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This study delves into the rheological and mechanical properties of a 3D-printable composite solid propellant with 80% wt solids loading. Polybutadiene is used as a binder with ammonium sulfate, which is added as an inert replacement for the ammonium perchlorate oxidizer. Further additives are introduced to allow for UV curing. An in-house illumination system made of four UV-A LEDs (385 nm) is employed to cure the resulting slurry. Rheological and mechanical tests are conducted to evaluate the viscosity, ultimate tensile strength and strain, and compression behavior. Viscosity tests are performed for both pure resin and complete propellant composition. A viscosity reduction factor is obtained for the tested formulations when pre-heating slurry. Uniaxial tensile and compression tests reveal that the mechanical properties are consistent with previous research. Results emphasize the critical role of temperature and solid loading percentage. Pre-heating resin composites may grant a proper viscosity reduction while keeping mechanical properties in the applicability range. Overall, these findings pave the way for the development of a 3D printer prototype for composite solid propellants.

Composite solid propellants have used cast molding production technology for many decades, with intrinsic limitations on production flexibility, promptness, and grain geometry, as well as environmental implications on toxicity and global carbon footprint. This traditional method involves the use of toxic chemicals, has a long processing time, requires high temperature, and the products have limited geometries. To overcome those issues, different photo-curable resins have been evaluated as possible matrices. In fact, the UV-curing process is fast and has low energy consumption. The photocuring reaction parameters of six different pristine formulations were evaluated by Fourier transform infrared spectroscopy analysis. After finding the optimal curing parameters, different composites were prepared by adding 75 or 80 wt% ammonium sulfate particles used as an inert replacement for the oxidant. The thermomechanical properties and thermal resistance of the UV-cured composites were characterized via dynamic thermal-mechanical and thermogravimetric analysis. Subsequently, the mechanical properties of the inert propellants were investigated by tensile tests. The most promising resin systems for the production of solid rocket propellants were then 3D printed by an in-house developed illumination system and the obtained object micro-structure was evaluated by X-ray computed tomography.