Electrical,rheological and electromagnetic interference shielding properties of thermoplastic polyurethane/carbon nanotube composites

Electrically conducting rubbery composites based on thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) were prepared through melt blending using a torque rheometer equipped with a mixing chamber. The electrical conductivity, morphology, rheological properties and electromagnetic interference shielding effectiveness (EMI SE) of the TPU/CNT composites were evaluated and also compared with those of carbon black (CB)‐filled TPU composites prepared under the same processing conditions. For both polymer systems, the insulator–conductor transition was very sharp and the electrical percolation threshold at room temperature was at CNT and CB contents of about 1.0 and 1.7 wt%, respectively. The EMI SE over the X‐band frequency range (8–12 GHz) for TPU/CNT and TPU/CB composites was investigated as a function of filler content. EMI SE and electrical conductivity increased with increasing amount of conductive filler, due to the formation of conductive pathways in the TPU matrix. TPU/CNT composites displayed higher electrical conductivity and EMI SE than TPU/CB composites with similar conductive filler content. EMI SE values found for TPU/CNT and TPU/CB composites containing 10 and 15 wt% conductive fillers, respectively, were in the range ?22 to ?20 dB, indicating that these composites are promising candidates for shielding applications. © 2013 Society of Chemical Industry     

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.     

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 filler geometry on internal structure and physical properties of polycarbonate composites prepared with various carbon fillers

BACKGROUND: The effects of filler geometry are important for understanding the internal structure and physical properties of polymer composites. To investigate the effects of filler geometry on electrical conductivity as well as morphological and rheological properties, three types of polycarbonate (PC) composites were prepared by melt compounding with a twin‐screw extruder. RESULTS: The electrical conductivity of PC/carbon black (CB) and PC/graphite (carbon) nanofibre (CNF) composites did not show a percolation threshold through the entire filler loading ranges. However, PC‐blend‐carbon nanotube (CNT) composites showed a percolation electrical threshold for a filler loading of 1.0 to 3.0 wt% and their maximum electrical conductivity approached 10^?3 S m^?1. PC‐blend‐CB and PC‐blend‐CNF composites showed Newtonian behaviour like pure PC matrix, but PC‐blend‐CNT composites showed yield stress as well as increased storage modulus and strong shear thinning behaviour at low angular frequency and shear rate due to strong interactions generated between CNT–CNT particles as well as PC molecules and CNT particles on the nanometre scale. CONCLUSIONS: The electrical conductivity of the PC composites with different carbon constituents was well explained by the continuous network structure formed between filler particles. The network structure was confirmed by the good dispersion of fillers as well as by the yield stress and solid‐like behaviour observed in steady and dynamic shear flows. Copyright © 2009 Society of Chemical Industry     

Electrical conductivity and EMI shielding effectiveness of polyurethane foam–conductive filler composites

The morphological, electrical, and thermal properties of polyurethane foam (PUF)/single conductive filler composites and PUF/hybrid conductive filler composites were investigated. For the PUF/single conductive filler composites, the PUF/nickel‐coated carbon fiber (NCCF) composite showed higher electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) than did the PUF/multiwall carbon nanotube (MWCNT) and PUF/graphite composites; therefore, NCCF is the most effective filler among those tested in this study. For the PUF/hybrid conductive fillers PUF/NCCF (3.0 php)/MWCNT (3.0 php) composites, the values of electrical conductivity and EMI SE were determined to be 0.171 S/cm and 24.7 dB (decibel), respectively, which were the highest among the fillers investigated in this study. NCCF and MWCNT were the most effective primary and secondary fillers, and they had a synergistic effect on the electrical conductivity and EMI SE of the PUF/NCCF/MWCNT composites. From the results of thermal conductivity and cell size of the PUF/conductive filler composites, it is suggested that a reduction in cell size lowers the thermal conductivity of the PUF/conductive filler composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44373.     

