We study the microscopic
structure properties and early thermal
decomposition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine
(HMX)/hydroxyl-terminated polybutadiene (HTPB) composites on the basis
of density functional theory calculation and quantum-based molecular
dynamics simulation. The results show that the HMX crystal surfaces
are significantly stabilized by electrostatic adsorption between nitro-O
and HTPB-H (both for alkyl and hydroxyl H). The corresponding electronic
structure has an obvious modification, with some impurity states derived
from HTPB in the forbidden band area. The initial reaction energy
barrier may be reduced due to the extra active electron, but the earliest
reaction sites of HMX thermal decomposition are not considerably changed.
The thermal dissociation of HMX is mainly initiated with the breaking
of the C–N bond, which is followed by NO2 elimination
and alkyl dehydrogenation. After that, many HTPB-Hs are transferred
to nitro-O to form water molecules, resulting in a delay of carbon
and hydrogen oxidation of HMX. More intriguingly, the carbon chains
of HTPB display considerable stability. Most of them even keep their
original carbon backbone, which would act as an initial carbon nucleus
and promote the carbon aggregation of small molecular residues. The
presence of the HTPB binder should retard the reaction progress and
reduce the reaction intensity of the HMX thermal decomposition.