Thermal Stability Of Silicone Rubber Research Articles

Effect of NO2 Aging on the Surface Structure and Thermal Stability of Silicone Rubber with Varying Al(OH)3 Contents

In this study, silicone rubber (SiR) with 0, 90, and 180 parts of aluminum hydroxide (Al(OH)3, ATH) contents prepared in the laboratory was treated in a certain concentration of NO2 for 0, 12, 24, and 36 h. Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry (TG) were used to study the changes in the surface structure and thermal stability of SiR, as well as the influence of Al(OH)3 on the properties of SiR. According to AFM, the root-mean-square roughness of ATH-90 SiR was 192 nm, which was 2.7 times of ATH-0 SiR. With the incorporation of ATH, the surface of SiR became more susceptible to corrosion by NO2. According to FT-IR and XPS, with the increase in aging time, the side chain Si-CH3 of polydimethylsiloxane (PDMS) was oxidized gradually and a few of nitroso -NO2 groups were formed. According to TG, the incorporation of ATH caused the maximum decomposition rate temperature of PDMS to advance from 458.65 °C to 449.37 and 449.26 °C, which shows that the thermal stability of SiR degraded by adding ATH. After NO2 aging, a new decomposition stage appeared between 75 and 220 °C (stage Ⅰ), and this decomposition trend was similar to aluminum nitrate, which was proven to reduce the thermal stability of PDMS. The effects of NO2 on the surface structure and thermal stability of different ATH contents of silicone rubber were preliminarily clarified by a variety of characterization methods, which provided ideas for the development of silicone rubber resistant to NO2 aging.

Research on the preparation and thermal stability of silicone rubber composites: A review

Silicone rubber has excellent mechanical properties and thermal stability and is widely used in aerospace, mechanical manufacturing, and high-temperature sealing. However, with the development of industrial technology, the gap between the matrix's thermal stability and industrial requirements is gradually expanding, which has also attracted the attention of many scholars. Recent advances in formula innovation and process design provide paths to improve the thermal stability of silicone rubber. Metal oxide-containing compounds (CeO2, Al2O3, Fe2O3), carbon nanomaterials (carbon black, carbon nanotubes, graphene) are commonly used as functional additives to enhance the high temperature resistance of silicone rubber composites. The selection and dispersion of additives, the improvement of the preparation process, and the exploration of thermal aging mechanism are all key steps to improve the thermal stability of silicone rubber composites. This review presents the research ideas and the latest research progress on the thermal stability of silicone rubber composites. Meanwhile, based on our research and understanding, we discussed the complexity of the aging mechanism of silicone rubber in high-temperature environment and hope to provide new ideas for further research and applications.

Synergistic effect and mechanism of polysilazane and platinum on the thermal stability of silicone rubber

Polysilazane and platinum were adopted to enhance the thermal stability of silicone rubber. The effect and mechanism of polysilazane and platinum on enhancing thermal stability were investigated via thermogravimetry, scanning electron microscopy-energy dispersive X-ray spectrometry, thermogravimetry-Fourier transform infrared spectrometry, and Fourier transform infrared spectrometry. Remarkable synergism between polysilazane and platinum was found in enhancing thermal stability of silicone rubber. When 1.34 wt% polysilazane and 8 ppm platinum were added, the degradation temperatures were elevated. Furthermore, the thermal residues of silicone rubbers were increased from 30–45 to 66–76 wt%, and maximum degradation rates were reduced from 8.81–15.8 to 4.55–5.02 wt%/min. Besides, silicone rubber demonstrated excellent shape retention at high temperature in the presence of polysilazane and platinum. The mechanism may be that platinum cooperated with polysilazane and efficiently catalyzed radical crosslinking between polysilazane and silicone chains. As a result, a tightly crosslinked network was developed, and degradation of silicone rubber was suppressed.

