LONDON-Retreading is ``the best method of reducing environmental damage from discarded tires,'' according to a report by Rubber Consultants, a commercial arm of the Malaysian Rubber Producers Research Association. A close second is the reuse of tire buffings in recycled products.
However, for scrap rubber in general, the report claims incineration for energy recovery is the most promising way to dispose of large volumes of scrap rubber.
The economic viability of other methods of recycling is almost always questionable in a free economy, but may be viable with government subsidies or in closed economies, the study concluded.
The report said that, with a few notable exceptions, the deliberate crumbing of tires for use in low-value products is unlikely to be economically justifiable.
Because tires-especially steel-reinforced tires-are designed to be both tough and highly resistant to cuts and abrasion, crumbing processes are energy-intensive and relatively expensive ways of creating low-value raw material for use in low-value products.
Cryogenic grinding, where liquid nitrogen is used to cool the rubber to the point of brittleness, is particularly expensive and should not be considered for general purpose crumbing, unless there are particular circumstances that may make it a sensible choice.
Tire buffings, on the other hand, are created as a by-product of the retreading process. Sale of these buffings improves the cost-efficiency of the retreading process and makes high-quality, uncontaminated rubber granules available to a limited aftermarket.
The expense of crumbing tires also may jeopardize the economics of using tire granulate for modifying asphalt in road surfaces.
Further, the technical performance of this type of asphalt compared with conventional road surfaces is questionable, according to the report.
There are two reasons why rubber goods are so difficult to recycle: the irreversible reaction that takes place during the curing of the rubber component; and the fact that few products are made from 100-percent rubber.