Study Of Relationship Between Mechanical And Electrical Properties Of Polymer Composites Filled By Conductive Inclusions

The study of relationship between mechanical and electrical properties of conductive polymercomposites will help to deeply understand the conductive mechanism and the change ofconductivity under compression load, and it can provide reasonable and reliable basis for theapplication ofconductive polymers. In this paper, the following research works are discussed:Firstly, in order to study the effects of micro-damage due to interfacial debonding betweenshort conductive fibers and the matrix under compressing loading on conductivity of thecomposites, as well as the mechanism of change of electrical properties due to the decrease ofspace between fillers under loading, interface strength model based on cohesive model ofinterfacial debonding between single fiber/single spherical inclusion and the matrix in linearviscoelastic materials under transverse loading are achieved. According to the principle ofconservation of energy, these studies are carried out by means of meso-mechanical method and thetheoryofEshelbyequivalent inclusion.Secondly, changes of the conductivity of stainless steel short fibers/carbonnanotubes/polyamide (SSFs/CNTs/PA6) conductive composite materials under compressing forceare studied by experimental methods. Because of the viscous effect of polymer, the material willtake on obvious rate sensitivity. The rate sensitivity will significantly influence the conductivityofthe material. The effects of strain rates on piezoresistive effect are analyzed, and theory modelcoupling strain rate of strain-resistance effect is proposed. The results show that change ofresistivity under compressing loading is affected by two kinds of competitive mechanism. Onemechanism is that the decrease of space between conductive fillers under loading will lead to thedecrease of resistivity; another mechanism is the increase of barrier height result from the damageevolution in composites will lead to the increase ofresistivity.Thirdly, the effect of filler contents on conductivity has been experimentally studied. Thecontents of stainless steel short fibers are0%,2%,4%,6%,4%,10%and12%, carbon nanotubesare0%,1%,3%and5%. The experimental results show that the electronic conductivity of theconductive composites with filler contents displaythe characteristic of3stages, according to whichthe percolation thresholds ofthe conductive polymer are determined. Fourth, thermal performance of conductive polymer are studied by dynamic mechanicalanalysis (DMA), thermogravimetric analysis (TGA) method, and differential scanning calorimetrymeter (DSC) analysis. Storage modulus and loss factors with temperature, thermal decompositionof composite, and crystallization process, crystallinity, the melting and crystallization temperatureofcomposites with different filler contents are discussed.Fifth, dielectric properties of SSFs/CNTs/PA6composites are studied. Dielectric constant anddielectric loss of the conductive composites with electric field frequency, influence of filler contentonthe dielectric constant and dielectric loss are discussed in this paper.Finally, the research work and its significance are summarized, the innovation ofthe paper areinduced, and the further research based on the studyareprospected.