Characteristics of Electrical Insulation in PDMS-ATH Composite for High Voltage Insulators

Summary  The electrical insulation properties and the tracking and erosion resistances of high-temperature vulcanized silicone rubber were investigated as to the concentration of alumina trihydrate (ATH) therein for the fabrication of silicone rubber with optimum ATH content. Controlling the ATH concentration has been found to be an important factor in the enhancement of the tracking and erosion resistances of silicone rubber. In addition, the silicone rubber showed constant electrical resistivity and dielectric breakdown voltage without any decrease due to the interfacial problems with the addition of ATH to the silicone rubber. Therefore, this fabricated silicone rubber that contains an optimum ATH concentration can be applied to outdoor high-voltage insulators.     

Improving the tracking and erosion resistance of silicone rubber using Fe2O3 and platinum catalyst

In typical HTV silicone rubber for composite insulators subjected to a 4.5 kV inclined plane (IP) test, alumina trihydrate loading exceeds 40 wt%, which limits the rubber content and weakens the antiaging properties. This study compares two methods for enhancing tracking and erosion resistance while reducing ATH content to meet IP test requirements. Increasing Fe₂O₃ content from 1.5 wt% to 3 wt% promotes the formation of mullite. The formed ceramic layer isolates heat and oxygen and hence facilitates the specimen to pass the IP tests with less content of ATH. By contrast, Pt/NS system cannot suppress the tracking efficiently by forming the Si O C ceramics at high ATH loading. The decomposition of ATH will generate water vapor and lead to holes in the surface. Both moisture and oxygen absorbed have a detrimental effect on the suppression mechanism of the Pt/NS system. Consequently, it is recommended that the content of Fe₂O₃ can be increased slightly to lower the ATH content in the traditional HTV SiR formula used for the composite insulator. Besides, when the content of ATH is relatively high, the use of the Pt/NS system is not recommended.     

Effect of ultraviolet-A radiation on surface structure,thermal, and mechanical and electrical properties of liquid silicone rubber

Liquid silicone rubber (LSR) products outdoors are often subjected to high intensity of ultraviolet (UV)-A radiation. However, the influence of UV-A radiation on LSR is rarely studied. To study the influence of UV-A radiation on LSR, the surface of LSR with UV-A aging time was characterized by tests at different detection depths [X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR)]. The operation properties (thermal stability and mechanical and electrical properties) for outdoor insulators were also analyzed. It was found that the porous surface and the loose layer of LSR increased, but the growth rate of them decreased as UV-A aging time increased. SiO₂ fillers were lost in the surface. C H bonds in  CH₃ and  CH₃ in Si CH₃ increased with aging time. The increased crosslinking density increased the thermal stability, hardness, dielectric loss tangent, relative dielectric constant, and volume resistivity and decreased elongation-at-break. The mechanical strength initially increased and then decreased. Based on the proposed aging mechanism, the UV-A resistance of LSR can be improved by reducing the amount of hydrogen-containing silicone oil and by increasing the molecular weight of raw rubber. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47652.     

舰船用辐射交联无卤阻燃电缆护套料的研究

应用γ射线辐射交联技术,制备出以乙烯－醋酸乙烯/茂金属聚烯烃弹性体/纳米级改性氢氧化铝（EVA/POE/ ATH）为基材的舰船用无卤阻燃电缆护套料,探讨了共混物配比、ATH的种类与用量以及辐射剂量对材料力学性能和阻燃性能的影响。结果表明,随着POE用量的增加,材料的拉伸强度和断裂伸长率增加,耐热老化性能提高,但硬度降低;纳米ATH的加入使材料具有较好的阻燃性能;材料的辐射交联工艺可弥补阻燃剂对材料力学性能的影响,在辐射剂量为80 kGy的条件下,采用EVA /POE/ATH ＝90/10/60（质量份数,下同）的共混体系可制备出综合性能优异的护套料。     

Comparison of four commonly used high temperature vulcanized silicone rubber formulas for outdoor insulator and their regional adaptability

