Strain-induced crystallization of natural rubber subjected to biaxial loading conditions as revealed by X-ray diffraction

Strain induced crystallization (SIC) in carbon black-filled natural rubber (NR) is investigated by wide-angle X-ray diffraction (WAXD) using synchrotron radiation for three deformation states: uniaxial, biaxial (but non-equibiaxial) and equibiaxial tension. The crystallites size is of the same order of magnitude and the lattice parameters are similar for the three states. But the orientation of the crystallites varies: as the crystallites are highly oriented accordingly to the tensile direction for uniaxial loading condition, they are oriented (but with a higher degree of disorientation) along the tensile direction (highest stretch ratio) for biaxial loading condition, and they are not oriented in the plane of tension for equibiaxial loading condition.