Multi-walled Carbon Nanotubes Loading Research Articles

Cut growth and abrasion behaviour, and morphology of natural rubber filled with MWCNT and MWCNT/carbon black

Various amounts of predispersed multi-wall carbon nanotubes (MWCNT) were mixed with natural rubber (NR), with and without carbon black (CB), for preparing MWCNT-filled NR (NC) and MWCNT/CB-filled NR (NH) vulcanizates. All NH vulcanizates contained 30 phr CB and the amount of MWCNT for both NC and NH was varied from 0 to 8 phr. Helium ion microscopy (HIM) and FE-SEM images showed that MWCNT in the NH was dispersed much better than in the NC. Additionally, the well dispersed CB and MWCNT in the NH functioned synergistically in promoting an increase in longitudinal crack growth, leading to enhancement of edge-cut tensile strength (CTS) with increasing MWCNT loading. In contrast, all NC specimens ruptured in a simple lateral direction relating to their lower CTS. Results also revealed that abrasion resistance of the NH was not significantly changed with increasing MWCNT, whereas that of the NC increased. Nevertheless, abrasion resistance of both vulcanizates showed good correlation with the average value of ridge spacing on their abraded surfaces. It was also found that tensile strength of the NH was almost unchanged when the MWCNT loading was increased because the reinforcement by CB predominates over the MWCNT. However, 100% modulus and hardness of both NC and NH increased with increasing MWCNT content.

Conductive polyaniline composite films from aqueous dispersion: Performance enhancement by multi-walled carbon nanotube

The intractable multi-walled carbon nanotube (MWNT) was dispersed in aqueous solutions of conductive polyaniline (cPANI) by externally doping of MWNT/polyaniline (PANI) employing an organic polymeric phosphate acid as the dopant. Free-standing composite films were obtained from the MWNT/cPANI aqueous dispersion after drying. In comparison with the cPANI, the conductivity of MWNT/cPANI composites showed a 2 order of magnitude increase with the maximum value 1.2Scm−1, at the MWNT loading of 1.0wt% because of the doping effect of MWNT on PANI. Under the strong π–π interactions between PANI and MWNT which were discussed by FT-IR and UV–vis analysis, the redox performance of the MWNT/cPANI composites was significantly modified compared with the pure cPANI. In addition, the capacitive behaviors of the MWNT/cPANI films varied with the difference of the MWNT loading due to the morphology variation resulted from the established interactions. The enhanced specific capacitance with the highest value of 371Fg−1 at a current loading of 0.5Ag−1 was obtained for the MWNT/cPANI films containing MWNT content of 1.0wt%, as well as the better cyclability.

Nanocomposites from styrene–butadiene rubber (SBR) and multiwall carbon nanotubes (MWCNT) part 2: Mechanical properties

Due to their high aspect ratio, strength, and modulus, multiwall carbon nanotubes (MWCNT) have attracted interest as a reinforcing filler in the automotive tire industry. In part 1 of this study, we demonstrated that styrene–butadiene rubber (SBR) composites containing up to 15 wt. % of well-dispersed, discreet MWCNTs can be prepared using MWCNTs with a specific surface modification and controlled aspect ratios. The melt rheology of the composites with discreet MWCNT was best described in terms of an effective aspect ratio and by considering the discrete MWCNT to be flexible rather than rigid rods. In this work, the effect of tensile strains, up to values of 6, for cured SBR composites containing discreet MWCNT concentrations up to 12% by weight were investigated. The deformation behavior indicates good adhesion between these MWCNT and the SBR. Mooney–Rivlin plots derived from the composite tensile stress–strain data displayed a dramatic change in mechanical behavior as the MWCNT loading exceeded about 5 wt. % attributed to a combined reinforcing effect of tubes on SBR plus overlap of curved or coiled MWCNT. Beyond tensile strains of about 1.7, strain hardening increases dramatically at MWCNT loading greater than 5 wt. % that is attributed straightening of the initially curved nanotubes such that they behave as rigid rods or fibers. Mechanical hysteresis and swelling in toluene on cured composites samples revealed that MWCNTs are in fact well bonded to the SBR. Studies with SBR and a combination of carbon black and discreet MWCNT demonstrate dramatically improved resistance to fracture by tearing.

