Researchers at The Ohio State University in the US have discovered and developed a patent-pending technology that turns food waste, specifically eggshells and tomato peels, into a viable rubber filler alternative to carbon black.
In tests, rubber made with the new fillers exceeds industrial standards for performance, which may ultimately open up new applications for rubber. The researchers said the technology has the potential to solve three problems: it makes the manufacture of rubber products more sustainable, reduces American dependence on foreign oil, and keeps waste out of landfills.
About 30% of a typical automobile tyre is carbon black. It is a petroleum-based filler that has been used in manufacturing tyres for more than a century. It is also the reason tyres appear black. It makes the rubber durable, and its cost varies with petroleum prices. However, carbon black is getting harder to come by.
“The tyre industry is growing very quickly, and we don’t just need more natural rubber, we need more filler, too,” explained Katrina Cornish, an Ohio Research Scholar and Endowed Chair in Biomaterials at Ohio State. “The number of tyres being produced worldwide is going up all the time, so countries are using all the carbon black they can make. There’s no longer a surplus, so we can’t just buy some from Russia to make up the difference like we used to.
“At the same time,” she added, “we need to have more sustainability.”
So Cornish and her team are getting eggshells and other food waste from Ohio food producers.“We’re not suggesting that we collect the eggshells from your breakfast,” Cornish said. “We’re going right to the biggest source.”
According to the USDA, Americans consume nearly 100 billion eggs each year. The shells from cracked eggs are hauled to landfills by the ton. There, the mineral-packed shells don’t break down.
The second most popular vegetable in the US—the tomato—also provides a source of filler, the researchers found. Americans eat 13 million tons of tomatoes per year, most of them canned or otherwise processed.Commercial tomatoes have been bred to grow thick, fibrous skins so that they can survive being packed and transported long distances. As a result, these skins aren’t easily digestible.
Cindy Barrera, a postdoctoral researcher in Cornish’s lab, found in tests that eggshells have porous microstructures that provide larger surface area for contact with the rubber, and give rubber-based materials unusual properties. Tomato peels, on the other hand, are highly stable at high temperatures and can also be used to generate material with good performance.
“Fillers generally make rubber stronger, but they also make it less flexible,” Barrera said. “We found that replacing different portions of carbon black with ground eggshells and tomato peels caused synergistic effects—for instance, enabling strong rubber to retain flexibility.”
“We may find that we can pursue many applications that were not possible before with natural rubber,” Cornish added.
The new rubber doesn’t look black, but rather reddish brown, depending on the amount of eggshell or tomato in it. With doctoral student Tony Ren, Cornish and Barrera are now testing different combinations and looking at ways to add color to the materials.
Current Ohio State doctoral student Jessica Slutzky and former master’s student Griffin Michael Bates participated in the research.The university has licensed the patent-pending technology to Cornish’s company, EnergyEne, for further development.