High-toughness flame-retardant carbon fiber and method for preparing the same

Abstract

This invention relates to the field of carbon fiber interface engineering, specifically a high-toughness flame-retardant carbon fiber and its preparation method. The high-toughness flame-retardant carbon fiber comprises a carbon fiber substrate and a sizing layer on its surface. The sizing layer is formed by a solid composite of epoxy resin, 4,4′-diaminodiphenyl sulfone, P / Si reactive flame-retardant silane intermediate, and P / Si / epoxy functional core-shell nanoparticles, with controlled sizing pick-up. This design effectively balances flame-retardant properties, dispersion stability, and high toughness guidance in the sizing layer, mitigating the adverse effects of interface layer stiffening, embrittlement, and increased viscosity of the sizing solution. It improves uniform sizing conditions and processing adaptability, making it suitable for the preparation of carbon fibers for flame-retardant composite materials.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber interface engineering, specifically to a high-toughness flame-retardant carbon fiber and its preparation method. Background Technology

[0002] Carbon fiber reinforced resin matrix composites are widely used due to their lightweight and excellent mechanical properties. Modification methods for carbon fiber surfaces include electrochemical oxidation, plasma treatment, chemical grafting, and sizing. Among these, sizing is considered a common approach that balances economy, controllability, and minimal damage to the carbon fiber. Publicly available information also indicates that the near-surface interfacial layer of carbon fibers is influenced by both the carbon fiber bulk and the composition of the sizing agent. For carbon fiber systems requiring flame retardancy, the sizing layer, in addition to its protective and interfacial bonding functions, is often endowed with phosphorus-, silicon-, or other reactive structures to achieve flame retardancy at relatively low addition levels. However, unstable dispersion, increased viscosity of the sizing solution, or non-uniform film structure can easily lead to stiffening and embrittlement of the interfacial layer, compressing the processing window. Therefore, achieving a balance between flame retardancy, film stability, and high toughness guidance remains a key challenge in this type of technology.

[0003] Chinese patent CN105064030A discloses a carbon fiber sizing agent and its preparation method. The method involves adding oligomeric silsesquioxane organic-inorganic nanoparticles to the carbon fiber sizing agent to improve its heat resistance, toughness, and interfacial properties. Chinese patent CN113429596B discloses a sizing carbon fiber cloth reinforced flame-retardant epoxy resin and its preparation method. The method uses a lignin-based flame retardant, a lignin-based epoxy resin, and a silane coupling agent to construct a flame-retardant epoxy resin and sizing carbon fiber cloth system. Based on the publicly available information, the former focuses more on general sizing modification and silicon-containing nanoparticle enhancement, while the latter focuses more on the composite construction of flame-retardant epoxy resin system and sizing carbon fiber cloth. For the technical route of directly forming a sizing layer containing both P / Si reactive flame-retardant silane intermediate and P / Si / epoxy functional core-shell nanoparticle solid on the surface of carbon fiber substrate, and achieving high toughness, flame retardancy and uniform sizing with low sizing pick-up amount, there is still a lack of more direct publicly available solutions, and there is also room for further optimization of the targeted limitation of the continuous preparation window. Summary of the Invention

[0004] The purpose of this invention is to provide a high-toughness flame-retardant carbon fiber and its preparation method, which solves the problems of interface layer stiffening and embrittlement, poor dispersion stability of sizing liquid and narrowing of processing window that are easily caused by the introduction of phosphorus-containing and silicon-containing flame-retardant components into the existing carbon fiber sizing system.

[0005] This invention introduces a P / Si reactive flame-retardant silane intermediate and a P / Si / epoxy functional core-shell nanoparticle solid into a sizing layer, and combines it with epoxy resin and 4,4′-diaminodiphenyl sulfone. This allows the phosphorus-containing component, silicon-containing component, epoxy functional structure, and core-shell structure to work synergistically within the same sizing layer. This approach maintains flame retardancy while mitigating interface stiffness, and balances the dispersibility, film-forming properties, and sizing pick-up control of the sizing layer.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A high-toughness flame-retardant carbon fiber includes a carbon fiber substrate and a sizing layer disposed on the surface of the carbon fiber substrate; the solid components of the sizing layer, by weight, include:

[0008] a. 40–70 parts by weight of epoxy resin, wherein the epoxy resin is selected from one or two of bisphenol A type epoxy resin and 4,4′-methylenebis(N,N-diglycidylaniline);

[0009] b. The curing agent is 4,4′-diaminodiphenyl sulfone, and the amount of curing agent used is 5–20 parts by weight;

[0010] 5–25 parts by weight of cP / Si reactive flame-retardant silane intermediate;

[0011] 5–25 parts by weight of dP / Si / epoxy functional core-shell nanoparticles;

[0012] The amount of sizing pick-up in the sizing layer is 0.5–2.0 wt% relative to the mass of the carbon fiber substrate.

[0013] Furthermore, the P / Si reactive flame-retardant silane intermediate is prepared via the following steps:

[0014] A1. Raw material preparation: Weigh 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 3-glycidyloxypropyltrimethoxysilane, control the molar ratio of the two to be 0.30–0.55:1, and introduce nitrogen gas as an inert protective atmosphere.

[0015] A2. Addition reaction: react at 90–130℃ for 2–6 h;

[0016] A3. Deviation and cooling: After devastation for 30–90 min at an absolute pressure of 0.001–0.010 MPa, the product is cooled to obtain a P / Si reactive flame-retardant silane intermediate.

[0017] A4. Endpoint Criteria and Quality Control: The epoxy equivalent of the P / Si reactive flame-retardant silane intermediate is 430–800 g / eq, and the volatile matter is ≤1.0 wt%.

[0018] Furthermore, the shell layer of the P / Si / epoxy functional core-shell nanoparticle solid contains a phosphorus-based methacrylate reaction intermediate, which is prepared through the following steps:

[0019] B1. Raw material preparation: Weigh 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and glycidyl methacrylate, controlling the molar ratio of the two to be 0.95–1.10:1; add 4-methoxyphenol as a polymerization inhibitor, the amount of 4-methoxyphenol added is 0.01–0.10 wt% relative to the total raw material mass in B1; and purge with nitrogen as an inert protective atmosphere.

[0020] B2. Addition reaction: react at 110–135℃ for 2–8 h;

[0021] B3. Deviation: Deviation was carried out at an absolute pressure of 0.001–0.010 MPa for 30–120 min to obtain phosphorus-based methacrylate reaction intermediates;

[0022] B4. Endpoint Criteria and Quality Control: The residual epoxy group content of the phosphorus-based methacrylate reaction intermediate is ≤0.02mol / 100g, and the volatile content is ≤1.0wt%.

[0023] Furthermore, P / Si / epoxy functional core-shell nanoparticles were prepared via the following steps:

[0024] C1. Aqueous phase preparation: Add sodium dodecyl sulfate and sodium bicarbonate to water, wherein the amount of sodium dodecyl sulfate is 0.2–1.5 wt% relative to the water mass and the amount of sodium bicarbonate is 0.05–0.5 wt% relative to the water mass; and purge with nitrogen for deoxygenation for 10–60 min;

[0025] C2. Initiation: After heating to 70–85℃, add potassium persulfate. The amount of potassium persulfate is 0.1–1.0 wt% of the total mass of the core and shell monomer mixture.

[0026] C3. Core-layer polymerization: Add the core-layer monomer n-butyl acrylate and polymerize for 1–3 hours;

[0027] C4. Shell polymerization: A mixture of shell monomers is added dropwise and polymerized for 2–6 hours. The shell monomer mixture includes methyl methacrylate, glycidyl methacrylate, 3-(methacryloyloxy)propyltrimethoxysilane, and a phosphorus-based methacrylate reaction intermediate. The mass fractions of methyl methacrylate, glycidyl methacrylate, 3-(methacryloyloxy)propyltrimethoxysilane, and phosphorus-based methacrylate reaction intermediate are 35–89 wt%, 5–25 wt%, 1–10 wt%, and 5–30 wt%, respectively. The sum of the mass fractions of all components is 100 wt%.

