PP recycling gets a boost.
Bale wrap is a tube of basket-woven PP fiber used to cover raw cotton or other fibers for shipping and storage. A related product is bulk bags of woven PP capable of shipping up to 2000 lb, like a gaylord. Like bale wrap, bulk bags usually make only one trip (in fact, recyclers sign statements that bags turned over to them won't be reused, since a company's name is usually printed on them).
Efforts to recycle woven PP from bale wrap and bulk bags is driven by textile companies that want an outlet for their waste, since several states, including the big textile states of North and South Carolina, ban landfilling of plastics. Bale wrappers weigh 2-3 lb each, and bulk bags 6-9 lb. So to keep textile customers from going back to jute, PP fiber companies have to take the wraps back and reuse them somehow.
The problem with bale wrap is that dirt, metal, paper and cotton fiber get caught in the weave. Cotton is particularly difficult to wash out. In a wet-washing line, cotton fibers swell up with water and plug the equipment. Bulk bags make other problems. They are reinforced with nylon slings and straps and polyester sewing thread, though the industry is converting to PP straps and thread to help recycling.
Prior contents of bulk bags are another issue. "Before we take bags, we get a Material Safety Data Sheet to be sure they didn't contain something that will make someone sick," says Amoco recycling coordinator Douglas Moore. "We've had only one load rejected, which contained agricultural pesticide."
FIBERS TO FENCE POSTS
Four companies are taking up the challenge of recycling PP bale wrap and bulk bags. Two are resin companies that supply the original PP fiber and are therefore obliged to take it back from customers. And two are independent recyclers with no deep pockets for R&D that hope to make a profit at this activity.
Amoco Recycling, located at an Amoco Fabric & Fiber plant in Hazelhurst, Ga., converts bale wrap into profiles for fence posts (2-6 in. diam. round or 4-in. square). The plant, which started up a year ago, went into commercial production last April. It was set up on a shoestring. "Some equipment we bought, some we built, some was on hand," says plant supervisor Roger Varnadore. Amoco reused idle grinding equipment from reprocessing carpet backing scrap, including a shredder from Shredding Systems Inc. (SSI) in Wilsonville, Ore., and a 3/8-in. grinder from Polymer Systems in Berlin, Conn. Granulate is then densified in a mill from California Pellet Mill Co. of Crawfordsville, Ind. This compresses it into pellets like rabbit food, which are blended with PE diaper tailings, pigment and fillers, and extruded as white, black or orange fence posts in a highly automated plant where robots lift posts in and out of cooling tanks.
Amoco is considering installing washing equipment, but for now the only cleaning is magnetic separation of metal. Amoco doesn't attempt to remove cotton fiber. Instead, after being chopped up fine with everything else, any cotton goes right into the finished product, where it doesn't show because it's white, says Amoco's Moore.
Only four people work on the line, which was developed in cooperation with Cairo Manufacturing Corp. of Cairo, Ga., a firm that also makes posts out of PP and PE industrial scrap. Amoco worked with Cairo to develop automation and computer controls to blend raw materials and robots to remove and stack fence posts.
Amoco expects to add larger grinders next year and has ordered molds for lumber profiles (2 x 4, 2 x 6, etc.). That will double current throughput of about 2.2 million lb/yr (500 posts in a 24-hr/day, five days a week). With higher output, Amoco hopes to break even. Amoco's PP/PE posts, like other plastic lumber, are heavier and more expensive than chemically treated wood. Amoco's 3 x 8 in. post, for example, weighs 17 lb vs. 12 lb for wood and costs $2/board ft vs. $1.25 for wood. But it lasts longer and doesn't present the environmental problems of chemically treated wood.
BANKING ON PELLETS
Cycle-Tex Inc. in Dalton, Ga., has been recycling bale wrap for two and a half years, making it the oldest in the business. It has been recycling long enough to feel squeezed by falling PP virgin resin prices and rising waste-material costs. At first Cycle-Tex got its bale wrap for free; but now, with competition entering the market, it has to pay 2-3|cents~/lb. Cycle-Tex makes mostly mixed-color pellets or black, which it sells to automotive compounders and injection molders of flower pots.
