The characteristics of rubber bands
Rubber bands are a general term for highly elastic polymer compounds. Because they have excellent high elasticity, good flexibility, fatigue resistance, high wear resistance, electrical insulation, water resistance, good medium resistance, corrosion resistance, high and low temperature resistance and other special properties that no other products have, rubber bands are also called elastomers.
The high elasticity of rubber bands is manifested in:
First
It has a particularly large elastic deformation and can be stretched to 700% or even more;
Second
After deformation, it can quickly restore its original shape when external force is removed, and permanent deformation is very water;
Third
The elastic modulus is particularly low, only 105~105Pa. In other words, a smaller force will cause a larger deformation of the rubber band.
High elastic deformation comes from the fact that the bonds in its macromolecular chain are relatively easy to rotate. Under the action of external force, the entire macromolecule is easy to deform. Because the rotation barrier of its bonds is relatively low, the modulus is low. After the external force is removed, the molecular thermal motion can easily restore the original deformation automatically, that is, change in the direction of increasing entropy. The entropy value of the rubber band stretched system decreases and becomes hot. Therefore, the modulus is high and the stretch becomes cool.
To what extent does the high elastic deformation reach, and at what speed and to what range does it recover after the external force is removed. The definition in ASTM D1566 is as follows: The material of the rubber band is rubber, and rubber is a material that can quickly and effectively recover its deformation under large deformation and can be modified. The modified rubber is substantially insoluble in (but can expand in) boiling benzene, methyl ethyl ketone, ethanol-toluene mixture and other solvents. The modified rubber is stretched to twice its original length at room temperature (18°-29° degrees) and maintained for 1MIN. After the external force is removed, it can recover to its original length within 1MIN.