[0028] C5. Post-processing and quality control: After the reaction is completed, the mixture is cooled to obtain an aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles, which is then further dehydrated and dried to obtain solid P / Si / epoxy functional core-shell nanoparticles. The particle size D50 of the P / Si / epoxy functional core-shell nanoparticles is 80–150 nm, and the solid content of the aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles is 15–45 wt%.

[0029] Furthermore, the sizing layer is formed through the following steps:

[0030] D1. Preparation of sizing solution: Epoxy resin, 4,4′-diaminodiphenyl sulfone, P / Si reactive flame-retardant silane intermediate, and P / Si / epoxy functional core-shell nanoparticles are added to acetone to form a sizing solution with a solid content of 5–25 wt%.

[0031] D2. Sizing: Bringing the carbon fiber substrate into contact with the sizing solution and squeezing out excess sizing solution;

[0032] D3. Drying: Dry at 60–110℃ for 1–15 min;

[0033] D4. Endpoint and Quality Control: After drying, the amount of sizing picked up should be 0.5–2.0 wt% relative to the carbon fiber substrate mass, and the residual solvent should be ≤0.5 wt%.

[0034] Furthermore, the epoxy resin is a combination of bisphenol A type epoxy resin and 4,4′-methylenebis(N,N-diglycidylaniline), and the mass ratio of the two is 9:1–3:7.

[0035] Furthermore, in the solid component of the sizing layer, the mass ratio of P / Si / epoxy functional core-shell nanoparticles to P / Si reactive flame-retardant silane intermediates is 1:3–3:1.

[0036] As a concept of this invention, an epoxy resin, 4,4′-diaminodiphenyl sulfone, a P / Si reactive flame-retardant silane intermediate, and P / Si / epoxy functional core-shell nanoparticles are used to construct a sizing layer. The epoxy resin forms a continuous phase compatible with the subsequent resin system, the 4,4′-diaminodiphenyl sulfone provides a curable structure, the P / Si reactive flame-retardant silane intermediate introduces phosphorus- and silicon-containing reactive units, and the P / Si / epoxy functional core-shell nanoparticles regulate the local structure of the sizing layer. By controlling the weight proportions of each component and the amount of sizing picked up, an interface-controlled structure with both flame-retardant properties and high toughness guidance is formed on the surface of the carbon fiber substrate, thereby alleviating the interface layer stiffening and embrittlement problems that easily occur after the introduction of phosphorus- and silicon-containing flame-retardant components.

[0037] This invention also discloses a method for preparing high-toughness flame-retardant carbon fiber, comprising the following steps:

[0038] S1. Preparation of P / Si reactive flame-retardant silane intermediates;

[0039] S2. Preparation of phosphorus-based methacrylate reaction intermediates;

[0040] S3. Using the phosphorus-based methacrylate reaction intermediate obtained in step S2, continue to prepare P / Si / epoxy functional core-shell nanoparticles;

[0041] S4. According to the weight proportions of the solid components of the sizing layer as described in claim 1, epoxy resin, 4,4′-diaminodiphenyl sulfone, P / Si reactive flame-retardant silane intermediate, and P / Si / epoxy functional core-shell nanoparticles are added to acetone to form a sizing solution with a solid content of 5–25 wt%. The carbon fiber substrate is brought into contact with the sizing solution, and excess sizing solution is squeezed out. Subsequently, it is dried at 60–110°C for 1–15 min to obtain high-toughness flame-retardant carbon fiber.

[0042] Furthermore, after drying in step S4, a B-stage treatment step is also included, which involves processing at 120–170°C for 2–30 min.

[0043] Furthermore, the intermediates obtained in steps S1 and S2 are both subjected to vacuum devolatilization treatment, with an absolute pressure of 0.001–0.010 MPa. The devolatilization time in step S1 is 30–90 min, and the devolatilization time in step S2 is 30–120 min.

[0044] Furthermore, the addition reaction step for the preparation of the P / Si reactive flame-retardant silane intermediate was carried out under mechanical stirring conditions at a stirring speed of 100–600 rpm.

[0045] Furthermore, the vacuum devolatilization step for the preparation of P / Si reactive flame-retardant silane intermediates is carried out at 80–120°C, with mechanical stirring maintained during the devolatilization process, and then cooled to 20–40°C after the devolatilization is completed.

[0046] Furthermore, the epoxy equivalent of the P / Si reactive flame-retardant silane intermediate was determined by titration using the hydrochloric acid-acetone method; the volatile matter was determined by the loss-in-weight method in an oven at 105°C for 2 hours.

[0047] Furthermore, the addition reaction step for the preparation of phosphorus-based methacrylate reaction intermediates was carried out under mechanical stirring conditions at a stirring speed of 100–600 rpm.

[0048] Furthermore, the vacuum devolatilization step for the preparation of phosphorus-based methacrylate reaction intermediates is carried out at 80–120°C, with mechanical stirring maintained during the devolatilization process, and then cooled to 20–40°C after the devolatilization is completed.

[0049] Furthermore, the residual epoxy group content of the phosphorus-based methacrylate reaction intermediate was determined by titration using the hydrochloric acid-acetone method; the volatile matter was determined by the loss-in-weight method in an oven at 105°C for 2 hours.

[0050] Furthermore, in the emulsion polymerization of P / Si / epoxy functional core-shell nanoparticles, the total water usage, including C1 aqueous phase water and pre-emulsion water, is 1.2–5.0 times the total mass of the core layer monomer and the shell layer monomer.

[0051] Furthermore, the mass ratio of the core monomer n-butyl acrylate to the shell monomer mixture is 30:70 to 70:30.

[0052] Furthermore, the emulsion polymerization process of P / Si / epoxy functional core-shell nanoparticles was carried out under mechanical stirring conditions, with a stirring speed of 200–800 rpm.

[0053] Furthermore, in the shell polymerization step, the shell monomer mixture or the pre-emulsion obtained therefrom is added dropwise at a rate of 0.05–5.00 mL / min, or the total dropping time is controlled within 30–180 min.

[0054] Furthermore, in the shell polymerization step, the shell monomer mixture is emulsified in an aqueous phase to prepare a pre-emulsion before being added; the pre-emulsion is prepared by dispersing 0.5–2.0 times the mass of the shell monomer mixture of deionized water and 0.2–1.0 wt% of the mass of the shell monomer mixture of sodium dodecyl sulfate under mechanical stirring at 500–1500 rpm for 5–20 min.

[0055] Furthermore, the solid content of the P / Si / epoxy functional core-shell nanoparticle aqueous dispersion was determined by drying at 105℃ to constant weight method. The constant weight criterion was that the mass difference between two consecutive weighings was 30 min apart and did not exceed 0.1%. The particle size D50 was determined by dynamic light scattering method at 25℃ after dilution in deionized water, and D50 was calculated based on volume distribution.

[0056] Furthermore, the P / Si / epoxy functional core-shell nanoparticle solid was prepared from the P / Si / epoxy functional core-shell nanoparticle aqueous dispersion by spray drying or freeze drying; the spray drying inlet air temperature was 60–120℃, and the outlet air temperature was 40–80℃; the freeze drying pre-freezing temperature was -40 to -20℃, the sublimation stage shelf temperature was -20 to 0℃, and the system absolute pressure was 0.001–0.050MPa.

[0057] Furthermore, when preparing the slurry, each solid component is added to acetone and mechanically stirred at 25–50°C for 30–180 minutes until it is evenly dispersed. The endpoint criterion for even dispersion is the absence of visible agglomerates observed with the naked eye. The slurry is then filtered through a 100–200 μm filter before use.

[0058] Furthermore, the sizing step adopts an immersion method, in which the carbon fiber substrate is immersed in the sizing solution for 1.0–10.0s, and then the excess sizing solution is squeezed out by roller pressing, with a roller gap of 0.05–1.00mm.

[0059] Furthermore, the residual solvent content was determined by gas chromatography.

[0060] Furthermore, in steps A1 and B1, after purging the reactor with nitrogen 2–5 times, nitrogen is continuously introduced during the addition reaction stage at a flow rate of 0.05–0.5 L / min; during the vacuum devolatilization stage, the continuous nitrogen supply is stopped and depressurized devolatilization is performed; after the devolatilization is completed, the vacuum is broken with nitrogen or the nitrogen seal is restored.

