Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2007
Publication Date: 12/5/2007
Citation: Jong, L. 2007. Viscoelastic properties of natural rubber composites reinforced by defatted soy flour and carbon black co-filler. Journal of Applied Polymer Science. 106(5):3444-3453.
Interpretive Summary: Defatted soy flour (DSF) is an abundant renewable commodity and has a lower material cost than carbon black (CB). In many rubber related applications, rubber products are filled with reinforcement materials such as CB. In the present development, a mixture of DSF and CB is used as reinforcing fillers in natural rubber composites. The reinforcement effect is characterized by dynamic mechanical methods. At 100 degrees C, a 40% co-filler reinforced composite with one to one ratio of DSF to CB exhibited a 90-fold increase in the strength compared with unfilled natural rubber, showing a significant reinforcement effect by the co-filler. This development will have potential in developing new rubber products and will be useful to soybean farmers by creating new markets for soybean products.
Technical Abstract: Filler mixtures of defatted soy flour (DSF) and carbon black (CB) were used to reinforce natural rubber (NR) composites and their viscoelastic properties were investigated. DSF is an abundant and renewable commodity and has a lower material cost than CB. Aqueous dispersions of DSF and CB were first mixed and then blended with natural rubber latex to form rubber composites using freeze-drying and compression molding methods. A 40% co-filler reinforced composite with a 1:1 DSF:CB ratio exhibited a 90-fold increase in the rubber plateau modulus compared with unfilled natural rubber, showing a significant reinforcement effect by the co-filler. The effect, however, is lower than that observed in the carboxylated styrene-butadiene rubber composites reported earlier, indicating a significant effect from the rubber matrix. The co-filler composites have elastic moduli between those of DSF and CB reinforced composites. Stress softening and recovery experiments indicated that the co-filler composites with a higher CB content tend to have a better recovery behavior; however, this can not be simply explained from the recovery behaviors of the single filler (DFS and CB) composites. CB composites prepared by freeze-drying show a strain-induced reorganization of fillers. Strain sweep experiment data fit with the Kraus model indicates the co-filler composites with a higher CB content are more elastic, which is consistent with the recovery experiments.