Cleaning contaminated plastic film with water only transfers the contamination from the film to tim water. Water treatment is an added expense. "But when you clean dry, you remove the problem," says Heinz Schnettler, engineer at the Systec div. of Duales System Deutschland, which administers the "Green Dot" program for recycling packaging waste in Germany. He also notes that if you remove paper labels while dry, you preserve their value for waste-to-energy incineration. If paper gets wet, it gains weight and costs more to dispose of.

Systec cleans film and flake with a Waterless Mechanical Purifier, which comes in two sizes, both with throughput capacity of 2000 to 4500 lb/hr of plastic, but one provides more cleaning time. The MR 75 is 3 meters long, has a 100-hp drive, and tackles plastic with average contamination. The MR 110 is twice as long, has a 150-hp drive, and tackles difficult problems like removing paper labels.

Systec has 26 dry recycling units installed worldwide that are reclaiming film, post-consumer mixed plastics, and plastic/paper composites. One system in Canada removes paper labels from PET flake. Systec recently gave a license to shredder maker Kurimoto Ltd.

Cleaning with air
The Systec process starts with a buffer silo that holds 4 to 8 m3 of shredded film. Feed augers inside the silo are configured for specific film weights from 10-micron stretch film to heavy industrial film.

From the silo, flake goes onto a shaker to break up the clumps that could clog downstream devices. The flake then travels up an angled auger. At each stage, the material moves a little faster to fluff it up before it undergoes air separation. The first separation step occurs in a free-fall chamber, which removes rocks and bottles that could damage the purifier.

The purifier is essentially a dry centrifuge that uses very high-speed air flow and runs continuously, not in batches. It's a horizontal, cylindrical chamber with a central rotor armed with paddles turning at high speed inside a polygonal screen basket. Specially shaped rotor blades apply high friction, removing the paper from the plastic and tearing the paper into very small particles, which pass through the holes in the screen basket and are sucked out one end of the chamber by a fan. Plastic flakes, which remain inside the screen basket, are driven by the paddles to the opposite end of the chamber and sucked out. Each flake spends only 2 to 3 sec in the chamber.