Preparation method and application of low-temperature plasma surface modified silica powder

Abstract

The invention relates to the technical field of preparation of low-temperature plasma surface modified silicon micro-powder, in particular to a preparation method and application of low-temperature plasma surface modified silicon micro-powder, and the preparation method comprises the following steps: S1, taking original silicon micro-powder, adding ethanol-deionized water mixed liquor, adding a silane coupling agent, tetrabutyl titanate and KH-560, performing temperature-controlled stirring, and then performing centrifugal drying to obtain silicon micro-powder; pre-treated silica powder is obtained; s2, putting the pretreated silica powder into a plasma reaction cavity, introducing argon-oxygen-ethylene mixed gas, spraying a dopamine-graphene quantum dot-chitosan composite liquid, and treating to obtain preliminarily modified silica powder; and S3, adding N, N-dimethylformamide into the preliminarily modified silica powder, adding isocyanate-terminated polyether, hydroxy acrylic resin and maleic anhydride, stirring at a controlled temperature, dropwise adding a catalyst, filtering, washing and drying to obtain the modified silica powder. The method has the advantages of high modification efficiency, low energy consumption, strong stability of the modified layer, capability of customizing the function of the silica powder, adaptation to different resin matrixes, improvement of the performance of the composite material, environment-friendly and controllable process and convenience in industrial production.

Description

Technical Field

[0001] This invention relates to the field of preparation technology of low-temperature plasma surface-modified silicon micropowder, specifically to a composite coating for battery separators, its preparation method, and its application. Background Technology

[0002] Silica powder is widely used as a filler in composite materials due to its good chemical stability, high hardness, and excellent dielectric properties, especially in resin-based composites such as epoxy resin and polyamide, where it can improve the mechanical properties and reduce costs. However, the surface of raw silica powder is inert and contains a small amount of hydroxyl groups, resulting in poor compatibility with organic resin matrices. Direct addition can easily lead to agglomeration, resulting in weak interfacial bonding within the composite material. This, in turn, reduces key properties such as tensile strength and impact strength, limiting its application range.

[0003] To address this issue, existing technologies often employ surface modification methods to improve the compatibility between silicon micropowder and resin. Common methods include coupling agent modification, organosilane coating, and polymer grafting. Coupling agent modification is currently the most widely used technique. For example, silane coupling agents such as KH-550 and KH-560 are used, where the alkoxy groups in the coupling agent molecule react with the hydroxyl groups on the surface of the silicon micropowder to introduce organic functional groups. However, this method has significant drawbacks: the grafting rate of the coupling agent on the surface of the silicon micropowder is low, typically less than 30%, and the modified layer is thin and easily detaches during resin mixing. Furthermore, the types of functional groups introduced by a single coupling agent are limited, making it difficult to simultaneously meet the multi-dimensional requirements of composite materials for mechanical properties, dielectric properties, and processing performance.

[0004] While organosilane coating modification can form a thick coating layer, it requires a long reaction time at high temperatures (120-180℃), resulting in high energy consumption and a tendency for silica powder agglomeration. Furthermore, the adhesion between the coating layer and the silica powder surface relies on physical adsorption, making it prone to peeling during subsequent processing and affecting material performance stability. Polymer grafting modification, which involves grafting polymer chains onto the silica powder surface via free radical polymerization, can significantly improve compatibility. However, the polymerization reaction easily produces homopolymers, requiring complex purification steps, and the grafting process is difficult to control, leading to uneven distribution of grafted chains and affecting the consistency of modification effects.

[0005] In recent years, low-temperature plasma modification technology has been gradually applied to the surface treatment of silicon micropowder. Its advantages lie in the ability to activate the surface of silicon micropowder at low temperatures, introducing active groups such as hydroxyl and carboxyl groups, without the need for high temperature and high pressure, and with low energy consumption. However, existing low-temperature plasma modification technologies still have shortcomings: First, the modification only stays at the surface activation stage, without combining with other modification methods to form a synergistic effect. The activated active groups are easily recombined, leading to a decrease in the modification effect. Second, the modification process lacks the introduction of targeted functional components, making it impossible to customize surface functional groups according to the needs of the target resin, thus limiting its applicability. Third, the reactivity of the active groups on the surface of silicon micropowder after plasma modification is insufficient, and the bonding force with subsequent resins still needs to be improved, making it difficult to fully exert the reinforcing effect of silicon micropowder.

[0006] Furthermore, existing modified silica powders face the problem of "limited performance" in applications: some modified silica powders can only improve the mechanical properties of composite materials, but lead to increased dielectric loss; others can improve processing fluidity, but reduce the heat distortion temperature of the material. For example, silica powder used in epoxy resin electronic packaging materials, if modified only by a single coupling agent, can improve tensile strength, but the dielectric loss tangent is likely to exceed 0.05, which cannot meet the requirements of high-frequency electronic devices; silica powder used in polyamide engineering plastics, if the modified layer is not hydrophobic enough, easily absorbs moisture from the environment, resulting in large fluctuations in the melt index of the plastic and affecting molding stability.

[0007] In summary, existing silicon micropowder surface modification technologies have technical bottlenecks in terms of modification efficiency, modified layer stability, functional diversity, and application adaptability. There is an urgent need to develop a new modification method that is low in energy consumption, high in modification efficiency, customizable in function, and can form a strong bond with the resin matrix to meet the demand of composite materials for high-performance modified silicon micropowder. Summary of the Invention

[0008] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for preparing low-temperature plasma surface-modified silicon micropowder and its application.

[0009] (II) Technical Solution A method for preparing low-temperature plasma surface-modified silicon micropowder includes the following steps: S1. Pretreatment of Silica Powder: Select raw silica powder with a particle size of 1-5 μm, a purity of not less than 99.8%, and a specific surface area of ​​5-20 m² / g. Add an ethanol-deionized water mixture to the silica powder, with a volume ratio of ethanol to deionized water of 2:1 and a solid-liquid ratio of silica powder to the mixture of 1:5-1:10. Add 0.5-2% of silane coupling agent KH-792, 0.3-1% of tetrabutyl titanate, and 0.2-0.8% of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) to the mixture. Place the mixture at 30-50℃ and stir at 300-500 rpm for 1-2 hours. During this time, tetrabutyl titanate undergoes hydrolysis to generate titanium dioxide. The reaction formula is as follows: The generated titanium dioxide further reacts with the hydroxyl groups on the surface of the silicon micropowder to form silicon-titanium bonds, as shown in the following reaction formula: After stirring, the mixture is centrifuged at 8000-10000 rpm for 10-15 minutes. The precipitate is collected and dried at 80-100℃ for 2-4 hours to obtain pretreated silica powder.

[0010] S2. Low-Temperature Plasma Synergistic Modification: Pretreated silicon micropowder is placed inside a plasma reaction chamber. An argon-oxygen-ethylene mixed gas is introduced into the chamber, with a volume ratio of 5:1:0.5-8:1:1 and a total flow rate controlled at 100-300 sccm. The vacuum level inside the reaction chamber is adjusted to 0.05-0.1 MPa, the plasma generator power is set to 100-300 W, and the temperature inside the reaction chamber is maintained at 40-60℃. The pretreated silicon micropowder undergoes plasma treatment for 15-40 minutes. Simultaneously, a dopamine-graphene quantum dot-chitosan composite solution is prepared, with a mass ratio of 3:1:0.5. The composite solution is introduced into the reaction chamber through a spray device, with a spray pressure set to 0.1-0.3 MPa and a spray rate of 0.5-2 mL / min. During the plasma treatment, the hydroxyl groups on the surface of the silicon micropowder are activated and react with the amino groups in the dopamine molecules. The reaction formula is as follows: After processing, preliminary modified silica powder is obtained.

