Curing of fluoroelastomers (FKM) can be accomplished commercially by three separate systems.
The first curing system was developed using hexamethylene diamine. Although cured articles with diamines gave excellent heat and chemical resistance, processing was an issue.
The bisphenol AF cure system was developed in the 1970s as an improvement to diamines and has since been used as the primary curing method for a wide variety of FKMs. Some FKM types, though, cannot be cured with bisphenol and need to use a third type of cure system, namely the peroxide system. This is accomplished by incorporating a cure site monomer in the polymer backbone, which participates in the crosslinking mechanism.
In this article we explore varying levels of metal oxides within the bisphenol curing system and their effects on properties. The two most widely used metal oxides are magnesium oxide and calcium hydroxide. They can be used individually, but it is more common to use them in combination at different levels to achieve desired properties. The effects of these different levels on cure rate are important while formulating an FKM compound.
It is hoped that the information presented will aid in developing formulations that can achieve a balance between final cured properties and molding cycle times.