Driving on eggshells—not walking on them—might be a good thing.
Stellantis is looking to patent a process for incorporating them, or other biowaste material, into tires in order to further lower their environmental impact.
In a patent filing published by the United States Patent and Trademark Office (USPTO) Jan. 23, 2025 and submitted in 2023, the automaker discusses using eggshells as a replacement for two common filler materials in tires: carbon black and silica.
As tires wear, both carbon black and silica are released into the air as dust, Stellantis points out. Indeed, a study published in 2023 found that tire dust could be a significant source of particulate emissions. But Stellantis believes these fillers can be replaced by calcium oxide (CaO) derived from eggshells.
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Hen egg shells are over 90% calcium carbonate (CaCO3), and CaO can be extracted using a calcination process—first washing them in acetone, then subjecting them to temperatures of at least 1,652 degrees Fahrenheit, causing the shells to decompose.
Decomposition gives off carbon dioxide (CO2), leaving behind CaO as a white solid, according to the patent filing. That material is then milled to the form factor of carbon black or silica tire filler material, and mixed in with rubbers and other materials to form a tire compound.
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It’s unclear if this one will prove commercially viable, especially considering that it originated with a company that makes cars, not tires. But actual tire manufacturers have been working to add more sustainable materials to their tires, which will be crucial in further lowering the environmental impact of driving. As tailpipe emissions continue to diminish with increased EV adoption, other sources of pollution will have to be tackled—like tires.
Bridgestone said last year that it was producing tires for the all-electric Audi E-Tron GT that used 55% recycled and renewable materials, and it’s incorporated natural rubber from a desert shrub into IndyCar racing tires. In 2022 Michelin said it would develop environmentally-friendly tires in partnership with Hyundai, and Goodyear showed a demonstration tire that cut down use of petroleum-based materials, as well as emissions from production.
