Effect of surfactant and electron treatment on the electrical and thermal conductivity as well as thermal and mechanical properties of ethylene vinyl acetate/expanded graphite composites

This study presents an investigation of the electrical and thermal conductivities of composites based on an ethylene vinyl acetate (EVA) copolymer matrix and nanostructured expanded graphite (EG). To improve the EG dispersion in EVA, EG sheets were modified by treating them with the anionic surfactant sodium dodecyl sulphate (SDS) in water. The modified SDS‐EG platelets, after being filtered and dried, were melt‐mixed with EVA to prepare the composites. Finally, both EVA/EG and EVA/SDS‐EG composites were subjected to 50 kGy electron beam (EB) irradiation. SEM images confirm that the irradiated EVA/EG samples had improved interfacial adhesion, while the irradiated EVA/SDS‐EG samples showed even better interfacial adhesion. The gel contents of the irradiated samples without and with SDS treatment increased with increase in EG loading. The EVA/EG composites exhibited a sharp transition from an insulator to a conductor at an electrical percolation threshold of 8 wt %, but with SDS‐EG the electrical conductivity was extremely low, showing no percolation up to 10 wt % of filler. The EB irradiation had no influence on electrical conductivity. The thermal conductivity linearly increased with EG content, and this increase was more pronounced in the case of SDS‐EG, but decreased after EB irradiation. The thermal properties were little influenced by EB irradiation, while better polymer–filler interaction and better filler dispersion as a result of SDS treatment, and the EB irradiation initiated formation of a cross‐linked network, had a positive effect on the tensile properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42396.     

Study of carbon black‐filled poly(butylene succinate)/polylactide blend

In this study, carbon black (CB) was used to control the conductivity and the compatibility of immiscible poly(butylene succinate)/polylactide (PBS/PLA) blend. It is shown that most of the CB particles are selectively dispersed in the matrix PBS phase because of the viscosity ratio of the blend components. The increasing viscosity of PBS phase prevents the coalescence of the dispersed PLA domain during the melt mixing. The domain sizes of PLA are refined when compared with that of blank PBS/PLA blend. The ternary composite shows an onset of the electrical conductivity at low filler loadings (1.5 wt %), which is attributed to a percolation of CB in the insulating matrix polymer. Moreover, the composites exhibited remarkable improvement of rheological properties in the melt state when compared with that of blank PBS/PLA blend. According to the van Gurp‐Palmen plot, the rheological percolation threshold for ternary systems is lower than 1.5 wt %. Furthermore, the ternary composites present improved mechanical properties and thermal stability even at very low loading levels of the CB. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electric‐field induced filler association dynamics and resulting improvements in the electrical conductivity of polyester/multiwall carbon nanotube composites

The effects of electric fields on the filler response dynamics and electrical percolation of poly(ethylene succinate)/multiwall carbon nanotube (MWCNT) composites are studied. When subjected to AC electric fields in their melt state, PESu/MWCNT composites exhibit dramatic improvements in their transverse electrical conductivity. More importantly, the elevated conductivity values are preserved after matrix solidification. Overall, the experimental results show that the electrified composites exhibit the same electrical conductivity levels as their non‐electrified counterparts at approximately threefold less filler content. The dynamics of the insulator‐to‐conductor transition under an electric field also are studied for these composites and correlate reasonably well with operating parameters, such as electric field intensity, matrix viscosity, and filler content through a relatively simple model. Such a model can serve as an enabling tool in the determination of process conditions for the manufacturing of electrically conducting MWCNT/polymer composites. POLYM. COMPOS., 38:1571–1578, 2017. © 2015 Society of Plastics Engineers     

Preparation of interfacially compatibilized PP‐EPDM thermoplastic vulcanizate/graphite nanocomposites: Effects of graphite microstructure upon morphology,electrical conductivity,and melt rheology

