A TG study of the solvolytic breakdown of a crosslinked double base propellant

Abstract

The solvolytic breakdown and dissolution of obsolete crosslinked propellants may be carried out with surprising ease with subsequent recovery of expensive constituents in high yields. An approach was adopted in which degradation was initiated in composites while they were swollen in an appropriate solvent containing additives capable of reacting with and cleaving chemical bonds located in the polymer chain. A kinetic study of the solvolysis reaction of the urethane linkages in a crosslinked double base propellant in ethanolamine solution was followed by thermogravimetry. Kinetic data were obtained using the propellant fraction reacted, which was expressed as the product of the TG fraction at 200°C and the molarity of the ethanolamine solution. First-order rate constants for the reaction were found to be higher in the mixed solvent of toluene-isopropanol compared with isopropanol probably because of their differences in swelling behavior. Activation energies for solvolysis were about 5 kcal mole −1 in toluene-isopropanol and about 8 kcal mole −1 in isopropanol. Nitroglycerin present as a plasticizer in double base propellants was extracted prior to kinetic analysis because it was found to react with the ethanolamine. The solvolytic degradation of the propellant binder with nitrocellulose was about three times as fast as the binder without nitrocellulose. A variable heating rate study showed that the binder with or without nitrocellulose had the same activation energy for thermal decomposition. Kinetic data indicates that nitrocellulose appears to catalyze the solvolytic degradation but not the thermal degradation of a crosslinked double base propellant binder.