A functionalized linear polycarbosilane modified vinyl silicone rubber composite material, and a preparation method and application thereof

Abstract

The application provides a kind of functional linear polycarbosilane modified vinyl silicone rubber composite material and its preparation method and application, belong to the field of ablation heat protection.The composite material includes the following weight parts of raw materials: ethoxy modified polycarbosilane 3~15 parts, vinyl silicone rubber 100 parts, functional filler 5~80 parts, crosslinking agent 0.5~10 parts.The application uses functional linear polycarbosilane to modify solid vinyl silicone rubber, and the chemical bond connection between the filler and the silicone rubber matrix is established by the condensation reaction between the hydroxyl structure of ethoxy and hydrophilic silicon dioxide.The introduction of ethoxy modified polycarbosilane improves the crosslinking density and rigidity of the composite material, significantly improves the overall heat protection performance of the composite material, especially significantly improves the ablation resistance of the composite material in high heat flow environment, so that the composite material has excellent mechanical properties and ablation resistance, and has good application prospect in the field of ablation heat protection.

Description

Technical Field

[0001] This invention relates to the field of advanced materials, specifically to a functionalized linear polycarbosilane-modified vinyl silicone rubber composite material, its preparation method, and its application. Background Technology

[0002] With the rapid development of hypersonic vehicles, reusable launch vehicles, and interplanetary reentry exploration technologies, the aerodynamic and thermal environments faced by these vehicles are becoming increasingly extreme and complex. Intense aerodynamic heating, strong thermo-coupling effects, and complex structural deformations place unprecedentedly stringent demands on thermal protection systems (TPS). Traditional rigid ablation thermal protection materials, such as carbon-phenolic resin-based composites, while relatively mature after years of development, suffer from inherent brittleness leading to poor impact resistance, susceptibility to microcracks, and difficulty in coordinating deformation with flexible load-bearing structures under thermal stress. These have become key technological bottlenecks restricting the performance and reliability of new vehicles. Therefore, developing a new type of flexible ablation thermal protection material that combines highly efficient thermal insulation and ablation performance with macroscopic flexibility is of great strategic significance to my country's aerospace technology development. This type of material can effectively adapt to structural deformation and release thermal stress through its own deformation, while maintaining the integrity and stability of the thermal protection layer. It plays a crucial role in ensuring the structural safety of vehicles under extreme thermal loads and extending their service life.

[0003] Against this backdrop, silicone rubber, with its unique materials science properties, has become an ideal matrix choice for developing a new generation of flexible ablation thermal protection materials. Its molecular backbone combines the high bond energy of inorganic -SO- bonds with the flexibility of organic side groups, endowing the material with excellent thermal stability and high elasticity over a wide temperature range, enabling it to maintain structural integrity without brittleness under extreme thermal shock. During high-temperature ablation, silicone rubber does not simply decompose, but rather undergoes a series of complex physicochemical changes to generate a porous silica-based ceramic residue layer in situ. This ceramic layer firmly adheres to the undecomposed matrix, effectively blocking heat transfer to the interior and resisting the erosion of high-speed airflow, achieving a highly efficient synergy between active heat dissipation and passive thermal insulation. Simultaneously, its inherent molecular flexibility gives the prepared composite material excellent macroscopic flexibility and fatigue resistance, perfectly adapting to deformations caused by complex aircraft structures and aerodynamic loads, releasing thermal stress, and thus overcoming the fundamental drawbacks of traditional rigid thermal protection materials, such as easy cracking and detachment. Therefore, developing high-performance flexible ablation materials based on silicone rubber is one of the most promising technical approaches to meet the stringent requirements of future aerospace vehicle thermal protection systems.

[0004] However, the ceramic layer formed by pure silicone rubber under prolonged exposure to extreme heat has limited strength and insufficient erosion resistance. To significantly improve its ablation performance, the introduction of ceramic precursors, such as polycarbosilane (PCS), has become an effective modification method (Ding W, Yan L, Huang M, et al. Polymer, 2023, 285: 126319. Long L, Cai Y, Chi X, et al. PolymDegrad Stab, 2024, 225: 110775). These precursors can be converted into high-performance ceramic phases such as SiC and SiOC at high temperatures, which can co-construct a denser, stronger, and more erosion-resistant multiphase ceramic barrier layer with the silica produced by the pyrolysis of the matrix. This greatly enhances the material's resistance to extreme aerodynamic-thermal coupling ablation, thereby achieving long-term thermal insulation protection. However, in polycarbosilane-modified silicone rubber systems, the compatibility between polycarbosilane and other functional fillers, as well as the solid silicone rubber matrix, is poor, resulting in weak interfacial bonding forces. Consequently, the ablation resistance of the resulting silicone rubber composite material cannot meet the requirements for use under extreme heat flux environments. Liquid silicone rubber exhibits better compatibility with modifiers, and some researchers have chosen liquid silicone rubber as a modifying matrix; however, its inherently lower mechanical properties limit its use under extreme heat flux environments.

