Studies of the Molecular Interaction Between Cellulose and Lignin as a Model for the Hierarchical Structure of Wood

Wood and dietary fiber products all belong to a class of biomolecular composites that are rich in cellulose and lignin. The interaction between cellulose and lignin determines such properties as mechanical strength (wood); creep, durability and aging; cellulose purity (pulp); and digestibility (nutrients). The understanding of the interaction between cellulose and lignin can be approached from various types of analyses involving the natural biocomposites, or it can be explored by studying the physical mixtures of the two types of macromolecules. The latter can be prepared by mixing the respective polymers in solid, solution or melt form within the constraints of solubility and melt-flowability. Such mixtures have been examined, and the results suggest that cellulose and its derivatives form two distinct phases with lignin and its derivatives; a crystalline polysaccharide-phase and a continuous amorphous phase that provides evidence for strong intermolecular interaction between the two components. In addition, results suggest that lignin and/or its derivatives are capable of contributing to the supermolecular organization of cellulose (derivatives). The interaction between lignin and cellulose varies in relation to chemical differences as well as molecular parameters. The results are consistent with the view that the hierarchical structure of the natural biocomposite wood is not only the consequence of a sequence of biochemical events, but that it is the result of various thermodynamic driving forces that are independent of the biosynthetic origin.