Imaging, spectroscopic, mechanical and biocompatibility studies of electrospun Tecoflex® EG 80A nanofibers and composites thereof containing multiwalled carbon nanotubes

The present study discusses the design, development, and characterization of electrospun Tecoflex® EG 80A class of polyurethane nanofibers and the incorporation of multiwalled carbon nanotubes (MWCNTs) to these materials. Scanning electron microscopy results confirmed the presence of polymer nanofibers, which showed a decrease in fiber diameter at 0.5% wt. and 1% wt. MWCNTs loadings, while transmission electron microscopy showed evidence of the MWCNTs embedded within the polymer matrix. The Fourier transform infrared spectroscopy and Raman spectroscopy were used to elucidate the polymer-MWCNTs intermolecular interactions, indicating that the C–N and N–H bonds in polyurethanes are responsible for the interactions with MWCNTs. Furthermore, tensile testing indicated an increase in the Young's modulus of the nanofibers as the MWCNTs concentration was increased. Finally, NIH 3T3 fibroblasts were seeded on the obtained nanofibers, demonstrating cell biocompatibility and proliferation. Therefore, the results indicate the successful formation of polyurethane nanofibers with enhanced mechanical properties, and demonstrate their biocompatibility, suggesting their potential application in biomedical areas.

The Effect of Hydrophilic and Hydrophobic Multi-Wall Carbon Nanotubes on Methane Dissolution Rates in Water at Three Phase Equilibrium (V−Lw−H) Conditions

Presently, gas hydrates are being studied for their potential applications in technologies involving natural gas transportation, carbon dioxide sequestration, and component separation. In order to optimize their use, research has focused on finding hydrate-promoting agents and understanding how they work. One such promoter, multiwall carbon nanotubes (MWNTs), was found to enhance hydrate growth. The current study investigates the effects of adding plasma-functionalized hydrophilic MWNTs and as-produced hydrophobic MWNTs on the dissolution stage of methane hydrate formation. It was found that the addition of the hydrophilic MWNTs increased methane dissolution rates with an increase in MWNT loading. Furthermore, the hydrophobic MWNTs initially enhanced dissolution up until a concentration of 5 ppm, at which point the rates began to return to their nominal values. It was also found that the addition of either type of MWNT did not significantly affect the total number of moles of methane dissolved in the water.

Study on the Reusability of Multiwalled Carbon Nanotubes in Biodegradable Chitosan Nanocomposites

The mechanical properties, water absorption, biodegradation, multiwalled carbon nanotubes (MWCNTs) recovery and reusability of chitosan/oxidized MWCNTs nanocomposites were investigated. The highest Young's modulus (E) was obtained by the nanocomposites with 0.1 wt.% MWCNTs, while further increase of MWCNTs loading decreases the tensile strength (TS) and E. The water absorption and degradation rate of the nanocomposites were decreased by the loading of MWCNTs; 89.7% of MWCNTs were recovered by physical base separation. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and tensile test results showed that the recovered MWCNTs displayed properties similar to the oxidized MWCNTs, suggesting the possibility of reuse and recycle.

Effect of fabrication method on the structure and electromagnetic response of carbon nanotube/polystyrene composites in low-frequency and Ka bands

Abstract Casting, forge-rolling, and stretching methods have been used for preparation of polystyrene composites with 0.25 wt.% loading of multiwall carbon nanotubes (MWCNTs). Electromagnetic properties of the composites were studied using impedance spectroscopy and microwave probing in the Ka band. Analysis of impedance spectra revealed capacitive behavior of the forge-rolled composite and charge tunneling through a polystyrene layer separating the nanotubes in two other composite samples. The stretched composite demonstrated anisotropy of microwave response due to predominant orientation of nanotubes along deformation direction. The near-isotropic shielding efficiency of the forge-rolled composite was attributed to strong fragmentation of MWCNTs under applied shear forces.