[0005] To address the aforementioned issues, this study prepared a functionalized linear polycarbosilane-modified solid vinyl silicone rubber composite material. The condensation reaction between ethoxy groups and hydrophilic silica effectively improved the interfacial bonding between fillers. The introduction of the polycarbosilane structure also enhanced the material's ceramization ability during ablation, forming a dense and complete carbon layer. The study shows that the functionalized linear polycarbosilane-modified vinyl silicone rubber composite material possesses excellent mechanical properties and ablation thermal resistance, demonstrating significant application potential in high heat flux environments and applications requiring dynamic deformation. Summary of the Invention

[0006] The purpose of this invention is to provide a functionalized linear polycarbosilane modified vinyl silicone rubber composite material, its preparation method, and its application.

[0007] This invention provides a functionalized linear polycarbosilane-modified vinyl silicone rubber composite material, comprising the following raw materials in parts by weight: 3-15 parts of ethoxylated modified polycarbosilane, 100 parts of vinyl silicone rubber, 5-80 parts of functional filler, and 0.5-10 parts of crosslinking agent.

[0008] Furthermore, the functionalized linear polycarbosilane-modified vinyl silicone rubber composite material comprises the following raw materials in parts by weight: 7-11 parts of ethoxylated modified polycarbosilane, 100 parts of vinyl silicone rubber, 10-45 parts of functional filler, and 0.5-2 parts of crosslinking agent.

[0009] Furthermore, the vinyl silicone rubber is a solid silicone rubber.

[0010] Further, the vinyl silicone rubber is selected from at least one of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, and methyl vinyl trifluoropropyl silicone rubber; the functional filler is silica, carbon fiber, or a mixture of silica and carbon fiber; the crosslinking agent is a peroxide crosslinking agent, preferably at least one of dicumyl peroxide, tert-butyl peroxide, benzoyl peroxide, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0011] Furthermore, the functionalized linear polycarbosilane-modified vinyl silicone rubber composite material comprises the following raw materials in parts by weight: 9 parts of ethoxylated modified polycarbosilane, 100 parts of vinyl silicone rubber, 30 parts of silica, and 1 part of crosslinking agent.

[0012] Furthermore, the functionalized linear polycarbosilane-modified vinyl silicone rubber composite material comprises the following raw materials in parts by weight: 9 parts of ethoxylated modified polycarbosilane, 100 parts of vinyl silicone rubber, 30 parts of silica, 15 parts of carbon fiber, and 1 part of crosslinking agent.

[0013] Furthermore, the ethoxy-modified polycarbosilane is prepared by the following method: after uniformly mixing triethoxysilane and catalyst, polycarbosilane is added, stirred evenly, and reacted to obtain ethoxy-modified polycarbosilane.

[0014] Furthermore, the reaction conditions for preparing ethoxylated modified polycarbosilane are: reaction at 60~100℃ for 0.5~2h.

[0015] Furthermore, the mass ratio of the triethoxysilane, the catalyst, and the polycarbosilane is 3~6:0.4~0.6:18~22.

[0016] This invention also provides a method for preparing a functionalized linear polycarbosilane-modified vinyl silicone rubber composite material, wherein the preparation method is as follows:

[0017] (1) Ethoxy-modified polycarbosilane, vinyl silicone rubber, functional filler and crosslinking agent are mixed together according to the weight parts to obtain a compound;

[0018] (2) Then the mixture is placed in a mold and heated and cured according to the set program to obtain a functionalized linear polycarbosilane modified vinyl silicone rubber composite material.

[0019] Furthermore, the temperature curing procedure is as follows: under a pressure of 8~12MPa, first at 75~85℃ o Curing at C for 1-3 hours, followed by heating to 170-180°C. o C cure for 20-40 minutes.

[0020] This invention also provides the application of functionalized linear polycarbosilane modified vinyl silicone rubber composites in aircraft thermal protection systems.

[0021] Furthermore, the aircraft thermal protection system includes an ablation-resistant layer for the solid rocket engine nozzle liner, the leading edge and heat-sealing parts of the hypersonic vehicle wing, and the backing material for the thermal insulation layer of the rocket engine casing.

[0022] This invention utilizes the hydrosilylation reaction between the carbon-carbon double bond in the polycarbosilane molecule and the silane-hydrogen bond in the triethoxysilane to prepare a functionalized linear polycarbosilane with both ethoxy and olefin bonds, namely, ethoxy-modified polycarbosilane. This invention further uses solid vinyl silicone rubber as a matrix, silica and carbon fiber as fillers, and ethoxy-modified polycarbosilane as a modifier to prepare an ethoxy-modified polycarbosilane-modified silicone rubber composite material through free radical reaction. One end of the ethoxy-modified polycarbosilane molecule is bonded to the silicone rubber molecular chain via a vinyl group, while the ethoxy group at the other end forms a chemical link with the hydroxyl groups on the surface of hydrophilic silica through a condensation reaction, thereby constructing an enhanced interfacial interaction in the composite material. Research results show that the addition of ethoxy-modified polycarbosilane increases the crosslinking density and rigidity of the composite material while maintaining the excellent ductility and mechanical properties of the matrix. Furthermore, it significantly improves the overall thermal protection performance of the composite material, especially its ablation resistance in high heat flux environments. This results in a composite material possessing both excellent mechanical properties and ablation resistance, enabling its widespread application even in extreme heat flux environments, and demonstrating broad application prospects in the field of ablation thermal protection.

