Chapter 10
A Resin Producer's Perspective and Experiences in Polyethylene Recycling W. Keith Atkins Solid Waste Management, Union Carbide Corporation, 39 Old Ridgebury Road, Danbury, CT 06817-0001
Recent trends in environmental marketing coupled with the need to comply with recycle-content packaging laws enacted in a number of states, have significantly increased the demand for high quality recycled polyethylene sourced from post-consumer feedstocks. Union Carbide's experiences in entering the mechanical recycling business are discussed with specific examples given that define quality requirements and future industry trends, including the need for color-sorted products that are consistent in quality and reproduceable.
Embarking on a new business venture has always been a prospect akin to a roller coaster ride. It's exciting, to be sure, but sometimes you leave the pit of your stomach at the top of the coaster loop while your car descends to the depths. Yet, ironically, when the roller coaster arrives at its terminal, you usually want to ride again. Union Carbide embarked on its own recycling business odyessy in 1991 with the opening of its Plastics Recycling Plant in Piscataway, New Jersey. This venture came with its own unique set of challenges. Plastics recycling is an industry still in its infancy - - there is no history to guide us, and rapid change is the only constant. When you contrast this situation with the well-established 50-year-old virgin polyethylene industry, you can readily understand why plastics recycling is a whole new world. Union Carbide's recycling raw materials, which come from community collection programs within a 250-mile radius of the plant, make their own journey from the curbside, to municipal recycling facilities (MRF's) where they are separated from other materials and baled, and finally, to our plant for processing. We actively seek out only those suppliers who can meet our contamination level requirement of less 0097-6156/95/0609-0104$12.00/0 © 1995 American Chemical Society
10. ATKINS
A Resin Producer's Experiences in Polyethylene Recycling 105
than 2%, because high quality recycle feedstock is required to produce high quality recycled resin. Carbide's primary objective is to provide our customers with post-consumer resins (PCR) whose quality and performance levels approach that of virgin resins. In Carbide's plant, sorting had been the first stage of a three-part operation that included sorting/grinding, washing/drying and extruding. In the early days, there was a lot of hand labor involved. On our 90-foot sortation line, which was one of the largest in the industry, the recyclables would move past sorters as they separated bottles by color and resin type into unpigmented PE bottles, pigmented detergent bottles, clear and green-tinted soda bottles and the like. After sorting, the bottles were delivered to one of four large grinders which whirled at high speed to cut up the bottles into confetti-like pieces, ready for washing and drying. Today, our new PRISMA™ resin color-sorting system allows unsorted bottles to be delivered by MRF's, then automatically color-sorted at the plant. The groundflakesare then conveyed to the washer/dryer system. In the first of three wash/rinse phases, the plasticflakesare loaded into a wash tank where they are agitated much like clothes in a washing machine. The chips are then transported into rinsing units where dirt, labels and glue are separated from the clean flakes. These chips are dried in large spin dry units and air-conveyed to extruders for pelletizing. The compounding and extrusion stages come next. Inside a 20-foot long extruder, a variety of additives and stabilizers are added to create the post-consumer resin which Carbide markets as CURBSIDE BLEND® PCR®. The resin is then packaged according to our customers* preferences in sizes from 1000-lb. boxes to 180,000-lb. rail hopper cars. Delivery is then made in truckloads by common carrier, or via a hopper carfleetdedicated exclusively to the recycling business. Automation. Because of the higher price of virgin PET and the fact that PET reclaimers are forward-integrated (i.e., consume their own product), PET recycling has attained profitability. Unlike PET, PE has yet to be a profitable business. A number of things have to happen first before that goal is reached. Companies throughout the recycling industry are actively looking for ways to decrease costs. One item that should help to reduce cost is manufacturing automation. Experience has shown that plant capacity must be at least 40 million pounds per year in order to enjoy economies of scale. To get to that point automation is needed that will allow us to get more volume out of existing investments, or allow people to build larger plants. So people went back to the laboratories and came up with automated sorting,
106
PLASTICS, RUBBER, AND PAPER RECYCLING
