September/October 2012
Combining tire rubber with plastic can create products that are more durable, less expensive, and more sustainable than the alternatives. Tire recyclers see opportunity in bringing these complementary commodities together.
By Nancy Mann Jackson
History is filled with the stories of unlikely duos. Such partnerships can be dynamic, explosive, or simply complementary. The latter seems to be the case with recycled rubber and plastic. Separately they make great products; together they can make products that are more durable and less expensive, with less impact on the environment. About 370 million pounds of recycled rubber go into products that combine the two each year, according to Michael Blumenthal, vice president of the Rubber Manufacturers Association (Washington, D.C.). The practice of adding scrap tire rubber to plastic has opened numerous new markets for tire recyclers, and industry leaders say they expect such markets to experience solid growth in the coming years as manufacturers come up with more products that make the best of both worlds.
Better Together
When manufacturers add rubber to plastic, the plastic product takes on some of the characteristics and benefits of rubber. Most notably, antioxidants in the rubber add durability and flexibility to the plastic, Blumenthal says. For more than a decade, transportation agencies have added recycled rubber to the asphalt in roads and highways, making the roads more durable and longer lasting, says Brett Barstow, CEO of tire processor Golden By-Products (Ballico, Calif.) and president of ISRI’s Scrap Tire Processors Chapter. “All the chemical and physical properties in rubber help fight off damage—aging and cracking [due to] ultraviolet rays, expansion, and contraction” in field-blended asphalt rubber road surfaces, he explains. “These properties benefit plastics just as they do roadways.”
Vast Enterprises (Minneapolis) combines scrap tires and a blended variety of scrap plastics ranging from food containers to CD cases in a proprietary process to produce AZEK Vast pavers, a lighter alternative to concrete and clay pavers. Recycled rubber is the main ingredient in the pavers, with the recycled plastics added “to bind and stabilize the mixture,” says Andy Vander Woude, the firm’s co-founder and owner. “Performance-wise, [the pavers] are extremely durable while strongly resembling the materials they replace,” he says. “[They] have a no-crack guarantee for the life of the structure for residential use.” The rubber is what gives the pavers their durability, resistance to cracking, and their “feel-good-under-your-feet” qualities, he says. The material also is “highly resistant to moisture, making it very stain-resistant, and with our state-of-the-art UV inhibitors, the colors will stay rich for years to come.” The company aligned with AZEK Building Products (Scranton, Pa.) last year to reach a broader, national audience.
One of the oldest products to combine scrap rubber and scrap plastic is Rumber, a wood lumber substitute made of recycled tire rubber and plastic by Rumber Materials (Muenster, Texas), founded in 1991. Though customers appreciate that Rumber is made from 100-percent recycled materials, its strongest selling point “is its durability and how long it lasts in comparison to wood” as flooring for horse and livestock trailers, heavy equipment trailers, wheel chock blocks, oilfield boards, and in several military applications, says J’Lynn Hare, general manager. “It is oil-resistant, water-resistant, and insects don’t bother it,” she says. “Traditional wood flooring in a trailer doesn’t last long at all, but Rumber flooring for trailers lasts more than 20 years. Some customers say it lasts even longer than that.” She touts the many benefits of the company’s proprietary rubber-plastic formulation, “from improving the health of animals [to] decreasing machine downtime [and] improving profitability.” Other common products made from a scrap tire-plastic combination include garbage cans; vehicle-control devices such as bumper guards and traffic cones; nursery and landscaping materials such as plant holders, fence posts, and outdoor furniture; and construction materials.
Performance isn’t the only advantage scrap tire rubber can give to plastic products, however. “Recycled rubber is very competitive [in price] with certain kinds of plastics, so you often get a cost savings” when you combine the two instead of producing a product from plastic alone, Blumenthal says. The rubber acts as a lower-cost filler that offsets the amount of plastic polymer the product requires, says Gary Champlin, general manager of Champlin Tire Recycling (Concordia, Kan.). “As petroleum prices keep rising and plastic becomes more valuable, that will increase the demand for rubber to be included in plastic products,” he predicts.
The prices for sustainable rubber materials also are more stable than primary or secondary plastics prices, says Bill Schreiber, technical director of Lehigh Technologies (Tucker, Ga.), which creates “micronized” rubber powder through the cryogenic processing of crumb rubber from scrap tires and industrial rubber. “The plastics industry is always looking for more predictable ways to reduce costs while simultaneously maintaining quality and other performance standards,” he says. Scrap rubber “affords the end user price stability in comparison to the ‘sawtooth’ economics that exists in the thermoplastic industry today.”
