Polyurethane coatings derived from vegetable oils with and without the addition of corrosion inhibitors: chemical, structural and corrosion resistance properties

Author(s)

Jéssica Verger Nardeli

• Document type: Doctoral Thesis
• Press: Araraquara. 2020-07-10.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Química. Araraquara
• Defense date: 2020-06-29
• Advisor: Assis Vicente Benedetti; Sidney José Lima Ribeiro

Abstract

Polyurethane (PU) coatings were prepared from vegetable oils (crambe and castor) and modified by the incorporation of corrosion inhibitors (condensed tannins). The reaction was monitored by characterizing the intermediate products (polyester and prepolymer). Polyester was characterized by solubility in methanol, acidity index, hydroxyl groups and attenuated total reflectance Fourier transform infrared spectroscopy (FTIR), and the prepolymer was characterized by solid content, solvent content, free-isocyanate (NCO) groups and FTIR. PU coatings were characterized by FTIR and water uptake. These coatings were applied on aluminum alloys with an extensometer. The curing process was carried out at room temperature (~25 oC). The thickness of the coatings was determined by scanning electron microscopy (SEM) and the adhesion was assessed using the ASTM D3359 standard. After the chemical and morphological characterization of the coatings, the electrochemical study was carried out. The corrosion resistance and the film degradation process (longevity of the coating action) were studied by open circuit potential measurements (EOCP) and electrochemical impedance spectroscopy (EIS) in 0.6 mol L-1 NaCl aqueous solution with the immersion time. Localized electrochemical techniques were also used, such as local electrochemical impedance spectroscopy (LEIS) in 0.005 mol L-1 NaCl aqueous solution and scanning techniques with vibrating electrode (SVET) and with ion-selective electrode (SIET), in aqueous solution 0.05 mol L-1 NaCl for 24 h. The results demonstrate that the modified tannin coatings provide effective protection against corrosion (|Z| ~ 1011Ω cm2) and have a self-healing effect, attributed to the formation of new hydrogen bonds. The local electrochemical techniques provided decisive information about the corrosion inhibition mechanism. Therefore, the present study is different and stands out for containing a variety of formulations that use natural products as raw material (crambe oil, castor oil, corrosion inhibitor - condensed tannin) that offer self-healing effect guaranteeing effective protection against corrosion of the AA2024-T3 aluminum alloy even when the surface is subjected to artificial scratch. (AU)

• FAPESP's process: 15/10554-9 - Polyurethanes Coatings derived from vegetable oil with and without addition of corrosion inhibitors: chemical, structural and corrosion resistance.
• Grantee: Jéssica Verger Nardeli
• Support Opportunities: Scholarships in Brazil - Doctorate