Novel latent epoxy curing agent for secondary insulation in electrical rotors and stators

A novel multifunctional epoxy curing agent 2-((4-(4-aminophenoxy) phenylamino) (4- hydroxyphenyl)hydrazine carbothioamide(APHCTA)) containing phenolic, thiourea, primary and secondary amines was synthesized by condensation technique and characterized using FTIR, ¹H NMR, ¹³C NMR spectroscopy. Thermal and curing studies were performed using Thermogravimetric analyzer (TGA) and Differential scanning calorimeter (DSC) respectively. The new compound was used as a curing agent for thermosetting epoxy resin Diglycidyl ether of Bispheol-A (DGEBA). The in built phenolic moiety accelerates the curing rate along with the amines thereby relatively lowering the curing temperature compared to the commercial aromatic curing agent such as diamino diphenyl ether (DDE) and also gives longer pot life compared to aliphatic amine such as triethyltriamine (TETRA). Cured polymer of DGEBA/APHCTA showed lower glass transition temperature(Tg) which imparts the flexibility and it also exhibits good thermal stability up to 340 °C. Activation energy (Eα) based on model free kinetics (MFK) method indicates the extent of curing of the reaction. Isothermal curing thermogram showed that the resin cures at lower temperature. Electrochemical Impedance study for the cured film of DGEBA/APHCTA coated on the copper plate exhibits good corrosion inhibition. The new curing agent containing amines, phenolic and thiourea is a potential candidate for use as a latent curing agent for single part epoxy resin for impregnation of AC motor rotors and stators.