Influence of Carbon Black Structure and Specific Surface Area on the Mechanical and Dielectric Properties of Filled Rubber Composites

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 C to C interval. The storage modulus increases with the increasing filler content in the C to + 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 ( ). also increases with temperature increasing. Higher frequency causes a decrease of 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 values increase up to 102–104. The 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. 1. Introduction Natural rubber (NR), produced by Hevea Brasiliensis whose chemical structure is cis-1.4-polyisoprene, possesses excellent physical properties of a general purpose rubber. Presently, conventional carbon black (N220, N330, N550, etc.) is its outstanding reinforcing filler [1]. NR-carbon-black-filled vulcanizates are characterized by high mechanical strength, remarkable resilience, excellent elasticity, abrasion resistance, good low heat built-up, and good dynamic properties [2] but they do not have the electrical and magnetic properties needed for some more special applications. With the development of electronic industry, some special dielectric materials with high and/or low dielectric permittivity are attracting notable attention of the academic and industrial circles. The dielectric properties of the insulation materials could be adjusted by dispersing different kinds of fillers into the polymer matrices, for example, the dielectric permittivity of the resulting composites is determined by the low or high dielectric permittivity of the inorganic or organic fillers added [3]. Moreover, the dielectric permittivity of polymer/filler composites could be changed by altering the filler