[0061] Furthermore, the B-order conversion step is carried out in an air atmosphere or a nitrogen atmosphere.

[0062] As another aspect of this invention, a continuous preparation path is established around the P / Si reactive flame-retardant silane intermediate, the phosphorus-based methacrylate reactive intermediate, the P / Si / epoxy functional core-shell nanoparticle solid, and the sizing process. By controlling the addition reaction, vacuum devolatilization, emulsion polymerization, sizing solution solid content, and drying conditions in steps S1-S4, the composition, particle size, volatile matter, and residual solvent of the sizing layer are kept within a controllable range. The purpose of this preparation method is to provide a repeatable, quality-controllable, and easily continuous process route for high-toughness flame-retardant carbon fibers, thereby reducing the adverse effects of increased sizing solution viscosity and unstable dispersion on uniform sizing.

[0063] In this invention, the P / Si reactive flame-retardant silane intermediate and the P / Si / epoxy functional core-shell nanoparticle solid are not simply added side-by-side. The former provides a phosphorus- and silicon-containing reactive structure, which can participate in film formation within the sizing layer and introduce flame-retardant enabling units into the interface layer; the latter provides local structural regulation within the sizing layer with its core-shell structure, wherein the epoxy functional structure is beneficial for maintaining compatibility with the epoxy resin system, and the core-shell nanostructure is beneficial for mitigating the embrittlement tendency caused by the concentration of purely rigid flame-retardant components. When combined with epoxy resin and 4,4′-diaminodiphenyl sulfone, a synergistic balance of flame retardancy, dispersion, and high toughness can be achieved without increasing the sizing pick-up to an uncontrolled level.

[0064] Beneficial technical effects

[0065] 1. This invention introduces P / Si reactive flame-retardant silane intermediates and P / Si / epoxy functional core-shell nanoparticles into the sizing layer simultaneously, so that the flame-retardant enabling unit and the sizing layer film-forming unit are configured in the same interface region, which is beneficial to achieve flame-retardant function introduction with a lower sizing pick-up amount.

[0066] 2. This invention constructs a curable system using epoxy resin and 4,4′-diaminodiphenyl sulfone, and adjusts the local structure of the sizing layer through a core-shell nanostructure. Compared with simply increasing the content of rigid flame retardant components, this is more conducive to alleviating the rigidity and embrittlement of the interface layer and improving high toughness guidance.

[0067] 3. This invention sets endpoint criteria and quality control indicators for P / Si reactive flame-retardant silane intermediates, phosphorus-based methacrylate reactive intermediates, P / Si / epoxy functional core-shell nanoparticle solids, and sizing steps, which helps to improve preparation consistency and process repeatability.

[0068] 4. The preparation method of the present invention limits the range of solid content, drying conditions, absolute pressure, particle size D50, and residual solvent in the sizing solution, which is beneficial to controlling the dispersion state of the sizing solution and the stability of continuous processing, and provides a process basis for industrial implementation. Attached Figure Description

[0069] Figure 1 The XPS high-resolution P2p spectra of Example 1, Comparative Example 2, and Comparative Example 3 are shown.

[0070] Figure 2 The images show the XPS high-resolution Si2p spectra of Examples 1, 2, and 3.

[0071] Figure 3 The XPS high-resolution N1s spectra of Example 1, Comparative Example 2, and Comparative Example 3 are shown.

[0072] Figure 4The above are XPS-fitted atomic percentage scatter plots for Example 1, Comparative Example 2, and Comparative Example 3.

[0073] Figure 5 The ATR-FTIR full spectrum overlays are for Example 1, Comparative Example 2, and Comparative Example 8.

[0074] Figure 6 The images shown are magnified ATR-FTIR 915 cm⁻¹ views of Examples 1, 2, and 8.

[0075] Figure 7 The figures show the DLS volume distribution curves for Example 1, Comparative Example 5, and Comparative Example 6.

[0076] Figure 8 The graphs show the DLS intensity distribution curves for Example 1, Comparative Example 5, and Comparative Example 6.

[0077] Figure 9 The DCB load-displacement curves are for Example 1, Comparative Example 3, and Comparative Example 6.

[0078] Figure 10 The DCBR curves for Example 1, Comparative Example 3, and Comparative Example 6 are shown.

[0079] Figure 11 The rotational rheological acceleration / deceleration flow curves for Example 1, Comparative Example 4, and Comparative Example 7 are shown.

[0080] Figure 12 The HRR curves of cone calorimetry for Example 1, Comparative Example 2, and Comparative Example 4 are shown.

[0081] Figure 13 The cone calorimetric SPR curves for Example 1, Comparative Example 2, and Comparative Example 4 are shown.

[0082] Figure 14 Macroscopic photograph of P / Si / epoxy functional core-shell nanoparticles prepared in Example 3.

[0083] Figure 15 A solid scanning electron microscope image of P / Si / epoxy functional core-shell nanoparticles prepared in Example 1.

[0084] Figure 16 Transmission electron microscopy (TEM) images of P / Si / epoxy functional core-shell nanoparticles prepared in Example 1, wherein... Figure 16 a is a bright field topography diagram. Figure 16 b is the contrast diagram of the core-shell structure. Figure 16 c is a magnified view of the core-shell interface. Figure 16 d is the selected area electron diffraction pattern.

[0085] Figure 17Scanning electron microscope image of the surface of the high-toughness flame-retardant carbon fiber prepared in Example 1. Detailed Implementation

[0086] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0087] Example 1

[0088] S1. Preparation of P / Si reactive flame-retardant silane intermediates

[0089] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 260 g of 3-glycidyloxypropyltrimethoxysilane were weighed, with a molar ratio of 0.42:1, and added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen three times, followed by continuous nitrogen flow at a flow rate of 0.25 L / min. The addition reaction was carried out at 110 °C for 4 h with stirring at 350 rpm. After the reaction, vacuum devolatilization was performed at 100 °C and an absolute pressure of 0.005 MPa for 60 min, with mechanical stirring maintained during the devolatilization. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 30 °C to obtain a P / Si reactive flame-retardant silane intermediate. The epoxy equivalent was determined to be 615 g / eq by hydrochloric acid-acetone titration, and the volatile matter content was determined to be 0.6 wt% by oven weight loss at 105 °C for 2 h.

[0090] S2. Preparation of phosphorus-based methacrylate reaction intermediates

[0091] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 64.5 g of glycidyl methacrylate were weighed, with a molar ratio of 1.02:1. 4-Methoxyphenol was added as a polymerization inhibitor at a rate of 0.055 wt% relative to the total raw material mass in B1. The mixture was added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen three times, followed by continuous nitrogen flow at a flow rate of 0.25 L / min. The addition reaction was carried out at 122 °C for 5 h with stirring at 350 rpm. After the reaction, vacuum devolatilization was performed at 100 °C and an absolute pressure of 0.005 MPa for 75 min, with mechanical stirring maintained during the devolatilization process. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 30 °C to obtain a phosphorus-based methacrylate reaction intermediate. The residual epoxy group content was determined to be 0.008 mol / 100g by titration using the hydrochloric acid-acetone method, and the volatile matter content was determined to be 0.5 wt% by oven weight loss method at 105℃ for 2 hours.

[0092] S3. Preparation of P / Si / epoxy functional core-shell nanoparticles

[0093] In a four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, dropping device, and nitrogen protection device, add 620 g of deionized water, 5.27 g of sodium dodecyl sulfate, and 1.71 g of sodium bicarbonate, and purge with nitrogen for 35 min to remove oxygen. Heat to 77.5 °C with stirring at 500 rpm, and add 1.1 g of potassium persulfate. Add 100 g of the core monomer n-butyl acrylate and polymerize for 2 h.

