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Raman spectroscopy combined with principle component analysis to investigate the aging of high energy materials

This paper attempts to investigate the possibility of using Raman spectroscopy for aged solid composite propellants. Propellant samples was prepared and aged by an accelerated mechanism in three different temperatures (50, 60 and 70 °C) and times. In the Raman spectrum of the unaged sample, vibrational modes of all structural substances consisting of hydroxyl-terminated polybutadiene as a binder, ammonium perchlorate (AP) as an oxidizer and aluminum as a metal fuel were observed. Comparison of the spectra of the aged samples shows the changes of several peaks with increasing aging times. The important changes are the elimination of NH3+ mode and intensity reduction of CH2 modes, which can be attributed to oxidative cross linking phenomena due to AP decomposition in the chemical structure. Intensity ratios of C–C, C=C and CH2 have been changed with aging and cross linking so that C=C bonds are converted into C–C bonds, as well as the intensity of CH2 modes, was decreased. A principle component analysis method is implemented in order to use all ranges of the spectrum and better discrimination of the samples, which show good results.