[0011] S3. Isocyanate-acrylate grafting: N,N-dimethylformamide is added to the reaction vessel, followed by pre-modified silica powder. The solid-liquid ratio of the pre-modified silica powder to N,N-dimethylformamide is 1:8-1:12. Then, 1-3% isocyanate-terminated polyether, 0.5-1.5% hydroxyl acrylic resin, and 0.1-0.5% maleic anhydride are added to the system. The number-average molecular weight of the isocyanate-terminated polyether is 2000-5000 g / mol, and the hydroxyl value of the hydroxyl acrylic resin is 50-100 mg KOH / g. The reaction system is heated to 60-80℃ and stirred at 400-600 rpm for 2-3 hours. During stirring, 0.1-0.3% dibutyltin dilaurate is slowly added dropwise as a catalyst. The isocyanate groups in the isocyanate-terminated polyether undergo an addition reaction with the hydroxyl groups in the hydroxyl acrylic resin. The reaction formula is as follows: After the reaction is complete, the reaction system is filtered, the solid product is collected and washed with ethanol and deionized water alternately, 3-5 times with each solvent. Finally, the washed solid is placed in a vacuum dryer at 60-80℃ for 3-5 hours to obtain low-temperature plasma surface-modified silicon micropowder.

[0012] Furthermore, the process includes an activation step following the S1-1 pretreatment: the pretreated silicon powder obtained in S1 is transferred to an ultraviolet irradiation chamber, with the ultraviolet wavelength set to 254-365 nm and the irradiation intensity controlled at 10-20 mW / cm², for 30-60 minutes of ultraviolet irradiation. Ultraviolet irradiation activates the residual hydroxyl groups on the silicon powder surface and the activity of the formed silicon-oxygen-titanium bonds, enhancing the reaction efficiency between the silicon powder surface and the modifier during subsequent low-temperature plasma modification. After activation, the hydroxyl density on the silicon powder surface can be increased to 3.0-4.5 mmol / g.

[0013] Furthermore, the process includes the S2-1 pre-dispersion step of the composite solution: In preparing the dopamine-graphene quantum dot-chitosan composite solution required in S2, firstly, graphene quantum dots with a particle size of 2-8 nm are taken and added to deionized water. Then, the mixture is placed in an ultrasonic device with an ultrasonic power of 200-400 W and an ultrasonic frequency of 25-35 kHz for ultrasonic dispersion for 20-30 minutes. After ultrasonic dispersion, a predetermined amount of dopamine and chitosan are added to the system. The mixture is then placed at 25-35℃ and stirred at 300-400 rpm for 4-6 hours to ensure thorough mixing and reaction of the three components. After stirring, the mixture is filtered through a 0.22 μm pore size filter membrane to remove any graphene quantum dot agglomerates, ensuring that the final composite solution has a dispersion uniformity of no less than 98%.

[0014] Furthermore, the γ-glycidoxypropyltrimethoxysilane (KH-560) molecule added to S1 contains an epoxy group, which can undergo a ring-opening reaction with the amino group in the silane coupling agent KH-792 molecule, as shown in the following reaction formula: This reaction forms a cross-linked structure on the surface of silicon micropowder. This cross-linked structure enhances the adhesion of the pretreated silicon micropowder surface and prevents the surface modification layer from falling off during subsequent modification processes. The degree of cross-linking of this reaction was controlled at 15-25%, and the degree of cross-linking was calculated by the peak area ratio of characteristic functional groups in the infrared spectrum.

[0015] Furthermore, the mixed gas introduced in S2 contains ethylene components. Under the action of plasma, ethylene undergoes a partial polymerization reaction, forming a slightly cross-linked hydrocarbon chain structure on the surface of the silicon micropowder. This hydrocarbon chain structure can significantly improve the hydrophobicity of the silicon micropowder surface. Testing showed that the water contact angle of the original silicon micropowder was 30-40°, while after this modification step, the water contact angle of the silicon micropowder can be increased to 70-90°, effectively improving the compatibility of the silicon micropowder with the non-polar resin matrix.

[0016] Furthermore, the maleic anhydride molecule added to S3 contains an anhydride group, which can undergo an esterification reaction with the hydroxyl groups in the hydroxyl acrylic resin, as shown in the following reaction formula: This reaction introduces carboxyl functional groups into the molecular chain of hydroxyl acrylic resin. The introduction of carboxyl functional groups can enhance the interaction between modified silica powder and polar resins (such as epoxy resins, polyamides, etc.). Tests showed that compared with modified silica powder without maleic anhydride, the compatibility between modified silica powder and polar resins improved by 20-30% after the addition of maleic anhydride. Compatibility was determined by measuring the viscosity change rate of the resin system before and after the addition of silica powder.

[0017] Furthermore, when adding dibutyltin dilaurate to S3, a batch-addition method is adopted, dividing the total catalyst into 3-5 additions, with each addition rate controlled at 0.1-0.2 mL / min. This addition method avoids excessively high catalyst concentrations in local areas, thereby reducing the occurrence of side reactions between isocyanate groups and water to form urea bonds. High-performance liquid chromatography (HPLC) analysis shows that using this addition method, the content of side reaction products in the system can be controlled below 0.5%.

[0018] Furthermore, the process includes S4. Post-processing optimization step: The modified silica powder obtained in S3 is placed in a hot air circulating oven, with the oven temperature set at 120-150℃ and the hot air velocity controlled at 1-3 m / s. The modified silica powder is then kept at this temperature for 1-2 hours. This heat preservation process promotes the complete reaction between the residual isocyanate groups on the surface of the modified silica powder and trace amounts of moisture in the air or its own residual hydroxyl groups, preventing adverse reactions between the isocyanate groups and resin components during subsequent applications. After heat preservation, the oven cooling rate is controlled at 5-10℃ / min, allowing the modified silica powder to cool naturally to room temperature. Subsequently, the cooled silica powder is sieved through a 200-300 mesh sieve. After sieving, the particle size distribution of the modified silica powder should not exceed 1.2, the moisture content should not exceed 0.5%, and the bulk density should be 0.6-0.8 g / cm³.

[0019] Furthermore, the oxygen content inside the hot air circulating oven in S4 needs to be strictly controlled at 5-10%. A lower oxygen content can prevent excessive oxidation of the silicon micropowder surface under high temperature conditions, thus avoiding the formation of an additional silica layer. X-ray photoelectron spectroscopy detection shows that under this oxygen content control condition, the increase in silica on the modified silicon micropowder surface does not exceed 0.3%, ensuring that the modification effect of the silicon micropowder is not affected by oxidation.

[0020] Furthermore, regarding the application of the low-temperature plasma surface-modified silica powder prepared by the method described above, this modified silica powder can be used as a filler in epoxy resin composites, with an addition amount of 10-30%. After addition, the tensile strength of the epoxy resin composite material can be increased by 15-30%, the impact strength can be increased by 20-40%, and the dielectric loss tangent of the composite material at a frequency of 1kHz can be reduced by 0.01-0.03, making it suitable for the electronic packaging field. In addition, this modified silica powder can also be used in polyamide 6 engineering plastics, with an addition amount of 5-20%. After addition, it can reduce the fluctuation range of the melt index of polyamide 6 engineering plastics, making the fluctuation no more than 5%, while increasing the heat distortion temperature of the plastic by 5-15℃, improving the molding and processing stability of the plastic, making it suitable for the automotive parts manufacturing field.

[0021] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: In terms of modification efficiency and energy consumption, this invention combines low-temperature plasma modification with coupling agent pretreatment and polymer grafting, eliminating the need for high temperature and high pressure. The overall reaction temperature is controlled below 100°C, and the energy consumption is reduced by more than 50% compared with traditional organosilicon coating modification. At the same time, the pretreatment step provides more active sites for subsequent plasma activation through the silicon-oxygen-titanium bond formed by the hydrolysis of tetrabutyl titanate, thereby increasing the density of active groups on the surface of silicon micropowder and shortening the plasma modification time to less than 40 minutes. The modification efficiency is significantly higher than that of existing technologies.

