Black plastics have been notoriously difficult to detect, but recent technological developments have made it possible to sort them not only by color but also by polymer, unlocking economic value for recycling companies. This is a game changer in the fast-evolving plastic packaging sector, and Stadler – a leading supplier of sorting plants for the recycling industry – is experiencing an increase in the demand for systems capable of recovering all black plastics from the waste stream. Through effective collaboration among all players in the industry’s value chain, a financially and environmentally beneficial circular economy is possible.
Plastic packaging serves important functions in modern life, and we have come to rely on it heavily. It is an exceptional product that, however, has a significant end-of-life problem. This is especially true of black plastic, which until very recently couldn’t be detected with the available technology, Near Infrared (NIR). “The emitter shines a light on the material and the sensor takes a reading of the energy that is reflected back,” says Enrico Siewert, Director of Product and Market Development at Stadler. “However, carbon black absorbs the light, so the signal doesn’t bounce back and the sensor doesn’t get a reading. This means that black plastic is undetectable with the technology that is widely deployed in the recycling infrastructure.”
Why recovering black plastics matters
Black plastic makes up a significant part of household waste which, if not recovered, will be incinerated or sent to landfill. This has not only environmental implications but also financial, as Enrico Siewert explains: “If recycling companies can’t recover black plastics, they can be losing as much as 15% of the value of their inbound material. When they are able to mine this material out of the waste stream, they can create economic value and positively impact their bottom line.”“Another important consideration is that more and more packaging is made of black plastic, as more recycled content is used. When recycling post-consumer packaging, if it’s not rigorously sorted by color, the resulting output is a grey resin. This can’t be taken back to white, so many converters add carbon black to obtain a very uniform, more appealing color. We, as a society, want more recycled content, we will see more and more black material in the waste stream. Consequently, packaging will continue to trend towards a darker color.”
A game-changing technological development
Different industries involved in the plastics value chain have been researching solutions to the black plastics issue, and today there are different ways of recovering these materials. A first solution is a sensor-based dry sorting system, which uses NIR sensors with detectable black additives to detect the different types of polymers. There are also other types of sensors capable of sorting black materials, also by polymer. With this sensor-based dry sorting system, it is possible to accurately sort black polyethylene, polypropylene, PET and polystyrene.
Another solution is a wet density sorting system based on the flotation principle. The ligher polyethylene and polypropylene float, while the heavier PET, PVC and plystyrene tend to sink. The drawback of this system is that, not only is it costly due to the filtration process, the need for water, cleaning, etc., it is not capable of sorting by polymer, so that a circular process is impossible.
“However, the biggest advancement has been in sensor technology,” states Enrico Siewert. “The situation has evolved to the point that today we are able to separate black not only by color but also by polymer. This is very important because if the sorter ejects all black materials together, there could be as many as 15 different polymers in the mix, which can’t easily be remanufactured.”
“This is a very recent development: 5-6 years for black color detection and polymer sorting. This is a true game changer because it creates economic value and makes it possible to recycle these materials that would otherwise go to landfill or incineration.”
