Thermal ageing of rocket propellant formulations containing ε-HNIW (ε-CL20) investigated by heat generation rate and mass loss

Abstract

New types of rocket propellant batches have been formulated with the objective of achieving higher burning rates. The main ingredients are (1) the energetic plasticizers glycidyl azide polymer-α,ω-diazide (GAP)-A (short chain GAP with azide end groups), trimethylolethane trinitrate (TMETN) and 1,2,4-butanetriol trinitrate (BTTN), (2) the energetic substances ammonium perchlorate (AP) and ε-CL20 (ε-HNIW, hexanitrohexazaisowurtzitane, crystallised in ε-phase). The binder is GAP (glycidyl azide polymer, diol component) cured with the polyisocyanate Desmodur™ N100. From the point of view of stability and ageing, the interesting fact is that the formulations contain none of the typical stabilisers for the nitric acid ester components TMETN and BTTN, although their contents range up to 21 mass%. One reason for doing so is to increase the content of the high energy ingredients. Seven formulations were examined in more detail. To assess basic stability the autoignition temperature test, Dutch mass loss test and vacuum stability test were used. To investigate ageing, two measurement quantities are applied: heat generation rate (heat flow) as function of time at 70, 80 and 89 °C and mass loss as function of time at the temperatures of 70, 80 and 90 °C. The evaluation of the measurements was done with reaction kinetic models. One batch (#189) containing BTTN shows significantly lower activation energy and pre-exponential factor. From mass loss one gets as activation energy for #189 of 101 kJ mol −1 in comparison to the range of 126–135 kJ mol −1 for the six other batches. But, based on the ageing caused by chemical decomposition reactions, all seven batches showed a good ageing behaviour. A use time period of up to 20 years of use seems realistic.