Effect of Hardener Stoichiometry on the Dielectric Properties of Epoxy Resin/Liquid Nitrile Rubber Composite Materials

As the driving force for the crosslinking of epoxy resin (EP) molecular segments to form a 3-D network structure, hardener can directly affect the crosslinking degree of composite materials and then affect the formation of the two-phase structure of EP/hydroxyl-terminated liquid nitrile rubber (HTBN) composite materials. By preparing EP/HTBN rubber composites with a different hardener stoichiometry, the effects of hardener stoichiometry on the two-phase structure and electrical properties of the system are analyzed by SEM cross Section characterization, dc resistivity, and broadband dielectric spectrum. The experimental results show that deviation of the hardener from the standard stoichiometry inhibits the crosslinking behavior, which in turn promotes the precipitation of the rubber phase. The deviation of hardener from the standard stoichiometry causes an increase in dc resistivity, an increase in interfacial polarization strength, and a decrease in epoxy
$\alpha $
relaxation strength. The Vogel–Fulcher–Tammann (VFT) fitting of EP
$\alpha $
relaxation peak frequency versus temperature inverse was performed to obtain the Vogel temperature by Havriliak–Negami (HN) model peak separation results, and the results show that the deviation of the hardener from the standard stoichiometry causes a decrease in the glass transition temperature, which is consistent with the relationship with the crosslinking degree. The above results may provide more effective solution designs for optimizing EP/HTBN composite insulating material curing formulations.