Effects of 2-ethyl-4-methylimidazole and tetraethylammonium bromide on the fracture properties of epoxidized soybean oil based thermoset

Abstract

In this paper, we aim to report the effects of catalyst (types and concentrations) on the fracture mechanics of epoxidized soybean oil (ESO) based thermosets. ESO resin was thermally cured using methylhexahydrophthalic anhydride curing agent in the presence of two types of catalysts, i.e., tetraethylammonium bromide and 2-ethyl-4-methylimidazole (EMI). The loading of the catalysts varied from 0.3 to 0.8 phr. The fracture behaviour of ESO thermoset was examined on the basis of the principle of linear elastic fracture mechanics (LEFM) and essential work of fracture (EWF). LEFM measurements were performed using single-edge notched tensile and double-edge notched tensile (DENT) tests, while, EWF measurements were carried out using DENT tests. The fracture morphologies of the ESO thermosets were characterized via field emission scanning electron microscopy. It was determined that the plane-strain fracture toughness (KIC), the specific EWF (we), and the specific plastic fracture work (βwp) of ESO thermosets were significantly influenced by the types and loading of catalysts. In addition, the fracture toughness properties were associated with the crosslink density of the ESO thermosets. In addition, it was found that the brittle–ductile transition of EMI-catalyzed ESO thermosets can be assessed by the combination of LEFM and EWF in the fracture toughness measurement.