Effect Of Aging On Structure And Properties Of PP/SSFs Conductive Composites

The aging problem of conductive polymer composites(CPCs)is a fact that cannot be ignored.Aging will lead to changes in the structure of material,and then affects its thermal,mechanical and electrical properties.In recent years,many scholars have paid extensive attention to the aging mechanism,conductive mechanism and anti-aging modification.However,the issues concerning the mechanism of the effects of aging on the conductivity of the material and the relationship between structure and performance have not yet been fully clarified,and this is crucial for the application of CPCs.In this paper,accelerated aging tests were first conducted on polypropylene(PP)/stainless steel short fibers(SSFs)conductive composites,and then the mechanism of aging on the structure and properties of PP/SSFs conductive composite was explored.Firstly,accelerated aging tests were performed on the materials using both hygrothermal aging and UV aging,and the micromorphology and structure of the samples before and after aging were studied.The results show that the degradation of SSFs fiber and PP matrix interface resulted in aging,and the content of oxygen in the sample after aging increased significantly.The crystallinity of the material decreases with the increase of SSFs content and the aging time.Secondly,the thermal properties of materials were studied by dynamic thermal analysis(DMA)and differential thermal analysis(DSC)in this paper.The results of DMA experiments show that aging will cause the storage modulus of PP/SSFs composites to decrease,and the longer the aging time,the more obvious the decline of storage modulus.Aging can also lead to a decrease in the glass transition temperature(Tg)of PP/SSFs composites.The results of DSC experiments show that aging will lead to lower melting point temperature of PP/SSFs composite and little effect on the crystallization temperature.UV aging causes twin peaks in the DSC curves of the material.Finally,the low-cycle cyclic deformation behavior and strain-resistance(strain sensing behavior)relationship of PP/SSFs conductive composites were studied by using cyclic loads of different frequencies.The results show that the PP/SSFs composites have typical dynamic viscoelastic properties of the polymer,and the hysteresis of the strain behind the stress is obvious;The overall trend of resistivity is increasing gradually and then become relatively stable,which is due to the destruction of the old conductive path and the formation of the new conductive path exist simultaneously in the composites material.With the increase of the loading frequency,the strain increases,and the amplitude of the resistivity curves decreases.Under a certain cyclic load,the strain increases with the increase of the aging time,stress-strain loops increases in overall width,and the amplitude of the resistivity curves increases.