Research On Dielectric Properties Of CB/CNTs/PP Conductive Polymers

Dielectric properties,thermal stability,and microstructure of PP conductive composites filled by carbon filler were studied in this paper.Carbon black(CB)and carbon nanotubes(CNTs)were applied as fillers.The composites were prepared by melt blending and injection molding method.Effects of filler type and content on morphology and structure were detected,and the effects of filler on thermal and dielectric properties were analyzed by experimental methods.Relationship between temperature/force and dielectric properties was investigated intensively.Firstly,effect of filler types and contents on the morphology,crystallization behavior and thermal properties were studied by SEM,XRD and FTIR.SEM results showed that the additives were uniformly distributed in PP,and white the increase of filler content,the distance between particles decreased.XRD results indicated that CB will induce the crystallization of ?-type PP crystal,while CNTs inhibited the effect of CB,and the higher the content of CNTs,the more obvious the inhibition effect was.FTIR spectroscopy results showed that CB would not affect functional group of PP,but its strong absorption in the infrared region will cover up the crystal related absorption peak of isotactic PP,thus,the characteristic peaks shifted to red region in FTIR spectra of the materials.Secondly,thermal properties of composite were studied by employing of DSC and TG.DSC results showed that the filler promoted the heterogeneous nucleation and increased the crystallinity of matrix.However,too much filler led to poor thermal stability of materials.TG results indicated that the addition of CB and CB/CNTs induced partially decomposition of PP.The higher content of additives added in the composites,the more obvious of the inhibition of decomposition rate of PP.Filler affected the beginning decomposition temperature,ending decomposition temperature,and the maximum thermal decomposition rate of PP.Thirdly,dielectric properties of composites could be affected by types and contents of filler.With the increases of filler contents,dielectric constant of the composites increased monotonously.When the filler content reached to the percolation threshold,dielectric constant increased most obviously.Proper amount of CNTs will further improve the dielectric constant of the material.With the increase of the electric field frequency,the dielectric constant and dielectric loss of the composite decreased rapidly at first,and then tended to be stable,namely,getting to a constant value.Finally,the influence of temperature/force on the dielectric properties of the composite was investigated.Experimental results showed that the dielectric constant decreased with the increase of temperature and force.It can be considered that due to the different thermal expansion coefficient and elastic modulus of filler and PP matrix,the capacitor structure network would be damaged,and which decreased the dielectric constant.While the force changed the relative position between the filler particles,in the end,the capacitor structure network inside the material damaged,which will result to the reduce of dielectric constant.In addition,when the filler contents were near the threshold of conduction percolation,the damage of capacitor structure was serious,and the dielectric constant decreased obviously.