Core-shell structure modified particle and preparation method thereof, polytetrafluoroethylene composite material, structural member and preparation method thereof

Abstract

The invention relates to the field of composite materials, in particular to core-shell structure modified particles, a preparation method of the core-shell structure modified particles, a polytetrafluoroethylene composite material, a structural part and a preparation method of the structural part. The core-shell structure modified particle comprises a filler particle and a fluororesin shell layer coating the surface of the filler particle, the fluororesin shell layer and the filler particles are combined through physical adsorption. The core-shell structure modified particles with filler particles as cores and fluororesin as shells are constructed, and the filler particles are subjected to surface coating modification. The interface compatibility between the modified particles with the core-shell structure and a polytetrafluoroethylene resin matrix is good, and the interface bonding force is high; meanwhile, the fluorine resin and the polytetrafluoroethylene suspension resin matrix of the modified shell layer have a mutual synergistic effect, so that the toughness, the tensile strength, the compression resilience, the dimensional stability and the like of the composite material are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and more specifically, to a core-shell structure modified particle and its preparation method, a polytetrafluoroethylene composite material, a structural component and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is often used to manufacture structural components in various fields such as aerospace, automotive, electrical, and chemical industries due to its excellent high temperature resistance, chemical corrosion resistance, and extremely low coefficient of friction, in order to achieve functions such as sealing, wear resistance, corrosion protection, and insulation.

[0003] However, pure polytetrafluoroethylene (PTFE) resin suffers from poor dimensional stability, insufficient creep resistance, and susceptibility to friction and wear, severely limiting its application in high-end fields. To improve the mechanical properties, dimensional stability, and creep resistance of PTFE, inorganic or organic fillers are typically introduced for modification. However, PTFE molecules have extremely low polarity and surface energy, resulting in poor compatibility with most fillers. This makes it difficult for fillers to disperse uniformly in the matrix, and weakens interfacial bonding. Excessive filler content often leads to filler agglomeration and interfacial defects, ultimately reducing the overall performance of the material.

[0004] Existing technologies often employ the modification of filler particles to improve their dispersion uniformity in polytetrafluoroethylene (PTFE) resin and their interfacial compatibility with the PTFE resin matrix. Common modification methods include coupling agent modification, compounding of multiple particles, and surfactant treatment. For example, patent CN120441977A uses tetraethyl orthosilicate to form a silica deposition layer on the carbon fiber surface. Combined with hydroxypropyl β-cyclodextrin, its surface contains numerous active hydroxyl sites, forming a skeletal support network with the silica deposition layer. This, combined with a ball milling pre-sintering process, improves the dispersion effect, thereby enhancing the tensile strength and resilience of the composite material. Another example is invention patent CN120289932A, which uses LDHs to modify ATP. This not only retains the original structure of ATP but also improves its surface roughness and compatibility with the matrix. LDHs are two-dimensional layered structures with a large specific surface area and exchangeable interlayer anions. They can also form hydrogen bonds with PTFE molecular chains, significantly improving the wear resistance of PTFE.

[0005] These methods often improve the interfacial compatibility between fillers and the matrix through external modification. Although they help improve the performance of PTFE composites to some extent, they still fail to solve the balance between filler dispersion and interfacial reinforcement under high filler content, and the process is often more complex and difficult to mass-produce.

[0006] Therefore, developing a process that can simultaneously achieve good filler dispersion and strong interfacial bonding has become the key to promoting polytetrafluoroethylene composites to high-end applications. Summary of the Invention

[0007] In view of the above-mentioned shortcomings in the prior art, the core objective of the present invention is to provide a core-shell structure modified particle and its preparation method, a polytetrafluoroethylene composite material, a structural component and its preparation method. By coating the surface of the filler particles with a shell layer of fluororesin, the filler particles are modified, so that they have better interfacial compatibility and stronger interfacial bonding ability with the polytetrafluoroethylene body, thereby preparing a polytetrafluoroethylene composite material with excellent mechanical properties.

[0008] This invention is achieved through the following technical solution: The present invention first provides a core-shell structure modified particle, including filler particles and a fluororesin shell layer covering the surface of the filler particles; the fluororesin shell layer and the filler particles are formed by physical adsorption.

