Covalently-grafted graphene oxide nanosheets to improve barrier and corrosion protection properties of polyurethane coatings

Surface modification of graphene oxide (GO) has been performed by grafting of polyisocyanate (PI) resin. Results obtained from X-ray photo electron spectroscopy, thermal gravimetric analysis and X-ray diffraction analysis revealed that the PI resin chains were successfully attached onto the surface of GO nanosheets through covalent bonding with hydroxyl and carboxylic groups leading to amides and carbamate esters bonds formation. Subsequently, the PI functionalized GO sheets were incorporated into the polyurethane (PU) matrix. The X-ray diffraction analysis showed that surface modification of GO nanosheets with PI enhanced the level of exfoliation of PI-GO in the PU matrix. Scanning electron microscope analysis showed the enhanced interaction between GO and PU matrix after functionalization by PI resin. The electrochemical impedance spectroscopy and salt spray tests were performed to reveal the effects of addition of 0.1 wt.% GO and PI-GO nanosheets on the corrosion protection properties of the PU coating. Also, the adhesion loss of the coatings was obtained by pull-off adhesion test after 30 days immersion in 3.5 wt.% NaCl solution. It was found that incorporation of 0.1 wt.% surface modified GO nanosheets into the PU matrix resulted in significant improvement of the coating corrosion protection properties and ionic resistance.