Polymers

Polymer is a large, long, chainlike molecule formed by the chemical linking of many smaller molecules. The small molecular building units are called monomers. Monomers are joined into chains by a process of repeated linking known as polymerization. A polymer may consist of thousands of monomers. Some polymers occur naturally. Others are synthetic. Many common and useful substances are polymers. For example, starch and wool are naturally occuring polymers. Starch is formed by plants from a simple sugar called glucose and wool is a variety of protein. Other examples of natural polymers are cellulose and silk. Proteins, DNA, Starch and Cellulose are the polymers found in living organisms and they are called Biopolymers. Nylon and polyethylene, a tough plastic material are synthetic polymers. Rayon, Teflon, Orlon, Polyester etc are other examples for man made polymers or synthetic polymers. Rayon is known as artificial silk and is used in carpets, tyre code, surgical dressings, fabrics etc. Teflon is a polymer used to coat the inside of nonstick kitchenware. The monomer of teflon is Tetrofluoroethylene. Rubber, another polymer, occurs naturally and is also made synthetically. The basic nature of Fiber, Plastic and Rubber is Polymer. Fibers are polymers suitable for making strong yarns. Whereas, Plastics are polymers that can be molded into various shapes and Rubber is a polymer that has elastic properties.

Polymerization

Polymerization is a chemical process important in the production of plastics, artificial fibres, synthetic rubber and paints. In this process, many small molecules called monomers combine to build much larger molecules called polymers. The process is known as homopolymerization if only one type of monomer is utilized. Copolymerization is the process of using many types of monomers. The solid plastic known as vinyl, or polyvinyl chloride, is created when the gas vinyl chloride is homopolymerized. The plastic used to wrap food is made by copolymerizing vinyl chloride with vinylidene chloride. Chemists also classify polymerization processes by the chemical reactions that occur.

Polymers and Monomers

1. Polyvinyl Chloride (PVC) - Vinyl Chloride

2. Polyvinyl Acetate (PVA) - Vinyl Acetate

3. Polythene - Ethene

4. Bakelite - Phenol and Formaldehyde

5. Polystyrene - Styrene

Types of Polymers

There are three types of polymers, namely, natural, semi-synthetic and synthetic polymers.

I. Natural Polymers

Both plants and animals contain them naturally. For instance, starch, cellulose, silk, rubber and wool. In addition, we have biopolymers, which are biodegradable polymers. Proteins, DNA, starch and cellulose are Biopolymers.

1. Starch

Starch is formed by plants from a simple sugar called glucose.

2. Cellulose

Cellulose is a substance that forms a major part of the cell walls of trees, grasses, vegetables and many other plants. Cellulose is a carbohydrate-that is, a substance composed of carbon, hydrogen and oxygen. All fruits and vegetables contain cellulose. Cellulose makes up an important part of many family products. Industries use strong acids and alkalis to modify the properties of cellulose for various purposes. For example, textile manufacturers strengthen cotton fibers by treating with an alkaline solution such as caustic soda.

3. Silk

Silk is a strong, shiny fibre that is used to make cloth. Silk has a natural beauty that few other fibres can equal and is often called the queen of fibres. Silk fibre is made from the cocoons of caterpillars called silkworms. Many other animals, including spiders and lacewings, spin silk threads. But their silk cannot economically be made into cloth. Silk is the strongest of all natural fibres. A thread of silk is stronger than the same size thread of some kinds of steel. Silk is highly elastic. It can be stretched and will still return to its original shape. Silk garments are extremely light in weight and are warmer than cotton, linen or rayon clothing. Dyed silk cloth has a deeper, richer appearence than most other dyed fabrics. Silk can be ironed easily and it resists wrinkling.

4. Wool

Wool is a fibre that comes from the fleece of sheep and some other animals. It is made into durable fabrics used in manufacturing blankets, clothing, rugs and other items. Wool fabrics clean easily and they resist wrinkles and hold their shape well. Wool also absorbs moisture and insulates against cold. All these features make wool popular for coats, sweaters, gloves, socks and other clothing. Wool fibres are nearly cylindrical in shape. Overlapping scales on the surface make the fibres mat and interlock under heat, moisture and pressure. This property of wool fibres is called felting. Felting increases the strength and durability of wool fabrics. It also enables wool to be made into felt.

II. Semi-synthetic Polymers

They undergo additional chemical alteration after being produced from naturally existing polymers. For example, cellulose derivatives like cellulose nitrate and cellulose acetate. Manufacturers produce substances called cellulose derivatives by combining cellulose with certain chemicals. The most widely used cellulose derivate is cellulose acetate. Other derivatives include carboxy methyl cellulose and cellulose nitrate. In the late 1940's, synthetic polymers prepared mainly from petroleum began to replace cellulose in some plastic, fibers and some photographic film. But some experts believe that a petroleum shortage and rising oil prices will probably lead to greater use of cellulose.

III. Synthetic Polymers

These polymers were created by humans. The most popular and extensively utilized synthetic polymer is plastic. It is utilized in many dairy products and industries. Other examples are Polyethylene, Rayon, Teflon, Orlon, Polyester, Polyether, Nylon-66, Nylon-6 etc.

1. Polyethylene

Polyethylene or polythene is the most commonly used plastic. It is a polymer, mainly used for packaging products like plastic bags, geomembranes, plastic films, and containers including jars, bottles, cups etc.

2. Rayon

Rayon is a manufactured fibre produced from wood pulp or cotton linens. It is widely used to make industrial materials and knit and woven textiles for clothing, upholstery, draperies and decorating fabrics.

3. Teflon

Teflon is the trade name for polytetra fluroethylene, which was discovered in 1938 by American chemist Roy.J.Plunkett. Plunkett discovered the material accidently while working to develop a non toxic refrigerant from gaseous tetrafluroethylene. Instead, he came up with a waxy white powder that indicated that the molecules had polymerized or combined with each other. Plunkett went on to develop a method for producing the powder commercially. Teflon was first used to manufacture gaskets and valves needed in the development of the atomic bomb. The first Teflon coated muffin tins and frying pans were sold in 1960. Teflon is now used for artificial corneas, substitute bones for chin, nose, hip and knee joints and other anatomical parts. Non stick kitchenware are coated with teflon and potassium hydrogen tartarate. It is anti-corrosive.

4. Orlon 

Orlon is also known as polyacrylonitrile. It is mainly used in the garment industry. It is a high resistive fibre to sunlight and greenhouse gas. 

5. Polyester

Polyester is the general name for any of a group of widely used synthetic products. Polyesters are strong, tough materials that are manufactured in a variety of colours, shapes and sizes.

6. Polyether

Polyethers are polymers consisting of monomers joined together by ether linkages. A variety of polyethers are manufactured ranging from elastomers to the engineering plastics.

7. Nylon-66

Nylon-66 is a synthetic fibre belonging to polyamide. Nylon-66 is prepared from hexa methylene diamine and adipic acid.

8. Nylon-6

Nylon-6 is a synthetic fibre belonging to polyamide. It exhibits highly tensile strength, better impact resistance and good abrasion resistance.