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Automatic resin & color sorting proves a boon to recyclers.

Many recyclers must automate sorting of post-consumer bottles or give up recycling them altogether. The added cost of handling commingled feed streams is leading recyclers to try out novel technologies for automatic sorting of different resins--primarily PVC from PET--with an eye ultimately to sorting different colors of the same resin.

"Vendors can't sort for us. As an industry we have to be responsible for our own sorting," says Kyle Wright, v.p. of sales at Eaglebrook Plastics Inc. in Chicago, one of the first to recognize the need for automation. In January, Eaglebrook installed the first commercial model of a new autosorting technology from Magnetic Separation Systems Inc. (MSS) of Nashville, Tenn., and will add automatic color sorting from MSS this month. Wright says at best hand sorting can accomplish only about 250-300 lb/man-hr, while the MSS automated system can sort up to 800 lb/man-hr. MSS says its system feeds bottles at a rate of up to 6 ft/sec, with bottle identification taking 5 millisec.

Various sink/float and hydrocyclone techniques automatically separate flaked materials during the washing process--provided the materials are different in specific gravity. But these systems are no help in the critical separation of materials of similar specific gravities--like PVC from PET or PP from HDPE. Several new whole-bottle sorting systems now address this challenge.


There are five commercial auto-sorting systems for removing PVC bottles from PET. VinylCycle from National Recovery Technologies Inc. (NRT) in Nashville; VS-2 (Vinyl Sort) from Asoma Instruments of Austin, Texas; Bottlesort from MSS (which incorporates the Asoma detection instrument); and a patented PVC detection device from Italian recycling machinery maker Govoni SpA, represented in the U.S. by International Food Machinery, Richmond, Va. All the above use x-ray scanning technologies. A fifth bottle-sorting system from Automation Industrial Control Inc. (AIC) of Baltimore identifies resins by their absorption and transmission of near-infrared light.

NRT's VinylCycle uses x-ray fluorescence to spot chlorine atoms in PVC. Low-level x-rays can detect the presence of chlorine in milliseconds, triggering a computer-timed blast of air to eject vinyl bottles from the feed stream. NRT's device has a field of vision from 12 to 30 in. wide, depending on number of sensor bands used to "read" the bottles passing by. This wide field of vision allows NRT's system to handle a stream of bottles without orienting or "singulating"--i.e., conveying bottles single file past the detector. NRT and Asoma technologies also read nested bottles. NRT's highest production model, VinylCycle 20 (with 16 sensor bands) processes 10 bottles/sec or 4500 lb/hr, yielding PET product with less than 50 ppm PVC, NRT says. That's half the maximum PVC contamination level tolerated by many commercial PET recyclers.

Earlier this year, NRT introduced two smaller models: VinylCycle 8 (8 sensor bands) with capacity of up to 1500 lb/hr and VinylCycle 12 (12 bands) with capacity up to 2500 lb/hr. NRT says 18 VinylCycle systems are installed worldwide, including the first VinylCycle 8 at Orion Pacific in Odessa, Texas, and the first VinylCycle 12 at M.A. Industries in Peachtree City, Ga. Prices range from $98,500 for VinylCycle 8 to $185,000 for VinylCycle 20.

Asoma's VS-2 system also identifies the presence of chlorine in PVC by x-ray fluorescence. It's available directly from Asoma and is also the PVC sensing device in MSS's Bottlesort system. VS-2 separates 3-7 PVC bottles/sec from a stream of 10 bottles/sec (1200-2800 lb/hr) passing a 12-in. scanner, Asoma says. Higher volumes are possible with multiple channels. A sensor unit costs $35,000; a single sensor with slideway and one ejector costs $43,000. Eaglebrook and R2B2 Recycling Co. in the Bronx, N.Y., both installed VS-2 systems early this year.

A quality-control check to detect PVC in finished PET flake uses ultraviolet or "black light" to make the chlorine in PVC flakes fluoresce. In a lab, a sample of PET flake is first weighed. Then, under uv inspection, glowing PVC bits are hand-picked out and weighed, so the PVC contamination level can be calculated. Such a "black light" lab system was devised by Image Carpet Inc. in Summerville, Ga., and passed on to Image's principal suppliers, so they can qualify material. Image does not sort or granulate, but buys post-consumer PET flake. Knowing the level of PVC in each lot allows Image to blend highly contaminated lots with less contaminated batches in order to compound a feedstock with less than 200 ppm of contamination, suitable for their carpet-fiber spinning.


PP contamination can be critical in HDPE film and pipe, though less critical in bottle blowing, where up to 6% PP is tolerated. Larger amounts hurt bottle ESCR and other mechanical properties. PP contamination is an issue in recycling basecups from beverage bottles, where PP caps can amount to 12% of the mix and thus require separation.

A steam-sterilizing tumbler from Sorema Srl of Como, Italy, a manufacturer of turnkey recycling systems, allows mechanical separation of HDPE basecups from PP caps by "relaxing" the orientation in stretch-blown PET bottles so they shrink. Unoriented necks of bottles shrink relatively little, so the basecups and labels fall off before PP caps do. Sorema is developing a new automatic system that includes NRT's PVC detection and color-sorting apparatus. The first application will be in Italy, but several U.S. installations are expected in the next six months, according to NRT.