[0022] Regarding the stability of the modified layer, this invention constructs a stable modified layer through multiple chemical bonds: in the pretreatment stage, tetrabutyl titanate forms covalent bonds with the hydroxyl groups on the surface of silicon micropowder; in the plasma modification stage, dopamine forms ether bonds with the activated hydroxyl groups; and in the subsequent grafting stage, isocyanate groups form urethane bonds with the hydroxyl groups. The synergistic effect of multiple chemical bonds greatly enhances the bonding force between the modified layer and the surface of silicon micropowder, reduces the peeling rate of the modified layer, and maintains stability during resin mixing and processing, avoiding the degradation of material properties caused by the peeling of the modified layer.

[0023] In terms of functional diversity, this invention achieves customized functionality of modified silicon micropowder by introducing different functional components in stages: the addition of dopamine-graphene quantum dot-chitosan composite liquid can introduce additional functions such as conductivity and antibacterial properties; the addition of maleic anhydride can introduce carboxyl functional groups, enhancing compatibility with polar resins; and the grafting of isocyanate-terminated polyether can improve the processing flowability of silicon micropowder. This multi-component synergistic design enables the modified silicon micropowder to simultaneously meet multiple requirements such as mechanical enhancement, dielectric property optimization, and improved processing performance according to the needs of different resin matrices, overcoming the shortcomings of existing modified silicon micropowders with limited performance.

[0024] In terms of application adaptability, the modified silica powder prepared in this invention exhibits excellent compatibility with different resin matrices: when used in epoxy resin composites, it can improve tensile strength and impact strength while reducing dielectric loss, meeting the high-frequency application requirements of electronic packaging materials; when used in polyamide engineering plastics, it can reduce melt index fluctuations, increase heat distortion temperature, and improve molding stability, making it suitable for high-precision processing scenarios such as automotive parts. Furthermore, the cross-linked structure and hydrophobic hydrocarbon chains introduced during the modification process enable the modified silica powder to maintain stable performance even in humid environments, broadening its application range.

[0025] In terms of environmental friendliness and controllability, the low-temperature plasma technology used in this invention does not require the use of toxic solvents, and the ethanol-water mixture can be recycled, reducing pollutant emissions. At the same time, the reaction parameters of each step (such as temperature, time, and concentration) can be precisely controlled, and the particle size distribution and surface functional group density of the modified silicon micropowder are highly consistent, which facilitates large-scale industrial production and provides key support for the preparation of high-performance composite materials. Attached Figure Description

[0026] Figure 1 This is a flowchart of a method for preparing low-temperature plasma surface-modified silicon micropowder proposed in this invention; Figure 2 This is a line graph showing the mass loss rate of modified silicon micropowder at different temperatures; Figure 3 This is a bar chart showing the interfacial bonding strength of modified silica powder in epoxy resin and the impact strength of the composite material; Figure 4 This is a line graph showing the effect of different addition amounts of modified silica powder on the melt index fluctuation of polyamide 6. Detailed Implementation

[0027] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: A method for preparing low-temperature plasma surface-modified silicon micropowder includes the following steps: S1. Pretreatment of Silica Powder: Select raw silica powder with a particle size of 1-5 μm, a purity of not less than 99.8%, and a specific surface area of ​​5-20 m² / g. Add an ethanol-deionized water mixture to the silica powder, with a volume ratio of ethanol to deionized water of 2:1 and a solid-liquid ratio of silica powder to the mixture of 1:5-1:10. Add 0.5-2% of silane coupling agent KH-792, 0.3-1% of tetrabutyl titanate, and 0.2-0.8% of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) to the mixture. Place the mixture at 30-50℃ and stir at 300-500 rpm for 1-2 hours. During this time, tetrabutyl titanate undergoes hydrolysis to generate titanium dioxide. The reaction formula is as follows: The generated titanium dioxide further reacts with the hydroxyl groups on the surface of the silicon micropowder to form silicon-titanium bonds, as shown in the following reaction formula: After stirring, the mixture is centrifuged at 8000-10000 rpm for 10-15 minutes. The precipitate is collected and dried at 80-100℃ for 2-4 hours to obtain pretreated silica powder.

[0028] S2. Low-Temperature Plasma Synergistic Modification: Pretreated silicon micropowder is placed inside a plasma reaction chamber. An argon-oxygen-ethylene mixed gas is introduced into the chamber, with a volume ratio of 5:1:0.5-8:1:1 and a total flow rate controlled at 100-300 sccm. The vacuum level inside the reaction chamber is adjusted to 0.05-0.1 MPa, the plasma generator power is set to 100-300 W, and the temperature inside the reaction chamber is maintained at 40-60℃. The pretreated silicon micropowder undergoes plasma treatment for 15-40 minutes. Simultaneously, a dopamine-graphene quantum dot-chitosan composite solution is prepared, with a mass ratio of 3:1:0.5. The composite solution is introduced into the reaction chamber through a spray device, with a spray pressure set to 0.1-0.3 MPa and a spray rate of 0.5-2 mL / min. During the plasma treatment, the hydroxyl groups on the surface of the silicon micropowder are activated and react with the amino groups in the dopamine molecules. The reaction formula is as follows: After processing, preliminary modified silica powder is obtained.

[0029] S3. Isocyanate-acrylate grafting: N,N-dimethylformamide is added to the reaction vessel, followed by pre-modified silica powder. The solid-liquid ratio of the pre-modified silica powder to N,N-dimethylformamide is 1:8-1:12. Then, 1-3% isocyanate-terminated polyether, 0.5-1.5% hydroxyl acrylic resin, and 0.1-0.5% maleic anhydride are added to the system. The number-average molecular weight of the isocyanate-terminated polyether is 2000-5000 g / mol, and the hydroxyl value of the hydroxyl acrylic resin is 50-100 mg KOH / g. The reaction system is heated to 60-80℃ and stirred at 400-600 rpm for 2-3 hours. During stirring, 0.1-0.3% dibutyltin dilaurate is slowly added dropwise as a catalyst. The isocyanate groups in the isocyanate-terminated polyether undergo an addition reaction with the hydroxyl groups in the hydroxyl acrylic resin. The reaction formula is as follows: After the reaction is complete, the reaction system is filtered, the solid product is collected and washed with ethanol and deionized water alternately, 3-5 times with each solvent. Finally, the washed solid is placed in a vacuum dryer at 60-80℃ for 3-5 hours to obtain low-temperature plasma surface-modified silicon micropowder.

[0030] This invention also includes an activation step after pretreatment (S1-1): the pretreated silicon powder obtained in S1 is transferred to an ultraviolet irradiation chamber, the ultraviolet wavelength is set to 254-365 nm, the irradiation intensity is controlled at 10-20 mW / cm², and the pretreated silicon powder is irradiated with ultraviolet light for 30-60 minutes. Ultraviolet irradiation can activate the residual hydroxyl groups on the surface of the silicon powder and the activity of the formed silicon-oxygen-titanium bonds, improving the reaction efficiency between the silicon powder surface and the modifier during subsequent low-temperature plasma modification. After activation, the hydroxyl group density on the surface of the silicon powder can be increased to 3.0-4.5 mmol / g.

[0031] This invention also includes step S2-1, the pre-dispersion step of the composite liquid: In preparing the dopamine-graphene quantum dot-chitosan composite liquid required in step S2, firstly, graphene quantum dots with a particle size of 2-8 nm are taken and added to deionized water. Then, the mixture is placed in an ultrasonic device, with the ultrasonic power set to 200-400 W and the ultrasonic frequency to 25-35 kHz, and ultrasonically dispersed for 20-30 minutes. After ultrasonic dispersion, a predetermined amount of dopamine and chitosan are added to the system. The mixture is then placed at 25-35°C and stirred at 300-400 rpm for 4-6 hours to ensure thorough mixing and reaction of the three components. After stirring, the mixture is filtered through a 0.22 μm pore size filter membrane to remove any graphene quantum dot agglomerates that may exist in the system, ensuring that the final composite liquid has a dispersion uniformity of not less than 98%.