[0023] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0024] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0025] Figure 1 A is a schematic diagram of the chemical reaction between LPCS and TES; Figure 1 B is (a) a homogeneous mixture of LPCS and TES after 1 hour of reaction, (b) a two-roll mixing diagram and (c) an optical image of the ELPCS-modified MVQ silica composite material; Figure 1 C represents the infrared and nuclear magnetic spectrum of the LPCS.

[0026] Figure 2This is the NMR spectrum obtained by the LPCS internal standard method.

[0027] Figure 3 The NMR spectra are for vinyltriethoxysilane (VTOS) and LPCS-VTOS.

[0028] Figure 4 (a) The homogeneous mixture of LPCS and TES after 1 h of reaction, (b) the NMR spectra of TES and LPCS before and after the reaction, and (c) the infrared spectra of the ELPCS-modified MVQ silica composite material before and after the reaction.

[0029] Figure 5 (a) Crosslinking density and (b) relaxation time of ELPCS-modified MVQ silica composite material.

[0030] Figure 6 Linear fitting analysis of DSC curves and onset temperature for LPCS self-curing and LPCS-TES hydrosilylation reaction.

[0031] Figure 7 (a) Tensile strength, elongation at break, and elastic modulus of ELPCS-modified MVQ silica composite material; (b) Tensile strength-stress curve; (c) Thermal conductivity test results.

[0032] Figure 8 Thermogravimetric properties of LPCS self-curing products in (a) air and (b) nitrogen atmospheres, and (cd) thermogravimetric and (ef) mass change rate curves of ELPCS modified MVQ silica composites in air and nitrogen atmospheres.

[0033] Figure 9 ELPCS-modified MVQ silica composite material at 2MW / m 2 (a) mass ablation rate and linear ablation rate under heat flux, (b) carbonization ablation rate, (c) maximum back surface temperature, (d) height distribution map and (e) surface morphology and 3D profile of the sample after ablation.

[0034] Figure 10 ELPCS-modified MVQ silica composite material at 5 MW / m 2 (a) mass ablation rate and linear ablation rate under heat flux, (b) carbonization ablation rate, (c) maximum back surface temperature, (d) height distribution map and (e) surface morphology and 3D profile of the sample after ablation.

[0035] Figure 11 ELPCS-modified MVQ silica composite material at 2MW / m 2 SEM morphology of the carbon layer after thermal ablation.

[0036] Figure 12ELPCS-modified MVQ silica composite material at (ab)2 MW / m 2 and (cd)5MW / m 2 A bar chart of the compressive strength of the carbon layer after thermal ablation and its compressive strength stress-strain curve.

[0037] Figure 13 ELPCS-modified MVQ carbon fiber composites at 5MW / m 2 (a) mass ablation rate, (b) linear ablation rate and (c) surface morphology and 3D profile of the sample after ablation under thermal flux.

[0038] Figure 14 ELPCS-modified MVQ carbon fiber composites at 5MW / m 2 Back temperature test results under heat flow.

[0039] Figure 15 ELPCS-modified MVQ carbon fiber composites at 5MW / m 2 (a) Histogram of compressive strength and (b) stress-strain curve of compressive strength of carbon layer after thermal ablation. Detailed Implementation

[0040] In the following examples and experimental cases, reagents and raw materials not specifically described are all commercially available products.

[0041] In the embodiments of this invention, "phr" represents the weight parts of the material; "room temperature" or "normal temperature" as referred to in this invention is 25±10℃; the materials used in the embodiments of this invention are as follows: liquid polycarbosilane (LPCS) was purchased from Forsmann Technology Co., Ltd., with a vinyl molar fraction of 0.25mol / 100g and a hydrogen content of 0.8595mol / 100g; methyl vinyl silicone rubber (MVQ) was purchased from Xinjin Branch of Zhonglan Chenguang Chemical Design and Research Institute Co., Ltd., with a molecular weight of 600,000 and a vinyl content of 0.08wt%; Karstedt catalyst and triethoxysilane (TES) were purchased from Aladdin Biochemical Technology Co., Ltd.; the crosslinking agent was dicumyl peroxide (DCP), purchased from Aladdin Biochemical Technology Co., Ltd.; hydrophilic silica (Cabot M5) was purchased from Shanghai Kaiyin Chemical Co., Ltd.; and carbon fiber (T700 SC) was purchased from Toray Industries, Inc. of Japan.

