Dissolution rate of propellant energetics from nitrocellulose matrices

Abstract : During firing, propellant residues are scattered onto the soil surface where their energetic compounds can be dissolved by precipitation. The residues, like the unfired propellants, are composed of nitrocellulose imbibed with either 2,4-DNT (single-base), nitroglycerin (NG) (double-base) or NG and nitroguanidine (NQ) (triple-base). Although nitrocellulose is insoluble, 2,4-DNT, NG, and NQ are soluble; and 2,4-DNT and NG are also toxic. Consequently, data on how quickly 2,4-DNT, NG, and NQ are dissolved from propellant residues are needed to determine the flux of these compounds to soil. Once in soil solution, the partition coefficient, Kd, and degradation rate, k values are needed to predict the transport of energetics through the vadose zone and to groundwater. We measured the 2,4-DNT, NG, and NQ dissolution rates for different propellants using laboratory batch and drip tests where no soil was present and soil column studies, which used similar propellant and residues as source terms, to determine partition coefficients and degradation rates. Because the surfaces of propellants and residues may play an important role in dissolution of the energetic constituents, we studied these using both light and electron microscopy. We found that 2,4-DNT is well bound to NC and dissolves out slowly, but that both NG and NQ have fast initial dissolution followed by slower mass loss. The amount of NG dissolved is a function of the NG/NC ratio in the propellant and both our mass loss data and our microscopy results suggest that NG exists as fine liquid droplets within an NC matrix rather than as dispersed molecules.