Unravelling the impact of lignin particle size and content on enhanced value in plastic composites

The shift towards a sustainable plastics economy is driving interest in agricultural waste and byproducts for plastic composites, offering benefits like enhanced sustainability, reduced costs, and improved mechanical properties. Lignin, one of the three main components of lignocellulosic biomass, is a promising filler for polymer composites due to its abundance, reactivity, and functional properties, despite challenges in extraction and processing. This review examines the impact of lignin particle size reduction, from microparticles (LMPs) to nanoparticles (LNPs), on the properties of polymer composites, focusing on poly(lactic acid) (PLA) and other polyesters. Reducing lignin particle size can enhance stress transfer and particle wetting in the matrix, although optimal size thresholds and filler contents for desired properties remain uncertain. The paper discusses lignin's characteristics based on source and size reduction method, its functionalization for better dispersion, and various preparation methods of lignin-containing composites. Applications in packaging and are agriculture are highlighted, with an emphasis on achieving a balance between improved properties, cost efficiency, and environmental impact. Finally, it highlights the need for standardized reporting on lignin’s origin, isolation method, molecular weight, T g , and particle size to enable effective comparisons and advancements in lignin-based polymer composites. • Lignin nanoparticles improve mechanical properties in polymer composites. • Particle size reduction enhances lignin dispersion and stress transfer in composites. • LNPs show promise in scalable, sustainable production for packaging and agriculture. • Continuous production methods improve LNP scalability and performance. • Standardized reporting on lignin’s properties is needed for effective comparisons.