Characterization of Multiwalled Carbon Nanotube-Reinforced Hydroxyapatite Composites Consolidated by Spark Plasma Sintering

Pure HA and 1, 3, 5, and 10 vol% multiwalled carbon nanotube- (MWNT-) reinforced hydroxyapatite (HA) were consolidated using a spark plasma sintering (SPS) technique. The relative density of pure HA increased with increasing sintering temperature, but that of the MWNT/HA composite reached almost full density at 900°C, and then decreased with further increases in sintering temperature. The relative density of the MWNT/HA composites increased with increasing MWNT content due to the excellent thermal conductivity of MWNTs. The grain size of MWNT/HA composites decreased with increasing MWNT content and increased with increasing sintering temperature. Pull-out toughening of the MWNTs of the MWNT/HA composites was observed in the fractured surface, which can be used to predict the improvement of the mechanical properties. On the other hand, the existence of undispersed or agglomerate MWNTs in the MWNT/HA composites accompanied large pores. The formation of large pores increased with increasing sintering temperature and MWNT content. The addition of MWNT in HA increased the hardness and fracture toughness by approximately 3~4 times, despite the presence of large pores produced by un-dispersed MWNTs. This provides strong evidence as to why the MWNTs are good candidates as reinforcements for strengthening the ceramic matrix. The MWNT/HA composites did not decompose during SPS sintering. The MWNT-reinforced HA composites were non-toxic and showed a good cell affinity and morphologyin vitrofor 1 day.

Composite Content Influence on Multiwall Carbon Nanotubes-SiO2 Film Humidity Sensors at AC Testing

MWNT –SiO2 composite film humidity sensors with different MWNTs proportions were fabricated and their performances under alternating current testing signals are investigated. Influence of MWNT content on humidity sensing characteristics of the sensors is explored and explained by vapor adsorption and capillary condensation effect. It is proved that 60% MWNT content sensors have humidity sensitivity of 1500% at 400 kHz testing frequency, much higher than those with other MWNT contents. In sensors’ sensitivity-frequency relation, maximum sensitivity comes from frequency section of 400kHz to 500kHz for sensors with higher MWNTs proportions.

Drying of polyacrylamide-multiwalled carbon nanotube (MWNT) composites with various MWNTs contents: a fluorescence study

We studied the drying of polyacrylamide (PAAm)-multiwalled carbon nanotube (MWNT) composites, prepared by free radical crosslinking copolymerization in water, with a steady state fluorescence technique. Composite gels were prepared at room temperature with pyranine (Py) doped as a fluorescence probe. Drying experiments were performed in air at various MWNT contents by real time monitoring of the Py fluorescence intensity (I) which increased as the drying proceeded. The Stern-Volmer equation, combined with the moving boundary diffusion model, was used to explain the behavior of I during drying. It was observed that the desorption coefficient (D) increased as the temperature increased. Drying energies (ΔE) were measured for the drying processes for each MWNT content gel, by using fluorescence, gravimetrical and volumetric methods. It is understood that ΔE values decrease by increasing MWNT content, until 1 wt% MWNT, and then increase above the level of this threshold value. The energy of drying is strongly correlated with the MWNT content in the composite. ΔE drops to its lowest value, at which conducting cluster starts to appear.

Thermal Conductivity of Epoxy Resin Reinforced with Magnesium Oxide Coated Multiwalled Carbon Nanotubes

Magnesium oxide coated multiwalled carbon nanotubes (MgO@MWNT) were fabricated and dispersed into epoxy matrix. The microstructures of MgO@MWNT and epoxy/MgO@MWNT nanocomposites were characterized by TEM and SEM. Electrical resistivity and thermal conductivity of epoxy nanocomposites were investigated with high resistance meter and thermal conductivity meter, respectively. MgO@MWNT has core-shell structure with MgO as shell and nanotube as core, and the thickness of MgO shell is ca. 15 nm. MgO@MWNT has been dispersed well in the epoxy matrix. MgO@MWNT loaded epoxy nanocomposites still retain electrical insulation inspite of the filler content increase. However, thermal conductivity of epoxy was increased with the MgO@MWNT content increasing. When MgO@MWNT content reached 2.0 wt.%, thermal conductivity was increased by 89% compared to neat epoxy, higher than that of unmodified MWNT nanocomposites with the same loading content.

Composite Content Influence on Multiwall Carbon Nanotubes-SiO2 Film Humidity Sensors at AC Testing

MWNT –SiO2 composite film humidity sensors with different MWNTs proportions were fabricated and their performances under alternating current testing signals are investigated. Influence of MWNT content on humidity sensing characteristics of the sensors is explored and explained by vapor adsorption and capillary condensation effect. It is proved that 60% MWNT content sensors have humidity sensitivity of 1500% at 400 kHz testing frequency, much higher than those with other MWNT contents. In sensors’ sensitivity-frequency relation, maximum sensitivity comes from frequency section of 400kHz to 500kHz for sensors with higher MWNTs proportions.

The Preparation and Properties of PEN/MWNT Nanocomposites

Polyarylene ether nitrile (PEN)/multiwalled carbon nanotube (MWNT) composites was prepared, and their rheological behavior and mechanical properties were studied. The PEN/MWNT composites have been fabricated via solution mixing by using ultrasound and dispersion agent, and then casting. This results show that the rheological and mechanical properties of the PEN/MWNT nanocomposites prepared by ultrasound treatment with sodium dodecyl sulfate increase more significantly than that of the ultrasound-treated PEN/MWNT composites and the untreated PEN/MWNT composites with the increase in the MWNT content. The rheological and mechanical properties of the PEN/MWNT composites were related with the content ratio of the MWNT and the preparation ways.

Thermal Degradation Study of Functionalized MWNT Reinforced Segmented Polyurethane Membrane

The thermal degradation of polytetramethylene glycol (PTMG, Mn 1/42900) based polyurethane (PU), along with four different weight contents (such as 0.25, 0.50, 1.0, and 2.5 wt%) of functionalized multiwalled nanotube (MWNT) reinforced PUs are studied in air as well as in nitrogen atmosphere. The degradation results are reported in 10 and 50% weight loss and derivative of thermogravimetry (DTG). As expected, PUs are thermally more stable in nitrogen than in air. However, the influence of MWNT content on thermal stability is unclear. At 0.25 and 0.50 wt% of MWNT content, thermal stability declined and a further increase of MWNT improved the thermal stability of PU. Fourier-transform infrared (FTIR) analysis is also performed for untreated and heat treated films in order to understand the degradation at different temperatures. Free C1/4O stretching neck dimension increases with increasing temperature which signifies breaking of H-bonding detected by FTIR measure ments.