The correlation between the mechanical properties of hydroxyl-terminated polyether (HTPE)/N-butyl-N-(2-nitroxyethyl)nitramine (Bu-NENA) binders with different plasticization ratios (pl/po), varied from 0.9 to 1.5, have been studied. The very early stage of evaporation of Bu-NENA from the HTPE/Bu-NENA binder, with a pl/po ratio of 1.2, has been investigated. The results revealed that the pl/po ratio has strong influences on the mechanical properties. When the pl/po ratio was 1.2, the mechanical properties of the HTPE/Bu-NENA binder were satisfactory, the maximum tensile strength and the elongation at break being 2.39 MPa and 93.27%, respectively. The evaporation rate constant of Bu-NENA from HTPE/Bu-NENA binder with a pl/po ratio of 1.2 increased from 0.31·10–5 to 2.32·10–5 s–1 as the temperature was increased from 50 to 90 °C. The value of the activation energy of evaporation was 51.47 kJ/mol and its pre-exponential factor was 6.14·102 s–1.
The kinetics of catalyzed urethane-forming reactions of hydroxyl-terminated polyether (HTPE) with toluene di-isocyanate (TDI) in the presence of bismuth complex catalysts was investigated by non-isothermal differential scanning calorimetry (DSC). Fourier transform infrared spectroscopy (FTIR) was employed to monitor the chemical interactions of relevant groups. The kinetic parameters, including the apparent activation energy (Ea) and reaction rate constants (k) at typical temperatures calculated by the Kissinger and Crane methods, were used to evaluate the catalytic activities of triphenylbismuth (TPB) and tris(3-ethoxyphenyl)bismuthine (TEPB). The variations of Ea were studied to obtain an insight into the consistency of catalytic mechanism for the bismuth complex catalysts. The viscosity build-up of HTPE-based polymer bonded explosive (PBX) slurry was then measured to verify the catalytic activity and the pot-life during an actual manufacturing process, which fitted with the kinetics of the catalyzed cure reaction. The cure process was evaluated by the hardness of the PBX grains maintained at a temperature below typical manufacturing conditions. The results showed that TEPB is an effective catalyst, reducing the Ea of the cure reaction and the manufacturing temperature and time with an acceptable pot-life. The mechanical, thermal characteristics and compatibility of the HTPE-based PBXs were also investigated. The results suggest that TEPB is compatible with HTPE-based PBXs and contributes to improving the mechanical properties and thermal safety.
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