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Nitrocellulose and stabilizers: DFT calculations of bond dissociation and reactions

: Nardai, Michael M.; Bohn, Manfred A.

Pachman, J. ; University of Pardubice, Faculty of Chemical Technology:
20th Seminar on New Trends in Research of Energetic Materials, NTREM 2017. Proceedings. Pt.2 : April 26-28, 2017, Pardubice, Czech Republic
Pardubice: University of Pardubice, 2017
ISBN: 978-80-7560-056-1 (Print)
ISBN: 978-80-7560-057-8 (CD-ROM)
Seminar on New Trends in Research of Energetic Materials (NTREM) <20, 2017, Pardubice>
Fraunhofer ICT ()

The reaction pathways of nitrocellulose degradation and stabilization are again a topic of current research activities. Experimentally, chain scission, analysis of gaseous products and evolved reaction heats can be measured. Apart from established facts such as the ONO2 bond being the weakest and effects of moisture on decomposition, the reaction pathway remains mostly unknown. In this contribution, first steps of quantum-mechanical calculations are shown: Starting from a semi-amorphous nitrocellulose bulk, with the goal to calculate thermodynamic quantities of degradation reactions. In order to generate a nitrocellulose simulation model (NC simulate), cellulose is nitrated by simple insertion of nitrate ester functionalities into a crystal supercell. The resulting structure is energetically highly unfavorable because of the comparably bulky –ONO2 groups. It is relaxed by a molecular dynamics simulation, which uses classical force fields as COMPASS II from Materials StudioTM from Accelrys, now Biovia. The resulting structure shows a partially amorphous structure: Each single nitrocellulose chain arranges in a helical twisted form, and several chains are arranged in a hexagonal pattern. From this pattern, representative single glucopyranose rings are identified and subjected to density functional theory (DFT) calculations using DMol3 from Materials StudioTM. The so-called level of theory is BLYP functional and a basis set similar to 6-31G* of Gaussian. Dissociation energies and enthalpies are calculated. The same procedure is applied to stabilizers such as diphenylamine. Although the applied functional and basis sets are rather coarse, results show quantitative agreement with experimental values for bond dissociation energies and enthalpies.