Stability and Population of Radicals in Electrical Trees in Epoxy Resins Based on Electron Paramagnetic Resonance Spectroscopy

The stability and population of radicals in aged epoxy resins with different electrical trees are investigated by electron paramagnetic resonance (EPR). Branch trees and bush trees of various sizes are produced in three types of epoxy resins, which are cured by different curing agents. By examining the lifetime of radicals in three epoxies, the mobility of polymer chains is found to act as a vital factor for stability. The recombination of radicals is faster in polymers with higher mobility, leading to a shorter lifetime of radical signals. A distinguishable singlet appears in specimens without visible tree channels, proving that radicals are a precursor of electrical trees. Among spectra from a series of branch trees, two species of radicals are found to be generated successively as tree size increases. By comparing the signal intensity of branch trees and bush trees of similar sizes, bush trees show a much smaller radical population, which is attributed to relatively low electrical stress at branch tips and slow degradation of polymer chains.

Automated summary

The stability and population of radicals in aged epoxy resins with different electrical trees are investigated using electron paramagnetic resonance (EPR). The mobility of polymer chains is found to be a crucial factor for stability, as it affects the recombination of radicals and their lifetime. Radicals are identified as precursors of electrical trees, and the generation of different radicals is observed as tree size increases. The radical population in bush trees is smaller than in branch trees due to lower electrical stress at the branch tips and slower degradation of polymer chains.