High-strength polyurethane composite carbon fiber sizing agent and preparation method thereof

Abstract

The invention provides a high-strength polyurethane composite carbon fiber sizing agent and a preparation method thereof, and belongs to the technical field of carbon fiber sizing agents. The three specific components are physically compounded, the comprehensive performance and the processing applicability of the carbon fiber sizing agent are remarkably improved under the condition of not depending on chemical reaction, and the beneficial effects of the carbon fiber sizing agent are reflected as follows: the interface bonding strength of carbon fibers and a resin matrix is greatly increased, the wetting spreadability of the fiber surface is effectively improved, and the application range of the carbon fiber sizing agent is widened. The excellent long-term storage stability of the sizing agent emulsion is ensured, meanwhile, the damage to a carbon fiber body is reduced to the maximum extent, and the inherent strength of the fiber is completely reserved.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber sizing agents, and in particular to a high-strength polyurethane composite carbon fiber sizing agent and a preparation method thereof. Background Art

[0002] Carbon fiber, with its exceptional strength-to-weight ratio, specific modulus, fatigue resistance, and low density, has become the preferred reinforcement for lightweight composite materials in cutting-edge fields such as aerospace, new energy vehicles, high-end sports equipment, and wind power generation. However, the surface of carbon fiber is highly inert and smooth, and brittle fibers are easily generated during the production process. This not only directly affects the fiber's processing performance (e.g., fuzzing and fiber breakage), but more importantly, severely limits the interfacial bonding strength between it and the resin matrix (such as epoxy, polyurethane, and BMI resin). As the critical bridge for load transfer in composites, the performance of the interface directly determines the composite's interlaminar shear strength, impact toughness, fatigue life, and even overall structural reliability. Weak interfaces lead to inefficient stress transfer, becoming a preferred area of material failure and significantly limiting the full utilization of carbon fiber's excellent mechanical properties. Therefore, surface treatment of carbon fiber, or "sizing," is an essential step in carbon fiber production and subsequent composite fabrication.

[0003] Sizing agent is a special coating solution applied to the surface of carbon fiber. Its core functions are mainly reflected in three aspects: first, it plays a role in bundling, lubrication and protection during fiber production and subsequent weaving, winding and other processing, effectively reducing the generation of lint and fiber damage, and ensuring smooth processing; second, and more critical, it is to significantly improve the physical and chemical compatibility between carbon fiber and the target resin matrix, by enhancing the wettability of the fiber surface, providing mechanical meshing points or introducing active groups that can participate in the resin curing reaction, etc., greatly improving the interfacial bonding strength between the two (often with interfacial shear strength IFSS as the key evaluation indicator); third, the ideal sizing film should be able to evenly and completely cover the fiber, and it should have good toughness and stability, so as not to have a negative impact on the strength of the carbon fiber itself.

[0004] Although existing technologies have achieved certain results, with the continuous improvement of performance requirements for composite materials, especially the higher pursuit of interface strength, long-term service stability and adaptability to extreme environments, traditional sizing agent systems are increasingly showing their limitations. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-strength polyurethane composite carbon fiber sizing agent and a preparation method thereof, which have excellent performance.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a high-strength polyurethane composite carbon fiber sizing agent, the raw materials of which include the following components: Waterborne polyurethane dispersion, nano-silica aqueous dispersion surface treated with silane coupling agent and non-ionic silicone surfactant.

[0007] Preferably, the average particle size of the nano-silica is 20-40 nm.

[0008] Preferably, the solid content of the sizing agent is 7.5-10.0 wt %; The pH value of the sizing agent is 7.5-8.5.

[0009] The present invention also provides a method for preparing the above-mentioned sizing agent, comprising the following steps: (1) Stirring the aqueous polyurethane dispersion at 23-28°C and 200-400 rpm; (2) adding the nano-silica aqueous dispersion to the system of step (1) at a rate of 3-8% of the total mass of component B per minute; (3) Increase the stirring speed to 700-900 rpm and continue for 20-60 minutes; (4) adding a nonionic silicone surfactant; (5) High-speed shear dispersion of the mixed system at 2500-5000 rpm for 20-60 minutes.

[0010] Preferably, the rotation speed of the high-speed shear dispersion is 3000~5000 rpm.

[0011] Preferably, the high-speed shear dispersion time is 30 to 45 minutes.

