Study On The Modification Of Carbon Black N990 And Carbon Black/HDPE PTC Composites

The modifications of carbon black N990 at high temperature under the stream of N₂, CO₂, vapor and activated by KOH respectively are studied. The influences of different preparing methods on the room resistivity and PTC effect of Carbon black /HDPE composites are investigated. Carbon black is treated in an pipe reactor at 950 ℃, and its product is then incorporated into HDPE to form PTC composites. Treated Carbon black is characterized with SEM, BET, XPS and XRD. Its conductivity is evaluated with self-made piston-cylinder equipment. The PTC curves of Carbon black composites are measured by self-established device.The conductivity of the treated carbon black gradually increases by sequence of heat treatment, KOH treatment, vapor treatment, CO₂ treatment at high temperature. The conductivity of the carbon black treated by CO₂ is one time more than that of the untreated. Evidences from microstructure of treated carbon black show that there is little influence of different modified methods on crystallites and particle size, but obvious influences of oxygen content and BET on carbon black surface, which also show an increase in pore volume and change of pore distribution. Further analysis reveals that the conductivity of treated carbon black is closely related to its BET.The influences of different treatments on the room resistivity of carbon black /HDPE composite are similar to that on carbon black conductivity. The resistivity of the composites decreases to some extents with an increase in carbon black content. Room resistivity of composite with the same content of modified carbon black decreases gradually by sequence of heat treatment, KOH treatment, vapor treatment, CO₂ treatment at high temperature.High PTC intensity is easily achieved by both the composite filled with treated or untreated N990. Its PTC intensity has tendency of dropping as carbon black content increases, especially for carbon black content higher than 70%. PTC intensity of carbon black composites treated by CO₂ decreases rapidly with the carbon black contents, while heat treatment keeps at 9 orders of magnitude.In general, treated and untreated carbon black N990 has characteristics of high PTC intensity above 6 orders of magnitude and low NTC intensity. The room resistivity of lQcm of composite can be achieved by using CO2 treatment of N990 at high temperature. Therefore, treated carbon black N990 is a prospective conductive filler of PTC composites for future applications.