Enhance the fracture toughness of RDX-based propellant: Design of mussel-activated RDX surface functionalized coating

• The fracture toughness of nitramine propellant was effectively improved by RDX surface functionalized coating design. • The interface interaction can be regulated by controlling the particle size of energetic crystals and the PDA coating time. • The impact strength of the nitramine propellant at low temperature reached 7.1 kJ/m 2 , an increase of about 14%. • The mechanism of enhancing the fracture toughness of PDA enhanced nitramine propellant was revealed in detail. The insufficient mechanical properties of hexogen (RDX)-based propellants with high solid content are the main obstacles affecting their reliable performance in barrel launch and rocket propulsion. To effectively improve the mechanical performance of nitramine propellants, this work investigates the design of surface-functionalized RDX coatings. Polydopamine (PDA) coatings with varying deposition times were applied to RDX crystals of different particle sizes via a simple solution oxidation method, and a series of RDX@PDA propellants were subsequently prepared. Scanning electron microscopy (SEM) and contact angle measurements demonstrate that the surface properties of RDX can be tuned by controlling both the particle size of the energetic crystals and the PDA coating duration, thereby effectively enhancing the interfacial interaction strength between RDX and nitrocellulose (NC) binders. Static contact angle measurements and calculation results indicate that as the PDA coating time increases, the water contact angle of RDX@PDA gradually decreases, showing a transition of the RDX crystal surface toward hydrophilicity. Furthermore, with longer coating times, both the surface energy of RDX@PDA and its adhesion work with the NC binder exhibit a progressive upward trend. Mechanical property analysis indicates that after coating PDA on the surface of RDX, the impact strength of the nitramine propellant has been significantly enhanced. The impact strength of the nitramine propellant at low temperature reached 7.1 kJ/m 2 , an increase of about 14%. Mechanism analysis indicates that the rough surface structure of RDX crystals enhances the mechanical anchoring effect within the NC matrix. The PDA coating on the RDX surface enhances the interfacial interaction between the RDX crystal and the NC substrate due to the weak molecular force effect, thereby improving the mechanical stress transmission of the nitramine propellant under external impact loads. This research is of great significance for enhancing the surface functionalization effect of energetic solid fillers and improving the performance of composite energetic materials.