Fluororubber-ethylene propylene diene monomer compatilizer and application thereof

Abstract

The invention relates to the technical field of rubber modification, in particular to a fluororubber-ethylene propylene diene monomer compatilizer and application. Silica (DMSN) with a dendritic mesoporous structure is synthesized and can be physically located at a two-phase interface, the effects of anchoring and reinforcing the phase interface are achieved, the size of a phase region is prevented from being too large, and therefore the compatibility is preliminarily improved. PFTS is further used for carrying out surface grafting modification on DMSN, PFTS is grafted to the surface of silicon dioxide through Si-O-Si, the compatibility of a perfluoro long chain at the other end and an FKM phase is good, and the interface bonding force between the filler and a rubber matrix is remarkably enhanced. The finally obtained composite material not only has the inherent high temperature resistance, oil resistance and chemical resistance of FKM, but also improves the low temperature resistance due to the introduction of EPDM, and greatly enhances the mechanical strength and toughness due to the enhancement of PFTS-DMSN.

Description

Technical Field

[0001] This invention relates to the field of rubber modification technology, specifically to a fluororubber-EPDM rubber compatibilizer and its application. Background Technology

[0002] Fluororubber is a special synthetic elastomer containing fluorine atoms in its main chain or side chains. Its excellent high-temperature resistance (long-term operation above 200°C), superior fuel resistance, and excellent resistance to most organic solvents and strong acids make it a preferred material in high-end sealing applications, widely used in the automotive, aerospace, petrochemical, and semiconductor industries. However, due to its glass transition temperature (Tg) of approximately -18°C, fluororubber faces limitations in high-latitude, cold regions. To address these limitations, the industry has developed specialty categories such as low-temperature resistant types (improved by introducing tetrafluoropropylene or perfluoroether monomers) and perfluoroether rubber (FFKM) (offering near-absolute chemical resistance and even higher temperature resistance, but at an extremely high cost). Therefore, the application of fluororubber is a process of seeking the optimal balance between extreme performance, environmental conditions, and cost control.

[0003] In stark contrast to FKM, ethylene propylene diene monomer (EPDM) rubber is renowned for its superior low-temperature performance. Due to its main chain being composed of saturated hydrocarbons, its chemical structure is highly stable, and its molecular chains are flexible, resulting in an extremely low glass transition temperature, typically -50°C or even lower. In such frigid environments, EPDM maintains good elasticity and flexibility, resisting hardening and embrittlement, making it ideal for seals in cold regions or refrigerated equipment. However, this structure also results in relatively poor mechanical properties for EPDM. Its molecular chains lack active groups, leading to generally lower tensile strength, tear resistance, and abrasion resistance compared to most general-purpose or specialty rubbers (such as fluororubber). Both FKM and EPDM may not fully meet the diverse requirements of various applications, particularly in terms of low-temperature resistance and high strength.

[0004] Due to the significant difference in molecular polarity, FKM and EPDM exhibit extremely poor compatibility. FKM is a highly polar rubber, while EPDM is a non-polar rubber; they are thermodynamically immiscible, and direct blending leads to phase separation, forming a clear phase interface that severely degrades the mechanical properties of the blend, rendering the blend unusable in practical applications. To overcome this challenge and achieve effective blending modification, compatibilizers must be used, such as maleic anhydride-grafted EPDM-g-MAH. However, EPDM-g-MAH has a low grafting rate, and the polar groups in EPDM-g-MAH are still not highly polar, resulting in insufficient improvement in the compatibility of the blend. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a fluororubber-EPDM rubber compatibilizer and its application.

[0006] The technical solution adopted in this invention is as follows: a fluororubber-ethylene propylene diene monomer (EPDM) rubber compatibilizer, comprising silica nanoparticles with a dendritic mesoporous structure, wherein the silica nanoparticles with a dendritic mesoporous structure are grafted and modified with perfluorodecyltriethoxysilane.

[0007] Preferably, the preparation process of the silica nanoparticles with dendritic mesoporous structure includes the following steps: using triethanolamine as a catalyst, and using cationic surfactant CTAB and sodium salicylate as structure directing agents, hydrolyzing and condensing tetraethyl orthosilicate to prepare silica nanoparticles with dendritic mesoporous structure.

[0008] Preferably, the perfluorodecyltriethoxysilane is connected to silica nanoparticles with a dendritic mesoporous structure via Si-O-Si chemical bonds.

[0009] Preferably, silica nanoparticles with a dendritic mesoporous structure are dispersed in a mixture of anhydrous ethanol and deionized water, the pH is adjusted to acidic, and then PFTS is added to react chemically with the silanol groups on the silica surface, so that PFTS is grafted onto the silica surface through chemical bonds.

