ABSTRACT
The filler distribution and the amount of interphase are determined for carbon black (CB) filled blends of natural rubber (NR) with butadiene rubber (BR) and styrene–butadiene rubber (SBR) and compared with fatigue crack propagation rates under pulsed excitation. A viscoelastic model is used to separate the contributions of the different polymer phases and the interphase to the total dissipated energy G″ during dynamic straining. The filler amount in any phase can be calculated from the increase of the energy dissipation. For NR/SBR blends a higher filler load of the SBR phase and the interphase and a lower filling of the NR phase are identified. In contrast NR/BR blends show a very low filled BR phase and higher filling of the NR phase and the interphase. The carbon black distribution also depends on mixing procedures. Through a batch mixing procedure, in which the filler is previously mixed in the NR only and then blended with BR, the filler transfer from NR to BR increases the filling of the BR phase. The phase morphological results deliver information for a better understanding of crack propagation in CB filled NR/BR and NR/SBR blends. The fracture behavior differs significantly if NR is successively replaced by BR or SBR, respectively. A less pronounced effect is found for the variation of mixing procedure, although it seems that the more heterogeneous filler distribution with a high amount of CB in NR of the batched samples delivers slightly reduced crack propagation rates.