5 Natural Polymers
Polymers are considered as giant molecules which are composed of a large number of small parts. These small parts are known as monomers which are bonded with each other through covalent bonds.
Overall polymers are composed of a large number of monomer units which are bonded together with some chemical bonds. It can be synthesised by chemical reactions or can be found naturally also.
On the basis of origin; polymers can be classified as synthetic and natural polymer.
Synthetic polymers are synthesised with the reaction of monomer units. Either the monomer unit must contain multiple bonds or there must be some functional group in the monomer units which results the formation of polymers.
If there are multiple bonds in the monomer unit; they combine through addition reactions to form a polymer. The formation of polymer from monomer units is known as polymerisation and such type of polymerisation is called as addition polymerisation.
On the contrary; the polymerisation through condensation reaction between monomer units is known as condensation polymerisation which is associated with the elimination of small molecules such as water, carbon dioxide or hydrogen gas.
For example; the polymerisation reaction between amino acids leads to the formation of polypeptide chain with the elimination of water molecule. Here the condensation reaction takes place between amino group of one amino acid and carboxy group of another molecule.
It results the formation of amide linkage between two amino acid molecules.The naturally occurring polymers can also classify in both types. Proteins, nucleic acids are best example of natural polymers.
Similarly cellulose is also a natural polymer which acts as main structural component of plants. Usually natural polymers are composed by condensation polymerisation with the elimination of water molecule. Starch is another example of such type of polymer which is formed by the condensation polymerisation of a large number of glucose molecules.
Therefore the hydrolysis of starch molecules leads to formation of glucose molecules again.This polymer is a major part of food group; carbohydrates and is also found in potatoes and grains. It is commonly known as poly-saccharide, as it is a polymer of monosaccharide units.
It is composed of two type of units; amylose and amylopectin.
Amylose is a straight chain polymer which contains around 200 glucose units while amylopectin molecule is composed of 1,000 glucose units but in branched manner.
The complete hydrolysis of amylopectin results the formation of glucose while the partial hydrolysis forms dextrins.
Dextrins are major components of food additives,mucilage, paste, paper and fabrics.The energy preserver in animals is also a natural polymer which is known as glycogen.
The structure of it is quite similar to amylopectin unit of starch. It is mainly stored in skeletal muscles and liver.
Cotton or cellulose is another example of natural polymer which forms the most abundant organic compound on Earth. It is also involved in the formation of woody parts of plants and also acts as supporting material in pants. It is also a polymer of glucose monomers but shows difference in the bonding of monomer units compare to amylose.
Chitin is another poly-saccharide which is mainly found in the exoskeletons of crustaceans.