BIO-based epoxy composites from epoxidized soybean oil, tannic acid and 2D-layered nanoclays

The replacement of petroleum-based, bisphenol A (BPA)-derived epoxy coatings with sustainable, high-performance alternatives is urgently needed for marine corrosion protection. This work presents a new family of fully bio-based epoxy nanocomposite coatings, synthesized from epoxidized soybean oil (ESO) and tannic acid (TA) and reinforced with two-dimensional nano-clays, montmorillonite (MMT) and kaolin (KAO). The incorporation of 1–5 wt% nano-clays into the ESO/TA matrix created a nacre-inspired “brick-and-mortar” structure, which significantly enhanced mechanical and barrier properties. Comprehensive characterization revealed that MMT, with its superior intercalation capacity, acted as a catalyst, lowering the optimal curing temperature to ∼100 °C and promoting char formation (residue up to 24%). In contrast, KAO contributed to a stiffer network. Electrochemical impedance spectroscopy (EIS) over 150 days demonstrated exceptional long-term anti-corrosion performance, with the optimal MMT-based coating maintaining an impedance >10 9 Ω·cm 2 , far exceeding the protective threshold of 10 6 Ω·cm 2 . Tafel analysis confirmed a corrosion rate reduction of approximately 65% compared to bare steel. These coatings also exhibited strong adhesion to carbon steel and tuneable mechanical properties (Young's modulus: 0.6–2.5 GPa). This study successfully developed a sustainable, high-performance coating system that effectively addresses the dual challenges of reduced environmental impact and corrosion resistance in marine applications. • Fully bio-based epoxy coatings developed from soybean oil and tannic acid. • Montmorillonite and kaolin nano-clays enhance mechanical strength and barrier performance. • Nacre-inspired brick-and-mortar structure significantly improves corrosion resistance in marine environments. • Montmorillonite lowers curing temperature and increases char yield through catalytic effects. • Long-term electrochemical tests show over 65% corrosion rate reduction.