High Temperature Elastomers for Extreme Aerospace Environments

Abstract

Abstract To meet the ever increasing environmental requirements imposed on sub-system components of advanced aerospace weapons systems, a comprehensive project to develop high strength, high temperature resistant elastomeric materials has been pursued. To attain this goal, research on reinforcement, stabilization, and crosslinking systems for butyl, ethylene propylene terpolymer, and fluoroelastomers was carried out. Results obtained in earlier work with the hydrocarbon elastomers disclosed that fine-particle-size, high-structure carbon black provided excellent tensile properties at high temperatures. Further work on stabilization systems resulted in the discovery that stannous oxide was effective for phenolic-resin-cured butyl at temperatures up to 500° F. For EPT, vulcanization-stabilization systems which provided a threefold improvement in useful life of this elastomer at temperatures in the range 300° F to 500° F were elucidated. Preliminary studies on fluoroelastomer reinforcement led to the finding that properly dispersed carbon fiber imparted not only better high temperature tensile strength, but also improved life at temperatures up to 600° F. In the present work, fibrous magnesium silicate, a material which normally would be used for dusting uncured rubber or as a paint filler, was found to be an effective reinforcing material for fluoroelastomers. Vulcanizates prepared with an acicular-platy form of this material have tensile strength at 400° F which is 80% greater than that with commonly used medium thermal carbon black. Hot tear strengths with even greater improvements were also realized, and as an added bonus, resistance to deterioration over a temperature range of 600° F to 700° F was also noteworthy. Primary implication of this work lies in renewed awareness that elastomeric vulcanizates are composite materials. Reinforcing materials as well as other additives are very influential in determining the engineering properties and performance of elastomers.