Silicone elastomers, also known as silicone rubbers, are a class of thermoplastic or thermosetting polymers that have gained widespread use in recent decades due to their unique properties and versatility.
What are Silicone Elastomers?
Silicone elastomers are polymers composed of silicone—a chain of alternating silicone and oxygen atoms, with organic side chains attached to the silicone atoms. They are produced through polycondensation reactions or hydrosilylation curing reactions from precursors like silicone fluids or Resins.
The main structural units that give silicone elastomers their distinct properties are polydimethylsiloxane (PDMS) backbones. PDMS backbones consist of repeating units of (CH3)2SiO that make the polymers highly flexible and amorphous at room temperature. The methyl groups that branch off from the silicone atoms make silicone elastomers thermally and chemically stable while also imparting hydrophobicity.
Some key properties of silicone elastomers that have made them an essential engineering material include:
- Heat resistance: Silicone elastomers can operate continuously in temperatures ranging from -55°C to 300°C. This makes them suitable for high-temperature applications.
- Weatherability: They are highly resistant to UV light breakdown and damage from exposure to sunlight, ozone, moisture and extreme pH levels.
- Flexibility: Silicone elastomers maintain pliability over a wide temperature range due to the flexibility of PDMS backbones.
- Biocompatibility: They are considered biologically inert and are used in numerous medical applications.
- Electrical insulation: Silicone elastomers have low dielectric constants and dissipation factors, making them great electrical and thermal insulators.
- Chemical resistance: They are not readily attacked by many organic solvents, acids, alkalis etc. rendering the polymers highly chemically resistant.
Major Application Areas
Thanks to their unique profile of properties, silicone elastomers have found numerous applications across various industries:
- Construction: Used in sealants, caulks, weatherproofing coatings and glass glazing sealants due to high weatherability.
- Automotive: Found in hoses, belts, gaskets, grease seals etc. owing to heat resistance and flexibility.
- Medical: Approved for use in prosthetics, wound care products, implants, drug delivery systems etc. given biocompatibility.
- Electrical: Used for potting, encapsulating and insulating applications like in motors, sensors due to great dielectric properties.
- Consumer goods: Enters into production of kitchen appliances, hair dryers etc. due to stablenature.
- Industrial: Adopted in tubes, diaphragms, rollers etc. for their chemical resistance.
Common Formulations and Processing
Silicone Elastomers formulations are commercially available in various two-component, addition cure systems. Pre-mixed and filled kits are also found containing catalyst, crosslinker and fillers. Curing can be accomplished in press molding or liquid injection molding. Extrusion is used to form tubing, profiles and seals using malleable silicone elastomer formulations. Understanding crosslinking chemistry and catalyst systems allows controlling the curing process.
Silicone elastomers have established themselves as a major synthetic polymer category due to their unique combination of properties. With advancements in catalyst technologies and new formulations, their performance characteristics will continue to improve. Emerging applications include use as dielectric elastomers in artificial muscles and smartRobotics. Biomaterial applications are growing due to increased biocompatibility. Overall, silicone elastomers will remain an essential material for the future as demands in high-performance industries intensify.
Silicone elastomers are highly specialized polymers with molecular structures rendering them heat resistant, weatherable, flexible and chemically inert. These distinctive material attributes have enabled their widespread usage in diversified industries from construction to medicine. As a versatile engineering material, silicone elastomers have moved from strength to strength over the years and continue making progress. Their future certainly looks bright with more enhancements and new adoption on the anvil.
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