[0010] Preferably, the reaction system of PFTS and silica is reacted at 60-80°C for 3-5 hours.

[0011] The fluororubber-EPDM compatibilizer described above is used in the preparation of low-temperature resistant rubber composites.

[0012] A low-temperature resistant rubber composite material includes: fluororubber, EPDM rubber, and the fluororubber-EPDM rubber compatibilizer as described above.

[0013] Preferably, the mass ratio of fluororubber, EPDM rubber, and the fluororubber-EPDM rubber compatibilizer as described in any one of claims 1-5 is 60-80:20-40:1-10.

[0014] Preferably, it includes the following steps: (1) Mix two types of raw rubber, fluororubber and EPDM rubber; (2) Add the fluororubber-EPDM compatibilizer as described in any one of claims 1-5, and mix evenly; (3) Add vulcanizing agent and vulcanizing agent, mix evenly to obtain compound rubber; (4) Place the compounded rubber on a vacuum vulcanizing machine to vulcanize it and obtain pre-vulcanized rubber; (5) Place the pre-cured rubber into the oven for two-stage curing.

[0015] Preferably, the co-curing agent is TAIC, and the curing agent is 2,5-dimethyl-2,5-dihexane.

[0016] The beneficial effects of this invention are as follows: 1. This invention synthesizes silica (DMSN) with a dendritic mesoporous structure. This structure possesses an extremely high specific surface area, abundant pores, and a radially oriented pore structure. This invention has found that adding the synthesized silica (DMSN) with a dendritic mesoporous structure to a blend of fluororubber and ethylene propylene diene monomer (FKM / EPDM) can significantly reduce the glass transition temperature of FKM, reaching -25.68°C in some embodiments of this invention. 2. This invention further utilizes perfluorodecyltriethoxysilane (PFTS) to perform surface grafting modification on DMSN, obtaining a novel filler (PFTS-DMSN). Adding the novel filler (PFTS-DMSN) synthesized in this invention to a blend of fluororubber and ethylene propylene diene monomer (FKM / EPDM) further reduces the glass transition temperature of the composite material FKM / EPDM / PFTS-DMSN. In some embodiments of this invention, the glass transition temperature can reach -28.49℃, while significantly improving the low-temperature resistance of the fluororubber composite material. 3. In some embodiments of the present invention, the tensile strength of FKM / EPDM with 5 phr PTFS-DMSN filler was further improved, increasing by about 45% compared with unmodified FKM / EPDM, while the elongation at break was only slightly reduced, still maintaining 95% of the original value. This indicates that while improving the low-temperature resistance of the composite material, the strength and toughness of the composite material are not affected. 4. Nanoscale silica particles with a dendritic mesoporous structure can physically reside at the interface between two phases, acting as "anchors" and "reinforces" the interface, preventing excessively large phase sizes and thus initially improving compatibility. PFTS has a very special molecular structure. One end (ethoxy group) can hydrolyze during processing and chemically react with the silanol groups (-Si-OH) on the silica surface to form a strong chemical bond. The other end (perfluorooctyl group) is similar to and compatible with the molecular structure of FKM, exhibiting good compatibility with the FKM phase and forming a "bridging" effect. This ensures that one end of the modified silica particle is firmly chemically bonded to the FKM phase. This modified silica particle with a "fluororubber tail" is redistributed at the interface between the two phases, with its fluoride-loving end embedded in the FKM phase, while the inorganic particle body is physically blocked at the interface. This greatly reduces the interfacial energy, enhances the interfacial adhesion, and blurs the originally clear and sharp phase interface, effectively promoting the compatibility of FKM and EPDM, and ultimately obtaining a blend material with a delicate phase and significantly improved mechanical properties. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0018] Figure 1 Schematic diagram of PFTS-DMSN fabrication; Figure 2 Schematic diagram of FKM / EPDM / PFTS-DMSN preparation; Figure 3 (a, b) SEM and TEM images of DMSN; (c, d) SEM and TEM images of PFTS-DMSN; Figure 4 (a) EDS plot of DMSN, (b) EDS plot of PFTS-DMSN; Figure 5 (a) Infrared spectra of DMSN and PFTS-DMSN; XPS spectra of DMSN and PFTS-DMSN (b) full spectrum, (c) F 1s, (d) O 1s, (e) Si 2p; Figure 6 Tensile strength and elongation at break of different composite materials; Figure 7 SEM images of cross sections of different composite materials: (a, d) FKM / EPDM, (b, e) FKM / EPDM / DMSN, (c, f) FKM / EPDM / PFTS-DMSN; Figure 8 DMA diagrams for different composite materials: (a) storage modulus (E'), (b) loss modulus (E"), (c) loss factor (tan δ); Figure 9 DSC and low-temperature compression set of different composite materials: (a) DSC, (b) low-temperature compression set. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] Example 1: Preparation of silica (DMSN) with a dendritic mesoporous structure: like Figure 1As shown, this embodiment uses an anion-assisted template method, with triethanolamine (TEA) as a catalyst and cationic surfactant CTAB and sodium salicylate (NaSal) as structure directing agents, to prepare DMSN by hydrolysis and condensation of tetraethyl orthosilicate (TEOS).

