High‐performance EMI shielding materials based on short carbon fiber‐filled ethylene vinyl acetate copolymer,acrylonitrile butadiene copolymer,and their blends

The composites of carbon fiber with EVA, NBR, and their blends have been made by melt mixing technique. Stress–strain plots of different composites show that the necking phenomenon is increasing with the increase in fiber concentration in the polymer matrix. The scanning electron microscopic analysis and swelling study exhibit poor interaction between the short carbon fiber and polymer matrix. The decrease in DC resistivity with the increase in short carbon fiber concentration has been explained on the basis of percolation theory. EMI SE increases slightly with the increase in frequency of electromagnetic radiation but increases sharply with the increase in fiber concentration. EMI SE also depends on blend composition and increases with the increase in EVA concentration in the blend. Return loss is decreasing but absorption loss is increasing with the increase in fiber loading. A linear relationship is observed between the EMI SE and thickness of the composites. The EMI SE is found to increase exponentially with the increase in conductivity of the composite. The permeability value is decreasing with the increase in frequency as well as fiber loading. Thermal properties of the composites have been evaluated by thermogravimetric analysis and dynamic mechanical analysis. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Optical and electrical properties of polyaniline‐cadmium sulfide nanocomposite

Polyaniline‐cadmium sulfide nanocomposite has been synthesized by the chemical oxidative polymerization of aniline with ammonium peroxodisulfate as an initiator in presence of cadmium sulfide nanoparticles. TEM, XRD, FTIR, TGA, UV–vis spectroscopy, and photoluminescence studies were done for the structural, thermal and optical characterization of the samples. The particle size of nanocomposites lies in between 7 and 10 nm. XRD spectrum shows that polyaniline is amorphous, but peaks present in the spectrum of polymer nanocomposites are for cadmium sulfide nanoparticles. TGA result shows that nanocomposite is more thermally stable. The band gap of nanocomposite decreases with increasing content of cadmium sulfide nanoparticles. An enhancement in photoluminescence has been observed in the nanocomposite than that in pure polyaniline. The dc and ac electronic transport property of polyaniline cadmium sulfide composites has been investigated within a temperature range 77 ≤ T ≤ 300 K and in the frequency range 20 Hz–1 MHz. The dc conductivity follows variable range hopping (VRH) model. The ac conductivity follows a power law whereas the temperature dependence of frequency exponent s can be explained by correlated barrier hopping (CBH) model. The dielectric behavior of the samples has been explained in terms of the grain and grain boundary resistance and capacitance. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Preparation and EMI shielding properties of nickel‐coated PET fiber filled epoxy composites

Electrically conductive composites were prepared using epoxy resin (EP) as matrix and nickel‐coated polyethylene teraphthalate (PET) fibers as filler. The fibers were coated with nickel by plating and ultrasonic electroless deposition techniques. The coaxial transmission line method was used to measure the electromagnetic interference (EMI) shielding effectiveness of the nickel‐coated PET fiber/EP composites. The contents of nickel and phosphorus in the coating were determined by X‐ray photoelectron spectroscopy (XPS). As a result, the ultrasonic electroless nickel‐coated PET fiber/EP composites showed excellent electrical conductive capability and better EMI shielding effectiveness due to higher content of nickel and lower content of phosphorus in the coating than conventional plated nickel‐coated PET fiber/EP composites. POLYM. COMPOS., 27:24–29, 2006. © 2005 Society of Plastics Engineers     

Electrical conductivity of vapor‐grown carbon nanofiber/polyester textile‐based composites

Polyamide 6/ethylene–propylene–diene metallocene terpolymer/(ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) blends with clay (3 and 5 wt % depending on the formulation), different clays (montmorillonite and sepiolite) and different surface functionalization (ammonium salts and silanes) were studied to analyze the effect of the shape of clay and type of modifier on their properties. The results have shown that sepiolite has higher influence on the morphology and on the mechanical properties than montmorillonite. In that sense, blends with 3 wt % of sepiolite have reached the best balanced properties, i.e., tensile modulus and impact strength, than their homologous with montmorillonite. Furthermore, the blends with 3 wt % of sepiolite have reached the highest mechanical properties compared with blends with higher montmorillonite content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of silanized vapor‐grown carbon nanofibers/epoxy shape memory nanocomposites

