Impact of PVC Pyrolysis on Gasoline Identification in Fire Debris Analysis

Abstract

To obtain a more comprehensive understanding of the matrix interference mechanism, polyvinyl chloride (PVC) devoid of olefinic structures but could form double bonds during the pyrolysis process was selected particularly. Based on the analysis of thermal behavior, residues with different pyrolysis degrees were prepared under simulated fire conditions using an internationally recognized standard heat source, a cone calorimeter. Qualitative and quantitative analyses were conducted by gas chromatography–mass spectrometry and Pearson product-moment correlation coefficient, respectively. Furthermore, an interpretation of the results was confirmed by thermogravimetric analysis coupled with infrared spectrum. The results showed that the frequently encountered compounds for gasoline identification could be detected in all the PVC residues formed under different pyrolysis conditions. Particularly, for the residues obtained after heating at 300°C for 2 min and 440°C for 7 min, the overall chromatograms profiles presented higher similarity to that of gasoline combustion residues. Based on the results above, it can be concluded that the pyrolysis process cannot be ignored when discussing the matrix interference of one typical matrix since fire conditions are extraordinarily complicated, and moreover the double bonds, which are not involved in molecules inherently but formed during heating due to the typical pyrolysis mechanism of side-group scission in PVC, are considered to be the functional group interfering to ignitable liquid residues identification further. The study provided a novel viewpoint for comprehensively understanding the matrix interference mechanism by combining chemical structure and pyrolysis process together, which can be used to predict and eliminate the impact of matrix interference.