The Project

Substitution of critical and toxic materials in products and for optimized performance

Executive summary

The project aims at reducing the amount of crystalline ZnO activator used in rubber curing processes, by replacing it with a novel activator, ZnO-NP@SiO₂-NP, composed of ZnO nanoparticles anchored to silica fillers. Employing ZnO-NP@SiO₂-NP entails a reduction of 50% of the conventional amount of ZnO enabling to produce rubber composites for tires with mechanical properties up to 10% better than those obtained with the traditional activator.

Popular Project Description

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” [1]. As such, the reduction of ZnO level in rubber is becoming an urgent issue in rubber production and particularly tire manufacturing. Besides, the presence of large amount of ZnO is also a drawback in the end-of-life tire recycling treatments.

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 [2,3], which has been already 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 􀀀 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. The project is complemented by comprehensive environmental assessment, to quantify the environmental benefits of the new process when compared to the traditional one, as well as on the lab and large scale of the new process, up to operational prototypes.

[1] Federal register (12 September 1995) Vol. 60, N. 176.

[2] R. Scotti et al., Chem.Eng.J.(2015) 275, 245-252.

[3] R. Scotti et al., Eur.Polym.J. (2017) 93, 63-74.