Laser-Induced Deflagration of Unconfined HMX - The Effect of Energetic Binders

The effect of three energetic binders [poly(3-methyl-3-nitratomethyloxetane (polyNIMMO), polyglycidyl nitrate (polyGLYN) and an energetic polyphosphazene (PPZ-E) - all at 10%] on the unconfined laser-induced deflagration of cyclotetramethylene tetranitramine, commonly known as High Melting point Explosive (HMX) by a near IR (NIR) diode laser (801 nm) has been examined. Hydroxyl terminated polybutadiene (HTPB) and PPZ (the precursor to PPZ-E - before nitration) were used as reference materials. The formulations required the addition of an optical sensitizer - carbon black (CB) - for ignition. At the designated threshold flux density of 2.3 kW cm(-2), a minimum of similar to 1 wt.-% CB was needed for the reliable ignition of unbound HMX and its formulations with polyGLYN, PPZ-E and PPZ. Under similar conditions HMX/polyNIMMO and HMX/HTPB required 3% CB. Ignition maps (ignition time versus laser flux density) have been constructed for the five formulations. Comparison of ignition times and ignition energy densities for HMX and HMX/polyGLYN showed this binder to have only a marginal effect. In contrast, HTPB, PPZ and PPZ-E all retarded HMX ignition at the threshold flux density, but showed negligible effect at higher flux densities. As PPZ and PPZ-E produced both similar delays in the ignition time and similar increases in the flame development times (10-90%) at the threshold flux density, the inhibition of the HMX ignition by these PPZs appears to be largely independent of the polymer energy content. Such characteristics could be useful for high performance and insensitive energetic formulations. PolyNIMMO (3% CB) increased the ignition time of HMX only slightly at 2.3 kW cm(-2). However, at this threshold flux level the HMX flame development times with polyNIMMO or HTPB were much longer than that for the unbound material: this effect is attributed to the enhanced CB content.