Most polymeric materials, the use of which is unavoidable today, are not biodegradable. From an environmental point of view, the recycling of such materials has become an important focus of research. Determining the chemical composition of waste generated from the recycling of polymers is crucial for further waste management, as it must comply with waste treatment regulations. To this end, I determined the content of polyamide 6 (PA6) oligomers and caprolactam (CPL) in residues from the recycling of PA6, which is a component of floor coverings, fishing nets, and textiles. Caprolactam was quantitatively determined by reversed-phase high-performance liquid chromatography (HPLC) with a C18 column and a mobile-phase gradient consisting of acetonitrile and Milli-Q water using a UV detector at a wavelength of 210 nm. The content of PA6 oligomers in the waste was determined by acid-catalyzed hydrolysis of PA6 and CPL to 6-aminocaproic acid (ACA), which was then quantified in hydrolysate using an isocratic HPLC method with a mobile phase consisting of acetonitrile, Milli-Q water, and trifluoroacetic acid in constant composition, a mixed stationary phase column, and taking into account the CPL content in the original waste sample. For both chromatographic methods, I optimized the HPLC separation conditions and the sample preparation procedure. By creating calibration curves that represent the peak areas of CPL and ACA in the chromatograms as a function of the concentrations of their standard solutions, I was able to successfully determine the contents of CPL and PA6 oligomers in the waste generated during PA6 recycling.
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