Thermogravimetric kinetics of degradation of HDPE based MWCNTs reinforced composites

High Density Polyethylene (HDPE) reinforced multiwalled carbon nano-tubes (MWCNTs) composites with MWCNTs loading between 0.0011 and 0.0044 volume fractions are fabricated by melt mixing. The prepared nano-composites are investigated by thermo-gravimetric analyzer (TGA) under nitrogen atmosphere at various heating rates. TGA thermograms indicate only a marginal enhanced thermal stability and no significant mass loss occurs up to ~400 °C. Thermal degradation kinetics of HDPE/MWCNTs nano-composites has been examined in light of five different analytical methods, viz., Coats-Redfern (CR) integral model fitting approach, ‘iterative’ based CR(modified) approach, integral form of the rate equation (i.e. FWO and KAS), the differential iso-conversional based method of Friedman. The CR integral model fitting based on 14 different kinetic models are analyzed for TGA data for multiple heating rates. Our analysis indicates that the degradation mechanism of the present nano-composites follows diffusion control (D2, D3 and D4) and first order reaction (F1) mechanisms. The apparent activation energy (E a ) as a function of conversion rate (α) estimated by CR (modified), FWO, KAS and FR methods are all in fair agreement with each other and confirms decrease in E a with increased loading of MWCNTs. The pre-exponential factor (A) calculated also decreases with MWCNTs concentration in HDPE. Activation energy (E a ) for different conversion rate (α) calculated by iso-conversional methods (CR(modified), FWO, KAS and FR) indicates contributions from at least two different degradation mechanisms, namely, diffusion controlled (D2, D3, D4) and first order reaction (F1), which are consistent with the findings of Coats-Redfern (CR) integral model.

Carbon nanotube-loaded mesoporous LiFe0.6Mn0.4PO4/C microspheres as high performance cathodes for lithium-ion batteries

A series of LiFe0.6Mn0.4PO4/C composites with different amount of multiwall carbon nanotubes (MWCNTs) has been successfully synthesized by introducing MWCNTs to LiFe0.6Mn0.4PO4 microspheres during the spray drying process. The as-prepared mesoporous spherical products (5–20 μm) are composed of primary nanoparticles (∼100 nm) and open-mesopores distribute both on the surface and inside the microspheres. XRD patterns and HRTEM images indicate that the as-prepared LiFe0.6Mn0.4PO4/C composites are well crystallized and no impurity phase is observed. As MWCNTs can entangle with the primary particles to form an interconnected conducting network, which can facilitate the electron transference, their existence can greatly enhance the conductivity between particles. Therefore, they can obviously increase the rate capability especially working at high current densities. Among the LiFe0.6Mn0.4PO4/C micro-spherical samples, the composite with 2% MWCNTs loading shows the best electrochemical performance, delivering a capacity of 163.3 mAh g−1 at 0.1 C, which is almost 96% of the theoretical capacity (∼170 mAh g−1). When discharged at 50 C, the composite still exhibits obviously higher capacity (64.23 mAh g−1) than the LiFe0.6Mn0.4PO4/C without MWCNTs (12.8 mAh g−1). Moreover, the MWCNTs embedded composite shows high cycle stability with no apparent capacity fading or voltage decay after 500 cycles at 45 °C.

The dielectric behavior and origin of high-k composites with very low percolation threshold based on unique multi-branched polyaniline/carbon nanotube hybrids and epoxy resin

New high-k composites based on unique multi-branched polyaniline (MSiPA)/multi-walled carbon nanotube (MWCNT) hybrids and epoxy (EP) resin were prepared. MSiPA/MWCNT/EP composite has much higher dielectric constant and lower dielectric loss than MWCNT/EP composite with the same loading of MWCNTs. Dielectric constant and loss at 100Hz of MSiPA3/MWCNT0.4/EP composite are 2.4 and 3.3×10−3 times the value of MWCNT0.4/EP composite, respectively; meanwhile the percolation threshold of MSiPA/MWCNT0.4/EP composites is as low as 0.51wt%, remarkably lower than that of available composites with coated MWCNTs. These attractive results are attributed to unique structures of MSiPA/MWCNT hybrids. The multi-branched structure, large polyaniline concentration and flexible Si–O chains make MSiPA have big ability to be coated on surfaces of MWCNTs through π–π interaction. Different from MWCNTs, MSiPA/MWCNT hybrids have good dispersion in EP matrix, forming more micro-capacitors and avoiding the loss of conductive currents. Equivalent circuits were built to further discuss the origin behind.

