Agricultural Research Service scientists Lei Jong and Jeffrey Byars are testing soy flour as a "green" filler for tires and other natural rubber products.

Today's fillers are typically petroleum-based particles called "carbon black." Tire manufacturers use them in rubber to improve tensile strength and wear resistance. But petroleum's many competing uses, rising costs and ties to pollution have rekindled interest in biobased alternatives, especially those derived from homegrown crops like soybeans.

Soy flour is primarily used in cooking and baking. But Jong and Byars' studies at the ARS Cereal Products and Food Science Research Unit in Peoria, Ill., indicate the flour also could serve as an inexpensive alternative to today's carbon-black tire fillers.

The researchers use defatted soy flour that's been dispersed in water to form aggregates 10 microns in diameter (about 1/1000th of an inch). Then they add the aggregates to rubber latex and freeze-dry the mixture. This causes the aggregates to form a tight interconnecting network through the rubber.

For lab tests, the researchers mold the soy-based rubber into samples and subject them to shearing and other forces. Of particular interest is the "storage modulus," which measures the elasticity of a material. On average, the storage modulus scores of composites containing 30 percent soy flour are 20 times higher than filler-free rubber, but somewhat lower than those reinforced with carbon black.

In addition to testing other biobased filler materials, the researchers are collaborating with rubber manufacturers to further explore the technology.

A report on the research was recently published online in the Journal of Applied Polymer Science.