Aging of HTPB/Al/AP rocket propellant formulations investigated by DMA measurements

Three HTPB-based rocket propellant formulations containing ammonium perchlorate and aluminum particles, with different aluminum content and particle size, have been manufactured. The study has focused on the change of mechanical properties with aging time by using dynamic mechanical analysis (DMA). Therefore, propellant formulations underwent an accelerated aging program, in air (RH<10%), between 60 degrees C and 90 degrees C with aging time adjusted to a thermal equivalent load of 15 to 20 years at 25 degrees C. DMA investigations revealed distinct changes in the shape of the loss factor curve. These curves were modeled with three exponentially modified Gaussian (EMG) functions in order to get the molecular interpretation of the involved aging phenomena by separating the binder fractions with different mobility. Aging of propellant formulations can be followed by considering only two parameters: the areas of the second and third loss factor transition peaks (A2, A3), and the corresponding maximum temperature values of the assigned Gauss peaks (Tc2, Tc3).