The market for crumb rubber has experienced significant growth in recent years, but for that growth to continue, many participants—producers and users alike—believe the industry needs to grow up. A key element of maturity in this case will be the development of tougher, more precise standards for the various classes of crumb rubber, thereby assuring users of a more consistent product, regardless of the supplier.
Scrap tires are a major source of crumb rubber. Other sources include retread buffing dust and factory waste generated by manufac-turers of other rubber products.
According to the Scrap Tire Management Council, 6 million waste tires were processed into crumb rubber in 1995. While the final data for 1996 are not yet available, the STMC estimates that number increased to between 8 million and 10 million tires, and expects it to grow another 15 to 20 percent this year.
One major use of crumb rubber from scrap tires is as a modifier in asphalt pavement. While efforts to mandate the use of rubber-modified asphalt in all federally funding highway projects have been blocked, the material has remained popular in several states, including California, Arizona and Florida.
In California and Arizona, in particular, the market for rubberized asphalt ``is as big as it can be right now,'' according to Michael Blumenthal, executive director of the STMC. And there is still room to grow, he added.
Other states, most notably New Mexico and Texas, are looking into use of the alternative paving material, and university research reports on the subject are due out this year, Mr. Blumenthal said.
He expects those reports to be positive for the asphalt rubber industry and to ``go a long way to alleviate doubt'' among highway and transportation agencies in other states that have been reluctant to use the rubber-modified material.
Another growing use for recycled crumb rubber is as a raw material in the manufacture of various molded products. This growth is being driven in part by advances in technology that are making possible the consistent production of very fine (100 mesh) particles, and in part by research and development efforts that affect the crumb rubber itself.
Companies that have reported advances in the R&D area include:
STI-K Polymers America Inc.—This Washington-based subsidiary of a Malaysian company has reported some commercial success with its DeVulc brand of crumb rubber, which it ``DeVulcanizes'' using a proprietary chemical process it calls De-Link. This chemical treatment restores up to 75 percent of the scrap rubber's virgin properties, the company said.
GreenMan Technologies Inc.—This company, based in Lynnfield, Mass., says it can create compounds using both crumb rubber and shredded plastic, with characteristics that vary according to the mix: from 2 to 85 percent rubber.
National Rubber Co. Inc.—Based in Toronto, National Rubber has developed a crumb rubber material—Symar-D—that, like DeVulc, performs in many ways like an unvulcanized compound.
Unlike DeVulc, however, Symar-D is produced using a non-chemical, ``high-energy'' process that modifies the surface of the rubber particles, said Andrej Kolinski, senior process engineer.
Symar-D moves recycled rubber beyond its traditional role as an extender or filler for virgin products, Mr. Kolinski said, to a position as a primary ingredient. ``A significant part of our compounds is recycled,'' he said. ``Virgin content is extremely limited.''
National Rubber currently uses all of its Symar-D production in its own manufacturing processes, but likely will begin marketing it outside the company in the not-too-distant future, Mr. Kolinski said.
Because applications for crumb rubber are becoming more complex and the product needed is becoming finer and more precise, establishing a set of commonly accepted standards is becoming increasingly important.
``Right now it (the lack of standards) is the biggest obstacle impeding the marketplace,'' Mr. Blumenthal said.
``Buyers are sometimes hesitant because they can't get the same quality material on a consistent basis,'' he said. ``There needs to be one established definition and standard protocol for ground rubber.''
That is the goal of the American Society for Testing and Materials, which is reviewing a proposed standards for crumb rubber that are much more specific and rigorous than the current ones.
The goal is to create specifications more useful to the recycled rubber industry—and to put more teeth into them, said Krishna C. Baranwal, chairman of the ASTM subcommittee on recycled rubber.
The more stringent standards ``will definitely improve the quality of the product,'' he added.