Extrusion was carried out using a corotating twin-screw extruder
(Hermann Berstorff Laboratory, ZE25×33D, Hannover,
Germany) with the length/diameter ratio of 870:25. The extruder
was equipped with a volumetric twin-screw feeder (K-Tron soder
AG 5702, type 20; Niederlenz, Switzerland), which could maintain
the solid feed rate at 22 to 23.6 kg/h.