Enhance of Anticorrosive Properties of Green-PU-Silica Coatings by Incorporation of Lignin

The tailored combination of organic polymers and inorganic ceramics can produce organic-inorganic hybrid (OIH) coatings to act as corrosion protection barriers. 1 ,2 In this work, we proposed the use of glycerol and lignin as polyol sources to prepare green polyurethane to be used in the sol-gel synthesis of PU-silica hybrid coating for steel corrosion protection. The PU pre-polymer was synthesized from MDI (4,4’-methylenebis (phenyl isocyanate)), glycerol and lignin, and then it was functionalized with APTES ((3-aminopropyl) triethoxysilane) to ensure the covalent conjugation with polysilanol network formed from TEOS (Tetraethyl orthsilicate) sol-gel reactions leading to a class II hybrid. Three samples were synthesized varying the proportion between the polyols, one sample containing only glycerol (ZL_PU-S) and the others with a molar ratio of Gly OH :Lig OH of 7.5 and 16.1 (FL_PU-S and HL_PU-S, respectively).The effects of lignin content on the structure and properties were evaluated. FTIR and 13 C NMR showed the formation of the PU-silica hybrid and the total incorporation of lignin to the PU chain. TGA showed that the presence of lignin into the OIH matrix improved the thermal stability allowing to continuous increase of the initial temperature of mass loss: T 5% = 173, 186 and 190 °C for ZL_PU-S, HL_PU-S and FL_PU-S, respectively. The steel substrate coated with the OIH show a water contact angle of 90° for the samples HL_PU-S and FL_PU-S and 80° for ZL_PU-S. The electrochemical impedance spectroscopy analysis performed in a three electrode cell configuration with a NaCl 3.5% solution, showed that the coating with the higher lignin concentration, FL_PU-S, have a |Z| of over 10 10 Ω.cm 2 for the lowest frequency point and a phase angle of approximately -90° during the 28 days of analysis. The FL_PU-S had better performance than the coating without lignin, ZL_PU-S, that presented |Z|=10 7 Ω.cm 2 on the initial period of immersion with a decrease of two decades in value through out the subsequent period of analysis. In summary, the addition of lignin to the PU polymeric matrix enables the production of a green OIH coating with high efficiency for corrosion protection of steel substrates. Acknowledgments: This work was supported by the Brazilian funding agencies CNPq, FAPESP, CAPES and by PROPe UNESP. Keywords: Renewable feedstock, green coating, PU-silica, lignin, corrosion protection, sol-gel process, hydrophobic coating. 1-BRAZ, Á. G.; PULCINELLI, S. H.; SANTILLI, C. V. Glycerol-based polyurethane-silica organic-inorganic hybrid as an anticorrosive coating. Progress in Organic Coatings, v. 169, p. 106939 2-HARB, S. V. et al. Siloxane–PMMA hybrid anti-corrosion coatings reinforced by lignin. Surface and Coatings Technology, v. 275, p. 9-16.