Preparation and Properties of Exfoliated Graphite/Polystyrene Composite
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Preparation and Properties of Exfoliated Graphite/Polystyrene Composite Peng Xiao, Luyi Sun1, Min Xiao, Kecheng Gong Polymer Structure & Modification Lab, South China University of Technology, Guangzhou, 510640, P. R. China 1 Department of Chemistry, University of Alabama, Tuscaloosa, AL 35487, U.S.A. ABSTRACT A composite based on exfoliated graphite (EG) and polystyrene was prepared by polymerization-filling technique. With the argument of the amount of filled EG, the molecular weight of polystyrene in the resulting composite increased and the molecular weight distribution decreased. The glass transition temperature of the polystyrene was determined by dynamic mechanical analysis (DMA) and showed the glass temperature of polystyrene increasing to 123.74 .The thermal degradation behavior was studied using thermogravimetry (TG) and showed higher thermal stability of the composite than that of pure polystyrene and polystyrene/EG composite prepared by melt-blending. Four-probe instrument and high resistivity meter were used to measure the volume conductivity of the composites. Composites prepared by both polymerization-filling technique and melt-blending exhibit increased electrical conductivity, while composite prepared by polymerization-filling technique has a conductive percolation threshold lower than 2.5wt%. Introduction Conducting polymer composites are of great interest from the practical point of view, because their electrical properties can be tailored by properly choosing the components and their relative concentration. The formation of conducting polymer composites by melt blending is the most straightforward. But due to the absence of specific interfacial interaction, the mechanical properties are often drastically reduced. Polymerization-filling technique is a new way to produce polyolefin-based composites with remarkably improved performances [1]. By this method, composites are produced in one-step as the olefin is polymerized by a coordination catalyst anchored on the surface of filler. One of the main targets of the polymerization-filling method is homogeneity of the final composites and the combination of high impact strength, ductile fracture, and high modulus that can be achieved by the polymerization-filling technique has been sought for a long time. Exfoliated graphite has excellent conductivity which can be obtained by exfoliation of graphite intercalate [2]. Exfoliated graphite flakes have an accordion-shaped appearance and the expansion along c-direction can be as much as two orders of magnitude when the intercalate was heated over a critical temperature. As a conductive filler, exfoliated graphite has been incorporated successfully into polymer matrix by mechanically mixing [3], static melt dispersion mixing [4] or in situ exfoliation [5] and these composites have many important uses such as electrode material [6], electrical and thermal conductors [7,8], sealing material [9], etc. More recently Shiratori and coworkers [10] prepared a poly(methyl methacrylate) (PMMA) encapsulated exfoliated gra
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