debating and other equipment that would save time, process faster and let processors enjoy those economies of scale. Production rates in plastics recycling are now beginning to parallel what happened in the virgin resin business. Virgin polyethylene reactors in the 1960's produced 2500 pounds/hour; today, these typically run at about 90,000 pounds/hour. The trend in plastics recycling is also toward larger sorting lines. Whereas 2000 pound/hour lines were considered optimum in the beginning (ca. 1990), we now see 60008000+ pound/hour lines. Color Measurement. The way we measure resin color today is a far cry from the recycling industry'sfledgingyears. In those days, the human eye was the only means of determining resin color quality. Samples were graded A, B or C - - it was as simple as that, based entirely on personal judgment calls. This system just will not do for today's needs. Customers have very specific resin color needs, so a subjective approach had to give way to a purely objective one. The industry recognized that a way had to be found to clearly communicate resin color values that were backed by analytical data. So, the right tool had to be found and it turned out to be a hand-held colorimeter. Carbide, and a growing number of reclaimers, use the HunterLab MiniScan. The Hunter unit makes color measurements along three axes in a 3dimensional color body matrix. One coordinate goes from red to yellow, another from blue to green. The third coordinate goes from pure white to pure black. The colorimeter makes measurements along the three axes and calculates a CIE number which we use as a measure of the whiteness of the natural PCR resin. During the recycling process, high dirt levels in the raw materials can give recycled resin an unattractive appearance. The colorimeter has been invaluable in determining dirt levels and helping us to control them. The lower this level is, the whiter the PCR - - and this is of prime importance to our customers. In addition, after grinding the flakes can be checked with the colorimeter for the whiteness level before they go on to the washing stage, to assist in determining process conditions in this stage. Now, color measurement is being used to characterize color-sorted materials, so that we can make process adjustments to ensure that the resulting PCR is acceptable to our customers. For example, before we got into machine-based color measurement, the red-orange-yellow PCR known in the industry as ROY, would wander in terms of box-to-box color consistency, varying from red to orange to tan or yellow. Since we've been using the colorimeter technology along with our new color
10. ATKINS
A Resin Producer's Experiences in Polyethylene Recycling 107
-sorting system, we can consistently produce PCR to our customers' increasingly demanding requirements. The codifying and standardizing of color measurement is not only helping to ensure better communication about the color quality of a recycled resin, it also is lending more credibility and professionalism to the whole recycling industry. Detergent. The above-described colorimeter also determines the amount of detergent that is required for the cleaning process. In the case of natural resins, color measurements of the flake are taken after cleaning. If the MiniScan indicates that these "PASS" our whiteness requirement, then theflakesare conveyed to the extrusion stage, but if they "FAIL" our requirement, they're sent back for further cleaning. Union Carbide realized early on that detergent cleaning of the flakes was a critical step in the reclamation process. We approached Oakite, a leading compounder and marketer of industrial cleaning chemicals, to get some help, and subsequently formed a joint development program with them. For our part, we gave Oakite our color requirements and samples that represented the material "dirtiness" issues we faced. Also, we provided Oakite with information on specific cleaning problems, such as residual glue and paper removal, etc. Oakite's scientists would work on these issues, then we would perform joint plant runs to determine if improvements had been made. Color Matching. Plastic Packaging (e.g., bottle, tub, overwrap, etc.) manufacturers are always concerned about the color quality of the items they produce, including item-to-item consistency, and fundamental color characteristics. These concerns are driven by the specifications imposed by customers of packaging manufacturers. The use of HDPE PCR as a component resin in the manufacture of packaging presents new challenges to those responsible for color quality. In the case of natural HDPE PCRs, these resins contain inherent color bodies, that vary in both type and intensity. For this and other reasons bottle manufacturers often use multilayer blowing molding equipment to produce PCR-containing products. The exterior, or "skin," layer of the bottle is composed of a pigmented virgin resin that masks the color variability of an interior layer, containing the PCR. Even with this technique, there is often a trade-off between pigment loading (and therefore cost) in the "skin" layer and achieving acceptable bottle aesthetics. To illustrate with an example, Helene Curtis' Salon Selectives shampoo bottles are manufactured by Silgan, using three-layer blow
108
PLASTICS, RUBBER, AND PAPER RECYCLING
