What Are Silicone Elastomers – The Complete Guide

Elastomers are a broad category of materials demonstrating elastic properties. As such, when subjected to stress, they can deform but return to their original form upon removal of the stress.

Silicone elastomers share certain aspects with rubber but are silicon-based.

Silicone elastomers can also be combined with other polymer material and additives such as crosslinkers, reinforcing agents and catalysts.

In this guide, we will explore everything about these types of silicones – let’s dive right in:

Advantages of Silicone Elastomers

A Network of Silicone Elastomers
A Network of Silicone Elastomers

Different applications across multiple industries utilize silicone elastomers in one form or another. You can credit this to the outstanding characteristics of silicone elastomer:

  • When you subject silicone elastomers to high temperature, you observe it performs remarkably well by maintaining its appearance. They are therefore suitable where heat exposure is high like in automotive engines, cookware and industrial seals.
  • Silicone elastomers remain unaffected when exposed to chemical substances. Their chemical inertness allows use where there is high exposure to harsh chemicals like in laboratories and chemical processing plants.
  • Another advantage of utilizing silicone elastomers is their excellent electrical insulation properties. They can effectively isolate electrical components offering protection against electrical shocks, ideal in electrical applications.
  • Silicone elastomers have low compression set easily recovering their original shape after being subjected to compression. This property is crucial in sealing applications where gaskets and O-rings under prolonged pressure can otherwise leak.
  • These materials can withstand repeated friction and with minimal wear ensuring long-term performance. This allows for their use where wear and tear are a performance concern.
  • Silicone elastomers resist water entry through absorption ideal in environments with high moisture content. Consequently, silicone elastomers maintain their integrity and performance in such situations allowing use in underwater applications.
  • The weatherability exhibited by silicone elastomers is such that it can maintain its properties after prolonged exposure to the elements. The formidable performance of silicone elastomer when exposed to sunlight or moisture allows for its application outdoors.
  • Silicone elastomers are biocompatible as their interaction with living tissues is with minimal risk of adverse reactions. They therefore find use in medical and healthcare applications such as implants, medical tubings and prosthetics.
  • While sustained ozone exposure can degrade and crack ordinary rubber materials, silicone elastomers exhibit resistant to ozone damage. Even with sustained exposure in outdoor environments registering high ozone levels, silicone elastomers maintain their structural integrity and performance.
  • Silicone elastomers have an impressive display of mechanical properties including rigidity and toughness. Their ability to withstand mechanical stress and deformation allows application where there is repeated bending, stretching, and impact.

Synthesis of Silicone Elastomers

Depending on the desired end qualities of silicone elastomers, the processing technology can take different forms. In synthesizing silicone, silicone monomers containing silicon atoms are bonded to methyl or phenyl organic groups. The reactive groups in the silicone monomers induce the hydrolysis and condensation processes.

During hydrolysis, silicon bonded with oxygen reacts with water forming silanol groups with either acid or base-based catalyst. A condensation reaction follows in which these substances form polymer chains with water as a byproduct in what is referred to as polymerization.

When the desired molecular weight is achieved, the reaction is quenched by adding terminating agents or cooling. Other additives can be added in additional processes like purification and dying to result in silicone elastomers with differing characteristics.

Formation of Silicone Elastomers
Formation of Silicone Elastomers

Types of Silicone Elastomers

The process used in synthesizing silicone elastomer ideally concerning the temperature and straight chain molecule will determine the type.  Each silicone elastomer type is tailored to for certain applications.

Heat Cured Rubber (HCR)

When in an uncured state, heat cured rubber is in solid form. Consequently, subjecting it to heat curing converts it into the desired state.  uncured form requiring heat curing to attain final properties. During the curing process, the material is brought to a stable state by heating to elevated temperatures for a defined period.

Heat Cured Rubber Curing Mechanism
Heat Cured Rubber Curing Mechanism

Liquid Silicone Rubber (LSR)

This is a two-part, platinum-cured elastomer of low molecular weight usually in liquid form until curing at elevated temperatures. LSR typically constitutes a base polymer, platinum catalyst and cross-linker finding use in electronics, medical devices and automotive components.

Liquid silicone rubber offers excellent tear strength, optical clarity, biocompatibility, and stability across a wide temperature range. Owing to its liquid state, LSR allows for high-volume production and reduced material wastage.

Liquid Silicone Rubber Process
Liquid Silicone Rubber Process

Room Temperature Vulcanization (RTV)

Silicone elastomers of this classification are cured at room temperature through cross-linking reaction catalyzed by moisture. Usually with soft to medium hardness, these elastomers offer the advantage of simple processing owing to low temperature curing.

RTV silicone can be made to different flexibility levels, hardness and chemical resistance. Common use of this elastomer is in sealing applications in aerospace and electronics, casting, and mold making.

Room Temperature Vulcanization Molecular Formula Overview
Room Temperature Vulcanization Molecular Formula Overview

Reinforcing Agents and Additives Used for Silicone Elastomers

Adding additives and reinforcing agents to silicone elastomer ensures achievement of specific characteristics or performance standards. Some of the parameters that can be altered include viscosity, pot life, hardness, conductivity, permeability and color.

Fillers

Fillers can be reinforcing or non-reinforcing, the former enhancing mechanical properties while the latter serving purposes beyond mechanical enhancement. Pyrogenic silica is a reinforcing filler that improves the silicone elastomer’s mechanical properties (tensile strength, tear resistance, abrasion resistance).

It is hydrophilic with a highly porous structure and hence large surface area, that facilitates strong polymer interactions enhancing stiffness. Furthermore, it regulates viscosity allowing use in coatings, sealants and adhesives.

