New protocol for the isolation of nitrocellulose from gunpowders: Utility in their identification

In this work, a new approach for the isolation of nitrocellulose from smokeless gunpowders has been developed. A multistep solvent extraction method was needed to purify nitrocellulose contained in gunpowders. For single-base or double-base gunpowders six consecutive solvent extractions were selected: three extractions with methanol (to remove nitroglycerin, 2,4-dinitrotoluene, ethyl-centralite, diphenylamine, and diphenylamine derivatives); one extraction with dichloromethane (to remove colorants and plasticizers of organic nature); one extraction with methanol (to facilitate a final polar extraction); and one extraction with water (to remove ionic components) were necessary at 35 °C. For the triple-base gunpowder studied, eight solvent extractions were needed due to a high concentration of the water-soluble nitroguanidine was present. In addition to the same five initial phases used for the single-base and double-base gunpowders, three water extraction phases at a higher temperature (75 °C instead of 35 °C) were also needed. A final step to solubilize nitrocellulose in methyl ethyl ketone was used to remove inert components (mainly graphite). Nitrocellulose isolated from these propellants was characterized by Fourier-Transformed Infrared Spectroscopy (FTIR spectroscopy). The same FTIR spectra were observed for nitrocelluloses isolated from different types of gunpowders. A comparison of FTIR spectra of nitrocellulose samples of different nitration degree evidenced that the bands regions most affected by this factor were: 3600–3400 cm−1, corresponding to the stretching vibrations of residual hydroxyl groups; 1200–1000 cm−1, attributed to the valence vibrations νCO of the glucopyranose cycle; and 750–690 cm−1, assigned to vibrations of the nitrate group. In both cases, the bands appearing in these regions were more pronounced in the spectra of nitrocellulose samples of low nitration degree.