[0009] This invention coats the surface of filler particles with a fluororesin shell through physical adsorption. The interfacial compatibility and interfacial bonding force between the filler particles coated with the fluororesin shell and the polytetrafluoroethylene matrix are significantly enhanced, thereby significantly improving the mechanical properties and dimensional stability of the polytetrafluoroethylene composite material. In addition, when this core-shell structure modified particle is applied to the matrix polytetrafluoroethylene suspension resin, the fluororesin in the shell and the matrix polytetrafluoroethylene suspension resin further form a synergistic effect, which can significantly improve the toughness, tensile strength, compression resilience and dimensional stability of the composite material.

[0010] Preferably, the filler particles of the present invention are first pretreated by a coupling agent with protonated groups and then coated with a fluororesin shell on their surface by physical adsorption.

[0011] Preferably, the filler particles are selected from one or more of the following: silica, carbon fiber, glass fiber, carbon black, graphite, carbon nanotubes, alumina, ceramic fiber, boron nitride, silicon carbide, molybdenum disulfide, and metal powder. More preferably, the filler particles have a nanometer or micrometer-scale particle size.

[0012] The addition of these filler particles can improve the mechanical properties and creep resistance of polytetrafluoroethylene (PTFE), and they are often used as fillers when preparing structural parts from PTFE resin.

[0013] Preferably, the fluororesin is selected from one or more of polytetrafluoroethylene, perfluoroethylene propylene, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer.

[0014] These fluororesins can form a stable shell on the surface of filler particles through physical adsorption, and they also have good compatibility with polytetrafluoroethylene, which can achieve strong interfacial bonding.

[0015] This invention also provides a method for preparing the above-mentioned core-shell structure modified particles, comprising the following steps: S1 Preparation of pretreated filler particles: The filler particles and coupling agent are added to an alcohol-water solution and mixed uniformly for 4-8 hours. The mixture is then separated and dried to prepare the pretreated filler particles. S2 Preparation of core-shell structure modified particles: The pretreated filler particles are prepared into a dispersion and mixed with a fluororesin dispersion to form a mixed dispersion. The pH of the mixed dispersion is adjusted to alkaline to ensure uniform dispersion of the pretreated filler particles and fluororesin particles. Subsequently, the pH of the mixed dispersion is adjusted to acidic to allow the fluororesin particles to coat the surface of the pretreated filler particles through physical adsorption. After separation and drying, the core-shell structure modified particles are obtained.

[0016] Preferably, in step S2 above, the pH values ​​of the pretreated filler particle dispersion and the fluororesin dispersion can be adjusted to alkaline before they are mixed to form a mixed dispersion; alternatively, the pretreated filler particle dispersion and the fluororesin dispersion can be mixed to form a mixed dispersion before adjusting the pH value of the mixed dispersion to alkaline.

[0017] This invention creatively constructs a method for forming a core-shell structure between filler particles and fluororesin, utilizing physical adsorption. Specifically, fluororesin dispersions, due to the presence of anionic surfactants, typically have a negatively charged surface. This invention first pretreats the filler particles with a coupling agent containing protonable groups, resulting in protonable groups on the particle surface. The pretreated filler particles and fluororesin dispersion are mixed to form a mixed dispersion. When the mixed dispersion is alkaline, the groups on the filler particle surface do not receive protons and remain neutral, while the hydroxyl and carboxyl groups carried by the filler itself deprotonate, giving the filler particle surface a negative charge. This negative charge interacts with the negative charge of the fluororesin particles, creating electrostatic repulsion and resulting in a stable dispersion. When the mixed dispersion is acidic, the protonated groups on the filler particle surface become positively charged, interacting with the negative charge of the fluororesin particles to form physical adsorption. This allows the fluororesin to coat the filler particle surface and condense from the dispersion to obtain stable core-shell structure modified particles. These particles are then separated and dried to obtain the final core-shell structure modified particles. This invention achieves surface potential regulation by sequentially adjusting the pH value of the mixed dispersion, and ultimately constructs a core-shell structure modified particle with surface fluorination.

[0018] Preferably, in step S1, the method for preparing the pretreated filler particles includes the following steps: (1) Add 100 parts of filler particles to 800-1200 parts of ethanol by mass and disperse evenly to obtain a filler particle dispersion; (2) Mix 1.5-3 parts of coupling agent, 10 parts of deionized water and 80-90 parts of ethanol evenly; hydrolyze at 60℃-70℃ for 0.5h-1.5h to obtain a coupling agent hydrolysate; (3) Add the coupling agent hydrolysate to the filler particle dispersion and react at 50℃-70℃ for 6-7h, then filter, wash and dry to obtain the pretreated filler particles.

