Análise da influência do envelhecimento sobre as propriedades mecânicas de propelentes de base dupla

Abstract

The present work evaluates the changes of different mechanical properties of double base propellants over aging and its relation to chemical and physical degradations. It was analyzed the effects related to natural aging, for samples manufactured in 1999, 2016 and 2019, and to artificial aging, carried out at 60 °C for times equivalent up to twenty years of natural aging. The mechanical properties were analyzed in terms of elastic and relaxation modulus in compression mode in a thermomechanical analyzer, and stress-strain curves parameters in tension mode in a universal testing machine. Chemical degradation was analyzed in terms of nitrocellulose depolymerization by gel permeation chromatography and physical degradation was evaluated in relation to plasticizers content by thermogravimetric analysis. Complementary analyses of Fourier transform infrared spectroscopy confirmed that the mass losses refer to the evaporation of nitroglycerin and diethyl phthalate. The chemical stability of the propellants was analyzed by heat flow calorimetry. The results showed that the mechanical properties of the propellants behave differently over ageing. It was observed an increase in the elastic and relaxation modulus in compression, but a reduction in the elastic modulus and in the rupture parameters on tension mode. The mechanical properties in tension are directly influenced by the NC chains scission. For the natural ageing, the relaxation time results indicate that the physical degradation is the main mechanism. On the other hand, for the artificial ageing, the results indicate that the physical degradation is the predominant mechanism in an initial stage, however, the chemical degradation seems to become the main mechanism in a later stage.