Figure 3.

Schematic figure illustrating length scales of plant biomass, its component polymers, and useful molecules and materials derived from them. Examples of poplar and sorghum (far left) at macroscale have mesoscale features of dense cellular organization in tissues (middle left micrograph, adapted from Ref. 126) and features of lignified secondary walls and compound middle lamellae (middle right micrograph, adapted from Ref. 87). Nanoscale structures comprise the cross-bridging of cellulose microfibrils by hemicelluloses in a co-extensive lignin matrix (adapted from Ref. 126) and cellulose microfibrils. At the molecular scale are several types of hemicelluloses and lignin with representative variations in linkage structure. Polymeric materials isolated from cell walls include cellulose nanocrystals and nanofibers (micrographs; courtesy of P. Ciesielski, National Renewable Energy Laboratory) and hemicelluloses that can then be functionalized with various chemical groups. These can be annealed to cellulose to form functionalized nanocrystals or nanofibers. Glucose and other monosaccharides from cellulose and hemicelluloses, and monolignols from depolymerization of polysaccharides and lignin can be catalytically transformed to a range of intermediates and subsequently deoxygenated using hydrogen to produce monomers for plastics, liquid fuel hydrocarbons and high-value aromatics, flavor compounds, and essential oils. Monomers for plastics include PLA, PHB, polybutylene-succinate (PBS), PET, and polyhydroxyurethane (PHU). Liquid hydrocarbon fuel substrates include paraffins, aromatics, levulinate, furfural, and hydroxymethylfurfural (HMF).