Relationships of cure kinetics and processing for epoxidized soybean oil bio-thermoset

Epoxidized soybean oil (ESO) resin was thermally cured using methylhexahydrophthalic anhydride (MHHPA) curing agent, in the presence of 2-ethyl-4-methylimidazole (EMI) catalyst at different temperatures (i.e., 130, 135, 140, 145 and 150 degrees C). Curing kinetics of the ESO/MHHPA systems was studied using Fourier Transform Infrared Spectroscopy (FTIR). The EMI-catalyzed ESO/MHHPA system showed autocatalytic behavior in the isothermal curing reaction. The kinetic parameters; reaction rate constants (k(1) and k(2)) and reaction orders (m and n) of the ESO/MHHPA systems have been determined based on Kamal's autocatalytic model. EMI catalyst content and curing temperature showed significant effect on, k(2), m and n. The overall reaction order (m + n) of the EMI-catalyzed ESO/MHHPA systems was about 1.5-3.0. The apparent activation energies (E-a1 and E-a2) were determined using the Arrhenius kinetic equation. As expected, the E-a1 and E-a2 had decreased with increasing EMI catalyst content. The critical conversion, alpha(c) was found to be in the range of 0.6-0.8. Curing reaction of ESO/MHHPA system as a function of EMI catalyst content can be well-described by introducing the diffusion factor, f(alpha) into Kamal's autocatalytic model. (C) 2012 Elsevier B.V. All rights reserved.