CBSE Class 8 Science Synthetic Fibres and Plastics Chapter Notes

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CBSE Class 8 Science Synthetic Fibres and Plastics Chapter Notes. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

SYNTHETIC FIBRES & PLASTICS

INTRODUCTION
The clothes which we wear are made up of fabrics. Fabrics are made from fibres.
A fibre is a thread or filament like material which is so strong & flexible that can be converted in to clothes, ropes and nets etc.
They are of two kinds :- (1) Natural fibres (2) Synthetic fibres

(1) Natural fibres : - These are long thin threads which are obtained from natural polymers obtained from animals or plants eg.

(i) Cotton & Jute – From cell wall of plant cells (Cellulose, is natural polymer)
(ii) Wool – From the fleece of sheeps & goats
(iii) Linen – From stalk of a plant (Flax)
(iv) Silk – From cocoons of silk worm.

(2) Synthetic fibres :- Those fibres which are synthetically man made, and are polymer of small units are called synthetic fibre.
• The word polymer is made up of two Greek words poly which means many and mer means unit.
• All the synthetic fibres are prepared from raw materials of petroleum origin called petrochemical. eg. Nylon, Polyester etc.

POLYMERISATION
Synthetic fibres are polymers. A polymer is a large molcule formed by the combining of many small molecules, each of which is called a monomer. The process of combining the monomers to form a polymer is called polymerisation. Polymerisation can be of various kinds, for example : addition polymerisation and condensation polymerisation.

Types of Synthetic fibres
1. Rayon 2. Nylon 3. Polyester 4. Acrylic 5. Spandex
1. RAYON
It was prepared by chemical treatment (viscose process) of wood pulp (cellulose). It is also called artificial silk because it resembles in appearance like natural silk.
Process :

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Properties :
(i) Rayon can absorb sweat because of its tendency to absorb moisture. So it is preferred over other synthetic fabrics in summer season.

(ii) It is shiny and lustrous and resembles to silk.

(iii) It can be dyed in a wide variety of colours.

Uses :
(i) Rayon is mixed with cotton to make bed sheets and mixed with wool to make carpets.

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(ii) Shirts, ties and linings are made up of rayon fibre.

(iii) It is used to manufacture tyre cords

(iv) It is used to make bandages and surgical dressings.

2. NYLON
8 Nylon was first introduced in 1930s.
8 It was developed in Newyork (Ny) & London (Lon) so it was named as Nylon.
8 It was the first man made fully synthetic fibre.
8 It is a polymer made from two monomers, a diacid and a diamine, by the process called condensation polymerisation.
8 There are various nylons such as nylon 6, nylon 6-6 and nylon 5-10.

Properties :
(i) Nylon has high strength and high elasticity. It does not lose strength even after repeated use.
(ii) It is lustrous and easy to wash.
(iii) It absorbs very little water hence known to have drip-dry property.
(iv) It is wrinkle resistant and keeps permanent creases.
(v) It is moth and mould resistant.
(vi) It is light, fine and durable.

Uses :
(i) In making socks, sarees, shirts and other garments.

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(ii) It is used to blend with wool to increase the strength & used in making carpets.

(iii) Used to make tents, parachutes, umbrella, fishing nets, climbing ropes, tyre cord, strings for sports goods.

(iv) It's fibres are used for making tooth brush, car seat belt, slipping bags and curtains.

(v) It is used to make machine parts.

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