Effect of filler type on the response of polysiloxane elastomers to cyclic stress at elevated temperatures

Abstract

A variety of inorganic fillers are investigated to determine their impact on the response of filled polysiloxane elastomers to cyclic stress in hot air and in hot poly(dimethylsiloxane) PDMS fluid environments. Three fillers stabilize the polysiloxane networks to cyclic stress: zinc oxide, tin oxide, and copper oxide. Four fillers enhance network degradation: aluminum oxide, calcium oxide, titanium oxide, and tungsten oxide. The roles of testing environment, of diphenylsiloxane content of the polysiloxane network, of filler loading, of the stoichiometric balance of network precursors, and of molecular weight between cross-links are investigated. Although each influences the response of the elastomer to cyclic stress at elevated temperature, filler type exerts the primary influence. Silane-treated fillers are used to demonstrate that differences based on filler type do not arise because of changes in the strength of polymer-filler interactions. No correlation between stability of the filled elastomer to cyclic stress in hot air and filler particle size distribution, filler surface acid/base character, or the presence of specific inorganic contaminants in the filler is observed. It is proposed that the intrinsic ability of certain inorganic oxides to catalyze and/or inhibit polysiloxane degradation reactions determines the response of the filled elastomers to cyclic stress at elevated temperature.