Technical Notebook: Devulcanizing scrap OTR tire rubber for compounding, molding solid tire idlers

Traditionally, one of the biggest issues facing the automotive and transportation ecosystem has been what to do with scrap tires. When they are no longer suitable for use on vehicles because of wear or irreparable damage, used tires can become a huge ecological problem. Indeed, about half a billion tires are scrapped each year in North America from passenger cars alone (one tire per person per year). And then you add to that trucks, buses, off-road vehicles, heavy machinery, etc.

While major strides were made in developing sustainable practices for the disposal and recycling of scrap tires, most of these do not add value. Plus, with new developments in technology and engineering practices continuing to emerge, sustainable tire recycling continues to be a moving target. Unlike thermoplastics that are theoretically infinitely recyclable (a plastic, heated, melts, then when let to cool, solidifies (into a product), and with heating (a discarded product), the plastic melts again (for making another product), rubber is a thermoset and once it cures it cannot go back to its pre-cure state. In fact, it takes about 600 years for a thermoset rubber to decompose naturally, and burning tires to get rid of them quickly presents huge economical and ecological disadvantages.

The idea is thus to try to break the bonds between molecular chains making for a cured thermoset rubber (without damaging the chains), then compounding the recyclate to improve its properties and make with the new compound a newly engineered product (and why not a new tire from a scrapped tire in a true economy, as tires make for close to 60 percent of all rubber applications). This paper presents emerging research in devulcanizing ground tire rubber and activities at WIDL to devulcanize, compound and manufacture industrial products out of scrap tires.