Odor characterization along the recycling process of post-consumer plastic film fractions

For complying with the recently set higher EU recycling targets, the quality parameters of polyolefin recyclates need improvements to enter new sales markets. Consequently, the plastics recycling sector is increasingly confronted with higher demands on the sensory properties of recycled plastics from post-consumer packaging material. The objective of this study was to examine the sensory properties of two different post-consumer film fractions along a conventional recycling process by a combined sensory-analytical approach. Accordingly, sensory evaluations of two post-consumer film fractions, the associated washing water, a washed waste fraction and conventional recycled pellets thereof were performed by an expert panel, followed by the characterization of the underlying odorants by means of gas chromatography-olfactometry and (two-dimensional) gas chromatography-mass spectrometry/olfactometry. Using this targeted approach, in sum, more than 50 odorants were successfully identified along the processing chain. Most dominant was an array of typical metabolites formed by microorganisms such as cheesy smelling short chain carboxylic acids as well as sulphur or nitrogen containing odorants exhibiting, amongst others, garlic-like or fecal smells. Furthermore, two post-consumer film fractions sorted according to a defined geometry showed great similarities in the odor profiles as well as in the odorant composition. The negligible effect of the applied washing and the still high odor pollution of the recycled pellets demonstrate the urgent need for odor removal strategies in this field. Thereby, the chemical structures of the odorants obtained within this study provide key information on potential sources and formation pathways of odorants supporting the development of targeted deodorization methods.