Innovative approach to corrosion protection using cardanol and vanillin porphyrins in alkyd resins

Porphyrins added to alkyd resins can be a way to enhance these organic coatings through a physical barrier, in order to reduce permeability, decrease porosity, and improve film adhesion. This helps prevent oxygen and ions from acting on metal structures, thereby extending their lifespan. This work aimed at the synthesis and characterization (UV–vis, FT-IR, 1 H and 13 C NMR, TGA) of a meso -porphyrin and its zinc metalated analogue derived from cardanol, the main constituent of Cashew Nut Shell Liquid (CNSL), and Vanillin, a molecule obtained from lignin. The goal was to incorporate these products into alkyd resins for use as anticorrosive agents, evaluating them through electrochemical studies, adhesion, gloss, hardness, and solvent resistance. The results of electrochemical impedance spectroscopy showed that the alkyd resin containing the zinc-metalated meso -porphyrin (Zn-PCV/Ak) exhibited higher impedance modulus values (|Z| 0,06 Hz greater than 10 9 Ω·cm 2 ), as well as increased solvent resistance, compared to pure alkyd resin (blank) (|Z| 0,06 Hz close to 10 9 Ω·cm 2 ) or alkyd resin with metal-free meso -porphyrin added (PCV/Ak) (|Z| 0,06 Hz value lower than 10 8 Ω·cm2). This latter may compromise protection due to strong coordination with transition metals, such as iron present in the metal plates. This indicates the potential use of meso -metalloporphyrin (Zn-PCV) as an additive for anticorrosive protection. Graphical Abstract