High temperature vulcanized silicone rubber (HTVSR) insulators are widely used in transmission lines. In this article, four formulas [fumed silica and precipitated silica as reinforcing agent, alumina trihydrate (ATH) and alumina as flame retardant, and Fe₂O₃ and Fe₃O₄ as colorant] widely used in the production of HTVSR insulators were investigated by performing a series of laboratory experiments. The surface morphologies of silicone rubber, mechanical characterization (hardness, tensile property, and tear strength), electrical properties (volume resistivity, dielectric property, and breakdown strength), hydrophobicity and its transfer property, and thermal property of these four formulas were analyzed. According to the test results, the formula composed of fumed silica, Fe₂O₃ colorant, and alumina trihydrate (ATH) were excellent in mechanical properties because of more secondary structures, more bound rubber, and uniform dispersion. Therefore, it can be used in strong wind and bird pecking regions. Due to the absence of crystal water, the formula composed of fumed silica, Fe₂O₃ colorant, and alumina was observed to be excellent in thermal stability and electrical properties, making it suitable for the regions with high temperature and humidity. The formula composed of precipitated silica, Fe₃O₄ colorant, and ATH was found to be excellent in hydrophobicity transfer characteristics because of more raw rubber and satisfactory performance could be expected when it was applied in polluted regions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47477.     

Flame Retardant Synergism of Hydroxy Silicone Oil and Al(OH)3 in EVA Composites

A synergistic effect on flame retardancy was found when hydroxy silicone oil (HSO) was incorporated into ethylene vinyl acetate/aluminum hydroxide (EVA/ATH) composite. The fire performance of EVA and EVA composites was studied by using limiting oxygen index (LOI), UL 94, and cone calorimeter test (CCT). Compared with the EVA/ATH binary composite, the LOI values of the EVA/ATH/HSO ternary composites at the same additive loading are all decreased. The CCT data indicated that the addition of HSO in EVA/ATH system not only reduces the heat release rate, but also prolonged the ignition time of the composite. Thermogravimetric analysis revealed that ATH accelerated the loss of acetic acid, but hydroxy silicone oil assisted to reduce ATH's accelerating effect.     

耐化学腐蚀的复合绝缘子用硫化硅橡胶的研制

通过测定混炼胶对不同酸碱性浓度溶液中憎水性的丧失快慢来判定胶料的耐腐蚀性能。结果表明通过使得补强剂与填料本身的表面具备与硅橡胶相容性的基团,使在混炼过程中补强剂与填补能充分湿润均匀分散于硅橡胶中,从而提高憎水性和耐电蚀损性能。并添加了经环氧树脂E-20改性后的有机硅树脂,并通过优化配方和工艺使硅橡胶具有良好的柔韧性、防水性,高绝缘性能和介电强度及高憎水性能,及优良的耐化学腐蚀性。     

1,1'-双(二苯基膦)二茂铁对RTV-2硅橡胶耐热性能的影响

以端羟基聚二甲基硅氧烷为基胶,沉淀法白炭黑为填料制得双组分室温硫化(RTV-2)硅橡胶。研究了1,1'-双(二苯基膦)二茂铁用量对RTV-2硅橡胶耐热空气老化性能的影响。结果表明:在300℃和320℃热空气老化条件下,1,1'-双(二苯基膦)二茂铁加入量为0.1～1.5份时,RTV-2硅橡胶的耐热性能明显提高,经340℃×50 h热空气老化后,二茂铁用量为0.1份和1.5份的RTV-2硅橡胶已经老化变脆,完全失去使用性能。而二茂铁用量为0.2份和0.5份的RTV-2硅橡胶仍具有一定的力学性能,此时RTV-2硅橡胶的抗热老化性能最优。     

Electrical insulation properties of silicone rubber under accelerated corona and thermal aging

A contactless method based on energy shift of high-energy cut-off of the x-ray bremsstrahlung, the so-called Duane Hunt Limit and a conventional low voltage electrical technique (three-probes technique) is applied on thermal and corona aged silicone rubber (SiR) to measure, respectively, the surface potential, V_s, and the surface resistivity, ρ_s. The effect of aging on these quantities, representing the dielectric properties, is studied. The results are highly reproducible and highlight a good correlation between V_s and ρ_s. It was observed that thermal aging combined with electrical aging deteriorates more the electrical properties of the polymer than thermal aging alone. Explanations for electrical characteristics (V_s, ρ_s) change with aging are supported by attenuated total reflection Fourier transform infrared spectroscopy spectra analysis and a chemical mechanism of aging in three steps (i.e., oxidation-polycondensation, degradation, and thermal cracking). The surface degradation of the polymer is revealed by images of surface morphology obtained by using scanning electron microscopy (SEM). Roughness is greater for combined thermal and corona aging mode compared to thermal aging alone. In addition, the surface degradation of SiR polymer is confirmed by the loss of its hydrophobicity.     

