Effect of Type and Amount of Accelerator on Reactivity and Curing Behavior of Epoxy/Dicyandiamide/Accelerator System

Hypothesis: 

The effects of four accelerators 2,4,6-tris(dimethyl aminomethyl) phenol (DMP30), 2-methylimidazole (2MI), 2-phenylimidazole (2PhI) and carbonyldiimidazole (CDI) at 0.6 and 1 phr contents on the curing behavior of a diglycidyl ether of bisphenol A epoxy resin and dicyandiamide (dicy), a  solid curing agent, was investigated. Obviously, by changing the type and amount of accelerator, the reactivity and curing behavior of the epoxy/daisy system can be controlled.

Measuring the viscosity build-up versus time, gelation time measurement at 110, 120 and 130°C, tack, non-isothermal differential scanning calorimetry (DSC) and glass transition temperature characterization were used to study the reactivity and curing behavior of epoxy/dicy system.

The CDI accelerator at 0.6 phr content showed the highest pot-life. The pot-life of formulations decreased by increasing the amount of accelerator particularly when CDI was used. This difference in pot-life was lower for 2PhI and was not changed for 2MI. Gel-time data showed that the reactivity of different accelerators at high temperature was in order: 2MI > DMP30 > CDI > 2PhI. DSC test results showed that by increasing the amount of accelerator the heat of reaction increased, curing profile became sharp and glass transition temperature remarkably decreased. The broadest curing profile of 14°C also was seen for CDI. The DSC results showed that the reactivity of different accelerators was in order: 2MI > CDI > DMP30 > 2PhI. In other words, 2PhI showed the lowest activity and the sharpest curing profile and 2MI showed the highest activity with the wide curing behavior. It seems that the CDI accelerator at 0.6 phr content would be the best accelerator regarding the highest pot-life at room temperature, high curing rate and maximum Tg.