[0019] Preferably, the coupling agent is a coupling agent with a protonable group, preferably one or more of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-ureapropyltriethoxysilane, and (N-imidazolyl)propyltriethoxysilane.

[0020] Preferably, in step S2, the pretreated filler particles and water are prepared into a dispersion in a weight ratio of 1:4 to 5; the pretreated filler particle dispersion and the fluororesin dispersion are stirred and mixed at a speed of 100-150 r / min for 2 to 4 hours; in the above mixing equipment, the stirring rod is a single propeller blade stirring rod.

[0021] Preferably, in step S2, the pretreated filler particles are prepared into a dispersion and mixed with a fluororesin dispersion, and the pH value is adjusted to 8-10 to ensure that the pretreated filler particles and the fluororesin particles are fully dispersed; then the pH value is adjusted to 3-5 to allow the pretreated filler particles and the fluororesin particles to adsorb each other and form the core-shell structure modified particles.

[0022] The pH value is preferably controlled at 8-10 and 3-5 respectively, which can achieve good dispersion and adsorption, and can better construct uniform and fully coated core-shell structured modified particles.

[0023] Preferably, in step S2, the fluororesin dispersion is specifically a fluororesin dispersion with a solid content of 50wt% to 65wt%.

[0024] The present invention also provides a polytetrafluoroethylene composite material, the raw materials of which include polytetrafluoroethylene suspension resin and the above-mentioned core-shell structure modified particles; the material is prepared by mixing the above-mentioned polytetrafluoroethylene suspension resin and the above-mentioned core-shell structure modified particles with a high-speed stirrer for a mixing time of 1-2 min.

[0025] The present invention also provides a structural component prepared from the above-mentioned polytetrafluoroethylene composite material, and specifically discloses a method for preparing the above-mentioned structural component, which includes the following steps: The composite material is placed in a mold and pressed to obtain a preform; preferably, the pressing pressure is 15-30 MPa, the pressing time is 20-40 min, and the pressing temperature is 25℃. The preform is sintered at 360-420℃ for 2-4 hours to form the final shape.

[0026] The present invention has at least the following advantages and beneficial effects: (1) This invention modifies the surface of filler particles by constructing core-shell structure modified particles with filler particles as the core and fluororesin as the shell. The modified core-shell structure modified particles can be well dispersed in the polytetrafluoroethylene resin matrix, have good interfacial compatibility with the polytetrafluoroethylene resin matrix, and have high interfacial bonding force, which can significantly improve the mechanical properties and creep resistance of polytetrafluoroethylene composite materials; at the same time, the fluororesin in the modified shell layer and the polytetrafluoroethylene suspension resin matrix have a synergistic effect, which can significantly improve the toughness, tensile strength, compression resilience and dimensional stability of the composite material.

[0027] (2) This invention pre-treats the filler particles to establish the basic conditions for surface potential regulation; and further regulates the surface potential of the particles in the mixed dispersion by adjusting the pH value, thereby achieving the purpose of electrostatic repulsion to promote dispersion and electrostatic adsorption to form coating; and finally successfully prepares core-shell structure modified particles with fluororesin as the shell and inorganic filler particles as the core.

[0028] (3) The composite material prepared by the present invention by blending core-shell structure modified particles and polytetrafluoroethylene suspension resin has superior mechanical strength, toughness, creep resistance and dimensional stability, which can better meet its high-end application needs in structural sealing, high-frequency communication, mechanical lubrication, biomedical fields. (4) The preparation method of the present invention is simple and easy to control. Only the pH value needs to be adjusted to achieve good process control and result control, which is convenient for industrial promotion and application. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image magnified 80,000 times of the core-shell structure modified particles prepared in Example 1; Figure 2 This is an EDS image of the core-shell modified particles prepared in Example 1, magnified 80,000 times. Figure 3 This is a 40,000x magnified scanning electron microscope image of the cross-section of the core-shell modified particles prepared in Example 1. Figure 4 This is a 40,000x magnified electron microscope scan of the cross-section of the sample prepared in Comparative Example 3. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. All features disclosed in this specification, except for mutually exclusive features and / or steps, can be combined in any way.

[0031] The following embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way.

