Chemical resistance

Acids and bases

Silicones are generally well resistant to diluted acids and bases, but can be damaged by strong, concentrated versions. Experiments show that silicones offer high resistance to diluted hydrochloric acid (2 mol/l), but that concentrated hydrochloric acid (10 mol/l) attacks some silicones. Silicones are also resistant to diluted caustic soda (2 mol/l), while concentrated caustic soda (50%) can attack some silicones.

Organic substances

Silicones are strong against animal and vegetable oils and against aliphatic, aromatic and oxygenated fuels. However, they do not cope well with ketones, paint solvents and certain esters and ethers. Tests show that silicones can swell in petrol. Acetone has a less strong swelling effect but still attacks silicones.

Solvents

In general, silicones are well resistant to many solvents, but they can have problems with halogenated hydrocarbons. On exposure to acetone and a number of other hydrocarbons, silicones can experience a serious effect.

Other substances

Silicones are well resistant to ammonia, silicone oil and many coolants. They are also well resistant to many types of alcohol. The resistance varies from excellent to a serious effect, depending on the substance.

Physically active substances

Substances that do not react directly with silicones but can make them swell, such as hydrocarbons, can affect the properties. The resistance depends on the polarity and the degree of cross-linking.

Temperature resistance

High temperatures

Silicones are very well resistant to heat, with a temperature range of about 200 to 230 degrees Celsius. Some special silicones can even withstand up to 300 degrees Celsius. Above 200 degrees Celsius, however, the material can start to break down. By adding special substances, silicones can better withstand heat.

Silicone oils also break down under prolonged heating. In contact with air, water, carbon monoxide, carbon dioxide and formaldehyde can then form. In the absence of air, that is, in closed spaces, cyclic silicones can form, in particular D3 and D4.

Low temperatures

Silicones remain flexible at low temperatures, down to about -60 degrees Celsius.

Breakdown

At high temperatures and in the presence of oxygen, silicones can become harder. Without oxygen, hydrolysis can occur, where the silicone chains break down and the material becomes softer. Special substances can be added to reduce this breakdown, especially when used without air.

Other properties

Strength

Silicones have a hardness of 0 to 80 Shore A, a tensile strength of 200 to 1500 PSI and can stretch between 100% and 480%. Their resistance to tearing is moderate to good, as are their flexibility, impact resistance and resilience. Vibrations are absorbed well and gas can pass through reasonably well. The friction resistance of silicones is often considerably lower than that of other elastomers.

Environment

Silicones are excellently resistant to ozone, oxidation, sunlight, weather influences and water. They have little odour and can be made in many colours.

Additives

Various substances can be added to improve silicones. For example, ELASTOSIL AUX stabiliser H can increase the heat resistance to 300 degrees Celsius. ELASTOSIL Farbpaste FL can improve the heat resistance of certain silicones. Special silicones such as ELASTOSIL R 756 and ELASTOSIL R plus 4450 perform better at high temperatures.

Surface treatment

For special purposes, silicone cables can be covered with substances such as Teflon, so that they can resist almost all chemicals.

Table of everyday chemicals and silicone resistance

In general, silicones are versatile with a good balance between chemical and thermal resistance, but they also have limitations depending on the circumstances. Consider this information as a starting point and test yourself whether silicones are suitable for your process.