Organic Zinc Salts as Pro-Ecological Activators for Sulfur Vulcanization of Styrene-Butadiene Rubber.

Magdalena Maciejewska,Anna Sowińska,Judyta Kucharska

doi:10.3390/polym11101723

Abstract

Organic zinc salts and complexes were applied as activators for sulfur vulcanization of styrene–butadiene elastomer (SBR) in order to reduce the content of zinc ions in rubber compounds as compared with conventionally used zinc oxide. In this article, the effects of different organic zinc activators on the curing characteristics, crosslink densities, and mechanical properties of SBR as well as the aging resistance and thermal behavior of vulcanizates are discussed. Organic zinc salts seem to be good substitutes for zinc oxide as activators for sulfur vulcanization of SBR rubber, without detrimental effects to the vulcanization time and temperature. Moreover, vulcanizates containing organic zinc salts exhibit higher tensile strength and better damping properties than vulcanizate crosslinked with zinc oxide. The application of organic zinc activators allows the amount of zinc ions in SBR compounds to be reduced by 70–90 wt % compared to vulcanizate with zinc oxide. This is very important for ecological reasons, since zinc oxide is classified as being toxic to aquatic species.

Highlights

Zinc oxide (ZnO) is widely used as an activator in the vulcanization of unsaturated elastomers by sulfur or sulfur donors
Despite the important role of ZnO in sulfur vulcanization, its concentration in rubber compounds, especially those used in aquatic environments, must be reduced to, at least, below 2.5 wt %, because zinc oxide is classified as being toxic to aquatic life
Rheometer measurements were performed to study the activity of organic zinc salts and complexes during the sulfur vulcanization of styrene–butadiene elastomer (SBR) compounds

Summary

Introduction

Zinc oxide (ZnO) is widely used as an activator in the vulcanization of unsaturated elastomers by sulfur or sulfur donors. Zinc oxide reduces the vulcanization time of rubber compounds and improves the processing and physical properties of vulcanizates [1]. It used as a crosslinking agent of elastomers containing suitable functional groups, such as carboxylated and chloroprene rubbers [2,3,4] or chlorosulfonated polyethylene [5]. A potential source of zinc in groundwater can be rubber granulates made from end-of-life tires used to build artificial sports fields Taking this into account, the problem of reducing the amount of zinc in rubber products becomes essential.

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