Vulcanization Method
Chemical crosslinking system that utilizes organic peroxides to create direct carbon-carbon bonds between polymer chains. Application of a peroxide cure results in a very stable network that is resistant to heat and hydrolysis. This method is used for a wide range of elastomers including silicone, ethylene propylene and fluoroelastomers.
It provides a cleaner vulcanization process with fewer residues compared to sulfur based systems.
Radical Mechanism
Thermal decomposition of the peroxide generates highly reactive free radicals that abstract hydrogen atoms from the polymer backbone. This creates radical sites on the chains that then pair up to form strong covalent bonds. Because these carbon-carbon links are stronger than the sulfur-sulfur bonds found in other systems, the final product exhibits superior thermal stability.
Polymer Property
Rubbers cured this way show excellent resistance to compression set at high temperatures. Resistance to steam and aggressive chemicals increases because the carbon-carbon bonds are less susceptible to chemical attack than ionic or sulfur crosslinks. The system is effective for automotive cooling hoses and industrial gaskets.
Processing Requirement
Exclusion of oxygen during the curing process is often necessary because atmospheric oxygen can inhibit the free radical reaction at the surface. This interference can result in a tacky or undercured exterior that compromises the part performance. Accurate temperature control is required to manage the half life of the peroxide and ensure a complete and uniform cure throughout the component.
Post curing in an oven is frequently employed to remove volatile byproducts and stabilize the final dimensions.
