Significantly enhanced thermal stability of HMX by phase-transition lysozyme coating

Abstract

A new robust bio-inspired route by using lysozyme aqueous solution for surface modification on 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) was described in this paper. HMX crystals were coated by in situ phase transition of lysozyme (PTL) molecules. The HMX decorated by PTL was characterized by SEM, XRD, FTIR and XPS, demonstrating a dense core-shell coating layer. The coverage of lysozyme on HMX crystal was calculated by the ratio of sulfur content. The surface coverage increased from 60.5% to 93.5% when the content of PTL was changed from 0.5 wt% to 2.0 wt%, indicating efficient coating. The thermal stability of HMX was investigated by in situ XRD and DSC. The thermal phase transition temperature of HMX (β to δ phase) was delayed by 42 °C with 2.0 wt% PTL coating, which prevented HMX from thermal damage and sensitivity by the effect of PTL coating. After heating at 215 °C, large cracks appeared in the naked HMX crystal, while the PTL coated HMX still maintained intact, with the impact energy of HMX dropped dramatically from 5 J to 2 J. However, the impact energy of HMX with 1.0 wt% and 2.0 wt% coating content ([email protected] and [email protected]) was unchanged (5 J). Present results potentially enable large-scale fabrication of polymorphic energetic materials with outstanding thermal stability by novel lysozyme coating.

Keywords

• HMX
• Lysozyme
• Phase transition
• Thermal stability
• Sensitivity