Continuous Process for Recycling Silane Cross-Linked Polyethylene Using Supercritical Alcohol and Extruders

In this study, we developed a continuous process using extruders in a pilot plant for recycling silane cross-linked polyethylene (silane-XLPE) via chemical reaction in supercritical alcohol. As a first step, an autoclave was employed to reveal the effects of temperature and pressure on the reaction that selectively decomposes the siloxane cross-linking bonds. Selective decomposition of the siloxane bond was found to occur in the supercritical alcohol. In the next step, an extruder was used to continuously feed silane-XLPE into a tube reactor containing supercritical alcohol. Silane-XLPE was then extruded with an injection of supercritical alcohol. Alcohol remained in the supercritical state inside the cylinders of the extruder and the tube reactor. The recycled polyethylene (PE) was continuously extruded from the reactor at a rate of 14 kg/h. The product produced by this continuous process was the same as that from the autoclave. The mechanical properties of the recycled PE satisfied the requirements for use as a wire and cable insulation material. These results suggest that the extruder proved to be useful for the continuous denaturation of a cross-linked polymer in supercritical alcohol.