Effect of soy protein concentrate in elastomer composites

Soy protein concentrate (SPC) is an abundant renewable material and is more economically favorable than soy protein isolate. SPC contains both soy protein and soy carbohydrate. An aqueous dispersion of SPC was blended with styrene-butadiene latex to form elastomer composites. The inclusion of soy carbohydrate in addition to soy protein in the composites increased the shear elastic modulus in the small strain region as well as improved the recovery behavior in the non-linear region. At small strain, the equilibrium elastic modulus of 30% filled composites at 140 °C was about 600 times higher than that of the unfilled elastomer, indicating a significant reinforcement effect generated by SPC. Compared with soy protein isolate, the stress softening effect and recovery behavior under dynamic strain indicated that the addition of soy carbohydrate might have increased the filler–rubber interaction. The behavior of modulus decrease with increasing strain is also different between SPC and protein composites.