Amino-functionalized cubic mesoporous silica composite filler and modified fluororubber

Abstract

According to the amino-functionalized cubic mesoporous silica composite filler and the modified fluororubber provided by the invention, mesoporous silica with a highly ordered cubic morphology is controllably synthesized by adopting an improved sol-gel method assisted by normal hexane; the microstructure endows the material with an extremely high specific surface area, a uniform mesoporous aperture and a regular cubic topological structure; according to the KH550-CMS / FKM nano composite material finally prepared by the preparation method disclosed by the invention, the problems of insufficient mechanical strength and delayed thermal response of the fluororubber are effectively solved while excellent high temperature resistance, oil resistance and chemical stability of the fluororubber are maintained. According to the modified filler, the tensile strength of the material can be greatly improved by about 233.3%, and meanwhile, the thermal stability and the heat conduction rate of the material are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of fluororubber technology, specifically to an amino-functionalized cubic mesoporous silica composite filler and modified fluororubber. Background Technology

[0002] Fluororubber (FKM) is a special synthetic polymer elastomer containing fluorine atoms on its main chain or side chain carbon atoms. Thanks to the extremely high bond energy of the CF bonds (approximately 485 kJ / mol) in its molecular structure, FKM exhibits excellent high-temperature resistance, superior chemical stability, and aging resistance, making it an irreplaceable key sealing material in cutting-edge fields such as defense, aerospace, semiconductors, and petrochemicals. However, the weak intermolecular forces in pure fluororubber result in low mechanical strength and poor wear resistance, rendering it virtually useless in practical engineering applications without reinforcing fillers. Therefore, reinforcing fillers must be introduced to meet the mechanical performance requirements under harsh service environments.

[0003] Compared to traditional carbon black fillers limited by color and non-insulating properties, nano-silica (SiO2) has attracted much attention due to its excellent insulation, rich surface chemical properties, and tunable transparency. However, existing commercially available fumed or precipitated silica particles are mostly spherical or near-spherical. This spherical geometry results in point contact with the polymer matrix, limited interfacial contact area, and weak mechanical interlocking. Furthermore, the extremely high specific surface energy of nanoparticles makes them prone to self-aggregation in viscous fluororubber matrices, forming microscopic defects that severely limit further improvements in reinforcing efficiency. Traditional physical blending or simple surface modification alone cannot completely resolve the contradiction between filler agglomeration and weak interfacial bonding.

[0004] To overcome the limitations of traditional spherical packings, developing a packing with anisotropic morphology is an effective solution. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide an amino-functionalized cubic mesoporous silica composite filler and a modified fluororubber.

[0006] The technical solution adopted by this invention is as follows: The first aspect of this invention provides an amino-functionalized cubic mesoporous silica composite filler, the preparation method of which includes the following steps: S1. Add ammonia to the surfactant solution and stir until clear. Then add n-hexane and tetraethyl orthosilicate in sequence. Stir and react at 30-50℃ for 10-14h to obtain a colloidal suspension. Centrifuge, wash and dry to obtain a solid powder. Calcine the solid powder at 550-650℃ for 5-7h to obtain cubic mesoporous silica powder. S2. Disperse cubic mesoporous silica powder uniformly in a solvent, add an aminosilane coupling agent under a protective atmosphere, heat to 100-120℃ and react for 22-26 hours, centrifuge, filter, wash and dry to obtain amino-functionalized cubic mesoporous silica composite filler.

[0007] Preferably, in step S1, the concentration of the surfactant solution is 5-8 g / L, the concentration of the ammonia water is 20-35 wt%, and the volume ratio of the surfactant solution to the ammonia water is (20-25):1.

[0008] Preferably, in step S1, the volume ratio of the surfactant solution to n-hexane is (7-9):1.

[0009] Preferably, in step S1, the volume ratio of the surfactant solution to tetraethyl orthosilicate is (30-35):1.

[0010] Preferably, in step S1, the surfactant is hexadecyltrimethylammonium bromide.

[0011] Preferably, in step S2, the aminosilane coupling agent is KH550.

[0012] Preferably, in step S2, the mass-to-volume ratio of cubic mesoporous silica powder to aminosilane coupling agent is 0.8-1.2 g / mL.

[0013] A second aspect of the present invention provides a modified fluororubber, which is obtained by compounding an amino-functionalized cubic mesoporous silica composite filler as described above into a fluororubber.

[0014] Preferably, the mass ratio of the amino-functionalized cubic mesoporous silica composite filler to fluororubber is (5-12.5):100.