[0032] In this invention, the γ-glycidoxypropyltrimethoxysilane (KH-560) molecule added in S1 contains an epoxy group, which can undergo a ring-opening reaction with the amino group in the silane coupling agent KH-792 molecule, as shown in the reaction formula. This reaction forms a cross-linked structure on the surface of silicon micropowder. This cross-linked structure enhances the adhesion of the pretreated silicon micropowder surface and prevents the surface modification layer from falling off during subsequent modification processes. The degree of cross-linking of this reaction was controlled at 15-25%, and the degree of cross-linking was calculated by the peak area ratio of characteristic functional groups in the infrared spectrum.

[0033] In this invention, the mixed gas introduced in step S2 contains ethylene. Under the action of plasma, ethylene undergoes a partial polymerization reaction, forming a slightly cross-linked hydrocarbon chain structure on the surface of the silicon micropowder. This hydrocarbon chain structure can significantly improve the hydrophobicity of the silicon micropowder surface. Testing showed that the original silicon micropowder had a water contact angle of 30-40°, while after this modification step, the water contact angle of the silicon micropowder can be increased to 70-90°, effectively improving the compatibility of the silicon micropowder with the non-polar resin matrix.

[0034] In this invention, the maleic anhydride molecule added in S3 contains an anhydride group, which can undergo an esterification reaction with the hydroxyl groups in the hydroxyl acrylic resin, as shown in the following reaction formula: This reaction introduces carboxyl functional groups into the molecular chain of hydroxyl acrylic resin. The introduction of carboxyl functional groups can enhance the interaction between modified silica powder and polar resins (such as epoxy resins, polyamides, etc.). Tests showed that compared with modified silica powder without maleic anhydride, the compatibility between modified silica powder and polar resins improved by 20-30% after the addition of maleic anhydride. Compatibility was determined by measuring the viscosity change rate of the resin system before and after the addition of silica powder.

[0035] In this invention, when adding dibutyltin dilaurate to S3, a batch-addition method is adopted, dividing the total amount of catalyst into 3-5 additions, with the dropping rate controlled at 0.1-0.2 mL / min for each addition. This addition method avoids excessively high catalyst concentrations in local areas, thereby reducing the occurrence of side reactions between isocyanate groups and water to form urea bonds. High-performance liquid chromatography (HPLC) analysis shows that using this addition method, the content of side reaction products in the system can be controlled below 0.5%.

[0036] This invention also includes step S4. Post-processing optimization: The modified silicon micropowder obtained in step S3 is placed in a hot air circulating oven, the oven temperature is set to 120-150℃, and the hot air velocity is controlled at 1-3 m / s. The modified silicon micropowder is then subjected to heat preservation treatment for 1-2 hours. The heat preservation process can promote the complete reaction between the residual isocyanate groups on the surface of the modified silicon micropowder and the trace moisture in the air or its own residual hydroxyl groups, avoiding adverse reactions between the isocyanate groups and resin components during subsequent applications. After the heat preservation is completed, the oven cooling rate is controlled at 5-10℃ / min to allow the modified silicon micropowder to cool naturally to room temperature. Subsequently, the cooled silicon micropowder is sieved through a 200-300 mesh sieve. After sieving, the particle size distribution range of the modified silicon micropowder does not exceed 1.2, the moisture content is not higher than 0.5%, and the bulk density is 0.6-0.8 g / cm³.

[0037] In this invention, the oxygen content inside the hot air circulating oven in S4 needs to be strictly controlled at 5-10%. A lower oxygen content can prevent excessive oxidation reaction on the surface of silicon micropowder under high temperature conditions, thus avoiding the formation of an additional silicon dioxide layer. X-ray photoelectron spectroscopy detection shows that under this oxygen content control condition, the increase in silicon dioxide on the surface of the modified silicon micropowder does not exceed 0.3%, ensuring that the modification effect of the silicon micropowder is not affected by oxidation.

[0038] In this invention, the low-temperature plasma surface-modified silicon micropowder is used as a filler in epoxy resin composites at an addition amount of 10-30%. After addition, the tensile strength of the epoxy resin composite can be increased by 15-30%, the impact strength by 20-40%, and the dielectric loss tangent at 1kHz can be reduced by 0.01-0.03, making it suitable for electronic packaging. Furthermore, this modified silicon micropowder can also be used in polyamide 6 engineering plastics at an addition amount of 5-20%. After addition, it can reduce the fluctuation range of the melt index of polyamide 6 engineering plastics to no more than 5%, while increasing the heat distortion temperature of the plastic by 5-15℃, improving the molding and processing stability of the plastic, making it suitable for automotive parts manufacturing.

[0039] The following three examples and one comparative example illustrate in detail the preparation method and performance of the low-temperature plasma surface-modified silicon micropowder described in this patent. The content of each component is calculated based on the mass of the silicon micropowder, and all raw materials used are of industrial grade purity. The performance testing methods are performed in accordance with GB / T31851-2015 "General Rules for Surface Modification Methods of Inorganic Powders".

[0040] Example 1 Raw material preparation and parameters: Raw silica powder: particle size 1-3μm, purity 99.8%, specific surface area 8m² / g, surface hydroxyl density 1.2mmol / g, bulk density 0.5g / cm³, no surface treatment, and the particle morphology is irregular angular.

[0041] Silane coupling agent KH-792: purity 98%, boiling point 255℃, refractive index 1.448, viscosity at 25℃ 8mPa・s, effective ingredient content not less than 97%.

[0042] Tetrabutyl titanate: purity 99%, density 0.996 g / cm³, boiling point 310℃, refractive index 1.465, moderate hydrolysis rate, solubility in water at 20℃ is less than 0.1 g / 100 mL.

[0043] γ-glycidoxypropyltrimethoxysilane (KH-560): purity 97%, epoxy value 0.45mol / 100g, boiling point 290℃, flash point 110℃, density 1.06g / cm³ at 25℃.

[0044] Dopamine: purity 98%, molecular weight 153.18 g / mol, appearance is white to pale yellow powder, solubility in Tris-HCl buffer is 10 g / L, melting point 218-220℃.

[0045] Graphene quantum dots: particle size 2-5nm, surface hydroxyl content 6%, fluorescence quantum yield 18%, aqueous dispersion concentration 1g / L, surface charge is negative, zeta potential -35mV.

[0046] Chitosan: Deacetylation degree 90%, molecular weight 50000 g / mol, viscosity of 1% aqueous solution 200 mPa·s, appearance is white powder, good solubility in dilute acid.

[0047] Isocyanate-terminated polyether: number average molecular weight 3000 g / mol, isocyanate group content 4%, viscosity at 25℃ 500 mPa・s, good storage stability, no obvious stratification.

[0048] Hydroxy acrylic resin: hydroxyl value 70mgKOH / g, glass transition temperature 30℃, solid content 50%, appearance is pale yellow transparent liquid, viscosity at 25℃ is 800mPa・s.

[0049] Maleic anhydride: purity 99%, melting point 52.8℃, boiling point 202℃, appearance is white needle-like crystals, solubility in ethanol is 20g / 100mL (20℃).

[0050] Dibutyltin dilaurate: purity 96%, density 1.066 g / cm³, refractive index 1.468, viscosity at 25℃ 300 mPa・s, appearance is a pale yellow oily liquid.

[0051] Ethanol: Analytical grade, purity 99.7%, boiling point 78.3℃, density 0.789 g / cm³, no obvious impurities.

[0052] Deionized water: conductivity 5 μS / cm, total dissolved solids content 3 mg / L, pH 7.0, no ion residue.

[0053] N,N-Dimethylformamide: Analytical grade, purity 99.5%, boiling point 153℃, density 0.948 g / cm³, moisture content less than 0.1%.

[0054] Preparation process: S1. Pretreatment of Silica Powder: Weigh 100g of raw silica powder and add 500g of ethanol-deionized water mixture, with a volume ratio of ethanol to deionized water of 2:1. After stirring evenly, add 1g of silane coupling agent KH-792, 0.5g of tetrabutyl titanate, and 0.3g of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) sequentially. Place the mixture in a 40℃ constant temperature water bath and stir at 400rpm for 1.5 hours. During this period, tetrabutyl titanate undergoes hydrolysis to generate titanium dioxide, which further reacts with the hydroxyl groups on the surface of the silica powder to form siloxane-titanium bonds. After the reaction is complete, place the mixture in a centrifuge and centrifuge at 9000rpm for 12 minutes, collecting the precipitate. Transfer the precipitate to an oven and dry at 80℃ for 3 hours to obtain pretreated silica powder. The surface hydroxyl density of the pretreated silica powder is measured to be 2.8mmol / g.

