Typical properties and uses of elastomers
Elastomers are special polymers that are exceptionally flexible and can regain their original shape after deformation. For example, after five minutes of 100% stretching, they recover to within 10% of their original length. |
The chemical structure of elastomers fundamentally differs from that of conventional plastics. In particular, the most significant distinction among polymers is the presence of numerous cross-linkages between polymer chains in elastomers. Moreover, these cross-linkages are responsible for the distinctive elasticity and resilience of elastomers. |
Elastomers are commonly referred to as either natural or synthetic rubber. Natural rubber comes from latex, produced by some trees. Today, numerous synthetic elastomers exist, including neoprene, silicone rubber, and fluorosilicone rubber. Each type is tailored for specific applications due to their unique properties. |
A common application for elastomers is in rubber production. Using a process called vulcanization, rubber (raw rubber) becomes flexible. Rubber vulcanization is a physical and chemical process that creates new cross-links between the chain molecules of rubber. Consequently, this makes the material more flexible. This elasticity is due to the cross-linking of the material, which prevents the molecules from moving away from each other in the event of resistance. When the force is released, the segments spring back into place.
The components of rubber compounds
The components of rubber compounds can vary depending on the specific application and desired properties. However, in general, rubber compounds typically consist of the following main components:
Rubber base: rubber compounds are based on rubber material or elastomer. These can be synthetic or natural rubbers, such as natural rubber, neoprene rubber, styrene-butadiene rubber (SBR), polyurethane, or silicone. The chosen rubber base determines the material’s elasticity, resistance, and other key properties.
Additives: improve or modify the properties of rubber materials. Examples of additives include:
- Fillers: such as carbon black or silica, which increase the stiffness and abrasion resistance of the rubber compound.
- Vulcanizing agents: these substances aid in the formation of cross-links in the rubber compound, such as sulfur or peroxides.
- Colorants: compounds that give the rubber compound its desired color.
- Antioxidants: substances that prevent aging and degradation of the rubber compound.
- Performance enhancers: these are compounds that impart special properties to the rubber compound. For instance:
- Antistatic agents: aimed at reducing static electricity.
- UV Stabilizers: protect the rubber compound from damage caused by UV radiation.
- Heat and Cold Resistant Additives: help improve the compound’s resistance to extreme temperatures.
The measurable characteristics of elastomers
Elasticity/Flexibility: the primary characteristic of elastomers is their elasticity, which is the ability of the material to deform in response to force and return to its original shape. This property indicates how much an elastomer can stretch or compress and then recover its initial form.
Temperature range: elastomers can operate effectively within specific temperature ranges. Measurable characteristics include the temperature range in which the material retains its elasticity and functional properties. For example, some elastomers may stiffen or crack at low temperatures.
Hardness: can be measured on a scale, such as the Shore hardness scale. Hardness indicates how resistant the material is to indentation or scratching and how pliable or rigid its surface is (ASTM D2240).
Wear resistance / Abrasion resistance: is crucial in applications where elastomers come into continuous contact with other surfaces. Measuring wear resistance can be done using various methods, such as measuring material loss or the extent of wear marks.
Tensile strength: reveals how much stress the material can withstand before it undergoes rupture. The measurement of tensile strength generally indicates the material’s load-bearing capacity (ASTM D412).
Elongation: measures how much an elastomer can stretch compared to its original length. This property is important in applications like rubber products, where flexibility and elongation are critical.
Recovery: capability shows how well an elastomer can return to its original shape after deformation. Recovery indicates the material’s durability and long-term performance.
Dielectric properties: determine their electrical insulating capacity and resistance to electrical current flow.
Chemical resistance: the reaction of elastomers to various chemical substances can be measured. This information is important when using the material in chemical environments.
UV stability: UV stability indicates how well elastomers resist premature aging and damage caused by ultraviolet (UV) radiation.
Compression set resistance: the percentage of the original specimen thickness after application and release of axially directed compressive forces at a specified temperature and time (ASTM D395).
Adhesion: ability of the material to cling to the metallic case (ASTM D429).
Modulus: is the stress required to produce a given force.
Tear resistance: is the capacity of a material to resist the growth of a cut when tension is applied (ASTM D624).
Resilience: the ability to absorb temporary energy without creating a permanent distortion (ASTM D945).