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NCERT Solutions for Class 8th Science

 

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Chapter 3. Synthetic Fibres And Plastics

Chapter Review

 

 

 

Chapter Review:

  • Fabrics are made from fibres obtained from natural or artificial sources.
  • Fibres are also used for making a large variety of household articles.
  • Natural fibres like cotton,wool, silk, etc., are obtained from plants or animals. 
  • The synthetic fibres, on the other hand, are made by human beings that is why these are called synthetic or man-made fibres.
  • Many such small units combine to form a large single unit called a polymer.
  • Polymers occur in nature also. Cotton, for example, is a polymer called cellulose.
  • Cellulose is made up of a large number of glucose units.
  • Such a fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk.
  • Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.
  • Nylon fibre was strong,elastic and light.It was lustrous and easy to wash.So ,it became very popular for making clothes and parachutes and ropes for rock climbing.
  • PET is a very familiar form of polyester. It is used for making bottles,utensils, films, wires and many other useful products.
  • Sweaters  and  shawls or blankets are prepared from another type of synthetic fibre called acrylic.
  • All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.
  • Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires.
  • Polythene (Poly+ethene) is an example of a plastic. It is used for making commonly used polythene bags.
  • Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics.examples: toys, combs and various types of containers.
  • There are some plastics which when moulded once, can not be softened by heating. These are called thermosetting plastics. examples: bakelite and melamine
  • Plastics do not react with water and air. They are not corroded easily. That is why they are used to store various kinds of material.
  • Plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals.
  • Plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screw drivers are made of plastic.
  • Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cookwares.
  • A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable
  • A material which is not easily decomposed by natural processes is termed as non-biodegradable.
  • The 4 R principle is Reduce, Reuse, Recycle and Recover.

 

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