Effect of soy spent flakes and carbon black co-filler in rubber composites

The rubber composites that are reinforced by a mixture of soy spent flakes (SSF) and carbon black (CB) are investigated in terms of their viscoelastic properties. Soy spent flakes is a plentiful renewable material from the waste stream of commercial soy protein extraction. SSF contains mostly soy carbohydrate and dry SSF increases rubber modulus significantly. The aqueous dispersions of SSF and CB were first mixed and then blended with styrene–butadiene latex to form rubber composites by freeze-drying and compression molding method. The mixtures of SSF and CB at three different ratios are investigated as co-fillers. A 30% co-filler reinforced composite exhibits about 100 times increase in the shear elastic modulus compared with unfilled SB rubber, showing a significant reinforcement effect by the co-filler. Compared with the SSF composites, the recovery behaviors of the co-filler composites after the eight consecutive deformation cycles of dynamic strain are improved and are similar to that of the CB composites. The comparison of viscoelastic properties of the composites prepared by freeze-drying and casting methods indicates the composites prepared by freeze-drying method have a lower elastic modulus, but have a better recovery behavior due to its polymer mediated filler network structure. The co-filler composites with 50–75% substitution of CB by SSF have a greater elastic modulus than the CB reinforced composites.