A Kinetic Study on the Decrosslinking Reaction of Crosslinked Polyethylene using Continuous Supercritical Extrusion Process

Abstract

The decrosslinking reaction of thermoset polymers under supercritical conditions have been sought out an environmentally friendly processing technique. In order to discover the most effective response solvent and a safe alternative medium during a continuous decrosslinking reaction, a kinetic study on the decrosslinking reaction of silane-crosslinked polyethylene (S-XLPE) in diverse sub- and supercritical solvents was undertaken. The decrosslinking reaction in the continuous reactor accorded well with the first-order reaction model in which the reaction rate was linearly proportional to the gel content. The reaction rate was linearly comparative to the gel content and related exponentially to the return temperature. The reaction rate constant values were observed as 2.806, 2.569, 2.383, and 2.130 min–1 in supercritical methanol, supercritical ethanol, supercritical 2-propanol, and subcritical water at 380 °C, respectively. Furthermore, the standards of activation energy calculated by Arrhenius equation were 124 kJ mol–1 for methanol, 123.6 kJ mol–1 for ethanol, and 124.7 kJ mol–1 for 2-propanol, 157.1 kJ mol–1 for water, individually. It was exposed that even though the rate constant was higher in order of methanol, ethanol, 2-propanol, and water, the rate constant for ethanol was corresponding to that for methanol. As regards to the reaction rate and solvents toxicity, ethanol was revealed as the best alternative solvent for the continuous decrosslinking reaction of S-XLPE.