Piezoresistive Properties Of PP/SSFs Conductive Composites Aging

The structure of conductive polymer composites will be changed after aging,and the mechanical and electrical properties of the materials will be changed accordingly.The composite materials,with piezoresistive effect,have the characteristics of loading dependency.Therefore,the piezoresistive effect of material will be changed after aging.In this paper,the effects of hygrothermal aging on the electrical and mechanical properties of PP/SSFs conductive polymer materials are studied by experimental methods.Meanwhile,the thermal properties of the polymers composites are also investigated.In this study,the following research works are discussed,Firstly,the composites were accelerating aged by controlling the aging temperature,humidity and aging time.Secondly,mechanical and electrical properties of the composite materials before and after aging are studied by uniaxial compression experiment.The results show that the conductive polymer material has obviously piezoresistive effect,and the volume resistivity is related to the content of the conductive fibers.The volume resistivity of the material is very large when the conductive fiber content is below the percolation threshold.While when the conductive fiber content is higher than the percolation threshold,the resistivity will decrease with the increasing compressive loading.The initial volume resistivity of the material will increase due to hygrothermal aging,and the initial volume resistivity is related to the aging time.In addition,the stress and electrical resistivity of the conductive polymer composites under the condition of stress relaxation are investigated by experimental method.The results show that there are three stages in stress relaxation process.In the first stage,the stress decreases rapidly with time.In the second stage of stress relaxation,the decrease rate in stress is slowed down.In the final stage,the stress tends to be stable.The resistivity of composites decreases rapidly at the beginning of relaxation,and then the resistivity fluctuates in a small range.Finally,thermal performance of conductive polymer are studied by dynamic mechanical analysis(DMA),thermogravimetric analysis(TGA)method,and differential scanning calorimetry meter(DSC)analysis.Scanning electron microscope(SEM)was used to observe the distribution of conductive filler and the bonding of fiber with matrix.