[0015] Preferably, the preparation method includes the following steps: (A) After thoroughly mixing fluororubber and amino-functionalized cubic mesoporous silica composite filler at 40-60℃, TAIC and bis(2,5-diphenyl) chloride are added sequentially and mixed evenly to form a homogeneous mixture; (B) The mixture is vulcanized at 150-190℃ for 5-15 minutes to obtain vulcanized fluororubber; (C) The vulcanized fluororubber is vulcanized in two stages at 180-220℃ for 10-14h to obtain modified fluororubber; The ratio of fluororubber, amino-functionalized cubic mesoporous silica composite filler, TAIC, and bis(2,5) is 100:(5-12.5):(1-3):(0.5-2).

[0016] The beneficial effects of this invention are as follows: 1. This invention employs a hexane-assisted modified sol-gel method to controllably synthesize mesoporous silica (CMS) with a highly ordered cubic morphology. This microstructure endows the material with an extremely high specific surface area, uniform mesopore size, and a regular cubic topology. Compared to traditional spherical or disordered silica, the regular pore structure of CMS facilitates the wetting of rubber molecular chains, and its cubic shape can produce a significant physical interlocking effect in the matrix, resulting in higher reinforcement efficiency. Further surface chemical grafting modification of CMS using γ-aminopropyltriethoxysilane (KH550) confirmed that KH550 is chemically anchored on the silica surface and within the pores through silicon-oxygen bonds (Si-O-Si). The active amino functional groups introduced at the end of KH550 play a key chemical coupling role: on the one hand, they significantly improve the dispersibility of inorganic fillers in hydrophobic fluororubber matrices and inhibit agglomeration; on the other hand, the amino groups can chemically react with fluororubber molecular chains or vulcanization systems to construct a stable interfacial crosslinking network, which significantly enhances the interfacial bonding force between the filler and the matrix.

[0017] 2. The KH550-CMS / FKM nanocomposite material finally prepared by this invention effectively solves the problems of insufficient mechanical strength and sluggish thermal response of fluororubber while maintaining its excellent high-temperature resistance, oil resistance, and chemical stability. Experimental results show that this modified filler can significantly improve the tensile strength of the material (by approximately 233.3%), while effectively improving the material's thermal stability and thermal conductivity. This invention provides structural design ideas and data support for the development of high-performance fluororubber sealing materials that operate under high temperature, high pressure, and dynamic conditions. Attached Figure Description

[0018] 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.

[0019] Figure 1 This is a schematic diagram of the preparation method of KH550-CMS composite packing. Figure 2 Flowchart for the preparation of FKM / KH550-CMS composite material; Figure 3 (a, b) SEM image of CMS, (c) TEM image of CMS, (d, e) SEM image of KH550-CMS, (f, g, k, l) EDS image of CMS, (hj, mo) EDS image of KH550-CMS. Figure 4The N2 adsorption-desorption isotherms and pore size distribution diagram for CMS; Figure 5 (a) XPS full spectrum and (b) infrared spectrum of CMS and KH550-CMS; Figure 6 (a) Stress-strain curves, (b) Tensile strength, (c) Elongation at break, and (d) Hardness of FKM / KH550-CMS composites prepared with different amounts of filler. Figure 7 SEM images of the fracture surfaces of FKM / KH550-CMS composites prepared with different amounts of filler; Figure 8 (a, c) Thermal infrared images of temperature rise and fall and (b, d) temperature rise and fall curves of FKM / KH550-CMS. Detailed Implementation

[0020] 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.

[0021] Example 1 like Figure 1 As shown in the figure, this embodiment provides a method for preparing KH550-CMS composite packing, and the specific steps are as follows: S1. Weigh 1.0 g of hexadecyltrimethylammonium bromide (CTAB) into a beaker, add 160 mL of deionized water, and stir magnetically until completely dissolved. Add 7.0 mL (28 wt%) of concentrated ammonia to the solution, and maintain stirring until a clear and transparent system is formed. Measure 20 mL of n-hexane and mix it evenly with the above solution. Add 5 mL of tetraethyl orthosilicate (TEOS) dropwise to the above aqueous system over 30 min. Place the reaction mixture in a 40°C water bath and stir continuously at 300 rpm for 12 h, during which time the system gradually changes from clear to a milky white colloidal suspension. After the reaction is terminated, collect the solid product by centrifugation and wash it repeatedly with deionized water and anhydrous ethanol alternately to remove residual reactants. Place the obtained white powder in a vacuum drying oven and dry overnight. Then transfer it to a tube furnace and calcine it at 600°C at 5°C / min under air atmosphere for 6 h to remove the organic template agent. After natural cooling, grind it for later use to obtain cubic mesoporous silica (CMS).

