Nanotube surface functionalization effects in blended multiwalled carbon nanotube/PVDF composites

A mixed fill system of multiwalled carbon nanotubes (MWCNT) and hydroxylated MWCNT (HO‐MWCNT) in a poly(vinylidene fluoride) (PVDF) matrix was investigated to improve nanotube dispersion and enhance electrical percolation for the bulk nanocomposites. Nonfunctionalized MWCNT were blended at various concentrations into dimethylformamide solutions containing PVDF with 0, 5, or 10 wt % HO‐MWCNT. Composite samples prepared from these solutions were examined by four‐point probe resistivity measurements. The percolation threshold decreased from 0.49 wt % MWCNT in binary MWCNT/PVDF composites to 0.25 wt % for ternary composites containing MWCNT/HO‐MWCNT/PVDF, with either 5 or 10 wt % HO‐MWCNT. In the case of the ternary composite with 10 wt % HO‐MWCNT, the lowest fill percent of MWCNT (0.25 wt %) measured a conductivity that was three orders of magnitude higher than the binary MWCNT/PVDF composite containing twice the concentration of MWCNT (0.5 wt %). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology,Thermal Stability,and Electrical Conductivity of Polymer Nanocomposites of Isotactic Polypropylene/Multi-Walled Carbon Nanotubes

Molecular weight of isotactic polypropylene (iPP) and concentration of multi-walled carbon nanotubes (MWCNT) effects on the morphology, thermal stability, and electrical conductivity for iPP/MWCNT nanocomposites were evaluated. Nanocomposites were prepared by solution mixing followed by non-isothermal crystallization from the melt. The samples were characterized by different physical-chemical techniques. Electrical conductivity was obtained from electrical resistance measured using a source meter. It was determined that the morphology of the nanocomposites shows a change from spherulitic to fibrillar to undefined depending on the molecular weight of iPP and concentration of MWCNT. Morphology was correlated with thermal stability and electrical conductivity.     

Comparative study of electromagnetic interference shielding properties of injection molded versus compression molded multi-walled carbon nanotube/polystyrene composites

This study compares electromagnetic interference (EMI) shielding properties of injection molded versus compression molded multi-walled carbon nanotube/polystyrene (MWCNT/PS) composites, i.e., properties such as EMI shielding effectiveness (EMI SE), electrical conductivity, real permittivity and imaginary permittivity. The injection molded (MWCNT-aligned) samples showed lower EMI shielding properties than compression molded (randomly distributed MWCNT) samples that was attributed to lower probability of MWCNTs contacting each other due to MWCNT alignment. The compression molded samples showed higher electrical conductivity and lower electrical percolation threshold than the injection molded samples. The compression molded samples at MWCNT concentrations of 5.00 and 20.0 wt.% showed real permittivity two times and imaginary permittivity five times greater than the injection molded samples. The EMI SE for the compression molded samples at MWCNT concentrations of 5.00 and 20.0 wt.% was 15.0 and 30.0 dB, respectively, significantly greater than EMI SE for the injection molded samples. Lower EMI SE for the injection molded samples was ascribed to lower electrical conductivity, real permittivity (polarization loss) and imaginary permittivity (Ohmic loss). Comparison of the EMI shielding properties of the compression molded versus injection molded samples confirmed that EMI shielding does not require filler connectivity; however it increases with filler connectivity.     

Preparation, crystallization, electrical conductivity and thermal stability of syndiotactic polystyrene/carbon nanotube composites

A homogeneous dispersion of multi-walled carbon nanotubes (MWCNTs) in syndiotactic polystyrene (sPS) is obtained by a simple solution dispersion procedure. MWCNTs were dispersed in N-methyl-2-pyrrolidinone (NMP), and sPS/MWCNT composites are prepared by mixing sPS/NMP solution with MWCNT/NMP dispersion. The composite structure is characterized by scanning electron microscopy and transmission electron microscopy. The effect of MWCNTs on sPS crystallization and the composite properties are studied. The presence of MWCNTs increases the sPS crystallization temperature, broadens the crystallite size distribution and favors the formation of the thermodynamically stable β phase, whereas it has little effect on the sPS γ to α phase transition during heating. By adding only 1.0 wt.% pristine MWCNTs, the increase in the onset degradation temperature of the composite can reach 20 °C. The electrical conductivity is increased from 10^{−10∼−16} (neat sPS) to 0.135 S m⁻¹ (sPS/MWCNT composite with 3.0 wt.% MWCNT content). Our findings provide a simple and effective method for carbon nanotube dispersion in polymer matrix with dramatically increased electrical conductivity and thermal stability.     

