Do We Need Very Stiff Fillers?

The influence of reinforcement fillers on the stretching of a rubber matrix is analyzed. It is shown that filler stiffness higher than a critical one does not further enhance the stiffness of the reinforced elastomer. The stiffer filler induces higher stress/strain concentration and causes filler-rubber dissociation or chain scission at a lower macroscopic strain. Reducing filler stiffness can reduce the stress/strain concentration and therefore delay rubber chain scission or dissociation from the filler surface. Accordingly, the toughness of the reinforced elastomer could be improved. A simple material model is developed in this paper to predict the maximum macroscopic strain without bond scission in a reinforced elastomer. It is shown that reduced filler stiffness is beneficial for cases with: (i) reduced bond strength, (ii) increased rubber matrix stiffness, and/or (iii) increased application strain of the reinforced elastomer. The model can be used to design the appropriate filler stiffness to balance trade-offs of stiffness and toughness of reinforced elastomers.