In 2007 the United States recycling industry reprocessed 576,000 tons of plastic bottles, according to the Institute of Scrap Recycling Industries (ISRI). But, as plastics recyclers know, that doesn’t mean recycling plastic is easy or simple. Plastic bottles may be made of any of several different types of material, including the plastics known by the acronyms PET, HDPE, PVC and others. That’s a problem, because to efficiently process salvaged plastics requires that the stream be sorted by type as well as color. And that’s where plastics separation systems come into play.

At National Recovery Technologies, Inc. in Nashville, engineering manager John Thomsen said one of the oldest and most persistent challenges in separating the different types of plastics is maintaining consistency in the way the material is prepared and presented to the sorting systems. “In these fast-acting machines, you can’t have 100 lbs. of material show up in one short time interval, followed by another interval of zero material,” said Thomsen. “It’s always been an issue and it’s one that we still have to address.”

Separating interlocked material, such as when two plastic bottles of different types are crushed together, presents another difficult problem. Much progress has been made, however, in cleaning bottles and other objects prior to sorting. That’s important because dirt can foil sorting technologies that use optical detection.

National Recovery Technologies uses X-rays in some applications. These are less affected by dirt. For instance, its VinylCycle systems separate polyvinyl chloride from a mixed stream of whole or crushed plastic bottles of HDPE, PET and PVC. The systems are designed to process up to 10 bottles per second, employing precision air jets to eject selected bottles from the feed stream.

National Recovery Technologies’ Multisort IR uses infrared sensing to detect specific polymers within a mixed stream of material. Also using air ejectors, it can achieve throughput rates of more than 10,000 lbs. per hour.

Its Multisort ES identifies materials by color, sorting bottles over a wide range of colors, tints, and transparencies. It can sort PET bottles by color, even separating out very lightly tinted bottles, as well as sorting PET from HDPE and natural from colored HDPE. It has throughput rates of up to 11,000 lbs. per hour.

National Recovery Technologies has long sold to second-stage separating applications where plastics are sorted just before being reclaimed. Recently, Thomsen has seen more interest from customers in general waste separation such as municipal recycling facilities. Overall, he said, demand has remained healthy. “It’s surprisingly good, considering the worrisome stories I hear from people in other businesses,” he said. “We seem to be doing okay now.”

At SiCon America in Venice, Florida, representative Norb Geiss said the company’s polyfloat technology employs different fluid densities to separate plastics according to their density and produce 99 percent pure separation at yields of more than 98 percent. “We build units up to 12,000 lbs. per hour which are turnkey and include storage, feeding, drying and electronic control,” said Geiss. “We can work with different densities to separate different grades of plastics.” SiCon polyfloat systems are delivered as turnkey installations and include measures for preparing and drying the materials. They can be used for any hard plastics, as well as for films.

SiCon’s most popular applications include separating plastics from household appliances and shredder residue as well as commercial plastics. Electronic scrap processing represents a growing market. “Increasing landfill cost and take-back regulations for electric/electronic devices are an advantage for our business,” Geiss said. The United States is a developing market for SiCon, which is based in Germany. “We are looking forward to supporting the introduction of polyfloat into the US market,” Geiss said.

At Magnetic Separation Systems, Inc. (MSS) in Nashville, sales director Felix Hottenstein said the company offers two types of separators for plastics. Its Sapphire module separates specific plastic resins or mixed plastics, as well as paper, from a materials stream. The company said typical removal efficiency is greater than 80 percent, while product purity exceeds 90 percent. Using a proprietary sensor to identify plastics, the Sapphire uses an upward firing air ejection to remove plastics from the stream. “In plastics processors like PET sorting plans, the Aladdin is normally the choice, because they need to sort out the green PET bottles from the clear PET bottles as well as remove PVC bottles,” Hottenstein said.

MSS’s Aladdin sorts material by plastic type and also by color. It can create three output streams from one input. The Aladdin incorporates both full spectrum color and near infrared detection in a single sensor, and employs transflectance sensing to sort transparent and opaque objects at the same time. The Aladdin has a capacity of four to six tons per hour.

Magnetic Separation Systems’ newest machine is its E-Sort unit, which is for electronics scrap. That equipment addresses some of the specific challenges with separating plastic and other materials from e-scrap. For instance, electronics scrap is usually much smaller in size, so it requires significantly higher resolution than for bottle sorting. “The technology is somewhat similar, but it has higher resolution,” said Hottenstein.

Another difference is the larger number of polymers that must be detected and sorted in e-scrap in addition to the usual PET, PVC and HDPE used in bottles. “On the electronic scrap side, there’s a whole variety of plastics that come into play,” Hottenstein said. “So it’s quite a bit more tricky.”