Surface modification of magnesium hydroxide by wet process and effect on the thermal stability of silicone rubber

This work reported the surface modification of magnesium hydroxide (MH) employing vinyltriethoxysilane (VTES) by wet process for the sake of improving the compatibility between magnesium hydroxide (MH) and silicone rubbers (SR). The morphology, surface property and dispersion stability in organic phase of VTES-modified MH (VTES-MH) were studied in detail. Fourier transform infrared (FT-IR) spectra and photoelectron spectra (XPS) proved that the VTES molecules were chemically bound to the surface of MH via the reaction between SiOC2H5 of VTES and hydroxyl group of MH. The contact angle tests implied that the surface of MH was transformed from hydrophilic to hydrophobic successfully with the interface energy of MH decreased from 63.35 to 25.13 mJ·m−2. Dispersion stability tests showed the dispersibility of MH nanoparticles in the organic phase was significantly improved after modification. Finally, the VTES-MH was applied as a flame retardant to enhance the thermal stability and reduce the flammability of SR. The VTES-MH showed good compatibility to SR even at high loading amount (5:5) and a high limit oxygen index (LOI) of 40.2% was obtained. The formation mechanism of SR/VTES-MH composites was also discussed.

Effect of incompletely condensed tri-silanol-phenyl-POSS on the thermal stability of silicone rubber

In most cases, incompletely condensed tri-silanol-phenyl-polyhedral oligomeric silsesquioxane (SSOH) was used as an intermediate to synthesize the polyhedral oligomeric silsesquioxane (POSS) with special structure. In this paper, SSOH was well synthesized and then immediately incorporated into hydroxyl-terminated polydimethylsiloxane (PDMS) as a co-cross-linking agent to prepare room-temperature-vulcanized (RTV) silicone rubber (SSOH-PDMS). Thermogravimetric analysis (TGA) results showed that the chemical incorporation of POSS into PDMS networks exerted significant enhancement of thermal stability for the rubber nanocomposites. For SSOH-PDMS with 5 wt% SSOH, the degradation temperature of 5% weight loss were delayed from 364.78 to 379.50 °C, while the temperature for 30% weight loss were increased by 47.4 °C. By monitoring the degradation behavior by TGA coupled with Fourier transform infrared spectroscopy (FTIR), the degradation mechanism of the modified RTV silicone rubber containing different concentration of the cross-linker SSOH has been investigated. The results showed that the SSOH greatly influenced the degradation mechanism of PDMS rubber in two ways: ① The reaction with the silanols in PDMS can diminish the degradation initiated by hydroxyl-terminal during the first degradation stage; ② the nanoreinforcement effect of POSS on the PDMS can delay the temperatures of the second thermal degradation stage.

Effect and mechanism of ureido-modified MQ silicone resin and platinum on tracking and erosion resistance of silicone rubber

How to effectively enhance the tracking and erosion resistance of silicone rubber is a significant topic in high-voltage insulation. In this work, ureido-modified MQ silicone resin (UHMQ) was synthesized and employed to improve tracking and erosion resistance of silicone rubber in combination with platinum (Pt). The effect and mechanism of UHMQ/Pt on tracking and erosion resistance were studied via inclined plane test, leakage current curves, scanning electron microscopy, thermogravimetry and thermogravimetry-Fourier transform infrared spectrometry. When 5–7 phr of UHMQ and 0.33 phr of Pt catalyst were added, the tracking and erosion resistance of silicone rubber were greatly improved. In this case, all specimens passed the inclined plane test at 4.5 kV with low eroded mass and undamaged surfaces. The thermal stability of silicone rubber containing UHMQ/Pt was also much higher than that without, and the leakage current and discharging frequency on the surface of silicone rubber were markedly decreased with the introduction of UHMQ/Pt. This was attributed to UHMQ/Pt catalyzing radical crosslinking of silicone chains under arc discharging so that a protective barrier was established on the surface to resist arc ablation. Also, the enhanced radical mechanism suppressed degradation of silicone chains, and thus reduced release of cyclic oligomers which would aggravate arc discharging. Furthermore, since UHMQ/Pt facilitated complete oxidation of pyrolysis gases, the carbon deposit was reduced and tracking was suppressed.

