Bio-inspired "green" nanocomposite using hydroxyapatite synthesized from eggshell waste and soy protein

Eco-friendly and inexpensive "green" nanocomposites with enhanced functional performances were developed by combining nanoscale hydroxyapatite (HA) synthesized from eggshell waste (nEHA) and protein-based polymer extracted from defatted soybean residues. nEHA was synthesized from chicken eggshells using an energy efficient microwave-assisted wet chemical precipitation method. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy studies confirmed the nanometer scale (diameter: 4-14 nm and length: 5-100 nm) of calcium-deficient (Ca/P ratio ∼1.53) needle-like HA. Uniform dispersion of nEHA in soy protein isolate (SPI) solution was obtained by modifying nEHA surface using a polyelectrolyte (sodium polyacrylate) dispersant via irreversible adsorption. Green nanocomposite films were prepared from SPI and surface-modified nEHA with the help of a natural plasticizer "glycerol" by solution casting. Significant improvements in tensile modulus and strength were achieved owing to the inclusion of uniformly dispersed nEHA in SPI sheets. Overall, this work provides a green pathway of fabricating nanocomposites using naturally occurring renewable polymer and inorganic moieties from eggshell waste that emphasizes the possibilities for replacing some petroleum-based polymers in packaging and other applications.