Dual role of lignin in waterborne polymer composites: Reinforcement and stimuli-triggered degradation

Improving the sustainability of polymer composites is a pressing priority, particularly in reducing reliance on fossil-derived components and minimizing environmental impact during synthesis. Lignin, an abundant and renewable natural polymer, offers significant potential as a bio-based additive due to its aromatic structure and intrinsic functionality. Conventional methods for incorporating lignin into polymer matrices often rely on non-sustainable, solvent-based routes, leading to poor dispersion and aggregate formation due to lignin’s incompatibility with polymers. This study presents a more sustainable approach using waterborne, in-situ semicontinuous miniemulsion polymerization to integrate lignin (0.5–1 wt%) into (meth)acrylic matrices. The resulting composite films, formed via water evaporation, exhibited enhanced UV and visible light absorption, improved mechanical strength, particularly at 1 wt% lignin and increased thermal stability even at low loadings. Despite lignin’s hydrophilicity, the composites demonstrated reduced water permeability. UV degradation studies showed that lignin’s chromophoric groups generate free radicals under UV exposure, triggering controlled photodegradation of both lignin and polymer phases. This controlled breakdown combined with the composite’s enhanced structural integrity highlights lignin’s dual function: reinforcing the material under standard conditions while enabling degradation under specific environmental stimuli.