Single-shaft extruder and use of a single-shaft extruder, and method for altering morphology of a superabsorbent polymer gel using a single-shaft extruder

A single-screw extruder (10) for changing a morphology of a superabsorbent polymer gel (SAP polymer gel) (24), having:

• an input aperture (36) for the introduction of SAP polymer gel (24),
• connected to the input aperture (36), a channel (16),
• arranged in the channel (16), a screw (12) for conveying, and changing the morphology of, the SAP polymer gel (24), and
• connected to the channel (16), an output aperture (30) for the discharge of the SAP polymer gel (44) with changed morphology,
• where the screw (12) has a shank (13) and has screw flights (14) arranged on the shank (13) and is arranged and configured to convey the SAP polymer gel (24) from the input aperture (36) to the output aperture (30) by means of the screw flights (14),
• where the channel (16) has an input zone (26) arranged at, or in the vicinity of, the input aperture (36), an output zone (28) arranged at, or in the vicinity of, the output aperture (30), and a conveying zone (18) extending along the channel (16) from the input zone (26) to the output zone (28),
• wherein
• the screw (12) has a pitch value of a pitch (G) of the screw flights (14) along the conveying zone (18) of the channel (16), and where the channel (16) has at least one mixing-element arrangement (49) with at least one mixing element which protrudes into the channel (16) of the single-screw extruder and which is configured for the mixing of the SAP polymer gel (24);
• wherein the mixing-element arrangement (49) has a pin arrangement (48) comprising at least one pin (48.1, 48.2) extending into an internal space (17) of the channel (16), and has at least one cutout (50) along the screw flights (14), the at least one pin (48.1, 48.2) extending in particular into the at least one cutout (50) of the screw flights (14);
• wherein the channel (16) has at least two pins (48) arranged along the channel (16) in the conveying direction (20) and separated from one another by a mixing-element separation (K), and there is a negative correlation between a value of the mixing-element separation (K1, K2, K3, K4) and a pitch value (G1, G2, G3) of the pitch (G) of the screw flights (14);
• the negative correlation between the mixing-element separation (K) and the pitch (G) is such that a smaller value of the mixing-element separation (K1, K2, K3, K4, K5) is provided when a larger pitch value (G1, G2, G3) is provided;
• and
• wherein the pitch values (G1, G2, G3, G4) change so as to increase along the conveying direction (20), and the change of the mixing-element separation values (K1, K2, K3, K4, K5) along the conveying direction (20) proceeds in an opposite manner with respect to the change of the pitch values (G1, G2, G3, G4) along the conveying direction (20).