[0012] The present invention also provides a sizing method for carbon fiber, using the above-mentioned sizing agent, comprising the following steps: a) dipping the carbon fiber bundle into the sizing agent for 3 to 5 seconds; b) removing excess sizing agent through a squeeze roller; c) Dry in three stages in a hot air drying oven.

[0013] Preferably, the pressure of the squeezing roller is 0.15~0.25 MPa.

[0014] Preferably, the three-stage drying comprises: Stage 1: 80-100°C, residence time 30-45 seconds; Stage 2: 120-140°C, residence time 45-60 seconds; The third stage: 160~180°C, residence time 30~45 seconds.

[0015] Preferably, the final sizing rate is 0.8~1.5wt%.

[0016] Technical effects and advantages of the present invention: The present invention significantly improves the comprehensive performance and processing applicability of the carbon fiber sizing agent by physically compounding three specific components without relying on chemical reactions. The beneficial effects are mainly reflected in: directly achieving a significant leap in the interfacial bonding strength between the carbon fiber and the resin matrix, effectively improving the wettability and spreadability of the fiber surface, ensuring the excellent long-term storage stability of the sizing agent emulsion, and at the same time minimizing the damage to the carbon fiber body and completely retaining the inherent strength of the fiber; the sizing agent successfully breaks through the performance bottleneck of traditional single or two-component systems, and its simple physical preparation process is easy to control in large-scale production. The obtained high-performance sized carbon fiber can be widely used in various advanced composite materials with strict requirements on lightweight and mechanical properties, providing key surface treatment technology support for the preparation of carbon fiber reinforced composite materials with higher interface load-bearing efficiency, longer service life and better structural reliability, and directly solving the problems of interlayer performance degradation and early failure of composite materials caused by weak interfaces. DETAILED DESCRIPTION

[0017] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0018] Example 1 This embodiment provides a high-strength polyurethane composite carbon fiber sizing agent for enhancing the interfacial bonding performance between carbon fiber and resin matrix, and a preparation and application method thereof.

[0019] Three functional components are compounded in specific proportions: water-based polyurethane dispersion (component A), surface-treated nano-silica dispersion (component B) and a non-ionic silicone surfactant (component C).

[0020] First, place a commercially available aqueous polyurethane dispersion (approximately 40% solids content) in a thermostatically stirred vessel, maintain the temperature at 25±2°C, and stir at 300 rpm for basic mixing. Subsequently, while stirring continuously, slowly and evenly add a pre-prepared aqueous dispersion of nanosilica (15% solids content) treated with a silane coupling agent and with an average particle size of 30 nm. The addition rate is controlled at 5% of the total mass of component B per minute. This process continues for approximately 20 minutes to ensure good dispersion of the nanoparticles. After the addition is complete, increase the stirring speed to 800 rpm and maintain this speed for 40 minutes to achieve initial homogenization. Next, while stirring at 800 rpm, add the calculated amount of a nonionic organosilicon surfactant (100% active ingredient) at a constant rate over approximately 10 minutes. Finally, the entire mixture was transferred to a high-shear dispersing emulsifier and dispersed at 3000 rpm for 30 minutes. This step further breaks down any possible agglomerates and ensures uniform physical mixing of the three components at the molecular level, resulting in the final sizing agent emulsion. The ambient temperature was maintained at 25 ± 2°C throughout the entire preparation process. The resulting sizing agent was a milky white, homogeneous liquid with a solids content adjusted to the target value of 8.5 ± 0.2%. The pH range was controlled between 7.5 and 8.5, and it was stable for over 90 days at room temperature without visible stratification or precipitation.

[0021] The sizing agent application method is as follows: the carbon fiber bundles to be treated (e.g., 12K specification) are continuously passed through a sizing tank filled with the prepared sizing agent emulsion. The sizing tank is equipped with a thermostat to maintain the bath temperature at 30±1°C. By precisely controlling the guide roller speed and immersion depth, the carbon fiber bundles are immersed in the bath for 4.0±0.2 seconds. Immediately after leaving the sizing tank, the fiber bundles pass through a pair of precisely adjustable squeeze rollers with a pressure between the rollers set at 0.15 MPa to remove excess sizing agent and ensure a uniform and controllable sizing amount. The sized fiber bundles then enter a three-stage hot air drying oven: the first stage is 80±5°C with a dwell time of 45 seconds; the second stage is 120±5°C with a dwell time of 60 seconds; and the third stage is 160±5°C with a dwell time of 45 seconds. The total drying time is controlled to 150±5 seconds. Finally, the sizing-treated carbon fiber tow is obtained by winding, and the target sizing rate (measured as the percentage of the dry weight of the sizing agent to the dry weight of the fiber) is controlled at 1.2±0.1%.