Silanized vapor‐grown carbon nanofiber/epoxy (silanized‐VGCNF/EP) shape memory polymer (SMP) nanocomposites are successfully fabricated by using a composite molding technology. The surface functionalization of VGCNF is performed using an acid treatment followed by a reaction with silane. The oxidation as well as silanization of VGCNF and silanized‐VGCNF/EP nanocomposites are systematically and explicitly characterized using various analytical methods. The influence of the silane‐functionalized VGCNF on the properties of VGCNF/EP nanocomposites is investigated using field emission scanning electronic microscopy (FE‐SEM) and a dynamic mechanical analysis (DMA). The shape memory properties of the silanized‐VGCNF/EP nanocomposites are evaluated by a fold‐deploy shape memory test. The results reveal that the silanized‐VGCNF is preferably dispersed in the epoxy resin matrix. Furthermore, the glass transition temperature of silanized‐VGCNF/EP nanocomposites is enhanced, and the shape memory properties of the silanized‐VGCNF/EP nanocomposites are significantly improved. POLYM. COMPOS., 35:412–417, 2014. © 2013 Society of Plastics Engineers     

Tensile properties and reinforcement mechanisms of natural rubber/vapor‐grown carbon nanofiber composite

Natural rubber (NR) composites with different contents of 1, 3, 10, and 20 wt% vapor‐grown carbon nanofibers (VGCFs) were synthesized using a solvent casting method. The initial modulus of composites was improved by 26.5 %/wt% as the VGCFs were added, and the NR/3 wt%VGCF composite had the largest tensile strength. The experiment values of initial moduli agreed well with the values predicted by the Halpin‐Tsai theory. The reinforcement mechanisms of the composites were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and wide‐angle X‐ray diffraction (WAXD). It was found that an efficient stress transfer occurred from NR to VGCFs under the uniaxial stretching. The addition of 10 wt% VGCFs could promote the nucleation process of NR, which resulted in the characteristic of the strain‐induced crystallization (SIC) in NR/10 wt%VGCF composite even for low strain. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Stability of electrical properties of carbon black‐filled rubbers

Conducting composites were prepared by melt mixing of ethylene–propylene–diene terpolymer (EPDM) or styrene‐butadiene rubber (SBR) and 35 wt % of carbon black (CB). Stability of electrical properties of rubber/CB composites during cyclic thermal treatment was examined and electrical conductivity was measured in situ. Significant increase of the conductivity was observed already after the first heating–cooling cycle to 85°C for both composites. The increase of conductivity of EPDM/35% CB and SBR/35% CB composites continued when cyclic heating‐cooling was extended to 105°C and 125°C. This effect can be explained by reorganization of conducting paths during the thermal treatment to the more conducting network. EPDM/35% CB and SBR/35% CB composites exhibited very good stability of electrical conductivity during storage at ambient conditions. The electrical conductivity of fresh prepared EPDM/35% CB composite was 1.7 × 10⁻² S cm⁻¹, and slightly lower conductivity value 1.1 × 10⁻² S cm⁻¹ was measured for SBR/35% CB. The values did not significantly change after three years storage. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological analysis of vapor‐grown carbon nanofiber‐reinforced polyethylene composites

The melt rheological analysis of high‐density polyethylene reinforced with vapor‐grown carbon nanofibers (VGCNFs) was performed on an oscillatory rheometer. The influence of frequency, temperature, and nanofiber concentration (up to 30 wt %) on the rheological properties of composites was investigated. Specifically, the viscosity increase is accompanied by an increase in the elastic melt properties, represented by the storage modulus G′, which is much higher than the increase in the loss modulus G″. The composites and pure PE exhibit a typical shear thinning behavior as complex viscosity decreases rapidly with the increase of shearing frequency. The shear thinning behavior is much more pronounced for the composites with high fiber concentration. The rheological threshold value for this system was found to be around 10 wt % of VGCNF. The damping factor was reduced significantly by the inclusion of nanofibers into the matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 155–162, 2004     

Improved specific capacity of sulfur/starch‐based activated carbon spheres composites by polyaniline‐based carbon encapsulation strategy

Lithium‐sulfur battery is one of the most promising electrochemical energy storage systems because of its high theoretical specific capacity and energy density. When carbon materials are used for immobilizing sulfur, the technical challenge is designing their framework to relieve the shuttle effect of polysulfides intermediates and the volume change of sulfur, and to improve the conductivity of sulfur. Herein, polyaniline‐based carbon (PANI‐C) coated corn starch‐based activated carbon spheres (ACS@PANI‐C) was prepared and used as hosts of sulfur, which can effectively combine the advantages of physical entrapment and chemical binding interactions of sulfur species. The results of electrochemical performance test indicate that S/ACS@PANI‐C composites exhibit much better electrochemical performance than S/ACS composites. Its reversible capacities at 320, 480, 800 and 1600 mA g^?1 are 687, 582, 504 and 393 mAh g^?1, respectively. The improved electrochemical performance can be attributed to the PANI‐C which can also act as a flexible cushion to accommodate volume changes of sulfur cathode as well as a barrier to trap soluble polysulfide intermediates during the charge–discharge process. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46544.     

