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)
Silicone Rubber Compounding from HEXPOL
- HCR Silicone, Fluorosilicones, and all Types of Silicone/EPDM Compounds
- Formulary with Hundreds of Compounds for Multiple Silicone Applications
- An Array of Physical Forms: Continuous Strips or Slabs, Preforms and Pigs-Rolls
- Silicones Pigmented to Almost any Color, Including Black, from Translucent to Opaque
- Strategic Raw Material Sources and Purchasing Relationships
- Compounds that Meet Typical Silicone Specifications & Standards
Silicone Elastomer Properties
Silicone’s strong silicon-oxygen chemical structure is the primary reason for the elastomer’s unique performance properties. As an inorganic elastomer, silicone rubber has chemical properties that make it ideal for providing extended service life in harsh environments and applications. These properties include:
- Weathering/Age Resistance – Because of its durability, silicone is able to withstand extremely harsh conditions and environments, resisting water, moisture, and steam.
- Thermal Stability – At extreme temperatures silicone can be far superior to conventional rubbers. It can operate normally from -75°C (-103°F) to +300°C (572°F).
- UV Resistance – Resists ultra violet light or sunlight, is oxidation resistant, maintains surface col- or and won’t fade.
- Low Volatility – Refers to a material’s tendency to vaporize. Silicones that maintain a desired, lower vapor pressure are less apt to vaporize. They retain softness indefinitely.
- Electrical Insulation Properties – Excellent insulating properties and flexibility. Silicone is nonconductive and maintains dielectric strength, exceeding all comparable materials in electrical applications.
- Elasticity, Pliability and Flexibility – High tear and tensile strength, elongation properties, and a durometer range of 5 to 80 Shore A.
- Microbial Resistance – Outstanding biocompatibility, silicone is odorless and tasteless, and can be formulated for medical products.
Industries and Applications
Silicone rubber gained widespread popularity in the 1960s and over the years has found to be the elastomer of choice in multiple industries. HEXPOL provides hundreds of custom and standard compounds used in industries such as:
- Transportation – Silicone components are used in automotive; light (pickup) and heavy trucks (semi); bus and rail mass transit; and aircraft to seal, insulate, and protect, providing safety, durability, and performance.
- Energy –Silicone delivers longer service life, resistance to extreme temperatures and higher pressure in oil & gas applications, as well as superior UV protection for solar and wind energy components.
- Building & Construction – Energy efficiency, structural protection, weatherproofing, window glazing and aesthetically pleasing attributes are some of the benefits provided by silicone.
- Wire & Cable – When flexibility, resistance to harsh environments, and insulating properties are paramount, silicone rubber is the right choice.
- Medical Technology – Silicone rubber is microbial resistant, clean, and traceable batch lot number, improving the performance of medical devices.