Process for producing a polypropylene composition, and polypropylene composition so produced

A process for producing a polypropylene composition using a compounding extruder comprising

• a) a melting section comprising
• ai) a first elongated cylindrical tube having
• an end portion having a first inlet port configured to receive, in operation, a propylene-based polymer and optional additives and
• an end portion having a first outlet port configured to discharge, in operation, a first melt composition comprising a melt of the propylene-based polymer and the optional additives and
• aii) a first screw arranged in the first elongated cylindrical tube and having a first length L1, a first outer screw diameter Do1 and a first inner screw diameter Di1 configured to, in operation, convey the propylene-based polymer and the optional additives to the first outlet port and
• b) a mixing section comprising
• bi) a second elongated cylindrical tube having
• an end portion having a second inlet port configured to receive, in operation, the first melt composition from the first outlet port,
• an end portion having a second outlet port and
• a side inlet port between the second inlet port and the second outlet port configured to, in operation, receive a further component,
• wherein the second outlet port is configured to discharge, in operation, a second melt composition comprising the first melt composition and the further component and
• bii) a second screw arranged in the second elongated cylindrical tube and having a second length L2, a second outer screw diameter Do2 and a second inner screw diameter Di2 configured to, in operation, convey the first melt composition and the further component to the second outlet,
• wherein the first screw and the second screw are operable at different screw speeds,
• wherein the process comprises the step of:
• A) feeding the propylene-based polymer and the optional additives to the first inlet and discharging the first melt composition from the first outlet, wherein the first screw is operated at a first screw speed,
• B) feeding the first melt composition from the first outlet to the second inlet and feeding the further component to the side inlet and discharging the second melt composition from the second outlet, wherein the second screw is operated at a second screw speed smaller than the first screw speed, and
• C) optionally forming the second melt composition into pellets.