Dynamic Electrical Analysis Research Articles

Dielectric and Viscoelastic Behavior of Polyvinyl Butyral Films.

Dielectric and thermal properties of polyvinyl butyral (PVB) were studied in this work, using dynamic electrical analysis (DEA) at frequencies from 100 Hz to 1 MHz and temperatures from 293 K to 473 K. Two electrical relaxation processes were investigated: glass transition and interfacial polarization. Above the glass transition temperature (~343 K), interfacial polarization dominates conductive behavior in polyvinyl butyral. The framework of the complex electric modulus was used to obtain information about interfacial polarization. The viscoelastic behavior was analyzed through dynamic mechanical analysis (DMA), where only the mechanical manifestation of the glass transition is observed. The experimental results from dielectric measurements were analyzed with fractional calculus, using a fractional Debye model with one cap-resistor. We were successful in applying the complex electric modulus because we had a good correlation between data and theoretical predictions. The fractional order derivative is an indicator of the energy dissipated in terms of molecular mobility, and the calculated values close to 1 suggest a conductive behavior at temperatures above the glass transition temperature of PVB.

Influence of Tire Rubber Particles Addition in Different Branching Degrees Polyethylene Matrix Composites on Physical and Structural Behavior.

Waste from pneumatic wheels is one of the major environmental problems, and the scientific community is looking for methods to recycle this type of waste. In this paper, ground tire rubber particles (GTR) from disused tires have been mixed with samples of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), and morphological tests have been performed using scanning electron microscopy (SEM), as well as the dynamic electric analysis (DEA) dielectric characterization technique using impedance spectroscopy. From this experience, how GTR reinforcement influences polyethylene and what influence GTR particles have on the branched polyethylene has been detected. For pure LDPE samples, a Debye-type dielectric behavior is observed with an imperfect semicircle, which depends on the temperature, as it shows differences for the samples at 30 °C and 120 °C, unlike the HDPE samples, which do not show such a trend. The behavior in samples with Debye behavior is like an almost perfect dipole and is due to the crystalline behavior of polyethylene at high temperature and without any reinforcement. These have been obtained evidence that for branched PE (LPDE) the Maxwell Wagner Sillars (MWS) effect is highly remarkable and that this happens due to the intrachain polarization effect combined with MWS. This means that the permittivity and conductivity at LDPE/50%GTR are high than LDPE/70%GTR. However, it does not always occur that way with HDPE composites in which HDPE/70%GTR has the highest values of permittivity and conductivity, due to the presence of conductive fraction (Carbon Black-30%) in the GTR particles and their dielectric behavior.

Application Properties Analysis as a Dielectric Capacitor of End-Of-Life Tire-Reinforced HDPE.

The purpose of the present research is to obtain waste of polymeric composite as an insulator capacitive application. Rubber materials, once they end their useful life, may be difficult to reuse or recycle. At present, research only uses one tire recycling method, which involves grinding and separating steel and fibers from vulcanized rubber, and then using the rubber particles for industrial capacitors. The methodology for this research is to compare the permittivity (ε′ and ε″) between high-density polyethylene (HDPE) and the polymer matrix compound, consisting of an HDPE polymeric matrix blended with end-of-life tire particles (ground tire rubber (GTR)), to analyze the feasibility of using such tires as electrically insulating materials (dielectrics). The incorporation of carbon black in the GTR compounds modifies conductivity; GTRs carry a significant amount of carbon black, and therefore some electrical properties may change significantly compared to highly insulating polymer substrates. The performed experimental study is based on a dynamic electric analysis (DEA) test developed in the frequency range of 10−2 Hz to 3 MHz and at different temperatures (from 35 to 70 °C) of different samples type: HDPE neat and HDPE compounds with 10%, 20% and 40% of GTR loads. A sample’s electrical behavior is checked for its dependence on frequency and temperature, focused on the permittivity property; this is a key property for capacitive insulators and is key for examining the possible applications in this field, for HDPE + GTR blends. Results for the permittivity behavior and the loss factor show different electrical behavior. For a neat HDPE sample, no dependence with frequency nor temperature is shown. However, with the addition of 10%, 20%, and 40% amount of GTR the HDPE compounds show different behaviors: for low frequencies, interfacial polarization relaxation is seen, due to the Maxwell–Wagner–Sillars (MWS) effect, performed in heterogeneous materials. In order to analyze thermal and morphological properties the differential scanning calorimetry (DSC) test and scanning electron microscopy (SEM) have been used. Results obtained show that adding waste tire particles in an HDPE matrix allows HDPE + 40% GTR blends to act as a dielectric in capacitors, increasing the capacitor dielectric efficiency in the low frequencies due to the MWS effect, which increases the dielectric constant.

