ANALYSIS | ODOUR AND EMISSIONS
Above: Fraunhofer assembles panels of trained “sniffers” to evaluate odours in a standardised way
as discouraging companies from using recycled plastics. Additionally, emissions from recyclate during subsequent industrial processing raised concerns regarding the health and safety of employees. Previous studies of the research group at
Fraunhofer IVV, carried out by Miriam Strangl, revealed that polyolefin packaging waste of post-consumer origin and its corresponding recyclates exhibit severe contamination by odorous substances. The studies said this needed to be addressed to enable a future circular economy for plastic packaging. Development of methods to effectively remove
Right: Fraunhofer’s solvent
assisted flavour extraction (SAFE)
technique can be used to isolate volatile components
odorous contaminants is a priority, according to Fraunhofer, and an important step in achieving that is identifying the chemical structures of the odorous compounds. This enables deeper insight into physicochemical properties, as well as sensory evaluation of specimen materials, in order to characterise the odorous compounds. Since potent odour-active compounds are often only detectable at trace levels, characterisation of causative odorants requires analytical approaches with high selectivity, as well as high sensitivity.
Sensitive selection This combination of selectivity and sensitivity is of particular importance in the field of plastics because odorous target analytes often coelute with other dominating, yet odourless, polymer-specific volatiles. The usually performed screenings on major volatile organic compounds (VOCs) using gas chromatography-mass spectrometry (GC-MS) can not provide detailed information on causative odorants and their corresponding chemical structure. To overcome this obstacle, researchers in the Department of Sensory Analytics at Fraunhofer IVV combine sensory evaluations performed by a trained human panel with comprehensive instru- mental olfactometric analyses. In terms of the human sensory methods, the panel is trained to
50 COMPOUNDING WORLD | March 2020
www.compoundingworld.com
evaluate odour on a standardised level (there is currently no norm allowing a standardised evalua- tion of perceived smell). For the plastics recycling sector, the ultimate goal is production of high odour quality recyclates, says Fraunhofer IVV. This has already been achieved in terms of the latest super-clean recy- cling processes for PET bottles. With regard to polyolefins, high and low-density polyethylene (LDPE/HDPE) and polypropylene (PP) are widely used for food packaging and also for packaging of various consumer goods. In contrast to PET bottles, however, which are commonly directed to a separate mono-stream collection system, polyolefin and other collected plastic packaging waste is typically more contaminated with food or other residue materials. This results in a greater contami- nation of plastic with odour-active substances.
Post-consumer odours The Department of Sensory Analytics of the Fraunhofer IVV, together with the FAU Erlangen, has now investigated the smell properties and odorant composition of different post-consumer recyclates in a number of studies. Earlier work evaluated odour removal strategies for recycled HDPE using a modified recycling process and disclosed odorant sources. However, because LDPE also plays a major role in various packaging applications, the latest study focused on post-
IMAGE: FRAUNHOFER IVV
IMAGE: FRAUNHOFER IVV
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