[0094] A pre-emulsion was prepared from the shell monomer mixture: 124 g of methyl methacrylate, 30 g of glycidyl methacrylate, 11 g of 3-(methacryloyloxy)propyltrimethoxysilane, and 35 g of phosphorus-based methacrylate reaction intermediate were weighed and mixed evenly. Then, 250 g of deionized water (1.25 times the mass of the shell monomer mixture) and 2.4 g of sodium dodecyl sulfate were added, and the mixture was dispersed at 1000 rpm for 12.5 min to obtain the pre-emulsion. The pre-emulsion was added dropwise to the reaction system at a uniform rate over a total time of 105 min. After the addition was complete, polymerization continued until the total shell polymerization time was 4 h. After the reaction was completed and cooled, an aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles was obtained. The solid content was determined to be 26.3 wt% by constant weight after drying at 105 °C. After dilution in deionized water, the particle size D50 was determined to be 115 nm by dynamic light scattering at 25 °C.

[0095] The P / Si / epoxy functional core-shell nanoparticle aqueous dispersion of this embodiment was prepared into a solid by spray drying. The inlet air temperature of the spray drying was 90°C and the outlet air temperature was 60°C, thus obtaining the P / Si / epoxy functional core-shell nanoparticle solid.

[0096] S4. Preparation of sizing solution and sizing

[0097] According to the weight ratio of the solid components in the sizing layer of this embodiment, 33g of bisphenol A epoxy resin, 22g of 4,4′-methylenebis(N,N-diglycidylaniline) (mass ratio of the two is 6:4, i.e., 1.5:1), 12.5g of 4,4′-diaminodiphenyl sulfone, 15g of P / Si reactive flame-retardant silane intermediate, and 15g of P / Si / epoxy functional core-shell nanoparticle solids were weighed and added to acetone to prepare a sizing solution with a solid content of 15wt%. The solution was mechanically stirred at 37.5℃ for 105min until it was evenly dispersed. The endpoint criterion for uniform dispersion was the absence of visible agglomerates observed by the naked eye. The solution was then filtered through a 150μm filter before use.

[0098] The carbon fiber substrate was sizing using an impregnation method. In this embodiment, the substrate was immersed in the sizing solution for 5 seconds, followed by removal of excess sizing solution by roller pressing with a roller gap of 0.5 mm. The substrate was then dried at 85°C for 8 minutes. After drying, the sizing pick-up amount was 1.25 wt% relative to the mass of the carbon fiber substrate, and the residual solvent was determined to be 0.2 wt% by gas chromatography.

[0099] After drying, the carbon fiber is subjected to B-stage treatment and treated at 145°C for 16 minutes in an air atmosphere to obtain the high-toughness flame-retardant carbon fiber of this embodiment.

[0100] Example 2

[0101] S1. Preparation of P / Si reactive flame-retardant silane intermediates

[0102] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 312 g of 3-glycidyloxypropyltrimethoxysilane were weighed, with a molar ratio of 0.35:1, and added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen three times, followed by continuous nitrogen flow at a flow rate of 0.1 L / min. The reaction was carried out at 95 °C for 2.5 h with stirring at 200 rpm. After the reaction, vacuum devolatilization was performed at 85 °C and an absolute pressure of 0.008 MPa for 40 min, with mechanical stirring maintained during the devolatilization. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 25 °C to obtain a P / Si reactive flame-retardant silane intermediate. The epoxy equivalent was determined to be 480 g / eq by hydrochloric acid-acetone titration, and the volatile matter content was determined to be 0.7 wt% by oven weight loss at 105 °C for 2 h.

[0103] S2. Preparation of phosphorus-based methacrylate reaction intermediates

[0104] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 67 g of glycidyl methacrylate were weighed, with a molar ratio of 0.98:1. 4-Methoxyphenol was added as a polymerization inhibitor, at a rate of 0.03 wt% relative to the total raw material mass in B1. The mixture was added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen three times, followed by continuous nitrogen flow at a flow rate of 0.15 L / min. The reaction was carried out at 115 °C for 3 h with stirring at 250 rpm. After the reaction, vacuum devolatilization was performed at 90 °C and an absolute pressure of 0.007 MPa for 50 min, with mechanical stirring maintained during the devolatilization process. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 25 °C to obtain a phosphorus-based methacrylate reaction intermediate. The residual epoxy group content was determined to be 0.012 mol / 100g by titration using the hydrochloric acid-acetone method, and the volatile matter content was determined to be 0.6 wt% by oven weight loss method at 105℃ for 2 hours.

[0105] S3. Preparation of P / Si / epoxy functional core-shell nanoparticles

[0106] In a four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, dropping device, and nitrogen protection device, add 300 g of deionized water, 1.2 g of sodium dodecyl sulfate (0.4 wt% of water), and 0.3 g of sodium bicarbonate (0.1 wt% of water). Purge with nitrogen for 15 min to remove oxygen. Heat to 72 °C with stirring at 300 rpm, and add 0.3 g of potassium persulfate. Add 52.5 g of the core monomer n-butyl acrylate and polymerize for 1.5 h.

[0107] A pre-emulsion was prepared from the shell monomer mixture: 76.05 g of methyl methacrylate, 7.8 g of glycidyl methacrylate, 1.95 g of 3-(methacryloyloxy)propyltrimethoxysilane, and 11.7 g of phosphorus-based methacrylate reaction intermediate were weighed and mixed thoroughly. Then, 68.25 g of deionized water (0.7 times the mass of the shell monomer mixture) and 0.29 g of sodium dodecyl sulfate (0.3 wt% of the mass of the shell monomer mixture) were added and dispersed at 700 rpm for 8 min to obtain the pre-emulsion. The pre-emulsion was added dropwise to the reaction system at a rate of 3.0 mL / min. After the addition was complete, polymerization continued until the total shell polymerization time was 3 h. After the reaction was completed and cooled, an aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles was obtained. The solid content was determined to be 29.2 wt% by constant weight after drying at 105 °C. After dilution in deionized water, the particle size D50 was determined to be 90 nm by dynamic light scattering at 25 °C.

[0108] The P / Si / epoxy functional core-shell nanoparticle aqueous dispersion of this embodiment was prepared into a solid by freeze-drying. The pre-freezing temperature was -30°C, the shelf temperature during the sublimation stage was -10°C, and the absolute pressure of the system was 0.010 MPa, thus obtaining P / Si / epoxy functional core-shell nanoparticle solid.

[0109] S4. Preparation of sizing solution and sizing

[0110] According to the weight ratio of the solid components in the sizing layer of this embodiment, 65g of bisphenol A type epoxy resin, 18g of 4,4′-diaminodiphenyl sulfone, 8g of P / Si reactive flame-retardant silane intermediate, and 10g of P / Si / epoxy functional core-shell nanoparticles were weighed and added to acetone to prepare a sizing solution with a solid content of 8wt%. The solution was mechanically stirred at 28°C for 60 minutes until it was evenly dispersed. The endpoint criterion for even dispersion was the absence of visible agglomerates observed with the naked eye. The solution was then filtered through a 100μm filter before use.

[0111] The carbon fiber substrate was sizing using an impregnation method. In this embodiment, the substrate was impregnated in the sizing solution for 1 second, followed by removal of excess sizing solution by roller pressing with a roller gap of 0.2 mm. The substrate was then dried at 65°C for 3 minutes. After drying, the sizing pick-up amount was 0.8 wt% relative to the mass of the carbon fiber substrate, and the residual solvent was determined to be 0.3 wt% by gas chromatography.

[0112] After drying, the carbon fiber is subjected to a B-stage treatment and then treated at 130°C for 8 minutes under a nitrogen atmosphere to obtain the high-toughness flame-retardant carbon fiber of this embodiment.

[0113] Example 3

[0114] S1. Preparation of P / Si reactive flame-retardant silane intermediates

[0115] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 210 g of 3-glycidyloxypropyltrimethoxysilane were weighed, with a molar ratio of 0.52:1, and added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen four times, followed by continuous nitrogen flow at a flow rate of 0.4 L / min. The addition reaction was carried out at 125 °C for 5.5 h with stirring at 500 rpm. After the reaction, vacuum devolatilization was performed at 115 °C and an absolute pressure of 0.002 MPa for 80 min, with mechanical stirring maintained during the devolatilization. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 35 °C to obtain a P / Si reactive flame-retardant silane intermediate. The epoxy equivalent was determined to be 720 g / eq by hydrochloric acid-acetone titration, and the volatile matter content was determined to be 0.4 wt% by oven weight loss at 105 °C for 2 h.

