Future automobile tires could come from the farm as much as the factory, thanks to a new way developed by scientists to convert waste tomato peels and eggshells into petroleum-based filler for sustainable rubber.
Researchers at The Ohio State University in the US have discovered that food waste can partially replace the petroleum-based filler that has been used in manufacturing tires for more than a century.
In tests, rubber made with the new fillers exceeds industrial standards for performance, which may ultimately open up new applications, researchers said.
According to researcher Katrina Cornish, the technology can make the manufacture of rubber products more sustainable and keep waste out of landfills.
Cornish developed the new method for turning eggshells and tomato peels into viable replacements for carbon black, a petroleum-based filler.
About 30 per cent of a typical automobile tire is carbon black; it is the reason tires appear black. It makes the rubber durable, and its cost varies with petroleum prices.
Carbon black is getting harder to come by, Cornish said.
"The tire industry is growing very quickly, and we do not just need more natural rubber, we need more filler, too," she said.
"We are not suggesting that we collect the eggshells from your breakfast. We are going right to the biggest source," Cornish said.
Commercial tomatoes have been bred to grow thick, fibrous skins so that they can survive being packed and transported long distances.
When food companies want to make a product such as tomato sauce, they peel and discard the skin, which is not 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," said Barrera.
"We may find that we can pursue many applications that were not possible before with natural rubber," Cornish added.
The new rubber does not look black, but rather reddish brown, depending on the amount of eggshell or tomato in it.