Thermal degradation of epoxy/silica composites monitored via dynamic mechanical thermal analysis

Abstract A dynamic mechanical thermal analyzer (DMTA) was used to monitor changes of dynamic mechanical properties during thermal degradation of two types of epoxy/silica composites, both of which are used as electrical insulation in power apparatus. It was found that the peak value of the dynamic loss factor (tan δ), glass transition temperature ( T g ), and dynamic storage modulus ( E ′) above T g changed considerably with increasing thermal degradation, while E ′ at the glassy state only underwent a moderate change with increased thermal degradation. It is concluded that the DMTA technique is very sensitive to the structural changes in the investigated epoxy composites due to the thermal degradation. It is also confirmed by DMTA tests that further cross‐linking and loss of dangling chains are occurring slowly during the stage prior to the onset of the severe degradation. © 1992 John Wiley & Sons, Inc.