Crude rubber, plastic flow

If no complications were involved, one would expect the plastic flow to increase continuously with the degree of extension, but for crude rubber it appears that the flow decreases after surpassing a limit of about 450% elongation. This can be explained by assuming that, above this limit, crystallisation results in the chains fitting so strongly in the crystalline lattice that plastic flow is more and more suppressed. 

Fig. 18. Plastic flow of crude rubber function of elongation (50 C).

Basically an elastomer is a rubber-like material that can be or already is modified to a state exhibiting little plastic flow and quick and nearly complete recovery from an extending force. These materials are sometimes referred to as rubbers. Before modification, an elastomer is referred to as a raw or crude rubber or a basic high polymer. 

CRUDE SOLVENT COAL TAR NAPHTHA (8030-31-7) Forms explosive mixture with air (flash point 100°-107°F/37°-42°C). Violent reaction with strong oxidizers. Incompatible with strong acids, nitrates, nitric acid. May attack some plastics, rubber, and coatings. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

---