Elastomers belong to the group of plastics and are therefore assigned to the general term polymer. Since elastomers represent a special group of plastics, we will explain everything that is important to you below.
What is an elastomer?
As already mentioned, elastomers are plastics. It is important to note, however, that they are singular. Together with thermosets and thermoplastics, they form the three most important groups of polymers.
The extraordinary thing about elastomers is that although they are dimensionally stable plastics, they are also elastic. They can be stretched to more than twice their length and therefore also have the property of rubber elasticity.
The glass transition point is the temperature at which a polymer changes from a solid to a rubbery or viscous state. In the case of elastomers, this temperature is even below room temperature.
How is an elastomer structured?
This type of polymer belongs to the group of organic substances. They have long-chain carbon-based macromolecules. Compared to thermosets, the density of cross-linking of the molecules is lower. If you start to pull the elastomer, however, from a certain point it behaves exactly like a thermoset. However, in order to be stretched, elastomers require an input of energy, which is generated by Brownian motion.
Thermal properties of elastomers
They react particularly strongly to temperature changes. At a rather lower temperature, they are not stretchable. Instead, they tend to be in a hard and brittle condition. At this point, the material is cross-linked by weak physical bonds. These include, for example, the van der Waals interactions or hydrogen bonds.
Mechanical properties of elastomers
From a mechanical point of view, it is again similar to thermoset. When heat is added to the elastomer, typical elastic behavior begins to show. The higher the temperature, the more stretchable the plastic becomes. If it gets too hot, the bonds begin to separate and the material breaks down into its basic components. Unlike thermoplastics, they are not meltable. Furthermore, they are not soluble in solvents. Adding one to them anyway can cause swelling.
Why are elastomers rubber-elastic?
How can it be that a plastic becomes so elastic? The whole thing can be explained with the help of entropy. This is the measure of the disorder. Molecules always strive for disorder. Therefore, they arrange themselves in a jumble, although they could also gather neatly. Molecules like it best when they are in a tangled state. For example, it could look like this:
Source: www.fu-berlin.de
As you can see, the molecular chains are arranged in a wild jumble. If you now pull on the elastomer, the molecular chains are forced to give up their disordered state or state rich in entropy. They must line up in the direction of the pulling force. At the same time, the entropy decreases. In the following you can see the resulting low-entropy state.
Source: www.fu-berlin.de
If you let go of the elastomer again, the molecular chains will arrange themselves disorderly again. Because they strive for entropy. This causes the elastomer to contract again.
Applications of elastomers
Due to their properties, elastomers are only used in special areas. They are used when rubber-elastic behavior is required. Typical areas of application are therefore tyres, rubber bands or seals. The raw material for elastomers is caoutchouc. Depending on the type of rubber, they have different properties.
properties of rubber
Natural rubber, for example, is highly elastic and therefore also tear-resistant.
Source: utopia.de
Acrylonitrile butadiene rubber, on the other hand, is only stable up to a temperature of 120°C and has good mechanical strength.
Source: rado.de
Finally, there is the silicone rubber. This type is particularly resistant to extreme temperature changes. It is also resistant to ozone and light exposure. It also has electrical properties.
Source: heimhelden.de
The plastic polyurethane is one of the elastomers. Polyurethane and acrylonitrile butadiene rubber are mainly used for clutch construction.
Elastomers and Recycling
If you’ve already read our other articles on plastics then you know that recycling them doesn’t turn out to be easy. Not only technological, but also economic hurdles have to be overcome. It is particularly important that attention is paid to sorted recycling. For most types of elastomers, it is not possible to process them according to type. Therefore, the utilization is limited to a secondary application.
- Sorted recycling
- processing
- Secondary Use/Reuse
Wherever a single-variety processing is possible, the residues are fed back into the starting mixture. From an economic point of view, however, this does not always make sense, because the residues produced are too small. Therefore, the effort for this is usually too great.
Nevertheless, it is extremely important to ensure that waste separation is observed and that plastics are disposed of properly. Because plastics and thus also elastomers are not degradable by our ecosystem. Instead, they pollute the environment and cause harm.
Elastomer – everything important at a glance
-
Is one of the three polymer groups
-
Possess rubber elasticity properties
-
The molecular chains of the elastomers can be stretched by energy
-
Finds use in tires and rubber bands
-
They are recyclable as secondary use or new manufacture
If you find the article exciting, please have a look at our other topics. We’re sure you’ll find something interesting!