Vanillin derived partially bio-based benzoxazine resins for hydrophobic coating and anticorrosion applications: Studies on syntheses and thermal behavior

Abstract

ABSTRACT The study mainly focuses on the synthesis, thermal, hydrophobic, and anticorrosion properties of environmentally friendly polybenzoxazines based on vanillic acid for applications such as water repellent coatings and anticorrosion. Vanillic acid (VA) was individually reacted with cyclohexylamine (cha), dodecylamine (dda), furfurylamine (ffa), and 3-trifluoromethylaniline (tfma) in order to develop structurally distinct benzoxazines. The synthesized monomers molecular structure was examined using ATR-FTIR and 1H-NMR. Thermal characteristics were also described using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The polymerization temperature (Tp) of benzoxazines synthesized was observed in the range of 203–245°C from DSC analysis. The polymerization temperature of VA-ffa was found to be 203°C, which has lower than that of other benzoxazine monomers. Typically, the early decomposition temperatures of all the developed polybenzoxazines were over 250°C, demonstrating remarkable thermal stability. Poly(VA-tfma), one of the polybenzoxazines, exhibits highest value of char yield of 43% at 850°C. Additionally heat resistance index obtained for all the polybenzoxazines was ranged between 147 and 158°C. The value of water interface angle noticed for polybenzoxazine ranges from 142° to 145°. Among the synthesized polybenzoxazines, poly(VA-tfma) showed excellent hydrophobicity with highest value of 145°. In addition, hydrophobicity of the benzoxazine coated cured cotton fabric was analyzed for its durability at various time intervals. SEM analysis was performed for all the four VA-based polybenzoxazines. Benzoxazines were coated on mild steel (MS) plates to study the corrosion resistant property. Poly(VA-tfma) has better corrosion resistant behavior than that of poly(VA-cha), poly(VA-dda) and poly(VA-ffa) according to electrochemical impedance measurements. Further, salt spray test was conducted on polybenzoxazine coated MS for 96 h, minimum weight loss was observed for initial and after 96 h. Data from several studies indicate that benzoxazine, which is based on vanillic acid, can be utilized for applications demand hydrophobic condition with corrosion protection.