Cellulose (C₆H₁₀O₅)ₙ

What is Cellulose?

Cellulose is an organic compound, with the chemical formula as, (C6H10O5)n. It is a polysaccharide, which contains a linear chain of many hundred to many thousands of β(1→ 4) units of the linked D-glucose. It is also an essential structural component of the primary cell wall of the green plants, various algae forms, and the oomycetes. A few bacteria species secrete it to form biofilms.

Cellulose is also the Earth's most abundant organic polymer. Cellulose content of the cotton fiber is 90%, that of dried hemp is approximately 57%, where that of wood is 40-50%.

Cellulose Applications Explained

Cellulose is primarily used to produce paper and paperboard. The smaller quantities of Cellulose are converted into a wide variety of derivative products such as Rayon and cellophane. Conversion of Cellulose from the energy crops into biofuels like cellulosic ethanol is under development as a renewable fuel source. Industrially, Cellulose used is mainly obtained from Cotton and wood pulp.

Some of the animals, particularly termites, ruminants, can digest the Cellulose taking the help of symbiotic microorganisms, live in their guts, like Trichonympha. Cellulose is a non-digestible constituent of insoluble dietary fiber in human nutrition, which works as a hydrophilic bulking agent for the feces and to aid potentially in defecation.

Properties of Cellulose

Most of the properties of Cellulose depend upon the chain length or degree of polymerization, and the glucose molecules count constituting the polymer molecule. It is insoluble in most of the organic solvents, water, and it is odorless, biodegradable, and chiral.

Let us look at the physical and chemical properties of Cellulose as tabulated below:

Cellulose Structure

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At high temperatures, it can be broken down into glucose by treatment with concentrated minerals acids. When compared to starch, it is more crystalline. Starch goes from crystalline to amorphous transition in 60-70 degrees, whereas Cellulose requires 320 degrees and a pressure of 25 Megapascal.

Processing of Cellulose

Processing of Cellulose can be achieved using various methods; where some of them are listed below.

Breakdown - Cellulolysis

It is defined as the process of breaking down the Cellulose molecules into further smaller polysaccharides, known as cellodextrins or completely into the glucose units. This is known as a hydrolysis reaction. Because the cellulose molecules strongly bind each other, the process of cellulolysis is relatively difficult to that of the breakdown of other polysaccharides. However, this process can be intensified significantly in the proper solvent. For example, in an ionic liquid.

Most mammals contain a limited ability to digest dietary fiber like Cellulose. A few ruminants such as sheep and cows contain certain symbiotic anaerobic bacteria (such as Ruminococcus and Cellulomonas) in the flora of the rumen, and these bacteria produce enzymes called cellulases, which hydrolyze Cellulose. Then, the breakdown products are used by the bacteria for proliferation. 

Later, the bacterial mass is digested by the ruminant in its digestive system (small intestine and stomach). Horses also use this Cellulose in their diet by fermentation in their hindgut. Some termites contain in the hindguts of certain flagellate protozoa cellulose producing such enzymes, whereas the others can produce cellulase or contain bacteria.

The enzymes that are used to cleave the glycosidic linkage in Cellulose are the glycoside hydrolases, including exo-acting glucosidases and endo-acting cellulases. Usually, such enzymes are secreted as a part of multienzyme complexes that may include carbohydrate-binding doctrines and modules.

Breakdown - Thermolysis

At temperatures falling above 350 °C, the Cellulose undergoes thermolysis (otherwise called 'pyrolysis'), decomposing into a vapor, solid char, aerosols, and also gases such as carbon dioxide. The maximum yield of vapors that condense to a liquid known as bio-oil obtains at 500 °C.

The semi-crystalline cellulose polymers react at pyrolysis temperatures (350 - 600°C) in some seconds; this transformation has been shown to occur through a solid-to-liquid-to-vapor transition, including the liquid (known as molten Cellulose or intermediate liquid Cellulose) existing for only one fraction of a second. The glycosidic bond cleavage produces a short cellulose chains that ranges from two-to-seven monomers comprising the melt. The vapor bubbling of intermediate liquid cellulose forms aerosols, consist of the short chain anhydro-oligomers that are derived from the melt.

Also, continuing decomposition of molten Cellulose produces volatile compounds, including furans, light oxygenates, levoglucosan, pyrans, and gases through the primary reactions. Within the thick cellulose samples, the volatile compounds like levoglucosan undergo into the 'secondary reactions' to the volatile products, including the light oxygenates - glycolaldehyde and the pyrans.

Commercial Application of Cellulose

Industrially, Cellulose used is mainly obtained from the Cotton and wood pulp.

• Fibers 

Cellulose is the primary ingredient of textiles. Synthetics (nylons) and Cotton each have about 40% market by volume. Other plant fibers such as sisal, jute, hemp represent about 20% of the market. Whereas the cellophane, Rayon, and other "regenerated cellulose fibers" have a small portion (5%).

• Paper Products  

Cellulose is also the primary constituent of paperboard, paper, and card stock.

• Electrical Insulation Paper  

Cellulose can be used in diverse forms as insulation in cables, transformers, and other electrical equipment.