Impedance spectra of carbon black filled high‐density polyethylene composites

Carbon black (CB) filled high‐density polyethylene (HDPE) composites are prepared by ordinary blending for use as an electrical conductive polymer composite. The composite changes from an electrical insulator to a conductor as the CB content is increased from 10 to 20 wt %, which is called the percolation region. For explanatory purposes, three models, namely, “conduction via nonohmic contacting chain,” “conduction via ohmic contacting chain,” and a mixture of them corresponding to the conductions in the percolation region, high CB loading region, and limiting high CB loading are proposed by the reasonable configurations of aggregate resistance, contact resistance, gap capacitance, and joining aggregates induction. The characters of the impedance spectra based on the three models are theoretically analyzed. In order to find some link between the electrical conductivity and the CB dispersion manner in the composites, the impedance spectra of three samples, HDPE/15 wt % CB (the center of the percolation region), HDPE/25 wt % CB (a typical point in the high CB loading region), and HDPE/19 wt % CB (the limiting high CB loading region), are measured by plotting the impedance modulus and phase angle against the frequency and by drawing the Cole–Cole circle of the imaginary part and real part of the impedance modulus of each sample. The modeled approached spectra and the spectra measured on the three samples are compared and the following results are found: the measured impedance spectrum of HDPE/15 wt % CB (percolation region) is quite close to the model of conduction via nonohmic contacting chain. The character of the measured spectrum of HDPE/25 wt % CB consists of the form of the model of conduction via ohmic contacting chain. The impedance behavior of HDPE/19 wt % CB exhibits a mixture of the two models. From the comparisons, it is concluded that the electrical conducting network in the percolation region of the CB filled HDPE composite is composed of aggregate resistance, nonohmic contact resistance, and gap capacitance, and that of the high CB loading region consists of continuously joined CB aggregate chains, which are possibly wound and assume helix‐like (not straight lines) conductive chains, acting as electrical inductions as the current passes through. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1344–1350, 2005     

Dynamic rheological behavior of high‐density polyethylene filled with carbon black

The dynamic rheological behavior of high‐density polyethylene (HDPE) composites filled with carbon black (CB) was studied by controlling periodic small shear strains at constant temperatures. The results shed light on the relationship between the behavior of dispersed fillers and polymeric matrix systems. At sufficiently high filler concentration a structural skeleton seems to appear, which significantly raises the modulus at the low frequency region. High structure, finer size acetylene black raises the modulus significantly more than does the low structure and larger size one (e.g., N550). Oxidized CB increases the modulus in the whole frequency region for the enhanced interaction between polymer matrix and CBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3527–3531, 2002     

Electrical resistivity of carbon black filled high‐density polyethylene composites

The electrical resistivity of high‐density polyethylene (HDPE) loaded with carbon black (CB) blends was evaluated as a function of the blending time and the melt index of HDPE. The relationship between the positive temperature coefficient effect and the room temperature volume resistivity was investigated. The positive temperature coefficient effect and reproducibility were improved significantly when the blending time of HDPE and CB was comparatively long. The effects of ⁶⁰Co γ‐ray and electron beam irradiation on the positive and negative temperature coefficient behavior of the blends were studied. The effect of thermal aging on the volume resistivity was studied to ascertain the structural stability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2440–2446, 2002     

Electric self‐heating behavior of acetylene carbon black filled high‐density polyethylene composites

The electric self‐heating behavior of carbon black (CB) filled high‐density polyethylene (HDPE) was studied in relation to the time‐dependent current and surface temperature under various voltages and to the voltage‐dependent surface temperature at electric–thermal equilibrium. The resistance increase due to self‐heating restricts the current flow through the sample and thus stabilizes the electric power and the self‐heating temperature to their saturation values, which vary with the voltage. A simple phenomenological model shows that self‐heating at electric‐thermal equilibrium is involved in the initial resistance, the electric field induced positive temperature coefficient (PTC) transition and the heat dissipation. The influences of annealing and irradiation crosslinking on the self‐heating behavior are discussed. Copyright © 2004 Society of Chemical Industry     

Room temperature resistance relaxation behavior for carbon black filled conductive polymer composites

