Chemical Aspects of Rubber Reinforcement by Fillers

Abstract

Abstract For decades, the rubber industry, and the tire industry in particular, have been using mainly carbon blacks as reinforcing fillers. Since their structure and specific surface area can be varied over a wide range, carbon blacks are capable of meeting a wide range of different requirements. Even today, we are unable to exert a specific influence on the third component of reinforcement, the “surface activity” (surface energy) of carbon blacks. This problem and new, more stringent tire performance requirements lend new significance to the need for further carbon black research and development. Silicas, which were developed during the nineteen forties and fifties, were mainly used in shoe soling materials. Specific surface area and structure of the silicas were constantly adjusted to meet new requirements in this area. As our knowledge of the reinforcing mechanism of silicas in rubber increased, the benefits and drawbacks of silicas in rubber, in comparison to carbon blacks, became more and more apparent. The challenge to improve their reinforcing effect was then taken up. Since the beginning of the nineteen seventies, the chemical industry has concentrated on developing silanes for the rubber industry. The significance of the formation of covalent rubber-to-filler bonds for rubber reinforcement was recognized, and ways and means for the optimum and most efficient use of silicas and silanes were found, in a long and difficult process. During the past ten years, research and development efforts were dominated by the demand for increasing abrasion resistance, improving wet traction, and achieving the lowest possible rolling resistance. The combined use of silicas and silanes opened up new possibilities for meeting the requirements of the tire industry. After first adapting silanes to the silicas available, research and development efforts have recently been focused on adjusting the silicas to the silanes in order to achieve optimum effectiveness of this reinforcing system. All in all, a process seems to have been initiated in the tire industry which aims at using the silica/organosilane system to much greater advantage.