2.3. Preparation of Filaments and Printing

Wool powders were separately blended with PCL pellets in a twin-screw extruder (Wayne, NJ, USA) to formulate wool/PCL pellets. There were two hoppers in the machine, the main hopper and the side hopper, used for separate input of PCL and wool. The feeding speed of wool powders was adjusted to 0.22 kg/h and 0.5 kg/h to obtain 10/90 and 20/80 wool/PCL combinations, respectively. A further high amount of wool was not considered due to breakage and poor results reported in the previous study [34]. The temperatures from Zone 1 to 6 were increasingly set from 82 to 93 °C and 96 °C for the die zone following previous wool/PCL extrusion work [34]. The extruded wool/PCL was passed through a water bath for cooling, and wool/PCL pellets were collected through a pelletiser.

The prepared filaments were then extruded through a desktop extruder (Wellzoom, Shenzhen Mistar Technology Co., Ltd, Shenzhen, China) to obtain the 3D printable filament. The temperature was maintained at 95 °C for preheating and 90 °C for extrusion stages [34]. The filaments were prepared at 2000 mm/min speed through a 1.75 mm nozzle, resulting in the final diameter of 1.40 ± 0.05 mm. A control filament was also prepared using the same parameter as the pure PCL pellets.

The 3D printing of dog-bone shapes was performed as per ISO 527-2 [37] 5A by an i3 MK3 3D printer (Prusa Research, Prague, Czech Republic) using a 0.4 mm nozzle. The printing temperature was tested and adjusted to 130 °C to obtain the optimised printability from the composite filaments. The printing bed temperature was set to 25 °C. A 50% infill was used to print specimens of concentric, rectilinear and gyroid patterns, while top and bottom fill patterns for all of the samples were monotonic. A 45° fill angle was used for the printing, and the speed of infill was 80 mm/min, though the first layer speed was set to 20 mm/min. The nomenclature of the printed specimens is shown in Table 1. Figure 1 shows the equipment used from powder preparation to 3D printing along with the designs used for printing and time, and filament consumption differed across filling patterns.

(a) Cutting machine, (b) attritor tank, (c) ring grinder, (d) twin-screw extruder used for pellet making, (e) filament extruder, (f) produced filament, (g) 3D printing with filament, (h) differences in filament length and printing time across different patterns when printing 10 samples at once, and (i) patterns used for infill.

Nomenclature of the 3D-printed specimens based on wool fineness and wool loading.