Study On NiCF Filled Polyethylene Conductive Composites

In recent years, more and more attentions have been paid to the conductive polymer naterials with the rapid development of the electron technology. Organic PTC composites is a (?)ovel functional materials with important research value. And this kind of composite have been widely applied in many fields such as self-regulating heaters, over-current protectors, electromgnetism shield materials and sensors due to their light weight, corrosion resistance, stable conductivity and simple processing technique. However, further research and mprovement are necessary for the PTC materials in both theory and practical application espects, which focus on the conductive mechanism, enhance of PTC intensity, elimination of NTC phenomenon and improvement of stability and reproducibility at high temperature.In present work, ultra-high molecular weight polyethylene (UHMWPE) was chosen as (?)olymer matrix, and Ni-coated carbon fiber (NiCF) was used as conductive filler, and JHMWPE-NiCF conductive polymer composite was successfully prepared by means of gelation/crystallization method. Thenγ-ray irradiation was carried out on this composites at omm temperature. The y-ray irradiation effect on this conductive composites was studied systematically by a variety of testing methods including different scanning calorimetry (DSC), (?)canning electron microscope (SEM), dynamic mechanical analysis (DMA), gel fraction neasurement and so on. Results demonstrated that the high conductivity of NiCF made the >ercolation threshold of electrical conductivity of the composites less than 4 vol% and the ;onductivity at room temperature reached 100S/cm when the filler content higher than 4 vol%. After irradiation, the UHMWPE-NiCF composites with NiCF content 4 vol% displayed very high PTC intensity which exceeded 108Ω-cm. A suitable irradiation dose level such as 300 cGy improved the mechanical properties of the composite films and its form stability at high emperature, eliminated NTC phenomenon, and decreased the electrical resistivity at room emperature at the same time.The mechanism of PTC effect was further investigated by means of volume expansion experiment and dielectric property analysis. Results of the former proved that sharp volume expansion occurred near melting point of UHMWPE, leading to the conductive paths (?)reaking up, which resulted in the abrupt increase of resistivity. On the other hand, this paper studied the dielectric behaviour of composites using resistor-capacitor circuit model. According to the dielectric properties combined with PTC effect, the PTC mechanism was studied furtherly. The results from dielectric behaviour of composites demonstrated that PTC effect can also be observed in the AC resitivity because the conduction networks are broken. And NTC phenomenon can also be observed because the component of contact capacitors has a strong dependence on frequency and temperature.The PTC jumping temperature afterγ-ray irradiation drifted to high temperature. This paper clarified the power ofγ-ray irradiation on electrical properties of composites by PTC effect which widened the application of this kind of electrical conductive composites.