Study and Characterization of the Dielectric Behavior of Low Linear Density Polyethylene Composites Mixed with Ground Tire Rubber Particles.

The waste rubber vulcanizate, on account of its stable, cross-linked and three-dimensional structural arrangement, is difficult to biodegrade. Thus, the ever-increasing bulk of worn-out tires is a serious environmental issue and its safe disposal is still a challenging task reported widely by the scientific community. The rubber materials, once they end their useful life, may present difficulties to be reused or recycled. At present, only one tire recycling method is used, which involves grinding and separating steel and fibers from vulcanized rubber, and then using rubber for industrial applications, such as flooring, insulation, footwear. In this paper, a new compound material is presented from a base of reused tire powder (Ground Tire Rubber: GTR) as a mixer and linear low-density polyethylene (LLDPE) as a matrix. The reused tire powder, resulting from grinding industrial processes, is separated by sieving into just one category of particle size (<200 μm) and mixed with the LLDPE in different amounts (0%, 5%, 10%, 20%, 40%, 50% and 70% GTR). Due to the good electrical properties of the LLDPE, this study’s focus is settled on the electrical behavior of the obtained composites. The test of the dielectric behavior is carried out by means of DEA test (Dynamic Electric Analysis), undertaken at a range of temperatures varying from 30 to 120 °C, and with a range of frequencies from 1 to 102, to 3·106 Hz, from which permittivity, conductivity, dielectric constant and electric modulus have been obtained. From these experimental results and their analysis, it can be drawn that the additions of different quantities of GTR to LLDPE could be used as industrial applications, such as universal electrical cable joint, filler for electrical applications or cable tray systems and cable ladder system.

Sublinear dispersive conductivity in polyetherimides by the electric modulus formalism

It can be seen by Dynamic Electrical Analysis that the electrical properties of polyetherimide at temperatures above the glass transition are strongly influenced by space charge. We have studied space charge relaxation in two commercial grades of polyetherimide, Ultem 1000 and Ultem 5000, using this technique. The electric modulus formalism has been used to interpret their conductive properties. In both grades of polyetherimide, asymmetric Argand plots are observed, which are related to a sublinear power-law dependency ($\omega^{n}$ with $n<1$) in the real part of the conductivity. This behaviour is attributed to correlated ion hopping. The imaginary part of the electric modulus exhibits a peak in the low frequency range associated to conduction. Modelling of this peak allows us to obtain the dependence, among other parameters, of the conductivity ($\sigma_0$), the fractional exponent ($n$) and the crossover frequency ($\omega_\mathrm{p}$) on the temperature. The $\alpha$ relaxation, that appears at higher frequencies, has also to be modelled since it overlaps the conductivity relaxation. The study of the parameters in terms of the temperature allows us to identify the ones that are thermally activated. The difference between the conductivity relaxation time and the Maxwell relaxation time indicates the presence of deep traps. The coupling model points out that the correlation of the ionic motion diminishes with temperature, probably due to increasing disorder due to thermal agitation.