[0055] S1-1. Activation after pretreatment: The pretreated silicon powder was placed in a UV irradiation chamber, with the UV wavelength set to 300 nm and the irradiation intensity to 15 mW / cm², and the pretreated silicon powder was continuously irradiated with UV light for 45 minutes. After activation, the surface hydroxyl density of the silicon powder was measured to increase to 3.5 mmol / g, and it was ready for use.

[0056] S2-1. Pre-dispersion of the composite solution: Weigh 0.3g of dopamine and dissolve it in 100mL of Tris-HCl buffer solution with a pH of 8.2. Add 0.1g of graphene quantum dots to the buffer solution and stir at 25℃ for 5 hours. Then add 0.05g of chitosan and continue stirring for 1 hour. Place the mixture in an ultrasonic device, set the ultrasonic power to 300W and the ultrasonic frequency to 30kHz, and ultrasonically disperse for 25 minutes. After ultrasonication, filter the mixture through a 0.22μm pore size filter membrane to obtain the dopamine-graphene quantum dot-chitosan composite solution. The dispersion uniformity of the composite solution was found to be 98.5%.

[0057] S2. Low-Temperature Plasma Synergistic Modification: Activated silicon micropowder was placed inside a plasma reaction chamber, which was then closed and evacuated to a vacuum level of 0.08 MPa. An argon-oxygen-ethylene mixture was introduced into the reaction chamber at a volume ratio of 6:1:0.8, with a total gas flow rate of 200 sccm. After the gas flow stabilized for 3 minutes, the plasma generator was activated, with a power setting of 200 W and the internal temperature of the reaction chamber maintained at 50°C. Simultaneously, a spray device was activated, spraying the prepared composite solution into the reaction chamber at a spray pressure of 0.2 MPa and a spray rate of 1 mL / min for 25 minutes. During this process, dopamine molecules reacted with the activated hydroxyl groups on the surface of the silicon micropowder to form ether bonds. After treatment, the mixture was allowed to cool naturally to room temperature, yielding preliminarily modified silicon micropowder. The water contact angle of the preliminarily modified silicon micropowder was measured to be 80°.

[0058] S3. Isocyanate-acrylate grafting: 800g of N,N-dimethylformamide was added to a 500mL three-necked flask, followed by the addition of pre-modified silica powder. After stirring until homogeneous, 2g of isocyanate-terminated polyether, 1g of hydroxyl acrylic resin, and 0.3g of maleic anhydride were added sequentially. The three-necked flask was heated to 70℃ and stirred at 500rpm for 2.5 hours. During stirring, 0.2g of dibutyltin dilaurate was added dropwise in four portions, with each drop rate of 0.15mL / min. After the reaction was complete, the reaction system was filtered, and the solid product was collected. The solid product was washed alternately with ethanol and deionized water, four times with each solvent. After washing, the solid product was placed in a vacuum drying oven and vacuum dried at 60℃ for 4 hours to obtain the modified silica powder intermediate.

[0059] S4. Post-processing optimization: The modified silica powder intermediate was placed in a hot air circulating oven. The oven temperature was set to 130℃, the hot air velocity to 2m / s, and the oxygen content inside the oven was controlled at 8%. The intermediate was kept at this temperature for 1.5 hours. After the heat treatment, the oven cooling rate was controlled at 8℃ / min, allowing the modified silica powder to cool naturally to room temperature. After cooling, the silica powder was sieved through a 250-mesh sieve to obtain the final modified silica powder product. The particle size distribution of the finished product was 1.0, the moisture content was 0.3%, the bulk density was 0.7g / cm³, and the surface oxidation increment was 0.2%.

[0060] Example 2 Raw material preparation and parameters: Raw silica powder: particle size 3-5μm, purity 99.9%, specific surface area 15m² / g, surface hydroxyl density 1.5mmol / g, bulk density 0.55g / cm³, no surface treatment, and the particle morphology is irregular angular.

[0061] Silane coupling agent KH-792: purity 99%, boiling point 255℃, refractive index 1.448, viscosity at 25℃ 8mPa・s, effective ingredient content not less than 98%.

[0062] Tetrabutyl titanate: purity 99%, density 0.996 g / cm³, boiling point 310℃, refractive index 1.465, moderate hydrolysis rate, solubility in water at 20℃ is less than 0.1 g / 100 mL.

[0063] γ-glycidoxypropyltrimethoxysilane (KH-560): purity 97%, epoxy value 0.45mol / 100g, boiling point 290℃, flash point 110℃, density 1.06g / cm³ at 25℃.

[0064] Dopamine: purity 98%, molecular weight 153.18 g / mol, appearance is white to pale yellow powder, solubility in Tris-HCl buffer is 10 g / L, melting point 218-220℃.

[0065] Graphene quantum dots: particle size 2-5nm, surface hydroxyl content 6%, fluorescence quantum yield 18%, aqueous dispersion concentration 1g / L, surface charge is negative, zeta potential -35mV.

[0066] Chitosan: Deacetylation degree 90%, molecular weight 50000 g / mol, viscosity of 1% aqueous solution 200 mPa·s, appearance is white powder, good solubility in dilute acid.

[0067] Isocyanate-terminated polyether: number average molecular weight 4000 g / mol, isocyanate group content 4.5%, viscosity at 25℃ 600 mPa·s, good storage stability, and no obvious stratification.

[0068] Hydroxy acrylic resin: hydroxyl value 85mgKOH / g, glass transition temperature 35℃, solid content 50%, appearance is pale yellow transparent liquid, viscosity at 25℃ is 850mPa・s.

[0069] Maleic anhydride: purity 99%, melting point 52.8℃, boiling point 202℃, appearance is white needle-like crystals, solubility in ethanol is 20g / 100mL (20℃).

[0070] Dibutyltin dilaurate: purity 96%, density 1.066 g / cm³, refractive index 1.468, viscosity at 25℃ 300 mPa・s, appearance is a pale yellow oily liquid.

[0071] Ethanol: Analytical grade, purity 99.7%, boiling point 78.3℃, density 0.789 g / cm³, no obvious impurities.

[0072] Deionized water: conductivity 5 μS / cm, total dissolved solids content 3 mg / L, pH 7.0, no ion residue.

[0073] N,N-Dimethylformamide: Analytical grade, purity 99.5%, boiling point 153℃, density 0.948 g / cm³, moisture content less than 0.1%.

[0074] Preparation process: S1. Pretreatment of Silica Powder: Weigh 100g of raw silica powder and add 800g of an ethanol-deionized water mixture (ethanol to deionized water volume ratio 2:1). After stirring evenly, add 1.5g of silane coupling agent KH-792, 0.8g of tetrabutyl titanate, and 0.6g of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) sequentially. Place the mixture in a 45℃ constant temperature water bath and stir at 450rpm for 2 hours. During this time, tetrabutyl titanate undergoes hydrolysis to generate titanium dioxide, which further reacts with the hydroxyl groups on the silica powder surface to form siloxane-titanium bonds. After the reaction is complete, place the mixture in a centrifuge and centrifuge at 10000rpm for 15 minutes, collecting the precipitate. Transfer the precipitate to an oven and dry at 90℃ for 3.5 hours to obtain pretreated silica powder. The surface hydroxyl density of the pretreated silica powder is measured to be 3.2mmol / g.

[0075] S1-1. Activation after pretreatment: The pretreated silicon powder was placed in a UV irradiation chamber, with the UV wavelength set to 320 nm and the irradiation intensity to 18 mW / cm², and continuously irradiated for 50 minutes. After activation, the surface hydroxyl density of the silicon powder was found to have increased to 4.2 mmol / g, and it was ready for use.

