Process for producing a multimodal polyolefin composition in an extruder device

A continuous process for preparing a multimodal polyolefin composition comprising one or more antioxidants, comprising the steps of:

• a) preparing a multimodal polyolefin in form of a polyolefin powder having a mass-median-diameter D50 in the range from 300 μm to 2500 μm, in a series of two or more polymerization reactors by polymerizing one or more 1-olefins in the presence of an olefin polymerization catalyst at pressures from 0.5 MPa to 10 MPa and temperatures from 30° C. to 160° C., wherein the multimodal polyolefin being a multimodal polyethylene;
• b) providing an organic peroxide in an amount from 20 ppm to less than 100 ppm, with respect to the polyolefin powder;
• c) mixing the polyolefin powder and the organic peroxide at a temperature in the range from 10° C. to 100° C., without melting the polyolefin powder, thereby forming a polyolefin peroxide mixture;
• d) melting and homogenizing the polyolefin peroxide mixture within an extruder device, wherein at least 90 wt. % of the organic peroxide decomposes, thereby forming a molten polyolefin composition;
• e) adding one or more antioxidants to the molten polyolefin composition, thereby forming a combination of molten polyolefin composition and antioxidant;
• f) homogenizing the combination of molten polyolefin composition and antioxidant, thereby forming an antioxidant equipped molten polyolefin composition;
• and
• g) pelletizing the antioxidant equipped molten polyolefin composition.