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Elastomers constitute a very important group of polymers out of two other groups; thermosets and thermoplastics. Because of their physical characteristics, elastomers find very important applications areas in engineerin and daily life. In here, we discuss these general properties of elastomers.
The most important characteristic of elastomers is that they can be stretched extensively compared with thermoplastics and thermosettings. This strecthing property of elastomers comes from the very long molecular chains and some degree of cross-linking in molecular structure. But this cross-linked structure is not high as thermosets, in elastomers. The kinked long molecular chains of elastomers give the ability of stretching. And returning into the original shape is done by cross-linking structure.
The classification of elastomers can be done as;
Very low forces can stretch the elastomer materials extensively. But with the increasing force, stretching decreases, but in the mean time, mechanical properties increases in stretched form.
To show elastomeric characteristics like stated above, the elastomer material must be above the glass transition temperature(Tg). At below these temperatures, elastomer polymer will be much more rigid, which will not show any elastomeric characteristics.
There is a difference between elastomers and thermoplastics that their temperatures are above the glass transition temperature. Elastomers can return their original shape after the force is withdrawn, but thermoplastics do not turn. This is because that there is a low degree of cross-linked molecular structure which provides this ability for elastomers. But thermoplastics, there is no cross-linked structure. Because of that, thermoplastics show ‘viscoelastic’ behavior which is special for this situation.
Elastomeric materials also called as ‘rubbers’ in market. Their level of cross-linking is adjusted with some processes. Crude natural rubbers are very elastic that thet can strecthed with very low forces. With the process called as ‘vulcanization’, the number of cross-linked structure can be increased. With that increased cross-linked structure of natural rubber, much more stiff ‘vulcanized rubber’ is obtained. Also if the cross-linking is increased, much more harder rubbers can be produced. After a level, thet can not be called as rubber, they are thermoset polymers.
The general cross-linking density for rubbers can range from 1 to 10 in 100 carbon atoms in their molecular structure.
These are the general characteristics of rubbers or elastomers. Do not forget to leave your comments and questions below about properties of elastomers. Your precious feedbacks are very important for us.