Effects of secondary structure of fillers on the mechanical properties of silica filled rubber systems

A study was carried out on the mechanical properties of silica filled styrene–butadiene rubber systems in relation to the secondary structure formed by silica particles in the systems, which was controlled by a surface chemistry of silica particles and by a strain applied to the samples. The breakdown of the secondary structure was successfully detected by transmission electron microscopy (TEM) observations when the strain was applied to silica filled vulcanizates. The degree of breakdown was more prominent in the larger agglomerates of which the size was controlled by the number of silanol group per unit surface area of silica particles. The existence of the entrapped rubber within the agglomerate was suggested by the TEM image analysis. A part of the entrapped rubber might be released when the filler network was broken by a strain. The initial modulus of the filled rubber systems increased with the increase in the size of agglomerate. At a larger strain, the modulus decreased with the increase in the strain. The decrease was more prominent in the filled rubber, which had larger agglomerates. The reduction of modulus by the strain was closely related to the reduction of entrapped rubber phase within the agglomerates and to the breakdown of secondary structure of silica particles.