Manawwer Alam

A sustainable bio-metal-organic framework (bio-MOF)-inspired polyurethane coating was developed from technical cashew nutshell liquid (tCNSL) and furfural, coordinated with Ni(II) ions for advanced anticorrosion applications. Furfurylated tCNSL acts as a bio-derived multidentate organic linker, while Ni(II) ions serve as coordination nodes, forming a MOF-like architecture chemically integrated into the polyurethane network. FTIR confirmed successful urethanation and Ni–O coordination, whereas XRD revealed a predominantly amorphous structure with short-range ordering induced by metal–ligand interactions. The Ni(II)-coordinated coating exhibited a high gel fraction (~98%), indicating extensive crosslinking and excellent network integrity. Optical microscopy, FE-SEM, and SEM-EDX analyses demonstrated a uniform, defect-free microstructure with homogeneous nickel distribution. TEM revealed well-dispersed spherical Ni-rich nanodomains (~10 nm in diameter), confirming nanoscale organization via in situ metal–ligand self-assembly. BET analysis indicated limited mesoporosity (<10 nm) arising from coordination-induced free-volume domains. Ni(II) incorporation significantly improved coating performance, including scratch hardness (2.0 kg), adhesion (~105%), gloss (~96 at 45°), flexibility, and hydrophobicity (water contact angle ~95°), thereby reducing moisture permeability. TGA and DSC demonstrated enhanced thermal stability (up to ~200 °C) and increased glass transition temperature (Tg ~169 °C), attributed to coordination crosslinking. Electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution provided excellent long-term corrosion protection, maintaining high coating resistance after 27 days of immersion, owing to a dense, hydrophobic, and coordination-reinforced polymer network that effectively inhibited ionic diffusion. These findings demonstrate that tCNSL-derived bio-MOF-inspired polyurethane coatings integrate renewable feedstocks with coordination chemistry to achieve robust thermal, mechanical, and anticorrosion performance.

This research focuses on the synthesis and detailed evaluation of waterborne polyurethanes (WBPUs) developed using cardanol formaldehyde (CF) resin as a renewable polyol and hexamethylene diisocyanate (HMDI) as the isocyanate source. The CF resin was prepared through a condensation reaction between cardanol, a renewable phenolic compound derived as a byproduct of cashew nut processing, and formaldehyde. This resin was subsequently reacted with HMDI to produce a prepolymer, forming the basis of the WBPU system. The multi-step synthesis pathway included the generation of CF resin and its subsequent chain extension using HMDI. The resulting WBPUs were systematically characterized to assess their structural, thermal, mechanical, and film-forming attributes. FTIR spectroscopy confirmed the successful polymer formation and curing, while crosslink density results specified the establishment of robust protecting layer. TEM discovered uniformly distributed spherical nanoparticles with a size of 10±5 nm. SEM and XRD analyses illustrated an amorphous surface structure characterized by densely packed, rough morphology with embedded nanostructures and voids. The coatings exhibited excellent mechanical behaviour, including high scratch hardness (3 kg), perfect crosshatch adhesion (100%), strong gloss and wear resistance, high flexibility (passed 1/6 inch bend test), and superior impact resistance (150 lb/inch). Chemical resistance tests showed minimal degradation when exposed to 3.5% solutions of HCl, NaCl, NaOH, ethyl methyl ketone and water, indicating long-term durability. The formulation with 20% amine content demonstrated the most desirable performance, showing enhanced hydrophobicity and thermal stability up to 240 °C. The fabrication of cardanol-based WBPU nano-dispersions offers a clean, sustainable, and a high-efficiency substitute for traditional coatings across various applications. This work underscores the potential of renewable cardanol in producing environmentally responsible WBPUs with strong adhesion, flexibility, and water resistance, emphasizing their suitability for modern protective coating technologies.