Reactive core-shell nano-toughening agent for epoxy resin and preparation method and application thereof

Abstract

The application provides a preparation and application of a reactive core-shell nano-toughening agent for epoxy resin. The reactive core-shell nano-toughening agent has a three-layer core-shell structure, the inner core is introduced by rubber (nitrile-butadiene rubber, styrene-butadiene rubber, polybutadiene) emulsion containing butadiene segments, the outer shell is a crosslinked copolymer obtained by copolymerization of a vinyl monomer, a reactive monomer and a crosslinking agent, and an interface transition layer with controllable thickness exists between the core-shell interface. The provided reactive core-shell nano-toughening agent forms a uniform segment physical entanglement transition layer through a pre-dispersion process, the thickness of the transition layer is controlled by the polarity of the monomer and the pre-dispersion time, the core-shell interface is combined through intermolecular interaction, the stress transmission efficiency of the interface is enhanced, and the toughening effect on the epoxy resin is improved. When the provided reactive core-shell nano-toughening agent is applied to the toughening of the epoxy resin, the reactive functional groups provided by the reactive monomer in the shell structure can react with the epoxy groups or curing agents in the epoxy resin matrix to form a strong covalent bond interface, thereby improving the stability and compatibility of the toughening agent in the epoxy resin matrix. By improving the interaction between the interface of the core-shell toughening agent itself and the interface of the epoxy matrix, the technical problems of poor compatibility of the existing core-shell toughening agent with the epoxy resin, low toughening efficiency and deterioration of the mechanical properties of the matrix after toughening can be effectively solved, and the application range of the epoxy resin in the high-end engineering field can be expanded.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, specifically to a reactive core-shell nano-toughening agent for epoxy resin, its preparation method and application, and is particularly suitable for toughening modification of epoxy resin. Background Technology

[0002] Epoxy resin, as a high-performance polymer material, possesses excellent mechanical strength, adhesion, chemical stability, electrical insulation, and weather resistance, and has been widely used in aerospace, electronics, civil engineering, composite materials, and many other fields. However, after curing, epoxy resin forms a highly cross-linked three-dimensional network structure with rigid molecular chains and weak mobility, resulting in significant inherent brittleness, poor fracture toughness, and poor impact resistance. It is prone to cracking and failure when subjected to external impacts, temperature fluctuations, or complex stresses, severely limiting its widespread application in high-end engineering fields such as aerospace structural components and precision electronic packaging, where material toughness is crucial.

[0003] To improve the toughness of epoxy resins, liquid rubber is commonly used as a toughening agent in existing technologies. Commonly used liquid rubbers include carboxyl-terminated nitrile butadiene rubber, amino-terminated nitrile butadiene rubber, and hydroxyl-terminated polybutadiene rubber. However, these liquid rubber toughening agents have low molecular weights and extremely poor mechanical properties. Although they can provide a toughening effect after addition, they significantly deteriorate the key mechanical properties of epoxy resins, such as strength and modulus. It is difficult to achieve the technical goal of balancing rigidity and toughness, and it is impossible to take into account both the toughening effect and the inherent properties of the matrix.

[0004] Core-shell structured rubber toughening agents, with their unique "soft core and hard shell" structural advantages, have become a research hotspot in the field of epoxy resin toughening modification in recent years. The soft core, composed of rubber elastomers, can undergo elastic deformation when subjected to external impact, effectively absorbing impact energy and inhibiting the initiation and propagation of streaks. The outer shell, composed of rigid polymers, can form a good interfacial bond with the epoxy resin matrix, preventing the toughening agent from agglomerating in the matrix and effectively maintaining the original strength and rigidity of the epoxy resin matrix, thus achieving a synergistic improvement in both toughness and rigidity.

[0005] Currently reported conventional core-shell rubber toughening agents mostly use elastomer materials such as polybutadiene rubber, polyacrylate rubber, and silicone rubber as the core, and polymethyl methacrylate, polystyrene, etc. as the shell. These core-shell toughening agents are generally synthesized using multi-step polymerization methods. However, the core-shell interface lacks an effective interfacial transition layer, resulting in insufficient bonding strength. Under stress, the core-shell interface is prone to debonding, making it difficult to efficiently transfer loads to the elastic core over a long period. This weakens the energy dissipation mechanism of "cavitation-shear bands" and may even trigger early crack propagation, reducing material toughness and long-term reliability. Furthermore, a loose core-shell interface can lead to particle aggregation, which in turn affects the material modulus, making it impossible to achieve the design goal of a rigidity-toughness balance.

[0006] Therefore, developing a reactive core-shell nano-toughening agent with strong core-shell interfacial forces, good compatibility with epoxy resin, and high toughening efficiency, while providing a simple, controllable, and environmentally friendly preparation method, is of great engineering significance and application value for improving the comprehensive mechanical properties of epoxy resin and expanding its application range. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to overcome the deficiencies in current epoxy resin toughening technologies, such as poor compatibility between the toughening agent and the matrix, uneven dispersion, low toughening efficiency, and deterioration of the matrix's mechanical properties after toughening. The invention provides a reactive core-shell nano-toughening agent for epoxy resins. By rationally designing the core-shell structure composition and process parameters, it solves the technical problems of weak interfacial strength and low stress transfer efficiency in core-shell toughening agents, achieving a high-efficiency improvement in epoxy resin toughness while simultaneously maintaining the strength and rigidity of the matrix.

