Reinforcement effect of soy protein nanoparticles in amine-modified natural rubber latex

Abstract

Mechanical properties of natural rubber reinforced with soy protein nanoparticles are useful for various rubber applications. However, the properties is further improved by improving interactions between soy protein and rubber. A novel method is used to modify particle surface of natural rubber latex by grafting with diallylamine. The improved polymer-filler interactions caused tensile stress at 300% elongation to match that of carbon black, which is a breakthrough for organic fillers. The grafting was demonstrated with infrared and particle size measurements. The size of natural rubber latex particles increased 8% after the grafting and the infrared spectra showed an increase of amine groups in coagulated NR latex. The curing rate of modified NR reinforced with soy protein matches that of carbon black composite. With the addition of 10% soy protein nanoparticles, the tensile strength of natural rubber and modified natural rubbers increased from 9 to 15MPa to 19–25MPa. Both dynamic mechanical strain and swelling measurements indicate modified natural rubber composites have a higher degree of polymer-filler interaction. The change of reinforcement factors with filler fraction can be described by modified Mooney model that includes anisotropic reinforcement elements. Tanδ at 60°C indicates the modified composite has a better rolling resistance than carbon black.