Curing and degradation kinetics of crosslinked epoxidized soybean oil with isosorbide-based curing agent

Abstract

This work explores the synthesis of the isosorbide-based curing agent with methyltetrahydrophthalic anhydride (MTHPA). Synthesized for the first time, the isosorbide methylphthalate acid (IMPA) and its effects on the crosslinking of epoxidized soybean oil (ESO) are investigated. The curing and degradation kinetics of the synthesized compounds were investigated for molar ratios 1:1, 1:0.50 and 1:0.25 for ESO/IMPA and 1:1 ESO/MTHPA. ESO/IMPA 1:0.50 had the lowest cure activation energies during the highest cure conversion range, between 10% and 55%, and the highest degradation activation energies during the 30 and 60% conversion. The Friedman and Vyazovkin isoconversional models provided R2 > 0.99 for cure, except for the ESO/MTHPA composition, presenting a lower R2. In degradation kinetics, the Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) kinetic models presented R2 > 0.99, while the degradation mechanisms were adequately adjusted with Avrami-Erofeev (An) and autocatalytic (n,m)th order (Cnm) during the first and second degradation step. Microstructural analyzes and deeper investigations into the degradation mechanisms in the solid state indicated that in the ESO/IMPA and ESO/MTHPA compounds the processes are controlled by diffusion.