[0008] Another objective of this invention is to provide a method for preparing a reactive core-shell nano-toughening agent for epoxy resin that is simple in process, highly controllable, and has a high product yield.

[0009] Another objective of this invention is to provide the application of the above-mentioned reactive core-shell nano-toughening agent for epoxy resin in the modification of epoxy resin, so as to improve the toughness of epoxy resin without losing modulus and stiffness.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A reactive core-shell nano-toughening agent for epoxy resin is disclosed. The toughening agent has a three-layer core-shell structure, with a rubber core and a reactive crosslinked copolymer outer shell. A physically entangled transition layer of controllable thickness is present at the core-shell interface. The rubber is introduced from a rubber emulsion. The reactive crosslinked copolymer is formed by emulsion copolymerization of vinyl monomers, reactive monomers, and a crosslinking agent. The thickness of the interfacial transition layer is controlled by the polarity of the monomers and rubber, and the pre-dispersion time. The particle size of the core-shell nano-toughening agent is 80–300 nm, which ensures uniform dispersion of the toughening agent in the epoxy resin matrix, maximizing its toughening effect.

[0012] Preferably, by weight percentage, the raw material composition of the shell is: 50-90% vinyl monomer, 5-40% reactive monomer, and 0.5-25% crosslinking agent; the vinyl monomer is at least one of styrene, α-methylstyrene, methyl methacrylate, acrylonitrile, and methacrylonitrile, used to improve the rigidity of the shell and its compatibility with the epoxy resin matrix; the reactive monomer is at least one of methacrylic acid, glycidyl methacrylate, and N-isopropylacrylamide, which can provide active functional groups and enhance the interfacial bonding force between the shell and the epoxy resin matrix; the crosslinking agent is at least one of divinylbenzene, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, propylene glycol dimethacrylate, trimethylolpropane triacrylate, triallyl isocyanurate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate, used to improve the crosslinking density and structural stability of the shell and prevent the shell from deforming during the epoxy resin curing process.

[0013] Preferably, the rubber core is one or a blend of nitrile rubber, styrene-butadiene rubber, and polybutadiene rubber containing butadiene segments, with a glass transition temperature ≤ -30℃. This butadiene segment structure can balance the elasticity of the rubber core and its compatibility with the shell. The glass transition temperature can ensure that the rubber core maintains good elasticity in both room temperature and low temperature environments, effectively absorbing impact energy. In the core-shell structure, the weight ratio of the core to the shell is 1:(0.8~1.6). This ratio can achieve synergistic performance of the soft core and the hard shell, ensuring both toughening effect and maintaining the rigidity of the matrix.

[0014] This invention also discloses a method for preparing the above-mentioned reactive core-shell nano-toughening agent for epoxy resin, which adopts a seed emulsion polymerization method. This method does not require the addition of additional emulsifiers, and the process is controllable and environmentally friendly. The specific steps are as follows:

[0015] (1) Seed emulsion pretreatment: High solid content rubber latex is diluted with deionized water and the solid content is adjusted to 5-25%. The diluted seed emulsion is added to a reaction vessel equipped with a stirring device, a temperature measuring device and a vacuum device. The vacuum is drawn to a vacuum degree ≤-0.08MPa and deoxygenated for 15-30 minutes. Inert gas is introduced into the reaction vessel to obtain a uniformly dispersed seed emulsion without bubbles. No additional emulsifier is added throughout the process.

[0016] (2) Pre-dispersion treatment: Mix vinyl monomer, reactive monomer, crosslinking agent and oil-soluble oxidant evenly to obtain a mixed monomer system. Slowly add the mixed monomer system to the seed emulsion in step (1). Stir at a stirring speed of 40 to 250 rpm for 0.5 to 16 hours in a temperature range of 10 to 50°C. Control the thickness of the physical entanglement transition layer at the core-shell interface by adjusting the pre-dispersion time.

[0017] (3) Seed emulsion polymerization: Water-soluble reducing agent is slowly added dropwise to the reactor over a period of 10 to 40 minutes. After the addition is complete, the stirring speed is adjusted to 50 to 350 rpm and the reaction is carried out at a constant temperature for 2 to 5 hours under a temperature of 10 to 50°C. The reaction is then stopped.

[0018] (4) Post-processing: The reaction product is cooled to below room temperature, degassed to remove unreacted monomers, and then spray-dried to obtain reactive core-shell nano toughening agent powder.

[0019] Preferably, the inert gas in step (1) is nitrogen; the oil-soluble oxidant in step (2) is cumene hydroperoxide, and its addition amount is 0.5-4.0% of the total mass of the mixed monomers, which can initiate the polymerization reaction under low temperature conditions and avoid latex particle agglomeration caused by high temperature; the water-soluble reducing agent in step (3) is ferrous sulfate, and its addition amount is 10-50% of the mass of the oxidant, which forms an oxidation-reduction initiation system with cumene hydroperoxide, reducing the polymerization reaction temperature and increasing the reaction rate and monomer conversion rate; the inlet air temperature of the spray drying in step (4) is 85-110℃ and the outlet air temperature is 40-60℃, ensuring that the dried product is a uniform powder without agglomeration.

