SPHERULITIC STRUCTURE AND PTC PROPERTY OF ISOTACTIC POLYPROPYLENE FILLED WITH CARBON BLACK

Abstract

The present paper examined the positive temperature coefficient (PTC) property of carbon black (CB) filled isotatic polypropylene which was crystallized isothermally at 150°C, the fusion property of the matrix polymeric crystals and the distribution of CB particles in the matrix during spherulitic growing, then found out their relation. Two melting peaks were observed in thermograms of differential scanning calorimetry of these samples. The area of the lower melting peak decreased with increasing of crystallization time, outstripped area of higher melting peak at 25h. PTC peak temperature from lower melting peak shifted to higher melting peak at 25h, PTC intensity increased till 25h, suddenly decreased at 25h, again mildly increased after 25h. It was found from optical micrographs that 25h was just right a critical time, at which the spherulitics first contacted each other, CB particles crowded together around the spherulitic porphyries.