[0042] The examples and comparative examples were prepared according to the following method:

[0043] (1) Synthesis of ELPCS: In a Schlenk flask under nitrogen protection, 4.3248 g of triethoxysilane (TES) and 0.51 g of Karstedt catalyst were added sequentially. After being magnetically stirred and mixed evenly, 20.4 g of liquid polycarbosilane (LPCS) was added and stirred continuously until the system was homogeneous. Then, the mixture was reacted in an oil bath at 80 °C for 1 h to obtain homogeneous liquid ethoxy modified polycarbosilane (ELPCS).

[0044] The reaction diagram of LPCS and TES is shown below. Figure 1 As shown in Figure A, the homogeneous mixture after 1 hour of reaction is as follows: Figure 1 As shown in B(a).

[0045] (2) Preparation of ELPCS-modified MVQ silica composite material: ELPCS and hydrophilic fumed silica (Cabot M5) were mixed together with methyl vinyl silicone rubber (MVQ) raw rubber according to the formulation in Table 1, and then mixed evenly by two rollers. Figure 1 As shown in B(b), a crosslinking agent (DCP) is then added and the mixture is further kneaded until homogeneous. The mixture is then placed in a mold, covered with a polytetrafluoroethylene film, and subjected to 80 cycles at 10 MPa. o C curing for 2 hours and 175 o After curing at C for 25 min, a series of ELPCS-modified MVQ silica composite materials were finally obtained.

[0046] Its macroscopic morphology is as follows Figure 1 As shown in B(c), the number of ELPCS added from left to right are 0 phr, 3 phr, 6 phr, 9 phr and 12 phr respectively.

[0047] Table 1 Formulation of ELPCS-modified MVQ silica composite material

[0048]

[0049] (3) Preparation of ELPCS-modified MVQ carbon fiber composite material:

[0050] According to the formulation in Table 1, ELPCS and MVQ with added Cabot M5 were thoroughly mixed on a two-roll mill until uniformly dispersed. Then, carbon fiber (CF) was added and mixed evenly. After that, DCP was added and mixed evenly. Then, the mixture was placed in a mold and subjected to 80 cycles at 10 MPa. o C curing for 2 hours and 175 o After curing at C for 25 minutes, a series of ELPCS-modified MVQ carbon fiber composite materials were finally obtained.

[0051] Table 2 Formulation of ELPCS-modified MVQ carbon fiber-based composite materials

[0052]

[0053] The samples prepared in the embodiments and comparative examples of the present invention were characterized structurally using the following methods:

[0054] (1) Fourier transform infrared spectroscopy (FTIR): The infrared spectrum of the test sample was recorded using a Nicolet 570 FTIR spectrometer (Wisconsin, USA); the measurement range was 400-4000 cm⁻¹. -1 The test resolution was 1cm. -1 .

[0055] (2) Low-field NMR (1H): The cured sample was tested using a low-field NMR analyzer (Newman Corporation, China) with model VTMR20-010 VI. The test conditions were a proton resonance frequency of 22MHz and a sampling frequency of 100kHz. The test was conducted at room temperature.

[0056] (3) 1H NMR: First, the sample was dissolved in CDCl3. Then, the dissolved sample was measured using an AV II NMR spectrometer (Bruker, Germany) at 400 MHz and room temperature.

[0057] Infrared spectroscopy analysis showed that LPCS was at 2140 cm⁻¹ -1 It shows obvious Si-H bond characteristic absorption peaks at 30-40 cm⁻¹, and at 30-40 cm⁻¹... -1 Stretching vibration peaks belonging to vinyl groups (-CH=CH2) were observed nearby, and characteristic proton signals of Si-H and -CH=CH2 were clearly visible in the proton spectrum, such as... Figure 1 As shown in C; comprehensive spectral analysis results confirm that LPCS is a polycarbosilane with a linear structure. Its molecular chain contains both active silane-hydrogen bonds and vinyl functional groups, indicating that LPCS has certain self-crosslinking properties; because it has a linear structure, the ELPCS prepared is also linear.

[0058] The vinyl content in LPCS was quantitatively analyzed using NMR internal standard method, with DMSO as the internal standard reagent. The analysis was performed on three independent samples, and the average value was taken. The 1H NMR data are shown below. Figure 2 As shown, the calculated average molar fraction of vinyl groups in LPCS is 0.25 mol / 100 g, corresponding to a mass fraction of 6.80 wt%.

