Extrusion International 3-2023

47 Extrusion International 3/2023 in place, the end product is a mix of different polymer types and, in some cases, numerous colors. Since this fraction contains several distinct product types, its qual- ity levels are low and it can only be used for lower-grade applications, for which demand and value are marginal. The demand for superior secondary feedstock on the other hand is skyrocketing, spurred by stringent recy- cled content targets as well as the improvement of in- dividual sustainability credentials. With advanced flake sorting, recyclers can easily upgrade their products and create new revenue streams. High volumes of superior feedstock at hand A plastic recycler can process more than 100,000 tonnes of polymer flakes per year, depending on mar - ket demand and material availability. With recent short- ages of available materials, adaptability is key to main- taining profitable business. Waste streams and market demands are, in fact, highly dynamic. If the supply of recyclable polymers on the market is limited, but de- mand is high, plant operators often have little choice but to turn to more contaminated post-consumer waste to meet market demands. Exceptional purity require- ments persist regardless of the volume to be processed and the type of recoverable feedstock, challenging re- cyclers to reach even higher qualities from increasingly more contaminated sources. Compared to other processing machinery, flake sort - ers are a gateway to overcoming feedstock volatility. Compact in size, easy to install and flexible in opera - tion, they prove to be a sound investment for small and large operations alike. Advanced flake sorting can process fluctuating levels of contamination without compromising recovery and purity levels. Equipped with a set of sophisticated technologies that are a fun- damental part of the recycling process, they help turn low-quality input material into pure flakes that meet even the strictest quality requirements. This gives re- cyclers access to material that previously couldn’t be recovered, squeezing out the maximum value from available fractions. A good example of creating new revenue streams is the sorting of polyolefins. Holding the lion’s share in global plastic production, the availability of PO on the market is abundant and offers a lot of potentials as the industry strives to use more recycled PO in the manufac- ture of high-quality products. Nevertheless, upgrading polyolefins presents its own set of challenges. Whereas PET bales processed in a recycling facility mostly consist of only one target material (PET), PO bales are a mix of two valuable materials: polyethylene (PE) and poly- propylene (PP). The share of each material type in the PO infeed is hard to predict and can change with each bale. One bale could be a 50/50 mix of PE and PP, and the next could be a 70/30 mix. Irrespective of the input composition, both PE and PP flakes must be accurately identified and separated to create high-purity fractions for recycling. Until advanced flake sorting and purification meth - ods were introduced, the infrastructure lacked the tech- nology to separate PP from PE cost-effectively. Less so- phisticated flake sorters can solely purify one material type and remove only small amounts of contaminants, thereby often limiting their use to PET recycling plants. Furthermore, higher throughputs were hard or impos- sible to realize. For example, if a recycling plant uses less advanced flake sorters to process a PO bale com - posed of 60% HDPE and 40% PP (not considering other contaminants), the infeed would have to be sorted by belt-sorters before shredding, when the material size is big enough to allow for accurate separation of PE and PP. Consequently, shredding, washing and flake sorting would have to happen in parallel on two different lines, driving up costs significantly. With the aim to operate more profitably, recycling plants would prefer to pro - cess the material in batches on a single line. The down- side of this approach is a reduction in total throughput. Moreover, it remains costly due to extensive material handling, such as re-baling, storage and manpower. These are some of the main challenges impeding the upgrading of PO to higher quality recyclates. Modern sensor-based flake sorters are a game-chang - ing technology for the industry in the above-mentioned Mixed plastic waste Sensor-based sorting accurately separates red and blue PP flakes