CBSE Class 8 Science Revision Notes Chapter 3

CBSE Class 8 Science Revision Notes Chapter 3 – Synthetic Fibres and Plastics 

Extramarks has provided Class 8 Science Chapter 3 Notes for students to gain conceptual clarity which comes in handy while answering the most tricky questions of the chapter during exams. These notes are curated by the subject-matter experts according to the latest CBSE Syllabus. Students can refer to these notes for the Class 8 exam as well as for competitive exams.

Extramarks notes will be a student’s last-minute revision guide providing all the necessary information in a nutshell, to revise the entire syllabus quickly and easily. 

Synthetic Fibres:

Synthetic fibre is a type of man-made fibre created utilising petrochemicals (products derived from petroleum). Class 8 Chapter 3 Science Notes by Extramarks explains the various procedures involved in producing synthetic fibres in detail. Rayon, nylon, and polyester are a few examples of synthetic fibres that are frequently used.

These fibres are composed of small chemical units, or monomers, that are linked together to form long chains or polymers.  The term ‘polymer’ is a Greek word, wherein  ‘poly’ means many and ‘mer’ means units.

Unlike natural fibres that are derived from animals and plant sources, synthetic fibres are obtained by the chemical processing of petrochemicals.

Types of Synthetic Fibres:

Fibres are all different from one another in terms of their strength, burning characteristics, cost, availability, durability, and water absorption capacity, among other characteristics.

Based on the chemicals employed in their production, synthetic fibres are categorised as:

• Rayon: Popularly known as artificial silk, it is known as viscose-rayon regenerated cellulose. Although it is made from cellulose that is obtained from a natural source of wood pulp, it is a man-made fibre because it is made by chemically treating wood pulp. It is dyed in many colours and can be woven like silk fibres. It is used for making car upholstery, carpets, fabrics, bedsheets, etc. 
• Nylon: Nylon is a polymer of adipic acid hexamethylenediamine. It is strong, light, elastic, durable and lustrous and was the first fully synthetic fibre made from coal, water and air. It is a good-quality fabric and dries up quickly. This fibre is utilised for many purposes, such as in fabrics, parachutes, toothbrushes, car seat belts, ropes, and curtains, and due to its strength as ropes for rock climbing.
• Polyester: Polyesters are important man-made fabrics that are made up of monomer esters. They are wrinkle-free since they are of excellent quality, remain crisp, and are easy to wash, so they are used for making suits, dresses, rainwear, etc. PET or Polyethylene terephthalate, a type of polyester is quite popular for making wires, kitchen products, bottles, etc.
• Acrylic: Acrylics are made up of monomers and polyacrylonitrile. They are very much similar to wool and since they are affordable, cheap and durable in comparison to natural woollen fibres, they are used for making shawls, sweaters, blankets, etc. They are being widely used in recent times as they are light, soft, warm and resistant to chemicals, moths and sunlight. 

Plastics:

Unlike synthetic fibres, plastics are also polymers that have a different arrangement of polymer units. A typical example of plastic is polythene. 

Polymer units are typically arranged linearly or cross-linked in plastics. They are frequently used  because they are simple to reuse, melt, mould, or roll into various shapes and sizes. Plastics are used to make a wide range of goods, including bags, buckets, chairs, toys, kitchen items, etc.

Characteristics of Plastics:

Chapter 3 Science Class 8 Notes explain the characteristics of plastics in detail.  Some of the characteristics are given below: 

• Non-reactive: Plastics do not corrode as they are not affected by air, water, soil, etc. As a result, they can be used for the storage of materials.
• Light, strong and durable: Since plastics are light, strong and durable, they can be easily moulded into different shapes and are therefore used for several purposes. Plastics are also comparatively less expensive than metals. 
• Poor Conductors: Plastics do not allow heat and electricity to flow through them, as they are poor conductors of heat and electricity. This is why it  can be used for making screwdriver handles, wires, frying pan handles, etc.

Effect of Plastics on the Environment:

• Plastics are not environmentally-friendly products. They can keep accumulating in the environment for years without disintegrating.
• Toxic gases are released into the atmosphere when plastics are burned, which can cause health hazards to humans, animals, and plants. 
• Plastics do not naturally decompose by the action of bacteria and hence are not biodegradable.
• If plastic bags are  disposed of freely anywhere, it can lead to choking in animals when they consume them and also lead to clogging of drains.

The 5 Rs, i.e., Reduce, Reuse, Recycle, Recover and Refuse, must be followed to control the harmful effect of plastics on the environment. This will help in keeping the environment safe and clean for survival, as well as sustainable development. There is also a need to switch over to more eco-friendly ways by minimising the use of plastics and relying on eco-friendly products such as steel utensils in place of plastic ones, cloth bags for shopping‌ and other purposes.

Uses of Synthetic Fibres:

Class 8 Science Notes Chapter 3 provides a detailed description of the different uses of synthetic fibres. Just like natural fibres, synthetic fibres can also be woven into fabrics. As synthetic fibres are quick to dry, cheap, durable, and easy to maintain, they are excellent dress materials. They can also be used for making umbrellas due to these qualities.

Apart from this, synthetic fibres are used in making household articles like bottles, buckets, chairs, toothbrushes, raincoats, carpets, bedsheets, microwave utensils, textiles, etc. Due to the strength of the synthetic fibres, they are used to make sails for boats, fishing nets, and ropes for rock climbing.  Some specialised uses include glass fibre in aircraft, parachutes, surgical gowns in healthcare, etc.