Sustainable l-tyrosine based bio-benzoxazines for efficient protection of mild steel surfaces from marine environment

In the present work, a new type of bio-based tyrosine-dipeptide (TB) was successfully synthesized and it was converted into a structurally modified benzoxazine (TB-Bz) using three different amino compounds (aniline (a), dodecylamine (dd) and furfurylamine (ff)) and formaldehyde at appropriate reaction conditions. The molecular structure of these benzoxazines (TB-a, TB-dd and TB-ff) was elucidated using Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance spectroscopy. The curing behaviour and thermal stability of the benzoxazines were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) respectively. The ring opening polymerization of TB-a, TB-dd and TB-ff benzoxazines were observed at 222 °C, 231 °C and 233 °C respectively. Data obtained from thermal analysis, the char yield of corresponding polybenzoxazines (poly(TB-a), poly(TB-ff) and poly(TB-dd)) were observed at 43%, 51% and 25% at 850 °C respectively. The hydrophobic behaviour of poly(TB-a), poly(TB-ff) and poly(TB-dd) was ascertained from the measurement of water contact angle studies and the values obtained are 139⁰±2, 143⁰±2, 146⁰±2, respectively. The corrosion protection studies of the mild steel specimen surfaces were carried out using open-circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization. Among the mild steel specimens, coated with different benzoxazines, the poly(TB-ff) coated specimen was found to be less aggressive towards corrosion and possesses about 98.3% corrosion protection efficiency. The data obtained from different studies suggest that the bio-based tyrosine dipeptide benzoxazines developed in the present work can be considered as a better coating material for the protection of surfaces of mild steel against corrosion under adverse environmental conditions.