Epoxy-free polyphenalkamine one-pack sustainable coating from technical cashew nut shell liquid: fabrication and electrochemical studies for anti-corrosive applications

Abstract

Phenalkamines (PhAA) are commonly used as curing agents for epoxies and polyureas. This study reports the polymerization and crosslinking of virgin PhAA resin and its conversion to anti-corrosive coatings for commonly used mild steel substrate. In this work polyphenalkamine (PolyPhAA) resin was prepared in four different ratios via., one-step reaction between technical cashew nut shell liquid, aldehyde, and amine through an environment-friendly route without any catalyst. The coating properties were compared with trivial PhAA-cured-epoxy coatings. Standard spectral techniques were performed to confirm the formulation of PolyPhAA. X-Ray diffractionand scanning electron microscopy confirmed the amorphous behavior and nano-roughness of the coating surface. PolyPhAA2 (with 1:2:1) coatings depicted excellent hydrolytic stability up to 16 h, anti-icing ability (−15 to −18 °C for 24 h) and strong adhesion with the substrate. Electrochemical impedance spectroscopy and open circuit potential measurements revealed the formation of stable, well-adhered coating with a uniform impedance value in 106 Hz range, throughout the 40 days of immersion studies. Apart from expressing excellent corrosion protection ability, PolyPhAA2 coating showed high reflectiveness, hydrophobic character (contact angle 120°–135°), mechanical robustness, thermal stability (>300 °C), and chemically resistance. The in-expensive, sustainable, environment-friendly, and non-toxic one pack coatings could be an alternative to petroleum-based two-pack epoxy coatings in various engineering applications.