molding equipment. The center layer contains natural HDPE PCR provided by Carbide. During the development of these bottles Carbide made a step-change improvement in the "whiteness" of its natural HDPE PCR. In spite of the pigments used in the exterior layer of the bottle, the change in the "whiteness" of the PCR changed the apparent color of the bottle. As a result, Silgan and its color concentrate supplier, Allied Color, had to go back to the laboratory to formulate a modified concentrate to offset the change resulting from the PCR improvement. Concerning a related subject, the color characteristics of PCR derived from random mixtures of recovered, post-consumer, pigmented HDPE bottles have been the primary impediment to developing high valueadded markets, e.g., packaging uses, for these resins. Typically, the PCR resin recovered from these types of bottles is a "muddy" green or gray color. These unaesthetic and variable color characteristics are difficult to hide, except in the darkest, e.g., black, and most opaque coloring schemes. Because of these characteristics the demand for postconsumer pigmented bottles has, historically, been weak, resulting in a lower value for this raw material source. Communities have been more reluctant, therefore, to collect this type of container. To illustrate this point, in 1993 the recycling rate of pigmented bottles was about 9%, compared to a rate of 25% for unpigmented milk, water, juice, etc., bottles. At Carbide, we believe that the best approach to achieving a higher value for pigmented bottles is to produce recovered resins that have uniform and more marketable colors. The processing approach we have taken to achieve this higher value is a sophisticated color-sorting system which allows Carbide to market a line of products trade-named PRISMA™. It is our hope that the availability of this approach will stimulate communities to add pigmented HDPE bottles to existing recyclables collection programs. PRISMA™ PCR Copolymer Resins. Union Carbide installed a unique color sorting system at its Piscataway plant in late 1993. This system represents a significant departurefromthe way plastics had been sorted previously. With this system, unsorted bottles can be delivered by municipal recovery facilities, then in-process material is color sorted at the plant using automated machines. It is a high-speed system that provides our customers with unparalleled batch-to-batch color consistency. Any color that can be obtained from the feedstock mixture, can be reproduced for a consistent batch-to-batch color quality, within very narrow tolerances. So, customers simply select the desired resin color, which is programmed into the system, and the same shade is produced within a narrow band each time a PCR batch is run.
10.
ATKINS
A Resin Producer's Experiences in Polyethylene Recycling109
PRISMA® resins produced by the system are true "value-added" products. Batches of PCR with a targeted color are typically produced in 40K pound lots. Our customers prefer this lot size not only because of the excellent color uniformity, but also because of the uniform processability and continuous superior performance over long production campaigns. Our customers normally adjust extrusion hardware once per blend with PRISMA PCR's vs. the continuous adjustments they have experienced with competitor's color-sorted PCR®, resulting from box-to-box color variation. Minimum adjustments to customer hardware results in reduced staffing requirements and higher profits. Based on the mix of post-consumer pigmented bottles currently available the types and yields of color-sorted PRISMA resins produced by the system are as follows: orange-based resin, 35-40%; blue-greenbased resin, ca. 30%; white resin, 30-40%; and residual (predominantly black), 5%. While expanding the number of available colors is technically feasible, it is our view that the slate of products listed above is the best compromise between the investment cost in color-sorting hardware, and the value of the resulting products. More broadly, creating a viable market for post-consumer pigmented bottles is essential. The demand for post-consumer HDPE packaging is likely to exceed the supply of PCR available from recovered unpigmented milk, water, juice, etc., bottles. As a result, increased collection of post-consumer pigmented HDPE bottles is needed. The availability of the PRISMA resin color-sorting system is, in our view, instrumental in providing sufficient value to both material recovery facility operators and packaging manufacturers to support increased collection of post-consumer pigmented HDPE bottles. FDA Letter of "No Objection". Because FDA clearance is crucial to the use of post-consumer resins in food, drug and cosmetic applications, Union Carbide has embarked on comprehensive testing of its postconsumer products and resin operations to prepare a clearance application. Our current goal is to secure an FDA letter of "No Objection" for our process technology to reclaim polyethylene from natural, post-consumer bottles. The tests we're conducting are those recommended by the joint Society of the Plastics Industry, Inc., and National Food Processors Association Plastics Recycling Task Force protocol. The point of these tests is to determine if a recovery process is able to reduce contaminants in PCR to FDA "de-minimus" criteria - that's the minimum allowable human exposure without hazard. If these conditions are met reproducibly, the FDA could consider Union Carbide-produced natural PCR to be within its clearance guidelines.
