Effect of isophorone diamine on curing kinetics and mechanical properties of 2-ethyl-4-methylimidazole/epoxy resin crosslinked network

Fast curing resins are the material basis for large-scale production of fiber reinforced polymer (FRP) composites. In this study, diglycidyl ether of bisphenol A (DGEBA) was cured with 2-ethyl-4-methylimidazole (2E4MI) as the main curing agent, and allyl glycidyl ether (AGE) was added to improve the processability. Based on this curing system, the effect of isophorone diamine (IPD) content on curing kinetics and mechanical properties was studied to obtain the optimal fast curing resin formulation. Both the curing kinetics and the glass transition temperature (Tg) were characterized by non-isothermal DSC, and the impact, flexural, and tensile behaviours of the cured products were tested. The gel and curing time of the curing system were characterized by rheometry and isothermal DSC test, respectively. The results demonstrated that the increasingly evident first shoulders from the non-isothermal DSC curves indicated the incorporation of addition reaction of IPD with epoxy groups in the first curing stage. The correlation between activation energy (Ea) and degree of curing (α) determined by Ozawa-Flynn-Wall methods strongly depended on the content of IPD. Moreover, the curing time of the optimal resin system was shortened to 15 min at 120 °C with guaranteed mechanical properties and the Tg was 102.50 °C.