[0022] Example 2 This embodiment provides a high-strength polyurethane composite carbon fiber sizing agent for enhancing the interfacial bonding performance between carbon fiber and resin matrix, and a preparation and application method thereof.

[0023] Three functional components are compounded in specific proportions: water-based polyurethane dispersion (component A), surface-treated nano-silica dispersion (component B) and a non-ionic silicone surfactant (component C).

[0024] First, place a commercially available aqueous polyurethane dispersion (approximately 40% solids content) in a thermostatically stirred vessel, maintain the temperature at 25±2°C, and stir at 300 rpm for basic mixing. Subsequently, while stirring continuously, slowly and evenly add a pre-prepared aqueous dispersion of nanosilica (15% solids content) treated with a silane coupling agent and with an average particle size of 30 nm. The addition rate is controlled at 5% of the total mass of component B per minute. This process continues for approximately 20 minutes to ensure good dispersion of the nanoparticles. After the addition is complete, increase the stirring speed to 800 rpm and maintain this speed for 60 minutes to achieve initial homogenization. Next, while stirring at 800 rpm, add the calculated amount of nonionic silicone surfactant at a constant rate over approximately 20 minutes. Finally, the entire mixture was transferred to a high-shear dispersing emulsifier and dispersed at 3000 rpm for 30 minutes. This step further breaks down any possible agglomerates and ensures uniform physical mixing of the three components at the molecular level, resulting in the final sizing agent emulsion. The ambient temperature was maintained at 25 ± 2°C throughout the entire preparation process. The resulting sizing agent was a milky white, homogeneous liquid with a solids content adjusted to the target value of 7.8 ± 0.2%. The pH range was controlled between 7.5 and 8.5, and it was stable at room temperature for over 90 days without visible stratification or precipitation.

[0025] The sizing agent application method is as follows: the carbon fiber bundles to be treated (e.g., 12K specification) are continuously passed through a sizing tank filled with the prepared sizing agent emulsion. The sizing tank is equipped with a thermostat to maintain the bath temperature at 30±1°C. By precisely controlling the guide roller speed and immersion depth, the carbon fiber bundles are immersed in the bath for 4.0±0.2 seconds. Immediately after leaving the sizing tank, the fiber bundles pass through a pair of precisely adjustable squeeze rollers with a pressure between the rollers set at 0.15 MPa to remove excess sizing agent and ensure a uniform and controllable sizing amount. The sized fiber bundles then enter a three-stage hot air drying oven: the first stage is 80±5°C with a dwell time of 45 seconds; the second stage is 120±5°C with a dwell time of 60 seconds; and the third stage is 160±5°C with a dwell time of 45 seconds. The total drying time is controlled to 150±5 seconds. Finally, the sizing-treated carbon fiber tow is obtained by winding, and the target sizing rate (measured as the percentage of the dry weight of the sizing agent to the dry weight of the fiber) is controlled at 1.2±0.1%.

[0026] Example 3 This embodiment provides a high-strength polyurethane composite carbon fiber sizing agent for enhancing the interfacial bonding performance between carbon fiber and resin matrix, and a preparation and application method thereof.

[0027] Three functional components are compounded in specific proportions: water-based polyurethane dispersion (component A), surface-treated nano-silica dispersion (component B) and a non-ionic silicone surfactant (component C).