Reduction of percolation threshold of multiwall carbon nanotube (MWCNT) in polystyrene (PS)/low‐density polyethylene (LDPE)/MWCNT nanocomposites: An eco‐friendly approach

In this article, we introduce an eco‐friendly approach to achieve electrical conductivity at sufficiently lower loading of MWCNT in the PS/LDPE/MWCNT nanocomposites through judicious control of temperature during melt blending. The percolation threshold was achieved at 0.21 wt% of MWCNT following this method, which is lower, compared to the result obtained from direct mixing as well as the previously reported data. The morphological analysis revealed a co‐continuous structure of the (70/30, PS/LDPE)/MWCNT nanocomposites in such a high asymmetric composition of blend constituents, which facilitates in the lowering of percolation threshold through selective dispersion of MWCNT in the minor LDPE phase. The electron conduction in the nanocomposites has well been explained in terms of tunneling mechanism, supporting thin coating of polymer over individual CNTs. The morphological, electric and dielectric properties have been well explained in this article. POLYM. COMPOS., 36:1574–1583, 2015. © 2014 Society of Plastics Engineers

Evaluation of multi-walled carbon nanotube concentrations in polymer nanocomposites by Raman spectroscopy

A new Raman spectroscopic methodology is proposed to monitor the weight fraction of Multi-Walled Carbon Nanotubes (MWCNTs) in polymeric nanocomposites. In order to disentangle the parameters affecting the frequency of the Raman bands and their intensity, this methodology involves the acquisition of sets of Raman spectra as a function of MWCNTs loading, excitation laser power and temperature. In the specific case of isotactic polypropylene (iPP), any interaction of the carbon nanotubes with the polymeric host has minimal effect on the frequency of the MWCNTs G band (∼1584cm−1); the same holds for the influence of residual stresses acting on the MWCNTs. The parameter that primarily alters the CNTs Raman bands frequency is temperature, determined by the excitation laser intensity, the MWCNTs concentration and the thermal properties of the polymer matrix. This is demonstrated by confocal micro-Raman spectra collected from agglomerates and from micro-Raman spectra of samples containing either poorly or well dispersed MWCNTs. A direct correlation of the G band frequency with the effective MWCNT wt% loading in the nanocomposites is confirmed after careful and systematic experiments performed on prototype well-dispersed samples.

Facile and controllable assembly of multiwalled carbon nanotubes on polystyrene microspheres

Herein a facile and controllable heterocoagulation between polystyrene (PS) microspheres and multiwalled carbon nanotubes (MWCNTs) is introduced based on colloid thermodynamics. The MWCNTs play the role of steric stabilizer for stabilizing the metastable PS microspheres and thus immobilize spontaneously on the surface of PS microspheres. The synthesized MWCNTs-coated PS composite particles have been extensively characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetry and Raman spectroscopy. The results indicate that the structure and morphology of the resultant MWCNTs-coated PS composite particles are significantly affected by the weight ratio of PS and MWNCTs and the amount of poly(vinylpyrrolidone) that is injected into PS dispersion before they are mixed with MWCNTs. Therefore, these composite particles have the potential to produce MWCNTs-based composite materials with controllable mass loading and dispersity of MWCNTs.

Transparent conductive multiwall carbon nanotubes-polymer composite for electrode applications.

Disperse Multiwall carbon nanotubes (MWCNTs) are incorporated aqueous N-hydroxy methyl acrylamide, which is subjected to crosslinking to develop a transparent conductive composite free standing film. The effects of the concentration of MWCNTs and temperature on optical and electrical properties of nano-composites are investigated. Interestingly, only 0.06 mg/ml of MWCNTs is sufficient to reach the percolation threshold (Phi) for transition in electrical conductivity up to 10(-4) S/cm, with a visible transmittance over 85%, which is well above the reported for such a low level of MWCNTs loading. The electrical conductivity of the composite was measured at 120 degrees C. It has been observed that electrical conductivity increases significantly with the increase in temperature, signifying the semiconducting nature of nano-composites. Finally, current-voltage (I-V) characteristics show liner behaviour, confirms Ohmic nature of nano-composites and metal contact.

