Millions of tonnes of egg shells and tomato skins are left over all round the world every year – most of them attributable to industrial processing operations. Up to now, these shells and skins have been disposed of as waste. Scientists from Ohio State University in the USA wondered whether it was not possible to make something better than waste out of these natural materials. The answer is both encouraging and surprising: if the right technology is applied, important fillers based on mineral oil of the kind that are used in the production of car tyres can be substituted with promising results by materials made from egg shells and tomato skins.
What we are talking about here is not the use of natural or synthetic rubber for the production of car tyres. This short article focusses entirely on a substance based on mineral oil that is added to the (natural or synthetic) rubber in order to increase the abrasion and ageing resistance of the tyre.
Everyone knows that mineral oil is a resource that is only available in finite and therefore limited amounts. It is generally accepted that it is necessary to find an alternative in good time and to replace the fossil resource as soon as possible by a different resource that is, ideally, renewable and/or sustainable. Scientists from Ohio State University think they have identified interesting candidates to assume the role of substitute:
In tests carried out by Katrina Cornish and her team, egg shells and tomato skins have proved to be fillers with surprisingly good properties; the results have been better than required by the specifications of industrial standards.
It is reported that this is probably due to the special nature of the material: in view of their porous microstructures, egg shells have a larger surface area than soot particles, which evidently leads to a better bond between the two materials and, as a result, to unusual tyre properties.
Tomato skins, in turn, remained very stable even at high temperatures and could improve the performance of a car tyre substantially when used as an additive. If various parts of soot were replaced by ground egg shells and tomato skins, this would lead to synergy benefits, e.g. rubber that is otherwise abrasion-resistant, tends to be stiff and has unfavourable asphalt gripping properties suddenly becomes more flexible, which improves road grip.
Katrina Cornish and her team are still in the early stages of their work. It is becoming apparent, nevertheless, that there are further potential application areas apart from sustainable tyre production. A central design problem still has to be solved first, however: colour. While conventional car tyres are black – due to the use of soot, which is based on mineral oil – the use of egg shells and tomato skins gives them more of a reddish-brown colour. GD