The eutectic mixture of bis(2,2-dinitropropyl) acetal (BDNPA) and bis(2,2-dinitropropyl) formal (BDNPF), commonly known as Nitroplasticizers (NP), is one of the components of the adhesive binders that lowers the shock sensitivity and improves the manufacturability of plastic-bonded explosive (PBX) materials. In efforts to understand the aging process of PBX 9501, the degradation mechanism of BDNPA/F has been the main focus for many studies. Early studies and much of our works are dedicated to the hypothesis of nitrous acid (HONO) elimination as initial step of NP degradation (i.e., NP → NP’ + NO + NO2 + H2O). While an increasing concentration of water has been detected throughout the aging process, NOx molecules were nowhere to be found in NP samples aged under various conditions. Using High Performance Liquid Chromatography Tandem Quadrupole Time of Flight (LC-QTOF), a large quantity of unidentified masses were detected, but the mass-to-charge (m/z) at 308.068 Da and 353.053 Da quickly caught our attention due to their associations with Dinitropropanol (DNPOH), one of NP degradation products. Through careful analysis of the MSMS fragmentation pattern and based on a high mass accuracy of &lt;5 ppm, the 308.068 m/z and 353.053 m/z are suspected to be the product of antioxidant, N-Phenyl-2-naphthylamine (PBNA), capturing two NO2 and three NO2 molecules, respectively. Following this important finding, the signals of different PBNA variations are identified from our data and their patterns are analyzed to verify the validity of this theory. In this study, in-depth evaluation of fragmentation patterns will be given, and the Arrhenius law of PBNA decay over the aging process will be discussed. Overall, this work not only demonstrates the analytic power of LC-QTOF, but most importantly, providesthe evidence thatsupports the theory of HONO elimination as an initial degradation step in the NP thermal degradation.

Liquid chromatography tandem quadrupole time of flight mass spectrometry analysis of a nitroplastizer degradation profile: Identification of antioxidant variations

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