Lignin's structure

Structure of lignin powder

Lignin is a complex phenolic polymer formed by three alcohol monomers (p-coumarin, coniferol and mustard alcohol).

Lignin is one of the components of plant cell wall, which has the function of connecting cells. Lignin is a kind of polycyclic polymer organic matter containing many negative groups, which has strong affinity for high valence metal ions in soil.

Due to different monomers, lignin can be divided into three types: syringyl lignin (s-lignin) polymerized from syringyl propane structural monomer, guaiacyl lignin (g-lignin) polymerized from healing wood propane structural monomer and para hydroxyphenyl lignin (h-lignin) polymerized from p-hydroxyphenylpropane structural monomer; Gymnosperms mainly contain guaiacyl lignin (g), dicotyledons mainly contain guaiacyl syringyl lignin (G-S), and monocotyledons mainly contain guaiacyl syringyl p-hydroxyphenyl lignin (g-s-h). From the botanical point of view, lignin is a substance that surrounds the fiber bundle cells and thick walled cells such as tracheids, ducts and wood fibers, and makes these cells have a specific color reaction (add a drop of phloroglucinol solution, wait for a moment, and then add a drop of hydrochloric acid to show red); From a chemical point of view, lignin is a polymer randomly polymerized by highly substituted phenylpropane units. It forms the main component of plant skeleton together with cellulose and hemicellulose, which is second only to cellulose in quantity. Lignin is filled in the cellulose framework to enhance the mechanical strength of plants, which is conducive to the water transport of tissues and resist the invasion of adverse external environment.

Lignin is abundant in hard tissues such as wood, but rarely in vegetables. It is generally found in the seed parts of beans, wheat bran, cocoa, strawberries and raspberries. Its most important function is to adsorb bile acids, the main component of bile, and exclude them from the body.

In addition, although the details are not known, the structure of lignin is very similar to polyphenols. Therefore, lignin and polyphenols should have a close relationship. In short, both have good effects on the body.

Due to the existence of aromatic, phenolic hydroxyl, alcohol hydroxyl, carbon based conjugate double bond and other active groups in the molecular structure of lignin, it can carry out many chemical reactions such as oxidation, reduction, hydrolysis, alcoholysis, acid hydrolysis, methoxy, carboxyl, photolysis, phthalylation, sulfonation, alkylation, halogenation, nitration, polycondensation or graft copolymerization. Among them, oxidation, phthalylation, sulfonation, polycondensation and graft copolymerization play a particularly important role in the study of the application of lignin, and it is also an important way to expand its application. In this process, sulfonation reaction is the basis and premise of lignin application. So far, the application of lignin is mostly used in the form of lignin sulfonate. In the process of pulp production by sulfite method, it is precisely because the sulfite solution has a sulfonation reaction with the original lignin in the wood powder, the sulfonic acid group is introduced to increase the hydrophilicity, and then the lignosulfonate is further hydrolyzed in the acidic cooking solution to depolymerize the hemicellulose combined with lignin, so as to dissolve the lignosulfonate and realize the separation of lignin, cellulose and hemicellulose, At the same time, it also makes the application of lignin possible.