[0116] S2. Preparation of phosphorus-based methacrylate reaction intermediates

[0117] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 60.9 g of glycidyl methacrylate were weighed, with a molar ratio of 1.08:1. 4-Methoxyphenol was added as a polymerization inhibitor at a rate of 0.08 wt% relative to the total raw material mass in B1. The mixture was added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen four times, followed by continuous nitrogen flow at a flow rate of 0.35 L / min. The addition reaction was carried out at 130 °C for 7 h with a stirring speed of 480 rpm. After the reaction, vacuum devolatilization was performed for 105 min at an absolute pressure of 0.003 MPa and a temperature of 110 °C, with mechanical stirring maintained during the devolatilization process. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 35 °C to obtain a phosphorus-based methacrylate reaction intermediate. The residual epoxy group content was determined to be 0.005 mol / 100g by titration using the hydrochloric acid-acetone method, and the volatile matter content was determined to be 0.3 wt% by oven weight loss method at 105℃ for 2 hours.

[0118] S3. Preparation of P / Si / epoxy functional core-shell nanoparticles

[0119] In a four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, dropping device, and nitrogen protection device, add 630 g of deionized water, 8.19 g of sodium dodecyl sulfate (1.3 wt% relative to water), and 2.65 g of sodium bicarbonate (0.42 wt% relative to water). Purge with nitrogen for 50 min to remove oxygen. Heat to 82 °C with stirring at 700 rpm, and add 1.28 g of potassium persulfate. Add 97.5 g of the core monomer n-butyl acrylate and polymerize for 2.7 h.

[0120] A pre-emulsion was prepared from the shell monomer mixture: 22g of methyl methacrylate, 10g of glycidyl methacrylate, 4g of 3-(methacryloyloxy)propyltrimethoxysilane, and 14g of phosphorus-based methacrylate reaction intermediate were weighed and mixed evenly. Then, 90g of deionized water (1.8 times the mass of the shell monomer mixture) and 0.45g of sodium dodecyl sulfate (0.9wt% of the shell monomer mixture) were added, and the mixture was dispersed at 1400 rpm for 18 min to obtain the pre-emulsion. The pre-emulsion was added dropwise to the reaction system at a rate of 1.5 mL / min. After the addition was complete, polymerization continued until the total shell polymerization time was 5.5 h. After the reaction was completed and cooled, an aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles was obtained. The solid content was determined to be 40wt% by constant weight after drying at 105℃. After dilution in deionized water, the particle size D50 was determined to be 138 nm by dynamic light scattering at 25℃.

[0121] The P / Si / epoxy functional core-shell nanoparticle aqueous dispersion of this embodiment was prepared into a solid by spray drying. The inlet air temperature of the spray drying was 110°C and the outlet air temperature was 75°C, thus obtaining the P / Si / epoxy functional core-shell nanoparticle solid.

[0122] S4. Preparation of sizing solution and sizing

[0123] According to the weight ratio of the solid components in the sizing layer of this embodiment, 25g of bisphenol A epoxy resin, 20g of 4,4′-methylenebis(N,N-diglycidylaniline) (mass ratio of the two is 5:4, i.e., 1.25:1), 8g of 4,4′-diaminodiphenyl sulfone, 22g of P / Si reactive flame-retardant silane intermediate, and 20g of P / Si / epoxy functional core-shell nanoparticles were weighed and added to acetone to prepare a sizing solution with a solid content of 20wt%. The solution was mechanically stirred at 46°C for 150min until it was evenly dispersed. The endpoint criterion for even dispersion was the absence of visible agglomerates observed by the naked eye. The solution was then filtered through a 200μm filter before use.

[0124] The carbon fiber substrate was sizing using an impregnation method. In this embodiment, the substrate was impregnated in the sizing solution for 8 seconds, followed by removal of excess sizing solution by roller pressing with a roller gap of 0.85 mm. The substrate was then dried at 102°C for 13 minutes. After drying, the sizing pick-up amount was 1.7 wt% relative to the mass of the carbon fiber substrate, and the residual solvent was determined to be 0.15 wt% by gas chromatography.

[0125] After drying, the carbon fiber is subjected to B-stage treatment and treated at 162°C for 25 minutes in air atmosphere to obtain the high-toughness flame-retardant carbon fiber of this embodiment.

[0126] Example 4

[0127] S1. Preparation of P / Si reactive flame-retardant silane intermediates

[0128] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 352 g of 3-glycidyloxypropyltrimethoxysilane were weighed, with a molar ratio of 0.31:1, and added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen four times, followed by continuous nitrogen flow at a flow rate of 0.48 L / min. The addition reaction was carried out at 128 °C for 5.8 h with stirring at 570 rpm. After the reaction, vacuum devolatilization was performed for 85 min at an absolute pressure of 0.0015 MPa and a temperature of 118 °C, with mechanical stirring maintained during the devolatilization. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 22 °C to obtain a P / Si reactive flame-retardant silane intermediate. The epoxy equivalent was determined to be 460 g / eq by hydrochloric acid-acetone titration, and the volatile matter content was determined to be 0.5 wt% by oven weight loss at 105 °C for 2 h.

[0129] S2. Preparation of phosphorus-based methacrylate reaction intermediates

[0130] 100 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 68.5 g of glycidyl methacrylate were weighed, with a molar ratio of 0.96:1. 4-Methoxyphenol was added as a polymerization inhibitor at a rate of 0.095 wt% relative to the total raw material mass in B1. The mixture was added to a four-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen protection device. The reactor was purged with nitrogen four times, followed by continuous nitrogen flow at a flow rate of 0.47 L / min. The addition reaction was carried out at 133 °C for 7.5 h with a stirring speed of 580 rpm. After the reaction, vacuum devolatilization was performed for 115 min at an absolute pressure of 0.0012 MPa and a temperature of 117 °C, with mechanical stirring maintained during the devolatilization process. After the devolatilization was completed, the vacuum was broken with nitrogen and the mixture was cooled to 22 °C to obtain a phosphorus-based methacrylate reaction intermediate. The residual epoxy group content was determined to be 0.007 mol / 100g by titration using the hydrochloric acid-acetone method, and the volatile matter content was determined to be 0.4 wt% by oven weight loss method at 105℃ for 2 hours.

[0131] S3. Preparation of P / Si / epoxy functional core-shell nanoparticles

[0132] In a four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, dropping device, and nitrogen protection device, add 720 g of deionized water, 10.22 g of sodium dodecyl sulfate (1.42 wt% of water), and 3.38 g of sodium bicarbonate (0.47 wt% of water). Purge with nitrogen for 56 min to remove oxygen. Heat to 71 °C with stirring at 750 rpm, then add 1.43 g of potassium persulfate. Add 48 g of the core monomer n-butyl acrylate and polymerize for 2.8 h.

[0133] A pre-emulsion was prepared from the shell monomer mixture: 37g of methyl methacrylate, 24g of glycidyl methacrylate, 9g of 3-(methacryloyloxy)propyltrimethoxysilane, and 30g of phosphorus-based methacrylate reaction intermediate were weighed and mixed thoroughly. Then, 190g of deionized water (1.9 times the mass of the shell monomer mixture) and 0.95g of sodium dodecyl sulfate (0.95wt% of the shell monomer mixture) were added, and the mixture was dispersed at 1450rpm for 19min to obtain the pre-emulsion. The pre-emulsion was added dropwise to the reaction system at a rate of 0.8mL / min. After the addition was complete, polymerization continued until the total shell polymerization time was 5.7h. After the reaction was completed and cooled, an aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles was obtained. The solid content was determined to be 15.3wt% by constant weight after drying at 105℃. After dilution in deionized water, the particle size D50 was determined to be 146nm by dynamic light scattering at 25℃.

[0134] The P / Si / epoxy functional core-shell nanoparticle aqueous dispersion of this embodiment was prepared into a solid by freeze-drying. The pre-freezing temperature was -38°C, the shelf temperature during the sublimation stage was -2°C, and the absolute pressure of the system was 0.005 MPa, thus obtaining P / Si / epoxy functional core-shell nanoparticle solid.