[0021] The specific process is as follows: First, 0.068 g of TEA was mixed with 25 ml of deionized water, and the mixture was stirred in an 80°C water bath for 30 min. Then, 0.38 g of CTAB and 0.168 g of NaSal were added, and the mixture was heated and stirred for another 2 h. Next, 4 ml of TEOS was added dropwise to the mixture, and the mixture was heated and stirred for another 6 h. After the reaction was complete, the centrifuged solid was washed three times with anhydrous ethanol and water, respectively. Finally, the white solid was calcined at 600°C for 6 h to remove the template agent, yielding DMSN. The obtained blocky DMSN was then ground into powder.

[0022] Example 2 Preparation of modified dendritic mesoporous silica (PFTS-DMSN) modified with perfluorodecyltriethoxysilane (PFTS): like Figure 1 As shown, in this embodiment, perfluorooctyltriethoxysilane (PFTS) is further grafted onto the surface of the DMSN prepared in Example 1 to prepare a novel filler-modified dendritic mesoporous silica (PFTS-DMSN).

[0023] The specific process is as follows: A certain amount of DMSN was dispersed in a mixture of anhydrous ethanol and deionized water, and then PFTS (10% by weight of DMSN) was added. The pH of the mixture was adjusted to 3 using 0.1 mol of dilute hydrochloric acid. The prepared solution was stirred in a water bath at 70°C for 4 hours. After the reaction was completed, the centrifuged solid was washed three times with anhydrous ethanol and water, and then dried under vacuum at 80°C for 12 hours to obtain PFTS-DMSN.

[0024] Example 3: Preparation of composite material FKM / EPDM / PFTS-DMSN: According to the formulations of different composite materials in Table 1, calculate and weigh the corresponding contents of fluororubber, EPDM rubber, different fillers, TAIC, and 2,5-dimethyl-2,5-dihexane. Add raw FKM rubber to a two-roll mill with a roll gap of 0.2 mm and a roll temperature of 50 ℃. After the FKM raw rubber wraps around the rolls, add 25 parts of EPDM raw rubber, repeating the triangular wrapping process 10 times to mix the two raw rubbers evenly. Then, add 5 parts of different fillers and mix evenly. Next, add the vulcanizing agent TAIC and the vulcanizing agent 2,5-dimethyl-2,5-dihexane sequentially, repeating the triangular wrapping process until evenly mixed. Adjust the roll gap to 10 mm and sheet out. Take a certain amount of the compound and vulcanize it for 10 min in a vacuum vulcanizing machine at 180 ℃ and 15 MPa. Demold to obtain square rubber sheets. Then, place the pre-vulcanized rubber in an oven at 160 ℃ for a second-stage vulcanization for 12 h. The entire manufacturing process is described as follows: Figure 2 As shown.

[0025] Table 1 Raw material composition of different composite material samples 1. Morphological characterization and elemental analysis of DMSN before and after modification: The surface morphology and microstructure of DMSN before and after modification were compared using SEM and TEM. The results are as follows: Figure 3 As shown. By Figure 3 (a, c) show that DMSN has a mesoporous spherical structure before and after modification, with uniform spherical size and a particle size of approximately 200 nm. After PFTS grafting modification, DMSN is not significantly affected in terms of morphology and particle size, and its dispersibility is better. This structure has a large specific surface area and roughness, which can provide more crosslinking sites for fluororubber and EPDM rubber, and form a crosslinking network with fluororubber and EPDM rubber molecules, thereby improving the mechanical properties of the composite material.

[0026] Figure 3 Results (b, d) show that DMSN exhibits a honeycomb morphology before and after modification, with an internal dendritic tunnel pore structure, confirming that DMSN is dendritic mesoporous silica and that its morphology remains dendritic mesoporous even after PFTS grafting modification. Elemental composition analysis of DMSN before and after modification was performed using energy dispersive spectroscopy (EDS), and the results are as follows: Figure 4 As shown in (a, b), a uniform distribution of Si and O elements can be observed, further confirming that DMSN is a silicon dioxide material. Meanwhile, from Figure 4 (b) It can be seen that PFTS was successfully grafted onto DMSN.

