Simulation of Heat Flow Curves of NC‐Based Propellants – Part 1: Determination of Reaction Enthalpies and Other Characteristics of the Reactions of NC and Stabilizer DPA Using Quantum Mechanical Methods

Abstract

The heat flow curves of nitrocellulose (NC)‐based propellants are now an important assessment quantity for their quality and safety in storage and service. The measurable heat flow is the summarized effect of the rates of all the reaction heats of the reactions going on in the material. To get a detailed assessment instead the only global one requires knowing the heat flow parts caused by NC and by stabilizer reactions. For this, in turn, one needs to find the reaction enthalpies of the essential NC decomposition reactions and the stabilizer reactions at the temperature of the measurement of the heat flow. These data are not available in the literature. To get meaningful data it was necessary to use quantum mechanical calculations, here so‐called DFT (density functional theory) methods, to screen the possible reactions by transition states and the energetic situation between educts and products. For the calculation of the reaction enthalpies and the transition states, the reactants were embedded in a polarizable continuum, which simulates the NC environment for the reactants in NC and for the stabilizer reactions. In addition, to calculate bond dissociation enthalpies of NC and of nitroglycerine a type of shell model was used called ONIOM (‘Our own N‐layered Integrated molecular Orbital and molecular Mechanics’ model). The results from the determinations of reaction enthalpies are used in the second part of the publication.

Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry: A Strategy for Optimization, Characterization, and Quantification of Antioxidant Nitro Derivatives

“…N -Phenyl-β-naphthylamine (PBNA) is a widely used antioxidant in numerous industrial applications, such as the manufacture of rubber, plastic, dyes, various greases, lubricating and transformer oils, and energetic materials. − In the presence of oxidative or hydrolyzing agents such as oxygen, nitrogen oxides (NO x ), and nitrous and nitric acids (HNO x ), this secondary arylamine stabilizer can effectively protect energetic materials from oxidation or hydrolysis by scavenging the free radicals (e.g., NO 2 radical) and hence reducing the acidity. ,,,, In a similar class of antioxidants (e.g., diphenylamine and triphenylamine), nitration of arylamines generally forms nitro derivatives by reacting with nitrogen oxide radicals − ,− and can be characterized using mass spectrometry (MS) through rationalization of fragmentation . Accordingly, PBNA can also form mononitro derivatives when it undergoes similar reactions.…”

Density functional theory investigation of green stabilizer reactions: curcumin in nitrocellulose-based propellants

“…Investigations of curcumin as a stabilizer are recent [3,5] compared to the most used stabilizers [2,7,[11][12][13]16]. Even for the widely used DPA, the stabilization process is complex, and the nature of the captured nitro compounds might be considered "speculative" in some sense [8,17,18]. For curcumin, the reactions are less known.…”

“…For curcumin, the reactions are less known. This substance is supposed to react with nitro compounds, such as NO2, HNO2, and HNO3 [17], but the lack of nitrogen in curcumin avoids the formation of nitroso-amines as byproducts of N-nitrosation reactions, which are carcinogenic agents [5]. Therefore, C-nitrations are more likely for curcumin, contrasting with DPA, methyl centralite, ethyl centralite, akardite I and akardite II [17,19].…”

“…It contributes to forming a sufficiently stable reactant (Figure 2), which allows posterior nitration. Regarding the degradation processes, there are results related to the NC decomposition and determination of enthalpies and free energies for stabilization reactions with DPA [8,17] and with curcumin [21], but no work was found presenting curcumin transition states and activation energies for degradation. Our group has employed quantum chemistry simulations based on the density functional theory (DFT) to investigate the impact sensitivity of energetic materials [22][23][24][25][26][27][28][29][30] and excited states [31][32][33][34][35].…”

Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry Analysis of Eutectic Bis(2,2-dinitropropyl) Acetal/Formal Degradation Profile: Nontargeted Identification of Antioxidant Derivatives

“…In some energetic materials, the eutectic mixture of bis-2,2-dinitropropyl acetal/formal (BDNPA/F), commonly known as nitroplasticizer (NP), is used to improve shock absorptivity and manufacturability. − However, NP inevitably decomposes, which releases reactive species, such as H 2 O, NO, NO 2 , HONO, and later HNO 3 . , These species can trigger the catalytic deterioration of both NP and polymeric binders, which directly impacts the properties of these materials. To counter this effect, approximately 0.1 w/w% of n -phenyl-β-naphthylamine (PBNA) is added to NP after production. , PBNA is an aromatic amine antioxidant that extends the service life of NP by scavenging the radical species generated from NP decomposition (i.e., NO x ). , In the presence of such reactive species, amine antioxidants can undergo successive nitration (C–NO 2 ) and/or nitrosation (N–NO), as shown in Scheme , − but no conclusion can be made with respect to the reaction mechanism between PBNA and species of nitrogen oxides (HONO, HNO 3 , and NO x ) because the transition states and energy barriers are still in question. However, the reactant at play is likely starting with HONO since HONO elimination (+28 kcal mol –1 ) is more energetically favorable than C-NO 2 homolysis (+56 kcal mol –1 ) as the first step of NP decomposition.…”