Improving Mechanical Strength of Nitramine Gun Propellants by Constructing Bio-inspired Polydopamine-modified HMX Composites and Tuning Thermal and Combustion Properties

Nitramine propellants have garnered significant attention owing to their high-energy characteristics. However, it always encounters insufficient mechanical strength at low temperatures. In this study, the catechol polymerization product polydopamine (PDA) was incorporated into the microstructure of gun propellants through constructing 1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocane@polydopamine (HMX@PDA) energetic composites, thereby improving the comprehensive performances of the gun propellants. In-depth characterizations confirmed the uniform distribution of PDA on the surfaces of HMX crystals. Differential scanning calorimetry (DSC) was employed to analyze the thermal decomposition behavior and kinetics of the samples through the Kissinger, Ozawa, and Friedman methods. The apparent activation energy of thermal decomposition of the blank sample (169.682   kJ·mol -1 ) and gun propellant with HMX@PDA-24h (170.178   kJ·mol -1 ) indicate that the thermal stability of gun propellants remained favorably. Additionally, experimental results confirmed that the burning rate coefficient ( a ) and the burning pressure exponent ( n ) can be effectively modulated by adjusting the PDA coating time. This demonstrates that the incorporation of PDA-coated HMX does not compromise the combustion stability of gun propellants. Furthermore, the mechanical properties of the HMX@PDA-modified gun propellants improved significantly with a 12-hour PDA coating. Improvements of 14.40%, 21.15%, and 21.18% were observed under low-, normal-, and high-temperature conditions, respectively. Based on these findings, a schematic mechanism for the enhancement of the mechanical properties of gun propellant by constructing composite core-shell structure is proposed. Consequently, this study pioneers the introduction of PDA into nitramine gun propellants, providing application prospects and fundamental supporting for high-energy and high-strength gun propellants.