Selective Localization Of Multiwalled Carbon Nanotubes Research Articles

Selective Localization of Multi-walled CNT in Polylactic Acid/Thermoplastic Polyurethane Blends and Its Effect on Mechanical Properties

Background: Due to excellent properties such as degradability, high strength, and biocompatibility, polylactic acid (PLA) has received enormous attention recently as a promising potential candidate material to replace petroleum-based polymers. However, PLA shows high brittleness as well as low toughness which may limit its application. Objective: In this work, PLA was melt blended with thermoplastic polyurethane (TPU) and then filled with carbon nanotubes (CNTs) to produce environmentally friendly polymeric materials with improved mechanical properties. Method: The specimens were prepared by using an internal mixer, followed by compression molding. Morphology of the matrix and particles dispersion state in the composite was investigated by using Scanning Electron Microscopy (SEM), while mechanical properties were evaluated via impact and tensile tests. Results: Observation from SEM's micrograph showed that two distinct phases were present in the blend, with selective localization of CNTs at one of the phases in the system. Thermodynamic calculation using Owen and Wendt’s equation predicted that the CNTs were preferably dispersed at TPU phase. As CNTs content increased, the toughness of TPU/CNT and TPU/PLA/CNT composites increased whereas the toughness of PLA/CNT composite decreased, that might be ascribed to the phenomenon of selective localization of the CNTs. Other than that, the elongation at break of PLA/CNT, PLA/TPU/CNT and TPU/CNT also increased with the addition of CNT. The incorporation of TPU in the TPU/PLA blends also imparted ductility to the blends. Conclusion: In conclusion, the selective localization prediction is in line with the trends observed in mechanical properties of PLA/TPU/MWCNT composites. Keywords: Selective localization, multi-walled carbon nanotubes, polylactic acid, thermoplastic polyurethane, polymer blends, toughness enhancement.

Achieving Large Dielectric Property Improvement in Poly(ethylene vinyl acetate)/Thermoplastic Polyurethane/Multiwall Carbon Nanotube Nanocomposites by Tailoring Phase Morphology

In this work, multiwall carbon nanotubes (MWCNTs) were melt compounded with a poly(ethylene vinyl acetate)/thermoplastic polyurethane (EVA/TPU) blend to prepare EVA/TPU/MWCNT blend nanocomposites. The effects of the blend morphology and selective localization of MWCNTs on the dielectric properties including dielectric constant and loss were systematically investigated. The results show that when the blend exhibits sea–island morphology accompanying MWCNT selective localization in island droplets, the dielectric constant was increased to 1200@100 Hz with addition of 5 wt % MWCNTs; in addition, the growth of dielectric loss is suppressed and the values of dielectric loss always remain around 1 with varying the loading of MWCNTs. Furthermore, based on the investigations of rheological percolation testing, morphological observation, and selective localization, the microcapacitor model was evoked to explain the underlying mechanism for the improvement of the dielectric constant for the blend with sea–island mo...

Effect of the selective localization of carbon nanotubes in polystyrene/poly(vinylidene fluoride) blends on their dielectric, thermal, and mechanical properties

The selective localization of multiwalled carbon nanotubes (MWNTs) in immiscible polystyrene (PS)/poly(vinylidene fluoride) (PVDF) blends (volume ratio of both components is 1/1) and its effect on composites’ dielectric, thermal, and mechanical properties are systematically studied. Employing two-step mixing process can make MWNTs localize in PS or PVDF phase successfully. When three components are simply mixed together by one-step processing, the MWNTs are selectively distributed in PVDF phase, which is supported by the dielectric measurements and the SEM observations and is consistent with the wetting coefficient evaluation. For the two-step mixing, when the fillers are first mixed with PS in the first step, some of them will migrate into PVDF phase in the second step although the migration is very slow. When the overall volume fraction of MWNTs is 3.9vol%, the selective localization of MWNTs in PVDF phase produces higher dielectric constant (ε′, ca. 485) than the case when the fillers are only in PS phase (ε′ of ca. 16) at 100Hz and room temperature of 25°C. Differential scanning calorimetry (DSC) measurements and mechanical tests show that the selective localization of all the fillers in PVDF phase produces little change of the melting point and crystallinity of PVDF component but slightly higher tensile strength. In contrast to the one-step mixing process, the two-step mixing to selectively localize the fillers in their favorite phase could be used to control the dielectric and mechanical properties of the materials.

Positive temperature coefficient and structural relaxations in selectively localized MWNTs in PE/PEO blends

The dispersion state of multiwall carbon nanotubes (MWNTs) in melt mixed polyethylene/polyethylene oxide (PE/PEO) blends has been assessed by both surface and volume electrical conductivity measurements and the structural relaxations have been assessed by broadband dielectric spectroscopy. The selective localization of MWNTs in the blends was controlled by the flow characteristics of the components, which led to their localization in the energetically less favored phase (PE). The electrical conductivity and positive temperature co-efficient (PTC) measurements were carried out on hot pressed samples. The neat blends exhibited only a negative temperature coefficient (NTC) effect while the blends with MWNTs exhibited both a PTC and a NTC at the melting temperatures of PE and PEO respectively. These phenomenal changes were corroborated with the different crystalline morphology in the blends. It was deduced that during compression molding, the more viscous PEO phase spreads less in contrast to the less viscous PE phase. This has further resulted in a gradient in morphology as well as the distribution state of the MWNTs in the samples and was supported by scanning electron and scanning acoustic microscopy (SAM) studies and contact angle measurements. SAM from different depths of the samples revealed a gradient in the microstructure in the PE/PEO blends which is contingent upon the flow characteristics of the components. Interestingly, the surface and volume electrical conductivity was different due to the different dispersion state of the MWNTs at the surface and bulk. The observed surface and volume electrical conductivity measurements were corroborated with the evolved morphology during processing. The structural relaxations in both PE and PEO were discerned from broadband dielectric spectroscopy. The segmental dynamics below and above the melting temperature of PEO were significantly different in the presence of MWNTs.