Salah Mahrous

Dielectric analysis of the α‐relaxation of PVC stabilized with cadmium laurate

The dielectric permittivity and losses of PVC stabilized with cadmium laurate were measured in the temperature range 300-400 K and frequency range 1 kHz-1 MHz. The relaxation behaviour was found to obey the Williams-Landel-Ferry (WLF) equation. The observed activation energy was 1.1 eV which is in fair agreement with that of the α-relaxation in the literature. The α-relaxation peak was found to be due to both C-Cl and -OOC groups. A plasticization effect of the polymer was observed.

Thermally stimulated current study of relaxation in PVC stabilized with zinc carboxylate

Abstract The effect of zinc carboxylate addition on the dielectric α relaxation of PVC was studied. It was noticed that zinc carboxylate lowers the relaxation temperature and that the peak width becomes larger and higher. The higher value of the α relaxation for the stabilized sample is due to a reduction in the polymers degree of crystallinity. The higher values of activation energies for stabilized samples are related to the cooperative nature of relaxations at Tg .

Effect of 1-chloro-2,3-epoxy-propane on the conduction mechanism in polyvinyl chloride

Abstract The nature of the electrical conduction in polyvinyl chloride (PVC) containing 1-chloro-2,3-epoxy-propane has been studied at a constant temperature of 297 K. In the first region of the I-V characteristics (slope ≈ 1), the conduction is Ohmic because there is no injection of carriers from the electrode contact. The Richardson-Schottky effect is the predominant conduction mechanism in the second region (slope ≈ 2). The variation of dc conductivity, σ, may be due to the combined effect of change in σ with temperature, and the nature of trap distribution in the sample. At higher temperatures, the increase in σ may be due to the sample softening.

DIELECTRIC RELAXATION OF POLY(VINYL CHLORIDE) STABILIZED WITH DIBUTYLTIN LAURATE-MALEATE

The dipolar relaxation mechanisms of polyvinyl chloride stabilized with dibutyltin laurate-maleate have been studied by dielectric relaxation spectroscopy. The study was carried out in the frequency range 1 k–1 MHz at fixed temperatures above and below the glass transition temperature. The broadening of the loss peaks was considered because of the multiplicity of molecular conformations, which stablizer molecules can form. The results show a distinct broad relaxation process with activation energy of 0.5 eV. The dielectric strength increases with temperature and the origin of the relaxation was ascribed to the reorientation of the polar C–Cl and C=O groups.

Dielectric Properties of PVC Plasticized with Dioctyl Sebacate (DOS)

Abstract The dielectric properties of PVC plasticized with dioctyl sebacate (DOS) was studied. The dielectric loss tangent was found to decrease for the plasticized samples which interpreted according to the increase in the intermolecular interactions upon plasticization. The plasticizer contribute to the dielectric strength not only via its own polarity but also by markedly changing the nature of the relaxation process. The calculated Frohlich-Kirwood “g” factor indicates that there is a strong interaction between the C-Cl group (of the polymer) and the C = O group (of the plasticizer).

Space Charge Limited Currents and Trap Distribution in PVC Stabilized with Lead Stearate

Abstract The current-voltage characteristics at different temperatures had been studied for PVC stabilized with lead stearate. At low voltages, Ohms law is seen to be followed, while at high voltages space-charge-limited current was observed. The obtained results were interpreted in terms of a Schottky emission type of conduction operating over the temperature range studied. By using an analytical method the density of states is calculated.

Use of thermally stimulated discharge current for the study of rotational mobility of 4-mercaptoacetamidodiphenylamine in poly(vinyl chloride)

Thermally stimulated depolarization current (TSDC) of PVC contain- ing 4-mercaptoacetamidodiphenylamine was studied. The current peak height (a- relaxation peak), maximum temperature, and activation energies were found to be influenced by the additive. The results suggest that no internal plasticization occurs in the system. The a-relaxation broadening was found to originate from a distribution of activation energies according to the rotation of the amide group of the additive.

Study of hopping conduction in polyisoxazoline

Temperature and frequency-dependent ac-conductivity of polyisoxazoline have been measured. The ac conductivity is found to be proportional to y s . The values of the exponent s decrease with the increase in the temperature, in the high temperature region. The hopping over the barrier model appears to be not valid. Longs polaron model is the suitable one to interpret the obtained data.

Study of dielectric relaxation of chlorinated polyvinyl chloride (CPVC)-poly(ethylene succinate) (PES) blend

Abstract Thermally stimulated depolarization current (TSDC) technique was used to study the dielectric relaxations of chlorinated polyvinyl chloride (CPVC) blended with poly (ethylene succinate) (PES) over the temperature range 300–400K, covering α and ρ regions, α-relaxation was suggested to be due to cooperative motion of both C-Cl and -COO groups of the blend, while ρ-relaxation is of space-charge nature. Thermal peak cleaning was used to deconvolute the global TSDC spectra, giving apparent activation energies (Ea ) over the temperature range 360–400K. Maximum value of Ea was found at Tg . Thermal peak cleaning data were fitted using Frohlich method.

Influence of Magnetic Field on the Resistivity of Polyisoxazoline

Abstract The effect of magnetic field on the electrical resistivity of polyisoxazoline was studied in the temperature range 300–413 K. It is noticed that the resistivity was reduced by the application of a magnetic field with 1000 Oe.