PTC Properties Of Conductive Polymer Composites With Special Morphology

In order to obtain conductive polymer composites with very low percolationthreshold and excellent positive temperature effect (PTC effect), in this paper themethod that conductive particles were first reacted with compatibilizer and thenmelting blended with immiscible polymer blends,has been employed to prepare thecomposites of which CB localized at the interface. The conductive particles wereexpected to localize at interface due to the induced effect of compatibilizer. The effectof conductive particle shape and morphology of polymer blends on percolationthreshold and PTC performance of composite was investigated.For carbon black (CB) filled ethylene butyl acrylate copolymer/nylon6(EBA/PA6) immiscible blends, in which Ethylene butyl acrylate-graft-maleicanhydride copolymer (EBA-g-MAH) was employed as compatibilizer, the resultsshow that CB can be induced by EBA-g-MAH to localize at the interface, resultingthat the conductive path was fabricated by CB at interface.The localization of CB atinterface causes that the lowest percolation thresholds of EBA/PA6/EBA-g-MAH/CBcomposites is0.75wt%, which is far lower than that of EBA/PA6/CB with CBdistribution in the PA6phase. For the EBA/PA6/EBA-g-MAH composites employedcarbon nanotubes (CNTs) as the conductive particles，CNTs can be induced by EBA-g-MAH to localize at the interface and PA6phase, resulting that the conductive path isconstituted by PA6phase and phase interface. The lowest percolation threshold valueof EBA/PA6/EBA-g-MAH/CNTs composites is0.5wt%, which is far lower than thatof EBA/PA6/CNTs with CNTs distribution in the PA6phase. For CNTs filledpolystyrene/nylon6(PS/PA6) immiscible blends, in which styrene-graft-maleicanhydride copolyme(SMA) was employed as compatibilizer，CNTs can be inducedby SMA to localize at the interface and PA6phase, causing that the conductive path isconstituted by PA6phase and phase interface. The lowest percolation threshold value of PS/PA6/（SMA-CNTs) is0.112wt%, which is far lower than that of PS/PA6/CNTswith CNTs distribution in the PA6phase.The influence of morphology on PTC effects was investigated. In the compositeswith dispersed PA6phase, the double PTC effect was observed. The first PTC effectwas caused by the phase transition of the continuous phase. The second PTC effect canbe attributed to the the phase transition of dispersed phase (PA6). The PTC effect hasnothing to do with the structure of conductive path. In the composites with continuousPA6phase, the PTC effect depent on the structure of conductive path greatly. For theCNTs filled blends, in which the conductive path was fabricated by PA6phase andinterface, the phase transition of dispersed phase can not break the conductive path,resulting in a single PTC effect. For the CB filled blends, in which the conductive pathwas fabricated by interface, the phase transition of dispersed phase and continuousphase can both break the conductive,resulting in the double PTC effect. For thecomposites with co-continuous morphology, the PTC effect was influenced by thestructure of conductive path and physical property, resulting that the phenomena ofPTC effect is much complex.