Structure–property relationships in isotactic polypropylene/multi-walled carbon nanotubes nanocomposites

In this work, the influence of multi-walled carbon nanotubes (MWCNT) on electrical, thermal and mechanical properties of CNT reinforced isotactic polypropylene (iPP) nanocomposites is studied. The composites were obtained by diluting a masterbatch of 20 wt.% MWCNT with a low viscous iPP, using melt mixing. The morphology of the prepared samples was examined through SEM, Raman and XRD measurements. The effect of MWCNT addition on the thermal transitions of the iPP was investigated by differential scanning calorimetry (DSC) measurements. Significant changes are reported in the crystallization behavior of the matrix on addition of carbon nanotubes: increase of the degree of crystallinity, as well as appearance of a new crystallization peak (owing to trans-crystallinity). Dynamic mechanical analysis (DMA) studies revealed an enhancement of the storage modulus, in the glassy state, up to 86%. Furthermore, broadband dielectric relaxation spectroscopy (DRS) was employed to study the electrical and dielectric properties of the nanocomposites. The electrical percolation threshold was calculated 0.6–0.7 vol.% MWCNT from both dc conductivity and dielectric constant values. This value is lower than previous mentioned ones in literature in similar systems. In conclusion, this works provides a simple and quick way for the preparation of PP/MWCNT nanocomposites with low electrical percolation threshold and significantly enhanced mechanical properties.     

Widely dispersed PEI-based nanocomposites with multi-wall carbon nanotubes by blending with a masterbatch

High performance poly(etherimide) (PEI)-based nanocomposites (PNs) with multi-walled carbon nanotubes (MWCNT) were obtained via melt mixing. To achieve this, PEI was mixed with a well-dispersed commercial poly(butylene terephthalate) (PBT)/MWCNT master-batch in an attempt to transfer the dispersed MWCNTs to a PEI matrix. A broad and homogeneous dispersion of MWCNTs throughout the PEI-based matrix was obtained. The electrical percolation threshold (p_c) was reached at only 1 wt.% MWCNT. This p_c showed a power law dependence of conductivity on filler concentration, with a critical exponent of 1.92, which indicates that a three dimensional percolated structure was achieved. The glass transition temperature and the pressure at the output end of the extruder decreased when the master-batch was added, indicating that the processability of PEI was improved. In addition to this, the modified PEI-based PNs presented ductile behaviour and an ameliorated (12% with 5 wt.% MWCNT) elastic modulus compared with pure PEI.     

Dispersions of carbon nanotubes/polyhedral oligomeric silsesquioxanes hybrids in polymer: the mechanical,electrical and EMI shielding properties

A hybrid was synthesized by grafting polyhedral oligomeric silsesquioxane (POSS) to multiwalled carbon nanotubes (MWCNTs). The MWCNT/polymer composites produced using silsesquioxane grafted MWCNTs as a filler had a high electromagnetic interference shielding effectiveness. Homogeneous dispersion of silsesquioxane grafted MWCNTs occurred throughout the polymer without any aggregation, while a pristine MWCNT aggregate that integrated several nanotube domains existed in the polymer matrix. A comparative study of the optical transmittance, electrical, and electromagnetic interference shielding properties of poly(l-lactide) (PLLA)/MWCNT composites based on pristine MWCNTs and silsesquioxane grafted MWCNTs was carried out. A high electromagnetic interference shielding effectiveness (15–16 dB) was obtained in the 36–50 GHz range at a relatively low filler loading (4 wt%) in the PLLA/silsesquioxane grafted MWCNT composite.     

Preparation and properties of chitosan nanocomposite films reinforced by poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) treated carbon nanotubes

Carbon nanotube-based nanocomposites of chitosan were successfully prepared by a simple solution-evaporation method. Multiwalled carbon nanotubes (MWCNTs) were treated by poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT-PSS) in water before mixed with a chitosan solution to improve the dispersion of MWCNTs and interfacial compatibility between MWCNTs and chitosan. The morphological and mechanical properties of the prepared PEDOT-PSS/MWCNT/chitosan nanocomposites have been characterized with field emission scanning electron microscopy (FESEM) and tensile tests. MWCNTs were observed to be homogeneously dispersed throughout the chitosan matrix. As compared with the neat chitosan, the tensile strength and modulus of the nanocomposite were greatly improved by about 61% and 34%, respectively, with incorporation of only 0.5 wt.% of MWCNTs into the chitosan matrix. The comparison of mechanical properties for PEDOT-PSS/MWCNT/chitosan and pristine MWCNT/chitosan nanocomposites has been made. The hardness of the nanocomposites was also evaluated by nanoindentation.     

