What is silicones’ temperature range?

Here at Viking extrusions, a common question that we get asked is ‘what temperatures can silicone withstand?’ Well, there

Here at Viking extrusions, a common question that we get asked is ‘what temperatures can silicone withstand?’ Well, there is not exactly a definitive answer as they have so many unique and general purposes.

Silicone rubber can withstand extreme temperatures, whereas other polymers such as polyurethane, nitrile and polyacrylate can not. Being able to withstand both low temperatures and high temperatures is truly what helps it to stand out amongst other rubbers.

How hot can silicone get before it melts?

 

Due to its impressively wide temperature range, silicon does not melt as a result of temperature alone.

Most plastics begin to melt when met with high temperatures. Silicone, however, exhibits unique behaviour when in high-temperature environments. Silicone does not have a melting point but instead remains solid until combustion occurs. At extreme temperatures (above 200 C) silicone slowly begins to lose its mechanical properties, becoming harder and more brittle.

This process is further accelerated when met with even higher temperatures of over 300 C. While there is no set temperature for high-temperature silicone auto ignition, it generally occurs at around 450 C.

What is silicone made of?

 

When discussing the temperature range of silicone, it is important to understand how the material is made and what the material is made of.

Silicon is a synthetic polymer made from the chemical element silicon. Silicon is the raw chemical element and silicone is the rubber material.

Silicon is most commonly found as silica which is an oxide of silicon. While primarily derived from silicon, the silicone formulation also includes hydrogen, carbon and oxygen.

In order to make silicone, silicon and silicon dioxide compound silica must be isolated from each other. To do this they heat quartz sand to temperatures up to 180 C. Then there are multiple processes to go through where silicon and methyl chloride are combined and heated. It is then distilled into a polymerised siloxane known as polydimethylsiloxane which can then be polymerised.

What are the other advantages of silicone rubber?

 

Silicone is used across a huge variety of different industries and products. Silicone products can are used in everyday life on a daily basis in everything from the caulk sealants around your bathtubs to the gaskets and sealants around your home appliances.

Silicone is so common due to its many unique properties such as:

  • Extreme durability – it’s flame-retardant and excellent resistance to heat help silicone to be impressively durable.
  • Low thermal conductivity
  • Elastomer – This means that they can stretch and return to their original form.
  • Repels water – this is brilliant for making watertight seals and gaskets.

Silicones behaviour during combustion

 

Silicone’s behaviour throughout the combustion process is very unique. Once the temperature of autoignition (around 450 C) has been reached the heat-resistant material will begin to smoke before cracking and combusting. At this point, the silicone will expand in volume and release volatiles. Following this, brittle, combusted materials will break away and disintegrate into a fine powder.

During combustion, both silicone and carbon dioxides are produced with the carbon monoxides and carbon dioxides being released into the atmosphere. The silicon dioxide, on the other hand, creates a white powder and acts as an insulating layer that helps slow down and prevent further combustion.

What temperatures can different grades of silicone withstand?

 

General Purpose Silicones – General purpose silicones like silicone sealants and gaskets tend to have a high-temperature limit of around 200 C to 250 C and also lower temperatures of -50 C to -75 C. This makes silicone the perfect material for applications with extreme temperature requirements.

Heat stabilised silicone – Heat stabilised silicones contain additives that increase their maximum operating temperature to 260°C.

High-temperature silicone – High-temperature grades of silicone contain additives that make them suitable for applications up to 300°C for intermittent periods. If the part is to be exposed to continuous temperatures over 300°C then the silicone’s properties would degrade with time.

Flame retardant silicone grades – Flame retardant grades can withstand intermittent temperatures up to 220°C (depending on the specific grade). These materials contain additives which enhance silicones’ self-extinguishing properties. A variety of flame retardant grades are available specifically formulated to meet standards such as:

  • UL94-VO
  • EN45545-2
  • CS 25.85

For detailed information on all of the silicone grades we offer, visit our technical datasheets page.

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