Castor oil-based transparent and omniphobic polyurethane coatings with high hardness, anti-smudge and anti-corrosive properties

Polymeric coating technology provides a cost-effective and convenient solution for the surface pollution and corrosion issues on various substrates. Herein, a series of transparent and omniphobic bio-based polyurethane (PU) coatings with high hardness, excellent anti-smudge and anti-corrosion properties were prepared by using castor oil as bio-polyol, hexamethylene diisocyanate trimer (HDIT) as a cross-linking agent, and a small amount of monocarbinol terminated polydimethylsiloxane (PDMS-OH) as an eco-friendly anti-fouling agent. Effects of the R-value (mole ratio of isocyanate groups to hydroxyl groups) and dosage of PDMS-OH (wt%) on the PU-PDMS coating's hardness, surface wettability, anti-smudge and anti-corrosion performance have been thoroughly investigated. It was found that the higher R-value led to increased coating hardness. The element content of silicon on the coating surface was confirmed to be higher than the theoretical value since the grafted PDMS chains partially enriched from the inner matrix to the coating surface for reducing overall surface energy. Various simulated water-based contaminants could quickly slide off from the coating surface without leaving any traces. Writing traces of oil-based marker could be shrunk immediately after writing and wiped clean from coating surface completely. Such anti-smudge properties could be maintained even after 1000 cycles of polishing. Moreover, the anti-corrosion performance of these PU-PDMS coatings has been investigated through electrochemical tests. The capacitance circular arc radius of PU1.5-PDMS4.0 is 10 times of tinplate and 4 times of PU1.5, indicating the obtained coatings could offer better corrosion protection for tinplate than the regular PU coatings. This work would broaden the polyurethane application in omniphobic anticorrosion coatings.