Investigations of polymer samples of polyamide 11 concerning the content of monomer, oligomers, and the oxidation stabilizer Irganox 1098 by utilizing inverse gradient HPLC in combination with a triple detection system (diode array detection/mass spectrometry/charged aerosol detection)

Abstract

The aim of this work was to develop a method to comprehensively characterize extracts from polyamide 11 powder samples used in the laser sintering process. Firstly, high resolution mass spectrometry was applied to identify low molecular compounds in the material. Secondly, by means of an inverse gradient high-performance liquid chromatography (HPLC) in combination with a triple detection system consisting of a diode array detector (DAD), a mass spectrometer (MS), and a charged aerosol detector (CAD), a method was established to determine the amount of monomer and oligomers up to the linear tetramer and cyclic pentamer. Furthermore, the oxidation stabilizer identified as Irganox 1098 was determined. The DAD was utilized for the quantification of the UV-active oxidation stabilizer. Thus, to be able to extract the low molecular weight compounds, various protocols were studied and finally accelerated solvent extraction was used. As there is a lack of commercial standards of polyamide 11 related oligomers, these compounds were detected with the CAD, taking advantage of its uniform response behavior in conjunction with an inverse gradient HPLC protocol. In addition, the MS was utilized as a qualitative detector for peak identification. The information regarding low molecular weight compounds are required as the powder is subject to the thermal loading of the sintering process, which influences the composition of the low molecular weight compounds. Thus, the method was applied to new and oven-aged polyamide 11 samples. Finally, it was possible to monitor the change of low molecular weight compounds in stressed polyamide 11 powder samples.