Recovering of components from plastic bonded propellants

Economic reasons and the protection of the environment demand methods of disposal allowing to recover and re-use materials, which have been in service as well as to avoid producing unwanted or harmful substances when doing so. This also applies for propellants and explosives. Recently developed propellants contain expensive crystalline energetic materials such as the nitramines, hexogen (RDX) and octogen (HMX), bonded in a chemical three-dimensional crosslinked polyurethane matrix. These substances are called “plastic bonded propellants”. In order to recover the components, the polyurethane matrix is broken solvolytically with pure water and alkaline water (0.05 n–0.5 n NaOH) at temperatures between 130 and 170°C in a pressure cell. From a model rocket propellant, consisting of a polyetherpolyol mixture (Lupranol 1000/2021) cured with Desmodur T80 and filled with 60 mass% ammonium perchlorate (AP), 84–90% of the polyetherpolyol component was recovered, and 98% of the AP content subsequently determined in the aqueous solvolysate. The polyetherpolyols were nearly not changed at the high solvolytic stress of 170°C and 2 h, as shown by the molar mass distributions, determined by using gel permeation chromatography. The solid gun propellant KHP consisting of 86 mass% hexogen (RDX) and 14 mass% GAP-N100 binder was solvolyzed at 130, 150 and 170°C with pure water and with 0.05 n NaOH for corresponding time periods of 10, 30 and 60 min. Hexogen is recoverable with high yields and with high purity. GAP (glycidyl azide polymer) is a polyetherdiol as Lupranol 1000, formally on the basis of propane-1,2-diol with azide (N3) groups attached to its lateral methyl groups. It does not behave in the same way as the Lupranol polyetherpolyols. Under exposure to solvolytic conditions, its molar mass distribution is broadened and its azide content is reduced, which was determined via infrared absorption of the asymmetric N3 stretching vibration, and via its energy content using DSC, in both cases in relation to the azide content of the unexposed GAP. The GAP-N100 binder is not split up, GAP is not recoverable. In the splitting-off of nitrogen from the N3 group, a nitrene functionality arises which forms solvolytically not scissionable C---N bonds by intermolecular insertion reactions. The gaseous main reaction products in the solvolysis of KHP are N2 and N2O, besides a little CO2, O2 and CO. NH3 and CH2O were not quantified. The following ionic decomposition products were found: NO2−, NO3−, HCOO− and NH4+. The product spectrum can be interpreted from the mechanisms and reaction products given in the literature for the decomposition of hexogen, as well as through reactions of the decomposition products with the solvolytic agent and reactions among the decomposition products themselves.