[0028] First, place a commercially available aqueous polyurethane dispersion (approximately 40% solids content) in a thermostatically stirred vessel, maintain the temperature at 25±2°C, and stir at 300 rpm for basic mixing. Subsequently, while stirring continuously, slowly and evenly add a pre-prepared aqueous dispersion of nanosilica (15% solids content) treated with a silane coupling agent and with an average particle size of 30 nm. The addition rate is controlled at 5% of the total mass of component B per minute. This process continues for approximately 20 minutes to ensure good dispersion of the nanoparticles. After the addition is complete, increase the stirring speed to 800 rpm and maintain this speed for 40 minutes to achieve initial homogenization. Next, while stirring at 800 rpm, add the calculated amount of a nonionic organosilicon surfactant (100% active ingredient) at a constant rate over approximately 10 minutes. Finally, the entire mixture was transferred to a high-shear dispersing emulsifier and dispersed at 5000 rpm for 45 minutes. This step further breaks down any possible agglomerates and ensures uniform physical mixing of the three components at the molecular level, resulting in the final sizing agent emulsion. The ambient temperature was maintained at 25 ± 2°C throughout the entire preparation process. The resulting sizing agent was a milky white, homogeneous liquid with a solids content adjusted to the target value of 8.5 ± 0.2%. The pH range was controlled between 7.5 and 8.5, and it was stable for over 90 days at room temperature without visible stratification or precipitation.

[0029] The sizing agent application method is as follows: the carbon fiber bundles to be treated (e.g., 12K specification) are continuously passed through a sizing tank filled with the prepared sizing agent emulsion. The sizing tank is equipped with a thermostat to maintain the bath temperature at 30±1°C. By precisely controlling the guide roller speed and immersion depth, the carbon fiber bundles are immersed in the bath for 4.0±0.2 seconds. Immediately after leaving the sizing tank, the fiber bundles pass through a pair of precisely adjustable squeeze rollers with a pressure between the rollers set at 0.15 MPa to remove excess sizing agent and ensure a uniform and controllable sizing amount. The sized fiber bundles then enter a three-stage hot air drying oven: the first stage is 80±5°C with a dwell time of 45 seconds; the second stage is 120±5°C with a dwell time of 60 seconds; and the third stage is 160±5°C with a dwell time of 45 seconds. The total drying time is controlled to 150±5 seconds. Finally, the sizing-treated carbon fiber tow is obtained by winding, and the target sizing rate (measured as the percentage of the dry weight of the sizing agent to the dry weight of the fiber) is controlled at 1.2±0.1%.

[0030] Example 4 This embodiment provides a high-strength polyurethane composite carbon fiber sizing agent for enhancing the interfacial bonding performance between carbon fiber and resin matrix, and a preparation and application method thereof.

[0031] Three functional components are compounded in specific proportions: water-based polyurethane dispersion (component A), surface-treated nano-silica dispersion (component B) and a non-ionic silicone surfactant (component C).

[0032] First, place a commercially available aqueous polyurethane dispersion (approximately 40% solids content) in a thermostatically stirred vessel, maintain the temperature at 25±2°C, and stir at 300 rpm for basic mixing. Subsequently, while stirring continuously, slowly and evenly add a pre-prepared aqueous dispersion of nanosilica (15% solids content) treated with a silane coupling agent and with an average particle size of 30 nm. The addition rate is controlled at 5% of the total mass of component B per minute. This process continues for approximately 20 minutes to ensure good dispersion of the nanoparticles. After the addition is complete, increase the stirring speed to 800 rpm and maintain this speed for 40 minutes to achieve initial homogenization. Next, while stirring at 800 rpm, add the calculated amount of a nonionic organosilicon surfactant (100% active ingredient) at a constant rate over approximately 10 minutes. Finally, the entire mixture was transferred to a high-shear dispersing emulsifier and dispersed at 3000 rpm for 30 minutes. This step further breaks down any possible agglomerates and ensures uniform physical mixing of the three components at the molecular level, resulting in the final sizing agent emulsion. The ambient temperature was maintained at 25 ± 2°C throughout the entire preparation process. The resulting sizing agent was a milky white, homogeneous liquid with a solids content adjusted to the target value of 8.5 ± 0.2%. The pH range was controlled between 7.5 and 8.5, and it was stable for over 90 days at room temperature without visible stratification or precipitation.