[0076] S2-1. Pre-dispersion of the composite solution: Weigh 0.45g of dopamine and dissolve it in 100mL of Tris-HCl buffer solution with a pH of 8.2. Add 0.15g of graphene quantum dots to the buffer solution and stir at 30℃ for 6 hours. Then add 0.075g of chitosan and continue stirring for 1 hour. Place the mixture in an ultrasonic device, set the ultrasonic power to 350W and the ultrasonic frequency to 30kHz, and ultrasonically disperse for 30 minutes. After ultrasonication, filter the mixture through a 0.22μm pore size filter membrane to obtain the dopamine-graphene quantum dot-chitosan composite solution. The dispersion uniformity of the composite solution was found to be 99%.

[0077] S2. Low-Temperature Plasma Synergistic Modification: Activated silicon micropowder was placed inside a plasma reaction chamber, which was then closed and evacuated to a vacuum level of 0.09 MPa. An argon-oxygen-ethylene mixture was introduced into the reaction chamber at a volume ratio of 7:1:0.9, with a total gas flow rate of 250 sccm. After the gas flow stabilized for 3 minutes, the plasma generator was activated, with a power setting of 250 W and the internal temperature of the reaction chamber maintained at 55°C. Simultaneously, a spray device was activated to spray the prepared composite solution into the reaction chamber at a spray pressure of 0.25 MPa and a spray rate of 1.5 mL / min, continuing the treatment for 30 minutes. During this process, dopamine molecules reacted with the activated hydroxyl groups on the surface of the silicon micropowder to form ether bonds. After treatment, the mixture was allowed to cool naturally to room temperature, yielding preliminarily modified silicon micropowder. The water contact angle of the preliminarily modified silicon micropowder was measured to be 85°.

[0078] S3. Isocyanate-acrylate grafting: 900 g of N,N-dimethylformamide was added to a 500 mL three-necked flask, followed by the addition of pre-modified silica powder. After stirring until homogeneous, 2.5 g of isocyanate-terminated polyether, 1.2 g of hydroxyl acrylic resin, and 0.4 g of maleic anhydride were added sequentially. The three-necked flask was heated to 75 °C and stirred at 550 rpm for 3 hours. During stirring, 0.25 g of dibutyltin dilaurate was added dropwise in 5 portions, with each drop rate of 0.15 mL / min. After the reaction was complete, the reaction system was filtered, and the solid product was collected. The solid product was washed alternately with ethanol and deionized water, 4 times with each solvent. After washing, the solid product was placed in a vacuum drying oven and vacuum dried at 70 °C for 4.5 hours to obtain the modified silica powder intermediate.

[0079] S4. Post-processing optimization: The modified silica powder intermediate was placed in a hot air circulating oven, with the oven temperature set at 140℃, hot air velocity at 2.5m / s, and the oxygen content inside the oven controlled at 7%. The intermediate was kept at this temperature for 2 hours. After the heat treatment, the oven cooling rate was controlled at 9℃ / min, allowing the modified silica powder to cool naturally to room temperature. After cooling, the silica powder was sieved through a 300-mesh sieve to obtain the final modified silica powder product. The particle size distribution of the finished product was 1.1, the moisture content was 0.25%, the bulk density was 0.75g / cm³, and the surface oxidation increment was 0.15%.

[0080] Example 3 Raw material preparation and parameters: Raw silica powder: particle size 2-4μm, purity 99.85%, specific surface area 12m² / g, surface hydroxyl density 1.3mmol / g, bulk density 0.52g / cm³, no surface treatment, and the particle morphology is irregular angular.

[0081] Silane coupling agent KH-792: purity 98.5%, boiling point 255℃, refractive index 1.448, viscosity at 25℃ 8mPa・s, effective ingredient content not less than 97.5%.

[0082] Tetrabutyl titanate: purity 99%, density 0.996 g / cm³, boiling point 310℃, refractive index 1.465, moderate hydrolysis rate, solubility in water at 20℃ is less than 0.1 g / 100 mL.

[0083] γ-glycidoxypropyltrimethoxysilane (KH-560): purity 97%, epoxy value 0.45mol / 100g, boiling point 290℃, flash point 110℃, density 1.06g / cm³ at 25℃.

[0084] Dopamine: purity 98%, molecular weight 153.18 g / mol, appearance is white to pale yellow powder, solubility in Tris-HCl buffer is 10 g / L, melting point 218-220℃.

[0085] Graphene quantum dots: particle size 2-5nm, surface hydroxyl content 6%, fluorescence quantum yield 18%, aqueous dispersion concentration 1g / L, surface charge is negative, zeta potential -35mV.

[0086] Chitosan: Deacetylation degree 90%, molecular weight 50000 g / mol, viscosity of 1% aqueous solution 200 mPa·s, appearance is white powder, good solubility in dilute acid.

[0087] Isocyanate-terminated polyether: number average molecular weight 3500 g / mol, isocyanate group content 4.2%, viscosity at 25℃ 550 mPa・s, good storage stability, no obvious stratification.

[0088] Hydroxy acrylic resin: hydroxyl value 78 mg KOH / g, glass transition temperature 32℃, solid content 50%, appearance is pale yellow transparent liquid, viscosity at 25℃ is 820 mPa・s.

[0089] Maleic anhydride: purity 99%, melting point 52.8℃, boiling point 202℃, appearance is white needle-like crystals, solubility in ethanol is 20g / 100mL (20℃).

[0090] Dibutyltin dilaurate: purity 96%, density 1.0 Continue writing to complete It has a viscosity of 66 g / cm³, a refractive index of 1.468, a viscosity of 300 mPa·s at 25℃, and an appearance of a pale yellow oily liquid.

[0091] Ethanol: Analytical grade, purity 99.7%, boiling point 78.3℃, density 0.789 g / cm³, no obvious impurities.

[0092] Deionized water: conductivity 5 μS / cm, total dissolved solids content 3 mg / L, pH 7.0, no ion residue.

[0093] N,N-Dimethylformamide: Analytical grade, purity 99.5%, boiling point 153℃, density 0.948 g / cm³, moisture content less than 0.1%.

[0094] Preparation process: S1. Pretreatment of silica powder: Weigh 100g of raw silica powder and add 650g of ethanol-deionized water mixture, with a volume ratio of ethanol to deionized water of 2:1. After stirring evenly, add 1.2g of silane coupling agent KH-792, 0.6g of tetrabutyl titanate, and 0.4g of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) sequentially. Place the mixture in a 42℃ constant temperature water bath and stir at 420rpm for 1.8 hours. During this period, tetrabutyl titanate undergoes hydrolysis to generate titanium dioxide, which further reacts with the hydroxyl groups on the surface of the silica powder to form siloxane-titanium bonds. After the reaction is complete, place the mixture in a centrifuge and centrifuge at 9500rpm for 13 minutes, collecting the precipitate. Transfer the precipitate to an oven and dry at 85℃ for 3.2 hours to obtain pretreated silica powder. The surface hydroxyl density of the pretreated silica powder is measured to be 3.0mmol / g.

[0095] S1-1. Activation after pretreatment: The pretreated silicon powder was placed in a UV irradiation chamber, with the UV wavelength set to 310 nm and the irradiation intensity to 16 mW / cm², and subjected to continuous UV irradiation for 48 minutes. After activation, the surface hydroxyl density of the silicon powder was found to have increased to 3.8 mmol / g, and it was ready for use.

[0096] S2-1. Pre-dispersion of the composite solution: Weigh 0.38 g of dopamine and dissolve it in 100 mL of Tris-HCl buffer solution with a pH of 8.2. Add 0.13 g of graphene quantum dots to the buffer solution and stir at 28 °C for 5.5 hours. Then add 0.06 g of chitosan and continue stirring for 1 hour. Place the mixture in an ultrasonic device, set the ultrasonic power to 320 W and the ultrasonic frequency to 30 kHz, and ultrasonically disperse for 28 minutes. After ultrasonication, filter the mixture through a 0.22 μm pore size filter membrane to obtain the dopamine-graphene quantum dot-chitosan composite solution. The dispersion uniformity of the composite solution was found to be 98.8%.

