Facile and eco-friendly fabrication of hierarchical superhydrophobic coating from eggshell biowaste

This study reports a facile and sustainable approach to fabricate superhydrophobic coating from eggshell biowaste. The coating was prepared by ball milling chicken eggshells, composed of hydrophilic calcium carbonate (CaCO3), to microsized particles followed by surface hydrophobilizing with stearic acid (C17H35COOH) to form low surface energy nanosized calcium stearate ((C17H35COO)(2)Ca) through the esterification of hydroxyl groups (-OH) absorbed on a surface of CaCO3 with carboxyl groups (-COOH) of stearic acid. Then, a layer of modified eggshell particles dispersed in polystyrene (PS) binder was dip-coated on a substrate. A coated surface with water contact angles of 151 degrees +/- 1 degrees on glass and 153 degrees +/- 1 degrees on cotton fabric substrates was achieved when a 4:1 weight ratio of the modified eggshell:PS was used. The uniform distribution of the modified eggshell particles throughout the coating led to a surface with high degree of hierarchical micro-nanoscale roughness which resulted in superhydrophobicity. The superhydrophobic eggshell coating showed good environmental stability, self-cleaning, and oil/water separation properties. These results suggest that eggshell biowaste can be utilized for superhydrophobic applications.