SYNTHETIC FIBRES

INTRODUCTION

The cloths 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. 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 FIBRES”.

OBJECTIVES

l To improve quality and effectiveness of education

l To meet the learning styles or needs of students

l To improve user-accessibility and time flexibility to engage learners in the learning process

l To augment the learning interest in students

l To make students understand the characteristics of “synthetic fibres”.

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. 1.1(a)]. Or, try to join a number of paper clips together to make a long chain, as in Fig. 1.1 (b). Is there any similarity between the two?

 

 

Fig. 1.1:(a) Beads and, (b)Paper clips joined to form long chains

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.

1.1 Types of Synthetic Fibres

 

A. 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. 1.2.)

 

Fig. 1.2

 

B. 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. 1.3).

 

 

               Fig. 1.3:Various articles made from Nylon

 

 

Is nylon fibre really so strong that we can make nylon parachutes and ropes for rock climbing?

 

 

Fig. 1.4 :Use of Nylon fibres

Nylon is also used for making parachutes and ropes for rock climbing (Fig. 1.4). A nylon thread is actually stronger than a steel wire.
Let us find out.

Activity 

Take an iron stand with  a clamp. Take a cotton thread of about 60cm length. Tie it to the clamp so that it hangs freely from it as shown from it as shown in fig 1.5.

 

                                                    

                        Fig 1.5:An iron stand with a thread hanging from the clamp

 

At the free end suspend a pan that weights can be placed in it. Add weights one by one till the thread breaks. Note down the total weight required to break the thread. This weight indicates the strength of the fibre. Repeat the same activity with threads of wool, polyester, silk and nylon. Tabulate the data as shown in table 1.2.Arrange the threads in order of their increasing strength.

 

S. No.	Type of thread/fibre	Total weight required to break the thread
1	Cotton
2	Wool
3	Silk
4	Nylon

 

 

                                                  Observation table 1.2

 

C. 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 nice 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.

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.

1.3 Characteristics of Synthetic Fibers

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

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 with the natural fabric.

CONCLUSION

Through this work, we could understand about the properties of synthetic fibres. Synthetic fibres are made pf very large units called polymers. While natural fibres are obtained from plants and animals, synthetic fibres are obtained by processing of petrochemicals. Synthetic fibres find uses ranging from many household articles like ropes, buckets, containers, ships, space crafts, health care etc. The fibres differ from one another in their strength, water absorbing capacity, durability etc.

 

FOLLOW UP ACTIVITY

1.Give eg which indicates that nylon fibres are very strong.

2.Match the following

          A                                                        B

1.Polyester                        1.Prepared by using wood pulp           

2.Teflon                              2.Used for making parachutes

3.Rayon                              3.Used to make non-stick cook wares

4.Nylon                               4.Fabrics do not wrinkle easily

 

REFERENCES      

1.Chemistry 8^th standard textbook -SCERT

2.www.ekshishka.org.in

3.www.practically.com