Interfacial chemistry and mechanical effects of a multifunctional processing additive on carbon black filled rubber

The interfacial effects of a multifunctional additive (MFA), the n-tallow-propane-1,3-diamine salt of carboxylic acid, on carbon black filled rubber have been studied. The surfaces of three normal-cure-rate carbon blacks, of differing nitrogen BET surface areas, were characterised by X-ray photoelectron spectroscopy (XPS) and vapour-phase chemical derivatisation and found to contain very few functional groups. The MFA has been found to decompose at ca. 120-degrees-C and the decomposition to generate diamine and a carboxylic acid species. Bound rubber, determined by o-xylene extraction, was found to decrease with the addition of MFA and a limiting bound rubber value was obtained at the MFA loading that corresponds to a monolayer coverage of the carbon black surface. The reduction of bound rubber with the addition of MFA is attributed to the release of rubber, immobilised within carbon black agglomerates, as a result of improved dispersion. The mechanical properties of the rubber were also found to improve with the addition of MFA and again this was attributed to the dispersing effect of the MFA on the carbon black. Optimum mechanical properties were observed at an MFA loading which approximately corresponds to a monolayer coverage of the carbon black surface.