Effect of Mixing Time on Filler-Matrix Interactions in Polyacrylic Acid, Epoxidised Natural Rubber and Carbon Black Composites

It is known that increased mixing times help carbon black disperse better in a polymer matrix. An experimental study was conducted to investigate the effect of mixing time on self-crosslinkable polyacrylic acid (PAA) and epoxidised natural rubber (ENR) blend, filled with HAF carbon black. The constituents were mixed at 180°C in a Brabender Plasticorder. Preliminary investigations show that there exists a critical mixing time, which varies with the filler loading as well as mixer rotor speed. The best dynamic mechanical and physical properties of the composites were obtained at the critical mixing time. These have been explained on the basis of maximum interaction between the filler particles and the rubber matrix at the critical mixing time due to: (1) increase in surface area of filler with increase in dispersion and (2) enhancement of carbon black promoted chemical interaction between PAA and ENR. Further mixing beyond the critical mixing time results in poorer properties of the composites, possibly because of mechanochemical degradation of ENR chains.