Effects of polymethylvinylsilicone oil with side tetraphenylphenyl groups on the radiation resistance of addition‐type silicone rubber

Polymethylvinylsilicone oil with side tetraphenylphenyl groups (called C₂ gum for short) as a low molecular additive was used in two kinds of addition‐type silicone rubber, polymethylvinyl silicone rubber and poly (dimethyl‐diphenyl) silicone rubber, and the radiation resistance of silicone rubbers obtained was investigated by γ‐rays radiation with the dose rate of 117 Gy/min at doses up to 350, 500, and 850 kGy, respectively. Moreover, the average molecular weight between crosslinks and mechanical properties of silicone rubbers after irradiated in air and N₂ were determined by toluene‐swelling method and on a XLS‐A rubber test instrument, respectively. The results show that C₂ gum can effectively improve the radiation resistance of silicone rubber. When C₂ gum is used in poly(dimethyl‐diphenyl) silicone rubber, phenyl groups and tetraphenylphenyl groups may have synergistic effect, and the radiation resistance is improved greatly. The suitable amount of C₂ gum used in silicone rubber is 10– 14 phr. The crosslinking density of vulcanizates irradiated in N₂ is higher than that of vulcanizates irradiated in air because of the oxidative degradation. The radiation protection mechanism of C₂ gum was also discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4144–4148, 2007     

Effect of hot air aging on properties of EPDM/SmBO3/EVA and EPDM/ATO/EVA composites

Ethylene–propylene–diene rubber (EPDM)/samarium borate (SmBO₃)/ethylene‐vinyl acetate (EVA) copolymer and EPDM/antimony‐doped tin oxide (ATO)/EVA composites are aged at 150°C for different intervals. Surface modification is used to improve filler to matrix interphase. The main aim is to investigate the effect of filler type and vinyl acetate (VA) content in EVA on stability of EPDM composites. It is found that acidic ATO particles can lower pH level of EPDM composites and then promote the degradation of acetic acid during aging. Moreover, when VA content exceeds 14 wt %, the instable VA content causes more acetic acids escape during aging. With the increasing of aging time, EPDM/SmBO₃ control and EPDM/SmBO₃/EVA composites tend to become darker while EPDM/ATO and EPDM/ATO/EVA composites would become yellow. And the color change is correlated well with the variation of carbonyl index. The chemical crosslink points prevent crystals in EVA from melting at aging temperature (150°C), and the variation of crosslink density influences the crystallinity during aging. The tendency of tensile strength is well consistent with that of swelling ratios, and electric properties are correlated with increased polar groups and crystallinity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

硅橡胶的物理改性研究进展

硅橡胶是一类以聚硅氧烷为主链的高分子材料,它具有优异的耐热性、耐寒性和电绝缘性,广泛应用于社会各种行业。但硅橡胶存在分子极性低,疏水性强,物理性能较差等缺陷,其改性研究受到广泛关注。本文主要综述了近年来硅橡胶与氟橡胶（FPM）、三元乙丙橡胶（EPDM）、聚氨酯橡胶（PU）、乙烯乙酸乙烯橡胶（EVM）、乙烯乙酸乙烯酯共聚物（EVA）和乙烯（PE）等共混改性的发展状况,以及矿物微粉与纳米粒子填充改性硅橡胶的研究进展,并比较了各种方法之间的优缺点,最后对目前存在的问题与未来的发展方向提出了一些看法。     

耐辐照苯撑硅橡胶

研究了配方因素对苯撑硅橡胶耐辐照性能的影响,对于这种橡胶,宜采用BDPMH与膏状BP或DCP并用作为交联剂,气相法白炭黑是有效的补强填料,金属氧化物可用于改善耐热性。苯撑硅橡胶可用于制造核能设施中应用的各种耐热和耐辐照橡胶件。     

室温硫化硅橡胶耐热性的研究进展

介绍了硅橡胶的热氧老化机理及室温硫化硅橡胶耐热性的研究进展,综述了提高室温硫化硅橡胶耐热性的主要途径:改变聚硅氧烷主链和侧基的结构、采用新型硫化体系、添加耐热添加剂、添加硅氮类化合物等,指出了提高室温硫化硅橡胶耐热性的发展方向。     

Effects of particle size of Al(OH)3 on electrical properties of EPDM compounds

Effects of particle size of Al(OH)₃ (ATH) filler on electrical properties of ethylene propylene diene terpolymer (EPDM)/ATH compounds were studied. It was found that tracking and erosion resistance of EPDM/ATH compounds decreased while dielectric properties and 90°C water resistance were improved with the increase of particle size. Homocharge accumulates in the compounds, which increases first and then decreases with the increase of particle size. This was explained by the change of particle‐to‐particle distance due to filler size.     

