Class 8 Synthetic Fibres and Plastics Notes
Synthetic Fibres and Plastics Notes
The synthetic fibres are man-made fibres which are made of small units of chemicals (monomers) joined together in the form of large chain.
- All the synthetic fibres are prepared using raw materials of petroleum origin, called petrochemicals.
Polymer:- A single large unit made up of many small repeating chemical substances (monomers) is called a polymer.
- Cotton is a natural fibre which is actually a polymer called cellulose. Cellulose is made up of a large number of glucose units.
Types of synthetic fibres:-
- Polyester and Acrylic
Rayon (Artificial silk):-
- It is obtained by chemical treatment of wood pulp.
- It has properties similar to that of the silk.
- It can be dyed in a wide variety of colours.
- Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.
- It is prepared from coal, water and air.
- It is the first fully synthetic fibre.
- It is strong, elastic and light.
- A nylon thread is actually stronger than a steel wire.
- It is lustrous and easy to wash.
- Nylon is used to make socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains, parachutes and ropes for rock climbing.
- Polyester (Poly+ester) is made up of the repeating units of a chemical called an ester
- Fabric made from this fibre does not get wrinkled easily.
- It remains crisp and is easy to wash.
- Terylene and PET (polyethylene terephthalate) are very popular form of polyester.
- PET is used for making bottles, utensils, films, wires etc.
- Polycot is a mixture of polyester and cotton and polywool is a mixture of polyester and wool.
- It is also called synthetic wool.
- Clothes made from acrylic are cheap.
- They are available in a variety of colours.
Characteristics of synthetic fibres:-
- They dry up quickly, are durable, less expensive, readily available and easy to maintain.
Harmful effects of synthetic fibres:-
- Synthetic fibres melt on heating.
If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.
- Synthetic fibers cannot absorb moisture. This makes them unsuitable to be worn during summers.
Plastic is also a polymer like the synthetic fibre. All plastics do not have the same type of arrangement of units. In some it is linear, whereas in others it is cross-linked.
Types of plastics:-
- Thermosetting plastics
The plastics which can be bent or deformed easily on heating are called thermoplastics.
Ex:- Polythene and PVC (Poly Vinyl Chloride).
- These are used for manufacturing toys, combs and various types of containers.
The plastics which when moulded once, cannot be softened by heating are called thermosetting plastics.
Ex:- Bakelite and Melamine.
- Bakelite is a poor conductor of heat and electricity.
- It is used for making electrical switches, handles of various utensils, etc.
- It resists fire and can tolerate heat better than other plastics.
- It is used for making floor tiles, kitchenware and fabrics which resist fire.
Characteristics of Plastics:-
- Plastics are non reactive and not corroded easily. So, plastics are used to store various kinds of material, including many chemicals.
- Plastic is light, strong and durable and so they are used in industry and for household articles.
- Plastics are poor conductors of heat and electricity. So, plastics are used for covering electrical wires, for making handles of screw drivers and frying pans etc.
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.
Harmful effects of plastics:-
- Plastic takes several years to decompose and so it is not environmental friendly.
- It produces harmful gases on burning and so it causes air pollution.
- Sometimes stray animals take in plastics along with the food kept in them which block their digestive system and they ultimately die.
- Plastics block the sewage system.
Measures to control the damaged caused by plastics:-
- Do not throw plastic wrappers on road. They then generally get carried into the city sewage system resulting in clogging of drainage.
- Biodegradable and non-biodegradable wastes should be collected and disposed off separately.
- Use bags made of cotton or jute instead of plastic while shopping.
- As a responsible citizen, remember and follow 4R’s principle:-