Electrically conductive PP/EPDM dynamically crosslinked thermoplastic vulcanizate (TPV)/expanded graphite (EG) has been successfully prepared via melt compounding of maleic anhydride grafted polypropylene (PP‐g‐MA)/EG masterbatch and a commercially available TPV material. Correlation between graphite microstructure, and electrical conductivity as well as melt rheological behavior has been studied. Natural graphite flake (NGF), graphite intercalated compound (GIC), and exfoliated graphite (EG) have been employed and compared. Scanning electron microscopy (SEM) showed the presence of 100–200 nm nanolayers in the structure of PP‐g/EG masterbatches, whereas thinner platelets (1.5–2.5 nm) were revealed by transmission electron microscopy (TEM). Better dispersion of the graphite nanolayers in the microstructure of TPV/PP‐g‐MA/EG composite was verified, as the 7.3 Å spacing between the aggregated graphite nanolayers could not be observed in the XRD pattern of this material. TPV/PP‐g/EG nanocomposites exhibited much lower conductivity percolation threshold (φ_c) with increased conductivity to 10^?5 S/cm at EG wt % of 10. Higher nonlinear and nonterminal melt rheological characteristics of dynamic elastic modulus (G′) at low frequency region was presented by the TPV/PP‐g/EG nanocomposites, indicating the formation of nanoscopic conducting multiple networks throughout the continuous TPV matrix. Maleated PP was found to be much more effective in separating EG nanolayers which is attributed to the higher interfacial interaction between PP‐g‐MAH and EG, synergized with its multiporous structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrical and mechanical properties of expanded graphite‐reinforced high‐density polyethylene

High‐density polyethylene (HDPE) was reinforced with expanded and untreated graphite in a melt‐compounding process. Viscosity increased upon addition of graphite phase, with the expanded graphite (EG) showing more dramatic rise than the untreated graphite (UG) in viscosity. The increase in viscosity was attributed to the increased surface‐to‐volume ratio for the EG filler after acid treatment. Electrical conductivity also increased from that pertaining to an insulator to one characteristic of a semiconductor. The EG system showed a lower percolation threshold for transition in conductivity compared to that in the UG system. DSC results indicated that the fillers acted as a nucleating agent in inducing the crystallization of HDPE in the composites. However, the overall degree of crystallinity and melting temperature of HDPE decreased with the addition of EG and UG. Mechanical properties improved as a function of filler content but the overall enhancement was not impressive. It was conjectured that the filler–matrix interface was not optimized in the melt‐mixing process. However, the role of EG as a reinforcement phase for both electrical and mechanical properties was unambiguously established. The EG composites demonstrated potentially useful attributes for antistatic, barrier, mechanical, electrical, and cost‐effective applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2781–2788, 2004     

Effect of filler size on thermophysical and electrical behavior of nanocomposites based on expanded graphite nanoparticles filled in low‐density polyethylene matrix

Various aspects of electrical and thermophysical properties of nanocomposites based on low‐density polyethylene matrix filled with nanostructuralized expanded graphite (EG) and standard, microsized graphite are presented in this article. A periodical method developed in the laboratory was used to measure simultaneously thermal conductivity, specific heat, and diffusivity of composites at room temperature. The effect of micro‐ and nanosized fillers on the final thermophysical and electrical behavior is investigated. It was found that the electrical conductivity of composites strongly depends not only on the filler content but also on the filler size. When the microsized graphite was used, the percolation concentration of the filler was found to be 15 vol%, whereas the percolation concentration of the filler in nanocomposites filled with EG of large sizes was significantly lower. Similarly, it was shown that the graphite significantly improves the thermophysical behavior of composites filled with micro‐ and nanofiller sizes. The thermal conductivity measured values were also compared with some theoretical models for the prediction of the thermal conductivity. POLYM. COMPOS., 2012. © 2013 Society of Plastics Engineers     

Properties of polyetherimide/graphite composites prepared using ultrasonic twin‐screw extrusion

The dispersion of various graphites in polymers is a challenging problem limiting their potential use. To solve this problem, an ultrasound assisted twin‐screw extruder was developed and utilized to compound polyetherimide (PEI) with untreated nature graphite (UG), modified graphite (MG) and expanded graphite (EG) at concentrations up to 10 wt %. The effect of ultrasonic amplitude on rheological, mechanical and electrical properties of the PEI composites was investigated. Ultrasonic treatment of PEI/UG composites showed little effect on these properties. In contrast, ultrasonic treatment of PEI/MG and PEI/EG composites led to an increase of the storage (G′), loss (G″) moduli and complex viscosity and to a decrease of the damping characteristics. In particular, the PEI/5 wt %EG composite ultrasonically treated at an amplitude of 10 μm showed a 45% higher complex viscosity than the untreated composite at a frequency of 0.5 rad/s. Also, the PEI/5 wt % EG composite treated at an amplitude of 10 μm showed a reduction in the electrical volume resistivity by almost three orders of magnitude leading to a lower percolation threshold. The untreated and treated PEI/UG and PEI/MG composites did not show any percolation within all graphite concentrations studied, due to large size of particles of UG and MG and their strong agglomeration. The ultrasonic treatment showed slight effect on mechanical properties of all these composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41397.     