탄소나노튜브와 스테인레스강 단섬유를 함유한 폴리프로필렌 복합체의 전기저항 및 기계적 특성

본 연구에서는 이축 스크류식 압출기를 이용하여 폴리프로필렌(PP)에 도전성 필러인 다중벽 탄소나노튜브 (MWNT)와 스테인레스강 단섬유(SSF)를 첨가하여 복합체를 제조하였으며, 이에 대한 표면저항 및 기계적 특성을 조사하였다. 표면저항을 측정한 결과 PP/MWNT에 소량의 SSF를 첨가하였을 때 더 낮은 MWNT 함량에서 percolation threshold가 나타났다. 그리고 제조된 복합체에 대한 인장시험 결과 순수 PP와 비교해서 파괴점 신장률은 감소하였으나 탄성률과 강도는 증가하였다. 또한 동역학분석을 통하여 MWNT와 SSF 복합체의 저장탄성률과 tan <TEX>${\delta}$</TEX>에 미치는 영향을 조사하였으며, SEM을 이용하여 필러들의 모폴로지 및 복합체의 파단면을 관찰하였다. Polypropylene (PP) composites containing conductive multi-walled carbon nanotube (MWNT) and stainless steel short fiber (SSF) were manufactured using a twin screw extruder and characterized their surface resistivity and mechanical properties in this work. Surface resistivity measurements showed that the percolation threshold appeared at a lower MWNT loading when a small amount of SSF was added to PP/MWNT composites. Tensile modulus and strength of the composites increased but elongation-at-break decreased greatly compared to pure PP. Also, the effects of MWNT and SSF on storage modulus and tan <TEX>${\delta}$</TEX> from dynamic mechanical analysis for the composites were examined, and the morphologies of fractured surface and the fillers were observed using a scanning electron microscope.

Effect of multiwalled carbon nanotube and temperature on dielectric and impedance spectroscopy of chlorobutyl elastomer nanocomposites

Dielectric relaxation characteristics of multiwalled carbon nanotube (MWCNT)-reinforced chlorobutyl (CIIR) nanocomposites have been studied as a function of frequency (100–106 Hz) at different filler loadings (0, 2, 4, 6 and 8 phr) over a wide range of temperatures (30–120°C). The effect of MWCNT loadings and temperature on the dielectric permittivity ( ∊′), dielectric loss tangent (tan δ), complex impedance ( Z*) and electrical conductivity ( σ) was studied. The variation of ∊′ with MWCNT loading has been explained based on the interfacial polarization of the fillers within a heterogeneous system. A significant effect of MWCNT loading on the real ( Z′) and imaginary ( Z′′) part of Z* was observed due to the relaxation dynamics of polymer chains at the CIIR-MWCNT interface. The non-linearity of CIIR nanocomposites has been studied from Nyquist plots. The dielectric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The permittivity and conductivity of the nanocomposites have been analyzed based on scaling theory at increasing temperatures. The frequency dependency and percolation phenomenon in the composites have been discussed in terms of σ. The percolation threshold ( Φcrit) occurred at around 6 phr of MWCNT loading irrespective of temperature. The dispersion of MWCNT in the CIIR matrix and agglomeration of the filler at higher loading have been studied using scanning electron microscopic photomicrographs.

Broadband dielectric properties of multiwalled carbon nanotube/polystyrene composites

This study investigates the dielectric properties of multiwalled carbon nanotube (MWCNT)/polystyrene (PS) composites over the broadband frequency range, i.e., 10−1 to 106 Hz. The results showed that the real permittivity and imaginary permittivity increased remarkably with increased MWCNT concentration. For instance, at 100 Hz, the real permittivity and imaginary permittivity of the pristine PS was 2.71 and 0.01, respectively, which increased to 5.22 × 104 and 3.28 × 107 at 3.50 wt%, respectively. The increase in the real permittivity was related to the formation of a large number of nanocapacitor structures, i.e., MWCNTs as nanoelectrodes and polymer matrix as dielectric material, i.e., interfacial polarization. The increase in the imaginary permittivity with MWCNT loading was attributed greater number of dissipating charges, enhanced conductive network formation, and boosted polarization loss arising from interfacial polarization. It was also observed that the real and imaginary permittivities were frequency independent in the insulative region, whereas they decreased drastically with frequency in the conductive region. The descending trend of real permittivity with frequency in the conductive region was related to charge polarization relaxation, whereas the reduction in imaginary permittivity with frequency was attributed to lower Ohmic loss and polarization loss. POLYM. ENG. SCI., 55:173–179, 2015. © 2014 Society of Plastics Engineers

