It’s not every day you discover a new raw material in your trash. But freezing and grinding up old tires into tiny particles is doing just that for rubber. It’s among a growing number of closed-loop industrial systems informed by industrial ecology.
Billions of old tires have been piling up in stockpiles around the world. As recently as 1990, only about 17% of the millions of tires discarded each year were headed into new products or power plants. Today, the equation is reversed. At least 80% of discarded tires end up "chipped" into rubber chunks for playgrounds, asphalt, or low-grade rubber material, or burned as low-cost fuel, estimates the Department of Transportation.
But as long as tire rubber--a pretty sophisticated blend of natural and synthetic rubber, as well as a dozen other chemicals--is treated as a low-tech commodity, applications are limited. So manufacturers are taking a second look at them as a cheap source of complex polymers to create fine powders, as small as 50 microns, more narrow than a human hair, to make everything from plastics to automobile parts significantly cheaper than those derived from natural or synthetic rubber. Ultimately, the goal is to close the loop on old tires.
Lehigh Technologies is one of the companies that has created a micronized rubber powder by freezing old tires them with liquid nitrogen and then running them through what amounts to a "turbo jet engine with teeth," says the company’s CEO, Alan Barton. "We’re basically acting as if we were a specialty chemical company to have new materials adopted by highly complex industries."
Although not a novel technique, Lehigh says its "cryogenic turbo mill" is creating the finest powders yet from old tires that lower cost and environmental impacts. The recycled material goes into new products, cutting oil and greenhouse gas emissions. So far, the company has put about 150 million new tires back on the road (composed of 10% old tires), and is aiming to start entering the market for roads and construction materials, as well as shoes and plastics.
With about one tire per person per year discarded in the U.S.--and with China now the world’s largest car market--the supply of raw materials shows no sign of diminishing. Mining our waste for new materials may our most abundant option.