The influence of layered,spherical, and tubular carbon nanomaterials' concentration on the flame retardancy of polypropylene

The characteristic influences of increasing concentrations of graphene, expanded graphite (EG), carbon black (CB), and multiwall carbon nanotubes (MWNT) are investigated on pyrolysis, reaction to small flame, burning behavior, and on electrical, thermal, and rheological properties of flame retarded polypropylene (PP‐FR). The property‐concentration dependency is different for the various material properties, as threshold, linear, and leveling off functions were observed. Increasing concentrations of carbon nanoparticles resulted in a decrease in the electrical resistivity of the polymer by crossing the percolation threshold. The developing nanoparticle network changes melt flow behavior for small shear rates, increases thermal conductivity and therefore, affects the UL 94 classification and oxygen index. The onset temperature of PP decomposition is shifted to temperatures up to 37°C higher; the peak heat release rate is reduced by up to 74% compared to PP‐FR. Both effects leveled off with increasing particle concentration. Among the four carbon nanomaterials tested, graphene presents superior influence on composite properties over the tested concentration range and outperforms commercial CB, MWNT, and EG. POLYM. COMPOS., 36:1230–1241, 2015. © 2014 Society of Plastics Engineers     

Thermal conductivity of poly vinylidene fluoride composites filled with expanded graphite and carbon nanotubes

The composites composed of Poly (vinylidene fluoride), expanded graphite (EG), and carbon nanotubes (CNTs) have been prepared by solution mixing, followed by compression. The structure of the composites was examined with scanning electron microscope and their electrical and thermal properties were investigated. About 1.2 wt % content of CNTs could present a percolated network in the polymer matrix, characterized by the electrical conductivity. The incorporation of EG and CNTs in the polymer caused an enhancement in thermal conductivity for the composites. However, a hybrid of EG and CNTs as filler of the polymer yielded a further improvement in thermal conductivity as compared to single component filler. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Blends of polypropylene and ethylene octene comonomer with conducting fillers: Influence of state of dispersion of conducting fillers on electrical conductivity

Blends of polypropylene/ethylene octene comonomer (PP/EOC) with conducting fillers viz., carbon black (CB) and multiwall carbon nanotubes (MWNT) were prepared using melt mixing technique with varying filler concentration and blend compositions. Thermo gravimetric analysis studies indicated that presence of filler enhanced the thermal stability of PP/EOC blends. Morphological analysis revealed the formation of matrix‐dispersed droplet and co‐continuous type of morphology depending on the blend compositions. Significant reduction in droplet size and finer ligament thickness in co‐continuous structure were observed in the blends with filler due to compatibilization action. Fillers were found to be aggregated in the EOC phase irrespective of blends compositions and could be related to the affinity of the fillers toward EOC phase. The electrical conductivity of PP/EOC blends with CB and MWNT was found to be highest for 80/20 composition and decreased as EOC content increased. The percolation threshold of CB was between 10 and 15 wt% for the 80/20 and 70/30 blends whereas it was 15–20 wt% for blends with EOC content higher than 30 wt%. The percolation threshold was 2–3 wt% MWNT for PP/EOC blends. This was attributed to the aggregated filler network preferentially in the EOC phase. The melt‐rheological behavior of PP/EOC blends was significantly influenced in presence of both the fillers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Improvement in properties of multiwalled carbon nanotube/polypropylene nanocomposites through homogeneous dispersion with the aid of surfactants

The effects of different surfactants on the properties of multiwalled carbon nanotubes/polypropylene (MWCNT/PP) nanocomposites prepared by a melt mixing method have been investigated. Sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (NaDDBS) were used as a means of noncovalent functionalization of MWCNTs to help them to be dispersed uniformly into the PP matrix. The effects of these surfactant‐treated MWCNTs on morphological, rheological, thermal, crystalline, mechanical, and electrical properties of MWCNT/PP composites were studied using field emission scanning electron microscopy, optical microscopy, rheometry, tensile, and electrical conductivity tests. It was found that the surfactant‐treatment and micromixing resulted in a great improvement in the state of dispersion of MWCNTs in the polymer matrix, leading to a significant enhancement of Young's modulus and tensile strength of the composites. For example, with the addition of only 2 wt % of SDS‐treated and NaDDBS‐treated MWCNTs, the Young's modulus of PP increased by 61.1 and 86.1%, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement in thermal conductivity and mechanical properties of ethylene‐propylene–diene monomer rubber by expanded graphite

