Ingredient and processing effects on the burning rates of composite rocket propellants utilizing a reduced-run mixture–process experiment design

Composite propellants are now being processed using twin screw extrusion (TSE) to enhance process safety, reduce production costs, minimize lot-to-lot variation, and in some cases, enhance performance. The process is a complex system consisting of multiple ingredient streams feeding into a continuous mixer with an output through an extrusion die producing a structure that is cut into 30-in. lengths of solid composite propellant. By exploiting transient effects of ingredient feeding rate changes during processing, the TSE can be used to easily process composite propellants over wide composition ranges to vary properties for creating rocket motor grains with compositional gradients or to develop new formulations through a combinatorial approach. Therefore, it is necessary to develop a systematic approach for quantifying ingredient and processing effects in TSE on composite propellants processed in a steady-state to serve as a baseline for comparison with composite propellants processed in a transient-state. Such an approach is described using a reduced-run mixture–process experiment design based on the KCV algorithm to minimize the number of samples required for testing over a wide composition range. A corresponding response surface analysis of the results from these experiments indicates a significant dependence of burning rate on both ingredients and processing conditions.