[0135] S4. Preparation of sizing solution and sizing

[0136] According to the weight ratio of the solid components of the sizing layer in this embodiment, 29.4g of bisphenol A type epoxy resin, 12.6g of 4,4′-methylenebis(N,N-diglycidylaniline) (mass ratio of the two is 7:3, i.e., 2.33:1), 6g of 4,4′-diaminodiphenyl sulfone, 24g of P / Si reactive flame-retardant silane intermediate, and 23g of P / Si / epoxy functional core-shell nanoparticles were weighed and added to acetone to prepare a sizing solution with a solid content of 23wt%. The solution was mechanically stirred at 48°C for 170min until it was evenly dispersed. The endpoint criterion for uniform dispersion was the absence of visible agglomerates observed by the naked eye. The solution was then filtered through a 105μm filter before use.

[0137] The carbon fiber substrate was sizing using an impregnation method. In this embodiment, the substrate was impregnated in the sizing solution for 9.2 seconds, followed by removal of excess sizing solution by roller pressing with a roller gap of 0.92 mm. The substrate was then dried at 107°C for 14 minutes. After drying, the sizing pick-up amount was 1.9 wt% relative to the mass of the carbon fiber substrate, and the residual solvent was determined to be 0.25 wt% by gas chromatography.

[0138] After drying, the carbon fiber is subjected to B-stage treatment and treated at 167°C for 28 minutes under a nitrogen atmosphere to obtain the high-toughness flame-retardant carbon fiber of this embodiment.

[0139] Example 1 employs a stable configuration with all core parameters selected at the median or moderately biased range to ensure process stability and reproducibility, representing an optimal balance. Example 2 focuses on high epoxy content and low flame retardant load, using 65 parts by weight of a single bisphenol A epoxy resin, with a low amount of flame retardant component and relatively mild process temperature and time, prioritizing the enhancement of mechanical properties. Example 3 adopts the opposite optimization direction to Example 2, enhancing flame retardant performance, using 22 parts by weight of P / Si intermediate, 20 parts by weight of core-shell particles, and only 45 parts by weight of epoxy resin, combined with a high-temperature, long-time reaction and curing process to achieve a high flame retardant load configuration. Example 4 verifies the feasibility of the parameter boundaries of the technical solution. Several key parameters are close to the edge of the range (e.g., 42 parts by weight of epoxy resin is close to the lower limit, 24 parts by weight of P / Si intermediate is close to the upper limit, 23 parts by weight of core-shell particles is close to the upper limit, and 1.9 wt% of sizing pick-up is close to the upper limit), and many boundary values ​​are also selected for process parameters, demonstrating the adaptability and robustness of the technical solution within a wide parameter window.

[0140] Comparative Example 1: Basically the same as Example 1, except that only 55g of bisphenol A type epoxy resin was used in the sizing layer, and 4,4′-methylenebis(N,N-diglycidylaniline) was not added, while other conditions remained unchanged.

[0141] Comparative Example 2: Basically the same as Example 1, except that the amount of P / Si reactive flame-retardant silane intermediate is 5g, and other conditions remain unchanged.

[0142] Comparative Example 3: It is basically the same as Example 1, except that the amount of P / Si / epoxy functional core-shell nanoparticle solid is 5g, and other conditions remain unchanged.

[0143] Comparative Example 4: Basically the same as Example 1, except that the mass ratio of bisphenol A epoxy resin to 4,4′-methylenebis(N,N-diglycidylaniline) was adjusted to 3:7, while other conditions remained unchanged.

[0144] Comparative Example 5: Basically the same as Example 1, except that the particle size D50 of the P / Si / epoxy functional core-shell nanoparticles is 70 nm, and other conditions remain unchanged.

[0145] Comparative Example 6: Basically the same as Example 1, except that the particle size D50 of the P / Si / epoxy functional core-shell nanoparticles is 160 nm, and other conditions remain unchanged.

[0146] Comparative Example 7: Basically the same as Example 1, except that the slurry solid content is 23wt%, and other conditions remain unchanged.

[0147] Comparative Example 8: Basically the same as Example 1, except that the B-stage step is not performed after drying, and other conditions remain unchanged.

[0148] Performance testing:

[0149] The filtered slurry was tested using a rotational viscometer at 25℃, with acceleration and deceleration rates of 0.5, 1, 5, 10, 25, and 50 s⁻¹. After standing for 300 s, the test was repeated, and the 25-s value was recorded. -1 Viscosity, thixotropic ring area, and recovery rate were measured three times for each sample. The temperature was maintained at 25±0.5℃ using a sealed solvent cup. Rheological curves were output and recovery rates were calculated to evaluate the construction viscosity and thixotropic recovery performance at higher solid contents, and to characterize shear thinning and structural recovery properties.

[0150] The aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles was diluted with deionized water to a suitable concentration. After equilibration at 25±0.1℃, dynamic light scattering was used to measure the dispersion three times consecutively. Z-average, D50, and PDI were recorded, and the volume distribution data were output. The particle size distribution CSV file was exported, and the D50 shift and distribution broadening were compared to evaluate the dispersion state and particle size window. The hydrodynamic particle size and distribution width were determined.

[0151] A sizing film of approximately 30 μm thickness was prepared on an inert substrate according to the respective formulations and drying step B regime. The film was scanned using ATR mode at 4000-650 cm⁻¹. -1 Wavenumber range, resolution 4cm -1 Each scan consisted of 32 scans, and each sample was tested 3 times. The characteristic absorption decay of epoxy was analyzed by FTIR to reflect the degree of crosslinking, and the P–O and Si–O related absorption bands were tracked. The epoxy conversion rate and characteristic peak area ratio were calculated to evaluate the degree of epoxy group consumption and the retention of P / Si functional groups.

[0152] Unidirectional laminates with a uniform resin system were prepared using carbon fibers from various samples. Samples were prepared according to a uniform layup and curing regime. Short beam specimens were prepared for three-point bending tests with a span-to-thickness ratio of 4:1. Five samples were prepared in each group. The failure load of the short beam specimens was tested and the interlaminar shear strength of the short beam was calculated. The average value, standard deviation and failure mode records were output to evaluate the interfacial load transfer capacity and interlaminar shear bearing capacity, reflecting the interlaminar shear strength that is dominated by resin / interface failure.

[0153] Unidirectional laminated double cantilever beam specimens were prepared using carbon fiber samples. Specimens were fabricated on a pre-cracked substrate, loaded at a constant displacement rate, and crack propagation was recorded simultaneously. Five specimens were used in each group. The ModeI interlaminar fracture toughness G was calculated using DCB load-displacement and crack length data. Ic Output G Ic Values, R-curves, and load-displacement overlays are used to evaluate the resistance to interlaminar crack initiation and propagation.

[0154] Strip specimens of laminated plates of uniform thickness were prepared using carbon fiber samples from each sample. Vertical specimens were prepared according to specified dimensions. The minimum oxygen volume fraction required to maintain continuous combustion was determined in an oxygen / nitrogen mixed atmosphere at ambient temperature. Five samples were used in each group. The specimen thickness and surface condition were kept consistent. The average value and standard deviation of the oxygen index were output and analyzed in conjunction with pHRR to evaluate the flame retardant efficiency.

[0155] Flat laminate samples with uniform resin content were prepared using carbon fiber samples. 100mm × 100mm samples were prepared, edged with aluminum foil, and ignited externally. Cone calorimeter tests were conducted under 50kW / m² thermal irradiation. Heat release rate (HRR), total heat release rate (THR), smoke generation rate (SPR), and residual mass were recorded. Three samples were used in each group. HRR / SPR curves and key pHRR and THR values ​​were output to evaluate heat and smoke release behavior under real-world fire conditions.

[0156] Figure 1 The XPS high-resolution P2p spectra of Examples 1, 2, and 3 are shown. X-ray photoelectron spectroscopy was used to analyze the chemical state of phosphorus on the surface of the curing system. The P2p characteristic peak of Example 1 is clearer and has a higher peak area, indicating that the phosphorus-containing structure is more fully introduced into the interface surface layer, which is beneficial to improving the flame-retardant interface construction effect of the system.

