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 substance s when doing so. This also applies for propellants and explosives. Rec ently developed propellants contain expensive crystalline energetic ma terials such as the nitramines, hexogen (RDX) and octogen (HMX), bonde d in a chemical three-dimensional crosslinked polyurethane matrix. The se substances are called ''plastic bonded propellants''. In order to r ecover the components, the polyurethane matrix is broken solvolyticall y with pure water and alkaline water (0.05 n-0.5 n NaOH) at temperatur es between 130 and 170 degrees C in a pressure cell. From a model rock et propellant, consisting of a polyetherpolyol mixture (Lupranol 1000/ 2021) cured with Desmodur T80 and filled with 60 mass% ammonium perchl orate (AP), 84-90% of the polyetherpolyol component was recovered, and 98% of the AP content subsequently determined in the aqueous solvolys ate. The polyetherpolyols were nearly not changed at the high solvolyt ic stress of 170 degrees C and 2 h, as shown by the molar mass distrib utions, determined by using gel permeation chromatography. The solid g un propellant KHP consisting of 86 mass% hexogen (RDX) and 14 mass% GA P-N100 binder was solvolyzed at 130, 150 and 170 degrees C with pure w ater 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, for mally on the basis of propane-1,2-diol with azide (N-3) groups attache d 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 re duced, which was determined via infrared absorption of the asymmetric N-3 stretching vibration, and via its energy content using DSC, in bot h 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 N-3 group, a nitrene functionality arises wh ich forms solvolytically not scissionable C-N bonds by intermolecular insertion reactions. The gaseous main reaction products in the solvoly sis of KHP are N-2 and N2O, besides a little CO2, O-2 and CO. NH3 and CH2O were not quantified. The following ionic decomposition products w ere found: NO2-, NO3-, HCOO- and NH4+. The product spectrum can be int erpreted from the mechanisms and reaction products given in the litera ture for the decomposition of hexogen, as well as through reactions of the decomposition products with the solvolytic agent and reactions am ong the decomposition products themselves. (C) 1997 Elsevier Science L td. All rights reserved.