H. H. Hassan

Influence of thermal aging on crosslinking density of boron carbide/natural rubber composites

Abstract Composites of natural rubber and boron carbide with different concentrations were prepared as thermal neutron radiation shielding materials. The maximum degree of swelling ( Q ), the penetration rate ( P ) and the average diffusion coefficient ( D av ) were studied. Using the Flory–Rehner equation, the crosslinking densities of the investigated samples were obtained. The effect of thermal oxidative aging on both the swelling behaviour and crosslinking density was also investigated.

A novel application of ADC/K-foaming agent-loaded NBR rubber composites as pressure sensor

Nitrile butadiene rubber (NBR) structure foam of different apparent densities was obtained by using different concentrations of foaming agent, azodicarbonamide, ADC/K. The true stress?strain characteristics, in case of compression, of foamed samples were measured. It was found that the theoretical values predicted from the simple blending model are in more agreement with the experimental results than those from the square-relationship model. The effect of cyclic loading?unloading and dissipation energy of rubber foams was studied. The results also indicated that foams with low density exhibited a small hysteresis. The electrical properties were found dependent on the foaming agent concentration. This study was assisted by Mott and Gurney equation. The effect of compressive strain on the electrical conductivity of rubber foams was studied. The free current carrier mobility and the equilibrium concentration of charge carrier in the conduction band were produced as functions of compressive strain. The results also indicate that there is a linear variation between pressure and conductivity for all samples, which means that these samples can be used as a pressure sensor. At a certain concentration of foaming agent (7.5?phr) a change of electrical conductivity by more than three orders is observed at 20% compression strain.

The mechanical behaviour of NBR/FEF under compressive cyclic stress?strain

Acrylonitrile butadiene rubber compounds filled with different concentrations of fast extrusion furnace (FEF) carbon black were experimentally investigated. The stress–strain curves of the composites were studied, which suggest good filler–matrix adhesion. The large reinforcement effect of the filler followed the Guth model for non-spherical particles. The effect of FEF carbon black on the cyclic fatigue and hysteresis was also examined. The loading and unloading stress–strain relationships for any cycle were described by applying Ogdens model for rubber samples. The dissipation energy that indicates the vibration damping capacity for all samples was determined. A simple model was proposed, to investigate the relation between maximum stress and the number of cyclic fatigue.

Natural rubber composites as thermal neutron radiation shields: I. B4C/NR composites

Abstract Different amounts of boric acid (H3BO3) were mixed with a conductive natural rubber (loaded with 40 phr of HAF carbon black) to get thermal neutron radiation shielding composites. It was found that the total macroscopic cross-section reaches 0.29 cm−1 at 30 phr of H3BO3. The dependence of thermal and electrical properties of such composites on the concentration of H3BO3 was also studied. Thermal oxidative aging was found to markedly affect the above properties.

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.

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.

Thermal effects of heat-resistant rubber composites III. Effect of type and concentration of carbon black

Abstract Butyl rubber (IIR) loaded with 20 parts per hundred parts rubber (phr) BaTiO3 was mixed with different concentrations of the various carbon blacks HAF, GPF, SRF and lampblack. Electrical conduction measurements of vulcanisates were carried out at various applied electric powers. The temperature change (ΔT) of the rubber samples as a result of Joule heating against time (t) was recorded. The ΔT-t characteristics were found to be markedly dependent on the carbon black type and concentration as well as the ambient temperature. No appreciable change in the above characteristics with thermal aging was observed over long times (up to 6 months). Theoretical calculations of the specific heat (Cp) were carried out and correlated with those obtained experimentally by the flash method.