Effects of temperature and pressure on the glass transitions of plastic bonded explosives

Various plastic bonded explosives (PBXs) contain about 5 wt.% polymer, plasticizer, and stabilizer as binder. The glass-transition temperature (Tg) determines, in part, if the binder will reduce or increase the sensitivity of the PBX to impact. A soft binder reduces the impact sensitivity; however, too soft a binder compromises the mechanical strength below that desirable for dimensional stability. Glass transitions were measured by temperature modulated DSC for PBXs before and after pressing. Pressing temperature was 90°C. The Tg of Estane, a polyester/polyurethane used in some PBX binders, was investigated. Only small changes were observed in the low temperature Tg of the soft segments but larger changes were seen in the higher temperature transitions due to the relaxation of the hard segments. The Tg of Kel F 800, a binder used in insensitive PBX 9502, was observed near ambient temperature. The PBX 9502 had a lower Tg than the neat polymer. Mechanical strength was measured for the samples of PBX 9502.