[0020] This invention further discloses the application of the above-mentioned reactive core-shell nano-toughening agent for epoxy resin. The toughening agent is added to epoxy resin for toughening modification of epoxy resin. The amount of toughening agent added is 2-15% of the mass of epoxy resin. When the amount added is less than 2%, the toughening effect is not obvious, and when it is more than 15%, it will cause a significant decrease in the strength and modulus of epoxy resin matrix. This range of addition can achieve the best balance between toughness and rigidity.

[0021] The toughening agent core of this invention is made of rubber containing butadiene segments. Its excellent elasticity allows it to undergo elastic deformation under external impact, effectively absorbing impact energy and inhibiting the generation and growth of streaks. The outer shell is formed by copolymerization of vinyl monomers, reactive monomers, and crosslinking agents. The vinyl monomers improve the compatibility between the shell and epoxy resin, while the active groups provided by the reactive monomers participate in the epoxy resin curing reaction, enhancing the interfacial bonding between the toughening agent and the epoxy resin matrix. This achieves good stress transmission at the interface between the epoxy matrix and the toughening agent shell, preventing the toughening agent particles from debonding. The crosslinking agent improves the rigidity and structural stability of the shell, preventing deformation of the shell during epoxy resin curing. The introduction of the crosslinking agent increases the shell hardness and the ability to constrain the morphology of the elastic core, which helps the toughening agent disperse in the epoxy matrix and optimizes the stress transmission effect at the core-shell interface. By precisely controlling the polymerization process parameters, the particle size of the core-shell structured nano-toughening agent is strictly controlled within the range of 80–300 nm. This particle size range ensures that the toughening agent has optimal dispersibility and toughening efficiency in epoxy resin, while avoiding performance degradation caused by particle agglomeration.

[0022] The preparation method of this invention uses diluted rubber latex as a seed, utilizing the emulsifying properties of the rubber latex itself, eliminating the need for additional emulsifiers, thus reducing production costs and avoiding the impact of emulsifier residues on product performance. A pre-dispersion step allows the mixed monomers and oxidant to fully diffuse into the latex particles, resulting in a physically entangled transition layer at the core-shell interface of the core-shell toughening agent obtained from the polymerization reaction. Controlling the pre-dispersion time controls the thickness of this transition layer, effectively improving the interfacial bonding strength and compatibility of the core-shell structure. An oxidation-reduction initiation system is used to achieve room temperature / low temperature polymerization, avoiding latex particle agglomeration and thermal degradation of the rubber core caused by high temperatures. Furthermore, by controlling the stirring speed at different reaction stages, the dispersibility and structural regularity of the particles are further optimized. The entire preparation process uses no toxic or harmful solvents, is environmentally friendly, and achieves a monomer conversion rate of over 95%, resulting in high product yield, making it suitable for large-scale industrial production.

[0023] The reactive core-shell nano-toughening agent of this invention is added to epoxy resin at a mass fraction of 2-15%. After mixing and curing, the toughening agent particles are uniformly dispersed in the epoxy resin matrix, forming a stable composite system. When subjected to external impact, the rubber core undergoes elastic deformation, absorbing a large amount of impact energy and preventing further expansion of streaks; the outer shell forms a strong interfacial bond with the epoxy resin matrix, avoiding debonding and agglomeration of the toughening agent particles, and enhancing stress transmission at the interface. Thus, while maintaining the original rigidity and strength of the epoxy resin, its fracture toughness and impact resistance are significantly improved, expanding the application range of epoxy resin in high-end engineering fields. Attached Figure Description

[0024] Figure 1Schematic diagram of the preparation principle of the three-layer structure of reactive core-shell nano-toughening agent

[0025] Figure 2 The images show the physical composition (left) and particle size distribution (right) of the reactive core-shell nano-toughening agent described in Example 1 applied to epoxy resin. Detailed Implementation

[0026] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and comparative examples. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0027] It should be noted that these examples are only for the convenience of those skilled in the art and should not be regarded as limiting the scope of protection of this invention. Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all commercially available conventional products. The following only provides some of the reagents used in the embodiments of this invention; different manufacturers and models of raw materials do not affect the implementation of the technical solution or the achievement of the technical effect of this invention.

[0028] Table 1 Raw Material and Manufacturer Information

[0029] The technical solution of the present invention will be described below through specific examples.

[0030] Example 1

[0031] Example 1 provides a reactive core-shell nano-toughening agent for epoxy resin, wherein the weight ratio of the core to the shell in the core-shell structure is 1:1; the shell raw materials, by weight percentage, are: styrene 70%, glycidyl methacrylate 20%, and divinylbenzene 10%; the particle size of the core-shell nano-toughening agent is 120-140 nm.

[0032] Its preparation method is as follows:

[0033] (1) Seed emulsion pretreatment: Dilute high solid content nitrile rubber latex with deionized water to a solid content of 10%, take 100g of the diluted latex, add the diluted seed emulsion to the reaction vessel, evacuate to a vacuum degree of -0.08MPa, continue to deoxygenate for 10min, and then introduce nitrogen to obtain a uniformly dispersed seed emulsion.

