. Each particle acts as an independent scattering center, generating a strong scattering effect on the incident light. After multiple scatterings between multiple particles, the propagation direction of most photons is deflected upwards towards the surface and finally exits from the surface of the composite material, macroscopically exhibiting a high solar reflectivity (up to 86.1%). This means that the surface of the composite material absorbs less than 14% of the solar radiation energy, significantly reducing the solar heating effect.

[0117] Meanwhile, the composite material itself, along with the small amount of heat absorbed from the environment, emits infrared thermal radiation. The stretching vibrations of Si-O-Si bonds in silica particles, the vibration modes of Zr-O bonds in zirconium dioxide particles, and the vibration modes of Ti-O bonds in titanium dioxide particles precisely cover the 8-13 μm atmospheric window band. Infrared radiation in this band can penetrate the Earth's atmosphere almost without damage and be directly dissipated into the cold source of outer space at a temperature of approximately 3 K. The emissivity of the composite material in this band reaches a maximum of 93.6%, approaching the level of blackbody radiation, indicating high infrared heat dissipation efficiency. When the radiative heat dissipation power exceeds the sum of the solar absorption power and the environmental heat conduction power, the surface temperature of the composite material can be lower than the ambient temperature, achieving passive, energy-free cooling. Experimental results show that the surface temperature of the carbon fiber composite material of this invention is up to 4.3°C lower than that of ordinary carbon fiber composite materials without functional particles under sunlight conditions.

[0118] Furthermore, the titanium dioxide and zirconium dioxide particles generated in situ within the matrix also possess an absorption and shielding effect against ultraviolet light. Titanium dioxide has a band gap of approximately 3.2 eV, corresponding to the absorption of ultraviolet light with wavelengths below approximately 387 nm; zirconium dioxide has a band gap of approximately 5.0 eV, corresponding to the absorption of deep ultraviolet light with wavelengths below approximately 248 nm. After being absorbed by these particles, the ultraviolet light is converted into harmless heat dissipation, without penetrating into the resin matrix to trigger photo-oxidative degradation of the epoxy resin macromolecular chains. Accelerated aging tests over 1000 hours confirmed that the examples containing the in-situ generated particles maintained high mechanical properties (ILSS retention rate 84%-95%) and optical properties (reflectance attenuation of only 3.5-5.4 percentage points) after aging, significantly outperforming the direct physical addition method and the coating method, verifying the ultraviolet shielding effect and long-term stability of the in-situ generated particles. Since ultraviolet light accounts for less than 5% of the total solar spectrum energy, the thermal gain from ultraviolet light absorption by the particles is almost negligible compared to the overall radiative cooling effect and will not significantly affect the cooling performance.

[0119] In summary, this invention generates different types of radiative cooling functional particles in situ within the epoxy resin and curing agent components of the carbon fiber composite matrix. Utilizing the chemical bonding between the particles and the matrix, strong interfacial adhesion and highly uniform dispersion are achieved, endowing the composite with efficient solar reflection, infrared thermal radiation, and ultraviolet shielding functions while maintaining its mechanical properties. Compared to coating methods, this invention avoids cracking and peeling caused by coating-substrate interface mismatch, exhibiting significantly superior performance stability during long-term use. Compared to direct physical addition methods, this invention fundamentally solves the particle agglomeration problem, achieving dual optimization of radiative cooling optical and mechanical properties. The combined use of titanium dioxide and zirconium dioxide in Example 5 further verifies the possibility of synergistic effects from multiple functional particles, providing a thermal management solution for carbon fiber composites in outdoor construction, automotive shells, and other applications that combines efficient radiative cooling, excellent mechanical properties, and long-term weather resistance.

[0120] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing carbon fiber composite materials with in-situ generated radiation-cooling particles, characterized in that, Includes the following steps: (1) Add coupling agent to epoxy resin and stir evenly, add silicate precursor solution, heat and stir to hydrolyze and condense silicate, generate silica particles in situ in epoxy resin, remove solvent to obtain epoxy resin containing silica particles. (2) Mix organometallic compounds, chelating agents and organic acids to obtain metal chelates, dissolve acid anhydride curing agents and organic solvents to obtain acid anhydride solutions, add the metal chelates to the acid anhydride solutions and stir to react, generate metal oxide particles in situ in the curing agent, heat to remove byproducts, and obtain a curing agent containing metal oxide particles. (3) The epoxy resin containing silica particles obtained in step (1) is mixed with the curing agent containing metal oxide particles obtained in step (2), a curing accelerator is added and stirred evenly, and the carbon fiber cloth is treated with a roller to make a prepreg. The prepreg is laid up and then hot-pressed to obtain a carbon fiber composite material with in-situ generated radiation cooling particles.

2. The preparation method according to claim 1, characterized in that, The silicate ester precursor in step (1) is tetraethyl orthosilicate, the coupling agent is silane coupling agent KH-560, and the silicate ester precursor solution is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol and deionized water.

3. The preparation method according to claim 2, characterized in that, In step (1), the mass ratio of tetraethyl orthosilicate, anhydrous ethanol and deionized water is 1:0.1:(0.35−0.45); the mass ratio of tetraethyl orthosilicate solution added to epoxy resin to epoxy resin is 1:(1.5−3); and the mass ratio of epoxy resin to KH-560 is 1:(0.1−0.15).

4. The preparation method according to claim 1, characterized in that, The organometallic compound mentioned in step (2) is isopropyl titanate and / or zirconium propoxide, and the metal oxide particles are titanium dioxide particles and / or zirconium dioxide particles.

5. The preparation method according to claim 4, characterized in that, The chelating agent in step (2) is ethylene glycol or acetylacetone, and the organic acid is glacial acetic acid; the molar ratio of the organometallic compound, the chelating agent and glacial acetic acid is 1:(0.5−1.2):0.

1.

6. The preparation method according to claim 4, characterized in that, The anhydride curing agent in step (2) is HK-021 anhydride, the organic solvent is acetone, the mass ratio of the anhydride curing agent to acetone is 10:1, and the mass ratio of the anhydride solution to the metal chelate is 1:(0.4−1).

7. The preparation method according to claim 4, characterized in that, When the organometallic compound contains zirconium propoxide, deionized water is added when the anhydride solution is mixed with the metal chelate, wherein the mass ratio of the anhydride solution to the deionized water is 1:0.

005.

8. The preparation method according to claim 1, characterized in that, The size of the silica particles generated in situ in step (1) is 300–600 nm; the size of the metal oxide particles generated in situ in step (2) is 300–600 nm.

9. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the epoxy resin containing silica particles to the curing agent containing metal oxide particles is 1:(0.9-1.2); the curing accelerator is DMP-30, and its amount accounts for 1%-3% of the total mass of the epoxy resin and the curing agent.

10. A carbon fiber composite material for in-situ generation of radiation-cooling particles, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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