Part of the appeal of plastics to manufacturers is the array of available colors. However, this diversity coupled with the array of resin types can pose challenges for recyclers, particularly when it comes to sorting and separating black plastics.
Black plastics are among the most complicated materials to sort, several equipment suppliers to the plastics recycling industry say. However, while a majority of recyclers are not separating black plastics from other mixed plastics, those who are have been doing so successfully —and with markets to sell to.
To cater to these recyclers and the growing plastics recycling sector, some manufacturers, such as Green Machine, based in Hampstead, New Hampshire, are beginning to tackle this issue, while others, including Hamos GmbH, headquartered in Penzberg, Germany, have been manufacturing equipment designed to separate black plastics for more than a decade.
In recent years, plastics have been sorted by optical scanners using camera systems that employ near-infrared (NIR) technology to analyze reflected light, identifying polymers and sorting material by color. X-ray fluorescence technology also is used to sort mixed plastics by analyzing their molecular structure, enabling sortation by density as well as by additives, removing brominated plastics, for example.
Optical sorting equipment can distinguish PS (polystyrene), ABS (acrylonitrile butadiene styrene), PC (polycarbonate), PPO (polyphenylene oxide), PP (polypropylene), PE (polyethylene) and PVC (polyvinyl chloride), for example.
However, because black doesn’t reflect light, black plastics cannot be sorted by scanners using NIR technology, says Green Machine President John Green.
As a result, equipment manufacturers have developed new processes to sort black plastics. A number of other suppliers are still in the development stage while others are straying away from the challenge.
“All suppliers of sorting equipment grapple with the challenges of black plastics,” says Christopher Simon, vice president of Redwave Solutions US, a subsidiary of Redwave, an Austrian-based supplier of sensor-based sorting equipment and turnkey sorting systems. Redwave is “developing systems to tackle this issue,” he says.
The reasons why processors have shied away from sorting black plastics are reasonable, according to Felix Hottenstein, sales director for optical sorting equipment manufacturer MSS Inc., Nashville, Tennessee. “The promising technologies to sort black plastics are still either slow, work only for larger particles or are very expensive,” he comments.
Alex Wolf, sales engineer for TITECH, a division of sensor-based sorting system designer and manufacturer Tomra Sorting Solutions, based in Norway, and distributed in North America by Van Dyk Recycling Solutions of Stamford, Connecticut, says, “For more complex material mixtures, [sorting black plastics] remains a technical and economically difficult task.”
He continues, “Sorting groups of polymers together is certainly possible under the right conditions, but a complete solution still remains to be developed.”
Green Machine recently completed R&D for sorting black plastics using the company’s Green Eye optical sorting system and its patent-pending technology, which looks at materials three dimensionally and at a molecular level, Green says. The processor can collect information at conveyor belt speeds of up to 900 feet per minute, Because Green Eye looks at materials on a molecular level, Green explains, the black plastics don’t blend in with the conveyor belt of the same color.
“Green Eye optical sorters provide positively sorted grades of black plastics,” Green says. “We are in the process right now of deploying machines to separate black plastics.”
Green says his equipment manufacturing company set out to find a solution to sorting black plastics after customers requested the removal of black ABS plastics from auto shredder residue (ASR). Green Machine has since secured 90 percent pick rates for black plastics, he says.
“We have been able to sort that material while ignoring other black materials, such as rubber.” Green says. “We are taking black ABS plastics and other black plastics and successfully sorting it on our optics at high rates,” he continues.
Since the Green Eye sorts plastics by color and polymer, Green says processors who sort only by color should reconsider.
He remarks, “Black plastics can consist of lower grade plastics and higher grade plastics. Sorting simply by color is not the answer. Selecting by polymer and color is what the industry needs.”
MBA Polymers, a plastics recycling company based in England, developed proprietary technology in-house for separating black plastics, says Paul Mayhew, global sourcing manager for the company. MBA Polymers processes plastics recovered from WEEE (waste electrical and electronic equipment) and ASR as well as mixed rigid plastics from municipal sources. It expects to handle more than 150,000 tons of material this year, says Mayhew.
MBA operates three facilities—in Austria, China and the U.K.—each of which is able to process, clean and sort black plastics that are then sent to extruders to be formed into high-quality pellets to meet customers’ specifications, Mayhew says.
