Electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer as a function of vinyl acetate content

The electrical conductivity of carbon black filled ethylene-vinyl acetate copolymer was measured as a function of carbon and vinyl acetate (VAc) content. For the composites whose matrices contain less than 32 wt% ofVAc content, a sharp break point of the relation between carbon content and conductivity was observed. The conductivity jumps as much as ten orders of magnitude at the break point. The critical carbon content corresponding to the break point can essentially be predicted by our previous model. This model was derived under certain assumptions, the most important of which is that when the interfacial excess energy introduced by carbon particles into the polymer matrix reaches a universal value,g ^*, the carbon particles begin to coagulate so as to avoid any further increase of energy and to form networks which facilitate electrical conduction. On the other hand, for the composites whose matrices contain more than 32 wt% ofVAc content, a sharp break of the relation between the carbon content and conductivity cannot be observed and conductivity increases continuously with increasingVAc content. In this region ofVAc content, carbon particles were dispersed well in theVAc rich matrices. This is because the presence of polar groups in aVAc component enhances its bonding to conductive fillers. In this case, the interfacial excess energy,g, seems to be the caseg0. Better dispersibility of fillers in this region ofVAc content can be shown from an electron micrograph (TEM).