Detailed understanding of the carbon black-polymer interface in filled rubber composites

To characterize the nature of the interface between styrene-butadiene rubber (SBR) and carbon black (CB) in a filled rubber compound, we introduce an extraction protocol that uses toluene solvent in a high-pressure autoclave with sequential temperature steps of 90, 110, and 150 degrees C. This new approach removes unbound and physically bound (physisorbed) polymer from the CB-filled SBR compound to leave only chemically bound polymer which is 0.86% (0.0172 g polymer/g CB) and not zero as implied from extrapolating prior literature results. Rheological time sweeps on the unfilled gum SBR indicate that significant crosslinking can occur during annealing at 150 degrees C for this unsaturated polymer. This was the motivation for using the sequential extraction procedure versus direct extraction at 150 degrees C which gives a nearly six-fold higher amount of unextracted polymer due to such crosslinking. Analysis of the temperature dependence of bound rubber from 23 to 150 degrees C indicates that the physical interactions between the polymer and CB surface have a weaker component with a desorption energy (E-d) of 6.8 kJ/mol and a stronger component with E-d = 90.7 kJ/mol, the latter requiring an extraction temperature of 110 degrees C to remove the majority of it from the CB.

Automated summary

The new extraction method allows for only 0.86% of the polymer to be bound to carbon black, rather than completely unbound; significant crosslinking can occur at 150 degrees C during annealing of the unsaturated polymer.