Room temperature resistance relaxation was studied with respect to carbon black (CB) volume fraction, the type of polymer matrix, and the environment. It was found that resistance of CB filled poly(methylvinylsiloxane) and polypropylene (PP) conductive composites changed at room temperature with different directions and amplitudes, depending on the filler volume fraction and the environment. The room temperature resistance relaxation was ascribed to the local Joule heat at the tunneling junction or the swelling effect of the solvents. On the other hand, CB filled immiscible PP/Nylon 1212 blends exhibited a stable electrical conduction due to the selective distribution of CB aggregates along the interface between polymer matrices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of isotactic polypropylene/high‐density polyethylene/carbon black conductive films with strain‐sensing behavior

Novel conductive films with a unique strain (ε)‐sensing behavior and based on a blend of isotactic polypropylene (iPP), high‐density polyethylene (HDPE), and carbon black (CB) were fabricated by an extrusion casting method. The morphology and ε‐sensing behavior of the films were investigated. Scanning electron microscope images showed that the oriented lamellae with a growing direction perpendicular to the extrusion direction were obtained in the HDPE phase and were accompanied by a cocontinuous structure of the iPP phase and HDPE/CB phase. The conductive percolation threshold (m_c) and resistivity–ε behavior of the thin films are affected by the drawing ratio during the process of film preparation. The m_c and electrical resistance of the iPP/HDPE/CB composite films increased with the drawing ratio. The gauge factor of the films within the elastic region decreased with increasing drawing ratio. Furthermore, the result of iPP/(HDPE/CB) 40/60 with a high drawing ratio shows that a reversible conductivity was obtained during the cyclic tensile testing (ε = 10%), but an irreversible conductivity makes the film fail during use at the applied ε values of up to 15%. This makes them good piezoresistive candidates for ε‐sensing materials. Moreover, a simple structural model was proposed to describe the reversible and irreversible phenomena in the electrical resistance behavior of the iPP/HDPE/CB films under tensile loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40686.     

Relaxation behavior of conductive carbon black reinforced chlorosulfonated polyethylene composites

Dynamic mechanical analysis and dielectric relaxation spectra of conductive carbon black reinforced chlorosulfonated polyethylene (CSM) composites were used to study their relaxation behavior as a function of temperature and frequency, respectively. A marginal increase in glass transition temperature has been observed upto 30 phr carbon black filled polymer composite, beyond which it decreases, which has been explained on the basis of aggregation of filler particles in the polymer matrix. The strain dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.1–200%. The nonlinearity in storage modulus increases with increase in filler loading. It can be explained on the basis of filler–polymer interaction and aggregation of the filler particulates. The frequency dependent dynamical mechanical analysis has also been studied at frequency range of 0.1–100 Hz. The variation in real and complex part of impedance with frequency has been studied as a function of filler loading. The effect of filler loading on ac conductivity has been observed as a function of frequency. An increase in conductivity value has been observed with increase in filler loading. This can be explained on the basis of formation of conducting paths between filler particulates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of ultrasonic oscillations on the rheological behavior and morphology of Illite‐filled high‐density polyethylene composites

The effects of ultrasonic oscillations on the rheological and viscoelastic properties and morphology of high‐density polyethylene (HDPE)/Illite (70/30) composites were studied. The experimental results showed that the die pressure and apparent viscosity of the HDPE/Illite (70/30) composites were reduced greatly, and so the mass‐flow rate significantly increased in the presence of ultrasonic oscillations during the extrusion. Scanning electron microscopy and linear viscoelasticity tests showed that ultrasonic oscillations improved the dispersion of the Illite particles into the HDPE matrix. The aggregation of the Illite particles disappeared on the fractured surfaces of HDPE/Illite (70/30) composites extruded in the presence of ultrasonic oscillations, and this indicated that ultrasonic oscillations promoted the homogeneous dispersion of Illite particles into the HDPE matrix. Ultrasonic oscillations caused the permanent reduction of the dynamic viscosity and zero‐shear viscosity of HDPE/Illite (70/30) composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 379–384, 2005     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Microwave absorbing properties of ternary linear low‐density polyethylene/carbonyl iron powder/carbon black composites

Linear low‐density polyethylene (LLDPE) was used as polymer matrix, carbonyl iron powder (CIP) and carbon black (CB) were used as fillers, and ternary composites with microwave absorbing properties were prepared by melt blending. Transmission electron microscopy was used to characterize the prepared samples. The absorbing ability (reflection loss) of the prepared composites was measured using the arch method, and the electromagnetic parameters of composites were determined by the transmission/reflection method. The filler contents of CIP and CB have effects on the absorbing peak positions and reflection loss, and there is the optimum filler content in composites to obtain the maximum microwave absorbing. The microwave absorption of LLDPE/CIP/CB composites comes from the combining contributions of the dielectric loss and the magnetic loss. The synergistic effects of CIP and CB effectively improve the microwave absorbing properties of polymer composites. CIP and CB are uniformly distributed in the polymer matrix. The theoretical calculation results of the absorbing ability are in agreement with the experimental results using the transmission line theory. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A preliminary study on mechanical‐electrical behavior of graphite powder‐filled high‐density polyethylene composites

