Harnessing plant lignin for sustainable materials and chemicals: integrating biosynthesis, structural diversity, and circular bioeconomy perspectives

Lignin is the most abundant renewable source of aromatic carbon on Earth and a central yet historically underutilized component of lignocellulosic biomass. Its complex and heterogeneous molecular architecture has long constrained efficient and selective conversion into value-added products, despite its high aromatic carbon content and chemical functionality. Recent advances in lignin extraction, fractionation, modification, and application-driven design have substantially expanded the range of achievable material and chemical performance within circular bioeconomy frameworks. This review provides a comprehensive and critically integrated assessment of lignin valorization that explicitly links plant biosynthesis and structural diversity to industrial convertibility, functional materials development, and sustainability performance. Green extraction technologies-including deep eutectic solvent and hydrotropic systems-are evaluated with respect to lignin structural quality, energy demand, solvent recovery, and downstream compatibility. Targeted chemical and enzymatic modification strategies enabling more reproducible lignin streams are discussed alongside applications in carbon fibers, nanomaterials, adhesives, bioplastics, cementitious systems, and additive manufacturing. Quantitative benchmarking against fossil-based incumbents identifies application domains where lignin-derived materials already achieve comparable performance, as well as areas where intrinsic structural limitations remain. In parallel, catalytic depolymerization pathways toward renewable aromatic chemicals are assessed from both mechanistic and systems-level perspectives. Environmental and economic implications are critically examined using recent life-cycle and techno-economic evidence, highlighting the influence of allocation choices, energy integration, and comparison with lignin incineration for energy recovery. Overall, this review clarifies how application-targeted lignin design and system-level sustainability assessment are essential for translating lignin's biological complexity into scalable, competitive solutions for sustainable materials and chemicals.