Effects of nanofiber treatments on the properties of vapor‐grown carbon fiber reinforced polymer composites

Vapor‐grown carbon fibers (VGCFs) were exposed to a series of chemical treatments and to electrochemical deposition of copper to modify their surface conditions and alter their electrical properties. The fibers were then mixed with polypropylene using a Banbury‐type mixer obtaining composites up to 5 wt % VGCFs. Rheological, electrical, and mechanical properties were evaluated and compared to unfilled polypropylene processed in a similar manner. The composites made with HNO₃‐treated VGCFs showed a lower electrical resistivity compared to the untreated samples. The composites containing VGCFs subjected to the copper electrodeposition process showed the lowest resistivity with no change in the mechanical properties. Changes in rheological properties demonstrated the effects of varying surface conditions of the VGCFs. Microscopic analysis of these composites showed a heterogeneous distribution of VGCFs forming an interconnected network with the presence of copper on the surface of the VGCFs and in the matrix. Both the interconnected network and the presence of copper led to a lower percolation threshold than those seen in a previous work where high dispersion was sought. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2527–2534, 2003     

Transient shear flow properties of carbon fiber–filled liquid crystalline polymer

Unsteady flow of filled polymer systems can cause some difficulties in their processing, such as injection or extrusion molding, in which flow in the molten state is involved. In order to determine the optimum conditions and thus improve the performance of the end products, it is necessary to understand the transient/unsteady flow behavior of these systems. In a previous work, we found remarkable non‐Newtonian properties and shear thickening flow behavior of liquid crystalline polymers (LCP) and their filled systems. This article deals with the dependence of transient flow properties, including shear thickening, of pure and carbon fiber‐filled LCP upon the shear rate and shear strain history; the effect of the filler content is also discussed. The results indicate that the abnormal flow behavior of the tested materials may be caused by gradual disintegration of the domain structure formed in LCP (materials exhibit apparent yield stress) and then continual orientation of molecules under shear flow. The shear thickening behavior of the materials seems to disappear with increasing fiber content. This behavior suggests that it is necessary to measure the flow properties under a sufficient ramp point delay time and equilibration time in order to obtain reliable data under stable conditions. POLYM. COMPOS., 26:470–476, 2005. © 2005 Society of Plastics Engineers.     

Microwave dielectric properties and EMI shielding effectiveness of poly(styrene‐b‐styrene‐ butadiene‐styrene) copolymer filled with PAni.Dodecylbenzenesulfonic acid and carbon black

Conducting composites of polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA), carbon black (CB) and poly(styrene‐b‐styrene‐butadiene‐b‐styrene) (STF) as supporting matrix were prepared by in situ polymerization. The influence of components and composition (% w/w) on the electromagnetic properties (dielectric constant ε′ and the dielectric loss ε″) and electromagnetic interference shielding effectiveness (EMI‐SE) of the materials were evaluated with a waveguide, using a microwave network analyzer from 8.2 to 12.4 GHz (X‐band). It was found that CB presence generates adverse effects on PAni.DBSA yield during synthesis, as it can be seen by X‐ray diffraction and TGA analyses. The type of PAni.DBSA formed modifies the composites properties. Dielectric constant, loss factor, and EMI shielding increase with conductive filler loading. Both the fillers, individually and in combination, increase the properties; however, the effect is not additive in nature. POLYM. ENG. SCI., 52:2041–2048, 2012. © 2012 Society of Plastics Engineers     

Thermal stability,aging properties,and flame resistance of NR‐based nanocomposite

Polymer/clay nanocomposites have some unique properties due to combination of flame resistance and improved mechanical and thermal stability properties which are important to enhance the material quality and performance. The objective of this work was to investigate the effect of organically modified montmorillonite (org‐MMT) on the thermal and flame retardant as well as hardness and mechanical properties of the nanocomposites based on the natural rubber (NR). It was shown that by the addition of 3 wt % of org‐MMT to NR, its aging hardness rise was decreased more than 55% and the ignition time was delayed about 150%. The reduction in heat release rate peak value was equal to 54% compared to the pristine NR. Addition of org‐MMT improved the thermal stability of the NR. Furthermore, nanocomposites which were calendared before curing showed much more thermal stability and fire resistance than those which contained similar amount of organoclay. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Response surface predictions of the viscoelastic properties of vapor‐grown carbon nanofiber/vinyl ester nanocomposites

