In situ synchrotron microbeam analysis of the stiffness of transcrystallinity in aramid fiber reinforced nylon 66 composites

One of the most interesting questions in the field of polymer composites concerns the microstructure of the transcrystalline (tc) layer which is developed in the polymer film around the reinforcing fibers. In the present study, a single aramid fiber was used to produce a unidirectional nylon 66 based composite. The transcrystallinity around the fiber was generated under different isothermal conditions. The structure of the tc layer, in particular the orientational properties of the crystallites, were investigated at the European Synchrotron Radiation Facility - ID-13 beamline. The samples were scanned with a high brilliance, microfocus X-ray beam, across the full width of the transcrystalline layer. Both static and dynamic diffraction measurements were performed. The main goal of the latter was to examine the behavior of the tc layer under tensile stress. Preliminary results are in excellent agreement with polarized microscope observations, revealing a well-defined orientation of the crystalline lamellae in the tc layer. Under stress the orientation of the tc layer is changed. An explanation for the reorientation of the microstructure of the transcrystalline layer is suggested.