Lignin

Lignin is deposited by woody plants for the purpose of providing the growing plant with mechanical support, of sealing a water conducting system which links roots with leaves (needles),1–3 and for protecting wood against degradation by weathering4 and biodegradation.5 Lignified plants contain between 20 and 30% lignin, depending on species, age, juvenile vs. mature wood, sapwood vs. hardwood, and normal vs. reaction wood.1,6 The 20–30% lignin content by weight corresponds to approximately 35–45% by energy content since lignin is the polymeric cell wall component with the highest energy content, consisting of more than 60% carbon and around 30% oxygen. This is contrasted by hemicellulose and cellulose with carbon contents of less than 50% and oxygen contents of nearly 50%.7