Synchrotron small-angle x-ray scattering study of linear low-density polyethylene under uniaxial deformation

Synchrotron time-resolved small-angle x-ray scattering studies were carried out on extruded sheets of linear low-density polyethylene (LLDPE) under tension. Stress-strain traces obtained simultaneously exhibited a double yield behavior. LLDPE initially exhibited lamellar morphology with a long period of 21.5 nm. Initial deformation increased the long period due to flow-induced crystallization. Between the first and second yield points, the lamellae were axially deformed by a slip process toward the tensile direction; off-meridional scattering was produced. In the second yield point region, there was a gradual rotation and thinning of the off-meridional scattering indicating that a shear process was destroying the lamellae. Simultaneously, amorphous scattering arise due to microvoids. Second, a weak meridional scattering was also produced. Strikingly, further deformation in the second yield region (SYR) increased the meridional long period suggesting a recrystallization process. From the cold-drawing region the long period decreased monotonically. The results suggest a melting and recrystallization process in the SYR.