A typical automobile tire is composed of about 30 percent carbon black, which is a filler that adds durability to the rubber. Carbon black is petroleum-based, however, meaning that it isn't entirely eco-friendly to manufacture. That's why Ohio State University scientists led by Katrina Cornish have been experimenting with a "greener" and more readily-available alternative – namely egg shells and tomato skins.
Obtained in the form of food industry waste, the shells and skins are dried and ground into a powder. When that powder is added to rubber, it reportedly makes the rubber stronger while allowing it to remain flexible (by contrast, most other strength-enhancing additives decrease the rubber's flexibility).
This attribute is partially due to the fact that the porous egg shell particles have a large surface area, allowing for greater contact with the rubber, while the tomato skin particles remain highly stable at high temperatures, plus they contain tough fibers.
According to Cornish, the Ohio State technology should serve to make tire production more sustainable, it should reduce American dependence on foreign oil, and it will keep waste from the food industry from ending up in the landfill. The tire rubber created thus far is a sort of reddish-brown, however, so the team is looking into adding black coloring agents.
Source: The Ohio State University