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Manufacturing optimization of HTPB composite propellants: rheological flow and viscoelastic behavior
Summary
This paper is actually about improving how rocket fuel is manufactured, not human health—it studies how to mix rocket propellant ingredients so they flow smoothly during production while still hardening into a strong, stable solid. While this doesn't relate to microplastics or personal health, it matters for aerospace safety: better manufacturing control means more reliable rocket motors, which reduces the risk of defects that could cause launch failures.
The mixing stage is the most critical phase in the production of high-energy composite rocket propellants, where balancing high solids loading with processability remains a major challenge. This experimental study investigates the rheological transition and the resulting viscoelastic properties of five different formulations. Studied samples include three binder matrix systems: cured hydroxyl-terminated polybutadiene (HTPB), a plasticized matrix with dioctyl adipate (DOA), and an aluminum loaded premix, alongside two complete propellants slurries ( solids) evaluated with and without tris-1-(2-methylaziridinyl) phosphine oxide (MAPO) as bonding agent. Rheological characterization at showed that while DOA reduced viscosity by to optimize processability, the addition of ammonium perchlorate (AP) triggers a pseudoplastic behavior accurately described by the Herschel-Bulkley model ( ). Furthermore, Dynamic Mechanical Thermal Analysis and Bohn’s deconvolution model revealed that while AP is the primary driver of the highly restricted mobility fraction ( ), the use of MAPO enhances interfacial efficiency, yielding a reduction in the loss factor magnitude, without compromising the bulk matrix crosslink density. Presented findings provide a quantitative framework for optimizing the trade-off between slurry processability and the structural integrity for pourable high-performance rocket motors. • Rheological transitions were accurately modeled using the Herschel-Bulkley model. • Aluminum loading (6 wt.%) maintained the Newtonian behavior of the binder premix. • MAPO addition slightly increased viscosity while enhancing the viscoelastic response. • Curing time and plasticizer content were optimized for manufacturing. • Perchlorate particle size distribution was tailored for optimal flow.