[0034] (2) Pre-dispersion treatment: Weigh 7g of styrene, 2g of glycidyl methacrylate and 1g of divinylbenzene by weight percentage, mix them evenly and then add 0.2g of cumene hydroperoxide (2.0% of the total mass of the mixed monomers), stir evenly to obtain a mixed monomer system; slowly add the mixed monomer system to the seed emulsion in step (1), and stir at 80rpm for 4 hours at 50℃ to allow the mixed monomers and oxidant to fully diffuse into the interior of the nitrile rubber seed latex particles;

[0035] (3) Seed emulsion polymerization: Slowly add 0.08 g of ferrous sulfate (40% of the mass of oxidant) to the reactor for 10 min. After the addition is complete, keep the temperature at 50 °C and adjust the stirring speed to 100 rpm. Stir and react at the constant temperature for 4 hours, then stop the reaction.

[0036] (4) Post-processing: The reaction product is cooled to room temperature and degassed to remove unreacted monomers; then it is spray-dried at an inlet air temperature of 100°C and an outlet air temperature of 40°C to obtain reactive core-shell nano toughening agent powder.

[0037] The reactive core-shell nano-toughening agent obtained in step (4) can be applied to epoxy resin. The reactive core-shell nano-toughening agent weighed according to the ratio is heated and stirred with epoxy resin 828 at 60°C. After stirring evenly, methyl nadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are added and stirring is continued. After stirring evenly, vacuum defoaming treatment is performed, and then it is poured into a mold and cured at 140°C for 5 hours.

[0038] Example 2

[0039] Example 2 provides a reactive core-shell nano-toughening agent for epoxy resin, wherein the weight ratio of the core to the shell in the core-shell structure is 1:1; the shell raw materials, by weight percentage, are: styrene 70%, glycidyl methacrylate 20%, and divinylbenzene 10%; the particle size of the core-shell nano-toughening agent is 120-140 nm.

[0040] Its preparation method is as follows:

[0041] (1) Seed emulsion pretreatment: Dilute high solid content nitrile rubber latex with deionized water to a solid content of 10%, take 100g of the diluted latex, add the diluted seed emulsion to the reaction vessel, evacuate to a vacuum degree of -0.08MPa, continue to deoxygenate for 10min, and then introduce nitrogen to obtain a uniformly dispersed seed emulsion.

[0042] (2) Pre-dispersion treatment: Weigh 7g of styrene, 2g of glycidyl methacrylate and 1g of divinylbenzene by weight percentage, mix them evenly and then add 0.2g of cumene hydroperoxide (2.0% of the total mass of the mixed monomers), stir evenly to obtain a mixed monomer system; slowly add the mixed monomer system to the seed emulsion in step (1), and stir at 80rpm for 4 hours at 50℃ to allow the mixed monomers and oxidant to fully diffuse into the interior of the nitrile rubber seed latex particles;

[0043] (3) Seed emulsion polymerization: Slowly add 0.08 g of ferrous sulfate (40% of the mass of oxidant) to the reactor for 10 min. After the addition is complete, keep the temperature at 50 °C and adjust the stirring speed to 100 rpm. Stir and react at the constant temperature for 4 hours, then stop the reaction.

[0044] (4) Post-processing: The reaction product is cooled to room temperature and degassed to remove unreacted monomers; then it is spray-dried at an inlet air temperature of 100°C and an outlet air temperature of 40°C to obtain reactive core-shell nano toughening agent powder.

[0045] The reactive core-shell nano-toughening agent powder obtained in step (4) can be applied to epoxy resin. The reactive core-shell nano-toughening agent weighed according to the ratio is heated and stirred with epoxy resin 828 at 60°C. After stirring evenly, methylnadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are added and stirring is continued. After stirring evenly, vacuum defoaming treatment is performed, and then it is poured into a mold and cured at 140°C for 5 hours.

[0046] Example 3

[0047] Example 3 provides a reactive core-shell nano-toughening agent for epoxy resin, wherein the weight ratio of the core to the shell in the core-shell structure is 1:1; the shell raw materials, by weight percentage, are: styrene 70%, glycidyl methacrylate 20%, and divinylbenzene 10%; the particle size of the core-shell nano-toughening agent is 120-140 nm.

[0048] Its preparation method is as follows:

[0049] (1) Seed emulsion pretreatment: Dilute high solid content nitrile rubber latex with deionized water to a solid content of 10%, take 100g of the diluted latex, add the diluted seed emulsion to the reaction vessel, evacuate to a vacuum degree of -0.08MPa, continue to deoxygenate for 10min, and then introduce nitrogen to obtain a uniformly dispersed seed emulsion.

