[Chemistry Class Notes] Natural Polymers Pdf for Exam

The biotic world that human beings inhabit is made up of smaller subunits called natural polymers. They are defined against synthetic polymers and are made up of organic molecules or atoms. The living component of the earth’s ecosystem functions in the presence of natural polymers. They are the building blocks on which every living interaction is predicated both in all the five biological kingdoms of the standard taxonomy. Their abundance in the natural world is explained by the very important role they perform in nature. Some of the important natural polymers are cellulose, chiton, carbohydrates, proteins, and nucleic acids.

The word polymer is made of two words poly meaning many and mer meaning unit. Polymers are large units and they are made of repeating units known as monomers. Whereas monomers are simple molecules that undergo polymerization. Polymerization is a process when two or more molecules react and join to form polymers to form a long chain of repeating units called polymers. Monomers can combine in two different ways, direct or indirect. In direct combination, they join together and form long chains and in the indirect combination they join together and release a water molecule. 

Polymers are of two types: natural or synthetic. Synthetic polymers are used in the medical field. Many materials used in the medical field are polymers. They have different properties that make them useful for application of biomaterials. 

Classification

Polymers can be classified on the  basis of different properties and the properties used to classify them include structure, molecular forces, source, mode of polymerization, and growth polymerization. 

1. Classification on the Basis of Source of Polymer

It is further divided into natural, semi-synthetic, and synthetic polymers. 

1. Natural Polymers: Polymers that are obtained from living organisms such as plants and animals. They are found in living beings and they sustain metabolic activities in plants and animals. Natural polymers form components in bodybuilding and maintenance in both kingdoms. They are ubiquitous and found everywhere. For example, cellulose, rubber, etc.

2. Semi-synthetic Polymers: These are derived from cellulose. The fundamental source of semi-synthetic polymers is natural polymers themselves. But they are modified through an artificial chemical treatment to either enhance or reduce certain properties. This human intervention ensures that a particular natural polymer is now better suited to function in the specific role it was destined for.

Examples: cellulose acetate, rayon, nitrocellulose, etc.

3. Synthetic Polymers: The polymers that are obtained from chemical processes and used in our daily lives are called synthetic polymers. They are derived from petrochemical sources like petroleum and oil. Like semi-synthetic polymers, they undergo treatment in order to build desirable properties like durability and flexibility. Thus they exhibit numerous desirable properties.

Example: Vulcanized rubber, nylon, Teflon, polyethylene, etc.

2. Classification on the Basis of the Structure of A Polymer

It is further classified as Linear polymers, branched chain polymers and cross linked or network polymers.

1. Linear Polymers: These are made by using straight and long chains of monomers. For example, polyester, nylon, teflon, etc.

2. Branched Chain Polymers: These are polymers formed by linear polymers when they divide into different branches. For example, polyethylene, glycogen, starch, etc. 

3. Cross-linked or Network Polymers: These polymers are formed by joining two linear polymers through strong covalent bonds.  For example, fiberglass, adhesives, polyester, etc. 

3. Classification on the Basis of Mode of Polymerization

It is further classified into different types such as addition polymers and condensation polymers. 

1. Additional Polymers: These are formed by repeated attachment of unsaturated monomers irrespective of the bond they possess (double or triple).

2. Condensation Polymers: These are formed by condensation reactions between two different monomers and they result in the removal of small molecules such as water, etc. 

4. Classification on the Basis of Molecular Forces

Polymers are used for different purposes depending on their elasticity, tensile strength, etc. The mechanical forces of polymers are determined by hydrogen bonds, ionic bonds, etc. 

On the basis of intermolecular forces, the polymers can be divided into the following types:

1. Elastomers: Elastomers are solids possessing elastic properties. These polymers have low molecular forces between each monomer which helps monomers to stretch easily. For example, polybutadiene, polyisoprene, etc.

2. Fibers: These are made of thread like structures and have high tensile strength. For example, terylene. 

3. Thermoplastic Polymers: These are  linear or branched chain polymers that become soft on heating and hard when cooled. For example, nylon, acrylic, etc. 

4. Thermosetting Polymers: These are highly branched polymers. When these polymers are heated they cannot be reversed back to the original shape and cannot be reused. For example, erasers, balloons, etc. 

