Energetic Characterization of Thermoplastic Fuels for Hybrid Rocket Propulsion Applications

Hybrid rocket propulsion systems are becoming increasingly popular due to their balance of safety, performance, and simplicity. With the growing adoption of additive manufacturing in propulsion research, 3D-printed thermoplastics are emerging as customizable and easily fabricated hybrid rocket fuels. However, limited energetic data exist for these materials, particularly those designed for additive manufacturing. This study experimentally characterizes the higher heating value (HHV) of several commercially available thermoplastics relevant to hybrid rocket development. Acrylonitrile butadiene styrene (ABS), polycyclohexylenedimethylene terephthalate glycol (PCTG), polyethylene terephthalate glycol (PETG-HF), acrylonitrile styrene acrylate (ASA), thermoplastic polyurethane (TPU 95A HF), and polyamide 6 (PA6) were evaluated using a Parr 6200 Isoperibol Bomb Calorimeter operating under constant-volume combustion in a pressurized oxygen environment. Each material was tested five times to ensure repeatability, and fuse-wire and system corrections were applied following ASTM D240 protocols. Results show that ABS exhibits the highest energy content, with Atomic Filaments ABS producing an average HHV of 34.75 MJ/kg, followed by Toner Natural ABS at 34.47 MJ/kg, IC3D ABS at 34.24 MJ/kg, Polymaker ASA at 31.92 MJ/kg, SunLu Nylon (PA6) at 26.30 MJ/kg, 3DXTECH PCTG at 23.25 MJ/kg, Bambu Labs TPU 95A HF at 23.18 MJ/kg, and Bambu Labs PETG-HF at 20.26 MJ/kg. These results follow expected trends based on polymer composition and confirm that ABS-based thermoplastics provide the highest energy release among the materials tested for hybrid rocket applications. The experimentally determined HHVs establish a quantitative baseline for selecting 3D-printable thermoplastics in hybrid motor design and will support future thermochemical performance modeling and combustion analysis.