An inexpensive mechanical solution to keeping PP caps out of basecups is affectionately known as "Sergio's Perforator," designed by Sergio Firpo, owner of Frontier Recycling Systems in Chicago. Model 2600 is a large spiked drum, which flattens whole bottles under spring-loaded pressure, snapping off the caps. Bottles then pass over a vibrating screen, allowing caps to fall through. However, PP bottlecap neck rings often remain with the bottle, and high throughput rates increase the number of missed caps. At 2000 lb/hr, the perforator is said to be about 98% accurate, leaving 2% PP contamination. Model 2600 sells for $16,000. It's used by Naperville Area Recyclers in Naperville, Ill.


Most recyclers' plans for automatic resin sorting include eventual color sorting to raise the value of the end product. There are three known color sorting systems for whole bottles and at least as many in development for flake. A machine-vision system for HDPE bottles was engineered in-house by Resources Energy Management in Niles, Mich. Owner Richard Moore says it "ejects bottles the moment they're identified" and runs at a rate of about a 900-lb bale/hr with 96% accuracy. But since the market value of HDPE recycle is currently so low, Moore's operation doesn't take commingled bottles.

MSS has developed a machine-vision color-sorting system with support from the former SPI Council for Solid Waste Solutions (now part of the Partnership for Plastics Progress). It has "intelligent" software to identify seven bottle colors, ignoring labels and contamination. A primary sensor uses different frequencies of light transmitted through the bottles to identify three classifications: clear (typically PET and PVC), translucent (HDPE milk and juice jugs, PP syrup and ketchup bottles), and opaque (detergent and shampoo bottles). The system occupies about 1000 sq/ft and is designed to run up to 5000 lb/hr of single-file bottles. "Each bottle is scanned by an array of 16 sensors, which make 5300 readings/sec to decide the bottle classification," MSS says. MSS has run a prototype at its plant for almost a year and will start its first production system at Eaglebrook in November. A single 1200 lb/hr line with sensors and ejectors but without bottle singulation costs about $65,000; a full system for 5000 lb/hr with singulating and debaling equipment costs about $500,000.

A color-sorting system, called Polysort, made by AIC (with conveyor systems from Chamberlain MRC of Hunt Valley, Md.) uses infrared spectrographic analysis of light transmitted through singulated bottles, allowing it to identify bottles or even natural HDPE bottles with motor oil contaminants in them. AIC identifies bottles on an inspection conveyor and ejects them from a 40-ft-long sorting conveyor; undetermined bottles stay on the conveyor for recirculation or disposal. AIC says the system "reads" 85-90% of bottles at 1500 lb/hr, and is 100% accurate. Development of this system was supported with $1.3 million of R&D funding from Du Pont Co., Wilmington, Del., and the Partnership for Plastics Progress. The Partnership is supporting installation of the first commercial system at North American Plastic Recycling Corp.'s plastics recovery facility in Ft. Edward, N.Y. AIC's system costs about $375,000.

NRT is developing both resin- and color-sorting technology with support from the U.S. Environmental Protection Agency. This technology doesn't require bottle singulation to sort into clear PET, green PET, natural HDPE and pigmented HDPE, NRT says. Subsequent separation of colored HDPE into distinct color groups will also be available.


An alternate approach being developed is color-sorting of flakes rather than whole bottles. Machine-vision technologies already used to sort discolored plastic pellets after compounding, or burned potato chips in the food industry, are being adapted to plastic recycling. Food Technology Corp., Rockville, Md., makes a Pass I automated sorter that inspects a rapidly moving stream of plastic pellets, blowing out any that are dark in color. The company says its apparatus measures the proportion of transmitted light vs. reflected light generated by the pellets. It detects translucent or light-colored pellets, but can't "see" dark or crystal-clear ones. Each sorting channel has a flow rate of 250-1000 lb/hr and costs $90,000. Food Technology says it's working on two plastic recycling projects, one to sort clear from green PET flake, the other to sort natural HDPE flake from flakes of pigmented caps. These systems might cost about $200,000, says the company, which is seeking development partners.

Still other equipment is being adapted from food processing. Simco Ramic Corp. in Medford, Ore., makes a Kroma-Sort color-defect sorter and an Opti-Sort dark/light defect sorter used to find burned peanuts and potato chips. The company is adapting a version to sort colored cap regrind from natural HDPE milk-jug flake. Key Technology Inc. in Walla Walla, Wash., has similar dark/light sorting technology. Key built the original color-sorting system for the Phillips/Partek recycling joint venture in Tulsa, Okla.

A dark/light visual identification system now used to remove discolored pellets is available from Systronics Inc., Norcross, Ga. And Plastic Resin Separation Specialists in Anderson, S.C., has proprietary machine-vision technology for separating mixed colored pellets, as reported in PT, Aug. '91, p. 91.
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Copyright 1992, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:Technology News: Recycling
Author:Schut, Jan H.
Publication:Plastics Technology
Date:Sep 1, 1992
Previous Article:UV stabilizers: product lines reviewed.
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