TECHNOLOGY | ODOURS AND EMISSIONS
to system designers as, depending on the specific process steps, targeted measures can be formu- lated to remove or reduce odorants and/or avoid the formation of new odorants.
Above: Researchers at Aimplas hope to develop microorganisms to eliminate odour from waste dairy packaging
used for new products. However, they often exhibit an intense smell, which can be traced back to high contamination of the input material. Elucidation of these off-odours can be extremely challenging. Fraunhofer IVV says that more than 60 odorous substances were identified in its study, using combined chemo-analytical methods, and the information gained will provide a targeted strategy for avoiding off-odours. Recyclates must have no off-odours if they are to be used as secondary raw materials for the manufacture of high-quality consumer products (necessary to meet the targets of the EU Packaging and Packaging Waste Directive). However, off- odours often prevent a closed cycle for the recycling of plastics packaging materials, particu- larly in the case of polyolefins. The Department of Sensory Analytics at Fraun-
hofer IVV characterises off-odours to help optimise plastics and recyclates. A number of studies concerning odorants in HDPE waste and the recyclates produced from packaging of body care products and detergents have already been conducted. Using various collection systems as part of the current study on post-consumer LDPE bags allows the effect of the collection strategy on the sensory impairment of the waste to be investigated. Fraunhofer IVV says that identification of the substances causing off-odours is an essential step toward determining measures for odour optimisa- tion. Most of the odorants identified in the study were typical metabolites of microorganisms and many had a cheese-like or faeces-like odour. The odorants included carboxylic acids and sulphur and nitrogen-containing components. Their chemical structures give key insights into their origin and this information can help to identify the pathways into the packaging waste and on via the recycling process into the recyclate. This is of value
58 COMPOUNDING WORLD | March 2021
Collection matters The study showed that the way packaging waste is collected has a large bearing on the odour quality of post-consumer LDPE bags. There are significant benefits through the use of Germany’s yellow bag separate collection system – the preferred collection method across the country. Waste collected in this way was found to have a significantly lower overall odour. In contrast, the waste fraction collected from general household waste had more intense odours — the higher organic fraction in the general waste favours formation of microbial degradation prod- ucts. The study also demonstrated that washing the post-consumer LDPE bags from the separate
collection system at 60℃ on a laboratory scale led to detection of fewer odorants and a reduced overall odour compared to unwashed bags. Scientists in the Department of Sensory Analytics
at Fraunhofer IVV used a combinatory sensory approach to identify the odours. Sensory evaluation of the sample materials was first undertaken by a trained sensory panel, with odorants then identified using comprehensive chemo-analytical methods such as two-dimensional gas chromatography- olfactometry coupled with mass spectrometry. This enabled the chemical structures to be determined and from that the possible formation pathways and sources of the odorants to be identified. These findings will now be used to develop customised solutions for optimisation of the odour of plastic recyclates, starting at the waste collection stage. Odour in recycled plastics is also one of the
targets of the Enzplast programme, which is underway at the Spanish Aimplas technical institute. Part of the two-stage project, which is funded by the EU through the Valencia regional authority’s ERDF programme, aims to develop a means to exploit microorganisms capable of eliminating odour from dairy packaging waste. According to Aimplas, early results indicate a significant reduction in odour intensity.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.byk.com �
www.nexamchemical.com �
www.gabriel-chemie.com �
www.color-service.de (Tosaf) �
www.alpha-mos.com �
www.ivv.fraunhofer.de �
www.aimplas.net
www.compoundingworld.com
IMAGE: AIMPLAS
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