The firm only recycles bale wrap used to contain synthetic fiber and rejects cotton bale wrap. "You couldn't pay us money to take it," says co-owner Bart Campbell. Any synthetic fiber residue blends with PP and doesn't clog extruder screen packs as cotton fiber does. (Early on, Cycle-Tex worked with Exxon in an unsuccessful attempt to develop ways to filter out the cotton fiber.) Cycle-Tex has capacity to reprocess 10-12 million lb/yr of bale wrap and works seven-day weeks now, up from a four-day week earlier this year.
Cycle-Tex puts incoming bales of used wrap on a Belgian-made Pierret cutting machine (represented in the U.S. by Better Industries Inc., Spartanburg, S.C.). The cutter slices the material before it goes into a commercial batch densifier that was considerably modified "so it bears no resemblance to the original," Campbell says. Then material is fed into a 6-in., 20:1 extruder with a slide-plate screenchanger. Screen packs have an average life of 20-30 min.
FIBER TO FIBER
Exxon Chemical Plastics Recycling Center in Summerville, S.C., is the most expensive project so far and the first to try washing bale wrap. Intended output is 20 million lb/yr, but technical snags in washing slowed the project, which is said to have cost about $4 million. Located behind the LINQ Industrial Fabrics Inc. plant (a recent leveraged buyout from Exxon, which makes woven PP fabric), the recycling center hopes to supply pellets to LINQ for applications like landscape fabric and geo-textiles.
Exxon's recycling line started up in January '92 and officially opened in March. It consists of a conveyor feeding a Herbold HGS-150/100 midsize guillotine bale shredder. In turn, that feeds a Herbold SMS 80/120 machine designed for wet granulating. Water may be fed over the rotor knives, so as to wash material as it chops. Most of the problems involve a separate commercial washing system, which reportedly passed the initial trials but didn't work in scale-up. Chopped bale wrap loaded with cotton fiber allegedly plugged pumps and wouldn't pass through pipes. The shaker table with the wash system was also slow and let too much moisture through.
Another source of problems was the filter socks on the hopper to catch dust. These filled up and clogged, so Exxon added an "air cannon" to shoot dust back into the hopper. Exxon also uses a long extruder (10-in. diam. x 36 ft long) with dual melt filtration and computer controls.
Exxon's line has been modified by Amplasco (American Plastics Recyclers) in Richmond, Va., which added four flow tanks to pull material out of the wash tank with vortexes, and a series of variable-drive pumps to hold pressure on the four hydrocyclones (from Krebs Engineers in Menlo Park, Calif.) that separate heavy paper, metal and fibers from light PP. A very large centrifugal dryer was custom built to handle the fine granulate, replacing the vibrating tunnel dryer that was used at first. It spins without heat. The material is then air transported to a storage hopper above the extruder.
BRANCHING OUT FROM BATTERIES
K.W. Plastics Inc. in Troy, Ala., is a reclaimer of lead batteries and PP battery cases, which is starting up a new plant this month to recycle PP bale wrap. Like Exxon, K.W. intends to accept cotton bale wrap and wash the cotton fibers out. But it's targeting injection molded automotive applications that are more forgiving than the fiber extrusion market Exxon wants to supply.
A new building will house four recycling lines: two 6000-lb/hr lines for bale wrap and PE film and two all-purpose 3000-lb/hr lines. One large and one small line are being set up now, says recycling division manager Arthur Ferguson. When complete, it will have an annual capacity of 110-150 million lb/yr--considerably more than all the bale wrap used in the U.S., which is estimated at 50-80 million lb/yr. So K.W. is pursuing industrial film scrap as well.
K.W. designed the bale-wrap/film recycling line itself, starting with shredders from SSI and from Shred Pax Corp. in Wood Dale, Ill., and a 200-hp grinder from SSI. This feeds a proprietary float-sink wash system built in-house. "You add something to it and the cotton sinks; wires and paper labels sink anyway," hints K.W.'s Ferguson. Material is then dried, extruded and pelletized. The process won't remove all cotton fiber, but extruding at 500 F will burn up much of it, and screen packs catch most of the rest.
After around 13 months of development, the company is confident of its process and is stockpiling "many millions of pounds" of bale wrap. K.W. either picks up the wrap or pays freight costs and "some remuneration," Ferguson says. Pellets may be custom compounded for automotive applications among others.
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|Title Annotation:||plastics recycling projects|
|Author:||Schut, Jan H.|
|Date:||Nov 1, 1992|
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