Amine-functionalized POSS as cross-linkers of polysiloxane containing γ-chloropropyl groups for preparing heat-curable silicone rubber

A series of heat-curable silicone rubber is designed and prepared through cross-linking reaction of two structurally similar amine-functionalized polyhedral oligosilsesquioxane (POSS), octa(aminophenyl)silsesquioxane, and N-phenylaminomethylsilsesquioxane, with polysiloxane containing γ-chloropropyl groups (CPPS). Curing characteristics measured with a rheometer show that the amine-functionalized POSS can participate in chemical cross-linking during curing. Scanning electron micrographs illustrate that silicone rubber prepared by solution mixing exhibits a homogeneous morphology. Mechanical and thermal properties of silicone rubber are evaluated through mechanical testing, thermogravimetric analysis, and differential scanning calorimetry. The effect of POSS distribution in the polymer matrix on vulcanizate properties is discussed. Compared with that prepared through melt mixing, the methyl chloropropyl silicone rubber prepared through solution mixing exhibits excellent mechanical properties. Concentrative cross-linking occurs in this network, and the mechanical properties are improved. The sample exhibits a tensile strength of 9.9 MPa and tear strength of 48.1 kN/m. Thermogravimetric analytical results show that introducing POSS can enhance the thermal stability of silicone rubber.

Effect of π–π interaction between carbon nanotubes and phenyl groups on the thermal stability of silicone rubber

To investigate the effect and mechanism of π–π interaction between carbon nanotubes (CNTs) and phenyl groups on the thermal stability of silicone rubber (SR), three kinds of silicone rubber with different phenyl content were used to prepare CNTs/SR composites in present study. Raman spectroscopy and X-ray photoelectron spectroscopy demonstrated that the π–π interaction between CNTs and phenyl groups in composites is enhanced with phenyl content increasing. The results of thermogravimetric analysis and tensile testing before and after aging indicted the π–π interaction makes CNTs improve the thermal stability of phenyl SR more efficiently than that of methyl vinyl SR. The T 5 (defined as the temperature for 5% mass loss) of CNTs/SR-3 (with 10–20% phenyl content) is increased by 19.4 °C compared to that of SR-3, and the final residual mass of CNTs/SR-3 (31.9%) is much higher than other samples under argon atmosphere.

Effect of vulcanization temperature and humidity on the properties of RTV silicone rubber

In order to study the difference in performance of room temperature vulcanized (RTV) silicone rubber in vulcanization environment with different temperature and humidity, static contact angle method, FTIR and TG is utilized to depict the properties of hydrophobicity, transfer of hydrophobicity, functional groups and thermal stability of RTV silicone rubber. It is found that different vulcanization conditions have effects on the characteristics of RTV silicone rubber, which shows that the hydrophobicity of RTV silicone rubber changes little with the vulcanization temperature but a slight increase with the vulcanization humidity. Temperature and humidity have obvious effects on the hydrophobicity transfer ability of RTV silicone rubber, which is better when vulcanization temperature is 5°C or vulcanization humidity is 95%. From the Fourier transform infrared spectroscopy, it can be concluded that humidity and temperature of vulcanization conditions have great effect on the functional groups of silicone rubber, and vulcanization conditions also have effect on thermal stability of RTV silicone rubber. When vulcanization temperature is 5°C or vulcanization humidity is 15% or 95%, the thermal stability of silicone rubber becomes worse.

Effects of Copper Oxide and Carbon Nanotubes on Thermal Stability of Silicone Rubber Nanocomposites

Silicone rubber (SR) filled with carbon nanotubes (CNTs), copper oxide (CuO) and CuO modified CNTs (CuO-CNTs) were prepared to detect the effects of these additives on thermal stability of SR by thermogravimetric analysis and tensile testing before and after aging. Flynn-Wall-Ozawa method was also employed to analyze the thermal degradation kinetics. The results indicated that all the additives could increase the initial thermal degradation temperature and thermal oxidative aging properties of SR and a synergistic effect was found in CuO-CNTs/SR. Meanwhile, activation energies of SR filled with additives increased significantly relative to neat SR and found to be optimal for CuO-CNTs/SR with activation energy increasing to 231.29, 121.68 kJ·mol-1 larger than that of blank sample. It is because that CNTs and CuO could promote each other to capture the free radicals generated by thermal oxidative reaction of the methyl side groups and thereby terminate the process.