热缩型硅橡胶复合绝缘子的研制

研究了乙烯醋酸乙烯共聚物（EVA）、硅橡胶（PDMVS）和氢氧化铝不同配比时所组成的共混物的力学性能和电学性能及辐射交联对EVA／KPDMVS共混物的凝胶含量和力学性能的影响规律，确定了适合的辐交联剂量及利用该共混物制备热缩型硅橡胶复合绝缘子的工艺条件。     

Thermal conductivity of silicone rubber filled with ZnO

Thermal conductivities of silicone rubber filled with ZnO in a wide volume range were measured in order to study the effect of formed conductive particle chains on thermal conductivities. With the increasing of content of ZnO particles in silicone rubber, the amount of formed conductive chains increases and the conductive chains tend linearly to increase the thermal conductivity of the composite. The experimental results obtained were also analyzed using the Nielsen and Agari models to explain the effect of ZnO filler on the formation of thermal conductive networks. Thermal conductivities of a polymer filled with high volume content of particles evidently increased with the adding of small size fillers. The scanning electron microscopy (SEM) showed that percolation threshold has been reached at 31.4 vol% ZnO filler loading, and the hybrid fillers are more densely packed than single fillers in the silicone rubber matrix. There occurs a positive temperature coefficient (PTC) phenomenon in thermal resistance in composites of silicone rubber filled with ZnO. POLYM. COMPOS., 28:125–130, 2007. © 2007 Society of Plastics Engineers     

Characteristics of surface wettability and hydrophobicity and recovery ability of EPDM rubber and silicone rubber for polymer insulators

As power lines are built in contaminated environments, the industrial usage of power‐line materials requires high reliability. Nonceramic insulators offer better anticontamination performance than that of the traditional ceramic insulators. Among the nonceramic materials, EPDM and silicone rubber provide much better long‐term pollution resistance performance than that of any other materials. This study investigated the long‐term pollution performance by a corona aging treatment on the surface of the test slabs, which were made of EPDM and silicone rubber. Experimental results showed good hydrophobicity of those materials and their transfer of the contaminant layer deposited on the shed surface of the insulator. The EPDM and silicone rubbers are synthetic polymers of low density and they maintain an outstanding resistance to attack by oxygen and ozone. This study measured the contact angle between water droplets and other materials to determine the hydrophobicity and recovery ability of these synthetic polymers. We also studied surface morphology for a visual confirmation of the migration phenomena. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2251–2257, 2001     

电缆用陶瓷化硅橡胶复合带性能的研究

采用熔融共混法制备了可陶瓷化硅橡胶复合材料,对其进行了拉伸性能、阻燃性能和体积电阻率测试.结果表明:随着助熔剂用量的增加,复合材料的拉伸性能下降,由于引入了更多的杂质离子,复合材料的电导率提升;SiO2的加入增大了填料网络结构的紧密性,复合材料的弹性形变和拉伸强度增大,载流子的迁移受到了阻碍,材料的体积电阻率提高;多种...     

Effect of tetraphenylphenyl‐modified fumed silica on silicone rubber radiation resistance

Two kinds of treated fumed silica were prepared by treatment with either tetraphenylphenyltriethoxysilane (TPHTS) or both tetraphenylphenyltriethoxysilane and hexamethyldisilazane (TPHMTS), and were used as reinforcing filler for silicone rubber. The resistance to irradiation of the silicone rubber obtained was investigated by gamma ray of dose 500 kGy in air. The mechanical properties and the average molecular weight between crosslinking points (Mc) of the silicone rubber were determined before and after irradiation. The results show that the fumed silica treated by tetraphenylphenyltriethoxysilane (TPHPHS) can effectively improve the radiation resistance of silicone rubber while the fumed silica treated by both tetraphenylphenyltriethoxysilane and hexamethyldisilazane (MM^N) cannot only effectively improve the radiation resistance of silicone rubber but also has excellent reinforcing effect on silicone rubber. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011