Carbon Black Transfer in Blends of Cis-Poly(Butadiene) with Other Elastomers

Abstract

Abstract The study of carbon black transfer by BR crystallization, elastic modulus, and electrical conductivity provides convincing evidence that carbon black does not transfer from SBR, BR, and NR—all highly unsaturated polymers— when compounds are made by conventional Banbury and mixing procedures. This agrees with the electron micrographic studies of Marsh and coworkers as well as the latest publication of Hess and coworkers. It was shown, however, that a change in the carbon black distribution occurs when a solution BR masterbatch is mixed with fresh BR, providing the former is not premasticated. Black migration also takes place from a low unsaturation polymer (chlorobutyl) toward a high unsaturation polymer (BR) in chlorobutyl—BR blends, irrespective of how the black is added. Electron micrographs reveal that even in this case black does not actually transfer, but migrates to the interface, in agreement with the observation of Marsh and coworkers for NR—CR blend. Black migration in chlorobutyl—BR blends can be reduced by increasing the chlorobutyl—black interaction by heat treating and by using a promoter. The advantages of the above techniques are that these methods are suitable for highly compatible SBR—BR blends as well as for highly loaded systems, which are difficult to examine by micrographical methods. Also, an idea of the degree of compatibility of the different elastomers with BR can be obtained from crystallization studies. The disadvantage of the crystallization method is that it depends on the melting endotherm of BR and is, therefore, unsuitable for combinations that do not include BR. It is evident from the work reported that the sequence of addition of elastomers and carbon black is of paramount importance to the properties of the finished compounds since carbon black migration is the exception rather than the rule: migration takes place only in limited cases and under well-defined conditions.