Mineral coupling, improved electrical properties

Improved retention of electrical properties - Coupling agents are also used to prevent degradation of electrieal properties under harsh environmental eonditions. Table 7 compares treated and imtreated clay and wollastonite fillers to imfilled thermoplastic polyurethane during one week of water immersion. With smface modification, both minerals are able to maintain or improve upon the electrical properties of the unfilled resin. 

Silane coupling agents are thus an extremely valuable range of compounds that can effectively and economically improve the adhesive bonding of a polymer to a mineral, giving superior hydrolytic stability and enhanced electrical and mechanical properties in composite materials. 

Initially, silanes were used in compounds based on EPM containing calcined clay and which were intended for electrically insulating applications. It was noticed that the insulating properties were improved and stabilised, especially in a moist environment mechanical properties were also improved. The same type of improvement was noted with hydrated alumina. The most suitable coupling agent, with peroxide crosslinking, is vinyl tri( 1-methoxy-ethoxy) silane with sulphur and accelerator crosslinking systems mercaptopropyl trimethoxy silane is recommended. Silanes have recently been made available as masterbatches and can be added directly to mineral fillers.The use of silanes has now extended to non-black compounds for applications other than cables when silicas and other types of filler (aluminium and calcium silicates) are used. 

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