[0027] 2. FTIR and XPS analysis before and after DMSN modification: The DMSN and PFTS-DMSN were characterized using Fourier transform infrared spectroscopy. Figure 5As shown in (a), the broad absorption peak at 3435 cm⁻¹ corresponds to the Si-OH groups on the surface of SiO₂ nanoparticles. Compared to DMSN, the Si-OH content of PFTS-DMSN is significantly reduced. Compared to DMSN, the spectrum of PFTS-DMSN shows a peak near 1166 cm⁻¹, representing the stretching vibration of PFTS, and is covered by a very strong Si-O-Si absorption peak.

[0028] PFTS-DMSN has two characteristic peaks at binding energies of 103.28 eV and 103.98 eV, corresponding to O-Si-C and Si-O-Si, respectively. Figure 5 The O 1s spectrum in (d) has two peaks at 532.68 and 533.18 eV, which are attributed to the Si-O-Si of SiO2 and the O-Si of PFTS. Furthermore, Figure 5 (c) The peaks at 688.88 eV and 684.88 eV indicate the presence of -CF2-CF2- and -CH2-CF2- groups, confirming that PFTS is grafted onto the surface of SiO2 nanoparticles via chemical bonds.

[0029] 3. Mechanical property analysis: To investigate the effect of DMSN modification on the tensile properties of FKM / EPDM composites, a universal tensile testing machine was used to test the tensile strength and elongation at break of the composites. The results are as follows: Figure 6 As shown, the tensile strength of fluororubber with 5 phr DMSN filler increased, by approximately 25% compared to unfilled FKM / EPDM. Furthermore, the tensile strength of the FKM / EPDM composite material with 5 phr PTFS-modified DMSN filler was further improved, increasing by approximately 45% compared to unfilled FKM / EPDM, while the elongation at break only decreased slightly, remaining at 95% of its original value. This demonstrates that PFTS-DMSN exhibits excellent strengthening and toughening effects.

[0030] Figure 7 The images show the SEM images of the tensile fracture surfaces of different composite materials. The fracture process of the unfilled sample consumes more energy, indicating that fluororubber is the continuous phase, while EPDM is the discontinuous phase; this phase separation is detrimental to the material's strength. However, the addition of DMSN and PTFS-DMSN results in a rougher fracture surface and a slight decrease in toughness. The two phases of rubber molecules are less distinct on the fracture surface, which is beneficial for strength improvement, consistent with the tensile property data mentioned above.

[0031] 4. Dynamic thermomechanical property analysis: Dynamic mechanical analysis (DMA) is a testing technique that measures the changes in mechanical responses, such as stress, strain, and modulus, of materials as a function of temperature, time, and frequency by applying periodic dynamic loads. It is primarily used to characterize the viscoelastic behavior of materials. Specifically: Storage modulus (E') reflects a material's ability to store elastic deformation energy, thus demonstrating the strength of the material's "elasticity." Loss modulus (E''): Reflects the energy lost by a material due to viscous deformation, and embodies the strength of the material's "viscosity"; Loss factor (tanδ): The ratio of E'' to E', representing the proportion of energy loss to energy storage, is a key indicator for measuring the viscoelastic balance of a material (the larger the tanδ, the more significant the viscosity).

[0032] This experiment measured the mechanical response of the sample at different temperatures, and the results are as follows: Figure 8 As shown. By Figure 8 (a) It can be seen that the modified composite material has a higher storage modulus. The nanofiller alters the low-temperature rigidity of the material, resulting in stronger fracture resistance in the range of -60℃ to -10℃. The increased storage modulus (E') in the low-temperature region makes it better suited for low-temperature environments, providing better rigidity and reducing the likelihood of fracture. Figure 8 (b) shows that the modified composite material has a higher loss modulus, and the peak value of the curve corresponds to the temperature of maximum loss. The higher the peak value, the greater the viscous internal loss, and the closer the material is to viscous flow. Figure 8 (c) It can be seen that the modified composite material has a higher loss factor and a lower glass transition temperature.

[0033] 5. Low-temperature performance analysis The glass transition temperature of the sample was determined using differential scanning calorimetry (DSC). When a polymer undergoes a glass transition, its heat capacity changes abruptly from a glassy state to a rubbery state, increasing the material's heat capacity. On the DSC curve, this abrupt change in heat capacity manifests as a "sudden shift in the baseline," forming a step-like change.

