Ligniny

Ligniny, known in English as lignin, is a class of complex phenolic polymers that form a major component of the secondary cell walls of vascular plants. They are synthesized from monolignol precursors—p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol—through oxidative coupling to produce a heterogeneous network containing H, G, and S units. The resulting polymer is highly cross-linked, largely hydrophobic, and resistant to enzymatic and microbial degradation, contributing to the rigidity and water-impermeability of plant tissues.

In plants, lignin fills the spaces between cellulose and hemicellulose in the cell wall, providing mechanical strength, compressive resistance, and protection against pathogens. It also constrains the digestibility of plant biomass, influencing the efficiency of processes that convert lignocellulose to fuels or chemicals. Lignin biosynthesis occurs via the phenylpropanoid pathway in specialized cells such as fibers and vessels, with polymerization driven by peroxidases and laccases in the cell wall.

Lignin is ubiquitous in wood and bark and represents one of the most abundant natural polymers on Earth. Its relative abundance and complex structure make it a major contributor to carbon storage in ecosystems and a significant source of recalcitrance in biomass processing. Industrially, lignin is a byproduct of chemical pulping and biorefineries, forming kraft lignin, lignosulfonates, and related streams. Ongoing research focuses on lignin valorization, aiming to convert it into value-added chemicals, materials like carbon fibers, and sustainable derivatives such as vanillin.