Lignin derived from coir fibre as a sustainable additive in paints for finer filler dispersion and UV protection

The coating industry is demanding sustainable and non-toxic materials that could replace the conventional ones. This has led to increased interest in developing eco-friendly paints with enhanced performance, and this concept was fulfilled here by the biopolymer lignin. This manuscript explores the synergistic effects of lignin and titanium dioxide in creating a UV-resistant paint formulation. Lignin–TiO₂ composites were prepared through the adsorption of lignin nanoparticles onto TiO₂ particles and characterised using FTIR, UV–Visible spectroscopy, FE-SEM, and thermogravimetric analysis. FTIR analysis confirmed interactions between lignin functional groups and the TiO₂ surface, while SEM observations revealed uniform distribution of lignin-decorated TiO₂ particles. The incorporation of TiO₂ improved the thermal stability of both alkali and organosolv lignin systems. UV–Visible analysis demonstrated enhanced UV-shielding performance, with the alkali lignin–TiO₂ composite exhibiting lower transmittance (0.16–2.8%) in the 320–400 nm region compared with the organosolv lignin–TiO₂ composite (1.2–4.1%), indicating superior UV absorption. Paint formulations containing lignin-modified TiO₂ displayed improved hiding power, enhanced hydrophobicity, and satisfactory viscosity (2217–2287 cP) and pH (8–9) values within industrially acceptable ranges. The lignin-modified systems also exhibited superior dispersion stability compared with unmodified TiO₂ dispersions, suggesting the exclusion of surfactants and dispersion agents in paints. These findings demonstrate that coir-fibre-derived lignin can serve as sustainable multifunctional additives for acrylic paints, providing enhanced UV protection, improved filler dispersion by eliminating additional surfactants and dispersion agents, and desirable coating performance while supporting the development of greener coating technologies.