Thermomechanical behavior of aerospace-grade RTV (silicone adhesive)

Measurements of mechanical properties of the commercial polysiloxane RTV 566 were conducted over a range of temperatures, with particular focus on characterizing isothermal behavior at reduced temperatures to reveal possible evidence of crystallization in this material. Conventional testing was performed using typical temperature sweeps to measure elastic flexural and tensile moduli, and thermal expansion coefficients with and without volumetric constraint. The glass transition temperature was determined to be about −115 °C. Measurements of the tensile moduli of RTV 566 specimens were also conducted under isothermal conditions at reduced temperatures. After exposure to temperatures below −75 °C for several hours, tensile moduli rose by as much as a factor of 40. Volumetric shrinkage of 0.35% was demonstrated after 50 h under isothermal condition at −80 °C. These measurements demonstrate previously unpublished manifestations of crystallization occurring in this material, which is based upon a polydimethylsiloxane with phenyl substituents for some of the methyl groups.