[0032] Example 1 This embodiment provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The specific preparation method includes: S1 Preparation of pretreated filler particles: (1) 100 parts by mass of filler particles (silica, particle size: 500 nm) were added to 1000 parts by mass of ethanol and dispersed evenly to obtain a filler particle dispersion; (2) 2 parts by mass of 3-aminopropyltriethoxysilane, 10 parts by mass of deionized water and 88 parts by mass of anhydrous ethanol were mixed evenly; hydrolyzed at 60°C for 0.5 h to obtain a coupling agent hydrolysate; (3) the coupling agent hydrolysate was added to the filler particle dispersion and reacted at 60°C for 6 h, then filtered, washed and dried to obtain the pretreated filler particles.

[0033] S2 Preparation of core-shell structure modified particles: (1) Weigh 40 parts of the above pretreated filler particles and disperse them in 60 parts of deionized water. After stirring evenly, add ammonia water to adjust the pH value of the system to 10 and prepare a dispersion. (2) Weigh 100 parts of polytetrafluoroethylene dispersion emulsion (PTFE, solid content 60wt%). Similarly, adjust the pH value to 10 with ammonia water. Under stirring conditions of 150r / min, slowly add the dispersion obtained in (1) to the polytetrafluoroethylene dispersion emulsion and continue mixing for 4h to obtain a mixed dispersion. (3) Adjust the pH of the above mixed dispersion to 4 with acetic acid so that the polytetrafluoroethylene resin coats the surface of the inorganic filler particles (silica) through physical adsorption. Add 200 parts of ethanol to break the emulsion. After standing, filter, wash and dry to obtain core-shell structure modified particles.

[0034] S3 Preparation of polytetrafluoroethylene composite material: The above-mentioned core-shell structure modified particles and polytetrafluoroethylene suspension resin are placed in a high-speed stirrer at a mass ratio of 5:5 and mixed for 2 minutes to obtain the polytetrafluoroethylene composite material of this embodiment.

[0035] S4 Preparation of polytetrafluoroethylene structural parts: The polytetrafluoroethylene composite material is loaded into a preform mold and pressed at 20 MPa for 20 minutes at 25°C to form a preform. The preform is placed in a sintering furnace and sintered at 380°C for 2 hours, and then cooled to room temperature with the furnace to obtain the structural parts of this embodiment.

[0036] Example 2 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, as well as a structural component made from the polytetrafluoroethylene composite material. The only difference from Example 1 is that the filler particle is glass fiber with a length of 3 mm and an average single filament diameter of 10 micrometers.

[0037] Example 3 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that the filler particle is carbon nanotubes with an average outer diameter of 15 nanometers.

[0038] Example 4 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that the polytetrafluoroethylene dispersion emulsion in step S2 is replaced with an equal mass of perfluoroethylene propylene dispersion emulsion (PFA) with the same solid content of 60 wt%.

[0039] Example 5 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that the polytetrafluoroethylene dispersion emulsion in step S2 is replaced with an equal mass of tetrafluoroethylene-perfluoroalkoxyethylene copolymer dispersion emulsion (FEP) with the same 60wt% solid content.

[0040] Example 6 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, and a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that in step S2, in step (1), the pH value of the pretreated filler dispersion is adjusted to 8; in step (2), the pH value of the polytetrafluoroethylene dispersion emulsion is also adjusted to 8; and in step (3), acetic acid is used to adjust the pH of the above mixed dispersion to 3.

[0041] Example 7 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, and a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that the specific operation of step S2 is as follows: (1) Weigh 40 parts of the above pretreated filler particles and disperse them in 60 parts of deionized water to prepare a dispersion; (2) Weigh 100 parts of polytetrafluoroethylene dispersion emulsion (solid content 60wt%), and under the stirring condition of 150r / min, slowly add the dispersion obtained in (1) to the polytetrafluoroethylene dispersion emulsion and continue mixing for 4h to obtain a mixed dispersion; (3) Use ammonia water to adjust the pH value of the mixed dispersion to 9, and stir and disperse for 1h; (4) Use acetic acid to adjust the pH of the above mixed dispersion to 5, so that the polytetrafluoroethylene resin coats the surface of the inorganic filler particles (silica) through physical adsorption, add 200 parts of ethanol to break the emulsion, let stand, filter, wash, and dry to obtain core-shell structure modified particles.

