Ingredient and processing effects on the burning rates of composite rocket propellants utilizing a reduced-run mixture–process experiment design Frederick M. Gallant a, ⁎ , Suzanne E. Prickett a , Mario Cesarec a , Hugh A. Bruck b a Naval Surface Warfare Center, Indian Head Division (NSWC, IHDIV), 101 Strauss Ave., Indian Head, MD 20640, USA b Department of Mechanical Engineering, Martin Hall, University of Maryland, College Park, MD 20, USA Received 2 November 2006; received in revised form 20 July 2007; accepted 1 August 2007 Available online 24 August 2007 Abstract 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. © 2007 Elsevier B.V. All rights reserved. Keywords: Design of experiments; Mixture experiment; Process variables; Response surface 1. Introduction 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 [1]. There are many factors that contribute to the burning rate of a composite propellant. For example, ingredient combustion properties, concentrations, and particle sizes [2,3], method of preparation [4,5], and testing conditions [6] are just a few factors that have been used in the engineering of composite propellant formulations with a desired burning rate. There is also empirical evidence that the TSE process variables can affect burning rate properties as well [5]. However there is no experimental data to systematically identify the quantitative effects of the ingredients and process variables (e.g., oxidizer particle size distribution, filler concentration, rate modifiers, screw geometry, extruder screw speed, etc.) on the burning rate of composite propellants processed using TSE. Thompson and Michienzi [7] have published a well-designed study for many of these ingredient effects on an experimental composite propellant for Naval applications, designated IH- AC3, an ammonium perchlorate (AP) based rocket propellant, using the batch process to support the development of a near infrared spectroscopy technique to predict burning rate. This data was important, but not relevant in light of the unaccounted differences in burning rate observed by Muscato [5] between batch and continuously processed IH-AC3. However, these observations have yet to be followed by a quantitative and systematic investigation to determine the influence of the process conditions relative to the oxidizer concentration on the strand burning rate in TSE-processed composite propellants. Available online at www.sciencedirect.com Chemometrics and Intelligent Laboratory Systems 90 (2008) 49 – 63 www.elsevier.com/locate/chemolab ⁎ Corresponding author. Naval Surface Warfare Center, Indian Head Division (NSWC, IHDIV), 101 Strauss Ave., Building D-69, Indian Head, Maryland 20640, United States. Tel.: +1 301 744 2456; fax: +1 301 744 6522. E-mail addresses: frederick.gallant@navy.mil (F.M. Gallant), suzanne.prickett@navy.mil (S.E. Prickett), mario.cesarec@navy.mil (M. Cesarec), bruck@eng.umd.edu (H.A. Bruck). 0169-7439/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.chemolab.2007.08.007