[0157] Figure 2 The XPS high-resolution Si2p spectra of Examples 1, 2, and 3 are shown. X-ray photoelectron spectroscopy was used to characterize the chemical state of silicon on the surface of the cured system. The Si-related characteristic peaks are more obvious in Example 1, indicating that the silicon-oxygen structure and the interface coupling structure are more fully formed, proving that the gradient interface layer design is reasonable.

[0158] Figure 3 The XPS high-resolution N1s spectra of Examples 1, 2, and 3 are shown. X-ray photoelectron spectroscopy was used to analyze the nitrogen-containing groups on the surface of the cured system. The N1s peak shape of Example 1 is more stable and the signal is stronger, indicating that the nitrogen-containing structure is more fully retained in the interface and participates in the reaction, which helps to synergistically enhance the interface bonding and flame retardant properties.

[0159] Figure 4 The XPS-fitted atomic percentage scatter plots for Example 1, Comparative Example 2, and Comparative Example 3 are shown. Based on the X-ray photoelectron spectroscopy peak fitting results, the relative contents of key elements such as P, Si, and N in the surface layer are compared. Example 1 is better in terms of multi-element synergistic enrichment, indicating that its interface composition regulation is more balanced and effective.

[0160] Figure 5 The ATR-FTIR full spectrum overlays of Examples 1, 2, and 8 are shown. The changes in functional groups of the cured samples were characterized by attenuated total reflectance Fourier transform infrared spectroscopy. Example 1 showed more consistent spectral characteristics in the phosphorus-silicon related absorption band and the epoxy curing related absorption band, indicating that the introduction of reactive functional components and the formation of cross-linking networks were more complete.

[0161] Figure 6 ATR-FTIR 915 cm⁻¹ for Examples 1, 2, and 8 -1The magnified view shows a localized analysis of the characteristic absorption bands of the residual epoxy using attenuated total reflectance Fourier transform infrared spectroscopy. Example 1 shows the bands at 915 cm⁻¹. -1 The weaker residual peaks nearby indicate a more complete epoxy reaction, proving that the designed system has better curing efficiency.

[0162] Figure 7 The DLS volume distribution curves for Example 1, Comparative Example 5, and Comparative Example 6 are shown. Dynamic light scattering was used to test the particle size distribution of the core-shell nanoparticle dispersion. The volume distribution peak of Example 1 is more concentrated and located in a moderate particle size range, indicating that the particle size control is more reasonable, which is beneficial to the synergistic effect of dispersion stability and interface toughening.

[0163] Figure 8 The following are DLS intensity distribution curves for Example 1, Comparative Example 5, and Comparative Example 6. Dynamic light scattering was used to analyze the scattering intensity distribution of core-shell nanoparticles. The distribution of Example 1 is more concentrated and the tailing of large particles is weaker, indicating that agglomeration is effectively suppressed and proving that its particle dispersion state is more stable.

[0164] Figure 9 The DCB load-displacement curves for Examples 1, 3, and 6 are shown. The load response during the interlaminar cracking process was characterized by the interlaminar fracture toughness test of the double cantilever beam. Example 1 has a higher load level and a smoother instability process, indicating that it has stronger interlaminar crack resistance and energy dissipation capacity.

[0165] Figure 10 The DCBR curves for Example 1, Comparative Example 3, and Comparative Example 6 are shown. The evolution of GIc during crack propagation was analyzed using the interlaminar fracture toughness test of a double cantilever beam. Example 1 maintained a higher GIc level during the crack propagation stage, indicating that its toughening mechanism is more stable and can continuously suppress crack propagation.

[0166] Figure 11 The rotational rheological flow curves of Example 1, Comparative Example 4, and Comparative Example 7 are shown. The flow behavior of the grout at different shear rates was characterized by rotational rheological testing. Example 1 showed a moderate viscosity level and a small hysteresis in the acceleration and deceleration, indicating that it has both good construction fluidity and structural stability.

[0167] Figure 12 The HRR curves of cone calorimetry for Example 1, Comparative Example 2, and Comparative Example 4 are shown. The heat release rate during the combustion process of the material was characterized by cone calorimetry. Example 1 has a lower heat release peak and a flatter curve, indicating that it can effectively suppress the combustion intensity and delay the concentrated occurrence of heat release.

[0168] Figure 13The cone calorimetry SPR curves for Example 1, Comparative Example 2, and Comparative Example 4 are shown. The cone calorimetry test was used to analyze the smoke generation rate during the combustion process of the material. Example 1 showed a lower smoke release level throughout the combustion stage, indicating that it has a more significant advantage in reducing smoke hazards.

[0169] Figure 14 This is a macroscopic photograph of the P / Si / epoxy functional core-shell nanoparticles prepared in Example 3. The sample is a white to light yellow powder with a loose and uniform texture, good flowability, and a fine matte surface, without obvious agglomeration or color difference. The light yellow hue of the powder originates from the intrinsic absorption of the DOPO structure contained in the phosphorus-based methacrylate reaction intermediate in the shell, while the fine surface texture is related to the microporous structure formed by the rapid evaporation of the solvent during spray drying. The sample remains stable at room temperature without moisture absorption or agglomeration, proving that the spray drying process parameters are reasonable and successfully achieved the transformation of the core-shell nanoparticle aqueous dispersion into a free-flowing solid powder, providing a convenient solid form for the subsequent preparation of the sizing solution.

[0170] Figure 15 Scanning electron microscope (SEM) images of the P / Si / epoxy functional core-shell nanoparticles prepared in Example 1 are shown. The images reveal that the nanoparticles obtained through spray drying exhibit a relatively regular spherical morphology with good dispersion and no severe large-sized agglomerates. This indicates that the core-shell emulsion polymerization combined with spray drying process successfully prepared structurally stable and size-controllable functionalized nanospheres. This uniform nanoscale morphology facilitates efficient dispersion in the subsequent epoxy resin slurry, ensuring the consistency of the final composite material's interfacial properties and demonstrating the correctness and feasibility of the core-shell nanoparticle preparation scheme.

[0171] Figure 16 Transmission electron microscopy (TEM) image of P / Si / epoxy functional core-shell nanoparticles prepared in Example 1. Figure 16 The bright-field image clearly shows the regular spherical morphology of the particles, with a particle size distribution in the range of 90 to 140 nm and an average particle size of about 115 nm. Figure 16 b shows that due to the density difference between the core layer n-butyl acrylate and the shell layer methyl methacrylate complex, and the introduction of phosphorus and silicon elements which increases the electron density of the shell, a significant difference in the contrast between the core and shell phases can be observed in the image. The light gray core region corresponds to the low-density soft core, while the dark gray ring around the periphery corresponds to the hard shell containing phosphorus and silicon functional groups. Figure 16 The magnified image (c) shows a continuous and clear core-shell interface, with the shell uniformly covering the core surface. The high-resolution image does not show clear lattice fringes, but rather a uniform amorphous scattering contrast. Figure 16The d-area electron diffraction pattern exhibits typical diffuse scattering halos without obvious diffraction spots, confirming that the sample has an amorphous polymer structure. These core-shell structural characteristics indicate that the semi-continuous emulsion polymerization process is rationally designed. The uniform dropwise addition of the shell monomer pre-emulsion successfully achieved uniform coating of the functional components on the core surface. The resulting clear core-shell interface and suitable shell thickness are beneficial for balancing the toughening effect of the core layer with the interfacial reactivity of the epoxy functional groups and phosphorus-silicon flame-retardant elements in the shell.

[0172] Figure 17 The image shows a scanning electron microscope (SEM) image of the surface of the high-toughness flame-retardant carbon fiber prepared in Example 1. The carbon fiber monofilaments exhibit a smooth and uniformly covered surface, indicating that the sizing agent formed a continuous and complete thin film layer on the fiber surface, without obvious sizing enrichment or incomplete coating defects. More importantly, uniformly embedded micro-particle protrusions can be clearly observed in the sizing layer on the fiber surface. These protrusions are direct evidence that the aforementioned P / Si / epoxy functional core-shell nanoparticles were successfully introduced and solidified in the interface layer. This morphology confirms that the complex sizing system containing reactive flame-retardant silane intermediates and core-shell nanoparticles has good wettability on carbon fibers. Through impregnation, drying, and B-stage treatment processes, a composite interface layer integrating flame retardancy and toughening functions was successfully constructed on the carbon fiber surface, verifying the rationality and effectiveness of the overall sizing modification scheme.

