Cellulose is the most abundant biopolymer on earth. It can be obtained from a lot of plant resources and derived biomass: wood, plants (such as cotton, ramie, sisal, potato tubers, and sugar cane), sea animals (such as tunicates), algae, and bacteria. The interest in this material is given by the fact that it is renewable, sustainable, and biodegradable; these three characteristics are of great interest in recent years to replace materials deriving from fossil fuels. Cellulose is a linear long-chain polysaccharide made up of two anhydroglucose rings linked together with oxygen covalent bond as repeating unit. The structure of cellulose is hierarchical: cellulose molecules align to form microfibrils, which have both crystalline and non-crystalline regions that merge together, and the cellulose microfibrils themselves are aligned and bound together into macrofibrils (or fibril aggregates) by a matrix of hemicellulose and either pectin or lignin.