Effect of Maleic Anhydride Modification on Electrical Resistivity of Carbon Black filled PE and PP

Abstract

An attempt was made to investigate the relation between the interfacial affinity and the electrical conductivity of carbon black (CB) filled polymer composites. High density polyethylene (HDPE) and polypropylene (PP) were examined as the matrix polymer. The interfacial affinity of CB particles with HDPE is higher than that with PP. The affinity of the matrix polymer can be improved by introducing the maleic anhydride (MAH) group. HDPE or PP was modified by the addition of the MAH grafted PE (MAH-PE 1 or MAH-PE 2) or the MAH grafted PP (MAH-PP 1 or MAH-PP 2), respectively. The graft ratios of MAH groups in MAH-PE 1 (0.5 wt%) and MAHPP 1 (0.6 wt%) are lower than those in MAH-PE 2 (3.0 wt%) and MAH-PP 2 (9.6 wt%). By the improvement of the interfacial affinity, it is expected that CB particles disperse finely and homogeneously in the matrix and the matrix resin may form the insulating skin around the CB particle. Experimental results obtained in this paper suggest the following conclusions on the relation between the dispersion state of CB particles and the electrical conductivity of the composite. (a) Owing to the finer dispersion of CB particles, the conductive network can be formed by the smaller content of CB. With the increase of CB content, the density of the conductive network increases and the electrical resistivity of the composite decreases. (b) By the homogeneous dispersion of CB particles, values of the measured resistivity become stable. (c) By the formation of insulating skin around the CB particle, the electrical resistivity shows the inclination to increase. When the temperature increases, the distance between CB particles extends widely with the thermal expansion of matrix polymer. Therefore, both of the electrical resistivity at the peak temperature and the PTC intensity (resistivity at peak temperature / resistivity at room temperature) increase. By the addition of 8 wt% of MAH-PE 2, the CB/HDPE composite exhibits the PTC intensity of 10^4.4 at the peak temperature 135℃.