[0034] The DSC test results of the three composite materials are as follows Figure 9 As shown in (a), the addition of DMSN significantly reduces the glass transition temperature of the composite material (-25.68℃). After modification with PFTS, the glass transition temperature is further reduced to -28.49℃, which significantly improves the low-temperature resistance of the fluororubber composite material.

[0035] Figure 9(b) The low-temperature permanent compressive deformation rate of the three different composite materials at -40℃. As shown in the figure, the permanent compressive deformation of the two composite materials significantly decreased compared to FKM / EPDM after the addition of DMSN and PTFS-DMSN. The FKM / EPDM / PTFS-DMSN composite material exhibited the lowest low-temperature compressive deformation rate at 7.54%. In summary, this invention synthesizes a dendritic mesoporous silica (DMSN). This structure possesses an extremely high specific surface area, abundant pores, and radially oriented pore structure. Compared to traditional silica, it provides more active sites, exhibits stronger interactions with rubber molecules, and theoretically offers higher reinforcement efficiency. Further surface grafting modification of DMSN is achieved using perfluorodecyltriethoxysilane (PFTS), a fluorinated silane. PFTS is grafted onto the silica surface via chemical bonds (Si-O-Si), while its long perfluorinated chain at the other end can physically entangle with the FKM molecular chain and even potentially chemically interact, significantly enhancing the interfacial adhesion between the filler and the rubber matrix. The resulting FKM / EPDM / PFTS-DMSN composite material not only possesses the inherent high-temperature resistance, oil resistance, and chemical resistance of FKM, but also exhibits improved low-temperature resistance due to the introduction of EPDM, and significantly enhanced mechanical strength and toughness due to the reinforcement of PFTS-DMSN.

[0036] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A fluororubber-EPDM rubber compatibilizer, characterized in that: It includes silica nanoparticles with a dendritic mesoporous structure, wherein the silica nanoparticles with the dendritic mesoporous structure are grafted and modified with perfluorodecyltriethoxysilane.

2. The fluororubber-EPDM rubber compatibilizer according to claim 1, characterized in that: The preparation process of the silica nanoparticles with dendritic mesoporous structure includes the following steps: using triethanolamine as a catalyst, and using cationic surfactant CTAB and sodium salicylate as structure directing agents, the silica nanoparticles with dendritic mesoporous structure are prepared by hydrolysis and condensation of tetraethyl orthosilicate.

3. The fluororubber-EPDM rubber compatibilizer according to claim 1, characterized in that: The perfluorodecyltriethoxysilane is connected to silica nanoparticles with a dendritic mesoporous structure via Si-O-Si chemical bonds.

4. The fluororubber-EPDM rubber compatibilizer according to claim 3, characterized in that: Silica nanoparticles with a dendritic mesoporous structure were dispersed in a mixture of anhydrous ethanol and deionized water, the pH was adjusted to acidic, and then PFTS was added to react chemically with the silanol groups on the silica surface, allowing PFTS to be grafted onto the silica surface through chemical bonds.

5. The fluororubber-EPDM rubber compatibilizer according to claim 4, characterized in that: The reaction system of PFTS and silica was carried out at 60-80℃ for 3-5 hours.

6. The application of the fluororubber-EPDM compatibilizer as described in any one of claims 1-5 in the preparation of low-temperature resistant rubber composite materials.

7. A low-temperature resistant rubber composite material, characterized in that, include: Fluororubber, EPDM rubber, and the fluororubber-EPDM rubber compatibilizer as described in any one of claims 1-5.

8. The low-temperature resistant rubber composite material according to claim 7, characterized in that: The mass ratio of fluororubber, EPDM rubber, and the fluororubber-EPDM rubber compatibilizer as described in any one of claims 1-5 is 60-80:20-40:1-10.

9. The preparation process of the low-temperature resistant rubber composite material according to claim 7, characterized in that, Includes the following steps: (1) Mix two types of raw rubber, fluororubber and EPDM rubber; (2) Add the fluororubber-EPDM compatibilizer as described in any one of claims 1-5, and mix evenly; (3) Add vulcanizing agent and vulcanizing agent, mix evenly to obtain compound rubber; (4) Place the compounded rubber on a vacuum vulcanizing machine to vulcanize it and obtain pre-vulcanized rubber; (5) Place the pre-cured rubber into the oven for two-stage curing.

10. The preparation process of the low-temperature resistant rubber composite material according to claim 9, characterized in that: The co-curing agent used is TAIC, and the curing agent is 2,5-dimethyl-2,5-dihexane.

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