Thermally conductive fillers are usually employed in the preparation of rubber composites to enhance thermal conductivity. In this work, ethylene‐propylene‐diene monomer rubber (EPDM)/expanded graphite (EG) and EPDM/graphite composites with up to 100 phr filler loading were prepared. Compared to EPDM/graphite compounds with the same filler loading, stronger filler network was demonstrated for EPDM/EG compounds. Thermal conductivity and mechanical properties of EPDM/graphite and EPDM/EG composites were compared and systematically investigated as a function of the filler loading. The thermal conductivity of both EPDM/graphite and EPDM/EG composites increased with increasing volume fraction of fillers, and could be well fitted by Geometric Mean Model. The thermal conductivity as high as 0.910 W · m⁻¹ · K⁻¹ was achieved for the EPDM/EG composite with 25.8 vol% EG, which was ∼4.5 times that of unfilled EPDM. Compared to EPDM/graphite composites, EPDM/EG composites exhibited much more significant improvement in thermal conductivity and mechanical properties, which could be well correlated with the better filler‐matrix interfacial compatibility and denser structure in EPDM/EG composites, as revealed in the SEM images of tensile fracture surfaces. POLYM. COMPOS., 38:870–876, 2017. © 2015 Society of Plastics Engineers     

Comparative study on the exfoliated expanded graphite nanosheet‐PES composites prepared via different compounding method

Composites made of polyethersulfone (PES) reinforced with exfoliated graphite nanoplatelets are fabricated by melt mixing, polymer solution, and coating. Coating is an efficient compounding method emphasized in this research, where expanded graphite (EG) and PES powder are premixed in isopropyl alcohol using sonication to disperse the EG by coating individual PES powder particles. The microstructure and property of EG/PES composites were investigated by X‐ray diffraction, scanning electron microscope, thermal gravimetric analysis, differential scanning calorimetric, and electronic tensile tester. The electrical conductivity was confirmed using electrochemical tester. It is found that the coating method is more effective than the polymer solution and directly melt mixing methods widely used, in terms of increasing the electrical conductivity and lowering the percolation threshold of thermoplastic composites, and enhancing the probability that the large platelet morphology of EG can be preserved in the final composite. The research reported here provides an understanding on how the compounding method used during the fabrication of composites is important to achieving the optimal mechanical properties, thermal properties, electrical conductivity, and percolation threshold. This method should have wide applicability to all thermoplastic matrix composite systems. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Electrical conductivity properties of expanded graphite–polycarbonatediol polyurethane composites

Conductive polymer composites of segmented polycarbonatediol polyurethane and expanded graphite (EG) have been synthesized with different amounts of EG conductive filler (from 0 to 50 wt%). SEM, X‐ray diffraction measurements, Fourier transform infrared and Raman spectroscopies demonstrated a homogeneous dispersion of the EG filler in the matrix. The dielectric permittivity of the composites showed an insulator to conductor percolation transition with increase in EG content. Significant changes in the dielectric permittivity take place when the weight fraction of EG is in the range 20–30 wt%. Special attention has been paid to the dependence of the conductivity on frequency, temperature and EG content. The addition of EG to the matrix causes a dramatic increase in the electrical conductivity of 10 orders of magnitude, which is an indication of percolative behavior. A percolation threshold of ca 30 wt% was evaluated by using the scaling law of percolation theory. © 2014 Society of Chemical Industry     

The influence of matrix viscosity on properties of polypropylene/polyaniline composite fibers—Rheological,electrical, and mechanical characteristics

Electrically conductive composites containing polypropylene (PP) and polyaniline (PANI) were prepared using PP with three different melt flow rates (MFRs) and a commercial PANI‐complex in proportions of 80% by weight and 20%, respectively. Composite blends were melt‐spun to fibers under different solid‐state draw ratios. Rheological studies of dynamic viscosity, as well as the storage modulus and loss modulus showed that the prepared PANI‐complex/PP blends exhibit different dynamic rheological behavior, depending on the PP used. This confirms the blends' morphological differences. PP matrix viscosity was found to play an important role in the electrical properties of the prepared fibers. Fibers prepared using the matrix with the lowest viscosity, showed a larger dispersed phase size in the cross‐sectional SEM micrographs, maximum conductivity observed at higher draw ratios and a more linear resistance–voltage relationship than those of the fibers prepared using the higher viscosity matrices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Melt rheology of polypropylene reinforced with polyaniline‐coated short glass fibers

