Synthesis and characterization of neem (Azadirachta indica) seed oil-based alkyd resins for efficient anticorrosive coating application

Neem (Azadirachta indica) is a fast-growing and evergreen tree with various medicinal values. During a severe drought, it sheds off its leaves and also produces fruits. The available literature revealed that the seeds from neem fruits contained oil varying in the range of 25–45% oil load. Neem oil was extracted from the dried neem seeds by the soxhlet extraction method using petroleum ether as an efficient solvent. Neem seed oil-based alkyd resins were synthesized by the alcoholysis–polyesterification process. The progress of the reaction was examined by determining the acid value at various time intervals. Further characterization of the oil and resins for the determination of molecular weight, structure, fatty acid composition, surface morphology and thermal stability was carried out by gel permeation chromatography, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, gas chromatography–mass spectrometry, scanning electron microscopy, thermogravimetry and differential scanning calorimetry, respectively. Attempts were made to study the effect of maleic anhydride content in the resins that changed the curing, anticorrosion, wettability and thermal properties of the resins and cured films. The curing of the alkyd resins was done by blending it with epoxy resin by gradually increasing the temperature from 60 to 210 °C. The coating of the alkyd resins over mild steel plates showed superior corrosion protection for several days. The wettability of the cured films was evaluated by measuring the water contact angle (WCA). The resin with the higher percentage of maleic anhydride showed better performance in different paints and surface coating applications. The synthesized alkyd resins from the neem seed oil possessed great application potential in beneath water marine vessel finish that opposed salt corrosion.