Silicone is an incredibly versatile material. Silicone generally refers to a family of materials that are based on polymer chains with alternate silicon and oxygen atoms. Silicon-oxygen linkages are found in other high temperature materials such as quartz, glass, and sand. This accounts for silicone's superior heat resistance when compared to other elastomers. The silicone family includes rubbers (addressed in this article), fluids, greases, gels, and solid resins.
The two most popular crosslinking systems used with silicone polymers are the platinum/addition cure and the peroxide/free radical cure. Shelf life varies dependent on cure system.
Addition cure systems rely on a metal catalyst (platinum) and feature a two-part process: one part contains the catalyst and the other a silicon cross linker. When mixed, an inhibitor is used to provide working time before cure. Free radical cure systems rely on a heat cure to decompose into two free radical components that react to a silicone polymer with vinyl or alkyl. Post-cure cycles are often required to remove residue from cured parts.
Silicone rubber is classified according to different curing methods, as listed below:
- HCR (High Consistency Silicone Rubbers) --These heat-cured rubbers, using either peroxides or platinum catalysts, form single component compounds that can be used in virtually all industries. They are similar to organic rubber compounds.
- LSR (Liquid Silicone Rubbers) – Two-component systems that are typically blended during pumping into an injection mold, where vulcanization takes place. They have very low viscosity compared to solid silicone rubbers.
- RTV (Room Temperature Vulcanizing) – Single or 2-component liquids that vulcanize at room temperature to form highly elastic silicone rubber.
Silicone's chemical structure allows for a spectrum of modifications that result in a variety of silicone products. Polymer modifications include:
- Methyl – The general-purpose workhorse
- Methyl Vinyl – Better compression set
- Phenyl – Improved low temperature
- Trifluoropropyl – Better solvent resistance (Fluorosilicone)