In a study conducted by the Fraunhofer Institute for Process Engineering and Packaging IVV , researchers sought to determine the source of the odour emitted by some recyclates. Off-odours are not conducive to the reuse of recycled materials in high-quality consumer products.
Yet if the targets of the new EU Packaging and Packaging Waste Directive concerning the recycling of packaging waste are to be met, new markets for recyclates produced from waste plastic packaging must be found.
While the PET recycling loop is relatively well established, with rPET from bottles finding application in various products, this is not the case for other packaging waste.
In the present study, the Fraunhofer IVV scientists focused on LDPE packaging, as, in a previous study they had previously analysed the odorants in HDPE waste and in the recyclates produced from packaging of body care products and detergents.
LDPE is a commonly used material to produce plastic shopping bags, and these tend to end up as packaging waste. The waste analysed by the researchers originated from different collection systems.
After first being sniffed by a trained sensory panel, the test samples then underwent chemo-analytical testing, enabling the chemical structures to be determined and also possible formation pathways into the packaging waste - and subsequently via the recycling process into the recyclate - and sources of the odorants to be identified.
Of the some 60 odorants identified in the study, most were typical metabolites of microorganisms. Many had a cheese-like or faeces-like odour. The odorants included carboxylic acids, sulphur-containing and nitrogen-containing components.
Waste collected separately in the yellow bag - the bag for plastic waste in Germany - had a significantly lower overall odour than the waste fraction collected in the general household waste.
While not a huge surprise, the scientists were thus able to establish conclusively that the collection route employed had a huge impact on odour development in the plastic waste and recycled materials derived from that waste.
Separate collection, therefore, improves the sensory properties of plastic waste and hence the quality of the resulting recyclates.
According to Fraunhofer IVV, these findings can now be used to develop customized solutions for optimization of the odour of plastic recyclates, starting at the waste collection stage.