Mechanical and electrical responses of graphite powder (GP)‐filled high‐density polyethylene composites to a uniaxial compression–decompression cycle were studied. Above a compression loading level, a large positive‐pressure coefficient effect of resistance was observed, for which a slide mechanism of GP in the matrix is believed to be responsible. In a step‐wise compressive loading and loading‐holding experiment, the critical compression level was also found, at which the resistance response changed from a time‐independent one to a time‐dependent, creep‐like one. The current‐voltage behavior of the composites showed that the GP contact was non‐ohmic, regardless of GP contents and pressure levels. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 792–796, 2000     

Conductivity of polyolefins filled with high‐structure carbon black

The electrical conductivities of various polyolefins filled with a high‐structure carbon black (CB) were studied. Typical percolation behaviors were observed in all of the materials studied. At a critical CB content, which defined the percolation threshold, CB formed conductivity pathways, and resistivity fell sharply from a value characteristic of an insulator into the range of 10–100 Ω cm. The dependence of the percolation threshold on the matrix viscosity was understood in terms of competing effects on CB dispersion during blending and CB flocculation during compression molding. For the conditions used in this study, polypropylene with a melt flow index of about 50 was optimum. Flocculation in the quiescent melt was studied directly by atomic force microscopy. Conductivity pathways formed over time by CB agglomeration. The temperature dependence of the percolation time was described by an Arrhenius relationship. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1799–1805, 2005     

Resistivity behavior of filled electrically conductive crosslinked polyethylene

The electrical resistivity of crosslinked high-density polyethylene loaded with conductive blacks and carbon fibers was studied as a function of filler concentration and temperature. A thermoelectric switching phenomenon (a sudden resistivity increase in the vicinity of the polyethylene melting point) in such semicrystalline conductive systems was investigated. Significant switching behavior was exhibited by compounds containing very low concentrations of carbon fibers. Some crosslinked compounds filled with mixtures of carbon black and carbon fibers were also studied.     

Mechanical and thermo‐physical properties of high‐density polyethylene modified with talc

The aim of this study was to examine the physical, mechanical, and thermo‐physical properties of high‐density polyethylene (HDPE) modified with talc. Different weight fractions of talc (up to 35 wt %) were compounded with an HDPE matrix containing 2.5 wt % of carbon black (CB) in a twin‐screw compounder. The composites were then processed by injection moulding to obtain specimens for testing. The results indicate that CB causes a significant decrease in the toughness, while talc not only enhances the thermal conductivity and thermo‐physical properties of the composites but can also play a role in compensating for the negative effects of CB on impact resistance. The experimental data show that the presence of CB reduces the impact resistance of HDPE by up to 34%, while addition of up to 8 wt % talc can return this value to close to that of pure HDPE. No significant effect on the composite tensile yield and fracture strength was observed for either component at all concentrations. The thermal conductivity, thermal diffusivity, and specific density values of the composites increased almost linearly, but the increase in moisture absorption in the long term showed nonlinear behavior in the concentration range of the experiment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of ultrasonic vibration on the rheological behavior of high‐density polyethylene composites filled with flash aluminum flake pigments

The metallic effect of polymer composites was produced through the loading of flash aluminum flake pigments (FAFPs) into polymers. This production method could eliminate postprocessing techniques, such as spray coating, painting, or metallization. We used a self‐improved, ultrasound‐assisted capillary rheometer to explore the rheological behavior of high‐density polyethylene composites filled with FAFPs in the absence and presence of ultrasound treatment. The effects of the ultrasound intensity, experimental temperature, filler content, and particle size on the composite viscosity were studied. The results show that the composite viscosity not only decreased as the ultrasound intensity, experimental temperature, and particle size increased but also decreased as the filler content decreased. A viscosity model of the polymer melts was proposed to illustrate the relationship between the viscosity and ultrasonic intensity. The viscosity obeyed the equations under ultrasonic vibration. The predicted results for the composite viscosity complied greatly with the experimental values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44906.     

