TECHNOLOGY | ODOUR AND EMISSIONS
Getting on top of odour
Upcycling post consumer recycled plastics into demanding applications means dealing with the challenge of unwanted
odours.Peter Mapleston looks at available options
Demand for plastic recyclates containing material from post-industrial and post-consumer waste is certainly growing. And the level of quality of that can be achieved from these materials is increasing too. One challenge that still needs to be overcome, however, is the unpleasant odour that some recyclates bring with them. Removing that is a prerequisite if plastic recyclates are to continue to substitute virgin plastic and if recyclates from different sources are to be used for the manufac- ture of new products. Odours are the result of volatile components that vaporise during processing or migrate out of finished parts over time. The volatile components may result from thermal breakdown of the plastic during processing, from impurities in the plastic, or from contamination by food products, oil residues, natural fillers, fragrance oils and more. To resolve and eliminate these odour problems it is important to identify the source and isolate the cause the problem. Some are quite familiar to polymer processors
— oxidation of a polymer such as HDPE as a result of multiple heat histories, for example, gives rise to a smell of burnt wax. An effective way to eliminate this odour is addition of an appropriate antioxidant and odour elimination masterbatch, according to US-based Addisperse. It offers its ON108 (pellet form) or ON106 (powder form) product for this purpose.
Additives and fillers (especially natural fillers) are
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a further common source of odour. They can break down during processing, developing low molecu- lar weight volatile components. Addisperse says its odour elimination masterbatch ON103 (pellet form) or ON104 (powder form) will effectively tackle odours based on a variety of chemicals containing sulphur and amines. The Addisperse masterbatches are said to work in the vapour phase, chemically interacting with volatiles. The company says it is currently develop- ing an odour elimination masterbatch that will be acceptable for use in food packaging applications, such as trays, boxes and film.
Fighting mould Some odours can be attributed to a build-up of bacteria, moulds and mildew within raw materials that may not have been stored or handled prop- erly. Recycled plastics hold onto and can intensify unpleasant smells, which is understandably a prime issue with items such as storage containers, bottles and packaging specifically associated with food and drink. The Covid-19 pandemic has increased aware-
ness of and raised concern over microbes and cleanliness. While adding antimicrobials has been on the radar for plastics compounders for some time, until recently there hasn’t been a real push to overcome the challenges associated with reworking formulations and meeting regulatory requirements,
March 2022 | COMPOUNDING WORLD 59
Main image: Upcycling PCR plastics for applications in demanding markets such as automotive means dealing with unwanted odour
IMAGE: SHUTTERSTOCK
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