Biodegradable Epoxy Thermosets Prepared by Mixing Diglycidyl Ether of Bisphenol A and Epoxidized Soybean Oil and Their Electrical and Mechanical Properties

Abstract

To develop a biodegradable epoxy resin matrix for high-voltage insulating composites, petroleum-based diglycidyl ether of bisphenol A (DGEBA) epoxy and epoxidized soybean oil (ESBO) were mixed, and their biodegradability and electrical and mechanical properties were studied. DGEBA/ESBO epoxy mixtures were in the ratios of 100/0, 90/10, 80/20, 70/30, 60/40, and 50/50, respectively. In the soil burial test, as ESBO content increased, DGEBA/ESBO thermosets disintegrated into smaller pieces by 4–6 months, while the DGEBA thermoset without any ESBO preserved its geometry throughout the degradation study for 8 months. Crosslink density was studied by a solvent swelling method and the Flory–Rehner equation, and glass transition temperature, Tg, was measured by a differential scanning calorimetry, and it was found that crosslink density and Tg were highest in the DGEBA/ESBO (80/20) thermoset. All mechanical strengths and electrical insulation breakdown strengths were obtained in the DGEBA/ESBO (80/20) thermoset, which could be used as a biodegradable matrix for high-voltage insulating composites.