G. M. Nasr

Determination of the crosslink density of conductive ternary rubber vulcanizates by solvent penetration

Swelling has long been used in the study of elastomeric networks. Swelling equilibrium data, for a new conductive tri-block rubber vulcanizates in different solvents, were generally analysed by the Flory-Rehner equation simply to obtain a measure of the crosslink density. Moreover, a number of factors which influence the penetration rate of solvents in those blends have been investigated. These are relevant to butyl (IIR) and/or styrene butadiene (SBR) rubber concentrations, type of the vulcanizing agent and solvent characterization.

Thermal properties of ceramic-loaded conductive butyl rubber composites

Abstract The thermal properties (thermal conductivity, thermal diffusivity, and specific heat capacity) of conductive butyl rubber composites loaded with different concentrations of BaTiO 3 powder and 50 phr of LAMP black were measured in the temperature range 30–150°C. It was found that, on addition of BaTiO 3 powder up to 20 phr, there is a marked increase of both specific heat capacity and thermal conductivity, and a slight increase of thermal diffusivity. On the basis of the Eierman theory, the marked increase of both thermal conductivity and specific heat capacity can be accounted for by rising temperature for composites loaded with 10 and 20 phr of powdered BaTiO 3 . An empirical formula was suggested to describe the dependence of the effective thermal diffusivity of the composites on the BaTiO 3 content.

Study of dielectric properties of particulate blends

The effect of the addition of high abrasion furnace (HAF) black on the dielectric properties of poly (ethylene-propylene-diene monomer) EPDM, polyethylene (PE) blend using both sulphur and peroxide vulcanizing systems was studied. It was observed that the increase in the permittivity is more pronounced with HAF black in the case of sulphur system than for the peroxide one. Many theories have been tested to calculate the effective permittivity of these particulate blends. The observed values of the permittivities are in close agreement with those calculated by Tsangariss model, taking into account the variation of the aspect ratio (a/b) of the HAF black with the volume fraction of the HAF black in the matrix and type of the vulcanizing system.

Thermophysical properties of butyl rubber loaded with different types of carbon black

Abstract The thermal properties (thermal conductivity λ, thermal diffusivity a , and specific heat capacity C p ) of butyl rubber with 100 phr of different carbon blacks (HAF, GPF, SRF and LAMP black) were measured in the temperature range 300–450 K. The thermal properties were slightly affected by the addition of the different carbon blacks, and there was a sharp increase in both λ and C p with temperature on addition of 20 phr of powdered BaTiO 3 ceramic only for samples containing SRF and HAF carbon blacks. The electrical conductivity, σ, was also measured for these composites. It increased appreciably with the surface area of the added carbon black. On addition of 20 phr of powdered BaTiO 3 ceramic, the electrical conductivity was observed to increase for all the butyl rubber composites.

Electrical properties and penetration rate of solvent into irradiated LDPE/SBR conductive blend

Abstract The effects of γ-irradiation on both the electrical conductivity σ and the penetration rate of benzene in low density polyethylene (LDPE)/styrene butadiene rubber(SBR) conductive blends have been studied. The diffusion coefficient ( D ) and the penetration rate ( p ) decrease with increasing γ-irradiation dose for unloaded and loaded samples with 1 and 3 phr of LDPE content, presumably due to crosslinking and polymer chain immobilization in the interfacial regions. Meanwhile, both D and p increase for samples loaded with 5 phr of LDPE. The carbon-carbon interspacing distance was found to be highly affected by the γ-irradiation dose, which in turn influences the electrical conductivity of these blends.

The influence of physical ageing on the electrical and swelling behaviour of ternary rubber vulcanizates

Abstract The effects of pre-annealing ageing time at 70 °C on the electrical properties and swelling behaviour in kerosene of a new tri-block rubber based on blends of natural rubber (NR) and different concentration ratios of both styrene-butadiene rubber (SBR) and butyl rubber (IIR), all incorporating 40 phr (parts per hundred parts of rubber by weight) of high abrasion furnace (HAF) carbon black, were investigated. It was found that the interspacing distance, d , between carbon particles or aggregates is greatly affected by physical ageing and also by the rubber ratios in the test specimens. Moreover, the degree of swelling, Q (%), in kerosene was found to decrease with both physical ageing and IIR content of the specimen.

Effects of radiation and storage time on conductive NBR/LDPE blends

Abstract The electrical conductivity, σ, of conductive acrylonitrile-butadiene rubber (NBR) mixed with different concentrations (1, 3 and 5 phr) of low-density polyethylene (LDPE) is presented. The effect of gamma radiation doses in the range 5 to 50 kGy on the electrical conductivity was determined for all samples. Storage of the unirradiated and irradiated samples for 7 days at 60 or 100 °C has a great influence on the electrical conductivity of these blends. The variation in the conduction mechanisms through these blends on both irradiation and storage is also discussed.

Influence of static and cyclic compression on the electrical conductivity of FEF black-loaded rubbers

SummaryThe influence of static and cyclic compression on the temperature dependence of the electrical conductivity σ(T) of 100 phr FEF black-loaded rubber vulcanizates (SBR, NR, IIR, BR and NBR) has been studied. It was found that σ increases with static pressure for all rubber vulcanizates. The temperature coefficient of conductivity proved to be negative; its maximum value α ranges between −0.1 and −0.01 deg−1 depending upon the applied stress and type of rubber vulcanizate. The pressure coefficient of conductivity γ at room temperature varies with the static pressure from 0.78 to 0.04 (kg/cm2)−1. Menwhile, a was found to decrease with the number and stress amplitude of the cyclic compressions, while α increases with the number of compression cycles.

Effect of molding pressure on the electrical conductivity of conductive NBR/PVC composites

Acrylonitrile butadiene rubber (NBR) was mixed with different concentrations (1, 3, 5, and 10 phr) of polyvinyl chloride (PVC) and all mixed with 40 phr of high abrasion furnace (HAF) black. The unvulcanizates obtained were subjected to electrical conductivity measurements at different values of moulding pressures. The moulding pressure was found to have an appreciable effect on the electrical conductivity. It decreases sharply as the sample is suddenly compressed and then increases exponentially with time. The interspacing distance between carbon particles or aggregates was calculated on the basis of a simple model proposed by Fernandez et al.

Absorption and velocity of ultrasonic waves in interlinked SBR composite

The ultrasonic properties of self-adhered SBR (single-, double- and triple-layered) have been investigated as a function of both carbon black (HAF) content in one layer and temperature. The propagation velocity and the absorption per wavelength of longitudinal ultrasonic waves of frequency 2 MHz have been measured in the temperature range from 27°C to 120°C, by pulse echo immersion technique. The variation of the longitudinal ultrasonic modulus with temperature has been derived from these measurements. The percolation concentration of HAF black was confirmed to lie at about 35 phr.