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Eingeladener Vortrag
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For analysis of the gaseous thermal decomposition products of polymers, the common techniques are thermogravimetry, combined with Fourier transformed infrared spectroscopy (TGA–FTIR) and mass spectrometry (TGA–MS). These methods offer a simple approach to the decomposition mechanism, especially for small decomposition molecules. Complex spectra of gaseous mixtures are very often hard to identify because of overlapping signals. In this paper a new method is described to adsorb the decomposition products during controlled conditions in TGA on solid-phase extraction (SPE) material: twisters. Subsequently the twisters were analysed with thermal desorption gas chromatography mass spectrometry (TDS–GC–MS), which allows the decomposition products to be separated and identified using an MS library. The thermoplastics polyamide 66 (PA 66) and polybutylene terephthalate (PBT) were used as example polymers. The influence of the sample mass and of the purge gas flow during the decomposition process was investigated in TGA. The advantages and limitations of the method were presented in comparison to the common analysis techniques, TGA–FTIR and TGA–MS.
Two commercial polyethylene grades were exposed to water at elevated temperatures and enhanced oxygen pressure. To characterize their aging behavior laser-induced photoluminescence spectroscopy was applied. Additionally, aging characterization was performed by established methods such as tensile testing, infrared (IR) spectroscopy, high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC) and UV–VIS spectroscopy. During the initial stages of aging, the overall concentration of phenolic antioxidants as well as oxidation onset temperatures decreased exponentially. Simultaneously, significant discoloration due to the formation of conjugated degradation products from phenolic antioxidants (e.g., quinone methides) was detected. After the consumption of antioxidants, photoluminescence started to grow continuously presumably due to the formation of photoluminescent unsaturated carbonyls. In the final stages of aging, embrittlement of the materials as characterized by the degradation of mechanical properties (i.e., loss in ductility) coincided with rising carbonyl index values as well as an increase in crystallinity due to chemicrystallization. Between integrated photoluminescence intensity and carbonyl index, a linear correlation was established. In the induction period, the photoluminescence method exhibited a significantly higher sensitivity to reflect aging induced material changes.