Aging effects on mechanical properties, plasticizer loss, and molar mass distribution of double base propellants

This work examines how aging alters the mechanical and chemical properties of double base propellants. Three formulations naturally aged for up to 20 years were analyzed through thermomechanical analysis, universal testing, thermogravimetry, infrared spectroscopy, and gel permeation chromatography. The results show that both elastic and relaxation moduli increased significantly with time, revealing higher rigidity and reduced chain mobility. Thermogravimetric analysis combined with FTIR identified mass losses as mainly due to nitroglycerin and diethyl phthalate evaporation, indicating a progressive reduction of plasticizer content. Gel permeation chromatography revealed that in the early years of aging, chain scission reduces nitrocellulose molar mass, but the main factor controlling stiffness is plasticizer loss. In longer storage times, mechanical properties reflect a combined effect of reduced plasticizer content and shifts in molar mass distribution, likely related to radical-mediated reactions. These findings highlight distinct early- and late-aging regimes and provide parameters for lifetime prediction of propellants.