Fabrication of homogeneous multi-walled carbon nanotube/poly (vinyl alcohol) composite films using for microwave absorption application

Poly (vinyl alcohol) (PVA)/multi walled carbon nanotubes (MWNT) nanocomposite films were fabricated and their microwave absorption behavior were evaluated using vector network analyzer in the frequency range of 8–12 GHz (Xband). The uniform, stable dispersion and well oriented MWNT within the PVA matrix were achieved through using sodium dodecyl sulfate (SDS) as dispersing agent. The surface morphology of the PVA/SDS/MWNT films was examined by scanning electron microscope (SEM). The SEM analysis of the film samples revealed the uniform appearance in the whole surfaces of the fabricated composite films. However, some roughness on the surface was observed due to the presence of MWNT in the film structure. The PVA/SDS/MWNT films show significant increase in microwave absorption which is improved by increasing the MWNT content. The PVA/SDS/MWNT nanocomposite film sample with MWNT loading of 10 wt% showed the maximum and the relatively high microwave absorption of 28.00 dB at the frequency of 8.6 GHz.

In situ polymerization, thermal, damping, and mechanical properties of multiwalled carbon nanotubes/polyisobutylene‐based polyurethane nanocomposites

Despite the development of strong, durable, and cost efficient polyisobutylene‐based polyurethane (PIB‐based PU) materials has yet to be achieved. The well dispersion and maximum interfacial interaction between the nanofiller and the PIB‐based PU at low loading have been scarcely studied. Here, the preparation of PIB‐based PU nanocomposites with Multiwalled carbon nanotubes (MWCNTs) using a simple in situ polymerization method is reported. The thermogravimetric analysis tests show that MWCNTs significantly improved the thermal stability of MWCNTs/PIB‐based PU nanocomposites. Compare to the pure PIB‐based PU the onset temperature of degradation for the nanocomposite was about 20°C higher at 0.7 wt% MWCNTs loading. Efficient load transfer is found between the nanofiller MWCNTs and PIB‐based PU and the mechanical properties of the MWCNTs/PIB‐based PU nanocomposite with well dispersion are improved. A 63% improvement of Young's modulus and slightly increased of tensile strength are achieved by addition of only 0.7 wt% of MWCNTs. The experimentally determined Young's modulus is in well agreement with the theoretical simulation. It is worth noting that the PIB‐based PU and MWCNTs/PIB‐based PU nanocomposites exhibit excellent damping properties (tan δ &gt; 0.3) from −45°C to 8°C. POLYM. COMPOS., 36:198–203, 2015. © 2014 Society of Plastics Engineers

Thermomechanical properties of nanotubes in a thermosetting polyimide matrix: Relationship to the percolation threshold

The objective of this research is to more fully understand the structure–property relationships in multiwalled carbon nanotube (MWNT)/high performance thermosetting polymer nanocomposites. Nanocomposites containing up to 7wt.% MWNTs and a polyimide matrix (PETI-330) were characterized after curing and these characterization results were compared against similar nanocomposites containing carbon nanofibers (CNFs). Glass transition temperature values and thermomechanical testing indicated that the physical properties of the MWNT nanocomposites followed different trends at MWNT loadings less than and greater than the percolation threshold. In contrast, the CNF nanocomposites roughly showed a single relationship between physical property changes and CNF loading at the loadings studied here, which were all less than the percolation threshold. Overall, these results highlight the challenges in improving the properties of high performance matrices and suggest that MWNT network formation reduces reinforcement efficacy and that MWNTs can interfere with free radical curing processes.