An ESR method was used to investigate the formation of free radicals during rubber mastication and filling of rubber with various carbon blacks. The ESR spectra of natural rubber and styrenebutadiene rubber with various carbon blacks are of a complex character. A narrow component line is superimposed on the much broader signal line of carbon black. The changes in this narrow spectral line with plasticization time and with carbon black content in the rubber–filler system result from interactions between the rubber macromolecules and filler particles.
The problem of rubber reinforcement is of great importance in rubber technology. Free radicals formed during mastication play an important role in the reinforcement of the rubber-filler system. The reinforcement of rubber systems is usually explained in terms of chemical interactions between rubber and filler; however, there are also opinions that the interactions are physical in nature. So far, the mechanism of reinforcement is an open question. Undoubtedly, reinforcement is influenced by free radicals formed during mastication and the physicochemical state of the surface of active fillers. The formation of free radicals during plasticization of rubbers has been already reported. Investigations by an ESR technique of free-radical formation during compounding of rubbers with various carbon blacks are described in the present paper.
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