Analysis of Automotive Polymers - Case Study

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Introduction
Polymers are present in daily life. From the wrappings around the food we eat to the sacks used for the garbage, polymers are practically everywhere. The automobile is no exception. Polymers comprise greater than 40% of a modern automobile; the carpet, seats, padding, knobs, switches, dashboard and cosmetic coverings are composed of one polymer or another.

This paper will describe the analysis of the various polymers in an automobile immediately accessible to investigation.
The traditional method of analysis for polymers is to make a thin film of the polymer and collect an infrared transmittance spectrum. Sample preparation can be time consuming, film thickness inconsistent and the use of solvents hazardous. Also, not all polymers can be dissolved in a solvent, heated or flattened enough to make an adequate thin film for analysis with infrared spectroscopy.

The Golden Gate™ Diamond ATR accessory requires no sample preparation and greatly simplifies the collection of FT-IR spectra.
The solid sample is placed onto the ATR crystal, pressure is applied, and the sample spectrum is collected. The sample is removed from the crystal surface and the accessory is ready to collect additional spectra. Fast and less complicated than using prepared thin films, the ATR method allows recovery of the original sample for other analysis methods. The resulting sample data can be searched against a digital database of ATR spectra for positive identification. Despite changes in relative peak intensity of the absorption bands, due to the internal mechanism of ATR accessories1, spectra can also be compared to transmission data. As an example, Figure 1 is a plot of the transmission and ATR spectra of polystyrene.

Experiment and Results
Spectra were collected using a Golden-Gate micro-ATR accessory equipped with ZnSe lenses and a single-reflection diamond ATR crystal. Sample sizes of 1-4 mm2 were collected from various parts of the vehicle. The individual polymer samples were placed onto the ATR crystal and the anvil was hand-tightened to apply pressure. No sample preparation was necessary to collect the spectra.

FT-IR spectra of 64 scans at 4 cm-1 resolution were coadded and averaged to obtain the single-beam background and sample spectra. To provide identification of the samples, the spectra were searched versus several library collections of polymer spectra.

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