The clothes which we wear are  made of fabrics. Fabrics are made from fibres obtained from natural or artificial sources. Can you name some natural fibres? Fibres are also used for making a large variety of household articles. Make a list of some common articles made from fibres. Try to separate them into those made from natural fibres and those made from artificial fibres. Make entries in Table 3.1.

Table 3.1 : Natural and Artificial Fibres

Why did you label some fibres as artificial?

You have read in your previous classes that natural fibres like cotton, wool, silk, etc., are obtained from plants or animals. The synthetic fibres, on the other hand, are made by human beings. That is why these are called synthetic or man-made fibres.

3.1 What are Synthetic Fibres?

Try to recall the uniform pattern found in a necklace of beads joined with the help of a thread [Fig. 3.1(a)]. Or, try to join a number of paper clips together to make a long chain, as in Fig. 3.1 (b). Is there any similarity between the two?

A synthetic fibre is also 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. The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit. So, a polymer is made of many repeating units.

Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

3.2 Types of Synthetic Fibres

Rayon

You have read in Class VII that silk fibre obtained from silkworm was discovered in China and was kept as a closely guarded secret for a long time. Fabric obtained from silk fibre was very costly. But its beautiful texture fascinated everybody. 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. (Fig. 3.2.)

Nylon

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. (Fig. 3.3).

 Nylon is also used for making parachutes and ropes for rock climbing (Fig. 3.4). A nylon thread is actually stronger than a steel wire.

Let us find out.

Polyester and Acrylic

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. You 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 yarn.

PET (polyethylene terephthalate) is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Look around and make a list of things made of polyester

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 aresold 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.

You have already performed an activity of burning natural and synthetic fibres (Activity 3.6 of Class VII). What did you observe? When you burn synthetic fibres you find that their behaviour is different from that of the natural fibres. You must have noticed that synthetic fibres  melt on heating. This is actually a disadvantage of synthetic fibres. If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in in the kitchen or in a laboratory.

All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.

3.3 Characteristics of Synthetic Fibres

Imagine that it is a rainy day. What kind of umbrella would you use and why? 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. Perform the following activity and learn for yourself.

Activity 3.2

Take two cloth pieces of the same size, roughly half a metre square each. One of these should be from natural fibre. The other could be a synthetic fibre. You can take help of your parents in selecting these pieces. Soak the pieces in different mugs each containing the same amount of water. Take the pieces out of the containers after five minutes and spread them in the sun for a few minutes. Compare the volume of the water remaining in each container.

Do synthetic fabrics soak less/more water than the natural fabrics? Do they take less/more time to dry?

What does this activity tell you about the characteristics of the synthetic fabrics?

Find out from your parents about the durability, cost and maintenance of these fabrics, compared to the natural fabrics.

3.4 Plastics

You must be familiar with many plastic articles used everyday. Make a list of such items and their uses.

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. (Fig. 3.6). Plastic articles are available in all possible shapes and sizes as you can see in Fig. 3.7. Have you ever wondered how this is possible? 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.

Now, try to bend a piece of plastic yourself. Can all the plastic articles be bent easily?

You 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, can not 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. Fig. 3.8 shows the various uses of thermoplastics and thermosetting plastics.

Fig. 3.8 : Some articles made of plastic

3.5 Plastics as Materials of Choice

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. The list is endless if we start counting articles like slippers, furniture, decoration pieces, etc.

Now, let us discuss the characteristic properties of plastics.

Plastic is Non-reactive

You 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.

Plastic is Light, Strong and Durable

Talk to your parents or grandparents about the types of buckets that were used in the past. What is the material of the buckets or mugs you are using today? What are the advantages of using a plastic container? Since plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals. They are widely used in industry and for household articles. Make a list of different kinds of plastic containers that you use in daily life.

Plastics are Poor Conductors

You have learnt above that plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screw drivers are made of plastic. As mentioned above, handles of frying pans are also made
of plastic.

3.6 Plastics and the Environment

When we go to the market, we usually get things wrapped in plastic or packed in polythene bags. That is one reason why plastic waste keeps getting accumulated in our homes. Ultimately, plastic finds its way to the garbage. Disposal of plastic is a major problem. Why?

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 non-biodegradable.

Look at Table 3.3.

Table 3.3

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 non-biodegradable wastes should be collected separately and disposed off separately. Practise this in your homes. Can you suggest some other ways in which you can contribute towards reducing the use of plastic materials?

It is better to recycle plastic waste. Most of the thermoplastics can be recycled. Make a list of items that can be recycled. However, during recycling certain colouring agents are added. This limits its usage especially for storage of food.

As a responsible citizen remember the 5 R principle. Reduce, Reuse, Recycle, Recover and Refuse. Develop habits which are environment friendly.

 

 

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