D.H. Damon

Space charge in polyethylene/ionomer blends

Measurements of thermally stimulated currents were made on ionomer/polyethylene blends. The objective of this work was to study space charge formation in these materials. Two ionomers were compared; both ionomers contained methacrylic acid, neutralized by zinc in one and by sodium in the other. A large current peak centered near 60/spl deg/C was observed in all blends and associated with the motion of space charges injected into the blends during poling. All blends accumulated large negative space charge concentrations. The approach to the equilibrium space charge distribution (negative and spatially uniform in all blends) is much more rapid in the blends containing the sodium ionomer than in the blends containing the zinc ionomer. >

What is TSC

The technical background for the thermally stimulated current (TSC) technique is presented. The effect of metal polymer contacts on the TSC method is discussed. The transitions in amorphous polymers are described. The dynamic properties of polyethylene using TSC method are given.<<ETX>>

Dielectric relaxation properties of filled ethylene propylene rubber

Thermally stimulated discharge currents and time domain dielectric spectroscopy were employed to characterize the behavior of clay-filled ethylene propylene rubber. Measurements were made on samples with different clay concentrations and particle sizes. The main effect of the clay filler on the electrical properties is on interfacial polarization which occurs at the clay polymer interface. The experimental results are sensitive to the shape of the clay particles. A few results indicate that other mechanisms also affect the electrical behavior of this material. >

Breakdown statistics for XLPE containing the volatile by-products of the cross-linking reaction

AC and impulse breakdown strengths have been measured on recessed samples of cross-linked polyethylene (XLPE) containing controlled amounts of the by-products (or residues) of the crosslinking reaction, i.e. acetophenone, cumyl alcohol, alpha methyl styrene, and cumene. The statistics used to describe the distribution of breakdown strengths are discussed. Weibull, Gumbel, and Gaussian statistics are compared. Other statistical distributions resulting from fluctuations in the character of the discharge sites at the metal-polymer interface are also examined. Despite the fact that a simple weakest link mechanism cannot be used to describe the breakdown strengths of recessed samples of XLPE containing the crosslinking residues, no reason has been found to discard the Weibull distribution. The results of this investigation can therefore be presented in tables of characteristics values and shape parameters.<<ETX>>

Electric strength of XLPE containing acetophenone and other volatile substances

Measurements have been made of the AC breakdown strength and the impulse breakdown strength of samples of XLPE (cross-linked polyethylene) to which known amounts of acetophenone, cumyl alcohol, alpha methyl styrene, and cumene were added. A Weibull analysis of the breakdown strengths shows that the presence of a small amount (less than 2 wt.%) of these substances has a small effect on the breakdown strength of unaged XLPE. All these substances have about the same effect: they increase the AC breakdown strength but decrease the impulse breakdown strength.<<ETX>>

Dielectric strength of crosslinked polyethylene: the effects of the volatile products of the crosslinking reaction

The breakdown field strength of recessed samples of XLPE (cross-linked polyethylene) containing varying amounts of acetophenone and cumene is shown to decrease with increasing sample thickness. This thickness dependence is more complicated than previously observed. The addition of small amounts of acetophenone to XLPE produces a small increase in the dielectric strength. Small concentrations of cumene have no effect. Results from both AC ramp to failure and impulse breakdown can be fit to Weibull distributions. The characteristic values obtained from ramp to failure measurements depend on the ramp rate as suggested by theory.<<ETX>>

Space charge formation in filled LDPE films

The effect of fillers on space charge formation or storage was studied. Thermally stimulated current (TSC) was measured to investigate the carrier traps in filled LDPE (low-density polyethylene) films. The characteristic relaxation time and activation energy of trapped carriers were calculated by computer simulation based on a single relaxation time model. Differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DTMA), and time-domain dielectric loss spectrometry (TDS) were also employed to analyze the effect of fillers on molecular relaxation behavior. The characteristic relaxation times for 10% 3A/LDPE and 5% 5A/LDPE are 4*10/sup -11/ s and 5*10/sup -11/ s, respectively. The corresponding activation energies are 0.5016 eV and 0.4878 eV.<<ETX>>

DC conductivity of low density polyethylene containing TiO/sub 2/

The conductivities of LDPE (low-density polyethylene) and LDPE plus 1 wt.% TiO/sub 2/ are compared. It is shown that the composite has a higher conductivity and that the temperature dependence of its conductivity is not described by an Arrhenius equation. A comparison of the temperature dependence at the measured current density in samples which have different thermal histories and different exposures to silicone oil shows that the shape of the log current density versus 100/t curve is undoubled due to the presence of the TiO/sub 2/ and is not the result of the presence of silicone oil or of morphological differences between filled and unfilled LDPE. The results of measurements of both the field dependence and the temperature dependence suggest that the conductivity may be represented as the product of a function of temperature and a function of field strength.<<ETX>>

Effect of clay on the dielectric relaxation of ethylene propylene rubber using thermally stimulated discharge current measurements

Clay filler in EPR (ethylene propylene rubber) causes a peak in the TSDC (thermally stimulated discharge current) spectra at about 40 /spl deg/C. The peak displays dipole behavior and has an activation of 0.48eV. It seems to consist of one single relaxation peak and two smaller peaks which have not yet been analyzed. Reducing the clay concentration and particle size reduces the size of the peak. The polarization mechanism which causes this peak is not clear. It is possible that aggregation of the clay, adhesion of the clay to the polymer, or particle-particle interactions may affect this mechanism.<<ETX>>

Electrical strength of XLPE cable insulation containing controlled amounts of the volatile products of the crosslinking reaction

Previous reports have shown that the addition of small amounts of acetophenone, cumyl alcohol, alpha methyl styrene, and cumene to devolatilized compression-molded samples of XLPE (cross-linked polyethylene) has a small effect on the breakdown strength of these samples. The AC breakdown strength is increased; the impulse breakdown strength is decreased. The question addressed is whether the results for the extruded XLPE cable insulation will be the same. The results presented suggest that, qualitatively, the results for the two types of XLPE are much the same. Quantitatively, the breakdown strength of the XLPE cable insulation is much less than that of the compression-molded XLPE.<<ETX>>