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 Cat approach. The E values (87-105 kJ mol(-1)) were found to be dependent on the crosslinking conversion (alpha) and DCP content. Kinetic mechanisms were determined by the Criado method from E alpha((T)), data through the use of the master plots of theoretical kinetic models. At 0.1 < alpha < 0.5. the EVA crosslinking obeys homogeneous kinetics with rate-controlled reactions (F(n) mechanisms). At alpha > 0.5, the medium becomes heterogeneous and EVA crosslinking occurs through a diffusion-controlled reaction (D(n) mechanisms). At alpha congruent to 0.9, the temperature increases and the EVA crosslinking follows homogeneous kinetics with F(n) mechanisms. (C) 2011 Elsevier Ltd. All rights reserved.