TECHNOLOGY | ODOUR AND EMISSIONS Odour indentification
Minimising odours is one thing but identifying them early enough to do anything about it is another. At German research organisation Fraun- hofer IVV (Institute for Process Engineering and Packaging), scientists are working on elucidation of plastic odours and development of analytical and sensory strategies, developing efficient analytical strategies to evaluate odour reduction and improve recycling processes, as well as investigating the mechanisms behind the use of odour barriers. “In order to approach the source and develop
Above:
SepSolve is developing end-to-end lab systems to reliably identify individual odour
components
Specialised recycling plants are required for the management of WEEE in which potentially harmful substances can be removed to leave behind a reusable plastic. Within the NonTox project, Aimplas reprocessed ABS ground waste fraction using a tandem extrusion process assisted by supercritical CO2
gas, which behaves as a fluid with high
diffusion and solubilisation capacity that allows extraction of VOCs from the polymeric matrix. Several sets of trials were performed at the pilot plant level to optimise processing parameters (temperature profile, screw rate and gas CO2
flow
rate). As a result, homogenous recycled ABS material was obtained in the form of ABS pellets with what is described as an exceptionally low total VOC content of less than 50 µg/g. The ABS recyclates obtained from the trial
processes displayed good flow and melt strength and were used to extrude filaments of 1.75mm diameter. These were used in successful 3D printing tests to assess processability, where it was found that the low volatile content avoided issues related to gas generation or printing nozzle clogging. The material was said to be characterised by good homogeneity and interlayer adhesion. Ecosorb odour neutralising products from OMI Industries feature a proprietary formulation based on natural plant oils for specific odour control applications and are said to be effective at remov- ing detrimental polymer odours without the use of masking agents or fragrances. For end-product specific odour control applications, they are available in additive formulations that neutralise odours connected with phenolic resins and the like. The company also offers Ecosorb products that it says can be compounded into consumer packag- ing conformimg to the US Occupational, Safety, and Health Administration (OSHA) Federal Hazard Communication Standard 29 CFR 1910.1200.
40 COMPOUNDING WORLD | July 2023
strategies to reduce the unwanted odour of recycled plastics, it is a prerequisite to identify the most odour active compounds on a molecular level,” says Helen Haug, in Fraunhofer’s Sensory Analytics & Technologies department. “At Fraunhofer, a multistep analytical procedure is applied, including sample preparation, as well as thorough analysis through instrumental techniques coupled with olfactometric detection (for example, two-dimensional gas chromatography - mass spectrometry/olfactometry, 2D-GC-MS/O), where the human nose plays a major role in describing the odour characteristics. Additionally, sensory investigations can be conducted to evaluate the overall odour characteristics. Beyond that, on-line measurement techniques (for example, proton transfer reaction - mass spectrometry, PTR-MS) are performed while investigating the dynamic emissions of volatile compounds,” she says.
Changing strategies Johannes Schneider, Process Development for Polymer Recycling, says strategies can be differenti- ated in waste treatment and recyclate treatment. “The former includes, for example, the effective- ness of washing and sorting plastic waste. Studies show that a hot washing step leads to a significant odour reduction of recycled pellets, while colour sorting into white and grey fractions did not. Another study indicated that advanced sorting of post-consumer packaging waste, i.e., sorting together categories with the lowest VOC load, could result in a reduction of the contamination levels for VOCs. However, the presence or absence of odour cannot be equated with the VOC load as certain odorants might be potent even in low concentrations. “Treatment of pellets with a hot air stream in a decontamination reactor could also bring favour- able results, and alternative strategies such as the use of probiotic bacteria have also been investi- gated,” Schneider says. Electronic noses (E-noses) are being used to
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IMAGE: SEPSOLVE
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