[0059] Because the determination of silane-hydrogen bond content using NMR internal standard method is easily affected by factors such as signal interference, relaxation time, dynamic exchange reaction, and solvent stability, leading to inaccurate quantitative results, an indirect method is used to determine the silane-hydrogen bond content in LPCS. The specific experimental procedure is as follows: First, a complete addition reaction is carried out under an inert atmosphere. Then, the integral area change of the vinyl characteristic peak is tracked by 1H NMR, and the consumed vinyl equivalent is calculated using the internal standard method. Finally, the accurate silane-hydrogen bond content in LPCS is obtained. The specific testing method is as follows:

[0060] 0.1016 g of LPCS (-CH=CH2 0.25 mol%) and 3.0066 g of vinyltriethoxysilane (VTOS, 190.31, 98%) were mixed, and 0.0306 g of Karstedt catalyst and 4 ml of toluene solvent were added. After stirring evenly, the mixture was placed at 80 °C. o The reaction was carried out in a vacuum oven at C for 12 hours. After the reaction, two NMR spectroscopy analyses were performed. The final yield of triethoxyvinylsilane showed a vinyl to ethoxy ratio of 0.48:1.5, and after the reaction, the vinyl to ethoxy ratio was 0.46:1.5. Figure 3 As shown, the silicon-hydrogen bond content is calculated as follows:

[0061] (0.98 3.0066 / 190.31 3 0.02 / 1.5 + 0.25% 0.1016) / 0.1016=0.8595mol / 100g;

[0062] Structural changes of materials before and after the ELPCS synthesis reaction, such as Figure 4 As shown in (b), the NMR spectrum shows that ethoxy groups, carbon-carbon double bonds and silicon-hydrogen bonds can be observed in the homogeneous system formed after 1 hour of reaction, indicating that the liquid polycarbosilane structure containing ethoxy groups has been initially formed. The carbon-carbon double bonds, silicon-hydrogen bonds and ethoxy groups in the system also endow it with the activity to further react with MVQ and its hydrophilic silica.

[0063] Infrared spectra of ELPCS-modified MVQ silica composite materials and their raw materials are as follows: Figure 4 As shown in (c), the results indicate that the infrared signal peaks attributable to the raw materials -CH=CH2 and Si-H disappear in the cured composite material, suggesting that ELPCS was successfully integrated into the molecular chain network of MVQ. Figure 5As shown, the introduction of ELPCS increases the crosslinking density of the composite material, with a maximum increase of 12.5% ​​compared to the unmodified composite material. Meanwhile, the relaxation time test results show that as the amount of ELPCS added increases, the peak relaxation time of the signal peak of the moving unit with a smaller relaxation time shifts to a lower direction, and it can be observed that the signal peak with a larger relaxation time gradually changes from two to one. This indicates that the addition of ELPCS changes the original molecular chain network structure and hinders the movement of some moving units, thus improving the rigidity of the material.

[0064] The samples prepared in the embodiments and comparative examples of this invention were characterized in morphology and tested in performance using the following methods:

[0065] (1) Differential Scanning Calorimetry (DSC) Test: Thermal analysis tests were performed on the samples using a DSC 3500 Sirius (NETZSCH) differential scanner at different heating rates (5K / min, 10K / min, 15K / min and 20K / min), with a temperature range of 20~200℃. o C.

[0066] (2) Thermal stability (TGA) test: The thermal stability of the samples was measured using a thermogravimetric analyzer (METTLER, Switzerland) model 2019BE5D in both N2 and air atmospheres. The gas flow rate was 60 mL / min, and the test temperature range was 30°C. o C to 800 o C, heating rate is 10 o C / min.

[0067] (3) Tensile property test: The tensile properties of the material were tested using an electronic universal testing machine (Instron 5567) in accordance with GB / T-528-2009. The sample was dumbbell-shaped, 100mm long, 5mm wide, and 2mm thick. A 20mm extensometer was added, and the tensile speed was 500mm / min.

[0068] (4) Ablation performance test: The ablation performance of the samples was tested using a fully automatic oxyacetylene ablation machine, and the test was conducted in accordance with the standard GJB 323A-2018. During the test, a self-made tensile fixture was used to stretch the silicone rubber samples, and the ablation angle was 90°. o C, heat flux is 2MW / m 2 4MW / m 2 and 5MW / m 2 The sample size is 30mm in diameter and 10mm in thickness. Each group of tests consists of at least 5 samples, and the ablation time is 30s.

[0069] The thickness of the sample before and after ablation is measured. The formulas for calculating the linear ablation rate (LAR) and mass ablation rate (MAR) are: LAR = Δd / t = (d1 - d2) / t; MAR = Δm / t = (m1 - m2) / t; where d1 is the original thickness of the sample, mm; d2 is the thickness of the sample after ablation, mm; m1 is the original mass of the sample, g; m2 is the mass of the sample after ablation, g; and t is the ablation time, s.

[0070] (5) Thermal insulation performance test: The temperature change on the back side of the sample during the ablation process was measured using a type K patch thermocouple.

[0071] (6) Carbon layer strength test: The carbon layer strength test is conducted by using a fixed fixture and a universal testing machine (UTM4000, Shenzhen Sansi Zongheng Co., Ltd.) to perform a puncture test on the peeled carbon layer. The diameter of the puncture rod is 2mm, the sensor load is 1000N, and the compression rate is 2mm / min to obtain the carbon layer compression strength.

[0072] (7) 3D profile test: The surface and 3D profile of the test sample after ablation were recorded using a 3D profile tester (VR-6000, Keyence Corporation, Japan).

[0073] (8) Scanning electron microscopy (SEM) test: The microstructure of the carbon layer after ablation of the sample was observed using a Phenom Nano (produced by Phenom-world BV in the Netherlands), and the corresponding electron microscope images were selected.

