Advancing polyallophanate powder coating performance and function with colloidal lignin particles

Polyallophanate powder coatings are increasingly attractive as sustainable, solvent-free finishing materials, yet their performance and functionality remain limited by the properties of conventional additives. Colloidal lignin particles (CLPs) offer a renewable alternative with intrinsic antioxidant, UV-absorbing, and antibacterial characteristics. In this study, CLPs were produced from organosolv lignin derived from palm oil lignocellulosic residues using three particle size-reduction approaches: sonication, antisolvent, and hybrid. The hybrid method produced the most stable dispersions, yielding spherical CLPs with reduced particle size and increased surface area compared to native lignin. CLPs were incorporated at 1-5 wt% into petroleum-based and lignin-based polyallophanate powder coating formulations to evaluate their influence on thermal, mechanical, surface, antibacterial, and UV-aging behavior. CLP addition enhanced the thermal stability of those petroleum-based coating systems and imparted measurable antibacterial activity against Staphylococcus aureus in both coating systems. CLPs also increased color change and gloss loss under UVB exposure, indicating their applicability as light-absorbing fillers. However, incorporating CLPs reduced the impact resistance of polyallophanate powder coatings, particularly at higher loadings. Overall, the results demonstrate that CLPs can impart new functional properties such as antibacterial behavior, while contributing to thermal reinforcement, highlighting their potential as bio-derived nano-additives for more sustainable and multifunctional powder-coating technologies.