Dynamic Mechanical and Molecular Weight Measurements on Polymer Bonded Explosives from Thermally Accelerated Aging Tests. II. A Poly(Ester-Urethane) Binder.

摘要

The molecular weight distribution and dynamic mechanical properties of an experimental polymer-bonded explosive, X-0282, maintained at 23, 60, and 74 exp 0 C for 3.75 y were examined, X-0282 is 95.5% 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclo-octane explosive and 4.5% Estane 5703, a segmented poly(ester-urethane). Two mechanical relaxations at about -24 and 42 exp 0 C were found in the X-0282 aged at room temperature for 3.75 years. A third relaxation at about 85 exp 0 C was found in X-0282 aged at 60 and 74 exp 0 C. The relaxation at -24 exp 0 C is associated with the soft segment glass transition of the binder. The relaxation at 42 exp 0 C is associated with the soft segment melting and may also contain a component due to the hard segment glass transition. The relaxation at 85 exp 0 C is probably associated with improved soft segment crystallite perfection. The molecular weight of the poly(ester-urethane) binder decreased significantly with increasing accelerated aging temperature. A simple random chain scission model of the urethane degradation kinetics in the presence of explosive yields an activation energy of 11.6 kcal/mole. This model predicts a use life of about 17.5 years under the worst military operating conditions (continuous operation at 74 exp 0 C). (ERA citation 06:014633)