Corrugation of the external surface of multiwall carbon nanotubes by catalytic oxidative etching and its effect on their decoration with metal nanoparticles

It was established that partial combustion of carbon constituting the walls of multiwall carbon nanotubes (MWCNTs) catalyzed by previously deposited CaCO₃ nanoparticles converts parallel graphene layers in a multiwall structure to aggregates formed by nano-onions with a diameter of 5–12 nm. The areas with positive curvature of graphene layers on the external surface of air-etched MWCNTs played the role of docking stations for nickel nanoparticles inserted by sonochemical deposition after removal of the CaCO₃. The nickel nanoparticles were located exclusively at the tops of the onions. Formation of nanoscale curvature at the MWCNT support surfaces decreased the average size of Ni nanocrystals at similar loading of 50–60 wt% from 8 to 2 nm. Partial catalytic combustion did not change the concentration of surface carbonyl groups measured by titration, which attributes the observed phenomena directly to the corrugation of the MWCNT surfaces. The catalytic tests revealed a significant increase of catalytic activity of supported Ni catalyst due to corrugating of the external surface of the MWCNT support. After oxidative etching of the MWCNTs, the rate of chloroacetophenone hydrogenation measured with a Ni–MWCNT catalyst increased by a factor of 2 without change in selectivity yielding chlorophenylethanol as the main product.     

Synthesis and characterization of well-dispersed multi-walled carbon nanotube/low-bandgap poly(3,4-alkoxythiophene) nanocomposites

In this study, we prepared nanocomposites of multi-walled carbon nanotubes (MWCNTs) and low-energy-bandgap conjugated polymers incorporating 3,4-alkoxythiophene monomers. Poly(3,4-dihexyloxythiophene) (PDHOT) and poly(3,4-dimethoxythiophene-co-3,4-dihexyloxythiophene) [P(DMOT-co-DHOT)] have relatively low-energy-bandgaps (ca. 1.38 and 1.34 eV, respectively), determined from the onsets of absorbances in their UV–Vis spectra, because of the electron-donating effects of their alkoxy groups. MWCNTs have poor solubility in common organic solvents; after surface modification with alkyl side chains using the Tour reaction, however, the p-hexylaniline modified MWCNT derivative (MWCNT-HA) was readily dispersed in CHCl₃ and could be mixed with the low bandgap polymers. Scanning electron microscopy images revealed that MWCNT-HA was dispersed well in each polythiophene derivative; only a few MWCNT-HA bundles could be observed at a high MWCNT-HA content (≧20 wt.%). The electrical conductivities of the MWCNTs/PDHOT composites were dependent on their MWCNT content, reaching 16 S/cm at 30 wt.% MWCNT-HA. We suspect that the two hexyloxy chains of PDHOT enhanced its solubility and allowed it to wrap around the surfaces of the MWCNTs more readily.     

Characterization of rheological behaviors of polypropylene/carbon nanotubes composites and modeling their flow in a twin-screw mixer

This paper focuses on the numerical simulation of the polypropylene/multi-walled carbon nanotubes (PP/MWCNT) flow into a twin-screw mixer, during the mixing phase. The PP/MWCNT behavior obeys an innovating Carreau law enriched temperature built on the rheological properties carried out previously. The polypropylene was mixed with different MWCNTs contents (1, 2, 4 and 8 wt.% of MWCNT content) and the rheological tests were performed at shear rate ranges from 10⁻¹ to 2 × 10⁴ s⁻¹ at four temperatures (180, 200, 220 and 240 °C). Thus the effects of the temperature and the MWCNTs content on the rheological properties of the PP/MWCNT composites were investigated. The finite element (FEM) analysis of the PP/MWCNT flow allows to compute the velocity, the shear rate and the temperature during the mixing phase period. A good agreement between the experimental measured torque on the screw and the calculated one is shown. Therefore, one can consider that the physical flow is generally well described, awaiting a numerical simulation of the PP/MWCNT mixing phase.     

