Crystallization of stretched network chains in cross-linked natural rubber

Relatively fast kinetics of strain-induced crystallization (SIC) of cross-linked samples with various network-chain densities ( ν ) of natural rubber and its synthetic analog was examined by the fast time-resolved wide angle x-ray diffraction and simultaneous tensile measurements. The lateral crystallite size was almost unchanged with elapsed time, though the crystallization proceeded considerably during the period. The rate of SIC was faster for the samples having the higher ν during the first tens of seconds. While the development of SIC obviously depends on ν , progress of relative stress relaxation with time was almost independent of ν . The different dependence of the experimental results on ν was explained by assuming coexistence of stretched and relaxed network chains. During SIC at a fixed strain ratio, the intensity of crystalline reflections increased without reducing the intensity of anisotropic amorphous halo on the equator. Accordingly, rather relaxed chains that had shown the off-equatorial scattering were thought to be consumed for the crystal growth.