By Jan H. Schut
Postconsumer polyethylene film recycling is coming back after a 15-year hiatus with investment in new plants and new R&D. Especially interesting are new processes to clean LLDPE stretch film. Two new plants started up in 2011 with new wash processes to recycle 100% LLDPE stretch film back into film, one for pallet wrap, the other silage wrap. Wisconsin Film & Bag Inc., Shawano, WI (www.wifb.com), devoted five years to bench top R&D in-house to invent a patented hot wash process (U.S. Pat. # 8567702) for postconsumer LLDPE pallet wrap that allows WIFB to reuse the material in translucent monolayer industrial films and can liners. Soreplastic S.A., Tenneville, Belgium (www.soreplastic.com), recycles heavily contaminated LLDPE silage stretch wrap with a single large washing and recycling line making 1200 kg/hour of black film grade material. The trick, the company says, is much finer shredding.
NEW HOT WASH FOR LLDPE PALLET WRAP
Wisconsin Film & Bag’s process for LLDPE pallet wrap is designed to remove paper labels. WIFB uses hot water and surfactant to sterilize film and remove paper fiber. Typically hot water is used with PET flake to remove adhesives, but WIFB uses hot water “to get the pulping action to remove paper,” explains Robert Kulesa, vice president of operations at WIFB. “Adhesives aren’t a problem, they stay with the plastic. But if any contaminants are left after washing, they reattach to the plastic in the dryer because of the tackifiers.”
WIFB processes 90% LLDPE and 10% LDPE. The LLDPE wash line was built by Herbold Meckesheim GmbH, Meckesheim, Germany (www.herbold.com), though the idea to use hot wash for pallet wrap was WIFB’s. The line starts with a Herbold wet grinder with knives modified for LLDPE. It cuts film into large pieces, which go into Herbold’s recently designed VWE 600 prewash unit with three integrated wash sections. The first segment is float/sink to remove rocks while up-currents of water move film to the second segment, which has two conveying screws over a perforated bottom and spray nozzles to rinse sand and paper off the film. The third segment is another float/sink tank to remove fine sand and sediment. Segments can have separate water circuits for very contaminated film.
Film then goes by screw conveyor to a wet grinder, which reduces it to 1.5-2 in. flake. Next comes the proprietary hot surfactant wash (140-190 F according to the patent), followed by hydrocyclones for density separation and mechanical dryers. Because the material is sticky, WIFB releases last moisture in an agglomerator, creating crumbles that are easier to store than thin flakes. Recycled material is used in WIFB’s monolayer ECO Blend industrial films and can liners and in customers’ bags at 25%-50% recycled content.
At least one other filmmaker puts recycled pallet wrap at high percentages into can liners and film, but using a dry cleaning process and putting the material into three-layer film. In 2008, Petoskey Plastics Inc., Petoskey, Mich., started its Greencore Recycling division with a new washing and recycling plant in Hartford City, IN (www.greencore.com). Petoskey recycles 36 million lb/year of LLDPE pallet wrap and contaminated LDPE redemption bags from MRFs. The company dry recycles the LLDPE pallet wrap, shredding it and re-pelletizing it with an extruder from Erema GmbH, Ansfelden, Austria (www.erema.at). Paper is removed with continuous melt filtration from Erema’s self-cleaning laser filter, which has some 500,000 laser-drilled holes. The wash line from Tecnofer Ecoimpianti Srl, Caneselli, Italy (www.tecnofer.bis), recycles the contaminated LDPE redemption bags. Recycled material goes into Greencore’s three-layer can liners and bags with up to 70% postconsumer content. Petoskey also dry recycles postconsumer bags and film in closed loops for customers and has done so since 1978.
NEW SHREDDING FOR 100% LLDPE SILAGE WRAP
Soreplastic’s new recycling plant for silage stretch wrap faces much higher contamination than pallet wrap. Silage film comes with up to 60% rocks and dirt. Soreplastic’s input is roughly 40 million lb/year of silage film collected from regional farm groups (which are part owners of Soreplastic). Output is 18 million-20 million lb/year of film-grade black pellets, sold for agricultural film and garbage bags. Soreplastic washes with cold water and no chemicals. Its recycling line starts with a wet shredder from Lindner ReSource GmbH, Grossbottwar, Germany (www.lindner-resource.com), with capacity for up to 15,000 lb/hour. The number and distribution of shredder knives is modified for stretch film. But the big difference is that the shredder cuts film unusually small–down to 2-4 in. pieces. Recycled stretch film is typically shredded to the size of a sheet of paper (bigger pieces reduce wear on knives).
Shredded film then goes to a Sorema wash line, starting with prewashing with a float/sink section to remove rocks and a spray wash section to screen paper out. Then the material goes to a wet grinder to reduce it to 1-1.5 in. flake—again smaller than usual. Film is typically ground into 1.5-2 in. pieces. Flake then goes to a water tank with stirrers to open up clumps of material and on to another float/sink tank for final density separation before friction washing in centrifuges. Friction washing is followed by a screw press to remove water. Soreplastic’s drying system is different from the hot air dryers typically used for HDPE film. Because of stretch film’s stickiness, Soreplastic dries flake mostly mechanically, being careful not to overheat it. Drying starts with a large double centrifuge, followed by mechanical drying.
Soreplastic isn’t the first or only company recycling LLDPE silage stretch film, but it’s believed to run the biggest single recycling line for silage film. British Polythene Industries in the U.K., a producer of LLDPE silage wrap, is the dean of agricultural film recycling with three plants recycling a total of 150 million lb/year of heavily contaminated LLDPE and LDPE agricultural film. BPI’s first plant, which started in Dumphries, Scotland, in 1995, has recycled 100% contaminated LLDPE silage wrap for 15 years. BPI’s newest plant in Rhymney, Wales, which started in 2007, recycles LLDPE silage wrap and LDPE agricultural film separately. The LLDP line starts with a drum washer from Pla.to GmbH in Goerlitz, Germany (www.plato-technology.de), to remove large contaminants. Shredding, washing, grinding and drying systems are from Tecnofer. Recycled film goes to a twin-screw extruder from MAS Maschinen-und-Anlagenbau GmbH, Pucking, Austria (www.mas-austria.com). BPI’s LDPE recycling uses a conventional dry system with manual sorting, size reduction and extrusion by an Erema TVE extruder. BPI uses recycled material in trash bags and construction films.