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zinc oxide used in rubber industry

Number of visits: Date:2011-09-29 15:53

Zinc oxide is a widely used compound in rubber industry due to the excellent properties that shows as activator for sulphur vulcanisation. The tire industry remains the largest single market for ZnO, consuming more than half of the total worldwide demand of 1,200,000 metric tons1. Traditionally, ZnO is used in rubber formulations in concentrations of 3–8 parts per hundred rubber (phr).

Despite its superior characteristics, there is an increased concern about the environmental effects that zinc oxide causes and over the years lower levels of zinc have been tried in order to decrease its impact and to minimise the production costs. Different approaches have been considered for reducing zinc levels. Between all the alternatives proposed, the use of nano–sized ZnO particles with high surface area seems to be promising. However, it was found that the use of more active forms of zinc oxide did not substantially reduce further the minimum zinc content that can be achieved with conventional zinc oxide although the dispersion of high surface area ZnO during mixing was found to be significantly better, which could enable low levels of this zinc oxide to be used in industry with more confidence.
There have been a number of studies comparing different metal oxides as vulcanisation activators in order to find substitutes for zinc oxide. Several metal oxides have been used, CaO, MgO, CdO, CuO, PbO and NiO. Among them, MgO is the most promising candidate since it is a non heavy metal oxide that provokes the breakdown of the accelerator to be faster than when ZnO is used and it is able to form active sulphurating agents. However the crosslink level achieved is lower than that obtained with zinc oxide, which has limited its industrial application.

In this article, a new approach to overcome the problems between ZnO and MgO is presented. It consists in the development of a new activator based in the mixture of both mixed oxides at nanoscale to take advantage of the behaviour of both zinc and magnesium oxides as nanoparticles. The new activator is nanometer–sized mixed metal oxide particles of zinc and magnesium (Zn1–xMgxO) with very precise stoichiometry prepared employing a polymer–based method. In this accelerator, magnesium is incorporated into the ZnO structure and this inclusion and its size are expected to show a better performance taking advantage of the behaviour of both ZnO and MgO in sulphur vulcanisation.

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