UPSC Chemistry Synthetic Fibers and Plastics Synthetic Fibers and Plastics

 Synthetic Fibers and Plastics

1.           Synthetic Fibres

• A synthetic fibre is a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer.
• Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.
• Silk fibre obtained from silkworm was discovered in China and was kept as a closely guarded secret for a long time. Attempts were made to make silk artificially. Towards the end of the nineteenth century, scientists were successful in obtaining a fibre having properties similar to that of silk. Such a fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk.
• Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. It is cheaper than silk and can be woven like silk fibres. It can also be dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.
• Nylon is another man-made fibre. In 1931, it was made without using any natural raw material (from plant or animal). It was prepared from coal, water and air. It was the first fully synthetic fibre.
• Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. So, it became very popular for making clothes.
• We use many articles made from nylon, such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains etc. Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.
• Polyester is another synthetic fibre. Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material.
• We must have seen people wearing polyester shirts and other dresses. Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yam.
• PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.
• Polyester (Poly+ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. Fabrics are sold by names like polycot, polywool, terrycot etc. As the name suggests, these are made by mixing two types of fibres, Polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and wool.
• We wear sweaters and use shawls or blankets in the winter. Many of these are actually not made from natural wool, though they appear to resemble wool. These are prepared from another type of synthetic fibre called acrylic. The wool obtained from natural sources is quite expensive, whereas clothes made from acrylic are relatively cheap. They are available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres.
• All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.
• Synthetic fibres possess unique characteristics which make them popular dress materials' They dry up quickly, are durable, less expensive, readily available and easy to maintain.

2.           Plastics

• Plastic is also a polymer like the synthetic fibre. All plastics do not have the same type of arrangement of units. In some it is linear, whereas in others it is cross-linked.
• Plastic articles are available in all possible shapes and sizes. The fact is that plastic is easily mouldable i.e. can be shaped in any form. Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires. That is why it finds such a variety of uses.
• Polythene (Poly+ethene) is an example of a plastic. It is used for making commonly used polythene bags.
• We will observe that some plastic articles can bend easily while some break when forced to bend. When we add hot water to a plastic bottle, it gets deformed. Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics. Polythene and PVC are some of the examples of thermoplastics. These are used for manufacturing toys, combs and various types of containers.
• On the other hand, there are some plastics which when moulded once, cannot be softened by heating. These are called thermosetting plastics. Two examples are bakelite and melamine. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.
• Today if we think of storing a food item, water, milk, pickles, dry food, etc., plastic containers seem most convenient. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metals, plastics are used in cars, aircrafts and spacecrafts, too.
• We know that metals like iron get rusted when left exposed to moisture and air. But plastics do not react with water and air. They are not corroded easily. That is why they are used to store various kinds of material, including many chemicals.
• Plastics find extensive use in the health-care industry. Some examples of their use are the packaging of tablets, threads used for stitching wounds, syringes, doctors' gloves and a number of medical instruments.
• Special plastic cookware is used in microwave ovens for cooking food. In microwave ovens, the heat cooks the food but does not affect the plastic vessel.
• Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cookwares.
• Fire-proof plastics: Although synthetic fibre catches fire easily, it is interesting to know that the uniforms of fireman have coating of melamine plastic to make them flame resistant.
• A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable. A material which is not easily decomposed by natural processes is termed as non-biodegradable.
• Since plastic takes several years to decompose, it is not environment friendly. It causes environmental pollution. Besides, the burning process in the synthetic material is quite slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution. How can this problem be solved?
• Avoid the use of plastics as far as possible. Make use of bags made of cotton or jute when you go for shopping. The biodegradable and nonbiodegradable wastes should be collected separately and disposed off separately. Practise this in your homes.
• It is better to recycle the plastic waste. Most of the thermoplastics can be recycled. However, during recycling certain colouring agents are added. This limits its usage especially for storage of food.

3.           Garbage in. Garbage out

• In some cities and towns municipalities provide separate dustbins for collecting two kinds of garbage. Usually one is coloured blue and the other green. The blue bin is for materials that can be used again - such as plastics, metals and glass. These are the materials that do not rot in the garbage heaps. The green bins are for collecting kitchen and other plant or animal wastes.
• Earthworm called redworm is used for composting. This method of preparing compost with the help of redworms is called vermicomposting.
• Redworms do not have teeth. They have a structure called 'gizzard', which helps them in grinding their food, powdered egg shells or sea shells could be mixed with the wastes. This would help redworms in grinding their food. A redworm can eat food equal to its own weight, in a day.
• Redworms do not survive in very hot or very cold surroundings. They also need moisture around them. If we take good care of our worms, in a month's time their number will double.
• Some kind of plastics can be recycled, but, not all of them. We often use plastic bags to store cooked food items. Sometimes these bags may not be suitable for keeping eatables. Consuming food packed in such plastic bags could be harmful to our health.
• All kind of plastics give out harmful gases, upon heating or burning. These gases may cause many health problems, including cancer, in humans.
• People often fill garbage in plastic bags and then throw it away. When stray animals lock for food in these bags, they end up swallowing these. Sometimes, they die due to this.
• The plastic bags thrown away carelessly on raod and other places get into drains and the sewer system. As a result, drains get choked and the water spills on the roads. During heavy rains, it might even create a flood like situation.