Cellulose is a naturally occurring carbohydrate and polymer composed of long, unbranched chains of glucose units. It is a major load-bearing component of plant cell walls and is widely described as Earth’s most abundant biopolymer. Its chains assemble into strong fibrils that reinforce biological tissues and provide the fibrous framework of wood and cotton. Cellulose is also an important industrial raw material for paper, regenerated textile fibers, films, and chemically modified materials. (pubmed.ncbi.nlm.nih.gov)
Discovery and chemical structure
The French chemist Anselme Payen reported the discovery of cellulose in 1838 after investigating the composition of plant material. His work identified a resistant carbohydrate fraction distinct from the substances surrounding it in woody tissues, establishing cellulose as a subject of chemical investigation. (acscell.org)
Cellulose consists of D-glucose residues connected by β(1→4) glycosidic bonds: the linkage joins carbon 1 of one residue to carbon 4 of the next through oxygen. Its conventional repeat-unit formula is (C₆H₁₀O₅)ₙ, where n represents the number of anhydroglucose units. The number of units per chain, or degree of polymerization, varies with biological source and processing; wood cellulose can contain hundreds to many thousands of residues. (pubchem.ncbi.nlm.nih.gov)
Multiple chains associate through hydrogen bonding and van der Waals interactions, forming cellulose microfibrils. These contain ordered crystalline regions together with less ordered structures and surface chains. Their organization influences stiffness, chemical accessibility, and resistance to enzymatic breakdown. Experiments that altered cellulose synthase in plants have demonstrated that changes in microfibril structure can increase the efficiency of conversion into sugars. (pmc.ncbi.nlm.nih.gov)
Occurrence and biological function
Cellulose commonly accounts for approximately 40–50% of dry wood by mass. Scoured and bleached cotton can contain about 99% cellulose. These materials differ not simply in cellulose concentration but also in chain length, crystallinity, and the organization of their fibers. (fpl.fs.usda.gov)
Within the cell wall, cellulose operates as part of a composite containing hemicelluloses, pectins, and other components. Many secondary walls also contain lignin, a chemically distinct polymer. The surrounding substances influence the mechanical properties of the tissue and the accessibility of cellulose to enzymes and processing chemicals. Cellulose should therefore be distinguished from wood itself, which contains several major polymers rather than a single substance. (genomicscience.energy.gov)
Microfibril orientation helps determine how a plant cell expands. Their rigidity restricts expansion differently in different directions, contributing to cell shape and tissue organization. Studies of celery supporting tissues, for example, have measured microfibrils only a few nanometers across and investigated how their internal packing contributes to wall structure. (research.usc.edu.au)
Biosynthesis
Plants manufacture cellulose using membrane-integrated cellulose synthase enzymes. These proteins use uridine diphosphate glucose, an activated sugar donor, to extend the polymer chain. Newly synthesized chains pass through channels in the enzymes’ transmembrane regions and emerge outside the cell membrane, where they associate into fibrils. (pubmed.ncbi.nlm.nih.gov)
In seed plants, synthases assemble into characteristic rosette-shaped complexes. Different combinations of synthase isoforms participate in primary and secondary wall formation. Structural studies support a model in which trimeric synthase units form a larger complex capable of producing an approximately 18-chain microfibril, although cellulose organization varies among organisms and tissues. (elifesciences.org)
Some bacteria also synthesize cellulose. Research comparing bacterial and plant systems has identified conserved features of the enzymatic architecture and chain-production mechanism, despite differences in the organization of their synthesis machinery. (elifesciences.org)
Physical properties and degradation
Purified cellulose is white and odorless, with properties strongly dependent on its physical form. It is insoluble in water and most common solvents, although specialized solvent systems can dissolve it. Water insolubility does not mean that cellulose cannot interact with moisture: cellulose-based materials can absorb water while retaining their polymeric framework. Dissolution, swelling, and chemical degradation are distinct processes. (pubchem.ncbi.nlm.nih.gov)
Cellulose can undergo hydrolysis, which cleaves its glycosidic bonds. Microbial cellulases are enzymes involved in this breakdown. Efficient conversion is difficult because chains are packed into fibrils and are embedded among other wall components. Experiments show that lignin, xylan, and accumulated breakdown products can inhibit cellulase binding or movement along cellulose. (energy.gov)
In human foods, cellulose contributes to dietary fiber because it resists digestion by enzymes produced by humans. This nutritional classification differs from its industrial classification as a fibrous polymer. (ncbi.nlm.nih.gov)
Processing and applications
Papermaking uses cellulose-rich fibers obtained from plant materials. Chemical pulping separates fibers by removing substantial amounts of surrounding wall material. Researchers also develop alternative pulping processes that produce cellulose-rich pulps suitable for subsequent nanocellulose isolation. (fpl.fs.usda.gov)
Wood pulp supplies cellulose for rayon and cellophane. Regenerated fibers are produced by dissolving cellulose and subsequently forming it again as a solid fiber; lyocell uses an amine-oxide solvent process. Chemical modification instead changes the polymer itself: cellulose acetate, for example, contains acetylated hydroxyl groups and is used as a fiber-forming material. (cottonworks.com)
Nanocellulose encompasses cellulose materials with nanoscale dimensions. Research applications include packaging films, coatings, composites, filtration materials, and cement additives. Their development involves controlling fibril dimensions, surface properties, and processing behavior rather than treating all cellulose sources as interchangeable. (research.fs.usda.gov)
Cellulose is also a feedstock for bioethanol. Industrial conversion typically requires pretreatment and enzymatic hydrolysis to release glucose, followed by fermentation into ethanol. The difficulty of making cellulose accessible to enzymes is a major technical constraint in this conversion pathway. (www1.eere.energy.gov)