Evaluation of microscopic structural changes during strain hardening of polyethylene solids using In situ Raman, SAXS, and WAXD measurements under step-cycle test

Abstract

We have examined the mechanism of strain hardening of polyethylene (PE) using a step-cycle test with in situ Raman spectroscopy, small-angle X-ray scattering, and wide-angle X-ray diffraction measurements. A stable fibrillar structure was formed at the onset of strain hardening. The fraction of the long-consecutive trans chains increased and decreased with increasing and decreasing strain during the stretching and unloading steps, respectively. The peak shift of the C–C stretching mode showed a red shift by applying the stretching stress to the specimen, accompanied by the broadening of the peak width. The broadening of the Raman band is interpreted as the strong stretching load becoming concentrated on the taut-tie chains. According to these results, we concluded that the strain hardening was caused by the increment of the modulus resulting from the increase in the number of taut-tie chains caused by chain pull-out from the crystalline structure. ・ Strain hardening of PE was investigated via various measurements. ・ The strain-hardening behavior was dominated by plastic deformation. ・ Increasing the amount of taut-tie chains dominates the strain-hardening modulus.