Recycled rubber can boost a plastic product’s green credentials, too. “A lot of entities are going for [Leadership in Energy and Environmental Design] certification, which requires them to use a certain percentage of recycled products,” Blumenthal says. “They are looking for competitive products that can perform well and also have recycled content.” Products made from a combination of recycled rubber and plastic can fit the bill. Vander Woude says AZEK Vast pavers “contribute to LEED certification more than any other pavers on the market,” for example. He touts the other environmental benefits of using recycled materials as well, calling end-of-life tires a “landfill culprit.” His company reduces the landfill and tire-pile problem by returning recycled tire rubber to the marketplace. When made from AZEK Vast pavers, “a 100-square-foot walkway will save approximately 50 tires and 1,500 gallon-sized plastic containers from entering U.S. landfills,” he says. Further, by using recycled materials, Vast Enterprises’ production process uses 95 percent less energy and emits 96 percent fewer carbon emissions than processes used to manufacture concrete pavers.
Creating the Blend
Rubber and plastic aren’t exactly oil and water—they’re more like oil and a different kind of oil. It takes some time to understand how the properties of plastic and rubber work together and the correct ratio of one to the other, but it’s a physical process, not a chemical one, that combines the two, with the addition of heat, pressure, or both, Blumenthal says. Because tire rubber comes in just one color, it might not be a good fit for plastic products manufactured in lighter colors. “The tire rubber will darken the material, which isn’t always the desired outcome,” he says.
Each company has its own specific blending process, but many of these processes follow similar patterns. The technical staff at Lehigh Technologies’ Application and Development Center works with each customer to determine the best formulations for its purpose, Schreiber says. Variables include the rubber particle size, the proportion of rubber to plastic, and whether or not the mixture requires processing aids and “compatibilizers.” The proportion of micronized rubber powder to plastic in a given product varies based on the application and target performance standards, he says, but it’s usually between 5 percent and 40 percent rubber by weight. Incorporation methods for Lehigh’s MRP include master batch compounding, dry blending using various mixing techniques, and adding the materials at the molding press directly.
Which plastics are manufacturers combining with tire rubber? Lehigh customers have added its micronized rubber powder to primary and recycled polyolefin-based plastics (low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and polypropylene) to create new products that include modular flooring, pallets, and industrial platforms, Schreiber says. Customers also have added the rubber powder to polyamides such as Nylon 6 and Nylon 66 as well as other thermoplastics. The granulated tire rubber used for these types of applications tends to fall in the 80-mesh to 120-mesh size range, Blumenthal says.
Though most tire recyclers sell their scrap tire rubber to manufacturers who combine it with plastic, some produce their own plastic and rubber products. Golden By-Products has provided recycled rubber to customers that combine it with plastic for about two or three years, Barstow says. Most of these customers purchase finely ground crumb rubber sizes 30 mesh or smaller and use it to create extruded products such as car bumpers and fence posts. His company is hopping on the bandwagon, however, adding its own extrusion and molding equipment to combine rubber, plastic, and even Nylon tire fluff on site. “This is the future of recycling tires,” he says.
Champlin Tire Recycling has been creating extruded products that combine scrap tire rubber and scrap plastic, primarily HDPE, for about seven years. “When we extrude, we take the temperature of the plastic up to 350 or 400 degrees F so that the rubber becomes encased in the plastic,” Champlin says. The company then turns the extruded material into boards and bases for outdoor furniture, often for state parks, schools, and government entities.
Sold on Synergy
With the vast number and variety of plastic products, tire recyclers see many opportunities to profit by entering this market. “Combining scrap rubber and plastic works for us because we’re a tire recycler, and we’re putting tires into these products and marketing them as recycled products,” Champlin says. “The future is very bright.” Anecdotally, some manufacturers say their plastic and rubber products are holding strong. The market for Rumber has more than doubled from 2011 to 2012, Hare says; Champlin’s sales of extruded plastic and rubber products have continued to increase “even through the recession,” he says.
The growing interest in such products might relate to a shift in manufacturers’ thinking about product life cycles, says Lehigh Technologies’ Schreiber. “As a society, we need to find useful ways to reuse, or up-cycle, the waste we generate. There are valuable, highly engineered materials that are being discarded that could otherwise be used as feedstock … to make quality products.” RMA’s Blumenthal also has high hopes for this market’s potential. “Rubber and plastic compound products will be the wave of the future,” he says. “That’s where you’ll get the greatest, best use of the recycled rubber. And there’s a lot more that can be done.”
Nancy Mann Jackson is a writer based in Huntsville, Ala.
Combining tire rubber with plastic can create products that are more durable, less expensive, and more sustainable than the alternatives. Tire recyclers see opportunity in bringing these complementary commodities together.