Synthesis and characterization of sol–gel derived CNSL based hybrid anti-corrosive coatings

Thermally cured cashew nut shell liquid based hybrid coatings have been successfully developed using three step processes of malenization, silane modification and subsequent hydrolysis and condensation with tetra ethyl orthosilicate for corrosion protection of mild steel. The synthesized precursor was then characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (¹H-NMR, ¹³C-NMR and ²⁹Si-NMR) for structural elucidation. Four different coating formulations were developed on the basis of silane content (5, 10, 15 and 20 %) in the coating and cured with hexabutoxymethylmelamine at 120 °C for 1 h. The completely cured coatings were evaluated for mechanical properties, solvent resistance, chemical resistance, hydrolytic stability and accelerated weathering properties. Scanning electron microscope/energy dispersive spectroscopy was used to analyse the morphological behaviour and elemental distribution of the coating. Results revealed that 20 % silane modification showed better overall properties as compared to other formulations due to formation of more metal–oxygen–silicon covalent bond at metal-coating interface.