CORVALLIS, Ore.—Wooden tires sound about as useful as wooden nickels—or buggy wheels on a Corvette. Yet, thanks to the work of wood science researchers at Oregon State University, tires reinforced with wood- or plant-based fibers could become commonplace.
Kaichang Li, associate professor of wood science and engineering at OSU, and graduate student Wen Bai have worked for the past three years on experiments in which microcrystalline cellulose, a micrometer-sized cellulose crystal, partially replaces silica as a reinforcing filler in rubber tire compounds.
The result, they said, is a tire that costs less and requires less energy to manufacture and achieves better fuel economy in hot weather while maintaining comparable traction with conventional tires on wet pavements.
Li and Bai's paper, “Partial Replacement of Silica with Microcrystalline Cellulose in Rubber Composites,” was published in a recent issue of the professional journal, Composites A: Applied Science and Manufacturing.
Although the research results have only been available a short time, OSU already has received a number of calls from tire makers and rubber processing firms that are interested in the technology, according to Li.
Microcrystalline cellulose is cheaply produced in an acid hydrolysis process on cellulose, which itself is the lowest-cost and most abundant substance in nature, Li said. About 40 to 50 percent of wood is cellulose.
Cellulose fibers have been used in rubber compounds for about the past 25 years, in such products as belts, hose, mats, ropes and insulation, the introduction of the study states. MCC, however, is very different from plain cellulose fibers, according to Li. Its crystalline structure makes it much stronger than cellulose fibers, and also gives it different and better properties in general, he said.
Cellulose fibers never have been used in tires, because carbon black and silica are more effective as tire reinforcing fillers, OSU said. But the university said finding alternatives to those substances is desirable because petroleum feedstocks for carbon black are increasingly expensive and silica requires a lot of energy for processing.
Most of the research in this study was conducted at the Struktol Co. of America headquarters in Stow, Ohio, with support from several Struktol technical experts, according to Li. Struktol's parent company, Schill+Seilachter “Struktol” A.G. of Hamburg, Germany, contributed about $300,000 in funding to OSU for the study and for other, unrelated research over two years, he said.
In their study, Li and Bai found that partial replacement of silica with MCC reduced the Mooney viscosity, apparent shear stress and apparent shear viscosity of rubber composites, which allowed easier, less energy-intensive processing.
Replacing silica with up to 18-percent MCC did not harm the mechanical properties of aged or unaged rubber composites, the study said, but a replacement of about 11.8 percent proved optimal for preserving wet traction and decreasing hot-weather rolling resistance.
Among the properties of the rubber composites, only tear strength and hot tear strength suffered slightly with MCC replacing silica, the study said.
There are no estimates of how much money tire makers could save by partly replacing silica with MCC, according to Li. “But if you process rubber in quantity, that would save quite a lot of energy,” he said.
Neither OSU nor Schill+Selachter stand to make any financial gain from the MCC technology, Li said.