Comparison of electrical properties between multi-walled carbon nanotube and graphene nanosheet/high density polyethylene composites with a segregated network structure

Multi-walled carbon nanotube (MWCNT)/high density polyethylene (HDPE) and graphene nanosheets (GNS)/HDPE composites with a segregated network structure were prepared by alcohol-assisted dispersion and hot-pressing. Instead of uniform dispersion in polymer matrix, MWCNTs and GNSs distributed along specific paths and formed a segregated conductive network, which results in a low electrical percolation threshold of the composites. The electrical properties of the GNS/HDPE and MWCNT/HDPE composites were comparatively studied, it was found that the percolation threshold of the GNS/HDPE composites (1 vol.%) was much higher than that of the MWCNT/HDPE composites (0.15 vol.%), and the MWCNT/HDPE composite shows higher electrical conductivity than GNS/HDPE composite at the same filler content. According to the values of critical exponent, t, the two composites may have different electrical conduction mechanisms: MWCNT/HDPE composite represents a three-dimensional conductive system, while the GNS/HDPE composite represents a two-dimensional conductive system. The improving effect of GNSs as conducting fillers on the electrical conductivity of their composites is far lower than theoretically expected.     

Effects of hybrid fillers on the electrical conductivity,EMI shielding effectiveness,and flame retardancy of PBT and PolyASA composites with carbon fiber and MWCNT

The effects of hybrid fillers of carbon fiber (CF) and multiwall carbon nanotube (MWCNT) on the electrical conductivity, electromagnetic interference shielding effectiveness (EMI SE), flame retardancy, and mechanical properties of poly(butylene terephthalate) (PBT)/poly(acrylonitrile-co-styrene-co-acrylate) (PolyASA) (70/30, wt %) with conductive filler composites were investigated. The CF was used as the main filler, and MWCNT was used as the secondary filler to investigate the hybrid filler effect. For the PBT/PolyASA/CF (8 vol %)/MWCNT (2 vol %) composite, a higher electrical conductivity (1.4 × 10⁰ S cm⁻¹) and EMI SE (33.7 dB) were observed than that of the composite prepared with the single filler of CF (10 vol %), which were 9.0 × 10⁻² S cm⁻¹ and 23.7 dB, respectively. This increase in the electrical properties might be due to the longer CF length and hybrid filler effect in the composites. From the results of aging test at 85 °C, 120 h, the electrical conductivity and EMI SE of the composites decreased slightly compared to that of the composite without aging. The results of electrical conductivity, EMI SE, and flame retardancy suggested that the composite with the hybrid fillers of CF and MWCNT showed a synergetic effect in the PBT/PolyASA/CF (8 vol %)/MWCNT (2 vol %) composite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48162.     

Effect of starch on pore structure and thermal conductivity of diatomite-based porous ceramics

Considering the low-cost and environmental protection, the porous ceramics with high porosity using natural diatomite powder were successfully prepared by utilizing hot injection moulding and sacrificial fugitives. The impacts of different content of starch as a pore-forming agent on the phase composition, mechanical properties, thermal conductivity, and micro-structure of porous ceramics were investigated. The results demonstrate that starch content can significantly affect the mechanical properties and thermal conductivity of diatomite-based porous ceramics. When the starch content increased from 0 wt % to 50 wt %, the porosity increased from 61.2% to 80%, while the thermal conductivity decreases from 0.239 W/(m K) to 0.098 W/(m K). The low thermal conductivity of porous ceramics may be related to the macroporous–mesoporous composite structure. With the starch content increased, a greater chance of starch granule contact, higher internal pore sizes and a wider pore size distribution in the prepared samples, which resulting in lower mechanical strength, such as the three-point bending strength from 2.83 MPa to 0.46 MPa.     

Influence of preparation methods on the electrical and nanomechanical properties of poly(methyl methacrylate)/multiwalled carbon nanotubes composites

Poly(methyl methacrylate)/multiwalled carbon nanotubes (PMMA/MWCNT) composites were prepared by two different methods: melt mixing and solution casting. For solution casting, two different solvents, toluene and chloroform, were used to prepare PMMA solutions with different concentrations of MWCNT. The dispersion of the CNT in the composite samples was verified by scanning electron microscopy. For the nanocomposites prepared by both methods, the electrical conductivity increased with increasing filler content, showing typical percolation behavior. In addition, an increase of 11 orders of magnitude in the electrical conductivity relative to the matrix conductivity was determined by broadband dielectric spectroscopy and four probe conductivity measurements. A maximum value of σ_DC ～ 1.6 S/cm was found for the highest filler loaded sample (3.67 vol %), which was prepared by solution casting from toluene. Nanoindentation analysis was used to characterize the surface mechanical properties of the composite samples prepared by the different methods. Indentation tests were performed at various penetration depths, and it was revealed that the melt mixing process resulted in stiffer neat PMMA samples compared to the solution casted PMMA samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41721.     