110
PLASTICS, RUBBER, AND PAPER RECYCLING
FDA clearance of recycled resins would provide many benefits. First, it would set the stage for us to enter the food, drug and cosmetics packaging markets. Second, a letter of "No Objection" will enable our customers to comply with the legion of plastics recycling-related initiatives throughout the country in such bellwether states as Oregon, California and Florida. Third and last, consumers and the environment will be beneficiaries. A significant amount of postconsumer plastics will be diverted from landfills, back into the marketplace. Consumers will also be able to feel a lot better about choosing plastic packaging, because it will comply with state-mandated recycled resin content. This will allow consumers to accept plastic packaging for the reasons they did in the first place: freshnesspreserving, tamper-resistant, lightweight packaging, with unique health and safety benefits, that can be recycled again and again. Feedstock Quality. Union Carbide's suppliers are still plagued by the quality of feedstocks, especially in the pigmented bottle area. Householders can do a lot to help remedy this problem. For example, they could remove caps, particularly those on "pump" bottles. These caps have metal springs and ball valves - - and they all wind up in the bottom of our float-sink tank. Time and again we've had to shut down operations due to dirt, sludge and springs in the bottom of the tank. Packagers must do their part to make recycling viable because the efficiency of each stage along the PCR manufacturing route can be severely compromised by packaging and labeling choices. Consider multi-layer packaging. The inner layer may be of a very different color, but the sorter sees only the outside layer. The blended final product is a muddy-toned PCR. Even worse is the case in which a bottle made from several different materials is identified only by the SPI code for the principal resin. While a barrier layer is there for product protection, the materials in all the layers ought to be melt compatible. Packaging choices can also foul the metal detector process that the materials go through before grinding. Aluminum foil seals come in two types: the pull-away seal and the destruct type. The pull-away is easy to handle, leaves no foil on the bottle, and is ideal for recycling. The destruct type has to be broken open and leaves foil on the ring which gets detected as metal contamination by the detector. If the detector stops the line each time foil appears, the efficiency suffers. On the other hand, if the detector is tuned too low, it will be unreliable for detecting actual metal in thick-layer bottles. This metal will get into the grinders and necessitate repairs. Labels are the worst problem in the wash and dry stage. Certainly printing inks containing toxic materials, such as lead, shouldn't be
10.
ATKINS
A Resin Producer's Experiences in Polyethylene Recycling111
used. As inks dissolve, they could put lead into the wash water and in contact with the plastics. Metallized labels look good, but they too introduce metal into the process. Glue becomes a culprit when labels are sealed over the entire surface, such as those on some PET bottles, rather than just at the seam. Minimizing the amount of glue used as well as using water-soluble glues should be important recycling goals. Because some packagers are concerned that labels will come off with condensation, we need a glue that will be solubilized when in contact with hot detergent water, but will not loosen on the store shelf or store cooler. Hot melt glues are real troublemakers. The types that soften only at very high temperatures use up energy and require more detergent to remove, as well as consuming very hot water that can be a safety hazard. Obviously preferred are those that melt with warm wash water and little or no detergent. During the rinse cycle, polyethylene floats and is skimmed off while PET sinks to the bottom of the unit. This is where some PVC cap liners will cause problems. With the same specific gravity as PET, the PVC will sink to the bottom with the PET and mix with it in the final product. When PET is refabricated, the molding temperature is so high that the PVC burns, showing up as a charred spot. When metal foil is heat-sealed onto plastic, the only place where foil can be removed is on the extruder melt filter. This greatly increases the amount and frequency of screen changes, creating high cost. It is to the advantage of processors, fabricators and their customers to work through packaging design questions themselves rather than have packaging design legislated. Applications. Our CURBSIDE BLEND® PCR shows up in an increasing variety of end-products. A quick look at our customer list discloses such uses as trash containers, oil bottles and drainage pans, bleach, shampoo and kitty litter bottles, book binders and dividers, money bags, consumer products containers, as well as various film and Household/Industrial/Chemical bottle applications. Future Industry Trends. As I look into my crystal ball, I see definite trends, some of which appear inevitable. I believe we're going to see: * Larger production line capacities and larger overall plant capacities. * Improved grinding because this is a high-cost maintenance operation. * Grinding shifted to the MRF's, which will eliminate the need to bale materials. * Increased emphasis on the recycling of durables, such as auto parts and computer housings. We have already seen the beginning of this
112
PLASTICS, RUBBER, AND PAPER RECYCLING
trend. For example, automotive companies are now making the effort to design recycle-friendly auto parts as well as technology that will allow easy disassembly of auto parts. * Automatic sorting technology for packaging. This could involve fixed position sensing and separation systems that would handle packaging. * Identification and sorting of durables. This ID system may be a portable one with a sensing head connected by afiberoptic system to allow correct identification of plastic type during disassembly of computer housings and other durables. An expansion of the present sorting commodity resins such as HDPE and PET to sorting some of the engineering plastics (such as nylon and polycarbonate) which have a higher intrinsic value. Plastics recycling is still in its infancy. Its future depends to a great extent on efforts to educate the public about plastics recycling, on cooperation between processors, fabricators and their customers, on the increasing use of pigmented bottles and on a more cost-effective manufacturing process. RECEIVED March 13,1995