[0050] (2) Pre-dispersion treatment: Weigh 7g of styrene, 2g of glycidyl methacrylate and 1g of divinylbenzene by weight percentage, mix them evenly and then add 0.2g of cumene hydroperoxide (2.0% of the total mass of the mixed monomers), stir evenly to obtain a mixed monomer system; slowly add the mixed monomer system to the seed emulsion in step (1), and stir at 80rpm for 4 hours at 50℃ to allow the mixed monomers and oxidant to fully diffuse into the interior of the nitrile rubber seed latex particles;

[0051] (3) Seed emulsion polymerization: Slowly add 0.08 g of ferrous sulfate (40% of the mass of oxidant) to the reactor for 10 min. After the addition is complete, keep the temperature at 50 °C and adjust the stirring speed to 100 rpm. Stir and react at the constant temperature for 4 hours, then stop the reaction.

[0052] (4) Post-processing: The reaction product is cooled to room temperature and degassed to remove unreacted monomers; then it is spray-dried at an inlet air temperature of 100°C and an outlet air temperature of 40°C to obtain reactive core-shell nano toughening agent powder.

[0053] The reactive core-shell nano-toughening agent powder obtained in step (4) can be applied to epoxy resin. The reactive core-shell nano-toughening agent weighed according to the ratio is heated and stirred with epoxy resin 828 at 60°C. After stirring evenly, methylnadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are added and stirring is continued. After stirring evenly, vacuum defoaming treatment is performed, and then it is poured into a mold and cured at 140°C for 5 hours.

[0054] Example 4

[0055] Example 4 provides a reactive core-shell nano-toughening agent for epoxy resin, wherein the weight ratio of the core to the shell in the core-shell structure is 1:1; the shell raw materials, by weight percentage, are: styrene 70%, methacrylic acid 20%, and divinylbenzene 10%; the particle size of the core-shell nano-toughening agent is 120-140 nm.

[0056] Its preparation method is as follows:

[0057] (1) Seed emulsion pretreatment: Dilute high solid content nitrile rubber latex with deionized water to a solid content of 10%, take 100g of the diluted latex, add the diluted seed emulsion to the reaction vessel, evacuate to a vacuum degree of -0.08MPa, continue to deoxygenate for 10min, and then introduce nitrogen to obtain a uniformly dispersed seed emulsion.

[0058] (2) Pre-dispersion treatment: Weigh 7g of styrene, 2g of methacrylic acid and 1g of divinylbenzene by weight percentage, mix them evenly and then add 0.2g of cumene hydroperoxide (2.0% of the total mass of the mixed monomers), stir evenly to obtain a mixed monomer system; slowly add the mixed monomer system to the seed emulsion in step (1), and stir at 100rpm for 8 hours at 50℃ to allow the mixed monomers and oxidant to fully diffuse into the interior of the nitrile rubber seed latex particles;

[0059] (3) Seed emulsion polymerization: Slowly add 0.08 g of ferrous sulfate (40% of the mass of oxidant) to the reactor for 10 min. After the addition is complete, keep the temperature at 50 °C and adjust the stirring speed to 100 rpm. Stir and react at the constant temperature for 4 hours, then stop the reaction.

[0060] (4) Post-processing: The reaction product is cooled to room temperature and degassed to remove unreacted monomers; then it is spray-dried at an inlet air temperature of 100°C and an outlet air temperature of 40°C to obtain reactive core-shell nano toughening agent powder.

[0061] The reactive core-shell nano-toughening agent powder obtained in step (4) can be applied to epoxy resin. The reactive core-shell nano-toughening agent weighed according to the ratio is heated and stirred with epoxy resin 828 at 60°C. After stirring evenly, methylnadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are added and stirring is continued. After stirring evenly, vacuum defoaming treatment is performed, and then it is poured into a mold and cured at 140°C for 5 hours.

[0062] Example 5

[0063] Example 5 provides a reactive core-shell nano-toughening agent, wherein the weight ratio of the core to the shell in the core-shell structure is 1:1; the shell raw materials, by weight percentage, are: styrene 70%, N-isopropylacrylamide 20%, and divinylbenzene 10%; the particle size of the core-shell structure nano-toughening agent is 120-140 nm.

[0064] Its preparation method is as follows:

[0065] (1) Seed emulsion pretreatment: Dilute high solid content nitrile rubber latex with deionized water to a solid content of 10%, take 100g of the diluted latex, add the diluted seed emulsion to the reaction vessel, evacuate to a vacuum degree of -0.08MPa, continue to deoxygenate for 10min, and then introduce nitrogen to obtain a uniformly dispersed seed emulsion.

[0066] (2) Pre-dispersion treatment: Weigh 7g of styrene, 2g of N-isopropylacrylamide and 1g of divinylbenzene by weight percentage, mix them evenly and then add 0.2g of cumene hydroperoxide (2.0% of the total mass of the mixed monomers), stir evenly to obtain a mixed monomer system; slowly add the mixed monomer system to the seed emulsion in step (1), and stir at 100rpm for 8 hours at 50℃ to allow the mixed monomers and oxidant to fully diffuse into the interior of the nitrile rubber seed latex particles;

[0067] (3) Seed emulsion polymerization: Slowly add 0.08 g of ferrous sulfate (40% of the mass of oxidant) to the reactor for 10 min. After the addition is complete, keep the temperature at 50 °C and adjust the stirring speed to 100 rpm. Stir and react at the constant temperature for 4 hours, then stop the reaction.

