Research Of Multiphase Polyolefin/Carbon Black Of Self-limiting Heating Composites

Carbon black (CB) filled polymer materials were widely used to prepare self-limiting temperature conductive composites, due to the high percolation threshold, higher CB content, high melt viscosity and difficult workability, the development of materials were limited. So how to reduce the content of CB and improve its processing become one of research focus in this area. Multiphase composited and CB modified were used to reduce the CB content and improve the stability of the Composite materials.The single-phase and multiphase polyolefin conductive composite materials were prepared by orthogonal design, the various factors of the electric properties were studied, and best formula was established. At the same time CB was modified to study the different modification methods to the effects of PTC material/NTC effect, heating power, crystalline properties and stability.Get the percolation threshold of HDPE/CB, PP/CB materials were 18%,21% and the PTC intensity were 4.5,4.0 through the experiments on different proportion of HDPE/CB, PP/CB, however the NTC effect are more significant. The electroconductive test of conductive composite materials of the different type PP/HDPE ratio shows that multiphase substrate can effectively reduce the room temperature resistivity of the composite materials, that when PP:HDPE=7:3 the material appears the best electroconductive. The percolation threshold of this kind is only 11%, 7% and 10% lower than the single-phase. The PTC intensity has also been increased by two orders of magnitude. The reason is that CB preferentially distributed in HDPE, PP phase added to increase the effective concentration of the CB, easier to form a conductive network.The orthogonal design establish the size of the impact of various factors on the electric properties of materials, the four factors (LDPE, PP, CB, ZnO) affected the size of the sample PTC intensity were CB> PP> ZnO> LDPE; the best formula was established at the same time.The result of the PTC texts show that the toluene can effectively remove the ash content of the CB surface, can significantly reduce the volume resistivity of the material to improve the conductivity with the room temperature resistivity reduced from 35.76 Ω·cm to 18.5 Ω· cm; the nitric acid treatment can form a strong physical adsorption to improve the PTC intensity with the PTC strength of the material increased by 25.65%; the CB processed by potassium persulfate can reduce the NTC effect of the materials by inhibited the high-temperature self-polymerization with the NTC strength of the material reduced from 0.675 to 0.339.The results of the materials heat stability shows that multiphase materials can improve the sample heat stability,80% of the single-phase polyolefin materials were burned at 220V,20% of the multiphase materials were burned with the heated temperature 86℃ for civilian. The modified CB can make the multiphase materials heat stability in the range 60 ℃ to-100℃, so that can make a wider range of application temperatures.The results of DSC test show that CB distributed in HDPE firstly by the PTC strength transition temperature and the melting curve of the composite materials, so that the composite materials can reach a larger PTC intensity at a lower temperature; The modified CB made a great influence on the crystal melting behavior, the CB modified by potassium persulfate weakened the second melting peak to reduce the NTC effect, in addition, the melting temperature was advanced so that the materials can be achieved an effect of self-limiting temperature at lower temperatures.