Home | | Science 7th Std | Fibres

Polymer Chemistry | Term 3 Unit 3 | 7th Science - Fibres | 7th Science : Term 3 Unit 3 : Polymer Chemistry

Chapter: 7th Science : Term 3 Unit 3 : Polymer Chemistry


We wear clothes, use bags, rope, blankets, etc. in our daily life. They are made of fibres. Once upon a time, people used natural fibres such as cotton and wool. Nowadays, we use a lot of synthetic fibres. All natural and synthetic fibres are polymers.


We wear clothes, use bags, rope, blankets, etc. in our daily life. They are made of fibres. Once upon a time, people used natural fibres such as cotton and wool. Nowadays, we use a lot of synthetic fibres. All natural and synthetic fibres are polymers.

Observe the difference between the natural and synthetic fibres:

Natural Coconut Rope vs. Nylon Fishing rope


1. Natural and Synthetic Fibres

Fibres are long strands of polymers interwoven to form linear, string-like structures. Fibres that are obtained from plant or animal sources are called natural fibres. Examples include cotton, coconut fibre, hair, wool and silk. Fibres that are made using raw materials from petroleum are synthetic fibres. Examples include polyester, acrylic and nylon. Historically, humans used natural plant fibres and animal fur for shelter, clothing and protection from the weather. Today, a large variety of natural fibres are still grown and processed such as cotton, silk, and wool. Natural fibres can be spun into filament, thread or rope. Then they can be woven, knitted, matted or bondedand are used to make clothing, containers, insulation materialand many other products we use in our daily life. Three main sources of natural fibres are : (i) Animal (e.g.) wool and silk.

The discovery of making synthetic fibres out of petrochemicals has replaced the use of many natural fibres. Synthetic fibres such as nylon, polyester and acrylic are used to make many different plastic items you use in your daily life such as clothing, blankets, tooth brushes and stuffing in cushions.


2. Types and Uses

Silk: Natural Fibre

Natural silk fibres are obtained from boiling the cocoons of silk worms from specific species of moths. There are four types of natural silk: Mulberry silk, Tasar silk, Muga silk and Eri silk. Most of the mulberry silk worldwide is produced in India. Silk is one of the strongest natural fibres and has many uses such as clothing, carpets and parachutes.

Rayon: A Semi-synthetic Fibre

In the 19th century scientists were successful in producing the first artificial silk known as rayon. The first rayon factory in India was established in Kerala in 1946. Rayon is a man-made fibre, but it is not considered fully synthetic as it is made out of natural cellulose collected from wood pulp. The cellulose that is collected from wood or bamboo pulp is treated with several chemicals. First sodium hydroxide is added followed by carbon disulphide. The cellulose dissolves in the chemicals added to it and produces syrup called Viscose. Viscose is forced through a spinneret (a device made of metal plates with very tiny holes) into a solution of dilute sulphuric acid. This produces silk-like threads that are cleaned with soap and dried. This new fibre is called rayon.

Some types of rayon are made from the short cotton fibres left on cottonseeds after ginning. Rayon is cheaper than silk, can be woven like natural silk fibre and can be dyed in a wide variety of colours. It can be mixed with cotton to make bed sheets or with wool in the production of carpets and home furnishing products. Rayon is also found in sanitary products, diapers, bandages and gauze for dressing wounds.

Nylon: Synthetic Fibre

Nylon is the first fully processed synthetic fibre. It was popular during the Second World War for the use of parachutes and rope materials for climbing. Nowadays, nylon has replaced natural silk in many textiles, and has become one of the most commonly used synthetic fibres.

Nylon fibre is strong, elastic and light. It islustrous and easy to wash, which has made it popular for the clothing industry.We use many products made from nylon such as socks, ropes, tents, toothbrushes, car seatbelts, sleeping bags, curtains, etc. Nylon thread is actually stronger than a steel wire.

Nylon is very strong and can be used for rock climbing!

Nylon is a plastic polymer made of chemical units called polyamides. olyamides are made with monomers – hexamethylenediamine and adipic acid. Solid chips of these polyamides are melted and forced through a heated spinneret which has very, very tiny holes.


How Strong is Nylon?

Take an iron stand with a clamp. Take samples of cotton, wool, nylon and silk threads of about 50cm in length.

First tie cotton thread to the stand so that it hangs freely from it. At the free end, attach a CD as plate so that weights can be placed on it. Add weights starting from 10 grams one by one, untilthe thread breaks. Note down the total weight required to break the cotton thread. Repeat the same activity with the wool, silk and nylon threads.

Iron clamp with a hold weights

NOTE: All the varieties of threads should be of same thickness.

Arrange the threads in the order of increasing strength.

Answer: Cotton, Wool, Silk, Nylon.

What do you infer from the above activity? 

Answer: Nylon thread is the strongest thread.

Which type of fibre is the strongest?  

Answer: Nylon.

Which type of fibre is the weakest? 

Answer: Cotton. 


Polyester and Acrylic: Synthetic Fibres

Polyester is another synthetic fibre. It can be drawn into very fine fibres that can be woven like any other yarn. Polyester is sold in the name of polycot, polywool, terrycot, etc. Polycot is a mixture of polyester and cotton; Polywool is a mixture of polyester and wool. PET (Polyethylene Terephthalate) is a very familiar form of polyester. It is used for making water and soda bottles, utensils, films and wires amongst many other useful products. Many of the clothes we wear are made out of polyester fibres. Fabrics made from this fibre do not get wrinkled easily and are easy to wash making polyester fabrics suitable for dress materials.

We wear sweaters and use shawls and blankets in the winter. Many of these are not made from natural wool although 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, where as clothes made from acrylic are relatively cheap because they are a byproduct of the production of plastics. They are available in a variety of colours. Synthetic fibres are more durable and affordable which has contributed to their widespread use.



Identify The Fibre : Let us do an activity. Look at the images below and identify and write down the name of the different types of fibre observed.


1. Jute - Natural

2. cotton - Natural

3. silk saree - Natural

4. Rayon material - Synthetic

5. wool - Natural

6. polyester - Synthetic


Synthetic or Natural Fibres : The teacher can give the learner a piece of each and every type of fibre. The learner can feel the fibre and write down the name of the fibre and state whether it is natural or synthetic fibre.

1. Jute – Natural

2. Cotton – Natural

3. Rayon – Synthetic

4. Wool – Natural

5. Polyester Synthetic

We have done four activities so far. Which activity helped you better to identify the type of fibre? Answer: Activity 3, 4

(Both the use of familiar images as well as touch can help us to identify the different types of fibres. Right!) We have learned about fabrics such as polyester, nylon and acrylic and their common uses. These synthetic fibres are polymers which we will learn about later in this chapter.


Tags : Polymer Chemistry | Term 3 Unit 3 | 7th Science , 7th Science : Term 3 Unit 3 : Polymer Chemistry
Study Material, Lecturing Notes, Assignment, Reference, Wiki description explanation, brief detail
7th Science : Term 3 Unit 3 : Polymer Chemistry : Fibres | Polymer Chemistry | Term 3 Unit 3 | 7th Science

Privacy Policy, Terms and Conditions, DMCA Policy and Compliant

Copyright © 2018-2023 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.