Carbon nanotube modification using gum arabic and its effect on the dispersion and tensile properties of carbon nanotubes/epoxy nanocomposites

In this study, the effects of a MWCNT treatment on the dispersion of MWCNTs in aqueous solution and the tensile properties of MWCNT/epoxy nanocomposites were investigated. MWCNTs were treated using acid and gum arabic, and MWCNT/epoxy nanocomposites were fabricated with 0.3 wt.% unmodified, oxidized and gum-treated MWCNTs. The dispersion states of the unmodified, oxidized, and Gum-treated MWCNTs were characterized in distilled water. The tensile strengths and elastic modulus of the three nanocomposites were determined and compared. The results indicated that the gum treatment produced better dispersion of the MWCNTs in distilled water and that gum-treated MWCNT/epoxy nanocomposites had a better tensile strength and elastic modulus than did the unmodified and acid-treated MWCNT/epoxy nanocomposites. Scanning electron microscope examination of the fracture surface showed that the improved tensile properties of the gum-treated MWCNT/epoxy nanocomposites were attributed to the improved dispersion of MWCNTs in the epoxy and to interfacial bonding between nanotubes and the epoxy matrix.     

Filler dispersion and electrical properties of polyamide 12/MWCNT-nanocomposites produced in reactive extrusion via anionic ring-opening polymerization

The reactive extrusion of lauryl lactam to polyamide 12 (PA12) of controlled molar mass was successfully performed in a microcompounder. The maximum residual monomer content was less than 1%. The in-situ polymerization in the presence of 1–5 wt.% multiwalled carbon nanotubes (MWCNTs) was studied and the processing conditions were optimized with respect to the electrical resistivity and MWCNT dispersion. Runs which yielded in higher molar mass PA12 resulted in better dispersion of MWCNTs, whereas nanocomposites with lower molar mass PA12 had lower electrical percolation thresholds (MWCNT concentration ∼1 wt.%). A high screw speed of 200 rpm was identified to cause best dispersion and the lowest percolation threshold.     

Mechanical performance of epoxy matrix hybrid nanocomposites containing carbon nanotubes and nanodiamonds

A novel class of epoxy matrix hybrid nanocomposites has been developed containing multiwalled carbon nanotubes (MWCNTs) and nanodiamonds (NDs) to explore the combined effect of nanoreinforcements on the mechanical performance of nanocomposites. Both the nanofillers were functionalized before incorporating into epoxy matrix to promote interfacial interactions. The concentrations of both MWCNTs and NDs in the nanocomposites were increased systematically, i.e. 0.05 wt.%, 0.1 wt.% and 0.2 wt.% while composites containing individual nanoreinforcements were also manufactured for comparison. The developed nanocomposites were characterized microstructurally by scanning electron microscopy (SEM) and mechanically by tensile, flexural, impact and hardness tests. Homogeneous dispersion of MWCNTs and NDs was observed under SEM, which resulted in the enhancement of mechanical properties of nanocomposites. The composites containing 0.2 wt.% MWCNTs and 0.2 wt.% NDs showed 50% increase in hardness while tensile strength and modulus enhanced to 70% and 84%, respectively. Flexural strength and modulus also showed a rise of 104% and 56%, respectively. Interestingly, fracture strain also increased in both the tensile and flexural testing. The impact resistance increased to 161% showing a significant improvement in the toughness of hybrid nanocomposites.     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

Preparation,morphology and properties of acid and amine modified multiwalled carbon nanotube/polyimide composite

The precursor of polyimide, polyamic acid, was prepared by reacting 4,4′-oxydianiline (ODA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA). Unmodified, acid-modified and amine-modified multiwall carbon nanotubes (MWCNT) were separately added to the polyamic acid and heated to 300 °C to produce polyimide/carbon nanotube composite. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) microphotographs reveal that acid-modified MWCNT and amine-modified MWCNT were dispersed uniformly in the polyimide matrix. The effect of the acid and amine-modified MWCNTs on the surface and volume electrical resistivities of MWCNT/polyimide composites were investigated . The surface electrical resistivity of the nanocomposites decreased from 1.28 × 10¹⁵ Ω/cm² (neat polyimide) to 7.59 × 10⁶ Ω/cm² (6.98 wt% unmodified MWCNT content). Adding MWCNTs influenced the glass transition temperatures of the nanocomposites. Modified MWCNTs significance enhanced the mechanical properties of the nanocomposites. The tensile strength of the MWCNT/polyimide composite was increased from 102 MPa (neat polyimide) 134 MPa (6.98 wt% acid modified MWCNT/polyimide composites).     