[0173] Table 1 Summary of performance of examples and comparative examples

[0174]

[0175] As can be seen from the performance of the examples and comparative examples in Table 1, Example 1 showed better performance in terms of apparent viscosity of the slurry, D50 of P / Si / epoxy functional core-shell nanoparticles, FTIR epoxy conversion rate, interlaminar shear strength of short beams, and G. Ic An optimal balance was achieved between the oxygen index and pHRR: Compared to Example 2, it significantly improved flame retardancy and interfacial toughness by increasing the reactive P / Si synergy level; compared to Examples 3 and 4, it avoided the interfacial stiffening and narrowing of the application window caused by high solids content, high particle size, and high sizing pick-up. In each comparative example, any disruption of the resin ratio, reactive flame retardant component, core-shell particle content / size, or B-stage step resulted in a decline in group performance, indicating that the advantages of this invention stem from the synergy of multiple factors, rather than the superposition of a single variable.

[0176] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-toughness flame-retardant carbon fiber, characterized in that, It includes a carbon fiber substrate and a sizing layer disposed on the surface of the carbon fiber substrate; the solid components of the sizing layer, by weight, include: a. 40–70 parts by weight of epoxy resin, wherein the epoxy resin is selected from one or two of bisphenol A type epoxy resin and 4,4′-methylenebis(N,N-diglycidylaniline); b. The curing agent is 4,4′-diaminodiphenyl sulfone, and the amount of curing agent used is 5–20 parts by weight; 5–25 parts by weight of cP / Si reactive flame-retardant silane intermediate; 5–25 parts by weight of dP / Si / epoxy functional core-shell nanoparticles; The amount of sizing pick-up in the sizing layer is 0.5–2.0 wt% relative to the mass of the carbon fiber substrate.

2. The high tenacity, flame retardant carbon fiber of claim 1, wherein, P / Si reactive flame-retardant silane intermediates are prepared via the following steps: A1. Raw material preparation: Weigh 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 3-glycidyloxypropyltrimethoxysilane, control the molar ratio of the two to be 0.30–0.55:1, and introduce nitrogen gas as an inert protective atmosphere. A2. Addition reaction: react at 90–130℃ for 2–6 h; A3. Deviation and cooling: After devastation for 30–90 min at an absolute pressure of 0.001–0.010 MPa, the product is cooled to obtain a P / Si reactive flame-retardant silane intermediate. A4. Endpoint Criteria and Quality Control: The epoxy equivalent of the P / Si reactive flame-retardant silane intermediate is 430–800 g / eq, and the volatile matter is ≤1.0 wt%.

3. The high tenacity, flame retardant carbon fiber of claim 1, wherein, The shell of the P / Si / epoxy functional core-shell nanoparticle solid contains a phosphorus-based methacrylate reaction intermediate, which is prepared by the following steps: B1. Raw material preparation: Weigh 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and glycidyl methacrylate, controlling the molar ratio of the two to be 0.95–1.10:1; add 4-methoxyphenol as a polymerization inhibitor, the amount of 4-methoxyphenol added is 0.01–0.10 wt% relative to the total raw material mass in B1; and purge with nitrogen as an inert protective atmosphere. B2. Addition reaction: react at 110–135℃ for 2–8 h; B3. Deviation: Deviation was carried out at an absolute pressure of 0.001–0.010 MPa for 30–120 min to obtain phosphorus-based methacrylate reaction intermediates; B4. Endpoint Criteria and Quality Control: The residual epoxy group content of the phosphorus-based methacrylate reaction intermediate is ≤0.02mol / 100g, and the volatile content is ≤1.0wt%.

4. The high tenacity, flame retardant carbon fiber of claim 3, wherein, P / Si / epoxy functional core-shell nanoparticles were prepared through the following steps: C1. Aqueous phase preparation: Add sodium dodecyl sulfate and sodium bicarbonate to water, wherein the amount of sodium dodecyl sulfate is 0.2–1.5 wt% relative to the water mass and the amount of sodium bicarbonate is 0.05–0.5 wt% relative to the water mass; and purge with nitrogen for deoxygenation for 10–60 min; C2. Initiation: After heating to 70–85℃, add potassium persulfate. The amount of potassium persulfate is 0.1–1.0 wt% of the total mass of the core and shell monomer mixture. C3. Core-layer polymerization: Add the core-layer monomer n-butyl acrylate and polymerize for 1–3 hours; C4. Shell polymerization: A mixture of shell monomers is added dropwise and polymerized for 2–6 hours. The shell monomer mixture includes methyl methacrylate, glycidyl methacrylate, 3-(methacryloyloxy)propyltrimethoxysilane, and a phosphorus-based methacrylate reaction intermediate. The mass fractions of methyl methacrylate, glycidyl methacrylate, 3-(methacryloyloxy)propyltrimethoxysilane, and phosphorus-based methacrylate reaction intermediate are 35–89 wt%, 5–25 wt%, 1–10 wt%, and 5–30 wt%, respectively. The sum of the mass fractions of all components is 100 wt%. C5. Post-processing and quality control: After the reaction is completed, the mixture is cooled to obtain an aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles, which is then further dehydrated and dried to obtain solid P / Si / epoxy functional core-shell nanoparticles. The particle size D50 of the P / Si / epoxy functional core-shell nanoparticles is 80–150 nm, and the solid content of the aqueous dispersion of P / Si / epoxy functional core-shell nanoparticles is 15–45 wt%.

5. The high tenacity, flame retardant carbon fiber of claim 4, wherein, The topcoat layer is formed through the following steps: D1. Preparation of sizing solution: Epoxy resin, 4,4′-diaminodiphenyl sulfone, P / Si reactive flame-retardant silane intermediate, and P / Si / epoxy functional core-shell nanoparticles are added to acetone to form a sizing solution with a solid content of 5–25 wt%. D2. Sizing: Bringing the carbon fiber substrate into contact with the sizing solution and squeezing out excess sizing solution; D3. Drying: Dry at 60–110℃ for 1–15 min; D4. Endpoint and Quality Control: The amount of sizing picked up after drying is 0.5–2.0 wt% relative to the mass of the carbon fiber substrate, and the residual solvent is ≤0.5 wt%.

6. The high tenacity, flame retardant carbon fiber of claim 1, wherein, The epoxy resin is a combination of bisphenol A type epoxy resin and 4,4′-methylenebis(N,N-diglycidylaniline), and the mass ratio of the two is 9:1–3:

7.

7. The high tenacity, flame retardant carbon fiber of claim 1, wherein, In the solid component of the sizing layer, the mass ratio of P / Si / epoxy functional core-shell nanoparticles to P / Si reactive flame-retardant silane intermediates is 1:3–3:

1.

8. A method for preparing the high-toughness flame-retardant carbon fiber according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation of P / Si reactive flame-retardant silane intermediates; S2. Preparation of phosphorus-based methacrylate reaction intermediates; S3. Using the phosphorus-based methacrylate reaction intermediate obtained in step S2, continue to prepare P / Si / epoxy functional core-shell nanoparticles; S4. According to the weight ratio of the solid components of the sizing layer as described in claim 1, epoxy resin, 4,4′-diaminodiphenyl sulfone, P / Si reactive flame-retardant silane intermediate and P / Si / epoxy functional core-shell nanoparticles are added to acetone to form a sizing solution with a solid content of 5–25 wt%. The carbon fiber substrate is brought into contact with the sizing solution and excess sizing solution is squeezed out. Then, it is dried at 60–110°C for 1–15 min to obtain high-toughness flame-retardant carbon fiber.

9. The production method according to claim 8, characterized by, After drying in step S4, a B-stage treatment step is also included, which involves processing at 120–170°C for 2–30 min.

10. The preparation method according to claim 8, characterized in that, The intermediates prepared in steps S1 and S2 are each subjected to a vacuum devolatilization treatment at an absolute pressure of 0.001 to 0.010 MPa, wherein the devolatilization time in step S1 is 30 to 90 min and the devolatilization time in step S2 is 30 to 120 min.

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