The science of silicones
What are Silicones?
Silicones are high-performance oligomers or polymers that can take a variety of physical forms, ranging from solids to water-thin liquids and semi-viscous pastes, greases and oils. They are noted for their ability to function in conditions that most conventional materials would not withstand.
Silicones are produced by reacting silicon—one of the earth’s most common elements- with methyl chloride and further reaction with water which removes the chlorine atom. This reaction mainly produces linear and cyclic siloxanes characterized by a chain of alternating silicon and oxygen atoms. Siloxanes are then further reacted into longer chains to form silicone polymers.
Where do silicones come from?
Silicones are essentially organically modified quartz. Silicon quartz consists of silicon and oxygen atoms. In the making of silicones, two oxygen atoms attached to every silicon atom have been replaced by methyl groups.
Silicon is a chemical element widely distributed on earth in various combinations with oxygen only (silica) or oxygen and other elements (silicates). Silicon is the second most abundant element on the earth’s crust after oxygen (approximately 28% by mass) and it naturally forms long-lived, stable compounds. In many biological systems silica is an essential element of mechanical structures.
Silicon is always found in chemically and thermally stable mineral combinations but never in its pure form. Silicon is the key to all silicone chemistry as its atomic structure dictates the properties of silicones.
How is silicon obtained?
Today elemental silicon is obtained through the electro-thermic reduction of SiO2 with carbon at 1,400 degrees Celsius.
Elemental silicon is dark grey, metallic shiny, hard, and brittle. It has a melting point of 1,423°C and a boiling point of 2,630°C. Like carbon, silicon has a crystalline structure, similar to that of diamonds. Read more about the similarities and differences between silicon and carbon in our factsheet.
SiO4 – the structure of silicon quartz
What are D4, D5, D6?
Cyclic siloxanes (cyclosiloxanes) are basic members of the broad family of silicone materials. All silicone materials share a common chemistry but each substance is different when it comes to its properties and use.
A common denominator for cyclosiloxanes is that they contain repeating units of silicone (Si) and oxygen (O) atoms in a closed loop, giving it a “cyclic” structure. The three most common cyclosiloxanes in commercial production are D4, D5 and D6.
Octamethylcyclotetrasiloxane (D4), contains four repeating units of silicone (Si) and oxygen (O) atoms in a closed (cyclic) loop.
Where is it used?
D4 is an odourless, colourless liquid mostly used as an intermediate or basic raw material in the production of silicone rubbers, gels and resins. When used as an intermediate during the manufacturing process, virtually all D4 is consumed with only a tiny amount remaining in final products.
Decamethylcyclopentasiloxane (D5), contains five repeating units of silicon (Si) and oxygen (O) atoms in a closed (cyclic) loop.
Where is it used?
D5 is an odourless, colourless liquid mostly used as an intermediate or basic raw material in the production of silicone rubbers, gels and resins. When used as an intermediate during the manufacturing process, virtually all D5 is consumed with only a tiny amount remaining in final products.
D5 can be added as an ingredient in silicone mixtures used in cosmetic applications such as skin creams and sunscreen, where it may be labelled "cyclomethicone" or "cyclopentasiloxane". D5 can also be used as a dry-cleaning solvent in closed systems, which significantly limits exposure to workers, consumers and the environment.
Dodecamethylcyclohexasiloxane (D6), contains six repeating units of silicon (Si) and oxygen (O) atoms in a closed loop, giving it a "cyclic" structure.
Where is it used?
D6 is also an odourless, colourless liquid mostly used as an intermediate or basic raw material in the production silicone rubbers, gels and resins. When used as an intermediate during the manufacturing process, virtually all D6 is consumed with only a tiny amount remaining in final products.
D6 can also be used as an ingredient in silicone mixtures used in cosmetic applications such as skin creams and sunscreen, where it may be labelled "cyclomethicone" or "cyclohexasiloxane".
How are silicones made?
Obtain & GRIND silicon
REACT
React silicon metal to make chlorosilanes
SEPARATE
Separate (distill) chlorosilanes
React with water and strip
SEPARATE
Separate (distill) siloxanes
Polymerise
Silicones have countless performance qualities
They play an increasingly important role supporting improvement, innovation and progress in a wide range of industry sectors, from automobiles to electronics to textiles. In essence, silicones make things work better. Their main characteristics can be divided according to the following concepts.
Adhesion
Adhesion
Stability
Stability
Insulation
Insulation
Lubrication
Lubrication
Foam control
Foam control
Surface protecting
Surface protecting
Spreading
Spreading
Biological compatibility
Biological compatibility
Forms of silicones
LIQUID/OIL
GEL
RUBBER
FOAM
SOLIDS
What are the major uses of Silicones?
The distinctive aspects of Silicones make them one of the world’s most important and adaptable raw materials, used in literally thousands of products and applications – from healthcare, aerospace and personal care, to electronics, transportation, construction and energy.
To read more about uses and benefits of silicones, click here.
FIND OUT MORE
Good manufacturing practices for organosilicon materials intended to come into contact with food
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