[0068] (4) Post-processing: The reaction product is cooled to room temperature and degassed to remove unreacted monomers; then it is spray-dried at an inlet air temperature of 100°C and an outlet air temperature of 40°C to obtain reactive core-shell nano toughening agent powder.

[0069] The reactive core-shell nano-toughening agent powder obtained in step (4) can be applied to epoxy resin. The reactive core-shell nano-toughening agent weighed according to the ratio is heated and stirred with epoxy resin 828 at 60°C. After stirring evenly, methylnadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are added and stirring is continued. After stirring evenly, vacuum defoaming treatment is performed, and then it is poured into a mold and cured at 140°C for 5 hours.

[0070] Example 6

[0071] Example 6 provides a reactive core-shell nano-toughening agent, wherein the weight ratio of the core to the shell in the core-shell structure is 1:1; the shell raw materials, by weight percentage, are: styrene 70%, glycidyl methacrylate 20%, and divinylbenzene 10%; the particle size of the core-shell structure nano-toughening agent is 110-130 nm.

[0072] Its preparation method is as follows:

[0073] (1) Seed emulsion pretreatment: Dilute high solid content styrene-butadiene rubber latex with deionized water to a solid content of 10%, take 100g of the diluted latex, add the diluted seed emulsion to the reaction vessel, evacuate to a vacuum degree of -0.08MPa, continue to deoxygenate for 10min, and then introduce nitrogen to obtain a uniformly dispersed seed emulsion.

[0074] (2) Pre-dispersion treatment: Weigh 7g of styrene, 2g of glycidyl methacrylate and 1g of divinylbenzene by weight percentage, mix them evenly and then add 0.2g of cumene hydroperoxide (2.0% of the total mass of the mixed monomers), stir evenly to obtain a mixed monomer system; slowly add the mixed monomer system to the seed emulsion in step (1), and stir at 100rpm for 6 hours at 50℃ to allow the mixed monomers and oxidant to fully diffuse into the interior of the styrene-butadiene rubber seed latex particles;

[0075] (3) Seed emulsion polymerization: Slowly add 0.08 g of ferrous sulfate (40% of the mass of oxidant) to the reactor for 10 min. After the addition is complete, keep the temperature at 50 °C and adjust the stirring speed to 100 rpm. Stir and react at the constant temperature for 4 hours, then stop the reaction.

[0076] (4) Post-processing: The reaction product is cooled to room temperature and degassed to remove unreacted monomers; then it is spray-dried at an inlet air temperature of 100°C and an outlet air temperature of 40°C to obtain reactive core-shell nano toughening agent powder.

[0077] The reactive core-shell nano-toughening agent powder obtained in step (4) can be applied to epoxy resin. The reactive core-shell nano-toughening agent weighed according to the ratio is heated and stirred with epoxy resin 828 at 60°C. After stirring evenly, methylnadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are added and stirring is continued. After stirring evenly, vacuum defoaming treatment is performed, and then it is poured into a mold and cured at 140°C for 5 hours.

[0078] Comparative Example 1

[0079] This comparative example omits the preparation steps of the reactive core-shell nano-toughening agent in Example 1. Without adding toughening agent, epoxy resin 828, methyl nadic anhydride curing agent and 2-ethyl-4-methylimidazolium accelerator are heated and stirred at 60°C in proportion. After stirring evenly, vacuum defoaming treatment is performed, and then the mixture is poured into a mold and cured at 140°C for 5 hours.

[0080] Comparative Example 2

[0081] Comparative Example 2 omits the preparation steps of the reactive core-shell nano-toughening agent in Example 1, and directly applies the ordinary nitrile rubber powder obtained after demulsification and drying of nitrile rubber latex to the toughening of epoxy resin.

[0082] Comparative Example 3

[0083] The preparation method of Comparative Example 3 is the same as that of Example 1, except that the raw materials used in step (2) of Comparative Example 1 are 7g of styrene, 2g of glycidyl methacrylate and 1g of divinylbenzene; the raw materials used in step (2) of this comparative example are 9g of styrene and 1g of divinylbenzene, that is, no reactive monomers are added.

[0084] Comparative Example 4

[0085] Comparative Example 4 omits step (2) of preparing reactive core-shell nano-toughening agent in Example 1. The reactive core-shell nano-toughening agent powder obtained by direct seed emulsion polymerization without pre-dispersion treatment is applied to the toughening of epoxy resin.

[0086] Effect Comparison

[0087] To verify the technical effect of the reactive core-shell nano-toughening agents in the above embodiments and comparative examples in epoxy resin, the epoxy resin materials prepared in Examples 1-6 and Comparative Examples 1-4 were used as test materials, and their impact strength and tensile strength were tested.

[0088] According to standard GB / T 1843-2008, the impact strength of epoxy resin materials was tested using an XJJD-5.5 cantilever beam impact testing machine. The sample size was 80mm×10mm×4mm. 7 to 10 samples were tested for each specimen, and the average value was taken.

[0089] The tensile strength of epoxy resin materials was tested using an MTS E43.104 electronic universal testing machine according to standard GB / T 1040.1-2025, at a test speed of 1 mm / min. The specimens were type 1A dumbbell-shaped, and 7–10 specimens were tested for each specimen; the average value was taken.

