COMPARISON OF KINETICS ANALYSIS TECHNIQUES AFTER AGEING OF THE POLYMER BONDED EXPLOSIVE, EDC37

摘要

Extensive experimental investigations have been performed in which samples of the HMX-based Polymer Bonded Explosive, EDC37, containing 1% nitrocellulose have been analysed after laboratory-scale thermal ageing and long-term storage. The molecular weight of the nitrocellulose polymer binder decreases on ageing and a good correlation exists between number average molecular weight (M_n) and flexure stress at failure (σ_F) for the explosive. After af Ekenstam, it is well established that nitrocellulose M_n degradation in EDC37 obeys the simple relationship (1) in which rates of reaction, k_M, resulting from chain scission reactions can be determined. 1/(M_n(t))=1/(M_n(0))+k_Mt (1) Since ageing experiments have been performed over a range of low temperatures (42.5°C < T < 66.1°C) and rate constants determined at each temperature, an Arrhenius plot can be constructed and values of activation energy, E_a, for M_n degradation derived. The aim of this work is to use accelerated ageing data to reliably predict a value of k_M at the lower storage temperature. To address this issue, the work reported herein considers 3 techniques for calculation of k_M from the relationship between 1/M_n and time, t. It is shown that the calculation of E_a and prediction of k_M at the storage temperature are influenced by scatter in experimental data and that a technique referred to as 'point-by-point' kinetics analysis provides a much improved, robust assessment of these kinetic parameters.