[0022] S2. Weigh 1.0 g of calcined CMS powder and disperse it in a three-necked flask containing 50 mL of anhydrous toluene. Sonicate for 30 min to ensure uniform particle dispersion. Under nitrogen protection and magnetic stirring, slowly add 1.0 mL of γ-aminopropyltriethoxysilane (KH550). After the addition is complete, heat to 110 °C and maintain reflux for 24 h to allow the coupling agent to fully bond with the hydroxyl groups on the silica surface. After the reaction, cool to room temperature and centrifuge to separate the solid product. Wash the product twice with anhydrous toluene to remove physically adsorbed silane monomers, and then wash twice with anhydrous ethanol to replace the solvent. Dry the product in an 80 °C vacuum oven for 12 h, and grind to obtain amino-functionalized cubic mesoporous silica (KH550-CMS).

[0023] Example 2 This embodiment provides an FKM / KH550-CMS composite material and its preparation method. The specific preparation steps are as follows: 100 parts by weight of fluororubber are placed inside a two-roll mill with a roll gap of 0.2 mm and a roll temperature of 50°C. After the fluororubber wraps around the rolls, 5 parts by weight of the composite filler KH550-CMS prepared in Example 1 are added and mixed evenly. The mixture is then rolled in a triangular shape 10 times to mix the filler and fluororubber evenly. Then, 1.75 parts by weight of TAIC and 1 part by weight of bis(2,5)-5 are added sequentially, and the mixture is rolled in a triangular shape repeatedly until it is evenly mixed. The roll gap is adjusted to 10 mm and the mixture is sheeted. A certain amount of the compound is vulcanized in a vacuum vulcanizing machine at 170°C and 15 MPa for 10 min. The mixture is demolded to obtain a square rubber sheet. Then, the pre-vulcanized rubber is placed in an oven at 200°C for two-stage vulcanization for 12 h. Finally, the FKM / KH550-CMS composite material is successfully prepared.

[0024] Example 3 The difference between this embodiment and Embodiment 2 is that 7.5 parts by weight of composite filler KH550-CMS are added.

[0025] Example 4 The difference between this embodiment and Embodiment 2 is that 10 parts by weight of the composite filler KH550-CMS are added.

[0026] Example 5 The difference between this embodiment and Embodiment 2 is that 12.5 parts by weight of composite filler KH550-CMS are added.

[0027] Comparative Example 1 The difference between this comparative example and Example 2 is that the composite filler KH550-CMS is not added.

[0028] Packing morphology characterization The surface morphology and microstructure of CMS before and after modification were compared using SEM and TEM. The results are as follows: Figure 3 As shown. By Figure 3 As shown in (a, b), CMS exhibits a regular cubic morphology with a smooth surface and distinct edges. It has good particle dispersion, uniform size, and an average side length of 400-600 nm. Figure 3 (c) The TEM image further reveals its internal microstructure, clearly showing highly ordered striped mesoporous channels arranged in parallel and running throughout the entire cube, confirming that CMS possesses a typical long-range ordered mesoporous structure. After KH550 grafting modification, the results are as follows... Figure 3 As shown in (d, e), KH550-CMS did not show significant changes in overall morphology and particle size, maintaining a complete cubic framework, indicating that the chemical modification process did not destroy the mesoporous structure of silica. Compared with the unmodified sample, KH550-CMS exhibited better dispersibility and a slightly rougher particle surface, attributed to the successful coating of organosilane molecular chains on the inorganic surface. This unique cubic mesoporous structure, combined with a high specific surface area, not only provides abundant physical anchoring points for fluororubber molecular chains, but also allows the active amino groups introduced by KH550 to form a chemical cross-linking network with the rubber matrix, thus significantly improving the mechanical properties of the composite material. Figure 3 As shown in (f, g, k, l), in the unmodified CMS sample, characteristic signals of silicon (Si) and oxygen (O) were mainly detected, and both exhibited a high-density, uniform distribution within the particle profile. This is consistent with the chemical composition of the silica framework, confirming the purity of the matrix. In contrast, for the KH550-CMS sample modified with KH550, as shown in (f, g, k, l), the characteristic signals of silicon (Si) and oxygen (O) were mainly detected, and both showed a high-density, uniform distribution within the particle profile. This is consistent with the chemical composition of the silica framework, confirming the purity of the matrix. Figure 3 As shown in (hj, mo), in addition to maintaining high-intensity Si and O elemental signals, the distribution signals of nitrogen (N) and carbon (C) elements were also clearly observed in the spectrum. Notably, the bright spots of N and C elements highly coincided with the cubic morphology of the particles and exhibited a uniform dispersion without obvious local agglomeration. Since the pure silica support does not contain nitrogen, this N signal originates solely from the amino group (-NH2) at the end of the silane coupling agent KH550 molecular chain. This result directly and strongly confirms that KH550 molecules have been successfully grafted onto the surface and pores of cubic mesoporous silica, achieving uniform surface amino functionalization coverage.