Synergistic effect and mechanism of platinum catalyst and nitrogen-containing silane on the thermal stability of silicone rubber

Platinum (Pt) catalyst and nitrogen-containing silane (NS) were introduced to improve the thermal stability of silicone rubber. The effects of Pt and NS on thermal stability and degradation mechanism of silicone rubber were investigated by thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDXS) and Fourier transform infrared spectrometry (FTIR). A significant synergism was found between Pt and NS for improving the thermal stability of silicone rubber. When 6.67ppm of Pt and 1.4 phr of NS were introduced, the temperature of 10% and 20% weight loss under nitrogen atmosphere were respectively increased by 36°C and 119°C. Meanwhile, the residue weight at 900°C was doubled to 68% in the presence of Pt/NS. The synergistic mechanism might be that the nitrogen atom coordinated with Pt and improved the catalytic efficiency of Pt. Additionally, NS preserved the catalytic activity of Pt under air atmosphere. Hence, Pt/NS efficiently catalyzed thermal crosslinking and suppressed degradation of silicone chains. Moreover, it revealed that the presence of Pt/NS protected silicone chains from oxidation. Thus, the unzipping depolymerization by silanol groups was reduced significantly.

Synergistic effect of iron oxide modified carbon nanotubes on the thermal stability of silicone rubber under different atmospheres

To investigate the synergistic effect and mechanism of γ-Fe2O3 modified carbon nanotubes (γ-Fe2O3–CNTs) on the thermal stability of silicone rubber (SR) under different atmospheres, a series of SR-based composites added with α-Fe2O3, γ-Fe2O3, CNTs and γ-Fe2O3–CNTs were prepared and subsequently investigated by Raman spectra, X-ray diffraction, thermogravimetric analysis and tensile testing before and after aging and swelling experiment. The results exhibited that γ-Fe2O3–CNTs had significant synergistic effect on the thermal stability of SR both under nitrogen and air atmosphere. Under nitrogen atmosphere, the depolymerization of SR was delayed greatly by γ-Fe2O3–CNTs in the whole temperature range. For example, T 50 (the temperature at which 50 % degradation occurs) of γ-Fe2O3–CNTs/SR was 56.9 °C higher than that of neat SR. The synergistic effect is attributed to the nice combination of thermal conductivity of CNTs in the relatively low-temperature range and enhanced interfacial reaction of γ-Fe2O3 in the relatively high-temperature range. Under air atmosphere, the initial degradation temperature of γ-Fe2O3–CNTs/SR was greatly improved by about 50 °C. The synergistic effect is mainly proposed to include that CNTs and γ-Fe2O3 can promote each other to capture the free radicals and thereby terminate the thermo-oxidative degradation process significantly. Owing to the excellent antioxidant ability of γ-Fe2O3–CNTs, the degradation mechanism of its SR composite is changed completely.

The effect of glass fiber and coupling agents in the blends of silicone rubber and liquid crystalline polymers

Blends of silicone rubber (VMQ) and liquid crystalline polymer (LCP) were prepared using a melt blending technique in the presence and absence of glass fiber and coupling agents. The effect of glass fiber and coupling agents on the thermal, dynamic mechanical, morphological pro-perties and cure characteristics of VMQ/LCP blends were studied. The vinyl silane coupling agent showed a significant effect on the above mentioned properties of VMQ/LCP blends by reacting at the interface between VMQ and LCP. The viscosity of the VMQ/LCP blends decreased with the addition of a coupling agent. A substantial improvement in storage modulus of VMQ/LCP blends was observed in the presence of glass fiber and coupling agents. However, as a coupling agent vinyl silane proved to be better than amine for the VMQ/LCP-glass-containing blends. The thermal stability of the pure silicone rubber was higher than those of the blends. This high thermal stability of silicone rubber was attributed to the Si−O−Si bonds. However, the thermal stability of the blends decreased further in the presence of a coupling agent, possibly due to a decrease in blend crystallinity.

Effect of compatibiliser, curing sequence and ageing on the thermal stability of silicone rubber, EPDM rubber and their blends

The thermal stability of the vulcanisates of silicone rubber, EPDM, their blends and aged specimens of these systems has been studied by non-isothermal thermogravimetry. The activation energy for the degradation process suggests that a different route is followed for the degradation of EPDM after ageing. The effect of a silane-grafted EPR and also the effect of a programmed two-stage curing process on thermal stability has also been studied. Both are found to contribute moderately to the thermal stability of the blends.