ANALYSIS | ODOUR AND EMISSIONS
The Heracles NEO electronic nose from Alpha MOS aims to provide fully automated aroma characterisation Image: Alpha MOS
consumer LDPE bags. Sample material for the LDPE study originated
from a variety of collection systems to determine the possible effects of a collection strategy on the odour profile of the LDPE waste. To this end, the odorant composition of LDPE bags collected in a separate plastic fraction were compared to LDPE bags originating from a non-separated collection comprised of all kinds of domestic waste. Informa- tion obtained from the performed analyses are essential to develop future odour reduction strategies and so broaden application of post-con- sumer recycled plastics.
Sensory analysis Comprehensive sensory analyses, as well as instrumental analyses such as two-dimensional gas chromatography-mass spectrometry/olfactometry (2D-GC-MS/O), enabled the structural elucidation of more than 60 odour active substances in the LDPE bags. Sensory analyses performed by a group of trained panellists revealed that the type of collection system had a noteworthy effect not only on the overall odour but also on the odour profile of the corresponding waste material. It was found that cheesy and faecal smelling
odorants and short chain carboxylic acids, both commonly representing typical metabolites of microorganisms, showed higher intensity ratings in the non-separated waste. This can be explained by bioconversion of organic waste being more abundant in the mixed waste. However, the smell of the waste separated at source was dominated by odorants described as earthy and mouldy. The pre-sorted waste also displayed a significantly lower overall odour intensity. The results suggest that pre-sorting of plastic packaging waste might
52 COMPOUNDING WORLD | March 2020
represent a first and fundamental step to odour- optimised post-consumer recycled polymers. In addition to the influence of the different collection systems, Fraunhofer IVV says the study also investigated the effect of hot water washing of corresponding waste material on the odour of post-consumer LDPE bags. It was found that washing the separately collected LDPE waste with clean water at 60°C led to a significant reduction of overall odour and therefore improved sensory properties. Fraunhofer IVV also takes part in the inter-sector and multidisciplinary research project Circular Plastics Network for Training (C-PlaNeT) within the framework of the EU’s Horizon 2020 scheme. Around 15 doctoral students in the areas of chemistry, process engineering, sociology and economics from eight European universities, together with 23 non-university partners (including Plastics Europe, Ellen MacArthur Foundation, Dow and Adidas), will take on the challenge of consider- ing the complex topic of the circular economy of plastics from a holistic point of view.
Automating smell Sensory instrumentation specialist Alpha MOS has developed its Heracles NEO electronic nose for aroma characterisations of products in all stages of production. “It is a fully automated system from sampling to data treatment for easy-to-understand results,” says Marion Bonnefille, Marketing and Communications Manager at Alpha MOS. “Up to 200 samples per day can be analysed using our automatic sampling system - all you have to do is insert the selected amount of samples into a flask and place it on the tray,” she says. “The prod- ucts are automatically heated for a few minutes to obtain the aromatic compounds — headspace — be- fore injection into the Heracles NEO aroma analyser. The separation of molecules contained in the aromatic mixture is achieved by ultra-fast gas chromatography in two columns. The nature and odour characteristics of these molecules can then be investigated with AroChemBase software module. The Heracles NEO’s software provides an easy-to-use quality control tool with a pass/fail result display.” The Heracles aroma analyser was recently used to
investigate off-flavours of caps for olive oil bottles. In this project, six samples were analysed with three batches that conformed and three that were out-of-specification. Chromatographs were obtained after analysis of the whole caps and the results displayed on statistical charts to quickly and easily make conclusions about the production quality. The most discriminating volatile compounds are
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