[0033] The sizing agent application method is as follows: the carbon fiber bundles to be treated (e.g., 12K specification) are continuously passed through a sizing tank filled with the prepared sizing agent emulsion. The sizing tank is equipped with a thermostat to maintain the bath temperature at 30±1°C. By precisely controlling the guide roller speed and immersion depth, the carbon fiber bundles are immersed in the bath for 4.0±0.2 seconds. Immediately after leaving the sizing tank, the fiber bundles pass through a pair of precisely adjustable squeeze rollers with a pressure between the rollers set at 0.15 MPa to remove excess sizing agent and ensure a uniform and controllable sizing amount. The sized fiber bundles then enter a three-stage hot air drying oven: the first stage is at 100±5°C with a dwell time of 30 seconds; the second stage is at 140±5°C with a dwell time of 45 seconds; and the third stage is at 180±5°C with a dwell time of 30 seconds. The total drying time is controlled to 105±5 seconds. Finally, the sizing-treated carbon fiber tow is obtained by winding, and the target sizing rate (measured as the percentage of the dry weight of the sizing agent to the dry weight of the fiber) is controlled at 1.2±0.1%.

[0034] Example 5 This embodiment provides a high-strength polyurethane composite carbon fiber sizing agent for enhancing the interfacial bonding performance between carbon fiber and resin matrix, and a preparation and application method thereof.

[0035] Three functional components are compounded in specific proportions: water-based polyurethane dispersion (component A), surface-treated nano-silica dispersion (component B) and a non-ionic silicone surfactant (component C).

[0036] First, place a commercially available aqueous polyurethane dispersion (approximately 40% solids content) in a thermostatically stirred vessel, maintain the temperature at 25±2°C, and stir at 300 rpm for basic mixing. Subsequently, while stirring continuously, slowly and evenly add a pre-prepared aqueous dispersion of nanosilica (15% solids content) treated with a silane coupling agent and with an average particle size of 30 nm. The addition rate is controlled at 5% of the total mass of component B per minute. This process continues for approximately 20 minutes to ensure good dispersion of the nanoparticles. After the addition is complete, increase the stirring speed to 800 rpm and maintain this speed for 40 minutes to achieve initial homogenization. Next, while stirring at 800 rpm, add the calculated amount of a nonionic organosilicon surfactant (100% active ingredient) at a constant rate over approximately 10 minutes. Finally, the entire mixture was transferred to a high-shear dispersing emulsifier and dispersed at 3000 rpm for 30 minutes. This step further breaks down any possible agglomerates and ensures uniform physical mixing of the three components at the molecular level, resulting in the final sizing agent emulsion. The ambient temperature was maintained at 25 ± 2°C throughout the entire preparation process. The resulting sizing agent was a milky white, homogeneous liquid with a solids content adjusted to the target value of 8.5 ± 0.2%. The pH range was controlled between 7.5 and 8.5, and it was stable for over 90 days at room temperature without visible stratification or precipitation.

[0037] The sizing agent application method is as follows: the carbon fiber bundles to be treated (e.g., 12K specification) are continuously passed through a sizing tank filled with the prepared sizing agent emulsion. The sizing tank is equipped with a thermostat to maintain the bath temperature at 30±1°C. By precisely controlling the guide roller speed and immersion depth, the carbon fiber bundles are immersed in the bath for 4.0±0.2 seconds. Immediately after leaving the sizing tank, the fiber bundles pass through a pair of precisely adjustable squeeze rollers with a pressure between the rollers set at 0.25 MPa to remove excess sizing agent and ensure a uniform and controllable sizing amount. The sized fiber bundles then enter a three-stage hot air drying oven: the first stage is 80±5°C with a dwell time of 45 seconds; the second stage is 120±5°C with a dwell time of 60 seconds; and the third stage is 160±5°C with a dwell time of 45 seconds. The total drying time is controlled to 150±5 seconds. Finally, the sizing-treated carbon fiber tow is obtained by winding, and the target sizing rate (measured as the percentage of the dry weight of the sizing agent to the dry weight of the fiber) is controlled at 0.8±0.1%.

