Manufacturing optimization of HTPB composite propellants: rheological flow and viscoelastic behavior

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.