Abstract:The electrical conductivity of extrinsically conducting polymer composite systems passes through a transition state known as percolation threshold. A discussion has been made on how different Sigmoidal models (S-models), such as Sigmoidal-Boltzmann (SB), Sigmoidal-Dose Response (SD), Sigmoidal-Hill (SH), Sigmoidal-Logistic (SL), and Sigmoidal-Logistic-1 (SL-1), can be applied to predict the percolation threshold of electrical conductivity for ethylene vinyl acetate copolymer (EVA) and acrylonitrile butadiene copolymer (NBR) conducting composite systems filled with different carbon fillers. An interesting finding that comes from these observations is that the percolation threshold for electrical conductivity determined by SB and SD models are similar, whereas, the other models give different result when estimated for a particular composite system. This similarity and discrepancy in the results of percolation threshold have been discussed by considering the strength, weakness, and limitation of the models. The percolation threshold value for the composites has also been determined using the classical percolation theory and compared with the sigmoidal models. Moreover, to check the universal applicability, these Sigmoidal models have also been tested on results from some published literature. Finally, it is revealed that, except SL-1 model, the remaining models can successfully be used to determine the percolation threshold of electrical conductivity for extrinsically conductive polymer composites.

Polymeric outdoor insulators derived from polydimethyl siloxane (PDMS) are replacing conventional ceramic insulators in high voltage power transmission lines because of their improved electrical, mechanical and hydrophobic performance. Major impediments like failure of polymeric insulators due to natural aging by UV radiation from sunlight and electrical tracking have limited their usage. Herein, it is demonstrated about the usage of manganese dioxide based nanoparticles as an effective agent to prevent the UV accelerated aging of polymeric insulators. MnO nanoparticles of different shapes and dimension were synthesized using a single step wet chemical reaction between KMnO and methyl acetate. Namely, 2D δ-MnO nanosheets, 1D α-MnO nanowires and 3D α-MnO nanorods were formed. These nanoparticles were extensively characterized by various techniques. In the scope of the study, the δ-MnO (10 S cm; 1 MHz) nanosheet demonstrated the lowest electrical AC conductivity and a higher band gap compared to the 1D (10 S cm; 1 MHz) and 3D variety (10 S cm; 1 MHz). Owing to the lower electrical conductivity of the δ-MnO nanosheet, it was further incorporated at different filler volumes in the polymeric matrix (blend of polydimethyl siloxane/ethylene vinyl acetate) as a UV protector material for the polymer based high voltage composite polymeric insulator. The UV protection ability, induced by the δ-MnO nanosheet, was achieved without adversely affecting other properties of the formulated insulator compound material. The optimum properties of the composite were found to be obtained at 3 phr (three parts of δ-MnO nanosheet per hundred parts of polymer) loading of the nanosheet. The current work will promise to pave a new pathway for the generation of UV resistant high voltage power transmission line insulator materials. It would be interesting in the future to study the effect of incorporation of manganese dioxide based nanosheets on the UV resistant properties of different polymeric matrices.

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Ceramic materials are commonly used as outdoor insulator for high voltage power transmission line. Presently these ceramic insulators are replaced by composite polymeric insulators with silicone rubber (PDMS) housing, especially in industrial area with pollution. Silicone rubber is chosen for housing material because of their excellent aging resistance, electrical property, tracking resistance, stable hydrophobicity which in turn controls the tracking resistance.However, the material has seen deficiencies like poor mechanical strength and high cost. To improve mechanical properties and reduce cost, silicone rubber is blended with ethylene vinyl acetate copolymer (EVA). The optimum blend composition is found to be PDMS/EVA 60/40 w/w. But in doing so there is some reduction in hydrophobicity is observed, thus adversely affecting the tracking resistance. To improve hydrophobicity, the addition of nanosilica in the level of 6 phr is found to be the optimum. Thus high performance outdoor insulator can be produced from PDMS-EVA blend containing 6 phr nanosilica. Different types of accelerated aging test were performed on insulator samples to simulate their aging behavior under different real life aging process.

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