NCERT Class 8 Science Chapter 3: Synthetic Fibres and Plastics YouTube Lecture Handout

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NCERT Class 8 Science Chapter 3: Synthetic Fibers and Plastics

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  • Clothes are made of fabric – artificial and natural

  • Natural fibre – cotton (cellulose), wool and silk

  • Artificial or Synthetic or manmade fibre

  • Synthetic fibre is chain of small units joined together – each unit is a chemical substance

  • Small units combine to form polymer (“poly” means many and “mer” means part/unit) – it has many repeating units

Types of Synthetic Fibre

Rayon / Artificial Silk

  • Obtained by chemical treatment of wood pulp

  • Can be dyed

  • Mixed with cotton to make bed sheets

  • Mixed with wool to make carpet

Nylon

  • In 1931 – was made without any natural raw material

  • Prepared coal, water and air

  • First fully synthetic fibre

  • Strong, elastic and light

  • Lustrous and easy to wash

  • Socks, ropes, tents, toothbrush, car seats

  • Making parachutes and ropes for rock climbing

  • Nylon is stronger than steel wire

Polyester

  • Does not get wrinkled, remains crisp and easy to wash

  • Used for dress material

  • Popular one is terylene – can be drawn into fine fibre

  • PET (polyethylene terephthalate) – popular polyester to make bottles, utensils, films and wires

  • Repeating units of a chemical called an ‘ester’ – ester are chemicals that have fruits like smell

  • Polycot =

  • Polywool =

  • Terycot =

Acrylic

  • Many resemble wool

  • Cheap and available in variety of colors

  • More durable and affordable

  • These melt on heating and sticks to body – hence is disastrous (not wear in kitchen and laboratory)

  • Cheap, light weight blankets which are washable at home

Petrochemicals: All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin

Characteristics of Synthetic Fibre

  • Dry quickly (umbrella)

  • Less expensive

  • Readily available

  • Easy to maintain

Plastics

  • Polymer like synthetic fibre

  • Arrangement is linear or cross linked

  • Available in various size and shapes

  • It can be easily moulded (shaped in any form)

  • Can be recycled, reused, colored, melted, rolled in sheets or wires

  • Some plastic bend while others break on bending

  • Thermoplastic – deforms on putting in hot water and bends; polythene and PVC – to manufacture toys and combs

  • Thermosetting plastic – once moulded retain shape and cannot be softened by heating – bakelite and melamine

  • Bakelite – poor conductor of heat and electricity – electrical switches, handles and utensils

  • Melamine – versatile, resists fire, tolerates heat – floor tiles, kitchenware and fabrics that resist fire

Benefits of Plastic

  • Light weight

  • Lower price

  • Good strength

  • Easy handling

  • Lighter

  • Non-reactive (not react with water and air), not corroded

  • Durable

  • Widely used in industry and household articles

  • Poor conductors (covering on electric wires, handles of screw drivers)

  • Used in healthcare – packing tablets, syringes, gloves and medical instruments

  • Cookware for microwave ovens

  • Teflon – plastic on which oil and water do not stick (nonstick coating of cookwares)

  • Fire proof plastics – uniform of firemen have melamine coating for flame resistance

Disposal of Plastics

  • It is a major problem

  • Biodegradable – decomposed by natural process (bacterial action)

  • Non-Biodegradable – not decomposed by natural process

  • Takes years to decompose and hence is not environment friendly

  • Burning releases poisonous fumes in atmosphere causing air pollution

  • Substitute – cotton and jute bags

  • Separate collection for biodegradable and non-biodegradable waste

  • Thermoplastics can be recycled – coloring agents added

  • Plastics choke the respiratory system of animals/form stomach lining and cause death

  • Polybags clog the drains – not throw it anywhere (Swachh Bharat)

5R Principle

  • Reduce

  • Reuse

  • Recycle

  • Recover

  • Refuse

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