[0097] S2. Low-Temperature Plasma Synergistic Modification: Activated silicon micropowder was placed inside a plasma reaction chamber, which was then closed and evacuated to a vacuum level of 0.085 MPa. An argon-oxygen-ethylene mixture was introduced into the reaction chamber at a volume ratio of 6.5:1:0.85, with a total gas flow rate of 220 sccm. After the gas flow stabilized for 3 minutes, the plasma generator was activated, with a power setting of 220 W and the internal temperature of the reaction chamber controlled at 52°C. Simultaneously, a spray device was activated, spraying the prepared composite solution into the reaction chamber at a spray pressure of 0.22 MPa and a spray rate of 1.2 mL / min for 28 minutes. During this process, dopamine molecules reacted with the activated hydroxyl groups on the surface of the silicon micropowder to form ether bonds. After treatment, the mixture was naturally cooled to room temperature to obtain preliminarily modified silicon micropowder. The water contact angle of the preliminarily modified silicon micropowder was measured to be 82°.

[0098] S3. Isocyanate-acrylate grafting: 850 g of N,N-dimethylformamide was added to a 500 mL three-necked flask, followed by the addition of pre-modified silica powder. After stirring until homogeneous, 2.2 g of isocyanate-terminated polyether, 1.1 g of hydroxyl acrylic resin, and 0.35 g of maleic anhydride were added sequentially. The three-necked flask was heated to 72 °C and stirred at 520 rpm for 2.8 hours. During stirring, 0.22 g of dibutyltin dilaurate was added dropwise in four portions, with each drop rate of 0.15 mL / min. After the reaction was complete, the reaction system was filtered, and the solid product was collected. The solid product was washed alternately with ethanol and deionized water, four times with each solvent. After washing, the solid product was placed in a vacuum drying oven and dried under vacuum at 65 °C for 4.2 hours to obtain the modified silica powder intermediate.

[0099] S4. Post-processing optimization: The modified silica powder intermediate was placed in a hot air circulating oven, with the oven temperature set at 135℃, hot air velocity at 2.2 m / s, and the oxygen content inside the oven controlled at 7.5%. The intermediate was kept at this temperature for 1.8 hours. After the heat treatment, the oven cooling rate was controlled at 8.5℃ / min, allowing the modified silica powder to cool naturally to room temperature. After cooling, the silica powder was sieved through a 280-mesh sieve to obtain the final modified silica powder product. The particle size distribution of the finished product was measured to be 1.05, the moisture content 0.28%, the bulk density 0.72 g / cm³, and the surface oxidation increment 0.18%.

[0100] Comparative Example Raw material preparation and parameters: Raw silica powder: Same as in Example 1, with a particle size of 1-3 μm, a purity of 99.8%, a specific surface area of ​​8 m² / g, a surface hydroxyl density of 1.2 mmol / g, and a bulk density of 0.5 g / cm³.

[0101] γ-glycidyl etheroxypropyltrimethoxysilane (KH-560): Same as in Example 1, purity 97%, epoxy value 0.45 mol / 100g.

[0102] Ethanol and deionized water: Same parameters as in Example 1.

[0103] Preparation process: 100g of raw silica powder was weighed and added to 500g of an ethanol-deionized water mixture, with a volume ratio of ethanol to deionized water of 2:1. After stirring evenly, 1g of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) was added. The mixture was placed in a 40℃ constant temperature water bath and stirred at 400rpm for 1.5 hours. After the reaction was complete, the mixture was centrifuged at 9000rpm for 12 minutes, and the precipitate was collected. The precipitate was transferred to an oven and dried at 80℃ for 3 hours to obtain the comparative modified silica powder. No UV activation, plasma modification, polymer grafting, or post-treatment steps were performed. The surface hydroxyl density was 1.8mmol / g, the water contact angle was 45°, the particle size distribution span was 1.5, the water content was 0.8%, and the modified layer peeling rate was 5.2%.

[0104] Performance test results Table 1: Comparison of basic properties of modified silica powder

[0105] This table focuses on the core fundamental characteristics of modified silicon micropowder. The surface hydroxyl density (3.5-4.2 mmol / g) of Examples 1-3 is significantly higher than that of the comparative example (1.8 mmol / g), the water contact angle (80-85°) is much larger than that of the comparative example (45°), and the particle size distribution range (1.0-1.1) is narrower, the water content (0.25-0.3%) is lower, and the modified layer peeling rate (0.15-0.2%) is extremely small. This fully demonstrates that the multi-step modification process of this patent can effectively improve the surface activity, hydrophobicity and dispersion stability of silicon micropowder, while the modification effect of the single coupling agent in the comparative example is limited and cannot meet the high performance requirements.

[0106] Table 2: Performance of modified silica powder in epoxy resin (addition amount 20%)

[0107] This table demonstrates the reinforcing effect of modified silica powder on epoxy resin composites. Examples 1-3 show that the tensile strength (85-92MPa), impact strength (28-32kJ / m²), and interfacial bonding strength (12-14MPa) of the composites are significantly higher than those of the comparative examples, and the dielectric loss tangent (0.022-0.025) is much lower than that of the comparative examples (0.065). This proves that the modified silica powder of this patent can strengthen the interfacial bonding with epoxy resin, improve mechanical properties while optimizing dielectric properties, and adapt to high-requirement scenarios such as electronic packaging.

[0108] Table 3: Performance of modified silica powder in polyamide 6 (addition amount 15%)

[0109] This table demonstrates the effect of modified silica powder on the processing and properties of polyamide 6. Examples 1-3 show that the melt index fluctuation of polyamide 6 (2.8-3.2%) is much smaller than that of the comparative example (8.5%), the heat distortion temperature (175-182℃) and flexural strength (95-102MPa) are significantly improved, and the water absorption rate (1.0-1.2%) is greatly reduced. This indicates that the modified silica powder of this patent can improve the processing stability, heat resistance and mechanical properties of polyamide 6, reduce the impact of environmental moisture, and is suitable for applications such as automotive parts.

[0110] Table 4: Test results of temperature stability and solvent resistance of modified silica powder

[0111] This table verifies the environmental adaptability of the modified silicon micropowder. The mass loss rate (0.25-0.3%), xylene immersion swelling rate (0.7-0.8%), hydrochloric acid immersion corrosion rate (0.08-0.1%), and particle size change rate (0.4-0.5%) after freezing at -40℃ in Examples 1-3 are all much lower than those in the comparative examples. This indicates that the modified layer of this patent has excellent resistance to high and low temperatures, solvents, and corrosion, and can maintain stable performance in complex processing and usage environments, while the modified layer in the comparative examples is easily affected by environmental factors and fails.

[0112] Table 5: Results of the processing compatibility test of modified silica powder in composite materials

[0113] The table highlights the industrial application value of modified silica powder. Examples 1-3 show that the increase in viscosity of epoxy resin mixture (7-8%) and the fluctuation of polyamide 6 extrusion melt pressure (0.25-0.3MPa) are much smaller than those of the comparative example. They also shorten the molding cycle of composite materials (12-15%) and improve the surface gloss (85-88°). This indicates that the modified silica powder of this patent has good compatibility with the resin matrix, which can optimize the processing, improve production efficiency and product appearance. In contrast, the comparative example increases the processing difficulty and reduces production efficiency.

[0114] Figure 2 The results clearly show that the modified silicon micropowders in Examples 1-3 have a mass loss rate of less than 0.5% at temperatures below 250°C, and the loss is slow as the temperature increases. In contrast, the mass loss rate of the comparative example reached 1.5% at 200°C. This demonstrates that the modified silicon micropowder of this patent has superior temperature stability and can meet the high-temperature processing requirements of composite materials.

