Changes in activation energy and kinetic mechanism during EVA crosslinking

The activation energy and kinetic mechanism throughout the crosslinking process of copolymer ethylene-vinyl acetate (EVA), initiated by dicumyl peroxide (DCP), were determined in the framework of a multi-step solid-state process. Crosslinking was performed in a differential scanning calorimeter (DSC) under non-isothermal conditions. The activation energy (E) was determined by means of the isoconversional integral method using the Cai approach. The E values (87-105 kJ mol−1) were found to be dependent on the crosslinking conversion (α) and DCP content. Kinetic mechanisms were determined by the Criado method from Eα(T) data through the use of the master plots of theoretical kinetic models. At 0.1 < α < 0.5, the EVA crosslinking obeys homogeneous kinetics with rate-controlled reactions (Fn mechanisms). At α ≥ 0.5, the medium becomes heterogeneous and EVA crosslinking occurs through a diffusion-controlled reaction (Dn mechanisms). At α ≅ 0.9, the temperature increases and the EVA crosslinking follows homogeneous kinetics with Fn mechanisms.