LOVA Propellant Aging: Effect of Residual Solvent

An investigation of LOVA propellant aging was performed to identify the cause of stabilization periods in certain propellant lots. The following results were obtained: (1) the level of residual solvent in propellant grains slowly decreases while in storage; mechanical properties of the grain were qualitatively observed to change in response to the loss of plasticization by residual solvent; the rate at which solvent is lost depends on storage conditions (e.g., fire volume in storage vessel, the frequency with which vessel is opened); (2) during the drying process and while in storage, plasticizer 'comigrates' with solvent, resulting in plasticizer accumulation at grain surfaces; and (3) during grain storage, residual solvent is oxidized to generate organic acids. Based on these results, it is proposed the stabilization periods result from processes related to migration, evaporation, and oxidation of residual solvent. The effect of solvent content and migration on the relaxation of mixing/extrusion-induced propellant stress was not examined in this study, but is suspected to be significant and is recommended as a topic for future investigation.