INTERFACIAL EFFECTS OF A MULTIFUNCTIONAL ADDITIVE ON CARBON-BLACK FILLED RUBBER

Interfacial effects of a multifunctional additive (MFA), i.e. n-tallow-1,3-propanediamine salt of a carboxylic acid, on carbon black filled rubber have been studied. Surfaces of several normal cure rate carbon blacks were characterized by XPS and vapour-phase chemical derivatization, and the carbon blacks were found to have very few functional groups on their surfaces. The MFA has been found to decompose at approximately 120-degrees-C and the decomposition generates a diamine and a carboxylic acid. Bound rubber, determined by omicron-xylene extraction, was found to decrease with the addition of MFA and a limiting bound rubber value was obtained at the MFA loading which corresponds to a monolayer coverage of the carbon black. The reduction of bound rubber with the addition of MFA is attributed to the release of the occuluded rubber within carbon black agglomerates as a result of improved dispersion induced by the MFA. Mechanical properties were found to improve with the addition of MFA and the improvement was again attributed to the dispersing effect of MFA. Optimum mechanical properties were again observed to occur at an MFA loading which approximately corresponds to a monolayer coverage of the carbon black surface.