[0074] The following are the results and analysis of morphological characterization and performance testing:

[0075] (1) ELPCS modified MVQ silica composite material

[0076] The self-curing of LPCS and its initial temperature during hydrosilylation reaction with TES were studied using the variable heating rate DSC method. The results showed that the reaction initiation temperature exhibited a regular decreasing trend as the heating rate decreased, such as... Figure 6 As shown, the self-curing initiation temperature of LPCS was determined to be 84.75°C using linear extrapolation. o C, while the onset temperature of the LPCS-TES hydrosilylation reaction is 71°C. o C, Based on this, choose 80. o C, as the synthesis temperature of ELPCS, can both ensure that the hydrosilylation reaction proceeds preferentially and effectively suppress the self-curing reaction of LPCS.

[0077] The tensile property test results of ELPCS modified MVQ composites are as follows: Figure 7As shown in (ab), with the addition of ELPCS increasing from 0 phr to 12 phr, the elastic modulus of the material significantly increased from 5.23 MPa to 10.95 MPa, indicating a significant restriction on the relaxation motion and slippage of the molecular chains. Simultaneously, the Si-C bond-dominated structural units of the ELPCS molecular chains exhibit higher intrinsic rigidity compared to the Si-O-Si flexible segments of traditional silicone rubber. Notably, although the tensile strength and elongation at break of the material showed a certain decreasing trend with increasing ELPCS content, the modified composite material still maintained excellent mechanical properties. Its tensile strength consistently exceeded 3 MPa, and the elongation at break remained above 230%, indicating that ELPCS, while enhancing the rigidity of the material, still maintained the excellent ductility and mechanical strength of the matrix.

[0078] Thermal conductivity test results are as follows Figure 7 As shown in (c), it can be seen that with the increase of ELPCS addition, the thermal conductivity of the composite material shows a non-linear trend of first decreasing and then increasing. Compared with the unmodified system, the thermal conductivity of the ELPCS-modified sample shows an overall decrease, which is in stark contrast to the significant increase in thermal conductivity usually exhibited by traditional filler-reinforced systems. This indicates that the introduction of ELPCS effectively inhibits heat conduction and optimizes the thermal resistance of the filler-matrix interface, which has a positive significance for the thermal protection performance of the composite material during the ablation process. It can effectively delay the transfer of heat to the interior of the material and improve its ablation resistance.

[0079] To determine the high-temperature thermal stability of LPCS samples after crosslinking, LPCS liquid was placed in a glass bottle and heated at 150°C. o C / 2h and 250 o The ceramicized sample was thermally crosslinked and cured in a vacuum oven at 0.5°C for 0.5 hours. The thermogravimetric properties of the ceramicized sample were then tested under air and nitrogen atmospheres. The test results are as follows: Figure 8 As shown in (ab), the results show that after LPCS self-cures, R in an air atmosphere 800 Reaching 95.3% under nitrogen atmosphere, R 800 It reaches 93.5%, which is significantly better than conventional silicone rubber, and shows good application prospects in the field of high temperature resistant materials.

[0080] Thermogravimetric test results of composite materials are as follows Figure 8 As shown in (cf) and Table 3, the introduction of ELPCS effectively improves the thermogravimetric properties of the composite material. DTG spectra show that the introduction of ELPCS inhibited the degradation loss of the MVQ composite material under air and nitrogen atmospheres. Specifically, nitrogen atmosphere significantly inhibited the thermal degradation of the material at temperatures around 500℃. Experiments demonstrate that the introduction of ELPCS substantially improves the thermogravimetric properties of the material under air and nitrogen atmospheres.

[0081] Table 3 Thermogravimetric properties of ELPCS-modified MVQ silica composites

[0082]

[0083] like Figure 9 As shown in (de), at 2MW / m 2 Under heat flow conditions, both unmodified and modified samples formed a complete carbonized protective layer and exhibited expansion. Notably, the modified samples showed more significant expansion behavior, with a significantly larger expansion amplitude than the unmodified samples. Figure 9 (c) Back temperature testing also showed that the modified sample exhibited superior thermal protection performance; in particular, the sample with an ELPCS addition of 9 phr showed a 23.8°C reduction in back temperature compared to the unmodified sample. o C, confirming the effectiveness of the ELPCS modification strategy in improving the ablation thermal resistance of materials. Meanwhile, at 2MW / m 2 Under heat flow conditions, ELPCS modification significantly improved the ablation resistance of the samples, such as Figure 9 As shown in (ab), compared with the unmodified sample, the mass ablation rate of the modified sample was significantly reduced. The mass ablation rate of the sample with an ELPCS addition of 9 phr was reduced by 65.6%, demonstrating excellent ablation resistance. Furthermore, its carbonization ablation rate was also reduced by 29.3%, which fully demonstrates that ELPCS modification not only inhibits thermal degradation but also promotes the formation of a more stable carbon layer, thereby improving the overall thermal protection performance.

