What is the Basic Unit of Cellulose?

The basic unit of cellulose--the tough, fibrous organic compound that gives structure and tensile strength to wood and plant fibers like cotton--is the simple sugar, glucose. Glucose is the same sugar that comprises starch in our food, and also glycogen, the carbohydrate energy that is stored in our bodies. What makes cellulose molecules different from other carbohydrates is not the components of the molecules, but the way they're arranged and held together.

History

We've been using cellulose to solve problems ever since we began using wood to build structures and plant fibers to weave cloth. But more modern incarnations of cellulose were born from an understanding of the cellulose molecule. The chemical structure of cellulose was first determined by Anselme Payen in 1838. In 1920 Hermann Staudinger expanded on that discovery by determining the polymer structure of cellulose. More recently, Shiro Kobyashi and Shin-ichiro Shoda developed a way to synthesize cellulose without biological enzymes. From 1938 to the present, industry has provided us with ingenious cellulose products including celluloid photographic media, cellophane wrapping, paper products, food fillers and rayon fabrics.

Identification

Cellulose is a polysaccharides polymer. Each cellulose molecule is made up of multiple glucose molecules, also called mono saccharides. Each glucose is composed of 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. The atoms of glucose molecule are held together by covalent bonds. Cellulose occurs naturally in plant cell walls which provide plants with shape and rigidity for vertical growth. Some bacteria also produce cellulose.

Function

A cellulose molecule may be made up of hundreds or several thousand glucose units. Glucose units in a cellulose molecule are arranged linearly so that adjacent glucose units share an oxygen atom. The linear shape of the cellulose polysaccharides is also dependent upon hydrogen bonds between hydrogen atoms and oxygen atoms within the cellulose molecule. Cellulose molecules are also bound to one another, in parallel fashion, by hydrogen bonds. Hydrogen bonds are not as strong as covalent bonds that bind the atoms of a molecule, but they are strong enough to give cohesiveness to cellulose fibers.

Significance

Up to 36 cellulose molecules may be bound together, forming a unit called a microfibril. The length of the polysaccharide chains in a microfibril determines its tensile strength. The shorter cellulose molecules of wood pulp, made up of 300 to 1700 glucose units, are not as strong as other plant fibers like cotton, hemp or flax which are made of 800 to 10,000 glucose units. So wood pulp is used to make relatively perishable products like paper and cardboard, while more durable products like fabric and rope are made from plant fibers like cotton, hemp or flax.

Potential

Wood pulp cellulose is not good for making fabrics because of its relatively short polysaccharide chains. Additionally, wood pulp contains non-cellulose polysaccharides that include hemi-cellulose and ligning, also composed primarily of glucose. But these lack the strength of cellulose and further inhibit the tensile performance of wood pulp. In a process called cellulose fiber regeneration, non-cellulose polysaccharides are removed. Then the cellulose molecules are broken down chemically, and reassembled as longer cellulose molecules better suited for making fabric. Cellulose fiber regeneration is the process used to make rayon.

Resources

• Carbohydrates -- Cellulose
• Regenerated Cellulose Fabrics: Facts Behind the Fibers