Natural Polymers

Natural Polymers - Cellulose, Chiton, Carbohydrates, Proteins and Nucleic acids

The word polymer is derived from two Greek words; poly means “many” and mer meaning “unit”. Polymers are large molecules made up of alike repeating blocks known as monomers. Whereas monomers are simple molecules which undergo polymerization (a phenomenon in which two or more molecules chemically react to combine and form polymers) in order to form a long chain of repeating units, polymers. Monomers bind in two different ways, direct and indirect. In the case of direct connection, they link together forming long chains and in the second kind, the linking results in liberation of a water molecule. Polymers can be natural or synthetic. Synthetic polymers are well-used in the medical department. A number of materials used in medicine contain polymers. They have many properties and this makes them very useful in the application for biomaterials. 







Polymers are classified based on different properties and they include source, structure, mode of polymerization, molecular forces and growth polymerization.

  • 1) Classification based on the source of polymer

  • Here, it is again subdivided into

    a) Natural polymers
    b) Semi-synthetic
    c) Synthetic

    a)Natural Polymers

    Polymers found in living organisms (only plant and animals)
    Example: rubber, cellulose, etc.

    b) Semi-synthetic Polymers

    Derivatives of cellulose are semi-synthetic polymers.
    Example: rayon

    c) Synthetic polymers

    Polymers used in daily life such as plastics, etc.

    2) Classification based on the structure of a polymer


    This is further divided into:

    a)Linear polymers
    b)Branched-chain polymers
    c) Cross-linked or network polymers

    a) Linear polymers
    Polymers made up of a straight and long chain of monomeric units.
    Example: Teflon, nylon, polyester, polyvinyl chloride, etc.

    b) Branched-chain polymers
    Linear polymers branch out in-between to form branched chain polymers.
    Example: glycogen, starch, low-density polyethylene, etc.

    c) Cross-linked or network polymers
    These polymers are formed by strong covalent bonds between different linear polymer chains.
    Example: polyester fiberglass, polyurethanes, adhesives, vulcanized rubber, etc.

    3) Classification based on the mode of polymerization


    This is further divided into:

    a) Addition polymers
    b) Condensation polymers

    a) Addition polymers
    These polymers are formed as a result of repeated attachment of unsaturated monomers irrespective of the bond they possess (double or triple).
    Example:

    b) Condensation polymers
    These polymers are formed due to the condensation reactions between two different monomers, resulting in the removal of small molecules such as water, etc.

    4) Classification based on molecular forces


    Polymers have different applications based on their mechanical properties such as elasticity, tensile strength, etc.

    These mechanical properties are monitored by forces such as hydrogen bonds, ionic forces, etc.

    Based on how strong the intermolecular forces, they can be further divided into:

  • 1. Elastomers- These are elastic property possessing solids. In these polymers, molecular forces between each monomer are very low which allows such polymers to be stretched.

  • Example: polyisoprene, polybutadiene, etc.

          2. Fibers- These are solids made up of a thread like structures. They have high tensile strength.
    Example: Terylene

           3. Thermoplastic polymers- Linear or branched-chain polymers that soften on heating and harden on cooling.
    Example: Acrylic, nylon, etc.

           4. Thermosetting polymers- Heavily branched polymers which when heated results in change and are irreversibly hardened and cannot be reused.

    Example: erasers, balloons, etc.

    5) Classification based on growth polymerization


    Addition and condensation polymers are also referred to as chain growth polymers.

    Natural Polymers


    Polymers that are naturally obtained or extracted from nature (living organisms) are referred to as natural polymers. They are present abundantly in plants, animals and human beings. Natural polymers include proteins, DNA, RNA, starch, glycogen, etc. When having takeaway food, the food is made up of several natural polymers, it can be proteins carbohydrates, etc. The packaging of the food that was delivered such as the packet, plastic containers, one-time use cutlery is also made up of several different polymers.

    The most important natural polymers are:


    1. Cellulose
    2. Chiton
    3. Carbohydrates
    4. Proteins
    5. Nucleic acids
    6. Rubber

  • 1) Cellulose- It is made up of long strands of glucose. It the most natural polymer, found abundantly in plants. The consist of stretched out fibers, which is a property of cotton plant, allowing it to be turned into a fabric. Water does not dissolve cellulose and hence why it is a key ingredient in paper manufacture.




  • Chiton- It is found in the cell wall of most parasitic cells. It is found on the External skeleton of spider, crab, etc.





  • 2) Carbohydrates- Polymers formed from glucose. Both sugars and starch are a form of carbohydrates and provide energy to plants and animals. Although both cellulose and carbohydrates are made up of glucose, they are structurally very different. One is a clustered chain while the other is a stretched chain. One significant difference is that carbohydrates are water soluble and are easily digested by human beings whereas cellulose is not digested as it is water-insoluble and humans lack the enzymes that breakdown cellulose into simpler molecules.



  • 3) Proteins- Proteins are polymers whose monomers are amino acids. Amino acids are organic compounds made of a carboxylic group, an amine group, and a side chain R which is specific for each amino acid. There are a total of only twenty amino acids. The different interaction between two or more amino acids produces a variety of proteins. Hence why even though there are only twenty amino acids, there are a huge number of proteins. Hair, fur, finger/toenails, feathers, etc fall under the category of protein polymers. In the case of animals, animal fiber such as wool, silk (strongest animal fiber) and leather made from animal fiber are all protein polymers.



  • 4) DNA and RNA- Nucleic acids, DNA and RNA are macromolecules made up of nucleotide which are organic molecules chiefly consisting of purines or pyrimidines also called nitrogenous bases, ribose sugar in case of RNA and deoxyribose sugar in case of DNA and a phosphate group. These polymers are formed as a result of condensation.





  • 5) Rubber- Natural rubber is formed from the addition polymerization of isoprene monomers. It possesses elastic properties and hence is also called an elastomer. It is obtained from rubber latex secreted by rubber tree which is richly cultivated in the Kerala state of India.





  • 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 gases.

    Copolymerisation


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

    Example: Acrylonitrile - styrene copolymer

    Biodegradable of polymers


    A large number of polymers due to their strong links are very hard to break and therefore be degraded. 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.