Submitted to: Polymer Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2005
Publication Date: November 1, 2005
Citation: Jong, L. 2005. Rubber composites reinforced by soy spent flakes. Polymer International. 54(11):1572-1580. Interpretive Summary: Soy spent flakes (SSF) is a plentiful renewable material from the waste stream of commercial soy protein extraction. SSF contains mostly soy carbohydrate and a small fraction of soy protein. In many rubber related applications, rubber products are filled with reinforcement materials. The raw material cost of SSF is comparable to that of inorganic fillers. Previously, we have used soy protein isolate, soy protein concentrate, and defatted soy flour to increase significantly the strength of rubber composites. The development is to use SSF in rubber composites, and measure the strength improvement. The reinforcement effect of SSF in rubber is characterized by static and dynamic mechanical methods. The results show that SSF can be used as low cost fillers for rubber composites. This development will be of general interest to technologists developing new rubber products and will be useful to soybean farmers by creating new markets for soybean products.
Technical Abstract: Soy spent flakes (SSF) is a plentiful renewable material from the waste stream of commercial soy protein extraction. SSF contains mostly soy carbohydrate and a small fraction of soy protein. The dry SSF is a rigid material and has a shear elastic modulus of ~4 GPa. The aqueous dispersion of SSF was blended with styrene-butadiene latex to form rubber composites. The soy carbohydrate increased the tensile stress in the small strain region, but also reduced the elongation at break. The shear elastic modulus of the composites showed an increase in the small strain region, consistent with its stress-strain behavior. The SSF composite shows a similar extent of modulus recovery as that of protein composite after eight strain cycles. At small strain, the shear elastic modulus of 30% filled composites at 140 deg C was about 160 times higher than that of the unfilled elastomer, showing a significant reinforcement effect caused by SSF. Compared with soy protein isolate, the stress softening effect and recovery behavior under dynamic strain suggest the SSF composite has a slightly stronger filler-rubber interaction. In general, the SSF composites gave slightly higher composite strength compared with the protein composites, but at a much lower cost.