ODOUR REDUCTION | TECHNOLOGY
With the increase in use of post-consumer recycled resin, there is a growing need for additive and processing solutions to remove offensive odours. Jennifer Markarian reports
Meeting the odour challenge head on
Malodours in plastic parts can come from a wide range of sources, including degradation products from plastic resin or, in the case of recycled plastics, from degraded polymer, degraded inks, or the previous contents of the package, for example. Eliminating odour is key for the consumer to accept the product. One solution is to mask the odour with a strong but pleasant fragrance. In many cases, however, masking is not enough, and the malodour must be removed via processing or additive technologies.
Odours typically come from volatile organic compounds (VOCs), some of which are regulated to control potential hazards from inhalation and some of which are “nuisance” odours that are not harmful but are unpleasant. The term “volatile” means that the molecules will evaporate easily and be released as “emissions,” which is why they can be noticed as odours (ie, detected by a person’s olfactory system). Smell is one of the important organoleptic properties (along with touch) considered in plastic part design, particularly for consumer-facing parts, such as consumer goods, packaging, or automotive interiors. Several standard test methods are used by the automotive industry to evaluate odour in parts as related to vehicle indoor air quality, including the German Automotive Industry Association (VDA) standard VDA 270, Volkswagen (VW) PV 3900 and
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others. In addition to odour, other automotive standards identify specific VOCs and measure fogging from semi-volatile organic compounds, but the odour tests are seen as stringent standards that can be challenging for plastics parts to meet, as they use a panel of people who examine and rate odour perception. Because malodours are prevalent in mechanically
recycled plastics, equipment providers have built solutions for removing some of the odour-causing compounds with devolatilisation and other methods. Coperion and Herbold Meckesheim offer a
variety of solutions for deodourisation at several points along the recycling process chain. Jochen Schofer, Head of Sales Recycling at Coperion, says that multiple steps are required to be certain that the recyclate will meet high mechanical and sensory demands, will not exhibit undesired odours, and will achieve the quality needed for the intended application. “In a first step, odours are eliminated as the waste plastic undergoes mechanical pretreatment during shredding, washing and drying. Further odours can be removed from the shredded plastic in a silo using fresh air circulation,” says Schofer. “The next, intensive devolatilisation step, which markedly improves the recompound’s sensory quality, takes place during compounding in a ZSK twin screw
July 2024 | COMPOUNDING WORLD 13
Main image: Smell is one of the most important organoleptic properties considered in consumer- facing plastic parts
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