[0042] Example 8 This embodiment also provides a core-shell structure modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the core-shell structure modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that in step S1, 2 parts of (N-imidazolyl)propyltriethoxysilane are used instead of 2 parts of 3-aminopropyltriethoxysilane in step S1.

[0043] Comparative Example 1 This comparative example provides a modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that the specific operation of step S2 is as follows: S2 Preparation of modified particles: (1) Weigh 40 parts of the above pretreated filler particles and disperse them in 45 parts of deionized water. After stirring evenly, add ammonia water to adjust the pH value of the system to 10 and prepare a dispersion. (2) Weigh 100 parts of polytetrafluoroethylene dispersion emulsion (solid content 60wt%) and adjust the pH value to 10 with ammonia water. Under stirring conditions of 150r / min, slowly add the dispersion obtained in (1) to the polytetrafluoroethylene dispersion emulsion and continue mixing for 4h to obtain a mixed dispersion. (3) Add 200 parts of ethanol to break the emulsion, let stand, filter, wash, and dry to obtain modified particles.

[0044] S3 Preparation of polytetrafluoroethylene composite material: The obtained modified particles and polytetrafluoroethylene suspension resin were placed in a high-speed stirrer at a mass ratio of 5:5 and mixed for 2 minutes to obtain polytetrafluoroethylene composite material.

[0045] Comparative Example 2 This comparative example provides a modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that step S1 is omitted, i.e., the filler particles are not pretreated with a coupling agent containing protonable groups. In step S2, silica is directly prepared into a dispersion and mixed with a polytetrafluoroethylene dispersion emulsion to form a mixed dispersion.

[0046] Comparative Example 3 This comparative example provides a modified particle and its preparation method, and provides a polytetrafluoroethylene (PTFE) composite material obtained by filling with the modified particle, as well as a structural component prepared from the PTFE composite material. The only difference from Example 1 is that step S2 is omitted; that is, the pretreated filler particles obtained in step S1 are directly mixed with PTFE suspension resin to prepare the PTFE composite material. Furthermore, in this comparative example, the pretreated filler particles and PTFE suspension resin are placed in a high-speed stirrer at a mass ratio of 2:8 and mixed for 2 minutes to obtain the PTFE composite material.

[0047] Comparative Example 4 This comparative example provides a modified particle and its preparation method, and provides a polytetrafluoroethylene composite material obtained by filling with the modified particle, as well as a structural component prepared from the polytetrafluoroethylene composite material. The only difference from Example 1 is that step S2 is omitted, and the polytetrafluoroethylene body in this comparative example is a polytetrafluoroethylene dispersion resin.

[0048] That is, the pretreated filler particles obtained in step S1 are directly mixed with polytetrafluoroethylene dispersion resin to prepare polytetrafluoroethylene composite material. In this comparative example, the pretreated filler particles and polytetrafluoroethylene dispersion resin are placed in a high-speed stirrer at a mass ratio of 2:8 and mixed for 2 minutes to obtain polytetrafluoroethylene composite material.

[0049] Experimental Example 1 The core-shell modified particles prepared in Example 1 and the modified particles prepared in Comparative Example 3 were subjected to scanning electron microscopy (SEM) analysis. The results are attached. Figure 1 -Appendix Figure 4 As shown.

[0050] Among them, the appendix Figure 1 Here is an 80,000x magnified scanning electron microscope image of the core-shell structure modified particles from Example 1; (Attached) Figure 2 The image shows an 80,000x magnified EDS image of the core-shell modified particles from Example 1. Numerous polytetrafluoroethylene (PTFE) particles are visible in the electron microscope image, while silica particles are difficult to observe directly. However, elemental analysis using EDS revealed significant amounts of silicon and oxygen, indicating that the PTFE dispersion resin completely coated the surface of the silica particles.

[0051] Appendix Figure 3 The image shown is a 40,000x magnified scanning electron microscope (SEM) image of the cross-section of the structural component prepared in Example 1. Figure 4 This is a 40,000x magnified electron microscope (SEM) image of the cross-section of the structural component prepared in Comparative Example 3. The comparison reveals that in the structural component sample prepared using Example 1, the interface between the silica particles and the matrix is ​​more blurred, and the polytetrafluoroethylene (PTFE) more fully encapsulates and adheres to the silica, indicating a good interfacial bonding ability between silica and PTFE. In contrast, in the sample prepared in Comparative Example 3, the interface between silica and PTFE is relatively clear, and PTFE does not effectively adhere to the silica particles, indicating a poorer interfacial bonding ability. This demonstrates that the core-shell structure modified particles of this invention can significantly enhance the interfacial bonding performance between the filler and the matrix in PTFE composite materials.