Shielding effectiveness of carbon‐filled polycarbonate composites

In this project, varying amounts of three different carbons [carbon black (CB), carbon nanotubes (CNT), and graphene nanoplatelets (GNP)] were added to polycarbonate (PC). The resulting single filler composites were tested for shielding effectiveness (SE). The effects of single fillers and combinations of two different carbon fillers were studied via a factorial design. At the highest single filler loadings, the following SE results were obtained at 800 MHz: 18.9 dB for 10 wt % CB/PC, 18.4 dB for 8 wt % CNT/PC, and 6.3 dB for 15 wt % GNP/PC. The highest SE value of 21.4 dB was measured for the 5 wt % CB/5 wt % CNT/PC composite and could be used in SE applications (typically > 20 dB is needed). Statistically significant equations were developed that could be used to predict the SE of composites containing these fillers. In addition, it was determined that the composite SE is higher than what would be expected from the additive effect of each single filler for the CB/GNP/PC composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42719.     

Electrical and thermal conductivity and tensile and flexural properties: Comparison of carbon black/polycarbonate and carbon nanotube/polycarbonate resins

Adding conductive carbon fillers to thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon black (CB) is very effective at increasing composite electrical conductivity at low loading levels. In this study, varying amounts (2 to 10 wt %) CB were added to polycarbonate (PC) and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. These results were compared with prior work done for carbon nanotubes (CNT) in polycarbonate. The percolation threshold was ～ 2.3 vol % CB compared to between 0.7 and 1.4 vol % CNT. At 8 wt % filler, the CNT/PC composite had an electrical resistivity of 8 ohm‐cm compared to 122 ohm‐cm for the CB/PC composite. The addition of CB to polycarbonate increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 8 wt % (5.5 vol %) CB in polycarbonate composite had a good combination of properties for semiconductive applications. Ductile tensile behavior is noted in pure polycarbonate and in samples containing up to 8 wt % CB. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrical conductivity and electromagnetic interference shielding effectiveness of carbon black/sisal fiber/polyamide/polypropylene composites

The effects of hybrid fillers on the electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) of polyamide 6 (PA6)/polypropylene (PP) immiscible polymer blends were investigated. Carbon black (CB) and steam exploded sisal fiber (SF) were used as fillers. CB was coated on the surface of SF, and this was exploded by water steam to form carbon black modified sisal fiber (CBMSF). CB/SF/PA6/PP composites were prepared by melt compounding, and its electromagnetic SE was tested in low‐frequency and high‐frequency ranges. We observed that SF greatly contributed to the effective decrease in the percolation threshold of CB in the PA6/PP matrix and adsorbed carbon particles to form a conductive network. Furthermore, an appropriate CB/SF ratio was important for achieving the best shielding performance. The results indicate that CBMSF was suitable for use as electronic conductive fillers and the CB/SF/PA6/PP composites could be used for the purpose of EMI shielding. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42801.     

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.     

Electrical conductivity modeling of carbon black/polycarbonate,carbon nanotube/polycarbonate,and exfoliated graphite nanoplatelet/polycarbonate composites

Adding conductive carbon fillers to electrically insulating thermoplastic polymers increases the resulting composite's electrical conductivity, which would enable them to be used in electrostatic dissipative and semiconductive applications. In this study, varying amounts of carbon black (CB: 2 to 10 wt %), multiwalled carbon nanotubes (CNT: 0.5 to 8 wt %), or exfoliated graphite nanoplatelets (GNP: 2 to 15 wt %) were added to polycarbonate (PC) and the resulting composites were tested for electrical conductivity (EC = 1/electrical resistivity). The percolation threshold was ～ 1.2 vol % CNT, ～ 2.4 vol % CB, and ～ 4.6 vol % GNP. In addition, three EC models (Mamunya, additive, and general effective media) were developed for the CB/PC, CNT/PC, and GNP/PC composites. The general effective media (GEM) model showed the best agreement with the experimental results over the entire range of filler concentrations (above and below the percolation threshold) for all three composite systems. In addition, the GEM model can be easily adapted for composites containing combinations of different conductive fillers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Flexible poly(styrene-b-(ethylene-co-butylene)-b-styrene) nanocomposites for electromagnetic interference shielding

