CHARACTERIZATION OF PLASTIC-BONDED EXPLOSIVES BY PYROLYSIS-GAS CHROMATOGRAPHY AND MULTIVARIATE DATA-ANALYSIS .2. AGING STUDIES

Application of Curie point pyrolysis gas chromatography (Py-GC) and pr incipal component analysis (PCA) in combination with a new normalizati on method could show the presence of patterns in PCA score plots not v isible with the commonly used normalization method. In the first four principal components (PC's), two patterns were observed which could be attributed to aging and the crosslink density (CD). Aging of PBX samp les has a complex effect on the peak loadings on PC1 and are difficult to reveal. This in contrast to the peak loadings on PC3 and PC4 where both PC's are dominated by only one compound (respectively, C5H6 and cyclohexene). This means that the formation of both these compounds pr oceeds independently from each other, i.e., by different mechanisms. I t was shown that aging is slowed down in samples containing more of th e antioxidant Flexzone. From the correlation matrix a few compounds we re found to have very high correlations (> 0.98). This was the case fo r methane, propane and n-butane in both unaged and aged samples indica ting that these compounds do not originate from moieties that are affe cted by aging. Also, cis- and trans-butene have such high correlations and were formed in a 0.86:1 ratio, probably through the same mechanis m. The absolute intensities decrease upon aging suggesting that both c om pounds originate from those parts of the polymer that are sensitive to aging. PC2 was related to saturated and unsaturated hydrocarbon co mpounds. The unsaturated compounds result from the elimination of wate r (free OH groups) from samples with CD values below 1.