Comparison of rheological and electrical percolation phenomena in carbon black and carbon nanotube filled epoxy polymers

Epoxy nanocomposite suspensions including multi-wall carbon nanotubes (MWCNTs) and carbon black (CB) were produced and investigated by means of combined rheological and electrical analysis. The rheological percolation behaviour was compared to the electrical percolation behaviour. Due to similar dynamic agglomeration mechanisms the difference between the rheological and the electrical percolation threshold in the cured state is identical for MWCNT and CB filled systems. Non-covalent matrix–nanoparticle interactions in uncured epoxy suspensions are negligible since the onset of electrical and rheological percolation in the uncured state coincidence. Furthermore, the electrical percolation threshold in the cured state is always lower than in the uncured state because of the high tendency of CB and MWCNTs to form conductive networks during curing. The difference between rheological and electrical percolation threshold is dependent on the curing conditions. Thus, the rheological percolation threshold can be considered as an upper limit for the electrical percolation threshold in the cured state. Due to the formation of co-supporting networks multi-filler (MWCNTs and CB) suspensions exhibit a similar rheological behaviour as the binary MWCNT suspensions. For both types of suspensions a rheological percolation threshold of around 0.2 and 0.25 wt% was determined. Conversely, the binary CB nanocomposites exhibit a four-times higher percolation threshold of about 0.8 wt%. The difference between the binary MWCNT suspension and the ternary CB/MWCNT suspension in storage shear modulus at high filler concentrations (~0.8 wt%) turns out to be less than expected. Thus, synergistic effects in network formation are already present in the epoxy suspension and get more pronounced during curing.     

Effect of (Mn + Cr) addition on the microstructure and thermal stability of spray-formed hypereutectic Al–Si alloys

This study aims to investigate the tensile mechanical behavior and fracture toughness of vinyl-ester/polyester hybrid nanocomposites containing various types of nanofillers, including multi- and double-walled carbon nanotubes with and without amine functional groups (MWCNTs, DWCNTs, MWCNT-NH₂ and DWCNT-NH₂). To prepare the resin suspensions, very low contents (0.05, 0.1 and 0.3 wt.%) of carbon nanotubes (CNTs) were dispersed within a specially synthesized styrene-free polyester resin, conducting 3-roll milling technique. The collected resin stuff was subsequently blended with vinyl-ester via mechanical stirring to achieve final suspensions prior to polymerization. Nanocomposites containing MWCNTs and MWCNT-NH₂ were found to exhibit higher tensile strength and modulus as well as larger fracture toughness and fracture energy compared to neat hybrid polymer. However, incorporation of similar contents of DWCNTs and DWCNT-NH₂ into the hybrid resin did not reflect the same improvement in the corresponding mechanical properties. Furthermore, experimentally measured elastic moduli of the nanocomposites containing DWCNTs, DWCNT-NH₂, MWCNTs and MWCNT-NH₂ were fitted to Halphin–Tsai model. Regardless of amine functional groups or content of carbon nanotubes, MWCNT modified nanocomposites exhibited better agreement between the predicted and the measured elastic moduli values compared to nanocomposites with DWCNTs. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to reveal dispersion state of the carbon nanotubes within the hybrid polymer and to examine the CNT induced failure modes that occurred under mechanical loading, respectively. Based on the experimental findings obtained, it was emphasized that the types of CNTs and presence of amine functional groups on the surface of CNTs affects substantially the chemical interactions at the interface, thus tuning the ultimate mechanical performance of the resulting nanocomposites.     

Influence of multiwall carbon nanotube functionality and loading on mechanical properties of PMMA/MWCNT bone cements

Poly (methyl methacrylate) (PMMA) bone cement—multi walled carbon nanotube (MWCNT) nanocomposites with weight loadings ranging from 0.1 to 1.0 wt% were prepared. The MWCNTs investigated were unfunctionalised, carboxyl and amine functionalised MWCNTs. Mechanical properties of the resultant nanocomposite cements were characterised as per international standards for acrylic resin cements. These mechanical properties were influenced by the type and wt% loading of MWCNT used. The morphology and degree of dispersion of the MWCNTs in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in mechanical properties were attributed to the MWCNTs arresting/retarding crack propagation through the cement by providing a bridging effect and hindering crack propagation. MWCNTs agglomerations were evident within the cement microstructure, the degree of these agglomerations was dependent on the weight fraction and functionality of MWCNTs incorporated into the cement.     

Temperature dependence of electrical conductivity in double-wall and multi-wall carbon nanotube/polyester nanocomposites

The aim of this study is to investigate temperature dependence of electrical conductivity of carbon nanotube (CNT)/polyester nanocomposites from room temperature to 77 K using four-point probe test method. To produce nanocomposites, various types and amounts of CNTs (0.1, 0.3 and 0.5 wt.%) were dispersed via 3-roll mill technique within a specially formulized resin blend of thermoset polyesters. CNTs used in the study include multi walled carbon nanotubes (MWCNT) and double-walled carbon nanotubes (DWCNT) with and without amine functional groups (–NH₂). It was observed that the incorporation of carbon nanotubes into resin blend yields electrically percolating networks and electrical conductivity of the resulting nanocomposites increases with increasing amount of nanotubes. However, nanocomposites containing amino functionalized carbon nanotubes exhibit relatively lower electrical conductivity compared to those with non-functionalized carbon nanotubes. To get better interpretation of the mechanism leading to conductive network via CNTs with and without amine functional groups, the experimental results were fitted to fluctuation-induced tunneling through the barriers between the metallic regions model. It was found that the results are in good agreement with prediction of proposed model.     