[0115] Figure 3 The results visually demonstrate that the interfacial bonding strength between the modified silica powder and epoxy resin in Examples 1-3, as well as the impact strength of the composite material, are all significantly higher than those in the comparative examples and the industry average. This indicates that the strong bonding interface constructed through multi-step modification in this patent can effectively transfer stress and significantly improve the mechanical properties of the composite material.

[0116] Figure 4 The results clearly show that when the modified silica powder in Examples 1-3 is added at a concentration of ≤20%, the melt index fluctuation of polyamide 6 is less than 5%, which meets the requirements of industrial production. In contrast, the comparative example exceeds the allowable upper limit when the added concentration is 15%. This proves that the modified silica powder of this patent can improve the processing stability of polyamide 6, adapt to a wider range of addition amounts, and meet the preparation of composite materials with different performance requirements.

[0117] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing low-temperature plasma surface-modified silicon micropowder, characterized in that, Comprising the following steps: S1. Silicon powder pretreatment: Select the original silicon powder, add ethanol-deionized water mixed solution to the silicon powder, the volume ratio of ethanol to deionized water in the mixed solution is 2:1, and the solid-liquid ratio of silicon powder to mixed solution is 1:5-1:10; add 0.5-2% silane coupling agent, 0.3-1% tetrabutyl titanate and 0.2-0.8% γ-glycidyl ether propyl trimethoxysilane; the mixed material is placed in an environment of 30-50°C and stirred at a rate of 300-500 rpm for 1-2 hours, during which the tetrabutyl titanate hydrolyzes to generate titanium dioxide, after stirring, the mixed system is centrifuged for 10-15 minutes, the precipitate is collected and dried at 80-100°C for 2-4 hours to obtain pretreated silicon powder; S2. Low temperature plasma synergistic modification: Put the pretreated silicon powder into the interior of the plasma reaction chamber, introduce argon-oxygen-ethylene mixed gas into the reaction chamber, the volume ratio of the three gases is 5:1:0.5-8:1:1, and the total flow rate of the gas is controlled at 100-300 sccm; adjust the vacuum degree in the interior of the reaction chamber to 0.05-0.1 MPa, set the power of the plasma generator to 100-300 W, control the temperature in the interior of the reaction chamber to maintain at 40-60°C, and perform plasma treatment on the pretreated silicon powder for 15-40 minutes; at the same time, prepare dopamine-graphene quantum dot-chitosan composite liquid, the mass ratio of the three components is 3:1:0.5, introduce the composite liquid into the reaction chamber through a spraying device, set the spraying pressure to 0.1-0.3 MPa, and the spraying rate is 0.5-2 mL / min; obtain the preliminary modified silicon powder after treatment; S3. Isocyanate-acrylate grafting: Add N,N-dimethylformamide to the reaction container, then add the preliminary modified silicon powder, the solid-liquid ratio of the preliminary modified silicon powder to N,N-dimethylformamide is 1:8-1:12; then add 1-3% isocyanate-terminated polyether, 0.5-1.5% hydroxy acrylate resin and 0.1-0.5% maleic anhydride to the system, wherein the number average molecular weight of the isocyanate-terminated polyether is 2000-5000 g / mol, heat the reaction system to 60-80°C, and stir at a rate of 400-600 rpm for 2-3 hours, slowly add 0.1-0.3% dibutyltin dilaurate as a catalyst during the stirring process; after the reaction is completed, filter the reaction system, collect the solid product and wash it with ethanol and deionized water alternately, each solvent is washed for 3-5 times, and finally the washed solid is placed in a 60-80°C environment for vacuum drying for 3-5 hours to obtain the low temperature plasma surface modified silicon powder.

2. The method for low temperature plasma surface modification of silica micropowder according to claim 1, characterized in that, It also includes a pretreatment activation step S1-1: transfer the pretreated silicon powder obtained in S1 to a ultraviolet irradiation box, set the ultraviolet wavelength to 254-365 nm, control the irradiation intensity to 10-20 mW / cm², and irradiate the pretreated silicon powder with ultraviolet light for 30-60 minutes.

3. The method for low temperature plasma surface modification of silica micropowder according to claim 1, characterized in that, Also including S2-1. Composite liquid pre-dispersion step: in the preparation of dopamine-graphene quantum dots-chitosan composite liquid required in S2, first take graphene quantum dots, the particle size is 2-8 nm, add graphene quantum dots into deionized water, then put the mixed system into ultrasonic equipment, set the ultrasonic power to 200-400 W, the ultrasonic frequency is 25-35 kHz, ultrasonic dispersion for 20-30 minutes; after ultrasonic dispersion is completed, add a preset amount of dopamine and chitosan to the system, place the mixed system in an environment of 25-35°C, and stir at a speed of 300-400 rpm for 4-6 hours to allow the three components to mix and react fully. After stirring is completed, filter the mixed liquid through a filter membrane with a pore size of 0.22 μm.

4. The method for low temperature plasma surface modification of silica micropowder according to claim 1, characterized in that, The γ-glycidyloxypropyltrimethoxysilane molecule added in S1 contains an epoxy group, which can undergo ring-opening reaction with the amino group in the silane coupling agent molecule, and the reaction formula is: A cross-linking structure is formed on the surface of the silicon micropowder through the reaction.

5. The method of claim 1, wherein the low temperature plasma surface modification of the silica micropowder is performed at a temperature of 100°C or less. The mixed gas introduced in S2 contains an ethylene component, which will undergo partial polymerization under the action of plasma to form a lightly cross-linked carbon-hydrogen chain structure on the surface of the silicon powder.

6. The method of claim 1, wherein the low temperature plasma surface modification of the silica micropowder is performed at a temperature of 100°C or less. The maleic anhydride molecules added in S3 contain anhydride groups which can esterify with the hydroxyl groups in the hydroxyl acrylic resin, the reaction formula is , and carboxyl functional groups are introduced on the molecular chain of the hydroxyl acrylic resin through the reaction.

7. The method of claim 1, wherein the low temperature plasma surface modification of the silica micropowder is performed at a temperature of 100°C or less. In S3, when adding dibutyltin dilaurate, the total amount of catalyst is added in batches, and the addition rate of each batch is controlled at 0.1-0.2 mL / min.

8. The method of claim 1, wherein the low temperature plasma surface modification of the silica micropowder is performed at a pressure of 0.1 to 10 Torr. Also including S4 post-treatment optimization step: place the modified silicon powder obtained in S3 into a hot air circulating oven, set the oven temperature to 120-150°C, control the hot air speed to 1-3 m / s, and perform 1-2 hours of heat preservation treatment on the modified silicon powder. After heat preservation is completed, control the oven cooling rate to 5-10°C / min to allow the modified silicon powder to cool naturally to room temperature. Then, sieve the cooled silicon powder through a 200-300 mesh sieve. After sieving, the particle size distribution span of the modified silicon powder is not more than 1.2, the water content is not higher than 0.5%, and the bulk density is 0.6-0.8 g / cm³.

9. The method of claim 8, wherein the low temperature plasma surface modification of the silica micropowder is performed at a pressure of 0.1 to 10 Torr. The oxygen content in the hot air circulating oven in S4 needs to be controlled at 5-10%. According to X-ray photoelectron spectroscopy detection, after using this oxygen content control condition, the increase of silicon dioxide on the surface of the modified silicon powder is not more than 0.3%.

10. Use of the low temperature plasma surface modified silica micropowder prepared according to the method of claim 1, characterized in that, The modified silicon powder can be used as a filler for epoxy resin composites, with an addition amount of 10-30%. After addition, the tensile strength of the epoxy resin composite can be increased by 15-30%, the impact strength can be increased by 20-40%, and the dielectric loss tangent at a frequency of 1 kHz can be reduced by 0.01-0.03, which is suitable for electronic packaging field. In addition, the modified silicon powder can also be used for polyamide 6 engineering plastics, with an addition amount of 5-20%. After addition, the fluctuation amplitude of the melt index of the polyamide 6 engineering plastic can be reduced to not more than 5%, and the heat distortion temperature of the plastic can be increased by 5-15°C, which is suitable for automobile parts manufacturing field.

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