The Effect of Modifier on Electret Properties and Hardness of Epoxy Composite Material

Abstract

The study focuses on the synthesis of thermoelectrets by combining epoxy oligomer, epoxy-urethane modifier (PEF-3A), and polyaminoamide curing agent (L-20) and the influence of the modifier and curing agent on electret properties and mechanical strength. The process involves polymer synthesis through curing the initial oligomer and modifier, as well as polarization in a constant electric field to create the electret state of the polymer dielectrics. The variation of the content (2.5–10.0 wt.%) of the modifier in the composition results in changes in the electret and mechanical characteristics, including surface potential, effective surface charge density, electrostatic field strength, and Shore D hardness. These changes are attributed to the interplay between reduced mobility of polar groups due to strong physical intermolecular interaction in the structure of the network of the 3-D polymer and an increased number of functional groups participating in polarization processes. Increasing the content of modifier PEF-3A in the composition of the basic oligomer DER-331 leads to a decrease in the frequency of the spatial mesh of the resulting 3-D structure due to the incorporation of an epoxy-urethane oligomer with a large molecular weight. The study of DER-331 and L-20 composite by the method of thermally stimulated depolarization (TSD) reveals the process of polymer devitrification and the occurrence of post-curing reactions. The dielectric spectroscopy method proves the dipole macromolecular group orientation of epoxy polymer material, typical for the electret state of polymer dielectrics. According to the calculation data of dielectric relaxation process activation energy, it is concluded that the electret state in the polymeric matrix formed during curing and fixed by the chemical bonds of a 3-D network is a free state of epoxyamine macromolecules. Dipole groups, mostly oriented in one direction, are “frozen” in the cured net structure, acting as thermoelectret charge carriers. An increase in the modifier content does not significantly impact hardness, while polarization results in a marked difference between the Shore D hardness of unpolarized and polarized samples. This difference can be attributed to the orientation of polar groups during the synthesis, which leads to the emergence of a denser mesh of physical bonds. Therefore, by changing the formulation of the epoxy composition, it is possible to regulate its electret and strength properties.