5. Classification on the Basis of Growth Polymerization

Addition and condensation polymers are also known as chain growth polymers. 

1. Natural Polymers: Polymers that are obtained from natural things are called natural polymers. They are mainly obtained from plants and animals and human beings. For example, DNA, RNA, glucose, etc. Natural foods are made of natural polymers such as carbohydrates, proteins, etc. The packages in which food is delivered are also made of polymers such as plastic containers, packets, one time use cutlery, etc. 

2. Important Polymers Include: Cellulose, nucleic acids, proteins, carbohydrates, rubber, and chiton. 

3. Cellulose: It is made of long chains of glucose. It is the most natural polymer, found abundantly in plants. They consist of stretched-out fibers, which is a property of cotton plants, allowing them to  become fabric. Cellulose is not dissolved by water and therefore it is used in the manufacturing of paper.

4. Chiton: It is present in the cell wall of parasitic cells. It is found in the external skeleton of crabs, spiders, etc. 

5. Carbohydrates: Polymers formed from glucose. Starch and sugars are a type of carbohydrates which can be  used for energy production by animals and plants. It is known that the Cellulose and carbohydrates are both made of glucose but only the difference is in their structure in which one has  clustered chain and the other has a stretched chain and there is one more  difference that is  carbohydrates are soluble in water and can be easily digested by human beings but cellulose is not digested by human beings because it is not soluble in water.  

6. Proteins: Proteins are made of aminoacids which are organic compounds which contain one carboxylic group, an amine group, and a side chain R which is specific to each amino acid. There are a total of twenty amino acids and two or more amino acids combine together to form different proteins. There are a large number of proteins which are found in feathers, fur, finger/toenails, hair, etc. In animals, wool, silk, and leather are the important fibers that are made of proteins. 

7. DNA and RNA: DNA and RNA are macromolecules and are made of nucleotides. Nucleotides are organic molecules and consist of purines and pyrimidines which are also called nitrogenous bases, ribose sugar in RNA and deoxyribose sugar in DNA and a phosphate group. These polymers are formed due to condensation. 

8. Rubber: Rubber is a polymer of isoprene monomers and it is formed by addition polymerization. It is obtained from latex secreted by rubber trees.

Synthetic Polymers

Synthetic polymers are advantageous as they are very stable. They can also be customized based on the requirements and purpose. 

Example: Plexiglas, styrofoam, nylon, etc.

Synthetic polymers have become a necessity in day to day life. Almost everything that we use is made up of artificial polymers. Being stable is not just an advantage but can be a disadvantage too as it means these polymers cannot be broken down naturally leading to accumulation in the environment resulting in various toxic conditions in the environment. One way to break down or destroy these artificial polymers is by burning them or heating them at very high temperatures but again this is also not an environmental approach as it causes the release of toxic gasses.

Copolymerisation

A variety of monomers react to undergo polymerization to form polymers known as copolymers.

Example: Acrylonitrile – styrene copolymer

Biodegradable Polymers

A large number of polymers due to their strong links are very hard to break and therefore degrade. This causes them to accumulate in the surrounding environment and become toxic and cause an imbalance in nature. To avoid such situations recently new varieties of artificial polymers are being manufactured which can easily be degraded and hence are as much toxic.

Awareness must be spread continuously to avoid the use of non-biodegradable polymers and to use biodegradable materials.

Conclusion

The accumulation of a large quantity of non-biodegradable synthetic and semi-synthetic polymers is posing a huge problem in the human environment. This problem is exacerbated by the fact that several of them require hundreds if not millions of years to break down into their monomeric units. They are often deposited in garbage dumps which cause soil pollution. Likewise, they can not be burnt or deposited in water sources. Plastic is the main representative of this category and human beings are suffering the brunt of overproduction and overuse of plastic in recent days. Similar is the case with other synthetic and semisynthetic polymers which are not organic or biodegradable.

People must be aware of the harmful effects produced by non-biodegradable polymers and they should be encouraged to use more biodegradable substances. In addition to this, synthetic and semisynthetic polymers should be made only after assessing and evaluating their environmental impact. The specific properties of natural polymers that make them degradable should be studied thoroughly and such a sustainable approach should be adopted in the synthetic polymer industry to save the planet from another pollution catastrophe.