Quartz occurs naturally as a form of silicon dioxide with a crystalline structure boasting larger particles than pyrogenic silica. As a non-reinforcing filler, it offers benefits other than enhancing mechanical properties like density control.

Crosslinkers

You can crosslink silicone elastomers with peroxide crosslinkers and platinum catalysts to enhance mechanical and thermal stability and also elasticity. Common peroxide crosslinkers used include dicumyl peroxide and benzoyl peroxide with the choice dependent on factors like curing temperature and rate.

Platinum catalysts are organometallic compounds with platinum strains alongside ligands like phosphines. They facilitate hydrosilylation reaction, which crosslinks polymer chains forming a three-dimensional network structure that enhances elasticity and mechanical strength.

Flame Retardants

Flame retardants help reduce flammability and improve fire resistance of silicone elastomers. They can be halogenated, phosphorus-based, inorganic, or nitrogen-based with their effectiveness dependent on factors like compatibility with other additives and chemical composition.

Flame retardants may act in different ways such as forming protective char layers, diluting flammable gases and interrupting combustion reactions. They can also release non-combustible gases to suppress flame propagation or cool the material surface.

Stabilizers

Adding stabilizers to silicone elastomers enhances resistance to degradation caused by oxidation, heat and UV radiation. Stabilizers enhance performance and extend the lifespan of silicone elastomers.

Heat stabilizers like phosphites help retain silicone elastomers’ color stability, mechanical properties and overall performance upon exposure to high temperatures. UV stabilizers work by absorbing or scattering UV radiation and include benzophenones, hindered amine light stabilizers and benzotriazoles.

Oxidation stabilizers protect silicone elastomers by inhibiting oxidation reactions caused by exposure to oxygen forming free radicals. This helps extend the elastomer’s lifespan while retaining its physical properties. Some common oxidation stabilizers include thioethers and hindered phenols.

Pigments and Colors

The high transparency offered by silicone elastomers allows for the addition of pigments to impart desired color or opacity. When selecting pigments for silicone elastomers, consider color stability, heat stability, chemical compatibility, opacity and coverage.

Pigments can be organic of synthetic or natural extraction, bearing chemical structures that absorb certain light wavelengths resulting in coloration. They can also be inorganic to allude their mineral-based origin with a broad spectrum offering excellent lightfastness and chemical stability e.g. metal oxides.

Characteristics of Silicone Elastomers

Silicone elastomers display strong bond and chemical structure formed by the high bond energy between silicon and oxygen molecules. The result is their ability to possess different viable properties ideal in different applications.

  • Excellent Mechanical Properties: Silicone elastomers can withstand deformation without permanent damage, owing to their resilience, high tear strength and elasticity.
  • Low Chemical Reactivity: These materials are less likely to react on interaction with other chemicals resisting the effects of acidic or basic elements.
  • Oxidation, Ozone and Radiation Resistance: Silicone elastomers resist degradation caused by sustained exposure to sunlight, oxygen and ozone when implemented in outdoor environments. This is thanks to their stable molecular structure and crosslinked network.
  • Low Temperature Flexibility: Their low glass transition temperature ensures silicone elastomers remain flexible and resilient at low temperatures from -100°C to -60°C.
  • Insulation Properties: Silicone elastomers demonstrate high dielectric strength, low dielectric loss, and resistance to tracking and arcing contributing to reliable insulation performance.
  • Insulation Properties: Silicone elastomers demonstrate high dielectric strength, low dielectric loss, and resistance to tracking and arcing contributing to reliable insulation performance.
  • Optical Transparency: You can synthesize silicone elastomers to allow light passage for specialized use in optical lenses and LED encapsulation.
  • Wide Temperature Range: Silicone elastomers can withstand extreme temperatures ranging from as low as -50oC to as high as 250oC . They also demonstrate impressive thermal oxidation resistance when exposed to elevated temperatures for extended periods.
  • Non-stick and Non-adhesive Properties: The low surface energy possessed by silicone elastomers gives it excellent non-stick properties allowing use in cookware and mold-making.
  • Low Toxicity: Silicone elastomers do not leach harmful chemicals when in contact with living tissue making them non-toxic and biocompatible.

Applications of Silicone Elastomers

Silicone elastomers find application in high-performance environments where similar polymeric materials are ineffective. Their use is prevalent across a diverse range of industries, thanks to their unique property combination, contributing to improved performance and reliability.

Automotive

Seals, gaskets, O-rings, and ignition cables used in automotive applications utilize silicone elastomers for their excellent temperature resistance, flexibility, and durability. They are also implemented in engine components like intake hoses, fuel system valves and grommets.

Aviation & Aerospace

Their resistance to extreme temperatures, fuels, lubricants, and hydraulic fluids sees the extensive use of silicone elastomers for sealing critical components. These materials are also featured in thermal protection systems and insulating electrical components.

Consumer Goods

From cookware, to care products and electronics, silicone elastomers use in consumer goods is ubiquitous. Their heat resistance and nonstick properties in cooking equipment, bio compatibility in cosmetic products and insulation and flexibility in electronics.

Healthcare

Silicone elastomers find use in catheters, medical tubing, prosthetics, and surgical implants where there’s direct contact with the body. This is thanks to their soft texture, biocompatibility and hypoallergenic properties, allowing use in sensitive medical applications.

Energy

Use of silicone elastomers in power generation, transmission, and distribution systems is down to their insulation, dielectric, thermal and degradation resistance qualities. These materials find application as sealants and encapsulants, in renewable power generation and oil industry.

Conclusion

If you are looking for high quality silicone elastomer manufacturer from China, LEGENDAY offer a wide range of options depending on your application requirements. From HCR, LSR to RTV silicone elastomers, we are the trusted supplier in China.

 

 

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