[0052] Experimental Example 2 The zeta potentials of the three types of filler particles were monitored, including the core-shell structure modified particles prepared in step S2 of Example 1, the modified particles prepared in step S2 of Comparative Example 1, and the unmodified silica particles of Comparative Example 2. The results are shown in Table 1.

[0053] Table 1. Zeta potential of filler particle dispersions in Example 1, Comparative Example 1, and Comparative Example 2

[0054] The results in Table 1 show that the core difference between Example 1 and Comparative Example 1 lies in the pH environment of the dispersion during surface potential control. In Comparative Example 1, the pH was 10. Under this condition, the ammonium groups on the filler surface could not gain protons and remained neutral. Simultaneously, the surface hydroxyl groups underwent deprotonation, resulting in a negative charge on the overall filler surface, consistent with the fluororesin. Under electrostatic repulsion, the entire system was stably dispersed, but there was no interaction between the filler particles and the fluororesin, preventing effective binding. In Example 1, the pH was first adjusted to 10, allowing the fluororesin and pretreated filler particles to disperse fully. Then, the pH was adjusted to 4, resulting in positively charged ammonium groups on the filler particle surface. These positively charged groups interacted with the negatively charged fluororesin particles, forming a physical adsorption effect. The difference between Example 1 and Comparative Example 2 is that the silica filler used in Comparative Example 2 was not aminated. Unmodified silica particles lack protonable groups on their surface, so pH changes have limited impact on the filler surface. Furthermore, the unmodified silica dispersion system showed poor stability and a tendency to aggregate, as indicated by the zeta potential.

[0055] Experimental Example 3 The structural component samples prepared in Examples 1-7 and Comparative Examples 1-4 were tested for density, tensile strength, elongation at break and linear thermal expansion coefficient using the same method. The test results are shown in Table 2.

[0056] Table 2 Performance test results of samples prepared in each embodiment and comparative example

[0057] Note: " / " in the table indicates that the density was not tested.

[0058] From the data in Table 2, we can see that: (1) The composite material structural parts prepared in Examples 1-8 all exhibit superior tensile strength, elongation at break, and linear coefficient of thermal expansion, demonstrating excellent tensile strength, good toughness, and significant dimensional stability. In contrast, the composite material structural parts prepared in Comparative Examples 1-4 cannot simultaneously satisfy the advantages of tensile strength, toughness, and dimensional stability. This indicates that the core-shell structure modified particles provided by this invention, when added to the polytetrafluoroethylene resin matrix, exhibit strong interfacial compatibility and bonding force, significantly promoting the performance improvement of the composite material.

[0059] (2) Comparing the data from Examples 1-3, it can be seen that polytetrafluoroethylene composite materials were successfully prepared using silica, glass fiber, and carbon nanotubes as fillers according to the preparation method of the present invention. These composite materials all exhibit excellent tensile strength, good toughness, and significant dimensional stability. This indicates that the preparation process provided by the present invention can achieve high performance improvement for different types of filler particles and has good applicability and universality.

[0060] (3) Comparing the data from Examples 1, 4, and 5, it can be seen that when polytetrafluoroethylene dispersion resin, PFA, and FEP were selected as fluoropolymers and inorganic particles to form core-shell structure modified particles, the prepared composite materials all exhibited strong mechanical strength, toughness, and dimensional stability. This demonstrates that the method of the present invention is applicable to different fluoropolymers and can meet the modification requirements under different conditions, thus possessing universality.

[0061] (4) Comparing the data of Example 1, Example 6 and Example 7, it can be seen that within the preferred pH range of the present invention, the surface potential can be well controlled, and uniform and stable core-shell structure modified particles can be prepared, and then the composite material with excellent mechanical strength, toughness and dimensional stability can be further prepared.

[0062] (5) Comparing the data of Examples 1 and 8, it can be seen that the composite materials prepared by using 3-aminopropyltriethoxysilane and (N-imidazolyl)propyltriethoxysilane as coupling agents for pretreatment of filler particles in Examples 1 and 8 respectively exhibit excellent mechanical properties, toughness, and dimensional stability. This shows that the present invention is applicable to different coupling agents with protonable groups and has universality.

