Difference Between Elasticity and Plasticity

Main Difference – Elasticity vs Plasticity

Elasticity is the ability of an object or material to resume its normal shape after being stretched or compressed. Hence, elasticity is a physical property. Materials showing a high degree of elasticity are termed elastic materials. Plasticity is also a physical property of matter. It is the quality of being easily shaped or moulded. Materials showing plasticity are known as plastics. The main difference between elasticity and plasticity is that elasticity causes reversible deformations of matter whereas plasticity causes irreversible deformations of matter. In polymer chemistry, elastomers show elasticity and thermoplastics and thermoset polymers  show plasticity. Metals also show elasticity to some extent by resizing and reshaping the metal lattice.

Key Areas Covered

1. What is Elasticity
     – Definition, Properties, Elastic Materials
2. What is Plasticity
     – Definition, Properties, Plastic Materials
3. What is the Difference Between Elasticity and Plasticity
     – Comparison of Key Differences

Key Terms: Elasticity, Elastic Limit, Elastic Modulus, Elastomers, Plasticity, Plastics, Polymers, Thermoplastics, Thermosets

What is Elasticity

Elasticity is the ability of an object or material to resume its normal shape after being stretched or compressed: stretchiness. The materials that show a high degree of elasticity are known as elastics. As an example, elastomers are polymer materials that show a high degree of elasticity.

Figure 1: Elastic Materials

The elasticity of a material is described using two parameters:

Elastic Modulus

Elastic modulus is the ratio of the force exerted upon a substance or body to the resultant deformation. Materials with a low degree of elasticity (hard to deform) have a high elastic modulus. Materials that have a low degree of elasticity have a low elastic modulus.

Elastic Limit

Elastic limit is the maximum extent to which a solid may be stretched without permanent alteration of size or shape. At elastic limit, materials no longer stretch. Instead, it permanently deforms into a different shape.

Elastomers

Elastomers are rubber-like materials and are usually amorphous polymers (there is no ordered structure). The elastic property of elastomers arises due to sufficiently weak Van Der Waal forces between polymer chains or the sufficiently irregular structure. If the forces between polymer chains are weak, it gives the polymer flexibility. Likewise, if the polymer has an unorganized structure, it allows the polymer to be more flexible. But in order for a polymer to be flexible, it should have some degree of cross-linking.

The most common example for elastomers is rubber. Natural rubber is composed mainly of polyisoprene polymer. Therefore, this compound is the reason for the elasticity of rubber. Natural rubber is obtained from the latex of rubber tree. But rubber can be synthesized to obtain synthetic rubber.

Metals

Metals also show some degree of elasticity. The elasticity of metals is due to the resizing and reshaping of the crystalline cells of the metal lattice under an applied force.

What is Plasticity

Plasticity is the quality of being easily shaped or moulded. This means it is the opposite of elasticity. Materials that show plasticity are plastics. Deformation of plastic materials is irreversible. Therefore, when a plastic material is deformed, it stays deformed without coming back to the initial state. Plastics do not stretch and are brittle.

Figure 2: Plastic Material

For stresses beyond the elastic limit, a material show plastic behavior. At the elastic limit, materials get deformed irreversibly and the initial state cannot be obtained back. This is plastic behavior. Materials that show a certain plastic deformation before breaking are known as ductile materials. Ex: copper metal. But materials that do not show any deformation before breaking are known as brittle. Ex: glass.

In polymer science, thermosetting plastics and thermoplastics are plastic polymer compounds. Thermoplastic polymers are compounds that can be recycled by heating and moulding. If a sufficient temperature is provided to thermoplastic polymers, the material can be melted, placed in a mould and cooled to get a new article. Thermosetting polymers are materials that cannot be recycled easily as thermoplastic polymers. These compounds cannot be recycled, remoulded or reformed upon heating.

Difference Between Elasticity and Plasticity

Definition

Elasticity: Elasticity is the ability of an object or material to resume its normal shape after being stretched or compressed.

Plasticity: Plasticity is the quality of being easily shaped or moulded.

Deformation

Elasticity: Deformation of elastic materials is reversible.

Plasticity: Deformation of plastic materials is irreversible.

Elastic Properties

Elasticity: Materials showing elasticity have elastic properties.

Plasticity: Materials showing plasticity do not have elastic properties.

Stretching

Elasticity: Materials showing elasticity do not break quickly apart when stretched.

Plasticity: Materials showing plasticity breaks apart quickly when stretched.

Stress

Elasticity: Materials that can reversibly deform to a high extent show elasticity.

Plasticity: Materials that are either ductile or brittle when comparatively a small stress is applied, show plasticity.

Conclusion

Elasticity and plasticity are physical properties of matter. Elasticity is the ability of a material to resume its normal state after releasing an applied stress. Plasticity is the opposite of elasticity, in which, the normal state cannot be resumed after releasing an applied stress. The main difference between elasticity and plasticity is that elasticity causes reversible deformations of matter whereas plasticity causes irreversible deformations of matter.

Reference:

1. “12.4: Elasticity and Plasticity.” Physics LibreTexts, Libretexts, 27 Oct. 2017, Available here.
2. Helmenstine, Anne Marie. “Elasticity Definition and Examples.” ThoughtCo, Aug. 10, 2017, Available here.
3. “Elasticity vs plasticity.” Elasticity vs plasticity – Energy Education, Available here.

Image Courtesy:

1. “2229753” (Public Domain) via Pixabay
2. “Plastic alphabet 03” By Martin Abegglen – (CC BY-SA 2.0) via Commons Wikimedia