UNESCO/IUPAC Workshop & Conference on Macromolecules & Materials, 7-10 September 2015, Port Elizabeth, SA THE IMPROVEMENT OF THERMO-SWITCH PROPERTIES IN POLYOLEFIN/CARBON BLACK ELECTRICALLY CONDUCTIVE COMPOSITES BY THE ADDITION OF WAX AND APP T.B. Motloung1, A.S. Luyt1,2 and D. Dudić1,3 1 Department of Chemistry, University of the Free State (Qwaqwa Campus), Phuthaditjhaba, South Africa 2 Centre for Advanced Materials, Qatar University, Doha, Qatar 3 Vinća Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia (E-mails: [email protected], [email protected], [email protected]) ABSTRACT Conductive polymer composites (CPCs) based on low-density polyethylene (LDPE), highdensity polyethylene (HDPE), isotactic polypropylene (iPP) and carbon black (CB) microparticles blended with atactic polypropylene (aPP) and medium-soft paraffin wax (M3 wax) were studied. The aim of this study is to determine the effect of wax, aPP, irradiation and zinc powder used as the second filler on the positive temperature co-efficient (PTC) behaviour of LDPE/CB, HDPE/CB and iPP/CB composites. Carbon black powder (activated charcoal) is used as filler to impart electrical conductivity to the composites. CPCs with 25 and 40 wt% CB content were prepared through melt-mixing, and the polyolefins were blended with either wax or aPP in fixed 90/10 mass ratios. The morphology, as well as thermal and thermoelectrical properties of the composites were investigated. The DSC results showed a decrease in the degree of crystallinity for all the irradiated composites, which could be due to disruption of the crystal-formation by newly-formed crosslinks. The resistivity values dropped steeply with an increase in CB content for all the CPCs but the iPP composites were more conductive than the LDPE and HDPE composites. Wax and aPP enhanced the conductivity in most of the composites. The resistivity-temperature co-efficient (RTC) values were similar for both compositions and increased with increasing temperature from ambient to just before the “switching” temperature. The irradiated iPP/CB composites showed high RTC values at 25 wt%, and similar behaviour was observed only at 40 wt% for the LDPE/CB composites. The irradiated composites generally showed higher electrical resistivity because of structural changes induced by gamma irradiation.
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