Elastomers compared - properties and structure

Elastomers are among the most important material groups in plastics engineering. They combine the flexibility of rubber with the technical performance of modern plastics. Their ability to deform greatly and then return almost completely to their original shape makes them indispensable materials in modern industry.

Whether in seals, vibration elements, membranes or flexible lines – elastomers ensure functionality, tightness and durability in numerous technical applications. In addition, their resistance to ageing, weathering and chemicals makes a decisive contribution to the reliability of machines and systems.

What are elastomers?

Elastomers are macromolecular materials with a special structure that gives them their characteristic, rubber-like behaviour. They consist of long, flexible polymer chains that are linked to one another by point-like chemical bridges – so-called crosslinks. These connections act like tiny elastic springs that pull the material back into its original shape as soon as the load subsides. As a result, elastomers can be stretched or compressed greatly without leaving permanent deformation.

An essential characteristic is their ability to undergo reversible deformation: when tension or compression is applied, the molecular chains align along the load, and afterwards – thanks to the crosslinking points – return to their disordered original position. This property fundamentally distinguishes them from brittle or meltable plastics.

In contrast to thermoplastics, which melt when heated and can therefore be shaped at will, elastomers retain their shape even at high temperatures until thermal degradation. They therefore do not melt, but decompose when the energy input becomes too great. They thus represent the third major material group in plastics engineering – alongside thermoplastics and thermosets.

Their mechanical properties are also unique: elastomers are soft, flexible, energy-absorbing and exhibit strongly non-linear elongation behaviour. This makes them particularly suitable for dynamically stressed components that must absorb vibrations or ensure sealing. Their high damping capacity protects machines and components from vibrations, while their elasticity compensates for material stresses.

In addition, many types of elastomer offer excellent chemical resistance to oils, greases, weathering, ozone and UV radiation. This combination of elasticity and resistance makes them key materials in virtually all technical industries.

Origin and types

The basis of many elastomers is natural or synthetic rubber. Vulcanisation, i.e. chemical crosslinking with sulphur or other reaction partners, produces the characteristic rubber-like structure. Well-known elastomer types are:

• EPDM (ethylene propylene diene rubber): excellent weathering and ozone resistance, frequently used outdoors.
• NBR (nitrile rubber): resistant to oils, fuels and greases, ideal for seals in hydraulic systems.
• CR (chloroprene rubber, neoprene): good flame retardancy and weathering resistance.
• FKM (fluoro rubber, Viton): extremely temperature- and chemical-resistant.
• VMQ (silicone rubber): high elasticity over a very wide temperature range.

Each of these materials has its own particular strengths, which is why the right elastomer should always be selected depending on the application.

Structure and chemical composition

The structure of elastomers is based on a network-like molecular framework that ensures both mobility and stability. Their polymer chains usually consist of saturated or unsaturated hydrocarbons, whose length and chemical composition are decisive for the material properties. Between the chains lie crosslinking points, which are formed by sulphur, peroxides or silicone bonds. These fix the molecular framework and prevent the chains from shifting against one another permanently.

Elasticity depends heavily on the density of these crosslinks: a low degree of crosslinking leads to soft, highly stretchable materials, while a high degree of crosslinking leads to stiffer but more dimensionally stable materials. In addition, fillers (e.g. carbon black or silica) influence hardness, colour, electrical conductivity and abrasion resistance.

Chemically, elastomers form an intermediate form between thermoplastic polymers and thermosets. This unique crosslinked structure is the key to their dimensional stability – it enables elastic behaviour without flowing or melting.

Molecular structure in detail

Each polymer chain in an elastomer is long, flexible and arranged in a random, coiled configuration. Under mechanical load, for example through stretching or compression, the chains straighten in the direction of the load and store potential energy in the process. After the load is removed, they return to their original configuration through thermal motion – the material fully regains its shape.

This process explains entropic elasticity: the restoring force does not arise primarily from chemical bonding, but from the statistical tendency of the molecular system to restore a state of maximum disorder. This behaviour is the reason why elastomers are soft yet at the same time dimensionally stable.

Modern simulations at the molecular level show that even small changes in the polymer structure – for example in the side-chain length or in the crosslinking pattern – can have major effects on elasticity, fatigue strength and temperature resistance. Precise formulations and controlled crosslinking processes are therefore decisive for reproducible properties.

Properties and mechanical behaviour

Elastomers exhibit complex elongation and stress behaviour that lies between that of a solid and that of a viscous liquid – this is referred to as viscoelastic behaviour. Important characteristic values are:

Property	Typical value / range	Remark
Elongation	up to 1000 %	depending on degree of crosslinking and filler content
Restoring capacity	>95 %	almost complete return after unloading
Temperature range	–50 °C to +250 °C	depending on elastomer type (e.g. silicone particularly heat-resistant)
Hardness	10–95 Shore A	controllable via formulation
Density	0.9–1.4 g/cm³	depending on fillers
Chemical resistance	high	to oils, greases, ozone and acids
Ageing resistance	variable	can be improved by additives

Elastomers react sensitively to environmental influences such as ozone, UV light or oxygen, which can lead to embrittlement. Targeted addition of additives – for example carbon black, waxes or stabilisers – can greatly delay this ageing.

