Process for preparation of ethylene homopolymers or copolymers, comprising the steps of a) polymerization of ethylene or of ethylene with one or more other 1-olefins in the presence of a chromium catalyst at temperatures of from 20 to 200° C. and at pressures of from 0.1 to 20 MPa, where the chromium catalyst can be prepared via application of one or more chromium compounds to a silicate support and subsequent thermal activation under oxidative conditions at temperatures of from 620 to 900° C.; b) mixing of the polyethylene in the melt in the presence of from 1000 to 2000 ppm of an antioxidant comprising at least one sterically hindered phenol and comprising at least one phosphite in a mixing ratio of from 1:5 to 5:1, with specific energy input of at least 0.17 kWh/kg.