Chemical Properties of Tires

by Tim McQuade
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During the 20th century, the tire became synonymous with industrialized societies. Although rubber represents a leading component, tires also contain a variety of chemicals. Manufacturing companies will vary the chemical properties within a tire depending on its intended use. For instance, racing tires must stand up better to heat than passenger-car tires, so companies use a higher percentage of synthetics and chemicals in these tires.

Rubber Chemical Properties

Approximately 40 to 60 percent of a tire is rubber. A tire typically consists of four different kids of rubber: natural rubber, styrene-butadiene rubber, polybutadiene rubber and butyl rubber. About 55 percent of a tire's rubber content is in the sidewall and tread, and companies use natural, styrene-butadiene and polybutadiene rubbers in these areas. Butyl rubber and halogenated butyl rubber makeup the inner liner of a tire. The rubber mixture in a standard-passenger-car tire is 55-percent synthetic rubber and 45-percent natural rubber.

Chemical Fillers

Fillers and additives add chemicals to tires. Reinforcing chemical agents represent a high percentage of the chemical fillers used; the most common are carbon black, silica and resin. Manufacturing companies use anti-degradants (antioxidants, paraffin and waxes) as well as adhesion promoters (cobalt salts, brass on wire and resin on fabrics) in tires. Sulfur serves as a curative agent. Oils, tackifiers, peptizers and softeners represent other chemical additives. Cotton, aramid fiber, steel fabric, rayon, polyester and fiberglass are also common additives.

Chemical Properties by Weight

According to The Goodyear Tire and Rubber Company, the most common tire is the P195/75R14 all-season passenger tire, weighing approximately 22 pounds. This tire consists of 6.0 lbs. of five different synthetic rubbers, and contains 4.5 lbs. of eight types of natural rubber. Carbon black represents 5.0 lbs. of the tire. The tire also consists of 1.5 lbs. of steel cord, and 2.0 lb. of polyester, nylon and steel beadwire. Finally, companies engineer this tire with 3.0 lbs. of 40 different chemical agents, waxes, oils and pigments.

Chemical Properties by Tire Byproduct Percentages

According to a July, 1995 report by CalRecovery, Inc. that analyzed the concentrations of chemicals in the ash of burnt tires, zinc oxide represented 37.8 percent of the tire byproduct, while 22.3 percent of the ash consisted of silica dioxide. Lime was 5.7 percent, ferrix oxide was 7.4 percent and sulfate ions were 7.0 percent of the tire ash. Titanium oxide, magnesium oxide, sodium oxide, potassium oxide and aluminum oxide represented a combined 5.9 percent of the tire byproduct.

Chemical Properties by Trace Elements

According to a 2002 study by researchers at the Aristotle University of Thessaloniki, a range of elemental metals also make up a tire's composition. Zinc represented the most prevalent chemical property found in the study, at 10,000 parts per million. Copper constituted about 75 ppm of the tire's particulate matter. Barium stood at approximately 25 ppm, and lead at 20 ppm. Other notable trace chemical properties include chromium, nickel, strontium and vanadium.

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