A single-screw extruder for changing a morphology of a superabsorbent polymer, specifically a polymer gel. The single-screw extruder has an input aperture, a channel, a screw and an output aperture. The screw has a pitch value of a pitch of the screw flights along the conveying zone of the channel, where the channel has a mixing-element arrangement with at least one mixing element which protrudes into the channel of the single-screw extruder and which is configured for the mixing of the SAP polymer gel.