Browsing by Author "Al-Hartomy O.A."

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    Dielectric and microwave properties of siloxane rubber/carbon black nanocomposites and their correlation
    (2011-01-01) Al-Hartomy O.A.; Al-Solamy F.; Al-Ghamdi A.; Dishovsky N.; Iliev V.; El-Tantawy F.
    In this paper, the dielectric and microwave properties of carbon black/siloxane rubber-based nanocomposites have been investigated in the frequency range from 1 GHz till 12GHz according to the content of carbon black and the frequency. It has been established that the increasing frequency and filler content lead to an increase in the relative permittivity and tangent of dielectric loss angle. At higher filler content, the effects become more pronounced, especially those upon dielectric loss. It has been also established that there are two well-distinguished areas in all dependences of microwave properties on frequency and filler content increasing. The first is between 1 and 8 GHz wherein the reflection and attenuation of microwaves do not change considerably with frequency and filler content alternation while shielding effectiveness worsens. The second area is between 8 and 12 GHz wherein the reflection and attenuation of microwaves increase drastically with the increasing frequency and filler content. Shielding effectiveness improves, too. It has been established that in all cases the degree of correlation between dielectric and microwave properties evaluated on the basis of the coefficients of correlation calculation is perfect. Copyright © 2011 Omar A. Al-Hartomy et al.
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    Influence of bis(triethoxysilylpropyl) tetrasulfide amount on the properties of silica-filled epoxidized natural rubber-based composites
    (2016-07-01) Al-Hartomy O.A.; Al-Ghamdi A.A.; Al Said S.A.F.; Dishovsky N.; Mihaylov M.
    The aim of the present article is to investigate the influence of the amount of bis(triethoxysilylpropyl) tetrasulfide on the curing characteristics and mechanical and dynamic properties of rubber composites based on epoxidized natural rubber (Epoxyprene 50) filled with 70 phr silica. The obtained results showed that although the interaction between the epoxy groups of epoxidized natural rubber and the silanol groups of silica through hydrogen bonds improves the dispersion of filler in the rubber matrix, the presence of silane coupling agents is necessary to obtain rubber compounds and vulcanizates with good vulcanization characteristics and mechanical and dynamic properties.
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    Influence of bis(triethoxysilylpropyl) tetrasulfide amount on the properties of silica-filled epoxidized natural rubber-based composites
    (2016-07-01) Al-Hartomy O.A.; Al-Ghamdi A.A.; Al Said S.A.F.; Dishovsky N.; Mihaylov M.
    The aim of the present article is to investigate the influence of the amount of bis(triethoxysilylpropyl) tetrasulfide on the curing characteristics and mechanical and dynamic properties of rubber composites based on epoxidized natural rubber (Epoxyprene 50) filled with 70 phr silica. The obtained results showed that although the interaction between the epoxy groups of epoxidized natural rubber and the silanol groups of silica through hydrogen bonds improves the dispersion of filler in the rubber matrix, the presence of silane coupling agents is necessary to obtain rubber compounds and vulcanizates with good vulcanization characteristics and mechanical and dynamic properties.
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    Influence of carbon black structure and specific surface area on the mechanical and dielectric properties of filled rubber composites
    (2011-01-01) Al-Hartomy O.A.; Al-Solamy F.; Al-Ghamdi A.; Dishovsky N.; Ivanov M.; Mihaylov M.; El-Tantawy F.
    Natural rubber based composites have been prepared using various amounts of two fillers: conventional Corax N220 carbon black or electrically conductive carbon black Printex XE-2B which has a very high specific surface area. The composites have been studied by dynamic mechanical thermal analysis, dielectric thermal analysis and SEM. It has been established that all vulcanizates investigated are in the glass state in the -80°C to -40°C interval. The storage modulus increases with the increasing filler content in the -40°C to +80°C interval when the vulcanizates are in the highly elastic state. DETA shows that the increase in filler content leads to an increase in the dielectric permittivity (ε′). ε′ also increases with temperature increasing. Higher frequency causes a decrease of ε′ values which becomes more pronounced with the increasing filler content. Obviously, when the content of Printex XE-2B carbon black in the vulcanizates is higher than 7.5 phr, the percolation threshold is reached and the ε′ values increase up to 102-104. The ε′ values for the vulcanizates comprising 20 and 50 phr Corax N220 carbon black are measurable with those for the vulcanizates comprising 5 and 10 phr Printex XE-2B carbon black respectively. The results obtained could be explained by the difference in the structure and specific surface area of the two types of carbon black - Printex XE-2B and Corax N220. Copyright © 2011 Omar A. Al-Hartomy et al.
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    Influence of carbon black structure and specific surface area on the mechanical and dielectric properties of filled rubber composites
    (2011-01-01) Al-Hartomy O.A.; Al-Solamy F.; Al-Ghamdi A.; Dishovsky N.; Ivanov M.; Mihaylov M.; El-Tantawy F.
    Natural rubber based composites have been prepared using various amounts of two fillers: conventional Corax N220 carbon black or electrically conductive carbon black Printex XE-2B which has a very high specific surface area. The composites have been studied by dynamic mechanical thermal analysis, dielectric thermal analysis and SEM. It has been established that all vulcanizates investigated are in the glass state in the -80°C to -40°C interval. The storage modulus increases with the increasing filler content in the -40°C to +80°C interval when the vulcanizates are in the highly elastic state. DETA shows that the increase in filler content leads to an increase in the dielectric permittivity (ε′). ε′ also increases with temperature increasing. Higher frequency causes a decrease of ε′ values which becomes more pronounced with the increasing filler content. Obviously, when the content of Printex XE-2B carbon black in the vulcanizates is higher than 7.5 phr, the percolation threshold is reached and the ε′ values increase up to 102-104. The ε′ values for the vulcanizates comprising 20 and 50 phr Corax N220 carbon black are measurable with those for the vulcanizates comprising 5 and 10 phr Printex XE-2B carbon black respectively. The results obtained could be explained by the difference in the structure and specific surface area of the two types of carbon black - Printex XE-2B and Corax N220. Copyright © 2011 Omar A. Al-Hartomy et al.
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    Properties of natural rubber-based composites containing fullerene
    (2012-01-01) Al-Hartomy O.A.; Al-Ghamdi A.A.; Al-Salamy F.; Dishovsky N.; Slavcheva D.; El-Tantawy F.
    In this study the influence of fullerenes in concentrations from 0.5 to 1.5 phr on both the vulcanization characteristics of the compounds and physicomechanical, dynamic, and dielectric properties and thermal aging resistance of nanocomposites on the basis of natural rubber has been investigated. The effect of the filler dispersion in the elastomeric matrix has been also investigated. Neat fullerene and the composites comprising it have been studied and characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). © 2012 Omar A. Al-Hartomy et al.