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Bio-based polybenzoxazines as an efficient coatings to protect mild steel surfaces from corrosion

New types of mono and bi-functional benzoxazine monomers were synthesized using cardanol (C) and 4-aminobenzonitrile (abn), p-phenylediamine (ppda) along with paraformaldehyde. The synthesized benzoxazine monomers structure was elucidated by 1H, 13C-NMR and FTIR spectroscopic techniques. The polymerization temperature (Tp) of C-abn and C-ppda are noticed at 280oC and 237oC, respectively. It was also noticed that bi-functional benzoxazine (C-ppda) possesses lower curing temperature than mono-functional benzoxazine (C-abn). The ring opening polymerization of benzoxazine was confirmed by FTIR spectroscopy. Thermal analyses indicate that, benzoxazine [poly(C-ppda)] possesses higher thermal stability than poly(C-abn). The surface roughness of the benzoxazine coated MS specimen was analysed by atomic force microscope. The values of water contact angles obtained for poly(C-abn) and poly(C-ppda) are 145o and 148o, respectively. It was noticed that the mild steel specimen coated with bio-based benzoxazine C-abn exhibit excellent resistance to corrosion.