WASHINGTON—In the grand scheme of things, paper recycling is relatively easy once all the different grades are separated. As is metal recycling—ferrous from non-ferrous and go from there. Plastic recycling can be more of a challenge because of the different molecular properties of each type of resin and the danger of contamination.
Then there's rubber recycling. And rubber recycling, for the most part, is tire recycling.
New statistics released during the latter part of 2020 show that scrap tire recycling in the U.S. has stalled, the U.S. Tire Manufacturers Association reported.
Tire recycling dropped 20 percent from 2013 to 2019, the association said in its latest look at the market issued in October. The report, with 2019 numbers as the latest statistics, showed recycling falling to nearly 76 percent from 96 percent over that time.
America continues to recycle scrap tires at a steady rate, but the issue has become a continued increase in the overall generation of scrap tires as years go on. USTMA looks at the tire recycling market every two years.
So when it comes to the numbers behind tire recycling, it's a denominator issue.
"There's sort of a hidden story here because scrap tire markets really didn't decline from 2017," said Sarah Amick, vice president of environment, health, safety and sustainability, and senior counsel for the trade group.
"I think the challenge is that we continue to have more scrap tires generated each year that we need to find a home for," Amick said. "I think the big takeaway here is that scrap tire markets are not growing at the same pace as annual generation."
Recycling markets are remaining relatively consistent, but the number of scrap tires generated each year increases by about 7 percent, according to USTMA data. "That's the real challenge," Amick said.
Recycling has fallen steadily since 2013, checking in at 87.9 percent in 2015 and 81.4 percent in 2017, the association reported.
While there are more used tires now than ever, that source of rubber is not ending up in illegal dumps. That's not always been the case.
Instead, the tires simply are being directed to landfills while there is no recycling market.
"We have not seen a corresponding increase in illegal stockpiles. In fact, stockpiles continue to come down," said John Sheerin, USTMA's director of end-of-life tire programs.
The U.S. Environmental Protection Agency breaks down municipal solid waste into a variety of categories to report on generation and recycling rates. That includes one category for both rubber and leather.
The latest EPA statistics from 2018 show 9.2 million tons of rubber and leather was generated in MSW. That's 3.1 percent of the total waste stream.
Paper essentially is dissolved in a slurry as part of the recycling process that recaptures fibers and reconstitutes them into new products. Metals are melted down for reuse, an energy intensive effort that's pretty straightforward.
Plastics commonly are cleaned, melted and sometimes purified, in preparation for reuse.
But rubber, because it undergoes vulcanization, is especially challenging to recycle compared with its material cousins.
Tires commonly are shredded into small pieces at room temperature or frozen at very cold temperatures before they are broken into small pieces.
These are processes to simply break down the size of the tires and because rubber maintains its physical properties there are fewer outlets for reuse. Crumb rubber, called that because the material is reduced to a small size, has found popularity for use on fields as a cushioning for athletes as they compete. Other applications include playgrounds and landscape projects.
Recycled rubber also can be made into products such as mats and flooring and be mixed in with asphalt in a process that backers say improves the life and performance of roads compared with traditional asphalt. There also is incineration as tires commonly are used as kiln fuel and burned. And then there is pyrolysis, a process that super heats, but does not burn, materials in the absence of oxygen to break them down into reusable constituents such as oil, synthetic natural gas and carbon black char.
It's the road applications that have a non-profit based in Georgia and the USTMA collaborating on a new research project.
The work to advance use of ground tire rubber is being backed by USTMA and The Ray, a non-profit that calls itself a "proving ground for the evolving ideas and technologies that will transform the transportation infrastructure of the future."
Research on using GTR, also known as crumb rubber, in asphalt will create what the collaborators are calling a "state of knowledge report" that will feature existing research and identify gaps in data for the use of the material in rubber modified asphalt.
Rubber modified asphalt creates long-lasting roads that rut less than traditional asphalt roads. Roads using recycled tires also are quieter and feature better vehicle grip and less spray in wet weather, a University of Arizona study indicates. These roads also reduce tire and road wear particles by half. Including used tire material in roads allows asphalt to be recycled repeatedly.
"Recycling scrap tires to create rubber modified asphalt appears to be a cost-effective way to reduce tire and road wear particles and advance the circular economy," USTMA CEO Anne Forristall Luke said in a statement. "This study will allow us to share what we know about the technology and what additional research is needed to build more sustainable roads and infrastructure."
The Ray is an offshoot of the Ray C. Anderson Foundation. Anderson was the founder of Interface Inc., a carpet company. He created a name for himself by promoting environmentalism as part of his business strategy. Research will include laboratory and field data, including performance and lifecycle information of GTR.
