Delor-Jestin Florence, Tomer Namrata S, Pal Singh Raj, Lacoste Jacques
Laboratory of Molecular and Macromolecular Photochemistry, Engineering School of Chemistry/University Blaise Pascal of Clermont-Ferrand, 24, Avenue des Landais, 63174 Aubiere Cedex, France.
National Chemical Laboratory, Polymer Division, Dr. Homi Bhabba Road, Pune 411-008, India.
Sci Technol Adv Mater. 2008 Jul 24;9(2):024406. doi: 10.1088/1468-6996-8949/9/2/024406. eCollection 2008 Apr.
Most applications of silicones are linked to their hydrophobic properties and (or) their high resistance to ageing (e.g. thermal ageing and photoageing). However, when placed in extreme environments, these materials can fail as in the case of epoxy/fiber glass composite powerlines insulators, where crosslinked polymethylsyloxanes (PDMSs) are used as the protective envelope (housing) of the insulator. We report on the behavior of both pure/noncrosslinked PDMSs and typical formulations used in industrial insulators, i.e. containing peroxide crosslinked PDMS, alumina trioxide hydrated (ATH) and silica. Special attention is paid on both (i) the sources of potential degradation and (ii) the best analytical methods that can be applied to the study of very complex formulations. (i) Aside from conventional types of ageing such as photo-ageing and thermal, hydrolytic, and service life ageings, treatments with acidic vapors, plasma and ozone possibly generating species from the reaction of a high electric field with air were also performed, which allowed to accelerate electrical and out-door ageings and to obtain differently aged materials. (ii) Aside from conventional analytical methods of polymer degradation such as FTIR/ATR spectroscopy and SEC, TG, hardness measurements, more specific methods like photo/DSC, TG/IR, thermoporosimetry, resistivity and density measurements were also performed to characterize the chemical and physical evolutions of polymer materials. In particular, it was found that treatment with nitric acid vapor has detrimental effects on the properties of both fire retardants (e.g. ATH) and PDMSs, affecting the hardness and resistivity of the formulated material.
有机硅的大多数应用都与其疏水性能和（或）高耐老化性（如热老化和光老化）有关。然而，当置于极端环境中时，这些材料可能会失效，就像环氧/玻璃纤维复合电力线绝缘子的情况一样，其中交联聚甲基硅氧烷（PDMS）用作绝缘子的保护外壳。我们报告了纯/非交联PDMS以及工业绝缘子中使用的典型配方的行为，即含有过氧化物交联PDMS、三水合氧化铝（ATH）和二氧化硅的配方。我们特别关注了（i）潜在降解的来源以及（ii）可应用于研究非常复杂配方的最佳分析方法。（i） 除了传统类型的老化，如光老化、热老化、水解老化和使用寿命老化外，还进行了用酸性蒸汽、等离子体和臭氧处理的实验，这些处理可能会因高电场与空气反应而产生各种物质，从而加速电气老化和户外老化，并获得不同老化程度的材料。（ii） 除了聚合物降解的传统分析方法，如傅里叶变换红外光谱/衰减全反射光谱（FTIR/ATR）、尺寸排阻色谱（SEC）、热重分析（TG）、硬度测量外，还进行了更具体的方法，如光/差示扫描量热法（photo/DSC）、热重/红外联用（TG/IR）、热孔率测定、电阻率和密度测量，以表征聚合物材料的化学和物理变化。特别是，发现用硝酸蒸汽处理对阻燃剂（如ATH）和PDMS的性能都有不利影响，会影响配方材料的硬度和电阻率。
