Unlocking the potential of lignin as a versatile and green additive for future materials

Abstract

The current attractive role of lignin as a multifunctional bio-based additive in polymer coatings has been reviewed, with emphasis on applications taking advantage of its inherent UV-bsorbing, antioxidant, antimicrobial, as well as flame-retarding features. Lignin is the largest source of renewable aromatic biopolymers in nature, but most of the industrial lignin is combusted for low-value heat energy despite its rich chemical motifs and compatibility with generation of sustainable materials. Within coatings and thin films, lignin and lignin-based nanoparticles have potential as environmentally friendly additions for UV protective layers, active packaging, or protective surfaces on thermoplastic substrates; however, the coatings literature is less mature than bulk thermoplastic composites.

The review focuses on the influence of lignin source (e.g., kraft, organosolv; milled wood vs. isolated), S/G/H ratio and processing treatment (e.g., esterification, grafting, nanoparticle formation) on performance in waterborne acrylic, polyurethane and bio-based polyester coatings. source structure performance relationships as regards UV-attenuating efficiency, transparency, mechanical performance, barrier properties and lifespan are highlighted. Common issues include aggregation and embrittlement at higher loadings, color penalties, lack of mechanistic understanding, and the use of solvent-intensive, non-scalable pathways. The review concludes with a research agenda on lignin-based coatings, which focuses on comparison of lignin types and mild modifications, optimization of loading and development of multi-functioning industry relevant coatings.