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Cellulose

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Cellulose is a vital organic compound found throughout the natural world. It is the most abundant organic polymer on Earth.

Cellulose spacefilling model
Cellulose spacefilling model

Chemically, it is a polysaccharide with the formula (C6H10O5)n. This formula tells us that cellulose is a long chain made of many repeating units. These units are known as D-glucose. Cellulose serves as a primary structural component for many organisms. It builds the cell walls of green plants, various algae, and oomycetes. Some bacteria even secrete it to create biofilms.

Leaf 1 web
Leaf 1 web

The structure of cellulose is what gives it such incredible strength. Each D-glucose unit connects to the next through a β(1→4)-glycosidic bond. This specific linkage creates a straight, unbranched chain. This is very different from starch, which coils or branches. Because of this, cellulose molecules take on a stiff, rod-like shape. These rods sit side-by-side and form hydrogen bonds with one another.

Cellulose strand
Cellulose strand

These bonds hold the chains together into bundles called microfibrils. In plant stems and wood, these microfibrils are meshed into a matrix. You can think of this like reinforcement bars in concrete. In this analogy, the cellulose fibers are the bars, and the lignin is the hardened cement holding them together.

Plant cell wall diagram-en
Plant cell wall diagram-en

Scientists have identified several distinct types of cellulose. These types are categorized by how the hydrogen bonds are arranged. Natural cellulose is known as cellulose I, which includes two structures called Iα and Iβ. Bacteria and algae often produce cellulose enriched in the Iα form. Higher plants mostly consist of the Iβ form. When cellulose is processed into fibers, it becomes cellulose II, also called regenerated cellulose. The change from cellulose I to cellulose II is irreversible. This suggests that cellulose I is metastable, while cellulose II is more stable.

The history of cellulose research spans nearly two centuries. In 1838, the French chemist Anselme Payen isolated it from plants. He was the first to determine its chemical formula. In 1870, the Hyatt Manufacturing Company used it to create celluloid. This was the first successful thermoplastic polymer. The late 1800s and early 1900s saw many more inventions. Rayon production began in the 1890s, and cellophane was invented in 1912. In 1920, Hermann Staudinger discovered the actual polymer structure. Finally, in 1992, Kobayashi and Shoda achieved the first chemical synthesis of cellulose without using biological enzymes.

Cellulose is found in massive quantities in many common materials. Cotton fiber is composed of 90% cellulose. Wood contains between 40% and 50% cellulose. Dried hemp contains approximately 57% cellulose. These high concentrations make cellulose a primary source for industrial products. Most paper and paperboard are produced from cellulose. It is also used to make cellophane and rayon. Today, researchers are even developing ways to turn energy crops into biofuels, such as cellulosic ethanol.

Cotton
Cotton

In living organisms, cellulose is built through a complex biological process. In plants, this happens at the plasma membrane using rosette terminal complexes, or RTCs. These are protein structures about 25 nm in diameter. They contain enzymes called cellulose synthases that "spin" microfibrils into the cell wall. These enzymes use UDP-glucose to build the chains.

Cellulose Struktur in Sesselform
Cellulose Struktur in Sesselform

While most mammals cannot digest cellulose, some animals can. Ruminants like cows and sheep have symbiotic microorganisms in their guts. These microbes produce enzymes called cellulases to break the cellulose down. Termites also use similar methods with protozoa or bacteria in their digestive tracts.

Cellulose also reacts to extreme heat through a process called thermolysis. When heated above 350 °C, it decomposes into char, vapors, and gases like carbon dioxide. If heated to 500 °C, it produces a maximum yield of vapors that condense into a liquid called bio-oil. During this process, the cellulose goes through a very fast transition from solid to liquid to vapor. This chemical breakdown is known as hydrolysis. In the human body, cellulose acts as an insoluble dietary fiber. It is hydrophilic, meaning it attracts water. This helps it act as a bulking agent to aid in digestion.

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🖼️ Images & Media (11)
File:X mark.svg
X mark.svg
File:NFPA 704.svg
NFPA 704.svg
File:Plant cell wall diagram-en.svg
Plant cell wall diagram-en.svg
File:Cellulose strand.svg
Cellulose strand.svg
File:Cellulose Struktur in Sesselform.svg
Cellulose Struktur in Sesselform.svg
File:Салфетка универсальная губчатая (вид сбоку).jpg
Салфетка универсальная губчатая (вид сбоку).jpg
File:Cotton.JPG
Cotton.JPG
File:Cellulose-Ibeta-from-xtal-2002-3D-balls.png
Cellulose-Ibeta-from-xtal-2002-3D-balls.png
File:Karl Johanssvamp, Iduns kokbok.png
Karl Johanssvamp, Iduns kokbok.png
File:Cellulose spacefilling model.jpg
Cellulose spacefilling model.jpg
File:Leaf 1 web.jpg
Leaf 1 web.jpg
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