In this report, multiwalled carbon nanotubes (CNT) embedded poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) microspheres (CNT/SEBS) were prepared by solvent evaporation method. Reduced graphene oxide (rGO) nanosheets were used to cover the surface of CNT/SEBS microspheres. The CNT/SEBS/rGO nanocomposites with special segregated conductive network were fabricated by hot pressing these as-prepared complex microspheres. The morphology, electrical percolation threshold, electrical conductivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of CNT/SEBS/rGO composites were characterized. The shielding mechanisms were discussed in detail. Analysis of electrical conductive performance shows that the electrical percolation threshold of rGO is 0.22 vol %. Results of EMI shielding test confirmed the synergistic effect between CNT and rGO. The EMI SE of the composite filled by 2.1 vol % CNT and 3.35 vol % rGO can achieve 26 dB in 8.2− 12.4 GHz (X band), which exceeds the basic requirement for commercial application (20 dB). Its reflectance coefficient (19–41%) indicates that the most part of incident electromagnetic (EM) wave energy is attenuated through absorption mechanism. This kind of absorptive EMI shielding material can be applied without serious secondary EM radiation pollution problems. The effects of filler content, molding temperature on EMI SE, and shielding mechanism were also investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48542.     

Tensile modulus modeling of carbon black/polycarbonate,carbon nanotube/polycarbonate,and exfoliated graphite nanoplatelet/polycarbonate composites

Conductive fillers are often added to thermoplastic polymers to increase the resulting composite's electrical conductivity (EC) which would enable them to be used in electrostatic dissipative and semiconductive applications. The resulting composite also exhibits increased tensile modulus. The filler aspect ratio plays an important role in modeling composite EC, and tensile modulus. It is difficult to measure the filler aspect ratio after the manufacturing process (often extrusion followed by injection molding) in the composite, especially when nanomaterials are used. The EC percolation threshold is a function of the filler aspect ratio; hence, knowledge of this percolation threshold provides a means to extract the filler aspect ratio. In this study, the percolation threshold of the composite was determined from EC measurements and modeling, which in turn was used to determine the filler aspect ratio for tensile modulus modeling. Per the authors' knowledge, this approach has not been previously reported in the open literature. The fillers; carbon black (CB: 2–10 wt %), multiwalled carbon nanotubes (CNT: 0.5–8 wt %), or exfoliated graphite nanoplatelets (GNP: 2–12 wt %); were added to polycarbonate (PC) and the resulting composites were tested for EC and tensile modulus. With the filler aspect ratio determined from EC values for CNT/PC and GNP/PC composites, the three‐dimensional randomly oriented fiber Halpin‐Tsai model accurately estimates the tensile modulus for the CNT/PC composites and the Nielsen model predicts the tensile modulus well for the CB/PC and GNP/PC composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Melt spinning of conducting polymeric composites containing carbonaceous fillers

Fibers produced by melt spinning of conductive polymer composites are attractive for several applications; the main drawback is however reduced processability at high filler concentrations. Carbon nanotubes (CNTs) are considered suitable fillers for conductive polymer composites, replacing conductive grades of carbon black (CB). In this study, the fiber‐forming properties of conductive polymer composites based on a conductive grade of CB and two masterbatches with CNT in a polyethylene matrix were investigated. The CB was also used in a polypropylene matrix for comparison. The rheological properties of the filler‐containing melts in shear and their extensional behavior were evaluated. A piston‐driven device was used to extrude the molten materials through a capillary; different capillary geometries were tested. Fibers were produced at various draw ratios, and their conductivity was determined. To assess the ultimate extensibility, a modified Rheotens method was used. The results showed that a conductive CB grade can have a lower percolation threshold and higher conductivity than a material with CNT. Conductivity decreased with increasing melt draw ratio for both types of fillers. The spinnability of the materials decreased with increasing concentration of filler material and correlations were found between spinnability and melt elasticity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synergistic effect of dual nanofillers (MWCNT and Ni–Al LDH) on the electrical and thermal characteristics of polystyrene nanocomposites

