Characteristics of Eco-Friendly Epoxy Resin Modified with Epoxidized Soybean Oil (ESO): Thermal, Mechanical, and Morphological Properties

A bisphenol-A epoxy resin mixed with epoxidized soybean oil (ESO) was cured with an acid anhydride curing agent and a tertiary amine accelerator. The thermal, mechanical, and morphological properties of the cured epoxy resin were investigated using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), impact tester, and scanning electron microscopy (SEM). As the content of ESO increased, the thermal stability and flexural strength decreased and the impact strength increased. This was thought to be due to the increase in phase separation in the ESO-rich region. As a result of DMA analysis and observation of morphology, it was determined that the increase in impact strength was due to the decrease in intermolecular crosslinking density due to the introduction of flexible long-chain ESO segments into the epoxy network structure and the absorption of external impact energy due to the increase in the roughness of the fracture surface. Therefore, it is believed that by mixing ESO in an appropriate amount with the epoxy resin according to the purpose and target properties, it is possible to manufacture a plant-based environmentally friendly epoxy resin capable of reducing carbon as well as improving impact strength.