ODOUR REDUCTION | INNOVATION
Plastics recycling researchers, machinery groups and material developers are trying out different processes and products to control the odours that hold back wider use of recycled materials. By David Eldridge
Lingering problem: bad smells need to be banished
Odours arise in recycled plastics from many sources, not just the residues present in post-con- sumer waste but also from VOCs and other effects of polymer processing and reprocessing. For recycled plastics to achieve their full potential and displace virgin material in as many applications as possible, the bad smell problem really needs to be solved. That is why academic and industry groups are working hard on the issue, using their expertise to develop a diverse range of processes and products that can mitigate the excesses of odour. The Fraunhofer Institute for Process Engineer- ing and Packaging (IVV) in Germany has been studying in detail the odour-active substances that occur in post-consumer recyclate originating from contaminants remaining from the first use of the plastic packaging. The Department of Sensory Analytics at Fraunhofer IVV deals with the charac- terisation and optimisation of plastics recyclates. It has previously studied the odorous substances in HDPE waste and recyclates from packaging of personal care products and detergents (Plastics
www.plasticsrecyclingworld.com
Recycling World July-August 2018). In a study published last year, conducted with the Chair for Aroma and Smell Research at the Friedrich Alexan- der University Erlangen-Nuremberg and the University of Alicante, it focused on another polyolefin commonly used in packaging: LDPE. LDPE shopping bags are recycled via many
packaging waste collection systems. The Fraun- hofer IVV investigated post-consumer LDPE shopping bags, analysing odours that are present. It is necessary to identify the source of an odour in order to decide how to deal with it when recycling. It says: “Identification of the substances causing off-odours is essential in order to be able to take measures for odour optimisation. Most of the odorants identified in the study are typical metabo- lites of micro-organisms. Many of these metabolites had a cheese-like or faeces-like odour. The odor- ants included carboxylic acids and sulphur-contain- ing and nitrogen-containing components. The chemical structures of the odorants gave key insight into their origin. Using this information, the
Main image: Post-consumer PP and HDPE packaging waste streams are usally contaminated by residues that affect the smell and quality of items these materials are recycled into
May/June 2020 | PLASTICS RECYCLING WORLD 27
IMAGE: SHUTTERSTOCK
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