Effect of Curing Agent on the Plateau Burning Mechanism of Solid Propellant Sandwiches

Abstract

This study focuses on further understanding of the plateau burning mechanism of sandwiches containing a matrix of fine ammonium perchlorate (AP) particles and low/high-melt binder as affected by the type of the curing agent. Pure binder sandwiches and matrix sandwiches of various fine AP/binder ratios with two different curatives, isophorone diisocyanate (IPDI) and toluene diisocyanate (TDI), are considered. The burning rate versus middle lamina thickness curves are obtained to examine the interaction between the leading-edge flames (LEFs) anchored over the lamina interface edges. Pressure variation on matrix sandwich burning rates is considered in 1–12 MPa range. High-magnification combustion images and quenched surface features and profiles of these sandwiches are also examined. The IPDI-cured binder causes larger LEF standoff and inter-LEF distances in both pure binder and matrix sandwiches than the TDI-cured one. Consequently, the disparity in the burning rates with middle lamina thickness of IPDI-cured matrix sandwiches is minimal. The binder melt-layer thickness and its melt viscosity determine the flammability limits and midpressure extinction regimes of matrices depending upon the curative. Plateau burning trends of matrix sandwiches with large middle lamina thickness (greater than ) are observed to coincide with midpressure extinction of their corresponding matrices.