Strain-induced crystallization amorphous rubber

Differential Thermal Analysis (DTA). One of the characteristics of a rubber useful in tire rubber compounds is that it is amorphous at room temperature but readily undergoes strain induced crystallization. For this reason, copolymers were prepared in order to appropriately adjust the crystalline melt temperature. 

Although elastomers are usually amorphous, strain-induced crystallization occurs in rubbers such as cA-l,4-polybutadiene, butyl rubber, and NR. Crystallization under stress, discovered 200 years ago [239], increases the modulus and most failure properties of rubber and is essential to performance in many... 

Further progress in understanding natural rubber had to await the discovery of more microscopic probes of matter. Jean Perrin (1870-1945) established that ordinary matter is composed of atoms of the currently understood size. What probe is also of this size X-rays or electrons Soon after the experimental field of X-ray scattering had been developed, natural rubber was examined by Johan R. Katz (1880-1938) of Amsterdam [16]. Rubber at rest yielded only an amorphous halo, characteristic of a liquid. When the sample was stretched until it crystallized, sharp features appeared. This confirmed the notion of strain induced crystallization. But, the shock was that the unit cell for crystallized natural rubber was quite small. If... 

Finite chain extensibility is the major reason for strain hardening at high elongations (Fig. 7.8). Another source of hardening in some networks is stress-induced crystallization. For example, vulcanized natural rubber (cw-polyisoprene) does not crystallize in the unstretched state at room temperature, but crystallizes rapidly when stretched by a factor of 3 or more. The extent of crystallization increases as the network is stretched more. The amorphous state is fully recovered when the stress is removed. Since the crystals invariably have larger modulus than the surrounding... 

---