Reinforcement Effect of Soy Protein/Carbohydrate Ratio in Styrene—Butadiene Polymer

Soy protein and carbohydrate at different ratios were blended with latex to form composites. The variation of protein-to-carbohydrate ratio has a significant effect on the composite properties, and the results from dynamic mechanical method showed a substantial reinforcement effect. The composites reinforced by the filler with higher protein content had higher moduli than the composites with higher carbohydrate content. Soy carbohydrate also appeared to have ability to immobilize polymer chains compared to soy protein. The fatigue experiments showed that the composites with higher protein content were more elastic than the composites with higher carbohydrate content after repeatedly stressed with dynamic strain cycles. The recovery experiments showed that the moduli of the composites with higher protein content had better long-time recovery after deformation. The analysis of equilibrated residual structure after the stress-softening cycles showed that the composites with higher protein content were resilient without yielding until a larger strain was applied, while the composites with higher carbohydrate content had a continuous yielding in their structures as the magnitude of the strain was increased. Overall, the study shows that soy fillers with higher protein/carbohydrate ratio have potential to be used as rubber reinforcement.