23 July 2009

Tires branch out into trees

The phrase “you drive me up a tree” may have a new meaning as tires may soon be made out of trees, which could cost less, perform better, and save fuel and energy.

There is some great potential for microcrystalline cellulose, a product that can come from almost any type of plant fiber, to partially replace silica as reinforcing filler in the making of rubber tires, said wood science researchers at Oregon State University.

By using wood, it could decrease the energy required to produce the tire, reduce costs, and better resist heat buildup. Early tests indicate the products would have comparable traction on cold or wet pavement, be just as strong, and provide even higher fuel efficiency than traditional tires in hot weather.

“We were surprised at how favorable the results were for the use of this material,” said Kaichang Li, an associate professor of wood science and engineering in the OSU College of Forestry, who conducted this research with graduate student Wen Bai.

“This could lead to a new generation of automotive tire technology, one of the first fundamental changes to come around in a long time,” Li said.

Cellulose fiber acts as reinforcement in some types of rubber and automotive products, such as belts, hoses, and insulation, but never in tires, where the preferred fillers are carbon black and silica. Carbon black, however, consists of increasingly expensive oil, and the processing of silica is energy-intensive. Both products are very dense and reduce the fuel efficiency of automobiles.

In the search for new types of reinforcing fillers that are inexpensive, easily available, light, and renewable, OSU researchers looked at microcrystalline cellulose, a micrometer-sized type of crystalline cellulose with an extremely well-organized structure. It works in a low-cost process of acid hydrolysis using nature’s most abundant and sustainable natural polymer, cellulose, that comprises about 40% to 50% of wood.

OSU researchers replaced up to about 12% of the silica used in conventional tire manufacture. This decreased the amount of energy needed to compound the rubber composite, improved the heat resistance of the product, and retained tensile strength.

Traction is always a key issue with tire performance, and the study showed traction of the new product was comparable to existing rubber tire technology in a wet, rainy environment. However, at high temperatures such as in summer, the partial replacement of silica decreased the rolling resistance of the product, which would improve fuel efficiency of rubber tires made with the new approach.

The team will have to conduct more research to confirm the long-term durability of tires made with partial replacement of silica, Li said. Further commercial development of this technology by a tire manufacturer could start up at any time, he said.

Tire manufacturing could also provide another market for large amounts of Pacific Northwest natural fibers and the jobs and technology needed to process them.

For related information, go to www.isa.org/manufacturing_automation.