Multifunctional Additives as Zinc-Free Curatives for Sulfur Vulcanization

Abstract

Abstract Concern about the release of eco-toxic zinc species from rubbers into the environment leads to an increasing interest in potential substitutes. This investigation reports on the application of Multifunctional Additives, amines complexed with fatty acids, for sulfur vulcanization of rubbers. Good physical properties can be obtained in s-SBR compounds using the MFA/S cure system, albeit at the cost of a shortened scorch time as compared to a ZnO/stearic acid system. Inclusion of ZnO lengthens the scorch time, though it reduces the state of cure and ultimate properties. The amount of ZnO used in the MFA-formulations is considerably lower than in the conventional systems. The introduction of CaO and MgO leads to an improvement in the state of cure and physical properties. Amines play a vital role in the vulcanization process, hence various amine-complexes have been synthesized and investigated as zinc-free curatives in s-SBR compounds. It is observed that the scorch time is related to the basicity of the amines. The results of Model Compound Vulcanization studies with MFAs reveal a fast decomposition of the accelerator and some differences in the distribution of the crosslinked products. The conclusion must be drawn, that the chemistry involved in the MFA-systems is fundamentally different from the conventional vulcanization systems.