Granular crosslinkable medium-density polyethylene (XLPE) without scorch inhibitor was prepared adding organic peroxide [2, 5-dimethyl-2, 5-di-(t-butylperoxy) hexyne-3] through extrution process, in industrial scale. Twin screw extruder was used to mix the polyethylene and the peroxide. The temperature zones of the extruder were controlled very carefully to prevent unwanted crosslinking during extrusion. Compression molding, rotational molding, and injection molding of XLPE at 155 degrees C made no crosslinking in PE, and then they were exposed to higher temperatures at which the organic peroxide decomposed to provide free radicals which led to the crosslinking of the MDPE. The thermal properties (using dynamic mechanical analysis, DMA, differential scanning calorimetric analysis, DSC, and thermogravimetric analysis, TGA, techniques) and mechanical properties (including strain at break and stress at break) of virgin PE, crosslinkable PE, and crosslinked PE have been compared. The crossliked PE and virgin PE were also studied by X-ray diffraction (XRD) technique. (c) 2007 Wiley Periodicals, Inc.