COMPATIBILISERS | MATERIALS
Finding ways to make polymers compatible
One approach to the problem of mixed plastics waste streams containing different polymers that cannot be reprocessed together is to use compatibilising additives. Mark Holmes reports on companies developing solutions
As the name suggests, compatibilisers are an essential group of additives that can form chemical linkages between materials that are normally incompatible. Used in plastics compounding for some time to improve physical and mechanical properties, as well as processability, compatibilisers are now receiving significantly more attention as the importance of the circular economy and the need to re-use mixed polymer streams continues to grow in importance. The market is growing for materials that can
compatibilise mixed resin streams, according to ExxonMobil. “Resins, or compounds that are made up of these resins, can be used to compatibilise recycled plastics whether it is post-consumer recycled (PCR) or even post-industrial recycled (PIR),” says Pam Cadile, Market Developer. “The continual growth is due to brand owners pushing to use these recycled plastics in their packaging products for consumer products, industrial contain- ers and material handling supplies.” There are a number of factors that need to be
considered when using compatibilisers for recy- cled plastics, says Cadile. These include how contaminated the waste stream is. For example, is the waste material 100% of a particular resin type,
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such as polypropylene, polyamide or polyethyl- ene? If so, data proof on the certificate of quality, for example FTIR (Fourier-transform Infrared Spectroscopy) or DSC (Dynamic Scanning Calorim- etry), for the specific batch is required. However, most waste resins are a mixed stream, so any one resin type is contaminated. Contamination can be of another resin or a filler, such as colourant, calcium carbonate, talc or even paper, and can affect the processing or performance properties. For compounds produced from recycled
plastics, another consideration is whether the compounder has already added a compatibiliser. “If so, will the supplier share what they have done with you so you can understand if the compatibi- liser has upgraded the resin at all and what processing or performance advantages are the result,” says Cadile. “They may be using a product that is not meeting your processing or performance needs at all and you need something specific for the overall system.” It is important to know the quality of a compati- biliser in a recycled compound. She says: “We are finding that many compounders use an off-spec plastomer. When one purchases off-spec resins they are introducing another variable into the
May/June 2020 | PLASTICS RECYCLING WORLD 39
Main image: Oil and water don’t mix, and neither do poly- ethylene and polypropylene unless they are helped by compatibilisers
IMAGE: SHUTTERSTOCK
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