Dynamic electrical thermal analysis on zinc oxide/epoxy resin nanodielectrics

The dielectric response of ZnO/epoxy resin nanocomposites was studied by means of dynamic electrical thermal analysis in the frequency range of 10−1 to 107 Hz, and over the temperature range of 30–160 °C, varying the content of the reinforcing phase. Scanning electron microscopy pictures were used for assessing the composites morphology and for examining the particles’ dispersion. The thermal properties of nanocomposites were examined by differential scanning calorimetry in the temperature range of 0–170 °C. Dielectric data were analyzed via dielectric permittivity and electric modulus formalisms. Recorded relaxation phenomena include contributions from both the polymeric matrix and the presence of the reinforcing phase. Processes related to the polymer matrix are attributed to the glass to rubber transition (α-relaxation) of the epoxy resin and local motions of polar side groups of the main polymer chain (β-relaxation). Finally, the slower process appearing at low frequencies and high temperatures, originates from interfacial phenomena due to the accumulation of unbounded charges at the system’s interface.

Modeling of DC Flashover on Ice-Covered HV Insulators Based on Dynamic Electric Field Analysis

In this paper, a model based on dynamic electric field analysis has been developed to predict the flashover voltage of the ice-covered HV insulators, under dc voltage. The potential and electric field calculation models before and after air gap breakdown are built respectively based on finite element method (FEM). The arc initiation process is determined based on the model before air gap breakdown. The critical applied voltage and leakage current to maintain an arc with certain length are obtained based on the electric field calculation model after air gap breakdown and the U-I characteristic of the arc. Moreover, the improved Hampton criterion has been employed to determine the critical flashover of the ice-covered insulator. The results obtained from the dynamic electric field analysis model have been compared with other mathematical and experimental results of other researchers and got a great agreement.

Effect of annealing on conductivity in XLPE mid-voltage cable insulation

A new study of the electrical conductivity of crosslinked polyethylene (XLPE) mid-voltage (MV) cable insulation is presented. Its main objective is to show the effect of annealing treatments on MV cables under actual service conditions. Complementary time domain (absorption/resorption currents) and frequency domain (dynamic electrical analysis) techniques are applied on different laboratory samples containing XLPE insulations: sections of XLPE insulated cable (with and without semiconducting screens) in the case of absorption/resorption currents and, in the case of dynamic electrical analysis, a thin ribbon obtained from the cable insulation by mechanical procedures. For annealing temperatures below a certain critical temperature, conductivity decreases both for XLPE cylinders (cable sections from which inner and outer semiconducting screens have been removed) and for real cables (sections of cable with semiconducting screens) but its value is smaller in the case of cables. If the annealing temperature is higher than the critical temperature, the behaviour of conductivity is more complex. In XLPE, cylinders conductivity initially decreases with the annealing time but after some annealing time it begins to increase, it passes over a maximum and eventually it decreases monotonically. In the case of real cable sections, conductivity grows, tending to a saturation value, which is noticeably higher than the corresponding value of the maximum obtained for XLPE cylinders. The experimental results are explained satisfactorily by means of the Mott equation that takes into account hopping conduction assisted both by temperature and electric field.

Sublinear dispersive conductivity in polymethyl methacrylate at temperatures above the glass transition

Dynamic electrical analysis shows that conductivity conditions the electrical properties of a polymer at high temperatures and low frequencies. In this paper we show the possibilities of the electric modulus formalism to study the properties of carrier transport and space charge relaxation processes in polymethyl methacrylate. Asymmetric Argand's plots are observed in the temperature range between 150 and 210 °C. This asymmetry is related to power-law dependencies in the real part of the conductivity, of the form ω n with n<1, as a result of correlated ion hopping. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with these conductive processes. In the case of the relaxation time related to conductive processes, it has been observed that Maxwell time is higher than the characteristic time associated with the crossover frequency which determines the transition from dc to ac regime. This fact is explained by the presence of deep traps. Finally, a maximum in the value of n is observed between 180 and 190 °C which may be related to coupling between charge transport and chain segment motions.