[0038] Experimental example To verify the synergistic effect and performance of this three-component composite sizing agent, the following experimental groups were set up for comparative testing: Experimental Group (ABC): Carbon fibers were treated with the complete three-component sizing agent prepared by the above method (A:B:C dry basis mass ratio = 85:10:5). Control Group A: Carbon fibers were treated with only Component A (aqueous polyurethane dispersion, adjusted to 8.5% solids). Control Group B: Carbon fibers were treated with only Component B (nanosilica dispersion, adjusted to 8.5% solids). Control Group C: Carbon fibers were treated with only Component C (organic silicone surfactant, diluted to a concentration equivalent to that of Component C in Group ABC). Control Groups AB: Carbon fibers were treated with a sizing agent consisting of Components A and B (same ratios as in Group ABC, excluding Component C). Control Group AC: Carbon fibers were treated with a sizing agent consisting of Components A and C (same ratios as in Group ABC, excluding Component B). Control Group BC: Carbon fibers were treated with a sizing agent consisting of Components B and C (same ratios as in Group ABC, excluding Component A). Blank Group: Carbon fibers from the same batch that were not sizing. All control groups maintained the same sizing process parameters (immersion time, extrusion pressure, drying temperature and time) as the experimental groups ABC, with the target sizing rate maintained at 1.2 ± 0.1%. At least five parallel samples were processed in each group for subsequent performance testing.

[0039] Performance testing mainly focuses on the fiber-resin interface performance and the characteristics of the sizing agent itself.

[0040] Interfacial shear strength (IFSS) testing was performed using the microdroplet debond test. A single carbon fiber treated with each of the above treatments was mounted on a glass slide. Bisphenol A epoxy resin (E-51) and curing agent (methyltetrahydrophthalic anhydride) were mixed at a mass ratio of 100:85 to prepare resin droplets approximately 80 μm in diameter. These droplets were attached to the fiber and cured at 120°C for 2 hours. A universal testing machine equipped with a dedicated droplet fixture was used to load the droplets at a crosshead speed of 0.5 mm / min until the droplets debonded from the fiber surface. The maximum load (F_max) was recorded, and the interfacial shear strength was calculated using the formula IFSS = F_max / (π * d_f * L_e), where d_f is the fiber diameter (approximately 7 μm) and L_e is the effective embedding length of the resin droplet. At least 30 valid data points were collected for each test.

[0041] Stability Assessment of Sizing Agent Emulsions: Place each freshly prepared sizing agent emulsion in a 25 ml stoppered graduated cylinder and incubate at 25 ± 1°C for 30 days. Record the initial height (H0) and the height of the sediment or layer interface after stabilization (Hs). Calculate the sedimentation rate (%) as [(H0 - Hs) / H0] * 100%.

[0042] Dynamic contact angle measurement: Using a contact angle meter, fix the carbon fiber monofilaments from each treatment group parallel to a glass slide. Add 5 μL of deionized water droplets to the fiber surface and record the static contact angle after 5 seconds. Measure 10 different locations for each group and take the average value.

[0043] Fiber Bundle Tensile Strength Retention: Measure the tensile strength of the carbon fiber bundles in the blank group and each treatment group according to ASTM D4018. Calculate the percentage retention of the tensile strength of the sizing fiber bundle relative to the blank group. Test at least 10 valid specimens per group.

[0044] The test results are shown in Table 1 below: Test Group Interfacial shear strength (IFSS, MPa) Sizing agent sedimentation rate (30 days, %) Contact angle (water, °) Fiber bundle tensile strength retention rate (%) Experimental group (ABC) 78.34 ± 3.21 0.82 ± 0.15 72.5 ± 2.3 98.7 ± 0.9 Control group A 52.18 ± 2.87 2.35 ± 0.28 86.2 ± 3.1 97.8 ± 1.2 Control group B 45.66 ± 3.05 15.83 ± 1.42* 91.8 ± 2.7 95.1 ± 1.5 Control group C 38.92 ± 2.54 Unstratified / turbid 68.3 ± 3.5 98.2 ± 1.0 Control group AB 63.75 ± 2.96 3.87 ± 0.41 88.7 ± 2.9 97.3 ± 1.1 Control group AC 58.41 ± 3.12 1.98 ± 0.32 74.6 ± 2.8 98.1 ± 0.8 Control group BC 42.83 ± 2.78 8.56 ± 0.95* 70.1 ± 3.2 96.5 ± 1.3 Blank group 36.25 ± 2.63 - 103.5 ± 4.2 100.0 (baseline) Note: Controls B and BC showed significant precipitation and high sedimentation rates; Control C showed no stratification but became slightly turbid after standing; all other groups were stable emulsions. Data are presented as mean ± SD.