Comparative study of EMI shielding effectiveness for carbon fiber pultruded polypropylene/poly(lactic acid)/multiwall CNT composites prepared by injection molding versus screw extrusion

The electrical conductivity and electromagnetic interference (EMI) shielding effectiveness of the composites of polypropylene/poly(lactic acid) (PP/PLA) (70/30, wt %) with single filler of multiwall carbon nanotube (CNT) or hybrid fillers of nickel‐coated carbon fiber (CF) and CNT were investigated. For the single filler composite, higher electrical conductivity was observed when the PP‐g‐maleic anhydride was added as a compatibilizer between the PP and PLA. For the composite of the PP/PLA (70/30)/CF (20 phr)/CNT (5 phr), the composite prepared by injection molding observed a higher EMI shielding effectiveness of 50.5 dB than the composite prepared by screw extrusion (32.3 dB), demonstrating an EMI shielding effectiveness increase of 49.8%. The higher values in EMI shielding effectiveness and electrical conductivity of the PP/PLA/CF (20 phr)/CNT (5 phr) composite seemed mainly because of the increased CF length when the composites were prepared using injection molding machine, compared with the composites prepared by screw extrusion. This result suggests that the fiber length of the conductive filler is an important factor in obtaining higher values of electrical conductivity and EMI shielding effectiveness of the PP/PLA/CF/CNT composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45222.     

Effects of carbon fiber modification with multiwall CNT on the electrical conductivity and EMI shielding effectiveness of polycarbonate/carbon fiber/CNT composites

The effect of carbon fiber (CF) modification with multiwall carbon nanotube (CNT) on the electrical, mechanical, and rheological properties of the polycarbonate (PC)/CF/CNT composite was investigated. The CF and multiwall CNT (MWCNT) were treated with sulfuric acid and nitric acid (3:1 wt %) mixture, to modify the CF with the CNT. For the PC with acid-treated CNT (a-CNT) modified acid-treated CF (a-CF) (PC/a-CF/a-CNT) composite, the electrical conductivity, and the electromagnetic interference shielding effectiveness (EMI SE) showed the highest values, compared with those of the PC/a-CF and PC/a-CF/CNT composites. The EMI SE of the PC/a-CF (10 wt %)/a-CNT (0.5 wt %) composite was found to be 26 (dB at the frequency of 10.0 GHz, and the EMI SE was increased by 91.2%, compared to that of the PC/a-CF composite at the same amount of total filler content. Among the composites studied in this work, the PC/a-CF/a-CNT composite also showed the highest values of relative permittivity (ε_r) and dielectric loss factor. The above results suggest that the CF modification with the a-CNT significantly affected the electrical conductivity and EMI SE of the composite, and the hybrid fillers of the a-CNT and a-CF resulted in good electrical pathways in the PC/a-CF/a-CNT composite. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47302.     

Morphological features and melting behavior of nanocomposites based on isotactic polypropylene and multiwalled carbon nanotubes

Nanocomposites based on low molar mass isotactic polypropylene (iPP) and a low concentrations (1–2 wt %) of multiwalled carbon nanotubes (MWCNTs) were studied using thermal analysis, optical and electronic microscopy, and X‐ray diffraction/scattering techniques. It was first determined that MWCNT decrease induction time and act as nucleating agents of the iPP crystals during nonisothermal crystallization. One of the consequences of the nucleation effect was that the original spherulitic morphology of iPP was transformed into a fibrillar‐like. The corresponding long period of the original well‐defined lamellar structure slightly increased suggesting the formation of thicker crystals in samples containing MWCNT. The nature of the α‐iPP crystalline structure was not affected by MWCNT. After nonisothermal crystallization, two melting endotherms were present during thermal scanning of the iPP/MWCNT nanocomposites their proportion changing with the heating rate. After resolving the total DSC signal in its components using MDSC, the overall evolution of such behavior could be explained in terms of the melting/recrystallization mechanism. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Microstructural characterization of corn starch‐based porous thermoplastic composites filled with multiwalled carbon nanotubes

