ARS | Publication request: Soy Protein Nanoparticles and Nanocomposites

Submitted to: American Association for the Advancement of Science Meeting
Publication Type: Abstract
Publication Acceptance Date: November 30, 2006
Publication Date: February 15, 2007
Citation: Jong, L., Peterson, S.C. 2007. Soy protein nanoparticles and nanocomposites [abstract]. American Association for the Advancement of Science Meeting. Poster 69, page 16.

Technical Abstract: Soy protein isolate (SPI) is obtained from soybean by removing soybean oil and soy carbohydrates. SPI contains more than 90% protein. Structurally, SPI is a globular protein and its aggregates in water consist of sphere-like protein particles. The number average aggregate size of SPI at pH=5.2 is ~6 micrometers. SPI nanoparticles were obtained by alkali hydrolysis and followed by centrifugation at pH=5.2 to remove large aggregates. Particle sizes of the swollen nanoparticles in water were determined by light scattering. The volume and number weighted mean particle size are 260 and 210 nm respectively, indicating a narrow size distribution. One of the potential applications of SPI nanoparticles is as reinforcement in polymer composites to increase their mechanical strength and elasticity. Nanocomposites were formed by mixing SPI nanoparticles with 120 nm carboxylated styrene-butadiene (SB) particles in the aqueous phase. The resulting particle mixtures were then freeze-dried and compression-molded to form nanocomposites. The properties of these nanocomposites were measured by a dynamic mechanical method where the composites were formed into torsion bars and subjected to oscillatory motion at a certain strain and frequency. Compared with unreinforced SB matrix, SPI/SB nanocomposites exhibited a significant increase in their shear elastic modulus. The elasticity of nanocomposites was characterized by measuring the ability of the composites to recover from deformation. The recovery experiments were conducted by subjecting the composite to a large shear strain followed by periodically recording its recovered modulus in the linear viscoelastic region. Nano-sized SPI particles were found to increase the elasticity of nanocomposites by forming a more flexible particle-matrix network.