Method for producing polymer compound

A method of producing a polymer compound by thermoplasticizing crosslinked polyethylene by an extruder, comprising the steps of:

• mixing the crosslinked polyethylene, first non-crosslinked polyethylene and an additive to generate a mixture;
• thermoplasticizing the crosslinked polyethylene by applying heat and shear stress to the mixture fed from a first feeding section of the extruder;
• and
• kneading the mixture after the thermoplasticizing step and second non-crosslinked polyethylene fed from a second feeding section of the extruder;
• wherein an amount of the first non-crosslinked polyethylene in the mixing step is 1 to 5 parts by weight per 100 parts by weight of the crosslinked polyethylene, wherein the additive includes at least one non-crosslinked polymer compound selected from ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer, ethylene methyl methacrylate copolymer, or ethylene ethyl methacrylate copolymer,
• wherein an amount of the additive is 0.1 to 3 parts by weight per 100 parts by weight of the crosslinked polyethylene,
• wherein the shear stress in the thermoplasticizing step is generated at a shear rate of 10,000 to 15,000 s−1 for 5 to 30 seconds, and
• wherein an amount of the second non-crosslinked polyethylene fed in the kneading step is 50 to 150 parts by weight per 100 parts by weight of the crosslinked polyethylene.