What Are Waste Tires?
Waste tires are one of the leading environmental hazards our world is currently facing. Bulky and made of components that do not easily break down under normal processes; tires are a persistent and significant presence in the world’s landfills. Their high flammability and toxicity present concerns for air and water quality. With the United States alone producing about 450 million waste tires a year, this is a problem with no foreseeable end.
While whole tires can be used for breakwaters, artificial reefs, playground equipment, crash barriers, and erosion control, and pulverized tires can be used as road building material, a great deal of waste tire material still finds its way into landfills.
This article will look at the challenges of tire recycling and what is being done to alleviate waste tire buildup.
(Courtesy: Pixabay)
Understanding Tires
One of the problems with tires from a waste standpoint is that they were designed with no end use in mind. A relatively low amount of material – less than ten percent – must be lost from the tire before it no longer qualifies as “roadworthy.” However, due to the way tires are constructed, it is not easy either to make the tire usable again or to recycle it.
Tires are comprised of an “inner wall” of woven steel encased in several layers of vulcanized rubber “outer wall.” While natural rubber and steel are highly recyclable, vulcanization – or the adding of sulfur or other curative agents to rubber via heat – creates a final product that is unsuitable for repurposing, even for more tires. Modern tires typically contain no recycled end products, as they reduce the tire’s performance. Because the carbon-sulfur linkages of vulcanized rubber cannot be easily (or affordably) broken, it is easier to exploit its flammability and use vulcanized rubber as fuel.
This is an imperfect solution, emitting tar- and carbon-laden emissions into the atmosphere and contributing to the accumulation of greenhouse gases. Worse, a waste tire does most of its environmental damage while it is still in use. Road wear debris, carbon dioxide emissions from rolling resistance, and greenhouse gas production from vehicle fuel consumption all combine to exceed the environmental impact of the waste tire at the end of its life.
An end-of-life tire that is still in good condition can be retreaded, or have new material added to it to support a new tread stamp. However, the popular perception that retreaded tires are unsafe limits their consumer appeal. In spite of research suggesting that retreaded American tires may in fact be safer than new imported tires, and the Environmental Protection Agency’s estimate that retreaded tires represent a 70% oil savings compared with new tires, there were only about 17.6 million retreads sold in North America in 2006. This number, however, has grown in subsequent years, in part due to Federal Executive Order 13149 (2012), which requires federal vehicles to use retreaded tires when available.
(Courtesy: Pixabay)
Devulcanization
New innovations in tire recycling may be breaking through the vulcanization ceiling at last. For example, it is now possible to “devulcanize” rubber. Rubber, in its natural state, has no shape memory and is extremely sticky. Any form molded into natural rubber will eventually lose definition as the rubber reverts to its liquid state. The addition of sulfur creates sulfur-carbon and sulfur-sulfur crossbonds, adding structure, similar to the function of gluten in bread.
In “devulcanization,” a dry additive is mixed with crumbled vulcanized rubber, which is then kneaded under pressure, or exposed to microwaves. This breaks the crossbonds, making the waste tire stock suitable to be revulcanized. This allows recycled materials to be added to virgin materials at ratios of up to 4:1 without losing integrity, leading to significant oil savings.
Another new methodology in devulcanization, using carbon dioxide as the primary agent, has led to a high conversion rate of crumb rubber to TDP (tire-derived polymer) with no byproducts.
Devulcanization is not the only way to recycle tires, either. Rubber mulch, which is used for landscaping and gardening, is made from waste tires ground into crumbs between 10 and 32 millimeters in width. Rubber mulch has been shown to be an effective weed barrier, working by dehydrating weed seeds. Rubber mulch is also good for retaining soil moisture, because vulcanized rubber is non-porous. With rubber mulch offering better heat insulation than wood mulches, it provides an excellent thermal break for soil. Finally, rubber mulch is elastic, exhibiting a springy quality when laid in thick layers. This makes rubber mulch ideal for playgrounds, underlay and inlay for athletic fields and running tracks, and equestrian footing.
Waste tires also have civil engineering applications: replacing polystyrene insulation blocks, drainage aggregate, and embankment fill, with significant material and energy savings.
Finally, through pyrolysis (low- or no-oxygen burning), waste tires can still be converted into fuel. As long as the process is properly regulated, tires can serve as a suitable alternative to fossil fuels. Tire-derived fuel has the same energy per volume as oil and 25% more energy than coal; the ash residue has a lower heavy metal content than that of some types of coal; and the nitrogen oxide emissions are lower than those of high-sulfur coals.
This are but the beginnings of the solution to the waste tire problem. Timberland is currently experimenting with ways to convert waste tires into footwear components. With end-users consuming 87.9 percent of all waste tires produced, as of 2015, the problem is significantly better now than it was.
The road to ending the waste tire problem will involve not only the creation of new end uses for tires, but also a commitment from all of us to help minimize the problem. Opting to retread your tires when possible and finding ways to repurpose your used tires will help minimize your company’s environmental impact. It’s also helpful to make sure your company has a well-defined recycling plan, which includes providing access to the right receptacles. Trashcans Unlimited offers the best prices on commercial and decorative trash cans and is a trusted source for all your trash can needs.