(617bz) Decrosslinking and Decomposition of Silane-Crosslinked Polyethylene in Supercritical Methanol and Water

Giyoung Hong, Jebin Ryu, Hee Suk Woo, Won-Su Son, Kuan Wwan Park and Youn-Woo Lee

In decades, the necessity of plastic recycling has risen due to increasing concerns about environmental pollution and oil depletion. The chemical recycling which recovers monomers or starting material from plastics by depolymerization or decomposition is a promising strategy because the recycled monomers obtained can be used for any application regardless of the property of the original polymer before recycling. However, to utilize this advantage of chemical recycling, the recovery of monomers having good quality with high yield is essential. Many researchers have reported that supercritical fluid technology will be the promising methods for recycling of the plastics because of its characteristic properties. For example, Water and alcohol are representative polar solvents at ambient conditions, however, their polarity decreases dramatically under supercritical conditions. so that supercritical water and alcohol can be applied as good solvent to treat nonpolar polymer. In this study, the decrosslinking reaction of silane-crosslinked polyethylene (S-XLPE) in supercritical fluids was investigated. Various experiments have been performed under conditions of different temperature, pressure, reaction time, kind of solvents, weight ratio of solvent to polymer in batch reactor system. The change of gel content and molecular weight along with reaction temperature and reaction time was analyzed and the kinetic parameters were calculated from the experimental data. The complete decrosslinking of S-XLPE was achieved at several conditions, and the reaction time for the decrosslinking was shortened as the reaction proceed. The decrosslinking rate of S-XLPE was fitted well with the first order reaction model. The molecular weight of de-crosslinked polyethylene (DXPE) decreased as reaction temperature and reaction time increased when the reaction temperature exceeded 360°C. The decrease of molecular weight of DXPE was also fitted well with the first order reaction model when it was assumed that the decreasing rate was linearly dependent on the molecular weight of DXPE.