Evaluation of Fatigue Crack Growh Resistance of Rubber-Silica Composites and Analysis of the Role of Filler-Filler Interaction and Interface Bonding

 Fatigue crack growth (FCG) of rubber composites as controlled by the viscoelastic losses, is strongly dependent on the polymer-filler interfacial phenomena. The type of filler-polymer bonding at the interface and the extent of mobility restriction of rubber chains resulting from the interaction by the filler are of the critical ones. In highly filled rubber compound, the amount of mobility restriction is almost dictated by the filler-filler interaction. Regulating the surface energy of the filler can be an effective method to control the filler-filler interaction, to distinguish the two interfacial phenomena, and to pave the way of studying their significance.

Ultrasil VN3 and solution styrene-butadiene rubber (SSBR) were of the base composite materials. Using two silanes with a short and a long aliphatic chain length, the surface of Ultrasil was modified in our lab to a certain level of grafting density which could bring the required surface energy and the filler-filler interaction. By controlling the surface energy of silica treated in the lab, and by making a systematic comparison of the resulting composites, it was possible to study the role of covalent bonding at the interface, the role of filler-filler interaction and severity of mobility restriction and finally the role of silane chain length.

Fatigue crack growth experiment revealed that the severity of mobility restriction and the filler-filler interaction of the composite have the highest impact on the amount of viscoelastic dissipation and the rate of crack growth.  The covalent bonding at the interface can deviate the crack from growing in the original direction and thus it may act as a physical barrier to improve crack growth resistance. For highly filled compounds where the properties are almost dictated by the filler-filler interaction, the role played by the chain length of silane is minor.