Studies on the emission behavior of polypropylene by gas chromatography/mass spectrometry with static headspace or thermodesorption

Abstract

Emissions from polypropylene (PP) may cause undesired smell, be harmful, or lead to so-called fogging which prohibits its use for car interiors. Thus, qualitative as well as quantitative emission studies are necessary. Thermodesorption (TDS) and static headspace (sHS) with subsequent GC-MS analysis are two powerful tools for analyzing the emission behavior of polymers with a minimum of sample handling. In this work we investigated the emission behavior of PP with TDS and sHS coupled to GC-MS paying special attention to quantitative considerations and to the relevance of emitted substances for fogging phenomena. After extraction for 30min and incubation for 2h, TDS-GC-MS and sHS-GC-MS results were satisfyingly repeatable (with relative standard deviations up to 5%). TDS allowed to introduce substances up to higher boiling points into the GC-MS system, but required to control sample geometry, as emission depended rather on sample surface than on sample mass. In sHS, emission was governed by partitioning between the gas and the sample phase rather than by full evaporation of the analytes. Above a certain analyte-dependent amount, peak area became independent of the sample amount. However, if the sample amount was kept constant, peak areas of emitted substances showed a linear dependence upon concentration of volatiles. Therefore, accurate quantitation was still possible. Typically alkanes, alkenes and dialkenes dominate TDS-GC-MS and sHS-GC-MS chromatograms of PP. They only contributed to fogging if they had a chain length higher than C16. These substances were only detectable when TDS was used for sample introduction, but not with sHS. sHS-GC-MS is thus not useful for judging fogging behavior.