Curing Characteristics and Thermal Properties of Epoxidized Soybean Oil Based Thermosetting Resin

Abstract Epoxidized soybean oil (ESO) was thermally cured using methylhexahydrophthalic anhydride (MHHPA) curing agent in the presence of 2‐ethyl‐4‐methylimidazole (EMI) catalyst. The curing characteristics of ESO/MHHPA/EMI systems were characterized using Fourier transform infrared spectroscopy (FTIR), a dynamic mechanical analyzer (DMA) and a differential scanning calorimeter (DSC). FTIR spectra showed that the polyesterification rate in ESO/MHHPA/EMI systems increased with increasing of the catalyst concentration. DSC thermograms indicated that EMI‐catalyzed ESO/MHHPA systems experienced enthalpy relaxation at low EMI concentration whereas the extent decreased with increasing of the EMI concentration. There is a direct relationship between the degree of conversion and crosslink density of the thermal cured ESO/MHHPA/EMI systems with EMI concentration. The curing characteristics of thermal curable ESO thermosetting resins were found to have influence on the thermal properties of the ESO systems. It was determined that the glass transition temperature ( T g ) and storage modulus ( E′ ) of cured ESO increased with increasing the EMI concentration whereas the damping properties of the ESO/MHHPA/EMI systems exhibited the reverse trend. It was found that the thermally curable ESO thermosetting resins experienced a two‐stage thermal decomposition process.