Synthetic Fibres and Plastics Class 8 Revision Notes CBSE Science Chapter 3 (Free PDF Download)

Synthetic Fibres:

• Synthetic fibre is a man-made fibre that is prepared by using raw materials that are mainly of petroleum origin, called as petrochemicals. A number of processes are involved in the preparation of the same. Some of the common synthetic fibres are rayon, polyester and nylon. 

• The synthetic fibres are made up of small units of chemicals (monomers) which are joined together to form a chain and these chains are called polymers. The name polymer is a Greek word that suggests: poly meaning many and mer meaning units.

• The synthetic fibres can be obtained by the chemical processing of the petrochemicals, unlike the natural fibres that are obtained from animals and plant sources.

Types of Synthetic Fibres:

1. Synthetic fibres are classified on the basis of the chemicals that are used in their manufacturing.

2. All these fibres differ from each other in terms of their strength, nature of burning, affordability, durability, availability, water absorption nature etc. 

The Different Types of Synthetic Fibres are Listed Below:

1. Rayon: It is popularly known as artificial silk. It is called viscose-rayon regenerated cellulose. Though it is made from cellulose obtained from the natural source of wood pulp, it is a man-made fibre as it is made by the chemical treatment of wood pulp. It can be woven like silk fibres and dyed in a variety of colours. It is used to make fabrics, bedsheets, carpets, car upholstery, etc.

2. Nylon: It is a polymer of adipic acid hexamethylenediamine. It was the first fully synthetic fibre that was made from coal, water and air. The nylon fibres are light, elastic, strong, durable and lustrous. This makes it a good choice for fabrics and it also dries up quickly. It has multiple uses in fabrics, car seat belts, ropes, curtains, toothbrushes and due to its strength, it is used in parachutes and ropes for rock climbing.

3. Polyester: It is made up of monomer esters. It is yet another important man-made fabric. It has an excellent quality of being wrinkle-free and remains crisp, and is easy to wash and so it is used for dresses, suits, rainwear, etc. A type of polyester known as PET or Polyethylene terephthalate is very popular for making kitchen products, wires, bottles etc.

4. Acrylic: It is made up of monomer, polyacrylonitrile. This is a fibre that is very much similar to wool. This is used to make sweaters, blankets, shawls, etc. as it is much affordable and cheap and durable in comparison to the natural woollen fibres. It is light, soft, warm and resistant to chemicals, moths and sunlight due to which they are being widely used.

Plastics: 

1. Plastics are also a polymer, and unlike synthetic fibres, they have a different arrangement of the polymer units. 

2. They may have a linear or a cross-linked arrangement of the units. An example of plastic is Polythene. 

3. Plastics are widely in use as they can be recycled, melted, reused, moulded or rolled into different shapes. They are used to make a variety of products like chairs, bags, toys, buckets, kitchen products etc.

Characteristics of Plastics:

1. Non-reactive: Plastics are not affected by air, water, soil, etc and so will not corrode due to which they can be used for storage of materials.

2. Light, strong and durable: Plastics are light, strong and durable. They have a property that they can be moulded into different shapes and sizes and so it is used for various purposes. And it is less expensive than metal.

3. Poor Conductors: They are poor conductors of heat and electricity and do not allow them to flow through them. This allows it to be used for wires, screwdriver handles, frying pan handles, etc.

Effect of Plastics on Environment:

1. Plastics are not at all environmentally friendly. They accumulate in the environment over years without disintegrating.

2. The burning of plastics releases toxic gases into the atmosphere which pose a health hazard for humans, animals and plants. 

3. The plastics are not biodegradable, that is, they cannot be decomposed naturally by the action of bacteria. 

4. Improper disposal of plastic bags can lead to choking in animals if they consume it and also clogging of drains.

5. We have to learn to follow the three R principles, which is Reduce, Reuse, Recycle, Recover and Refuse to keep our environment safe and clean for all of us to live. We should also switch over to more eco-friendly ways by minimising the use of plastics by following simple measures like using cloth bags for shopping, using steel utensils in place of plastic ones, etc.

Uses of Synthetic Fibres:

• Synthetic fibres can be woven into fabrics in the same way as natural fabrics.

• They are excellent dress material as they are quick to dry, cheap, durable, and easy to maintain. They are also a perfect choice for an umbrella due to these qualities.

• Synthetic fibres find their uses in many household articles and textiles. Some examples are chairs, buckets, toothbrushes, bottles, microwave utensils, sweaters, raincoats, bedsheets, carpets etc. 

• The strength of the synthetic fibres is the quality due to which it is used to make fishing nets, parachutes, ropes for rock climbing and specialized uses as glass fibre in aircrafts, sails of boats, surgical gowns in healthcare, etc.