Modulus enhancement of natural rubber through the dispersion size reduction of protein/fiber aggregates

•Mechanical properties of natural rubber are improved with protein/fiber aggregates.•Size reduction of protein/fiber aggregates enhanced rubber modulus.•Filler-filler networks caused the modulus enhancement.

Improved mechanical properties of natural rubber are required for various rubber applications. Aggregates of protein and fiber that constitute soy protein concentrate were shear-reduced and used to enhance the tensile modulus of the natural rubber. The aqueous dispersion of the shear-reduced aggregates has a higher viscosity and shear storage modulus. The reduced aggregates in the natural rubber increased the tensile modulus of the natural rubber significantly. Compared to the natural rubber, the tensile modulus of 30% filled rubber increased 10-fold at 200% elongation. The frequency dependent shear modulus, swelling experiments, and dynamic strain sweep experiments were used to analyze polymer-filler interactions. The result shows that the polymer-filler interaction is small and is not the dominant factor that enhances the tensile properties of the natural rubber. Instead, the filler-filler network is the cause for the mechanical enhancement of the natural rubber.