Second life for tires

About 300 million tires are discarded in the USA each year and more than half end up either as landfill or are burned for fuel in cement kilns and in other industries. Used rubber is hard to recycle because it is vulcanized - hardened and rendered chemically inert - by the addition of sulfur and other compounds to the material's long molecular chains.
Lehigh Technologies (Tucker, GA, USA) instead shatters rubber into a fine powder using a process that involves freezing old rubber and smashing it to pieces. This starts with tires that have been torn into half-inch chunks using conventional shredding equipment. Lehigh mixes these rubber pieces with liquid nitrogen, cryogenically cooling the rubber to -100°C. The rubber is then fed into a high speed "turbomill" that shatters it into particles no more than 180 microns in size. Creating such fine powder transforms the rubber from a highly inert filler material to one that can bond with other materials.