Microstructural characterization of corn starch‐based porous thermoplastic (TPS) composites containing various contents (0.1, 0.5, and 1 wt %) of multiwalled carbon nanotubes (MWCNTs) was performed. Corn starch was plasticized with a proper combination of glycerol and stearic acid. TPS composites with MWCNT were prepared conducting melt extrusion followed by injection molding. TPS containing 1 wt % of MWCNTs exhibited higher tensile strength and elastic modulus values than neat TPS. Moreover, TPS electrical conductivity was determined to increase with increasing content of MWCNTs. X‐ray diffraction measurements revealed that incorporation of MWCNTs increased the degree of TPS crsystallinity to some extent. Scanning electron microscopy examination revealed that MWCNT altered TPS surface morphology and tensile failure modes, significantly. Transmission electron microscopy investigation showed that dispersion characteristics of MWCNTs within TPS were in the form of tiny clusters around micro pores of TPS, which is considered influential on electrical conductivity of the resulting composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effect of processing parameters on the bond strength and electrical conductivity of multi-wall carbon nanotube/low-density polyethylene composite

The objective of this paper is to study the influence of processing parameters, such as melt temperature and mold temperature, on the adhesion of low density polyethylene (LDPE) to 2.5?wt/% multi-wall carbon nanotube-filled polyethylene (LDPE/MWCNT). The adhesion was obtained using two-component injection-molding method and measured using tensile experiments. The electrical conductivity of the two-component injection-molded specimens was also measured through DC voltage and compared to the volume resistivity of the LDPE and LDPE/MWCNT composite. It was found that the bond strength increases with increasing melt and mold temperatures. However, increasing the melt and mold temperatures over a certain limit can decrease the bond strength. The range of the electrical conductivity of the LDPE-LDPE/MWCNT two-component injection-molded samples was in the range of dissipative materials.     

Solution spinning of cellulose carbon nanotube composites using room temperature ionic liquids

Multiwall carbon nanotube (MWCNT)/cellulose composite fibers were processed from solutions in ethyl methylimidazolium acetate (EMIAc). Rheological percolation in MWCNT/Cellulose/EMIAc solution was observed above 0.01 mass fraction of MWCNT, while electrical percolation in oriented fibers was observed above 0.05 mass fraction of MWCNTs with respect to the weight of the cellulose. Cellulose orientation and crystal size were significantly higher in the composite than in the control cellulose fiber. In addition, in the composite fiber, carbon nanotube orientation was higher than cellulose orientation. At 0.05 mass fraction MWCNT, fiber tensile strength increased by about 25%, strain to failure increased by 100%, and modulus essentially remained unchanged. The composite fibers showed lower thermal shrinkage than the control cellulose fiber. The axial electrical conductivity at 0.1 mass fraction MWCNTs in these oriented fibers was more than 3000 S/m.     

Improved electrical conductivity of very long multi-walled carbon nanotube bundle/poly (methyl methacrylate) composites

Very long and highly dispersible multi-walled carbon nanotube (MWCNT) bundles were synthesized in large quantity by catalytic chemical vapor deposition, and their structural and electrical properties were characterized. It was found that the MWCNTs could be synthesized with either bundled (long-aligned) or short-entangled structure depending on the catalyst system. The aligned MWCNTs were found to be more conductive and more dispersible than the entangled ones. The MWCNT/poly (methyl methacrylate) composites were prepared using both entangled and aligned MWCNTs. The aligned MWCNTs were found to give the composite higher electrical conductivity, which might be attributed to long length and high dispersibility. It was further found that the longer the MWCNT bundle, the higher electrical conductivity of the composite.     

5‐Sulfoisophthalic acid monolithium salt doped polypyrrole/multiwalled carbon nanotubes composites for EMI shielding application in X‐band (8.2–12.4 GHz)

This article describes the synthesis and characterization of highly conductive polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites prepared by in situ polymerization of pyrrole using 5‐sulfoisophthalic acid monolithium salt [lithio sulfoisophthalic acid (LiSiPA)] as dopant and ferric chloride as oxidant. Several samples were prepared by varying the amounts of MWCNTs ranging from 1 to 5 wt %. Scanning electron microscope and transmission electron microscope images clearly show a thick coating of PPy on surface of MWCNTs. The electrical conductivity of PPy increased with increasing amount of MWCNTs and maximum conductivity observed was 52 S/cm at a loading of 5 wt % of MWCNTs. Pure PPy prepared under similar conditions had a conductivity of 25 S/cm. Electromagnetic interference (EMI) shielding effectiveness (SE) also showed a similar trend and average EMI shielding of ?108 dB (3 mm) was observed for sample having 5 wt % MWCNT in the frequency range of 8.2–12.4 GHz (X‐band). The light weight and absorption dominated total SE of ?93 to ?108 dB of these composites indicate the usefulness of these materials for microwave shielding. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45370.     

