Is Silicone a Rubber, Elastomer or Polymer? Find out with Silicone Engineering

You may have heard a number of terms for describing rubber-like materials such as polymers, elastomer and synthetics and thought what is the difference between them (if any at all)? Here we explain the difference between rubbers, synthetics, polymers and elastomers as well as focusing on our material – silicone. We explain what group silicone falls into to allow you to gain understanding when choosing a rubber material for application.

Rubber

Is essentially the original name given to Latex and is a natural product harvested from the rubber tree, shown in the picture below. Latex was the first “rubber-like” material invented and continues to be used in a number of applications today.

Rubber Tree

Rubber Tree

Synthetic

This just means something artificial or man-made. Synthetics are not naturally made unlike Latex.

Polymer

Is a large molecule made up of many repeated smaller units called monomers. A polymer can be natural or synthetic.

Elastomer

Is a polymer that displays elastic properties.

A part from Latex (the natural product), most elastomeric products fall into the category of “Synthetic Elastomer” the use of the word elastomer is used interchangeably with rubber nevertheless, Silicone is more correctly an “elastomer”.

What is an Elastomer?

As you can probably guess by our name, Silicone Engineering is a silicone elastomer manufacturer. This is where our expertise lies and has done since we first opened in 1959. In this section we will go into more detail about elastomers and in particular – silicone.

An elastomer is a polymer with viscoelasticity (having both viscosity and elasticity) and very weak inter-molecular forces, generally having low Young’s modulus and high failure strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber.

Each of the monomers which link to form the polymer is usually made of carbon, hydrogen, oxygen and/or silicon. Their primary uses are for seals, adhesives and molded flexible parts.

What is Silicone?

Silicone Elastomer, or to give it its scientific name – Polysiloxane, is an amazing material. It offers a unique combination of chemical and mechanical properties that organic elastomers cannot match.

Inorganic Synthetic Elastomer

To read a more indepth explanation of Silicone, please visit our What is Silicone guide.

Benefits of Silicone Elastomers

Silicone elastomers have many benefits over other elastomers. These include:

  • Excellent Environmental Resistance
    • Ozone
    • UV
    • General weathering (rain, snow, sleet, frost)
  • Low Compression Set
    • Good resistance to compression set at high temperatures
    • Great for sealing
  • High physiological inertness
    • Tasteless
    • Odourless
    • Non-toxic
    • Resistant to bacteria and fungi – neutraSil™

Negatives of Silicone Elastomers

Although having many benefits, silicone also has some negatives depending on what job you need the material to do or withstand.

  • Poor Abrasion
    • If you are looking for an elastomer with good abrasion properties then we would generally advise silicone is not your material.
    • Hence the reason you don’t see car tires or soles of shoes made from silicone as their lifespan would be short
  • Poor Oil/Petroleum Resistance
    • Silicone is prone to swelling if in contact with oil for a period of time.
    • In this instance we would suggest a Fluorosilicone be used due to its oil/petroleum resistance

To conclude, choosing the correct elastomer or rubber is very much down to the application and what job you need the elastomer to do. Silicone is an amazing material if high temperatures and environmental pressures are present but as explained it will most likely fail if oil/petroleum is in contact. Therefore selection is key to ensure long lifespan in service.

If you really aren’t sure which elastomer would suit your application or would like some information on our range of specialist silicone grades, one of our experts will be able to answer the question. You can send your question in by clicking on ‘Ask the Experts‘.

 

Understanding UL94v-0 : Silicone Rubber

UL94v-0 is a fire standard set by UL – an American worldwide safety consulting and certification company headquartered in Northbrook, Illinois. UL94V-0 is used to determine the flammability of a specified material and the burn time associated with it.

Why we test and measure to UL94v-0?

UL94v-0 is tested and measured to allow engineers to understand the flammability characteristics of a material, in this case silicone sponge/foam.

If the material passes and is verified by UL themselves, a material can then be used in specific applications where fire safety is of a critical nature.

fire

How UL94v-0 should be tested?

  • Five specimens firstly need to be prepared measuring 13mm (W) x 125mm (L). Maximum thickness should be 13mm
  • The test specimen needs to be clamped into a vertical position.
  • The Bunsen burner needs to have a flame height of 20mm.
  • The flame then needs to be applied to the bottom edge of the specimen, so that the top of the burner is 10mm lower than the specimen.
  • The flame is then applied for 10 seconds, moving the burner to allow for any movement of the specimen ensuring the flame keeps directly underneath the material.
  • After 10 seconds the flame is removed and the time is measured and recorded as to how long the specimen continues to burn for.
  • When the flame goes out the burner is reapplied to the specimen for a further 10 seconds.
  • Again the burner is removed after 10 seconds and time is recorded for how long the specimen continuous to burn for.

Requirements for a UL94v-0 Pass

  • The specimens should not have an after flame time for more than 10 seconds after either application of the test flame.
  • The total after flame time should not exceed 50 seconds for set of 5 specimens.
  • The specimens should not burn with flame or glowing up to the clamp.
  • The specimens should not drip flaming particles that ignite the cotton indicator.
  • The specimens should not have glowing combustion that persists for more than 30 seconds after the second removal of the test flame.

Market Considerations

There are many silicone rubber materials on the market that state a UL94v-0 rating however, unless the material has been officially approved by UL themselves and is listed on their database, the material must be checked to ensure it passes before using it in application.

Silicone Engineering’s UL94v-0 silicone sponge is listed on the UL Database

Also when selecting a UL94v-0 silicone material you must also take into consideration the thickness as UL verification only approve to certain thicknesses. For example, a silicone sponge material may be UL94v-0 approved to a minimum thickness of 12.7mm so any thickness lower than this would not be approved to UL and cannot be used for this purpose.

Where do UL94v-0 products get used

Generally, UL standards are used as a safety rating in a wide range of applications, from telephone receivers and computer screens to domestic ovens and hot water boilers. Whenever people are concerned about the hazards as a result of their product burning, then UL94 is becoming the most commonly referenced standard where there is no pre-existing industry norm.

Naturally, UL approved silicone parts are used where it is important that in the event of a fire, silicone would play its part in keeping the fire at bay. Silicone is usually laminated onto or becomes a part in a “composite” and it is this composite that needs to ultimately meet the UL standard for flammability.

Applications are too many to mention suffice to say that to enter into the American market, all household and domestic products such washing machines, televisions, vacuum cleaners as well as automotive and electrical/electronic wiring and components need to comply with UL at some point.

Industries where public safety is of the highest importance such as Rail, Automotive and Aerospace, UL94v-0 is seen as an essential safety standard. In the event of a fire would help to resist the flames, in turn reducing the risk of failure.

To find out more about Silicone Engineering’s range of flame retardant sponge materials click here

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