Development and application of an analytical method to quantify odour removal in plastic waste recycling processes

Europe is strongly committed to the recycling of plastics, especially packaging. In the development of closed loop recycling processes, recyclates must have appropriate properties, including lack of odour. The main objective of this study was to develop a technique to qualitatively and semi-quantitatively analyse the volatile contaminants in these complex plastic waste matrices before and after washing procedures. Three sampling methods were explored, SPME and purge and trap methods (activated carbon with solvent desorption and Tenax-TA with thermal desorption). All analyses were then carried out using gas chromatography – mass spectrometry. SPME was not repeatable due to the heterogeneity of the waste samples and the static character of the method. Solvent desorption with CS2 (RSD 14,5 %) and thermal desorption (RSD 13,4 %), were capable of measuring the removal efficiency of pollutants in a semi-quantitative way. A broad spectrum of chemically different, but mostly apolar volatiles can be detected. In addition, it became clear that also the analysis of the less volatile components is essential, as these are strongly adhered to the hydrophobic polymer matrix. A post-consumer film waste stream was analysed, before and after washing and pelletizing. A general decrease of 97 % and 44 %, was measured with respectively thermal and solvent desorption for the screened components. However, after reprocessing potentially odour-causing compounds are again released or formed, showing the complexity of odour removal processes in plastic recycling.