[0063] (6) Comparing the data of Example 1 and Comparative Example 1, it can be seen that the tensile strength and elongation at break of the composite material finally prepared in Comparative Example 1 are lower than those of Example 1, and the linear thermal expansion coefficient is significantly higher than that of Example 1. This indicates that the composite material prepared by this method is worse than that of Example 1 in terms of mechanical strength, toughness and dimensional stability. This is because after mixing the pretreated filler particle dispersion and the polytetrafluoroethylene resin dispersion emulsion in Comparative Example 1, the pH value was only adjusted to 10. Under this condition, the ammonium groups on the filler surface cannot gain protons and are neutral. At the same time, the surface hydroxyl groups are deprotonated and become negatively charged, resulting in the overall surface of the filler being negatively charged. This causes electrostatic repulsion between the filler and the equally negatively charged polytetrafluoroethylene latex particles, preventing effective physical adsorption. The two only form a stable dispersion system and do not form core-shell structured modified particles. Therefore, they do not promote the interfacial compatibility between the filler particles and the polytetrafluoroethylene resin matrix.

[0064] (7) Comparing the data of Example 1 and Comparative Example 2, it can be seen that the tensile strength and elongation at break of the composite material finally prepared in Comparative Example 2 are lower than those of Example 1, and the linear thermal expansion coefficient is significantly higher than that of Example 1. This indicates that the composite material prepared by this method is worse than that of Example 1 in terms of mechanical strength, toughness and dimensional stability. This is because the silica filler used in Comparative Example 2 was not pretreated by ammoniation modification. The surface of the unmodified silica particles is negatively charged. Even under pH control, they cannot be mutually adsorbed with the polytetrafluoroethylene dispersion emulsion, which is also negatively charged, through electrostatic interaction. Furthermore, due to the extremely poor interfacial compatibility between the unmodified silica and the polytetrafluoroethylene emulsion, the performance of the prepared composite material is greatly reduced.

[0065] (8) Comparing the data of Example 1 and Comparative Example 3, it can be seen that the tensile strength and elongation at break of the composite material finally prepared in Comparative Example 3 are lower than those of Example 1, and the linear thermal expansion coefficient is significantly higher than that of Example 1. This indicates that the composite material prepared by this method is worse than that of Example 1 in terms of mechanical strength, toughness and dimensional stability. This is because Comparative Example 3 only pretreated and modified the silica with a silane coupling agent, without coating its surface with a polytetrafluoroethylene shell, which resulted in limited improvement in the interfacial compatibility between it and the resin matrix. Therefore, the performance of the composite material prepared was significantly worse.

[0066] (9) Comparing the data of Example 1 and Comparative Example 4, it can be seen that the tensile strength of the composite material finally prepared in Comparative Example 4 is lower than that of Example 1, and the linear thermal expansion coefficient is significantly higher than that of Example 1, indicating that the composite material prepared by this method is worse than that of Example 1 in terms of mechanical strength and dimensional stability. Although Comparative Example 4 shows a higher elongation at break, highlighting the role of the dispersed resin in toughening, its linear thermal expansion coefficient is high and its compressive properties are poor. Further comparison of the data of Example 1, Comparative Example 3, and Comparative Example 4 shows that Example 1 is significantly better than the single resin system in several key indicators, indicating that the dispersed resin and the suspension resin play a clear synergistic reinforcing role in the composite system. While toughening the composite material, the dispersed resin effectively fills the internal defects of the material, improving the density and structural integrity of the composite material. The suspension resin provides rigid support for the composite material, and the combined effect of the two significantly improves the comprehensive performance of the composite material.

[0067] Experiment Example 4 Samples from Example 1, Comparative Example 3, and Comparative Example 4 were taken respectively, and their compression ratio, resilience (test method for compression ratio and resilience of gaskets for pipe flanges GB / T 12622-2008) and compressive strength (determination of compressive properties of plastics GB / T1041-2008) were tested using the same method. The results are shown in Table 3: Table 3. Test results of material performance parameters for samples from Example 1, Comparative Examples 3 and 4

[0068] From the data in Table 3, we can see that: In addition to exhibiting significantly better tensile strength, elongation at break, and linear coefficient of thermal expansion compared to Comparative Examples 3 and 4, the composite material of Example 1 also demonstrated higher compressive strength and resilience, as well as a lower compression ratio. This further illustrates the clear synergistic reinforcing effect of the dispersion resin and suspension resin in the composite system. The dispersion resin effectively fills internal defects in the composite material while toughening it, improving its density and structural integrity. The suspension resin provides rigid support to the composite material, and the combined effect of both significantly improves the overall performance of the composite material.