[0090] According to standard GB / T 9341-2008, the flexural strength of epoxy resin materials was tested using an MTS E43.104 electronic universal testing machine at a test speed of 2 mm / min. The specimen dimensions were 80 mm × 10 mm × 4 mm. 7–10 specimens were tested for each sample, and the average value was taken.

[0091] The results of the experiment are shown in Table 2 below:

[0092] Table 2. Test results for different embodiments and comparative examples.

[0093] Comparing the blank group (Comparative Example 1) with Examples 1-6, it can be seen that the reactive core-shell nano-toughening agent for epoxy resin prepared in this invention can significantly improve the impact strength of epoxy resin, while maximizing the maintenance of its tensile strength and flexural strength, achieving the technical goal of "rigidity-toughness balance". The impact strength of each example is 24.0 kJ / m. 2The above results represent a significant improvement of 127.8% to 185.2% compared to the control group. Meanwhile, the tensile strength and flexural strength of Examples 1 to 6 were maintained above 73.5 MPa and 139.4 MPa, respectively, with the decreases compared to the control group controlled within 16.6% and 10.4%.

[0094] Comparing Examples 1-6 with Comparative Example 2, it is evident that the toughening effect and protective effect on the mechanical properties of the matrix from ordinary nitrile rubber powder are far inferior to the core-shell toughening agent of this invention. The impact strength of Comparative Example 2 is only 13.9 ± 0.4 kJ / m. 2 The toughening efficiency was only 28.7%, far lower than in Examples 1-5. Simultaneously, its tensile strength decreased to 56.6±1.2 MPa and flexural strength decreased to 112.3±1.6 MPa, representing decreases of 35.8% and 27.8% respectively, indicating severe deterioration of the matrix's mechanical properties. This is because ordinary nitrile rubber has poor compatibility with cured epoxy resin, easily agglomerating in the matrix and failing to form a uniformly dispersed composite system. This results in low toughening efficiency and damages the three-dimensional cross-linked network structure of the matrix, leading to significant deterioration of both tensile and flexural strength. In contrast, the core-shell structure of this invention has a rigid shell with a solubility parameter closer to that of epoxy resin, and the reactive monomers can form a good interfacial bond with the epoxy resin matrix, preventing toughening agent agglomeration. This achieves increased toughness while maintaining material rigidity to the greatest extent possible.

[0095] Comparing Examples 1-6 with Comparative Example 3, it is evident that the reactive functional groups on the outer shell of the core-shell toughening agent have a crucial influence on the performance of the toughening agent of this invention. The impact strength of Comparative Example 3 is 19.7 ± 0.5 kJ / m. 2 Compared to Example 1, the tensile strength decreased by 82.4%, and the flexural strength decreased to 68.5±0.9MPa and 120.6±1.0MPa, respectively, which were far lower than those of Examples 1-5, indicating a severe deterioration in the mechanical properties of the matrix. This is because the core-shell particles without functional groups in the outer shell do not have a strong interaction with the epoxy resin matrix, resulting in a weak interface bond. During tensile testing, stress tends to concentrate at the interface, forming microcracks that propagate rapidly. Upon impact, the core-shell particles are prone to interfacial debonding and particle pull-out from the epoxy resin matrix, leading to low stress transmission efficiency and ultimately a significant reduction in impact toughening efficiency and a marked deterioration in tensile / flexural strength. In contrast, the outer shell layers of Examples 1-3 and Example 6 have epoxy functional groups, which are similar in structure to the epoxy resin matrix and exhibit good compatibility. The outer shell layers of Examples 4 and 5 have carboxyl and secondary amine groups, respectively, which can directly react with the epoxy groups of the epoxy resin matrix, participate in the curing reaction, and form covalent bonds connecting the toughening agent and the epoxy resin. The strong interactions of chemical bonds ensure that the core-shell nano-toughening agent of this invention has a good toughening effect.

[0096] Comparing Examples 1-6 with Comparative Example 4, it is evident that the pre-dispersion treatment step has a crucial impact on the performance of the toughening agent of the present invention. In Comparative Example 3, where the pre-dispersion treatment was omitted, the impact strength was 23.7 ± 0.5 kJ / m. 2 The improvement rate was only 119.4%, lower than all other examples; the tensile strength decreased to 70.5±0.9MPa, a decrease of 19.9%, and the flexural strength decreased to 125.6±0.8MPa, a decrease of 19.3%, both significantly worse than the other examples. This is because the pre-dispersion treatment allows the vinyl monomers, reactive monomers, crosslinking agents, and oxidants to fully diffuse into the interior of the nitrile rubber seed latex particles, ensuring that the subsequent emulsion polymerization reaction proceeds uniformly, forming a well-structured core-shell structure with tight interfacial bonding. This structure has good interfacial stress transmission and induces cavitation and shear banding, thus achieving the toughening purpose. If the pre-dispersion step is omitted, the mixed monomers cannot penetrate evenly into the interior of the latex particles, which easily leads to loose core-shell interfacial bonding and uneven shell reaction, thereby affecting the dispersibility and toughening effect of the toughening agent, and also reducing the tensile and flexural strength of the modified epoxy resin.

