STXM Studies on the Changes in the Spatial Distribution of Density and Chain Orientation of LLDPE with Strain

We have clarified how the spatial distributions of density and C–C bond orientation on submicrometer scales in linear low-density polyethylene (LLDPE), which exhibits two yield points, change with yield points under stretch using scanning transmission X-ray microscopy (STXM). After the first yield point, the stretch-induced spatial density inhomogeneity showed a bimodal distribution, and the C–C bond orientations parallel to the stretch direction were more enhanced in the lower-density regions. At the second yield point, the C–C bonds exhibit a higher degree of orientation along the stretch direction spatially uniformly, and the spatial inhomogeneity of density becomes unimodal with a wide distribution. The results of X-ray scattering and STXM revealed the following at each stretch ratio: Between the first yield point and the second yield point, the density fluctuations are enhanced with mechanical melting of the crystals and the orientation of the polymer chains occurring preferentially in the low-density region. On the other hand, at the second yield point, the mechanical melting and the alignment of crystalline structures occurred even in a high-density region.