Epoxy/Poly-etherimide blends for electrical insulation

In power electronics, electrical insulation encapsulation at high temperatures and/or high voltages is a challenge for the systems such as Insulated-gate bipolar transistor (IGBT). Different materials are used and tested in industry and literature. Silicone elastomers for example associated with a primary passivation layer of polyimide are considered to be good candidates but are limited to 180-200 °C. Epoxy thermosets are known to be good insulator to protect electrical devices from moisture, dust and short circuits electrical breakdown. Thermoset/thermoplastic blends can be another good candidate for electrical insulation properties. The thermoplastic percentages as well as the curing conditions control the final morphology (phase separation with disperse thermoplastic phase, bicontinuous phases or inverted structure ...) and thus the electrical properties of the sample. In our study, polyetherimide thermoplastic was introduced with different percentages into the epoxy system. Electronic microscopy images showed the different morphologies depending on the thermoplastic amount. The effect of the morphology on mechanical, electrical and thermal properties has been investigated. For example, the addition of 10%wt of PEI gives nodules of thermoplastic with a micrometer size inside the epoxy amine network where it did not affect either the storage modulus or the thermal resistance under air or nitrogen atmosphere. Whereas, the dielectric spectroscopy points out that the addition of polyetherimide into the epoxy system has decreases the permittivity by 15 % in all the temperature and frequency ranges compared with the pure epoxy amine network.