Research On Electrical Conduction And Thermal Stabilities Of Carbon Black-filled Immiscible Polypropylene/Polystyrene Blends

The research and development of conductive polymer composites was mainly focused on enhancing electrical conductivity while reducing percolation threshold, and improving thermal stabilities as well. Electrical conductivity is actually determined by the electrical conductive network formed by fillers so design of this network is one of the basic solutions to enhance electrical conductivity. The electrical conductivity network of composites prepared based on double percolation theory depends on CB selective distribution and composite morphology. On the other hand, One of the reasons that causes negative temperature coefficient (NTC), unstability of electrical properties and ageing is the thermal unstable of composites, including morphological unstability caused by these immiscible blends and the filler-polymer imbalance caused by excess interfacial free energy. When annealing, the former leads to coalescence while the latter leads to fillers aggregation, both can contribute to the negative temperature coefficient (NTC) and unstability of electrical properties.The influences of three different ways, including adding compatibilizer, changing compounding processes and blending sequences, on electrical conductivity and thermal stabilities of carbon black (CB) filled immiscible polypropylene (PP)/polystyrene (PS) (1/1) blends were investigated through CB selective distribution and composite morphology. Moreover, interfacial tension, viscosity and simultaneous measurement of resistance and dynamic rheology in annealing were used in this research.The immiscible CB/PP/PS composite with CB homogeneously located in PS phase exhibited the highest resistivity, and its rapidest variation amplitude of electrical resistivity and rheological parameters upon annealing showed the worst thermal stabilities. However, adding an optimal content of compatibilizer styrene-butadiene-styrene block copolymer (5 vol% SBS) could significantly lower p of composite because SBS with a high affinity to CB could induce CB particles to the PP/PS interfacial region. The SBS compatibilization could reduce phase size, forming finer co-continuous morphology. Moreover, the compatibilization, high viscosity and CB location in the interfacial region could slow down the coalescence and the CB aggregation, improving the thermal stabilities of CB/SBS/PP/PS. As for the compounding processes, in CB/SBS/PP/PS prepared with direct blending, the high viscosity of SBS blocked CB to get inside, resulting in limited volume of CB in the interfacial region. But in (SBS/CB)/PP/PS prepared with masterbatch blending, the high viscosity of SBS blocked CB to get outside, resulting in rich CB in the interfacial region, so (SBS/CB)/PP/PS got better electrical conductivity and thermal stabilities. As for blending sequences, in (SBS/CB)/PS+PP composite, the higher affinity between masterbatch and PP drived CB from PS to PP phase, but this movement was blocked by SBS’s high viscosity, so only a smaller fraction of CB traped in the interfacial region; while in (SBS/CB)/PP+PS composite, the masterbatch, lacking of driving force to move, just stayed in PP phase. Moreover, SBS tackified PS and PP respectively in composites above, leading to wores co-continuous morphologies. So both (SBS/CB)/PS+PP and (SBS/CB)/PP+PS showed worse electrical conductivity and thermal stabilities when compared with (SBS/CB)/PP/PS. In addition, the resistances, morphologies and CB distributes in these three comosits prepared by different blending sequences tended to be similar after annealling, which announced that enough annealing could eliminate the influence of blending sequences made on materials...