Haake minijet 2 pro

The compounding of the composite formulations was conducted in a parallel co-rotating twin screw extruder (Thermo Scientific Process 11, Thermo Fisher Scientific, Waltham, MA, USA) in accordance with the following temperature profile from hopper to die: 160-160-170-180-180-180-175-175 °C. A screw speed of 150 rpm and a feed rate (single screw feeder) of 5 were used. The Process 11 contains a 40:1 L:D ratio barrel with two 11 mm fully segmented, co-rotating screws. A standard screw configuration was employed, with conveying elements (helix pitch of 1 L/D) interspaced among three mixing sections obtaining alternating elements with 0° and 90° (length ¼ L/D). Finally, a discharge extrusion element (1 ½ L/D) with a single lead geometry was used to generate the needed extrusion pressure.
After compounding, the specimens for the thermal and mechanical analyses were obtained by injection moulding (Haake MiniJet II Pro, Thermo Fisher Scientific, Waltham, MA, USA) with a mould and loading cylinder kept at 50 °C and 175 °C, respectively. Samples were injected with a pressure of 600 bar held for 10 s and a post pressure of 60 bar maintained for another 10 s. Then, the mould was manually opened and prepared for the next injection cycle. All the manufactured composite formulations are listed in Table 1.

Specimens for the mechanical and thermal characterizations were manufactured by extrusion and injection molding. Prior to extrusion, materials were dried overnight at 80 °C. Extrusion was carried out in a co-rotating twin-screw extruder (Thermo Scientific Process 11, Thermo Fisher Scientific, Waltham, MA, USA) and the tensile, flexural and impact specimens were obtained by injection molding (Haake MiniJet II Pro, Thermo Fisher Scientific). The temperature profile (8 zones) inside the extruder was as follows (from feed to die): 170-180-180-190-200-200-290-190 °C. The screw speed was set at 200 rpm. The mold during injection molding was maintained at 35 °C, while the loading cylinder was heated at 190 °C. The injection procedure consisted of two steps: a first injection step at a pressure of 450 bar for 10 s, and a post injection step at 60 bar for an additional 10 s. All the formulations along with the characterization techniques used for each formulation are listed in Table 2.

All formulations produced and tested are listed in Table 1. Raw materials (pellets and fibres) were fed in a co-rotating twin-screw extruder (Thermo Scientific Process 11, Thermo Fisher Scientific, Waltham, MA, USA) and the tensile specimens were obtained by injection moulding (Haake MiniJet II Pro, Thermo Fisher Scientific). Prior to extrusion, the hemp fibre compound was dried at 115 °C for 2 h. Two different temperature profiles (8 zones) were used for basalt and hemp-based formulations, due to differences in viscosity of the blends and thermal stability of the fibres, namely 170–180–190–200–200–190–180–180 °C and 150–160–170–180–180–170–160–160 °C, respectively. Screw speed was set at 150 rpm. The mould during injection moulding was maintained at 40 °C, while the loading cylinder was heated at 220 °C for basalt composites and at 180 °C for hemp and hybrid formulations. The injection procedure included two steps: a first injection step at a pressure in the range of 350–550 bar, depending on the fibre amount, for 10 s and a post injection step at 60 bar for an additional 10 s.