[0029] The specific surface area and pore structure of the synthesized cubic mesoporous silica (CMS) were characterized using nitrogen adsorption-desorption isotherms, and the results are as follows: Figure 4 As shown, the corresponding hole structure parameters are listed in Table 1. Figure 4It can be seen that the adsorption-desorption isotherm of CMS exhibits typical Type IV characteristics conforming to the classification standards of the International Union of Pure and Applied Chemistry (IUPAC), and a significant H1-type hysteresis loop appears in the relative pressure (P / P0) range of 0.4–0.8. The steep capillary condensation steps observed in the adsorption branch indicate that the material has a highly ordered cylindrical mesoporous channel structure with a uniform pore size distribution, which is consistent with the striped channel results observed in TEM tests. Combining the pore size distribution curve and the data in Table 2, it can be seen that the CMS sample has an extremely high specific surface area (1105.8 m² / g) and large pore volume (1.03 cm³ / g), with its most probable pore size concentrated at around 3.45 nm. This three-dimensional cubic mesoporous structure with a huge specific surface area not only provides abundant highly active reaction sites for subsequent surface grafting of the silane coupling agent KH550, ensuring a high grafting rate, but also its suitable mesoporous size facilitates the penetration of fluororubber molecular chains into the pores during the mixing process, laying a microstructural foundation for improving the mechanical properties of the composite material.

[0030] Table 1. Hole structure parameters of CMS.

[0031] Mechanical property analysis of fluororubber composites To investigate the effect of KH550-CMS addition on the mechanical properties of fluororubber composites, a universal testing machine was used to test the tensile strength, elongation at break, and hardness of composites with different formulations. The results are as follows: Figure 6 As shown, the tensile strength of the composite material initially increases and then decreases with increasing filler content. When 10 phr KH550-CMS filler was added, the tensile strength of the fluororubber reached a peak of 15.6 MPa, an increase of approximately 233.3% compared to pure FKM (4.8 MPa) without filler. Simultaneously, the Shore A hardness of the composite material significantly increased from 61 HA to 74 HA, while the elongation at break remained within a suitable processing range. This indicates that the unique cubic morphology and abundant amino functional groups on the surface of KH550-CMS construct effective physical anchoring points and chemical cross-linking networks in the matrix, thus exhibiting excellent reinforcing and toughening effects on the fluororubber.

[0032] Figure 7The SEM morphology of the tensile fracture surfaces of composite materials with different amounts of KH550-CMS is shown. The pure FKM sample without filler exhibits a relatively smooth and flat fracture surface with minimal undulation and river-like crack propagation striations. This indicates that during tensile fracture, crack propagation in the matrix encounters less resistance and follows a relatively straight path, resulting in less energy consumption during fracture. This is attributed to the low cohesive energy of the pure fluororubber matrix itself, explaining its lower tensile strength. In contrast, the composite material with 10 phr KH550-CMS modified filler exhibits a rougher fracture surface, displaying significant unevenness and numerous wrinkles. This rough fracture surface is due to the hard cubic mesoporous silica particles acting as stress concentration points and barrier layers within the matrix, forcing the crack to deflect, branch, or detour during propagation, thus significantly increasing the crack propagation path length and consuming more fracture energy. Furthermore, almost no pores left by filler detachment were observed on the cross-section, indicating that a stable interfacial bond was formed between the modified cubic particles and the fluororubber matrix. This strong interfacial interaction, combined with the mechanical interlocking effect brought about by the cubic morphology, effectively promotes the transfer of stress between the two phases, which is conducive to a significant improvement in material strength. This is highly consistent with the data on the significant increase in strength shown in the tensile property tests mentioned above.