This research deals with the melt rheology of isotactic polypropylene (iPP) reinforced with short glass fibers (SGF) coated with electrically conductive polyaniline (PAn). Composites containing 10, 20, and 30 wt % PAn‐SGF were studied. Moreover, a composite of 30 wt % PAn‐SGF was also prepared with a blend of iPP and PP‐grafted‐maleic anhydride (iPP/PP‐gMA). The composites showed linear viscoelastic regime at small strain amplitudes. The onset of nonlinearity decreased as the concentration of filler increased. The time‐temperature superposition principle applied to all composites. The filler increased the shear moduli (G′, G″) and the complex viscosity η*. Steady‐state shear experiments showed yield stress for the composites with 20 and 30 wt % PAn‐SGF. Strikingly, the 10 wt % composite showed higher steady state viscosity than the 20 wt %. Rheo‐optics showed that shear induced disorder of microfibers at a concentration of 10 wt %. However, at 20 wt % concentration shear aligned the microfibers along the flow axis, this would explain the anomalous steady state viscosity values. The viscosity exhibited a shear thinning behavior at high shear rates for all composites. Creep experiments showed that the filler induced greater strain recovery in the composites and that the amount of strain recovery increased as the PAn‐SGF concentration increased. However, the enhancement of strain recovery (as well as shear viscosity) was more significant when using the iPP/PP‐gMA blend, suggesting greater adhesion between this matrix and the filler PAn‐SGF. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Graphene nanosheets‐filled epoxy composites prepared by a fast dispersion method

Graphene nanosheets‐filled epoxy composites (GNS/Epoxy) were prepared at different filler loading levels from 0.25 to 3.00 wt %. A fast dispersion method as short as 5 min is employed to disperse GNS in epoxy matrix, which was enough for the homogeneous dispersion of GNS with the help of high ultrasonic frequency of 100 kHz and power of 200 W and high heat treatment temperature of 70 °C. The maximum electrical conductivity and thermal conductivity of the composites achieved 0.058 S m^?1 and 0.57 W m^?1 K^?1, respectively, with a low electrical percolation threshold of 1.50 wt %. The electrical conductivities were further predicted by percolation theory and found to agree well with the experimental results, which indicated that the graphene nanosheets dispersed very well in the matrix even at very short processing time. The results showed that the microstructures, thermal, electrical, and mechanical properties of epoxy polymer were significantly improved by adding a low amount of graphene nanosheets. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45152.     

Thermal conductivity,electrical resistivity,mechanical, and rheological properties of thermoplastic composites filled with boron nitride and carbon fiber

Hybrid composites consisting of boron nitride (BN) platelets and carbon fibers (CF) in a polybutylene terephthalate (PBT) matrix were melt‐compounded, and their thermal and electrical conductivity, tensile, and rheological properties were investigated. While it does not lead to an enhancement in thermal conductivity with respect to PBT/BN composites, the results indicate that a combination of BN and CF in PBT can significantly reduce electrical conductivity of the composites compared to that of PBT/CF composites. The relative low thermal conductivity of the hybrid composites is attributed to CF breakage that occurred during the extrusion and alignment of CF in melt flow direction, which is normal to the heat flow encountered during the thermal conductivity tests induced by injection molding. The hybrid composites were, however, found to have better tensile properties and processibility than PBT/BN composites at the same total filler content. POLYM. COMPOS., 26:66–73, 2005. © 2004 Society of Plastics Engineers     

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     

Hybrid composites of ABS with carbonaceous fillers for electromagnetic shielding applications

This work evaluates the influence of two types of carbonaceous fillers, carbon black (CB) and carbon nanotubes (CNTs), on the electrical, electromagnetic, and rheological properties of composites based on poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) prepared by the melt mixing. Electrical conductivity, electromagnetic shielding efficiency (EMI SE) in the X‐band frequency range (8–12.4 GHz), and melt flow index (MFI) results showed that ABS/CNT composites exhibit higher electrical conductivity and EMI SE, but lower MFI when compared to ABS/CB composites. The electrical conductivity of the binary composites showed an increase of around 16 orders of magnitude, when compared to neat ABS, for both fillers. Binary composites with 5 and 15 wt % of filler showed an EMI SE of, respectively, ?44 and ?83 dB for ABS/CNT, and ?9 and ?34 dB for ABS/CB. MFI for binary composites with 5 wt % were 15.45 and 0.55 g/10 min for CB and CNT, respectively. Hybrid composites ABS/CNT.CB with 3 wt % total filler and fraction 50:50 and 75:25 showed good correlation between EMI SE and MFI. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46546.