How is liquid silicone made
Liquid silicone has become an increasingly popular material in recent years due to its versatile properties and applications. As someone working in manufacturing, I am often asked - how exactly is this unique compound made? In this article, I will provide an in-depth look at the production process for liquid silicone, the key ingredients, safety considerations, and how it differs from regular silicone.
What is liquid silicone?
Liquid silicone is a type of silicone polymer that has a syrup-like consistency and can be cured into various rubber-like materials. The liquid form allows it to be easily injected or poured into molds before being heated to transform into flexible, durable silicone rubber parts and products.
Some key properties that make liquid silicone useful:
High heat resistance - can withstand temperatures from -45°C to 200°C continuously
Excellent electrical insulation
Biologically inert - does not react with body tissues
Resistant to water, oils, and oxygen
Can be made food safe and medical grade
Easily pigmented to achieve various colors
So how does this material go from liquid to rubber? The answer lies in the chemistry of silicone itself.
Is liquid silicone safe?
An important question when working with any chemical substance. The good news is - when properly formulated, liquid silicone is considered very safe. Food grade liquid silicones are approved by the FDA and other regulatory agencies for use in food and pharmaceutical applications.
The base silicone polymer itself is chemically inert and non-toxic. Additional ingredients may be added to produce specific properties, including:
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Catalysts to control the speed of transformation from liquid to cured rubber
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Fillers like silica to provide reinforcement
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Pigments if color is desired
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Anti-foaming agents
Reputable silicone suppliers follow strict quality control to ensure impurities are kept to extremely low levels. As long as precautions are taken when handling the uncured liquid, exposure risks are very low. Food grade silicones are made with the highest purity ingredients to prevent leaching of chemicals.
Is silicone made of plastic?
This is a common misconception - silicone itself is not a plastic. The polymeric structure of silicone is very different from plastic polymers. Plastics like polyethylene, PVC, polystyrene are made by stringing together monomers into long carbon backbones. These carbon chains are what give plastics their typical properties.
In contrast, silicone consists of a silicon-oxygen backbone which alternates between silicon and oxygen atoms. Organic methyl groups are attached to the silicon atoms. No carbon backbone exists in 100% silicone.
So while plastics and silicone can feel similar to the touch, the underlying chemistry varies greatly. Silicone exhibits much higher heat resistance and chemical stability due to its molecular configuration.
What is liquid silicone made of?
The basic components to produce liquid silicone are:
Silicone polymer with reactive side chains
This provides the main polymeric structure to create the rubber-like materials. Common choices are vinyl, hydrogen, and hydroxyl functional polymers.
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Cross-linking agents
These bind the polymer chains together to transform the liquid into an elastic solid. Typical agents include hydrosilane or vinylsilane molecules.
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Catalyst
A platinum based catalyst helps accelerate the cross-linking reaction without becoming part of the structure itself.
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Fillers
Reinforcing fillers like silica provide strength and viscosity control.
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Pigments
Coloring agents can be added if needed. Carbon black is commonly used.
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The polymer, cross-linker, and catalyst are essential to catalyze the transformation into silicone rubber. The fillers and pigments adjust the properties as needed for particular applications.
How are silicones manufactured?
The basic steps to produce liquid silicone are:
Synthesis of the silicone polymer. This takes place via a controlled polymerization process of the basic monomers of silicone - siloxanes. The functional side chains are incorporated during polymer synthesis.
Addition of fillers like silica or diatomaceous earth. High speed mixers disperse the fillers homogeneously.
Degassing under vacuum to remove entrapped air bubbles. This avoids porosity in the final cured parts.
Incorporation of cross-linking agents, catalysts, pigments, or other additives
Standard QC testing to verify viscosity, appearance, and cure rate meet specifications
Packaging into drums, totes, or pails.
The cured silicone rubber parts are then made by pouring or injection molding the liquid silicone and activating cross-linking under heat. Mold design is important to achieve proper flow and de-molding after cure.
What is the difference between liquid silicone and regular silicone?
The main differences between liquid silicone and regular cured silicone are:
Liquid silicone is in an uncured state. It can be poured and injected. Regular silicone is fully cured into a rubber-like solid.
The liquid has low viscosity, typically from 100 centipoise to 50,000 centipoise. Cured silicone is a flexible but non-flowing solid.
Liquid needs to be cured with heat and time to achieve full properties. Regular silicone is already fully cross-linked.
The liquid can be compounded into two parts that must be mixed to activate curing. Regular silicone requires no mixing or activation.
So in summary, liquid silicone represents the uncured polymer in liquid form before full cross-linking. This state allows processing into molds. Regular silicone is already fully cured in its final rubber-like form.
How are silicones manufactured?
Silicones are synthesized by carefully controlled polymerization of chlorosilanes or alkoxysilanes.
The basic process is:
Monomers like dimethyldichlorosilane are mixed with water in a reactor with solvents.
The reaction produces the silicone polymer with hydrochloric acid as a byproduct.
The polymers are separated, then stabilized with alkaline solution.
Further reactions produce cyclic and linear polymers of various chain lengths.
Separation processes purify and fractionate the desired molecular weights.
End-capping reactions attach the functional groups needed for curing.
Compounding adds fillers, cross-linkers, pigments to make the final liquid silicone or silicone elastomer.
Silicone manufacturers carefully control the polymerization to achieve the desired physical properties in the final silicone material. This allows tailoring silicone for applications from medical devices to sealants and lubricants.
Conclusion
We've explored how liquid silicone goes from basic chemical ingredients to versatile finished products. Careful polymer synthesis and compounding produces a stable, safe liquid that can transform into cured rubber parts. Silicone has unique properties unattainable with plastic, allowing it to withstand high heat and stress across many industries. Yet it starts as a simple reactive liquid formed into useful shapes. With an understanding of the chemistry and production processes, manufacturers can continue innovating with this amazing material into the future.
Rolifyx is a supplier specializing in R&D, production, sales, service, and operation of silicone polymer materials. It continues to provide customers with silicone materials, novel technologies, and high-quality products and can customize them according to customer needs. It allows liquid silicone to be better modified and provides the best solution for customer needs.
In particular, it has outstanding advantages in innovative organic liquid foam rolls, sheets, foamed silicone strips, foamed silicone rings, thermal conductivity, potting, sealing, room temperature vulcanization rubber, research and production technology, etc.