The dependence of the non-linear creep properties for TATB-based polymer bonded explosives on the molecular structure of polymer binder

Abstract

The influences of molecular structure of polymer binders on the mechanical properties and non-linear time dependent creep of the 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-based polymer bonded explosives (PBXs) at different temperatures and stresses were investigated. A copolymer of chlorotrifluoroethylene and vinylidene fluoride (PF1) and a copolymer of chlorotrifluoroethylene, vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene (PF2) were used as polymer binders. An increase of the storage modulus and glass transition temperature was observed for PF2, compared to that of PF1. The compressive and tensile properties of TATB-based PBX with PF2 were higher than the one with PF1 at both ambient temperature and elevated temperature. The creep resistance also showed clear dependence on the molecular structure of polymer binders. It was found that the incorporation of tetrafluoroethylene and hexafluoropropylene comonomers in PF2 resulted in a decrease of the constant creep strain rate and the maximal creep strain values and an increase of creep rupture time for TATB-based PBX. Non-linearity in the creep response was modeled using the six-element mechanical model. The predicted theoretical results coincided quite well with the experimental data. Compared with the formulation containing PF1 as binder, an increase in the elastic modulus E₂, E₃ and bulk viscosity η₄ was observed for TATB-based PBX with PF2 under the same conditions. Three-point bending master curves of creep strain were constructed using a time–temperature superposition (TTS) concept. The formulation with PF2 showed consistently lower creep strain than the formulation with PF1 in the entire time scale.