By evaluating Zn release to the eluate with pH varying between 3 and 7, a reduction in release with pH increase could be observed. The toxicity test evaluated EC50 which means growth inhibition of 50% of the tested organisms and LC50, the mortality of 50% of the organisms present in solution. The Zn release and its toxicity on algae and frogs’ embryos was studied in NR compositions [ 6 6 Gualtieri, M., Andrioletti, M., Vismara, C., Milani, M., & Camatini, M. Effect of synthesized zinc stearate on the properties of natural rubber vulcanizates in the absence and presence of some fillers. In another utilization of zinc stearate as a substitute for ZnO and stearic acid, it wasĬoncluded that crosslinking was not effective, compromising vulcanization [ 5 5 Helaly, F. The results of the studied Zn complexes were similar to those of the current vulcanization system, without harm to the vulcanization process and further increasing the density of the elastomeric composition with half the amount of Zn. The author tried to develop novel activators which would contain only traces of Zn. In this sense, Heideman studied the reduction of ZnO levels during sulfur vulcanization of elastomeric compositions based on poly(ethylene propylene diene) (EPDM) and poly(butadiene styrene) (SBR).
According to the 2004/73/CE European Norm, Zn is classed as deleterious and toxic for aquatic organisms with lasting effects. Zinc is a metal easily encountered in the environment, however, amounts which exceed the safe limit that an organism can absorb and eliminate may cause a lack of equilibrium in the environment. Various ways to reduce zinc oxide levels in S-SBR rubber compositions. Zn release to the environment can occur during production, elimination and recycling of elastomeric products, however it is relevant to keep low ZnO levels in elastomeric formulations, not only for environmental, but also for economic reasons [ 2 2 Heideman, G., Noordermeer, J. Influence of the zinc oxide level in rubber compositions on the amount of zinc leaching. The reduction in ZnO content in elastomeric compositions has become a subject of technological and industrial interest due to the deleterious effect of zinc ions on aquatic organisms [ 1 1 Pysklo, L., Pawlowski, P., Parasiewicz, W., & Piaskiewicz, M.
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