Strategies for Paraffin-based Fuels Reinforcement: 3D Printing and Blending with Polymers

Although affordable and fast burning, paraffin waxes are rarely exploited as fuels in real flying systems because of their poor mechanical properties. To date, the identification of the paraffin-based formulations offering both high ballistic performance and structural integrity is still a tough challenge. The Space Propulsion Laboratory is exploring how to enhance the mechanical performance of paraffin waxes pursuing two strategies: blending with thermoplastic polymers, i.e. paraffin blends, and embedding a 3D printed reinforcement in the paraffin fuel, i.e. armored grains. The two approaches are eventually combined together to identify the most promising configurations in terms of mechanical and ballistic properties. Paraffin blends are manufactured by blending the pristine waxes with a thermoplastic polymer at different mass fractions. Armored grains are produced by inserting a 3D printed gyroid-like scaffold in the (unblended and blended) paraffin formulations. Comparative studies between paraffin fuels and armored grains have been carried out inspecting the pre-burning and burning behavior. Numerical and experimental studies are performed on armored grains to simulate their behavior at compression. The armored grains exhibit ductile behavior and high strain energy, overcoming the brittleness of the pure waxes and of paraffin blends. Moreover, the armored grains show higher regression rates than the paraffin-based formulations.