[0097] The above examples and comparative examples demonstrate that the reactive core-shell nano-toughening agent for epoxy resin of the present invention, using rubber latex and polymer monomers as raw materials, solves the technical problems of weak core-shell interfacial forces, poor compatibility between the core-shell toughening agent and epoxy resin, and uneven dispersion through the design of a functionalized and cross-linked network shell structure and a pre-dispersion process. Compared with traditional liquid rubber toughening agents and commercially available core-shell toughening agents, it has a superior toughening effect and can effectively maintain the strength and rigidity of the epoxy resin matrix. The preparation method of the present invention is simple, has a wide range of raw material sources, strong controllability, high product yield, and strong equipment applicability, making it suitable for large-scale industrial production. Applying this toughening agent to the modification of epoxy resin can significantly improve the fracture toughness and impact resistance of epoxy resin, expanding its application range in high-end engineering fields.

Claims

1. A reactive core-shell nanolubricant for epoxy resin, characterized by, The toughening agent has a core-shell three-layer structure, with a core of rubber and a shell of reactive cross-linked copolymer. The core-shell interface has a physical entanglement interface transition layer of controllable thickness. The rubber is introduced from a rubber emulsion; The crosslinked copolymer is formed by emulsion copolymerization of vinyl monomers, reactive monomers and crosslinking agents; The thickness of the interface transition layer is controlled by the ratio of monomers and rubber, polarity, and swelling time. The core-shell rubber nanoparticles have a particle size of 80–300 nm.

2. The reactive core-shell nanolubricant for epoxy resin according to claim 1, characterized by, The raw material composition of the shell, by weight percentage, is: 50-90% vinyl monomer, 5-40% reactive monomer, and 0.5-25% crosslinking agent.

3. The reactive core-shell nano-toughening agent for epoxy resin according to claim 1, characterized in that, The vinyl monomer is at least one selected from styrene, α-methylstyrene, methyl methacrylate, acrylonitrile, and methacrylonitrile; The reactive monomer is at least one of methacrylic acid, glycidyl methacrylate, and N-isopropylacrylamide; The crosslinking agent is at least one of divinylbenzene, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, propylene glycol dimethacrylate, trimethylolpropane triacrylate, triallyl isocyanurate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

4. The rubber-based core-shell structured nano-toughening agent according to claim 1, characterized in that, The rubber core is one or a blend of nitrile rubber, styrene-butadiene rubber, and polybutadiene rubber containing butadiene segments, with a glass transition temperature ≤ -30℃.

5. The reactive core-shell nano-toughening agent for epoxy resin according to claim 1, characterized in that, In the core-shell structure, the weight ratio of the core to the shell is 1:(0.8 to 1.6).

6. A method for preparing a reactive core-shell nano-toughening agent for epoxy resin as described in any one of claims 1 to 5, characterized in that, The seed emulsion polymerization method is employed, and the specific steps are as follows: (1) Seed emulsion pretreatment: High solid content rubber latex is diluted with deionized water and the solid content is adjusted to 5-25%. The diluted seed emulsion is added to the reaction vessel, and after vacuuming and deoxygenation, inert gas is introduced into the reaction vessel to obtain a uniformly dispersed seed emulsion. (2) Pre-dispersion treatment: After the vinyl monomer, reactive monomer, crosslinking agent and oil-soluble oxidant are mixed evenly, they are added to the seed emulsion in step (1) and stirred at a stirring speed of 40 to 250 rpm for 0.5 to 16 hours at a temperature of 10 to 50°C. The thickness of the core-shell interface transition layer is controlled by adjusting the pre-dispersion time. (3) Seed emulsion polymerization: Slowly add water-soluble reducing agent to the reactor for 10-40 min. Add water-soluble reducing agent to the reactor and adjust the stirring speed to 50-350 rpm under the condition of 10-50℃. Stir and react for 2-5 hours, then stop the reaction. (4) Post-processing: The reaction product is cooled to below room temperature, degassed to remove unreacted monomers, and spray-dried to obtain reactive core-shell nano toughening agent powder.

7. The preparation method according to claim 6, characterized in that, The inert gas mentioned in step (1) is nitrogen; The oil-soluble oxidant mentioned in step (2) is cumene hydroperoxide, and the amount added is 0.5% to 4.0% of the total mass of the monomer; The water-soluble reducing agent mentioned in step (3) is ferrous sulfate, and the amount added is 10-50% of the mass of the oxidant; The inlet air temperature of the spray drying in step (4) is 85-110℃ and the outlet air temperature is 40-60℃.

8. The application of a reactive core-shell nano-toughening agent for epoxy resin as described in any one of claims 1 to 5, characterized in that, The toughening agent is added to the epoxy resin for toughening modification of the epoxy resin. The amount of toughening agent added is 2 to 15% of the mass of epoxy resin.

9. The application of the reactive core-shell nano-toughening agent for epoxy resin according to claim 8, characterized in that, The reactive core-shell nano-toughening agent for epoxy resins is applicable to any type of epoxy resin, including glycidyl esters, glycidyl ethers, glycidyl amines, and alicyclic resins, and is not limited to any epoxy curing system from low temperature to high temperature.

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