EFFECT OF AGING ON STRUCTURE AND STRESS RELAXATION OF PP/SSFs COMPOSITES

Conductive polymer composites, with good flexibility, adjustable conductivity, easy forming and low production cost, can be used as functional material in many fields for its antistatic properties, electromagnetic shielding/microwave absorbing properties, and pressure/temperature sensitivity. However, in the process of processing, storage and use, due to comprehensive influence of many factors, aging will inevitably occur which will lead to deterioration of the properties. In this paper, PP/SSFs (stainless steel fibers) conductive composites were prepared by melt-blending and injection molding. The specimens were subjected to accelerated hygrothermal aging and UV aging. Stress relaxation curves, resistivity and crystallinity were experimentally measured. Micromorphology and elemental distribution of specimens before and after aging have been observed and dectected by scanning electron microscope (SEM) and energy spectrometer (EDS). The results show that the stress relaxation curves display three-stages in characteristics. And the stress reduces after hygrothermal aging due to the breaking and cross-linking of molecular chain caused by aging. The initial resistivity of PP/SSFs composites decreases with the increase of filler content, while it will increased with aging time. Due to the piezoresistive effect of the conductive polymer, the resistivity of the specimens decreases significantly with the increase of initial load, and then it tends to a stable value and fluctuation in a smaller range. The results of SEM/EDS analysis show that with the increase of aging time, the oxygen content on the specimens surface increases, and it will decreases with distance (depth) to the surface of specimen. XRD results show that the crystallinity of composites decreased with the increase of SSFs content and aging time. The present research will provide an experimental basis for the study of aging properties of conductive polymer composites.