Poly(butylene terephthalate)/poly(ethylene-co-alkyl acrylate)/carbon black conductive composites:: Influence of composition and morphology on electrical properties

Poly(butylene terephthalate)/poly(ethylene-co-alkyl-acrylate)/carbon black (PBT-EXA-CB) blends, prepared through extrusion, were characterized as electrical conductive materials. In the composition range studied (55 less than or equal to PBT % less than or equal to 75 w/w; 5.5 less than or equal to CB % less than or equal to 11.1 w/w), various conductive behaviors were observed depending mainly on composition and poly(olefin) crystallinity. The observed positive temperature coefficient (PTC) is quite small compared to poly(olefin)-CB systems, and our blends do not present a negative temperature coefficient (NTC) on complete melting of the CB-containing phase, thus offering new possibilities for a regular electric power control. Volume expansion of both PBT and EXA was postulated to be the main parameter responsible for the thermal resistivity evolution through the range +20 to +170 degreesC. A double-percolation system between both the co-continuous polymer phases and CB-particles included in the poly(olefin) phase is postulated to explain these results.