Exploring a pathway for time-resolved studies of polymer fatigue related to nanostructure evolution

An uniaxially oriented polymer blend based on high-density polyethylene (HDPE) that is reinforced by polyamide 6 microfibrils is subjected to slow mechanical fatigue tests. Simultaneously, the nanostructure evolution is monitored by two-dimensional (2D) patterns of the small-angle X-ray scattering (SAXS). The objective is to demonstrate that subtle changes of macroscopic strain and nanostructure parameters can be recorded with an accuracy that is sufficient to detect mechanisms that relate fatigue and nanostructure variation. The macroscopic deformation of the material is recorded by a video camera and the captured pictures are analyzed by automated image processing methods to compute the macroscopic strain. From the 2D patterns the multidimensional chord distribution function (CDF) is calculated, and the scattering power Q is determined. Peaks of the CDF that are related to the semicrystalline domain structure inside the HDPE are identified. The position of their centers of gravity is tracked automatically from the voluminous series of scattering patterns. The resulting curves demonstrate the relation between mechanical load and nanostructure evolution.