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Effect of Weathering on the Clear Coat Across Vehicles for Forensic Purposes

Madeline Dunn, Nuwan Perera, Department of Chemistry & Physics, Western Carolina University, 1 University Way, Cullowhee, NC 28723

In the event of a vehicular crime, paint chips or smears are often left behind at the crime scene. For decades forensic analysts have used infrared (IR) spectroscopy to identify paints, due to its sensitivity to molecular structure, it produces the most information from paint examination. Using the physical and chemical information obtained from IR spectroscopic analysis of automotive paints, it is possible to identify the make, model, and year of vehicles. The present study examines how the structure of a clear coat on a vehicle changes based on the location it was taken from on the vehicle. The effects of environmental exposure were investigated using Fourier-transform infrared spectroscopy (FTIR) with an attenuated total reflection (ATR) crystal. Six samples obtained from different locations on a 2004 Volvo were numbered based on expected weathering, sample number 1 being the least weathered and sample number 6 being the most weathered. All six samples were identified as Acrylic Urethane with significant changes in adsorption values. The spectra of the paint topcoat showed the formation of C=O and O-H bonds due to photo-oxidation and the formation of primary amines (N-H). The spectra also showed the loss of amides (C-H) and the breaking of C-O bonds and alkyl aryl ethers. The scratched spectra represent the non-weathered samples and are compared to the unscratched spectra to illustrate the effects of weathering. Comparing the scratched and unscratched spectra of each sample showed the unscratched sample peaks decrease at 1220 cm-1, 1363 cm-1, 1530 cm-1, and ~1720 cm-1, indicating the breaking of amide II and III bonds and C=O urethane linkages. More research needs to be done to systematically investigate the spectral differences between scratched and unscratched samples, to classify weathering patterns of different clear coat formulations.




Additional Abstract Information

Presenter: Madeline Dunn

Institution: Western Carolina University

Type: Poster

Subject: Chemistry

Status: Approved


Time and Location

Session: Poster 4
Date/Time: Tue 11:00am-12:00pm
Session Number: 3567