Preparation and characterization of multi-walled carbon nanotube/hydroxyapatite nanocomposite film dip coated on Ti–6Al–4V by sol–gel method for biomedical applications: An in vitro study

In the present research, the introduction of multi-walled carbon nanotubes (MWCNTs) into the hydroxyapatite (HA) matrix and dip coating of nanocomposite on titanium alloy (Ti–6Al–4V) plate was conducted in order to improve the performance of the HA-coated implant via the sol–gel method. The structural characterization and electron microscopy results confirmed well crystallized HA–MWCNT coating and homogenous dispersion of carbon nanotubes in the ceramic matrix at temperatures as low as 500 °C. The evaluation of the mechanical properties of HA and HA/MWCNT composite coatings with different weight percentages of MWCNTs showed that the addition of low concentrations of MWCNTs (0.5 and 1 wt.%) had improved effect on the mechanical properties of nanocomposite coatings. Moreover, this in vitro study ascertained the biocompatibility of the prepared sol–gel-derived HA/MWCNT composite coatings.     

Synthesis and relevant electrochemical properties of 2-hydroxypropyltrimethyl ammonium chloride chitosan-grafted multiwalled carbon nanotubes

The 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC)-grafted multiwalled carbon nanotubes (MWCNTs) composite (HACC–MWCNTs) was prepared via covalently grafting HACC onto the surfaces of MWCNT. The properties and morphology of the resulting materials were monitored by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of FTIR and TGA indicated that the interaction between MWCNT and HACC was grafting through covalent links. TEM and SEM images confirmed MWCNT stained with an extra phase after the grafting process that was presumed to come from HACC. The dispersion of MWCNT in H₂O was improved after the grafting of HACC,which was in agreement with the positive charge of HACC–MWCNT at any pH value. The electrochemical properties of HACC–MWCNT were investigated by cyclic voltammetry (CV). The dramatic improvement in the electrostatic interactions between HACC–MWCNT/electrode and anionic complexes was distinguished from the response of chitosan-MWCNT/electrode and non-modified electrode. According to the experimental results, the HACC–MWCNT had a possibility to serve as a novel material for innovative anionic sensor.     

Strain sensing in polymer/carbon nanotube composites by electrical resistance measurement

In this work multiwall carbon nanotubes (MWCNTs) dispersed in a polymer matrix have been used for strain sensing of the resulting nanocomposite under tensile loading. This was achieved by measuring the relative electrical resistance change (ΔR/R₀) in conductive polyvinylidenefluoride (PVDF)/MWCNTs nanocomposites prepared by melt-mixing with varying filler content from 0.5 wt.% to 8 wt.%. Two main parameters were systematically studied. The PVDF/MWCNTs mixing procedure that results in a successful MWCNTs dispersion, and the effect of MWCNTs content on material’s sensing behaviour. The samples were subjected to tensile loading and the longitudinal strain was monitored together with the longitudinal electrical resistance. The results showed that MWCNTs dispersed in insulating PVDF matrix have the potential to be used as a sensitive network to monitor the strain levels in polymer/carbon nanotube nanocomposites as the deformation level of each sample was being reflected by the resistance changes.     

Microwave-assisted synthesis and highly photocatalytic activity of MWCNT/ZnSe heterostructures

The multi-walled carbon nanotubes (MWCNTs) coated with the face-center cubic ZnSe nanoparticles with a uniform and small diameter have been prepared to form MWCNT/ZnSe heterostructures by microwave irradiation. The morphology, loading quantity and size of the ZnSe nanoparticles in the range of 15–50 nm can be controlled easily by adjusting the microwave power, pH value of the initial solution, the molar ratios of the Zn(AC)₂/MWCNTs and the appropriate complexing agent. The photoluminescence measurement indicates that the MWCNT/ZnSe heterostructures are blue-shifted compared to reported bulk ZnSe. The UV–vis absorption spectra of the heterostructures appears two sharp absorption peaks at 336 and 344 nm, respectively. It was demonstrated that the heterostructures could photodegrade the fuchsine acid in the solution with highly photocatalytic activity.