Study of space charge relaxation in PMMA at high temperatures by dynamic electrical analysis

Dynamic electrical analysis shows that at high temperatures (above the glass transition temperature), the electrical properties of polymethyl methacrylate are strongly influenced by space charge. In this paper we present an study of space charge in this material and its conductive properties by dynamic electrical analysis, using the electric modulus formalism. The complex part of the electric modulus was fitted to Coelho's model, which considers ohmic conductivity and diffusion as the prevailing mechanisms of charge transport.The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with space charge and a good agreement between experimental and calculated data is observed after the fitting process to the Coelho's model. The data obtained indicate that the electrode is partially blocked. The conductivity determined is thermally activated and it increases with the temperature due to an increasing mobility, that is also thermally activated.

Space charge relaxation in polyetherimides by the electric modulus formalism

Dynamic electrical analysis shows that at high temperatures (above the glass transition temperature), the electrical properties of polyetherimide are strongly influenced by space charge. In this article we have studied the relaxation of space charge in two commercial varieties of polyetherimide: Ultem 1000 and Ultem 5000. Their conductive properties were determined by dynamic electrical analysis, using the electric modulus formalism. The complex part of the electric modulus was fitted to Coelho’s model which considers ohmic conductivity and diffusion as the prevailing charge transport mechanisms. The complex part of the electric modulus exhibits a peak in the low frequency range that can be associated with space charge. A good agreement between experimental and calculated data is observed after the fitting process to Coelho’s model. Differences in the electrode behavior were required: blocking electrode conditions in the case of Ultem 5000 and partially blocking electrode for Ultem 1000. In both cases the conductivity determined is thermally activated and it increases with the temperature due to an increasing mobility, as their carrier densities do not vary significantly in the temperature range studied.

Comparative study of amorphous and partially crystalline poly(ethylene-2,6-naphthalene dicarboxylate) by TSDC, DEA, DMA and DSC

A comparative study of the relaxational behavior of amorphous and partially crystalline poly(ethylene-2,6-naphthalene dicarboxylate) (PEN), has been carried out by thermally stimulated depolarization currents (TSDC), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic electric analysis (DEA). As received, PEN (partially crystalline) shows, in the temperature range from −150 to 200°C, four relaxations located, in increasing temperature order, around −70°C ( β), 60°C ( β ∗), 130°C ( α) and 170°C ( ρ). Amorphous PEN has been crystallized thermally heating up to different temperatures between 170 and 200°C. The DSC measurements of these samples show a small endothermic premelting peak, once the crystallization of the sample is completed. This peak increases and shifts towards higher temperatures as the sample is further thermally treated. Associated with the presence of this endothermic peak, the ρ relaxation passes through a maximum and presents a sharp decrease as it is further thermally treated. The α-relaxation, detected by dynamic mechanical as well as dielectric (ac) measurements, shifts to higher temperatures and broadens as the crystallinity degree increases. The kinetic parameters of the observed relaxations have been determined fitting experimental data to standard models.

Relaxational study of poly(ethylene-2,6-naphthalene dicarboxylate) by t.s.d.c., d.e.a. and d.m.a.

A comparative study of the different relaxations present in poly(ethylene-2,6-naphthalene dicarboxylate) (PEN) is carried out by thermally stimulated depolarization current (t.s.d.c.), dynamic mechanical analysis (d.m.a.) and dynamic electric analysis (d.e.a.). In the temperature range from −150 to 200°C, PEN shows four relaxations located, in increasing temperature order, around −70°C (β), 60°C (β*), 130°C (α) and 170°C (ρ). The two sub-glass transition relaxations detected are attributed to dipolar motions of the polymer chain and their origin is discussed. Above the glass transition (α relaxation) the ρ peak is shown to be of non-dipolar origin and associated with free charge detrapping in the material. The kinetic parameters of the relaxations observed by these techniques in the aforementioned temperature range have been determined by fitting the experimental data to standard models. The activation energies calculated in this way vary from 0.5 eV for the β relaxation to 2.2 eV for the ρ relaxation. The β* and α relaxations are distributed and it is shown that they follow the compensation law.