A kinetic study of the decross-linking of cross-linked polyethylene in supercritical methanol

The recycling of cross-linked polyethylene (XLPE) by a decross-linking reaction in supercritical methanol was studied using a batch reactor. XLPEs with initial gel contents of 45, 55 and 65% were employed and subjected to reaction temperatures between 320 and 360 degrees C. Complete decross-linking of XLPE was achieved in 10 min in supercritical methanol at 360 degrees C and 15 MPa. For the first time, chemical kinetics for the decross-linking reaction is proposed based on the gel concentration, and applicable to the reactor design. With respect to the gel concentration, the first-order reaction model agreed well with the experimental results. The evaluated kinetic constant was 0.0867 +/- 0.0082 cm(3)/mg min at 350 degrees C, and the activation energy was 578 +/- 25 kJ/mol. (C) 2008 Elsevier Ltd. All rights reserved.