Disclosed is a process for preparation of a propylene-based polymer composition involving the steps of: (a) mixing a propylene-based polymer and a peroxydicarbonate in a mixing device, wherein the mixing takes place at a temperature of ≤30° C., wherein the peroxydicarbonate is introduced into the mixing process in a dry form; (b) keeping the mixed composition at a temperature of ≤30° C.; (c) feeding the mixed composition into a melt extruder; (d) homogenizing the mixed composition at a temperature where the propylene-based polymer is in solid state during an average residence time of ≥6.0 and ≤30.0 seconds; (e) further homogenizing the mixed composition at a temperature at which the propylene-based polymer is in the molten state; and (f) extruding the homogenized material from a die outlet of the melt extruder followed by cooling and solidification; wherein the steps (a) through (f) are conducted in that order.