Cell walls are biologically encoded nanocomposites of interwoven polymers—polysaccharides (pectins, cellulose, and hemicelluloses), proteins and lignin—that surround plant cells. These polymers are the targets of bioenergy research because their hydrolysis is needed to release free sugars to produce bioethanol. We already know what covalent crosslinks are within polysaccharides of the walls of key bioenergy grasses (e.g., sugarcane, maize, and miscanthus), so that we can choose most of the enzymes necessary to break them. However, besides covalent linkages, the way these polymers are assembled through weak linkages in plant cell walls holds another important barrier for production of bioethanol. Such chemical forces within the walls include hydrogen bonds between cellullose molecules and within microfibrils, between cellulose and hemicelluloses and, the interaction of pectins with divalent ions. This chapter reviews how those interactions act as barriers to biomass pretreatment and hydrolysis, thus affecting the improvement of bioethanol production from sugarcane.