[0045] Results Analysis and Summary: A significant synergistic effect is clearly observed in the interfacial shear strength data. The IFSS value of experimental group ABC reached 78.34 MPa, significantly higher than all single-component controls (A: 52.18 MPa, B: 45.66 MPa, C: 38.92 MPa) and the two-component control group (AB: 63.75 MPa, AC: 58.41 MPa, BC: 42.83 MPa), and significantly better than the blank control (36.25 MPa). This demonstrates that the interfacial strength enhancement achieved by physically compounding the three components alone is not simply additive (A+B+C≈136.77 MPa, far from the target value), but rather achieves a synergistic enhancement of 1+1+1>3. Specifically, the IFSS of group ABC was approximately 14.6 MPa (22.9%) higher than the best-performing two-component group AB and approximately 26.16 MPa (50.1%) higher than the best-performing single-component group A. In terms of sizing agent stability, the sedimentation rate of the ABC group was only 0.82%, demonstrating excellent storage stability, significantly superior to all control groups containing component B (B: 15.83%, AB: 3.87%, BC: 8.56%). This is attributed to the excellent wetting and dispersing effect of component C combined with the steric stabilization effect provided by component A, which effectively inhibited the sedimentation of nanoparticles B. Contact angle tests showed that the water contact angle of the ABC group was 72.5°, significantly lower than the blank group (103.5°) and the control groups containing only A or B (A: 86.2°, B: 91.8°), and close to that of the group containing C (C: 68.3°, AC: 74.6°, BC: 70.1°), indicating that component C dominated the improvement of the system's wettability, enabling the sizing agent to better spread and impregnate the carbon fiber surface. The fiber bundle tensile strength retention rates of all treatment groups were above 95%, and those of the ABC group reached 98.7%, indicating that the sizing process caused minimal damage to the carbon fiber body and met the application requirements. In summary, a high-performance carbon fiber sizing agent was successfully prepared by physically mixing three specific components: water-based polyurethane dispersion, surface-treated nano-silica, and non-ionic silicone surfactant, under optimized ratios and preparation processes. This sizing agent not only has excellent stability in itself, but more importantly, under the premise of not inducing a chemical reaction, the three components work synergistically to significantly improve the interfacial bonding strength between the carbon fiber and the epoxy resin. The effect far exceeds any single or two-component combination, fully demonstrating the physical synergistic effect of 1+1+1>3, and providing key surface treatment technology support for the preparation of high-performance carbon fiber composites.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A high-strength polyurethane composite carbon fiber sizing agent, characterized in that: The raw materials include the following components: Waterborne polyurethane dispersion, nano-silica aqueous dispersion surface treated with silane coupling agent and non-ionic silicone surfactant.

2. The high-strength polyurethane composite carbon fiber sizing agent according to claim 1, characterized in that The average particle size of the nano-silicon dioxide is 20-40 nm.

3. The sizing agent according to claim 1, characterized in that The solid content of the sizing agent is 7.5-10.0 wt %; The pH value of the sizing agent is 7.5-8.

5.

4. A method for preparing a sizing agent according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Stirring the aqueous polyurethane dispersion at 23-28°C and 200-400 rpm; (2) adding the nano-silica aqueous dispersion to the system of step (1) at a rate of 3-8% of the total mass of component B per minute; (3) Increase the stirring speed to 700-900 rpm and continue for 20-60 minutes; (4) adding a nonionic silicone surfactant; (5) High-speed shear dispersion of the mixed system at 2500-5000 rpm for 20-60 minutes.

5. The method according to claim 4, characterized in that The rotation speed of the high-speed shear dispersion is 3000-5000 rpm.

6. The method according to claim 4, characterized in that The high-speed shear dispersion time is 30 to 45 minutes.

7. A sizing method for carbon fiber, characterized in that: The method of using the sizing agent according to any one of claims 1 to 3 comprises the following steps: a) dipping the carbon fiber bundle into the sizing agent for 3 to 5 seconds; b) removing excess sizing agent through a squeeze roller; c) Dry in three stages in a hot air drying oven.

8. The method according to claim 7, characterized in that The pressure of the squeezing roller is 0.15~0.25 MPa.

9. The method according to claim 7, characterized in that The three-stage drying comprises: Stage 1: 80-100°C, residence time 30-45 seconds; Stage 2: 120-140°C, residence time 45-60 seconds; The third stage: 160~180°C, residence time 30~45 seconds.

10. The method according to claim 7, characterized in that The final sizing rate is 0.8~1.5wt%.