The Characterization of Motor Vehicle Body Fillers

The compositions of typical British motor vehicle body fillers are reviewed and a systematic scheme is presented for their characterization, which routinely employs sample colour and analysis by pyrolysis gas chromatography and occasionally employs X-ray fluorescence spectrometry in addition. Eighteen samples obtained from manufacturers were all distinguishable and, from the examination of 121 casework samples, the discriminating power of colour and pyrolysis gas chromatography was estimated to be at least 0·92. Twenty-three samples in the casework collection were all similar in colour and produced similar pyrograms. A brief examination of this large group of samples, by X-ray fluorescence spectrometry, indicated that inorganic analysis provided a useful increase in discrimination. The pyrolysis products of polythene were used to calibrate the retention scale of the gas chromatograms (in methylene units) and peak heights were recorded relative to the height of the largest peak (usually styrene). Using data recorded in this manner a computer based system was developed for the comparison of pyrograms and for establishing the evidential value of a particular analysis. It is suggested that a similar approach could be used for the interpretation of pyrograms from a wide variety of other materials.