[0033] Thermal property analysis of fluororubber composites To investigate the effects of KH550-CMS on the thermal conductivity and thermal response properties of fluororubber composites, infrared thermal imaging was used to record the surface temperature changes of pure FKM and composites with different filler contents during heating and cooling processes. The results are as follows: Figure 8 As shown. By Figure 8 Infrared thermal image of a and Figure 8 The temperature-time curves (b) show that pure FKM exhibits significant thermal inertia during heating, with a relatively slow heating rate; after 100 seconds of heating, the surface temperature only reaches approximately 83°C. In contrast, the composite material with KH550-CMS filler exhibits a more sensitive thermal response. With increasing filler content, the slope of the composite material's heating curve gradually increases, indicating a significantly faster heating rate. Particularly when the filler content reaches 10 phr and 12.5 phr, the surface temperature of the sample exceeds 105°C within 100 seconds, significantly higher than that of the pure rubber matrix. This trend is also confirmed during the cooling process. Figure 8 As shown in c and 8d, during the natural cooling phase after the heat source is removed, the heat dissipation of pure FKM is slow, and the temperature drop is significantly delayed; while the composite material with added KH550-CMS can dissipate the accumulated heat to the environment more quickly, and the cooling rate is significantly better than that of pure FKM.

[0034] The improved thermal response performance of the composite material is mainly attributed to the construction of a highly efficient thermally conductive network. On one hand, cubic mesoporous silica (CMS) itself has a higher intrinsic thermal conductivity than the rubber matrix; on the other hand, the chemical grafting of KH550 effectively improves the interfacial bonding between the inorganic filler and the organic matrix, significantly reducing the thermal resistance (phonon scattering) at the interface, allowing heat to be rapidly transferred along the uniformly dispersed cubic skeleton. This rapid thermal response characteristic is crucial for preventing aging failure of seals due to heat accumulation under dynamic operating conditions.

[0035] 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. An amino-functionalized cubic mesoporous silica composite filler, characterized in that, Its preparation method includes the following steps: S1. Add ammonia to the surfactant solution and stir until clear. Then add n-hexane and tetraethyl orthosilicate in sequence. Stir and react at 30-50℃ for 10-14h to obtain a colloidal suspension. Centrifuge, wash and dry to obtain a solid powder. Calcine the solid powder at 550-650℃ for 5-7h to obtain cubic mesoporous silica powder. S2. Disperse cubic mesoporous silica powder uniformly in a solvent, add an aminosilane coupling agent under a protective atmosphere, heat to 100-120℃ and react for 22-26 hours, centrifuge, filter, wash and dry to obtain amino-functionalized cubic mesoporous silica composite filler.

2. The amino-functionalized cubic mesoporous silica composite filler according to claim 1, characterized in that: In step S1, the concentration of the surfactant solution is 5-8 g / L, the concentration of the ammonia water is 20-35 wt%, and the volume ratio of the surfactant solution to the ammonia water is (20-25):

1.

3. The amino-functionalized cubic mesoporous silica composite filler according to claim 2, characterized in that: In step S1, the volume ratio of the surfactant solution to n-hexane is (7-9):

1.

4. The amino-functionalized cubic mesoporous silica composite filler according to claim 2, characterized in that: In step S1, the volume ratio of the surfactant solution to tetraethyl orthosilicate is (30-35):

1.

5. The amino-functionalized cubic mesoporous silica composite filler according to claim 1, characterized in that: In step S1, the surfactant is hexadecyltrimethylammonium bromide.

6. The amino-functionalized cubic mesoporous silica composite filler according to claim 1, characterized in that: In step S2, the aminosilane coupling agent is KH550.

7. The amino-functionalized cubic mesoporous silica composite filler according to claim 1, characterized in that: In step S2, the mass-to-volume ratio of cubic mesoporous silica powder to aminosilane coupling agent is 0.8-1.2 g / mL.

8. A modified fluororubber, characterized in that: It is obtained by compounding the amino-functionalized cubic mesoporous silica composite filler as described in any one of claims 1-7 into fluororubber.

9. A modified fluororubber according to claim 8, characterized in that: The mass ratio of the amino-functionalized cubic mesoporous silica composite filler to fluororubber is (5-12.5):

100.

10. A modified fluororubber according to claim 8, characterized in that, Its preparation method includes the following steps: (A) After thoroughly mixing fluororubber and amino-functionalized cubic mesoporous silica composite filler at 40-60℃, TAIC and bis(2,5-diphenyl) chloride are added sequentially and mixed evenly to form a homogeneous mixture; (B) The mixture is vulcanized at 150-190℃ for 5-15 minutes to obtain vulcanized fluororubber; (C) The vulcanized fluororubber is vulcanized in two stages at 180-220℃ for 10-14h to obtain modified fluororubber; The ratio of fluororubber, amino-functionalized cubic mesoporous silica composite filler, TAIC, and bis(2,5) is 100:(5-12.5):(1-3):(0.5-2).

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