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Title: Carbon nanomaterial/polymer composites with enhanced electrical and mechanical properties
Authors: Pan, Yongzheng
Keywords: DRNTU::Engineering::Materials::Composite materials
Issue Date: 2013
Abstract: Carbon nanomaterial is a class of materials built by a cluster of sp2- hybridized carbon atoms in different geometries, including zero-dimensional (0D) fullerenes, 1D carbon nanotubes (CNTs), and 2D graphene. A unique combination of large aspect ratio, high specific surface area, low density, and excellent mechanical, electrical and thermal properties makes them multi-functional nanofillers for light-weight and high-performance polymer composites. The main objective of this research is two-fold: i) development of effective routes for fabrication of polymer composites containing carbon nanomaterials with enhanced electrical and mechanical properties and ii) comprehension of the relationships among processing, structure and property of the carbon nanomateiral/polymer composites. First, the influence of dispersion of multi-walled carbon nanotube (MWCNT) on the electrical properties of MWCNT/polypropylene (PP) composite is studied. To improve the dispersion of MWCNTs, MWCNTs are chemically oxidized and a polymeric compatibilizer, maleic anhydride-grafted polypropylene (PP-g-MA), is added into the composites. It is revealed that oxidation of MWCNTs marginally improves the dispersion but largely enhances the interfacial adhesion between MWCNTs and the PP matrix in the presence of PP-g-MA. Because the improved MWCNT dispersion reduces the number of electrical contacts between MWCNTs, the composites containing both oxidized MWCNTs and PP-g-MA have the best dispersion and distribution of MWCNTs but exhibit lower electrical conductivity compared with the pristine MWCNT/PP composites. Therefore, it is crucial to balance between the MWCNT dispersion and their connections into conductive networks. Afterwards, the influence of the aspect ratio of MWCNTs is investigated. The MWCNT/PP composites display a synchronous increase in electrical conductivity with increasing aspect ratio of MWCNTs at a fixed MWCNT loading. MWCNTs with a larger aspect ratio also lead to a lower percolation threshold of the composites. By adding MWCNTs with an aspect ratio of 167, the composites exhibit an electrical percolation threshold of only 0.74 wt.% and reach an electrical conductivity of 1.2 S/cm at 10 wt.% loading of MWCNTs, which is higher than the conductivities reported in the previous literature for MWCNT/PP systems. Meanwhile, dynamic rheological properties of the composites are measured for investigating their percolation and gel-like behavior. The difference between rheological and electrical percolation thresholds is discussed and explained by the different stages of MWCNT network formation.
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