Оbjectives: to establish a process window for pilot-scale twin-screw compounding of polyethylene terephthalate glycol (PETG) with short carbon fibre for subsequent FFF filament production and to identify the parameters that are critical to material reproducibility.
Methods. Two formulations containing 5 and 10 wt% carbon fibre and 2 wt% maleic-anhydride-functionalised low-density polyethylene were analysed. PETG was dried at 65 °C for 3 h, milled to 50–150 μm and sieved. Compounding was performed in a 30 mm twin-screw extruder with L/D = 44 at 220 rpm, a melt pressure of 1.0 MPa and a drive load of 70%. Descriptive analysis included screw length, peripheral speed, component mass ratios and the 11-zone thermal profile.
Results. The thermal sequence comprised heating from 200 to 240 °C with a 240 °C plateau, controlled cooling to 210 °C, and terminal stabilisation at 230 °C. The active screw length was 1.32 m and the peripheral speed was 0.346 m/s. For 5 and 10 wt% fibre, PETG-to-fibre ratios were 18.6 and 8.8, while compatibiliser-to-fibre ratios were 0.40 and 0.20. A critical-parameter map covering initial polymer drying through final pellet drying was developed. Pilot-batch filament was processable on an open-frame FFF printer; the screening flexural modulus was 3.5–4.0 GPa.
Conclusions. Reproducible carbon-filled PETG requires coordinated control of moisture, feeding, thermomechanical history and strand drawing. The 3.5–4.0 GPa value is flexural modulus, not flexural strength. Separating fibre-content and supplier effects requires factorial experiments, rheology, microscopy and standardised mechanical testing.