Thermal aging assessment of epoxy-based nanocomposites by space charge and conduction current measurements

Abstract

Modification in the physico-chemical properties under long term operating stresses affects charge injection, transport and trapping. Hence space charge measurements are expected to provide an indication of the extent of material degradation. In the present work, space charge measurements are carried out using the Pulsed Electro Acoustic (PEA) technique on thermally aged, epoxy resin and epoxy alumina nanocomposites. Time domain dielectric spectroscopy is carried out on thermally aged specimens in order to compute the change in real and imaginary permittivity. Epoxy resin (LY 556) is used as the polymer matrix, and aluminium oxide particles (size <;50nm) are used as a nanometric filler. Accumulated space charge density, threshold field, apparent trap controlled mobility, and trap depths are computed from the space charge measurements. Further, change in the material due to thermal aging is investigated through Fourier Transform Infra-Red (FTIR) spectroscopy. It is observed that the nanocomposites accumulate less space charge than the base resin. From the results, it is evident that space charge characteristics like charge density and threshold field may be used as effective aging markers. Through space charge measurements as well as time domain dielectric spectroscopy, nanocomposites are observed to be comparatively more resistant to thermal aging.