“We’re taking the black plastics to the final stage of recycling, to the pellet, to be sold back into the industry,” he states.
Mayhew says MBA spent two decades developing its technology to sort black plastics. MBA adopted techniques from other industries, including agriculture and mining, to effectively sort these materials.
MBA’s postconsumer black plastic pellets are used in electronics, appliances, consumer products, building construction and automotive components.
“What we’ve proven at MBA is that with the right partner and feedstocks, you can successfully close the loop and create a truly circular economy,” Mayhew says.
He continues, “There’s a huge market out there for postconsumer black plastics.”
Several in the industry, however, do not see markets for recycled black plastics in such a positive light. Hottenstein says, “Currently, markets, even for nonblack sorted engineering plastics, seem to be limited due to the high quality demands by the end users.
“Also, integrating an expensive piece of equipment just to add a potentially marginal additional value could be questionable in the overall scheme of things,” he continues.
“One way this could have a higher chance of success is if legislation would demand that a certain percentage of black plastics be recovered,” Hottenstein adds.
Similarly, MBA’s Mayhew says, “There needs to be more drivers on the legislation side of using recycled materials, really closing the loop. You need investment—nothing is cheap—but you also need to have the end markets ready to take the final product. For the industry to take off, you need those drivers in place to incentivize manufacturers to buy the recycled resins.” Mayhew adds that incentives create demand from manufacturers.
Not investing in this market means black plastics will continue to be sent to landfill, Green says.
“The absence of a system’s ability to identify black plastics has relegated that material to end up mixed in with junk plastics, whereas the value to segregate different grades of black plastics carries a much higher value and [the material] can be more readily recycled into high-value products,” he adds.
“It’s a global problem that needs to be addressed; and the only way it’s going be tackled is if everyone in the supply chain is involved,” according to Mayhew.
When it comes to sorting plastics from WEEE, recyclers have used NIR technology as well as various density separation methods. Electrostatic separation is another route.
Ranier Kohnlechner, managing director and owner of Hamos GmbH, says his company has been manufacturing electrostatic equipment to separate black plastics for more than a decade. The company’s EKS plastic-plastic separators take 1,650 pounds per hour of mixed materials and separate them into clean, single polymer fractions, Kohnlechner says. Hamos’ machine is capable of separating black PS/ABS mixtures from WEEE or toner cartridges, rubber sealing from PVC windows, shrink labels and other impurities from PET (polyethylene terephthalate) bottles and cable as well as ASR and other materials, he says
“Hamos’ EKS electrostatic separators can easily separate completely black colored plastics fractions from WEEE or toner cartridge recycling,” Kohnlechner explains.
Kohnlechner says black plastics comprise from 60 to 80 percent of WEEE material. To separate them, electrostatic separators operate on the premise that mixed plastics take on different electrical charges, positive or negative, depending on resin type, he explains. With a mixture of PS and ABS, for example, the PS takes on a negative charge, and the ABS takes on a positive charge. Charged differently in this way, the particles are subsequently separated using an electrode of approximately 35,000 volts, Kohnlechner says. Positively charged ABS is attracted to the negative electrode, and negatively charged PS is attracted to the positive electrode.
As electrostatic separators can only separate positively or negatively charged plastic particles from one other, a mixture of two plastics is ideal, he says. Such mixtures are obtained, for example, using a separation process installed before electrostatic separation, such as density separation.
Kohnlechner says the company’s Wersag facility near Dresden, Germany, which uses a combination of wet (sink-float) and dry (electrostatic) technologies, has been producing clean, high-grade PS (of up to 98.5 percent purity) and ABS (of up to 99 percent purity) from WEEE, particularly small household appliances, computers and photocopiers. Working in three shifts, the Wersag facility processes 10,000 tons of WEEE plastics each year, he says.
The WEEE recyclers that use Hamos’ electrostatic separation equipment and that have installed complete plants, Kohnlechner offers, “do not have any problems selling black colored PS and ABS.
“This market for recycled ABS or PS from WEEE is continuously growing,” Kohnlechner adds. “Leading PS and ABS manufacturers are developing new compounds with a high content of recycled ABS or PS from WEEE.”
The ABS and PS regrind, which Wersag produces in less-than-three-eighths-inch size, is reused for production of new equipment, Kohnlechner says.
The author is associate editor of Recycling Today and can be emailed at email@example.com.