What is Lignin?
Lignin is the fiber in our food, the thing that makes vegetables crunchy and firm. It is a polymer found extensively in the cell walls of all woody plants, Lignin, one of the most abundant natural polymers, constitutes one-fourth to one-third of the total dry weight of trees. It combines with hemicellulose materials to help bind the cells together and direct water flow. Lignin is formed by removal of water from sugars to create aromatic structures. These reactions are not reversible. Lignin resists attack by most microorganisms, and anaerobic processes tend not to attack the aromatic rings at all. Aerobic breakdown of lignin is slow and may take many days. Lignin is nature's cement along with hemicellulose to exploit the strength of cellulose while conferring flexibility.
Several methods have been devised for isolating lignin from wood. Some isolation methods are based on acid treatments in which the carbohydrate components (cellulose and hemicelluloses) are hydrolyzed to water-soluble materials. However, with such procedures, serious doubts exist as to whether the isolated lignin is representative of the “native” lignin. Enzymatic digestion of the carbohydrate in wood meal is a lengthy, tedious procedure but offers the greatest promise of leaving lignin unaltered during isolation.
When extracted from timber and plant products, lignin can be included in a wide variety of things. It can be used as an emulsifying, sequestering, binding, or dispersal agent, depending on how it is processed and what it is used with, appearing in everything from paints to treatments for roadways. Many paper mills and lumber processing facilities view lignin as a valuable byproduct of their industrial processes, selling extracted lignin to other industries.
When producing Cellulosic ethanol lignin has to be dissolved, a very hard process.