A real-time simultaneous small- and wide-angle X-ray scattering study of in situ polyethylene deformation at elevated temperatures

A variety of polyethylenes were investigated over a range of drawing temperatures by the simultaneous measurement of the small- and wide-angle X-ray scattering patterns and the load-extension curve and were all found to undergo a similar sequence of deformation processes under 90 degrees C. Interlamellar separation was identified during preyield deformation. Crystallographic deformation via chain slip and a temperature- and crystallinity-dependent martensitic phase transformation were associated with macroscopic yielding in all cases. The lamellar to fibrillar transition occurred immediately after yielding as the load dropped. Once the load became constant, the fibrillar morphology had fully formed. Deformation of the microfibrils was detected during the load-extension curve plateau. The percentage crystallinity was the most important influence on the mechanical response whereas branch length had no effect. Above 90 degrees C, it was speculated that a greater amount of interlamellar deformation was activated in the less crystalline linear low-density polyethylene (LLDPE), and this accounted for the differences in mechanical behavior between LLDPE and high-density polyethylene (HDPE) above this temperature.