Accelerated hydrothermal aging of epoxy resin based syntactic foams with polymeric microspheres

Insulation systems have to interact with their environment. In outdoor applications they have to withstand atmospheric stress such as temperature and humidity. This leads to aging processes inside the insulation material and results in a change of material properties and consequently can lead to a failure of the high voltage component. Hence, knowledge about the aging behavior of syntactic foam is essential for its use in outdoor applications. Syntactic foam is a composite material consisting of a polymer matrix and hollow microspheres. This study focuses on the hydrothermal aging of epoxy resin based syntactic foam with polymeric microspheres. The aim of this study is to benchmark the use of syntactic foam in outdoor applications. The impact of different microspheres' diameters, filling degrees and additional silica particles on the aging process is presented. The aging behavior is investigated for different syntactic foam compositions for two aging methods - the climatic chamber and the pressure cooker storage. To evaluate the aging process of the material the mass, the dielectric constant and the breakdown voltage is monitored over several aging times in the climatic chamber and the pressure cooker, respectively. The parameter study shows very good hydrothermal aging behavior of syntactic foam in terms of water uptake and the development of the dielectric constant over the aging time. The use of small microspheres improves the breakdown voltage after the aging process significantly and features similar relative breakdown voltages as conventional silica filled epoxy compositions.