The advantage of using 3D hybrid filler containing carboxylic acid functionalized multiwalled carbon nanotubes (c‐MWCNTs) and sodium dodecyl sulfate modified Ni–Al layered double hydroxide (sN‐LDH) over c‐MWCNTs and sN‐LDHs acting alone was investigated. PS/c‐MWCNT composites proved to be good for improvement of properties, but not to an appreciable level, especially in case of electrical conductivity, flame retardancy, rheology, and water vapor permeability. Hence, a combination of 0.3 wt % of c‐MWCNT and 3 wt % of sN‐LDH was optimized as additives to assist in the full expression of the filler traits in the nanocomposite and to obtain a versatile nanocomposite with properties specific to both the fillers. This approach slightly decreases the dispersion challenge faced with handling high loadings of CNT and also the intrinsic limitations specific to the individual fillers (i.e., inertness of CNTs and low conductivity of LDHs). Moreover, the anion/anionic repulsion of organically modified CNT/LDH facilitates effective dispersion of the additive opposing adhesion. FTIR and Raman spectroscopy provided evidence for incorporation and proper dispersion of the additives in the polymer matrix, with XRD and TEM confirming a well‐dispersed morphology of the nanocomposites. In this work, focus is made on the improvement of thermal stability, flame retardancy, melt rheology, hardness, electrical conductivity, and water vapor permeability of PS/0.3 wt % c‐MWCNT/3 wt % sN‐LDH nanocomposites over PS/0.3 wt % c‐MWCNT, making use of the synergistic effect of c‐MWCNT coupled with sN‐LDH on polystyrene. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46513.     

ASA/graphite/carbon black composites with improved EMI SE,conductivity and heat resistance properties

Composites, comprised of acrylonitrile styrene acrylate copolymer (ASA)/graphite (GR) with high electromagnetic interference shielding effectiveness (EMI SE), were fabricated by the introduction of carbon black (CB). The effects of CB on properties such as EMI SE, morphology, heat resistance, rheological and mechanical performance of the composites were characterized using a scanning electron microscope (SEM), rotational rheometer, electromagnetic shielding measuring instruments. The graphite and carbon black exhibited positive synergistic action, which promoted the complete formation of conductive networks in ASA matrix. The EMI SE and electrical conductivity of the ASA/GR/CB composites increased with higher CB loadings. In the frequency range of 30–3000 MHz, the maximum EMI SE of ASA composites with 50 % fillers reached 40 dB, but with 40 % fillers this property reached its maximum value of 50 dB. The flexural strength of ASA/GR/CB composites started to decline as CB loading exceeded 5 %. The heat resistance of the composites was improved due to the addition of CB. In this respect, the vicar softening temperature (VST) of the composites with 40 % fillers increased from 115.1 to 132.7 °C, and the VST of the composites with 50 % fillers was elevated from 125.4 to 138.9 °C.     

Investigation of the electric conductivity and the electromagnetic interference shielding efficiency of SWCNTs/GNS/PAni nanocomposites

This work demonstrates the fabrications and characterizations of polyaniline (PAni) composites containing single-walled carbon nanotubes (SWCNTs), graphite nanosheets (GNS), or hybrid fillers (SWCNTs/GNS). The characterization of microstructure, examination of fracture surface morphologies, and measurement of electric conductivity and electromagnetic interference shielding efficiency (EMI SE) were performed. It was found that both the electric conductivity and the EMI SE increase with filler loading, and the nanocomposites filled with 1.0 wt.% SWCNTs/GNS possessed the highest electric conductivity of 16.2 S/cm and total EMI SE of 27.0 dB. The experimental results also show that absorption is the primary mechanism of EMI SE for all of the loadings and fillers.     