Preparation and properties of multi-walled carbon nanotube/carbon/polystyrene composites

Multi-walled carbon nanotube (MWCNT)/C/polystyrene (PS) composite materials were prepared by in situ polymerization of monomer in preformed MWCNT/C foams. MWCNT/C foams were preformed using polyurethane foam as template. The preformed MWCNT/C foams had a more continuous conductive structure than the carbon nanotube networks formed by free assembly in composites. The structure of the MWCNT/C foam network was characterized with scanning electron microscopy. The MWCNT/C/PS composites have an electric conductivity higher than 0.01 S/cm for a filler loading of 1 wt.%. Enhancement of thermal conductivity and mechanical properties by the preformed MWCNT/C foam were also observed.     

Improving electrical and mechanical properties of a conductive nano adhesive

In this experimental study, lap shear strength and electrical conductivity of nanohybrid adhesives containing multi-walled carbon nanotubes (MWCNT) and silver (Ag) nanoparticles were investigated. Ag nanoparticles were produced via arc-discharge method in liquid nitrogen. For characterizing the Ag nanoparticles, X-ray diffraction analysis, transmission electron microscopy, and scanning electron microscopy (SEM) were performed. Tensile lap shear properties were determined in accordance with ASTM D 1002-10 standard. Mechanical and the electrical properties of nanohybrid adhesives were compared with neat epoxy adhesive. The best electrical conductivity of nanohybrid adhesive was obtained for the 1% wt MWCNT-2% wt Ag-contained sample. However, the samples which contain 0.5% wt. MWCNT–0.5% wt. Ag nanoparticles reached the highest lap shear strength. The results showed that Ag nanoparticles enhance the conductivity in the presence of MWCNT. It is concluded that the MWCNT act as conductivity bridges among epoxy adhesive and facilitate the electron transfer. As seen in the tensile test results, the ductility of the adhesive was improved by adding the nanoparticles in to the epoxy resin.     

Improved conductivity and thermal stability by the formation of a charge‐transfer complex in β‐nucleation‐agent‐nucleated and MWCNT‐filled iPP composites

In this study, the influence of β‐nucleation agent (β‐NA) on the morphology and properties of multi‐walled carbon nanotube (MWCNT) filled isotactic polypropylene (iPP) composites was explored in details. The results show that the incorporation of β‐NA has promoted the dispersion of MWCNT in the iPP matrix, which is profitable for improving the thermal stability and conductivity properties of MWCNT‐iPP composites. Besides, the 0.05 wt % β‐NA nucleated samples exhibit higher impact toughness than that of un‐β‐NA‐nucleated ones. Further SEM observations show that the morphology of MWCNT changes from large agglomerations to small clusters with doping of β‐NA. The main reason is that the incorporation of β‐NA (TMB‐5) in MWCNT filled iPP matrix has led to the formation of a charge‐transfer complex. Some of these clusters act as nucleation sites for inducing crystallization of α spherulites, which have a compete growth with β‐NA induced β crystals. Meanwhile, other clusters exist in the inter‐lamella amorphous phase of β crystals, some of them even combine two adjacent β spherulites. Accordingly, a large conductive network comes into being. Based on the investigated results, a mechanism model is proposed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

High electromagnetic interference shielding with high electrical conductivity through selective dispersion of multiwall carbon nanotube in poly (ε‐caprolactone)/MWCNT composites

This study presents the preparation of electrically conducting poly(ε‐caprolactone) (PCL)/multiwall carbon nanotube (MWCNT) composites with very low percolation threshold (p_c). The method involves solution blending of PCL and MWCNT in the presence of commercial PCL beads. The PCL beads were added into high viscous PCL/MWCNT mixture during evaporation of solvent. Here, the used commercial PCL polymer beads act as an ‘excluded volume’ in the solution blended PCL/MWCNT region. Thus, the effective concentration of the MWCNT dramatically increases in the solution blended region and a strong interconnected continuous conductive network path of CNT−CNT is assumed throughout the matrix phase with the addition of PCL bead which plays a crucial role to improve the electromagnetic interference shielding effectiveness (EMI SE) and electrical conductivity at very low MWCNT loading. Thus, high EMI SE value (∼23.8 dB) was achieved at low MWCNT loading (1.8 wt %) in the presence of 70 wt % PCL bead and the high electrical conductivity of ∼2.49×10⁻² S cm⁻¹ was achieved at very low MWCNT loading (∼0.15 wt %) with 70 wt % PCL bead content in the composites. The electrical conductivity gradually increased with increasing the PCL bead concentration, as well as, MWCNT loading in the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42161.