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Abstract
Green tea has recently been reported to be a good dispersant of single-walled carbon nanotubes (SWCNTs) in aqueous media. In the current work, green tea extract powder was examined for dispersion of SWCNTs in organic solvents. Dimethyl sulfoxide (DMSO) was found to be a good solvent of green tea extract for dispersing SWCNTs. A combination of green tea (dispersant)/DMSO (solvent)/polyvinyl alcohol (PVA) (nanotube wrap) was obtained that resulted in the dispersion of SWCNTs almost to individual nanotubes or to very thin nanotube bundles. The reinforcing ability of highly dispersed SWCNTs was explored in a PVA matrix producing PVA-SWCNT gel-spun fibers. Extraordinary reinforcing effects on the tensile and dynamic mechanical properties of the composites were observed by incorporating a minute amount of SWCNTs (>1 wt% to PVA). The analysis revealed effective stress transfer through the PVA crystalline interfaces surrounding the nanotubes.
Keywords
Polymer-matrix composites, green tea, carbon nanotubes, tensile strength, toughness
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Single-walled carbon nanotubes (SWCNTs) are known to have an extremely high Young's modulus, close to 1 TPa, and tensile strength in the range of 50-150 GPa.1 They have generated a great deal of interest as ideal candidates for mechanical reinforcement of polymers and polymeric fibers. In spite of their excellent mechanical properties, their use in effective reinforcement of SWCNTs in composites has not been fully realized due to their poor dispersion in most solvents; this limits the effective surface area of nanotubes in composites and hinders stress transfer.2 To obtain the optimum reinforcing effect, the SWCNTs must be dispersed to the level of perfectly or nearly isolated tubes individually coated with polymer in polymer-based composites. The strength and toughness of the composites tend to be very sensitive to the quality of dispersion and adhesion of polymer/SWCNTs.3
A variety of methods have been attempted to improve the dispersion of nanotubes by non-covalent functionalization, including surfactants,4 polymers5,6 and biomolecules such as DNA,7 peptides,8 polysaccharides 9 and proteins.10 Recently, Nakamura et al.11 discovered that green tea can solubilize SWCNTs in water. Green tea is composed of a group of watersoluble polyphenol compounds, epigallocatechin gallate (EGCg), epicatechin gallate (ECg), epigallocatechin (EGC) and epicatechin (EC).12 Among these, EGCg is the most abundant component in green tea, and is acknowledged to have antioxidant, antitumor...