Effects of multiple carbon fillers on the rheology of polycarbonate‐based composites

Adding conductive carbon fillers to insulating thermoplastic polymers increases the electrical conductivity of the resulting composite, which could allow them to be used in electrostatic dissipative and semiconductive applications. Adding fillers often increases viscosity, which can make the material more difficult to process. In this study, three different carbon fillers [carbon black (CB), carbon nanotubes (CNT), and exfoliated graphite nanoplatelets (GNP)] were studied via three different combinations of two different fillers (CB/CNT, CB/GNP, and CNT/GNP). These filler combinations were studied via three 3² factorial designs, which considered the following loading levels: CB: 0, 2, and 5 wt%; CNT: 0, 1, and 5 wt%; and GNP: 0, 2, and 5 wt%. These composites were compounded, injection molded, and tested for electrical conductivity and steady shear viscosity. CB and GNP exhibited classic filler behavior, increasing the composite viscosity with increased filler loading. CNT acted differently, lowering the composite viscosity with increased filler loading. When CB and GNP were combined, the viscosity increase was additive. When CNT was combined with either CB or GNP, the resultant composite had a lower viscosity than the corresponding single filler composite with equivalent loadings of CB or GNP. This viscosity lowering effect of CNT, even at loadings as low as 1 wt%, allows for increased filler loadings of CB or GNP with little impact on processability. Five different formulations (four containing two filler combinations) could be used for electrostatic dissipative applications and seven different formulations (six containing two filler combinations) may be used for semiconductive applications. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Electrical and mechanical properties of acrylonitrile‐butadiene‐styrene/multiwall carbon nanotube nanocomposites prepared by melt‐blending

The electrical properties in polymer/carbon nanotube (CNT) nanocomposites are governed not only by the degree of dispersion but also to a greater extent on the aspect ratio of the CNTs in the final composites. Melt‐mixing of polymer and CNTs at high shear rate usually breaks the CNTS that lowers the aspect ratio of the nanotubes. Thus, homogeneous dispersion of CNTs while retaining the aspect ratio is a major challenge in melt‐mixing. Here, we demonstrate a novel method that involves melt‐blending of acrylonitrile‐butadiene‐styrene (ABS) and in situ polymerized polystyrene (PS)/multiwalled CNT (MWCNT) nanocomposites, to prepare electrically conducting ABS/MWCNT nanocomposites with very low CNT loading than reported. The rationale behind choosing PS/MWCNT as blending component was that ABS is reported to form miscible blend with the PS. Thus, (80/20 w/w) ABS/(PS/MWCNT) nanocomposites obtained by melt‐blending showed electrical conductivity value ≈1.27 × 10^?6 S cm^?1 at MWCNT loading close to 0.64 wt %, which is quite lower than previously reported value for ABS/MWCNT system prepared via solution blending. Scanning electron microscopy and differential scanning calorimetry analysis indicated the formation of homogenous and miscible blend of ABS and PS. The high temperature (100°C) storage modulus of ABS (1298 MPa) in the nanocomposites was increased to 1696 MPa in presence of 0.64 wt % of the MWCNT. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Perpendicular and In‐Plane Conductivity of Poly(methyl methacrylate) Composite Films Filled with Carbon‐Based Fillers Prepared from Solution Casting Process

In this study, poly(methyl methacrylate) (PMMA)/carbon black (CB), PMMA/carbon fiber (CF), and PMMA/carbon nanotube (CNT) conductive composite films with different filler concentrations are prepared using the solution casting technique. Both perpendicular and in‐plane direction conductivity of all the binary composite films are investigated, percolation thresholds (?_c) of both directions of PMMA/CB, PMMA/CF, and PMMA/CNT composite films are investigated and the experimental data are fitted using McLachlan’s equation. For all the three investigated films, the perpendicular ?_c,⊥ and in‐plane ?_c,∥ with different fillers show totally different behaviors. Pristine CB, CF, and CNT as well as PMMA/CB, PMMA/CF, and PMMA/CNT composite films are discussed. The gravity effect of the fillers is found to be most significant in the PMMA/CB system. A schematic diagram of PMMA composite films with CB, CF, and CNT as filler prepared from solution casting process is presented to explain the distribution gradient of the fillers in the perpendicular direction of the film after solution casting. A power law behavior is revealed for different filler types (CB, CF, CNT) correlating the exponent t for McLachlan’s equation and corresponding ?_c for in‐plane and perpendicular directions.     

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.