Electrical Properties and Crystallisation Behaviour of Polypropylene/Carbon Black Composites

Four different kinds of carbon black (CB) filled polypropylene (PP) composites were prepared by the melt-mixing method. The electrical properties of the PP/CB composites were studied. All PP/CB composites showed typical characteristics of percolation but noticeably different percolation thresholds. CB with higher structure, smaller particle diameter, and larger surface area resulted in the filled PP composites exhibiting better electrical conductivity and a lower percolation threshold. In particular, the percolation threshold of the PP/CB composite filled with hollow-structured CB was significantly lower than that of the others. The crystallisation behaviour of PP/CB composites filled with various amounts of V-XC72 CB was studied by differential scanning calorimetry. The non-isothermal crystallisation parameters showed that the CB particles could act as nucleating agents, accelerating the crystallisation of PP. The isothermal crystallisation kinetics studies showed the crystallisation kinetic constant K(T) and the rate of crystallisation of the PP/ CB composites were higher than those of PP. The values of the Avrami exponent n (ca. 3) indicated three-dimensional spherutitic growth in a spherical form. The free energy of chain folding for PP crystallisation of the PP/CB composites was lower than that of PP itself and it decreased further with increasing CB content.