Structural variations and morphological features of polyethylene/carbon black conductive composites after processing in an internal mixer

Polyethylene (PE) composites filled with carbon black (CB) were prepared using an internal mixer. Several analytical techniques, including rheometry, gel permeation chromatography, electrical conductivity measurements, differential scanning calorimetry, wide‐angle X‐ray diffraction, and transmission electron microscopy (TEM), were used to reveal the structural variations, thermal degradation, morphological features, and crystallization of the PE/CB conductive composites. It was found that the PE polymer chains were degraded, forming long‐chain branching structures after over 30 min of internal mixing. The electrical conduction of the PE/CB composites was determined by the filler content and distribution. The electrical percolation threshold of the PE/CB composites was determined to be between 20 and 30 wt %. The addition of CB had no significant influence on the crystallinity of the PE/CB composites. In contrast, the electron‐beam radiation dose had a significant effect on crystallinity. TEM micrographs of the PE/CB composites exhibit a random four‐phase morphology, including PE lamellae, PE amorphous, CB particles, and voids at the PE/CB interface. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1038‐1046, 2013     

Microwave‐absorbing properties of linear low‐density polyethylene/ethylene–octene copolymer/carbonyl iron powder composites

Using linear low‐density polyethylene (LLDPE)/ethylene–octene copolymer (POE) as a polymer matrix and carbonyl iron powders (CIPs) as filler, we prepared polymer matrix composites with microwave‐absorbing properties by means of melt blending. Scanning electron microscopy and transmission electron microscopy were used to characterize the samples. The absorbing properties of the composites were measured with the arch method in the range of frequency 2.0–18.0 GHz. The results indicate that the absorbing peaks moved to low frequency as the CIP content in composites increased and that there was an appropriate CIP content in LLDPE/POE/CIP composites to achieve the best absorbing effectiveness. The electromagnetic parameters of the composites were determined with the transmission/reflection method in the range 2.6–17.8 GHz. The experimental results show that there were both dielectric loss and magnetic loss in the LLDPE/POE/CIP composites. Therefore, the microwave absorption of the LLDPE/POE/CIP composites was attributed to the combining contributions of the dielectric loss and magnetic loss. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Processability‐enhanced bimodal high‐density polyethylene with comb‐branched high‐density polyethylene

Two solution reactors in series were utilized to synthesize comb‐branched high‐density polyethylene (HDPE), cbHDPE, where the first reactor prepares vinyl‐terminated HDPE macromers catalyzed by an organometallic catalyst favoring beta hydride transfer and the second reactor copolymerizes HDPE macromers with ethylene using a different organometallic catalyst capable of incorporating macromers. A bimodal HDPE, biHDPE with bimodalities in molecular weight, and hexene content of the desired composition distribution was also prepared in a gas phase reactor using silica supported dual organometallic catalysts. By blending 3% solution‐made cbHDPE into the gas‐phase biHDPE, the resulting trimodal HDPE preserves the excellent stiffness and toughness of the bimodal HDPE while having exceptional melt strength and processability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45755.     

High‐density polyethylene/carbon black conductive composites. I. Effect of CB surface modification on its resistivity–temperature behavior

The effect of the interaction between a polymeric matrix and conductive particles of carbon black (CB), especially the interaction enhanced by oxidizing CB (o‐CB), on the resistivity–temperature behavior of its composites was studied. The results reveal that the interaction between ethylene‐vinyl‐acetate and CB is stronger than that between high‐density polyethylene and CB. The room temperature resistivity of the o‐CB filled system subsequent to thermal cycles increases to a lower extent in comparison with those filled with virgin CB. Moreover, the resistivity decrease of composites filled with o‐CB needs a longer time than that of the virgin CB filled system during isothermal annealing, meaning that the resistivity–temperature behavior of the former is much more stable than that of the latter. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3112–3116, 2002; DOI 10.1002/app.10049     

Properties of high‐density polyethylene filled with waste crosslinked foam

Crosslinked polyethylene foam is widely used in packaging and as an insulation material. Finely ground waste of such crosslinked foam mesh size 7 or particle size less than 2815 μm is used as a filler in high‐density polyethylene (HDPE) of two different grades (7.5 and 21 MFI). Mechanical, thermal, and morphological properties of filled composites is studied experimentally. Waste foam powder concentration was varied up to 40% by weight basis. Impact strength of base HDPE increased by a factor of six. The overall changes in mechanical properties are similar to the crosslinking effect. It is believed that waste foam particles act as a point of entanglement with different chains of polyethylene. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 110–114, 2004