A full factorial design of experiments and response surface methodology were used to investigate the effects of formulation, processing, and operating temperature on the viscoelastic properties of vapor‐grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. Factors included VGCNF type (pristine, oxidized), use of a dispersing agent (DA) (no, yes), mixing method (ultrasonication, high‐shear mixing, and a combination of both), VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)), and temperature (30, 60, 90, and 120°C). Response surface models (RSMs) for predicting storage and loss moduli were developed, which explicitly account for the effect of complex interactions between nanocomposite design factors and operating temperature on resultant composite properties; such influences would be impossible to assess using traditional single‐factor experiments. Nanocomposite storage moduli were maximized over the entire temperature range (～20% increase over neat VE) by using high‐shear mixing and oxidized VGCNFs with DA or equivalently by employing pristine VGCNFs without DA at ～0.40 phr of VGCNFs. Ultrasonication yielded the highest loss modulus at ～0.25 phr of VGCNFs. The RSMs developed in this investigation may be used to design VGCNF‐enhanced VE matrices with optimal storage and loss moduli for automotive structural applications. Moreover, a similar approach may be used to tailor the mechanical, thermal, and electrical properties of nanomaterials over a range of anticipated operating environments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers     

Fluorination effects of carbon black additives for electrical properties and EMI shielding efficiency by improved dispersion and adhesion

Electrospinning and heat treatment were carried out to get nano sized carbon fibers (CFs) as a matrix for shielding the electromagnetic interference (EMI). In order to improve the electrical conductivity and EMI shielding efficiency of electrospun CFs, carbon black (CB) was fluorinated and embedded into the electrospun CFs. Electrospun fiber sheets embedded fluorinated CB were heat-treated at different temperatures to determine the effects on electrical properties. It is demonstrated that fluorination treatment of CB and heat treatment of electrospun sheets at higher temperature lead to higher electrical conductivities and EMI shielding efficiencies, because fluorination significantly improved its dispersion in electrospun CF webs and created good adhesion between the CB and the CFs. The electrical conductivity of carbon composite sheets (webs) reached ∼38 S/cm, and a high EMI shielding efficiency was obtained (∼50 dB).     

Characterization,prediction, and optimization of flexural properties of vapor‐grown carbon nanofiber/vinyl ester nanocomposites by response surface modeling

A design of experiments and response surface modeling were performed to investigate the effects of formulation and processing factors on the flexural moduli and strengths of vapor‐grown carbon nanofiber (VGCNF)/vinyl ester (VE) nanocomposites. VGCNF type (pristine, surface‐oxidized), use of a dispersing agent (no, yes), mixing method (ultrasonication, high‐shear mixing, and a combination of both), and VGCNF weight fraction (0.00, 0.25, 0.50, 0.75, and 1.00 parts per hundred parts resin (phr)) were selected as independent factors. Response surface models were developed to predict flexural moduli and strengths as a continuous function of VGCNF weight fraction. The use of surface‐oxidized nanofibers, a dispersing agent, and high‐shear mixing at 0.48 phr of VGCNF led to an average increase of 19% in the predicted flexural modulus over that of the neat VE. High‐shear mixing with 0.60 phr of VGCNF resulted in a remarkable 49% increase in nanocomposite flexural strength relative to that of the neat VE. This article underscores the advantages of statistical design of experiments and response surface modeling in characterizing and optimizing polymer nanocomposites for automotive structural applications. Moreover, response surface models may be used to tailor the mechanical properties of nanocomposites over a range of anticipated operating environments. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2087–2099, 2013     

Electrical and mechanical properties of carbon‐black‐filled,electrospun nanocomposite fiber webs

The development of flexible and compliant conductive polymer composites with textile‐like characteristics remains an important endeavor in light of the recent activity in polymer/textile‐based electronics and the need for compliant electrodes for electroactive polymer actuators. In this work, carbon black (CB) was dispersed in a polymer solution to form electrospun fiber webs consisting mainly of nanofibers. The effect of the filler content on the fiber‐web morphology, mechanical behavior, electrical conductivity, and thermal resistance was examined. The electrical conductivity percolation threshold of the fiber‐web structure was found to be around 4.6 vol %. Scanning electron micrographs of the fiber webs revealed a significant influence of the CB content on the fiber formation as well as the bond structure of the fiber web, which influenced the mechanical properties of the web. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2410–2417, 2007     

Effect of processing method on microstructure,electrical conductivity and electromagnetic wave interference (EMI) shielding performance of carbon nanofiber filled thermoplastic polyurethane composites

In this study, effect of processing method on microstructure formation and related electrical conductivity and electromagnetic interference shielding effectiveness of carbon nanofiber (CNF) filled thermoplastic polyurethane (TPU) composites, prepared via three different processing techniques; (i) melt compounding (MC) in a twin screw extruder, (ii) simple solution mixing (SM) on a magnetic stirrer, and (iii) solution mixing with sonication (SM-U) were investigated. It was found that the electrical conductivity values of samples decreased in the order of SM > SM-U > MC for a particular amount of CNF. The electromagnetic test results showed that the samples prepared with SM and SM-U methods yielded higher total shielding effectiveness (SE_T) values than those prepared with MC. SE_T values of samples including of 20 phr of CNF prepared with MC, SM-U and SM methods were varied in the range of 10–30 dB, 20–60 dB and 20–80 dB, respectively within a frequency range of 1–12 GHz.