Aspect ratio effects of multi‐walled carbon nanotubes on electrical, mechanical, and thermal properties of polycarbonate/MWCNT composites

Abstract

Two multi‐walled carbon nanotubes (MWCNTs) having relatively high aspect ratios of 313 and 474 with approximately the same diameter were melt mixed with polycarbonate (PC) in a twin‐screw conical micro compounder. The effects of aspect ratio on the electrical, mechanical, and thermal properties of the PC/MWCNT composites were investigated. Electrical conductivities and storage moduli of the filled samples are found to be independent of the starting aspect ratio for these high aspect ratio tubes; although the conductivities and storage moduli are still significantly higher than values of composites made with nanotubes having more commercially common aspect ratios of ∼100. Transmission electron microscopy results suggest that melt‐mixing reduces these longer nanotubes to the same length, but still approximately two times longer than the length of commercially common aspect ratio tubes after melt‐mixing. Molecular weight measurements show that during melt‐mixing the longer nanotubes significantly degrade the molecular weight of the polymer as compared to very similar nanotubes with aspect ratio ∼100. Because of the molecular weight reduction glass transition temperatures predictably show a large decrease with increasing nanotube concentration. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 73–83

Tough semiconductor polycarbonate/multiwalled carbon nanotubes nanocomposites by rubber modification

“…The modulus of the NCs increased upon addition of MWCNT. This increase (5% in the case of the 0.5-10% NC for instance) is consistent with that observed [17] in highly dispersed binary PC-based NCs (~8% with 0.5% MWCNT addition) obtained using an internal mixing method. The increase is facilitated by the large interfacial area-to-dispersed phase volume ratio characteristic of highly dispersed NCs, and indicates the presence of significant interactions between the polymer chains and the MWCNTs.…”

“…Moreover, electrically conductive NCs based on PC can be obtained at low MWCNT contents (0.1-2 %) by direct melt processing of both components [17,18], or by using previously prepared highly dispersed PC master-batches [19,20]. The presence of 4 relatively low MWCNT contents (2-3 %) seriously deteriorates the ductility of the PC matrix, which shows a dangerous tough/brittle transition at around these contents [21,22].…”

Benign reduction of carbon nanotube agglomerates using a supercritical carbon dioxide process

“…However, recent literature has recognized significant shortening of the nanotubes during processing. These methods include, but are not limited to, sonication, ball milling, and high-shear melt compounding [11][12][13][14][15][16]. Sonication has been known to cause damage to MWCNTs, evident in surface observations of the nanotubes and from aspect ratio calculations using scanning electron microscopy (SEM).…”

Depression in glass transition temperature of multiwalled carbon nanotubes reinforced polycarbonate composites: effect of functionalization

“…Guo et al reported the effect of aspect ratio of CNTs on composite properties, for concentration of SWCNT loading up to 3%. 22 They informed greater depression of T g and higher increment in storage modulus for CNTs with high aspect ratio as relative to the low aspect ratio CNTs.…”