The corrosion of metallic materials is one of the most common natural problems encountered in the different fields of engineering. To delay the corrosion effects, some kinds of organic inorganic hybrid (OIH) coatings were tested as protective barrier. In this work we proposed the use of glycerol as a renewable source reagent for the development of a sol-gel green-coating based on polyurethane (PU) and siloxane (PU-Sil). The PU was synthesized from diisocyanate, MDI (4,4'-methylenebis (phenyl isocyanate)) and glycerol and the effect of the ratio of APTES ((3-aminopropyl) triethoxysilane) and MDI in the properties and structure of the PU-Sil material evaluated. The FTIR characterization showed that the OIH material has carbamate groups in the polymer chain that are related to PU formation and urea groups due to the formation of the link between free NCO groups and the siloxane. ¹³C and ²⁹Si NMR/MAS spectra showed characteristic bands of the PU chain and siloxane polycondensation degree of about 80%, respectively. From the thermogravimetric analysis was possible to demonstrate the effect of APTES on the thermal stability of the material. The electrochemical impedance spectroscopy measurements performed on the PU-Sil coated carbon steel demonstrated the effect of the amount of siloxane in the corrosion protection performance in saline solution. Lifetimes longer than 125 days were verified from impedance over 106 Ohm.cm2 observed for PU-Sil coated carbon steel. The developed green sol-gel route allowed producing an OIH material of low cost, formed by cross-linked polymer chains with good performance for steel corrosion protection.

Keywords: green-coating, corrosion protection, polyurethane – siloxane.