[0084] like Figure 10 As shown in (de), at 5MW / m 2 Under high heat flux ablation conditions, the unmodified sample was almost completely eroded due to the fragile carbon layer structure, while the ELPCS modified sample formed a complete and dense carbon layer protective layer. The surface of the modified sample showed a smooth ablation pit morphology, and its ablation retreat was significantly reduced compared with the unmodified sample. Figure 10 (c) Back-side temperature testing showed that the sample with 9 phr of ELPCS had a 76.0°C lower back-side temperature than the unmodified sample. o The significant temperature drop of C confirms that ELPCS modification can substantially improve the thermal insulation performance of materials under extreme thermal environments. At 5MW / m 2 Under ultra-high heat flux conditions, ELPCS modification significantly enhances the ablation resistance of the material, such as Figure 10As shown in (ab), experimental data show that the mass ablation rate and linear ablation rate of the sample with 9 phr of ELPCS addition were significantly reduced by 48.4% and 46.4% respectively compared with the unmodified sample, indicating that the modification treatment effectively inhibited the thermochemical erosion and mechanical ablation of the material under extreme thermal conditions. Further carbonization behavior analysis showed that the carbonization ablation rate of the sample with 9 phr of ELPCS addition was reduced by 28.5%. The experimental results prove that ELPCS modification not only delayed the thermal decomposition process of the polymer, but also promoted the formation of a dense and stable carbon protective layer, significantly improving the overall thermal protection performance of the material system.

[0085] Figure 11 It is an ELPCS-modified MVQ silica composite material at 2MW / m 2 SEM images of the carbon layer after thermal ablation show that the unmodified sample exhibits a layered structure with numerous pores, resulting in lower strength. In contrast, the modified sample displays a continuous carbon layer structure with numerous tiny pores that allow for effective release of pyrolysis gases. The modified sample's carbon layer structure is more complete and lacks large pores, indicating that the introduction of ELPCS effectively improves the integrity of the carbon layer formed during ablation, thus enhancing ablation performance.

[0086] Figure 12 The carbon layer compressive strength test results shown indicate that introducing ELPCS can significantly enhance the compressive strength of the carbon layer, and this result is consistent with... Figure 11 The observed microstructure of the carbon layer is consistent with that of the previous study. Specifically, when the ELPCS addition amount was 9 phr, at 2 MW / m 2 Under heat flux conditions, the compressive strength of the carbon layer formed by the composite material increased from 1.56 MPa in the unmodified sample to 3.66 MPa, an increase of 134.6%; at 5 MW / m 2 Under heat flux conditions, its compressive strength increased from 0.185 MPa to 0.650 MPa, an increase of 251.4%; this indicates that the introduction of ELPCS significantly improved the mechanical properties of the carbon layer, especially under higher heat flux conditions.

[0087] (2) ELPCS modified MVQ carbon fiber composite material

[0088] Figure 13 (a) shows that at 5MW / m 2 Under the hot flow conditions, ELPCS-modified MVQ carbon fiber composites exhibited significantly improved ablation resistance, with a substantial decrease in mass ablation rate compared to the unmodified material. When the ELPCS addition was 9 phr, the mass ablation rate decreased by 44.1%; as the ELPCS addition increased from 0 phr to 12 phr, the linear ablation rate showed a trend of first decreasing and then increasing, such as... Figure 13As shown in (b), the linear ablation rate remained lower than that of the unmodified sample; with an ELPCS addition of 9 phr, the linear ablation rate decreased by 20.9%; these experimental results indicate that the introduction of ELPCS effectively improved the ablation resistance of the composite material in high heat flux environments. Furthermore, Figure 13 (c) The morphology analysis of the carbon layer after ablation shows that the degree of carbon layer depression in the modified sample is significantly reduced, which further confirms the improvement of its ablation resistance.

[0089] Figure 14 Back-side temperature test results show that the introduction of ELPCS significantly improves the thermal insulation performance of the composite material in high-heat-flux ablation environments. With increasing ELPCS addition, the maximum back-side temperature of the material first decreases and then increases. Compared to the unmodified sample, the maximum back-side temperature of the material with 6 phr of ELPCS is reduced by 28.0%, corresponding to a temperature drop of 17.8°C. o C exhibits excellent heat protection performance.

[0090] Figure 15 The carbon layer compressive strength test results show that the strength of the carbon layer after ablation of carbon fiber composite material gradually increases with the increase of ELPCS content. When the ELPCS addition amount is 12 phr, the compressive strength of composite material increases from 0.209 MPa to 2.001 MPa, an increase of 857.4%. This indicates that ELPCS effectively improves the strength and structural integrity of carbon layer through its own in-situ ceramization.

