Class 8 science chapter 3 summary

Chapter – 3 

Synthetic Fibres and Plastics 

• Synthetic fibres and plastics, like natural fibres, are made of very large units called 

polymers. Polymers are made up of many smaller units. Polymers are made up of many 

smaller units. 

• While natural fibres are obtained from plants and animals, synthetic fibres are obtained 

by chemical processing of petrochemicals. Like natural fibres, these fibres can also be 

woven into fabrics. 

• Synthetic fibres find uses ranging from many household articles like ropes, buckets, 

furniture, containers, etc. to highly specialized uses in aircrafts, ships, spacecrafts, 

healthcare, etc. 

• Depending upon the types of chemicals used for manufacturing synthetic fibres, they are 

named as Rayon, Nylon, Polyester and Acrylic. 

• The different types of fibres differ from one another in their strength, water absorbing 

capacity, nature of burning, cost, durability, etc. 

• Today, life without plastics cannot be imagined. Be it home, or outside, plastic is every 

where. 

• The waste created by plastics is not environment friendly. On burning plastics release 

poisonous gases. On dumping in the ground they may take years to degenerate. This is 

because of their non-biodegradable nature. 

• We need to use synthetic fibres and plastics in such a manner that we can enjoy their 

good qualities and at the same time minimise the environmental hazards for the living 

communities. 

• Types of Synthetic Fibers: 

(i) Rayon: It is made from cellulose obtained from wood pulp. It is used to make 

containers, car upholstery, etc. 

(ii) Nylon: A polyamide made from petroleum. It is lightweight, strong and durable. 

The fabric allows easy evaporation and dries quickly. It is used in parachutes, flak 

vest, combat uniforms, tires, etc.

(iii) Polyester: A versatile and important man-made fabric. It has an outstanding 

characteristic of resisting wrinkle and springing back into its crisp, smooth shape. 

It is strong and soft. It is used in dresses, suits, rainwear, etc. 

(iv) Acrylic: A fibre similar to that of wool and is used to make sweater, blankets, 

shawls, etc. It is lightweight, soft and warm. Also it is cheaper than natural wool. It 

is resistant to chemicals, moths and sunlight. Therefore, they are widely in use 

nowadays. 

• Plastics: Like synthetic fibres, plastic is also a polymer. Some plastics have a linear 

arrangement of the units and some have a cross-linked arrangement of the units. 

Examples: Polythene. 

• Characteristics of Plastics: 

(i) Non-reactive: Not affected by air, water, soil, etc. 

(ii) Light, strong and durable: Light, strong and durable and can be moulded into 

different shapes and sizes. 

(iii) Poor Conductors: Do not allow heat and electricity to flow through them. 

• Effect of Plastics on Environment: Natural materials like wood and paper are 

biodegradable (bio = living; degeradable = able to broken down). In contrast, most 

plastics do not decay, therefore, they are non-biodegradable. The lightweight nature of 

plastics can also be a problem. Burning of plastics also release poisonous fumes into the 

atmosphere. This way plastics pollute the environment.