Differences between elastomers and thermoplastics

The central difference lies in thermal behaviour. Thermoplastics can be reshaped and melted again by heat – a process that is not possible with elastomers. These have a fixed, permanent crosslinked structure.

Characteristic	Elastomers	Thermoplastics
Molecular structure	widely crosslinked	linear or branched, uncrosslinked
Deformability under heat	non-meltable, rubber-elastic	meltable, reshapeable
Restoring capacity	very high	limited
Hardness range	soft to medium-hard	from soft to hard
Processing	vulcanisation, pressing, injection moulding	extrusion, injection moulding, thermoforming
Recyclability	difficult	very good
Chemical resistance	very high	varies
Typical applications	seals, hoses, bearings	housings, sheets, profiles

Due to their structure, elastomers form the middle ground between soft thermoplastics and hard thermosets – flexible, but dimensionally stable.

Practical examples from industry

In the automotive industry, elastomers are indispensable. They are used in engine mounts, seals, tyres, vibration dampers, door profiles and hoses. Their function is to compensate for temperature and vibration fluctuations, prevent leaks and decouple components. Without elastomers, many comfort and safety functions – such as quiet vehicle cabins or vibration-free steering – would not be feasible.

In mechanical and plant engineering, elastomers ensure reliable energy and force transmission, e.g. in couplings, belt drives or bearings. Their high damping capacity protects sensitive components, extends service life and reduces maintenance effort.

In electrical engineering, elastomers serve as insulating materials and housing seals. Silicone and EPDM in particular are used in connectors, sealing caps and high-voltage components due to their high temperature and ageing resistance.

In medical technology, silicones are widely used due to their biocompatibility and physiological safety. They are used in catheters, breathing tubes, membranes and valves. Their chemical stability ensures that no undesirable reactions with medicines or body fluids occur.

Elastomers also play a key role in the construction sector: joint profiles, roofing membranes and membranes made of EPDM or CR permanently protect buildings from moisture, UV radiation and temperature changes.

Industrial processing and quality standards

The industrial processing of elastomers requires precise process control. Typical processes are compression vulcanisation, injection moulding, extrusion and calendering. The temperature is usually controlled between 150 and 200 °C to ensure complete vulcanisation. The crosslinking time varies depending on the elastomer type, component thickness and the catalyst used.

DIN and ISO standards are of central importance for quality assurance, for example:

• DIN ISO 37 – tensile test for elastomers (determination of tensile strength and elongation at break)
• DIN ISO 48-4 – hardness testing (Shore A and IRHD)
• DIN ISO 815 – determination of compression set
• DIN ISO 34-1 – tear strength of elastomers
• DIN EN ISO 1817 – resistance to liquids

These standards ensure consistent material quality and comparability between manufacturers. In addition, special tests for ageing resistance, chemical resistance or thermal stability are carried out to ensure the suitability of the material for the respective application.

Future prospects: intelligent elastomers

Research already provides impressive examples of the practical application of so-called smart elastomers. A particularly dynamic field is soft robotics, where electroactive polymers serve as artificial muscles that move or bend when electrical voltage is applied. This creates flexible, sensitive movements – ideal for medical gripper arms or adaptive manufacturing systems.

Industrial partners are likewise working on adaptive sealing systems that react to pressure or temperature changes. Such elastomers automatically adapt their shape or hardness in order to prevent leaks and increase efficiency. These developments show that intelligent elastomers are not merely theoretical concepts, but are already being tested in research and industry.

Materials research is currently developing intelligent elastomers that can react to external stimuli – so-called smart materials. These materials change their shape, hardness or conductivity depending on temperature, light, magnetic fields or electrical voltage. Examples are electroactive polymers that can move as artificial muscles or actuators in robotic systems.

Another approach is self-healing elastomers, which independently repair their structure in the event of mechanical damage through reversible chemical bonds. Such systems could drastically increase the service life of components in aviation, in sealing systems or in safety-critical applications.

Smart elastomers also open up new possibilities in the area of sustainability of engineering plastics: they can detect ageing effects themselves, take on sensor functions or communicate their condition digitally – an important step towards predictive maintenance and Industry 4.0.

Elastomers as a key material of the future

Elastomers combine a unique combination of elasticity, chemical resistance and dimensional stability. Their molecular crosslinking makes them robust yet flexible materials that are indispensable in virtually all technical industries. The difference from thermoplastics lies in the irreversible crosslinking, which keeps their shape stable even at high temperatures.

With new technologies, such as intelligent and recyclable elastomer systems, their importance in industry will continue to grow. In future, elastomers will not only damp or seal, but also react actively, store energy and process information. They are thus developing from a classic sealing material into a multifunctional high-tech material that bridges the gap between mechanics, electronics and sustainability.

FAQ

What are typical elastomers? EPDM, NBR, CR, FKM, silicone and natural rubber are among the most important representatives.

How do elastomers differ from thermoplastics? Elastomers are chemically crosslinked and non-meltable, while thermoplastics are meltable and can be reshaped multiple times.

What advantages do elastomers offer in industry? They damp vibrations, compensate for tolerances, are resistant to ageing and retain their shape even under changing temperatures.

Are elastomers recyclable? Only to a limited extent – however, devulcanisation and new TPE developments are increasingly making recycling options possible today.

What are thermoplastic elastomers (TPE)? A modern hybrid class that combines elasticity with thermoplastic processability – ideal for efficient, sustainable series production.