[0091] The above experimental results show that ethoxylated polycarbosilane-modified vinyl silicone rubber composites possess both excellent mechanical properties and ablation resistance; among them, the composite with an ELPCS addition of 9 phr exhibits the best ablation resistance; for the ELPCS-modified MVQ silica composite, its performance at 2MW / m 2 Under the same heat flux conditions, the back temperature decreased by 23.8°C compared to the unmodified sample. o C, the mass ablation rate decreased by 65.6%, the carbonization ablation rate decreased by 29.3%, and the compressive strength of the carbon layer increased by 134.6%; at 5MW / m 2 Under the heat flux conditions, the back surface temperature decreased by 76.0°C compared to the unmodified sample. o C, the mass ablation rate and linear ablation rate decreased by 48.4% and 46.4% respectively, the carbonization ablation rate decreased by 28.5%, and the compressive strength of the carbon layer increased by 251.4%; meanwhile, its tensile strength was 5.2 MPa and its elongation at break was 273%, exhibiting excellent mechanical properties. For ELPCS-modified MVQ carbon fiber composites, at 5MW / m 2Under heat flux conditions, compared to the unmodified sample, the mass ablation rate decreased by 44.1%, and the linear ablation rate decreased by 20.9%. It can be seen that under heat flux conditions, compared to the unmodified composite material, the composite material of this invention significantly reduces the back temperature, mass ablation rate, and carbonization ablation rate, improves the compressive strength of the carbon layer, and exhibits significantly improved ablation resistance. Furthermore, the improvement effect is more significant under high heat flux conditions than under low heat flux conditions.

[0092] In summary, ethoxylated polycarbosilane improves the compatibility between the filler and the solid silicone rubber matrix, enhancing the interfacial bonding force. The addition of ethoxylated polycarbosilane increases the crosslinking density and rigidity of the composite material, resulting in excellent mechanical properties. Furthermore, the addition of ethoxylated polycarbosilane inhibits the thermal decomposition process of the composite material, promotes the formation of a dense and stable carbon protective layer, significantly improves the overall thermal protection performance of the composite material, effectively inhibits thermochemical and mechanical erosion under extreme thermal environments, and greatly enhances the thermal protection efficiency and mechanical properties of the carbon protective layer under extreme thermal environments. In particular, it significantly improves the ablation resistance of the composite material in high heat flux environments. Therefore, this invention successfully prepares an ethoxylated polycarbosilane-modified vinyl silicone rubber composite material with both excellent mechanical properties and ablation resistance, broadening the application scope of silicone rubber composite materials in the field of ablation thermal protection and showing great application potential.

Claims

1. A functionalized linear polycarbosilane-modified vinyl silicone rubber composite material, characterized in that, The raw materials include the following parts by weight: 3-15 parts of ethoxy-modified polycarbosilane, 100 parts of vinyl silicone rubber, 5-80 parts of functional filler, and 0.5-10 parts of crosslinking agent; wherein the vinyl silicone rubber is a solid silicone rubber; wherein the vinyl silicone rubber is selected from at least one of methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber, and methyl vinyl trifluoropropyl silicone rubber; wherein the functional filler is silica, carbon fiber T700 SC, or a mixture of silica and carbon fiber T700 SC; wherein the ethoxy-modified polycarbosilane has both ethoxy groups and olefin bonds.

2. The functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to claim 1, characterized in that, The raw materials include the following parts by weight: 7-11 parts of ethoxylated modified polycarbosilane, 100 parts of vinyl silicone rubber, 10-45 parts of functional filler, and 0.5-2 parts of crosslinking agent.

3. The functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to any one of claims 1 to 2, characterized in that, The crosslinking agent is a peroxide crosslinking agent.

4. The functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to claim 3, characterized in that, The raw materials include the following parts by weight: 9 parts ethoxylated modified polycarbosilane, 100 parts vinyl silicone rubber, 30 parts silica, and 1 part crosslinking agent.

5. The functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to claim 3, characterized in that, The raw materials include the following parts by weight: 9 parts ethoxylated modified polycarbosilane, 100 parts vinyl silicone rubber, 30 parts silica, 15 parts carbon fiber T700 SC, and 1 part crosslinking agent.

6. The functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to any one of claims 1 to 2, characterized in that, The ethoxy-modified polycarbosilane is prepared by the following method: triethoxysilane and catalyst are mixed evenly, then polycarbosilane is added, stirred evenly, and reacted to obtain ethoxy-modified polycarbosilane.

7. The functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to claim 6, characterized in that, The mass ratio of the triethoxysilane, catalyst, and polycarbosilane is 3~6:0.4~0.6:18~22.

8. The method for preparing the functionalized linear polycarbosilane-modified vinyl silicone rubber composite material according to any one of claims 1 to 7, characterized in that, The preparation method is as follows: (1) Ethoxy-modified polycarbosilane, vinyl silicone rubber, functional filler and crosslinking agent are mixed together according to the weight parts to obtain a compound; (2) Then the mixture is placed in a mold and heated and cured according to the set program to obtain a functionalized linear polycarbosilane modified vinyl silicone rubber composite material.

9. The application of the functionalized linear polycarbosilane modified vinyl silicone rubber composite material according to any one of claims 1 to 7 in the field of ablation heat protection.

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