Inhomogeneous structure in natural rubber (NR) vulcanizate was examined by
1H pulsed NMR. The spin-spin relaxation times (
T2) under various extension ratios (α) were measured by the Hahn echo method and the solid echo method. The decay curves of NRs were resolved into three
T2 components,
T2SS,
T2HS, and
T2HL, which were respectively arising from the strain-induced crystalline chains, the network chains, and the more mobile chains that were less affected by crosslinks or entanglements.
T2HS and
T2HL decreased with increasing α. However,
T2HL leveled off at α beyond 4 while
T2HS kept decrease. The decrease in
T2HL with α was more rapid than that of
T2HS until
T2HL became constant. This indicates that the deformation of the more mobile chains was larger than that of the network chains. The increase in the fraction of
T2SS component with increasing α was observed in the region of α that
T2HL were almost unchanged. It was suggested that the strain-induced crystallization is closely related with the more mobile chains.
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