Precisely tuning the structure and properties of the explosive crystal by an interfacial initiated active polymerization grafting method was proposed in this work. The influence of surface modification, on mechanical performance, thermal properties and safety performance were studied. Firstly, inspired by the strong chemical adhesion of mussels, a novel PDA interfacial layer was introduced on energetic organic crystals through a simple immersion method. The mechanism of bio-inspired coating of PDA was proposed using combination characterizations. Secondly, surface grafted polymers on the explosive crystals were successfully demonstrated by two possible approaches, such as atomic transfer radical polymerization and two-step polyurethane reaction. Tunable surface wetting properties of the TATB crystals can be achieved with a contact angle of 68.2o to 66.9o after PDA modification. However, the contact angle was sharply increased to 75o after introduction of the initiator. Then the surface wetting property can be further manipulated by grafting with different kinds of polymers, i.e., 85.0o and 67.7o with PNIPAM and PHEMA, respectively. With the assistance of dopamine modification and toluene-2, 4-diisocyanate (TDI) as a bridge, various polymers with hydroxyl-end groups (e.g., Glycidyl azide polymer (GAP), Polytetrahydrofuran (PTMEG) and polyethylene glycol (PEG)) were grafted onto the explosive crystals and significantly changed their surface properties. The static mechanical performance (compression and tension) of the TATB based polymer bonded explosives (PBXs) were obviously enhanced by as-grafted polymers, in which PTMEG outperform best. The creep behavior of the PBX was also inhibited by grafting with polymers. According to the analysis of the fracture, the interfacial debonding between explosive crystals and polymer binders was significantly decreased for PBX after grafting with PTMEG, implying a strong interfacial interaction between TATB particles and binder matrix. In addition, the present work also demonstrated that dense surface coating played a key role in the significant inhibition of phase transition, the prevention of thermal damage on energetic crystals and decreasing sensitivity of polymorph explosives after heating. Present work provides a potential general method for the interfacial modification of small organic molecular crystals, facilitating the enhancement of the performance of the composite materials.

Grafting polymers on small molecular organic crystals

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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