Development of Methodology to Determine Stability of Single Based Propellant Through High Performance Liquid Chromatography

Abstract

The level of concentration of diphenylamine present in propellant samples reveals valuable information which can help in determining safe shelf life of propellants. Till to date, Abel heat test is a primary investigative technique being used for stability monitoring of propellants in our country. This testing technique inherits some drawbacks and may mislead to erratic results. Diphenylamine is the most commonly used stabilizer in single based propellants. The aim of this research is to suggest such methodology to investigate stability levels of single based propellants in order to estimate the safe shelf life accurately in accordance to international standards. Samples of propellants M1 and M6 were selected for this study. Diphenylamine is used as stabilizer in these propellants. Initial concentration of stabilizer in these propellants is 1 %. Chromatographic conditions were set up according to newly developed method. External standard method was used for calibration. Four solutions of different concentrations of diphenylamine in acetonitrile were prepared. Calibration curve was made by plotting HPLC readings of these solutions on graph. Diphenylamine was extracted from the propellant sample by dissolving samples in acetonitrile assisted by ultrasonic bath. Nitrocellulose was also removed from propellant sample by precipitation before analysis by adding aqueous solution of calcium chloride. Acetonitrile and water were used as mobile phase in HPLC analysis. C-18 bounded silica was used as stationary phase. Analysis of both naturally aged propellant sample and artificially aged sample was carried out. Artificial ageing of samples were realized at 90°C for 3.43 days so as to simulate 10 years of natural ageing at 25°C. The results show that after artificial aging of samples, stabilizer contents in M1 propellant is reduced from 0.84% to 0.48% and in M6 propellants reduced from 0.87% to 0.55%. It means that the particular lots of these propellants will remain stable for another 10 years in storage thus can be sentenced serviceable for 10 years. Experimental methods at each step are more elaborated deliberately so that methodology may be adopted in service without complications.