[0069] In summary, the core-shell modified particles of this invention, when added to polytetrafluoroethylene (PTFE) suspension resin, not only significantly enhance the interfacial compatibility and interfacial bonding strength between the filler and the matrix, but also enable different fluoropolymers and PTFE suspension resins to exert synergistic effects. Ultimately, this greatly improves the mechanical properties of the prepared PTFE composite material structural components, broadening their application in high-end scenarios.

[0070] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A core-shell structure modified particle, characterized in that, It includes filler particles and a fluororesin shell coating the surface of the filler particles; the fluororesin shell and the filler particles are formed by physical adsorption.

2. The core-shell structure modified particle according to claim 1, characterized in that, The filler particles are selected from one or more of the following: silicon dioxide, carbon fiber, glass fiber, carbon black, graphite, carbon nanotubes, aluminum oxide, ceramic fiber, boron nitride, silicon carbide, molybdenum disulfide, and metal powder.

3. The core-shell structure modified particle according to claim 1, characterized in that, The fluororesin is selected from one or more of polytetrafluoroethylene, perfluoroethylene propylene, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer.

4. The method for preparing core-shell structure modified particles according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1 Preparation of pretreated filler particles: The filler particles and coupling agent are added to an alcohol-water solution and mixed uniformly for 4-8 hours. The mixture is then separated and dried to prepare the pretreated filler particles. S2 Preparation of core-shell structure modified particles: The pretreated filler particles are prepared into a dispersion and mixed with a fluororesin dispersion to form a mixed dispersion. The pH value of the mixed dispersion is adjusted to alkaline so that the pretreated filler particles and fluororesin particles are uniformly dispersed. The pH of the mixed dispersion was then adjusted to acidic, allowing the fluoropolymer particles to be physically adsorbed and coated on the surface of the pretreated filler particles. After separation and drying, the core-shell structure modified particles were obtained.

5. The method for preparing core-shell structure modified particles according to claim 4, characterized in that, In step S1, the method for preparing the pretreated filler particles includes the following steps: (1) Add 100 parts of filler particles to 800-1200 parts of ethanol by mass and disperse evenly to obtain a filler particle dispersion; (2) Mix 1.5 to 3 parts of coupling agent, 10 parts of deionized water and 80 to 90 parts of ethanol evenly; hydrolyze at 60℃ to 70℃ for 0.5 to 1.5 hours to obtain the coupling agent hydrolysate; (3) The coupling agent hydrolysate is added to the filler particle dispersion and reacted at 50℃~70℃ for 6~7h. After filtration, washing and drying, the pretreated filler particles are obtained.

6. The method for preparing core-shell structure modified particles according to claim 4, characterized in that, In step S2, the pretreated filler particles and water are prepared into a dispersion in a weight ratio of 1:4~5; the pretreated filler particle dispersion and the fluororesin dispersion are stirred and mixed at a speed of 100-150 r / min for 2~4 h.

7. The method for preparing core-shell structure modified particles according to claim 4, characterized in that, In step S2, the pretreated filler particles are prepared into a dispersion and mixed with the diluted fluororesin dispersion, and the pH value is adjusted to 8-10 to ensure that the pretreated filler particles and the fluororesin particles are fully dispersed; then the pH value is adjusted to 3-5 so that the fluororesin particles are physically adsorbed and coated on the surface of the pretreated filler particles to form the core-shell structure modified particles.

8. A polytetrafluoroethylene composite material, characterized in that, The raw materials include polytetrafluoroethylene suspension resin and core-shell structure modified particles as described in any one of claims 1 to 3 or core-shell structure modified particles prepared by the preparation method described in any one of claims 4 to 7; the polytetrafluoroethylene composite material is formed by blending the components in the raw materials.

9. A structural component, characterized in that, It is prepared from the polytetrafluoroethylene composite material according to claim 8.

10. The method for preparing the structural component according to claim 9, characterized in that, The process includes the following steps: placing the composite material in a mold and pressing it to obtain a preform; sintering the preform at 360-420℃ for 2-4 hours to obtain the structural component.

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