Project duration: 1 January 2019 – 31 December 2021


Vulcanization is a consolidated process of the tire industry to improve the mechanical properties of rubber. In this context, ZnO is the most efficient curing activator worldwide employed to enhance and control its reaction rate. However, ZnO entails non-negligible potential environmental risks: according to the Environmental Protection Agency (EPA) zinc ion can become available from zinc oxide through several mechanisms and zinc ion can reasonably be anticipated to be toxic to aquatic organisms. As such, the reduction of ZnO level in rubber is becoming an urgent issue in rubber production and particularly tire manufacturing. Moreover, the presence of large amount of ZnO is also a drawback in the end-of-life tire recycling treatments.

The solution (technology)

The present project aims at reducing the amount of the traditional microcrystalline ZnO activator and at improving the efficiency of the curing process simultaneously, by replacing it with a novel activator ZnO-NP@SiO2-NP, constituted by ZnO nanoparticles anchored to silica, a common filler utilized in rubber composites for tires. The novel ZnO-NP@SiO2-NP behaves at the same time as curing agent and rubber reinforcing filler. It is synthesized by an easy-scalable and green sol-gel procedure, which has already been validated for the successful production of rubber composites with high mechanical performances emp ZnO-NP@SiO2-NP employed in common tires. Preliminary safety assessment also showed that ZnO-NP@SiO2-NP has lower toxicity than microcrystalline ZnO.
The substitution of the ZnO crystalline activator with ZnO-NP@SiO2-NP results in a remarkable curing efficiency, due to the high capability of the distributed zinc centres to react with the curatives in the rubber matrix during the vulcanization. This allows a reduction of around 50 % in the conventional amount of ZnO and enables to produce rubber composites for tire applications with curing and mechanical properties up to 10% better than those obtained with the traditional activator.


  • Università degli Studi di Milano – Bicocca (University of Milano- Bicocca), Italy (Lead Partner)
  • Commissariat à l’énergie atomique et aux énergies alternatives, CEA (French Alternative Energies and Atomic Energy Commission), France
  • Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. (Fraunhofer), Germany
  • Monolithos Ltd, Greece
  • Pirelli Tyre S.p.A, Italy
  • Stichting Katholieke Universiteit (Radboud University Nijmegen), Netherlands