science class 8 chapter 3 keywords
Answers
Answer:
Fibre
The clothes, which we wear are made of fabrics.
Fabrics are made from fibres obtained from natural or artificial sources.
Fibres are also used for making a large variety of household articles.
Polymer
The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit.
A polymer is a substance composed of many repeated similar subunits.
Synthetic Fibre
Fibres that are made or created by humans are known as synthetic or man-made fibres.
Humans have been able to make a variety of synthetic fibres. Eg: rayon, nylon etc.
Natural Fiber
The naturally occurring fibres that humans derive from plants or animals are known as natural fibres. Eg: cotton, wool, silk, etc.
The Story of the Silkworm
Silk
Silk fibre is obtained from the cocoon of a silkworm. It takes 10 kg of the cocoon material to create 1kg of silk.
The process was discovered in China where it was kept as a closely guarded secret for a long time.
Silk is costly due to the material quality and production process involved. It is used in making sarees, ties, etc.
Raving about Rayon
Rayon
Rayon is made from purified cellulose, which is chemically converted into a soluble compound.
Rayon comes from natural sources such as wood pulp but is considered as a man-made fiber. This is because rayon can be treated chemically.
When rayon is compared with silk, it is inexpensive but can be woven like silk fibres.
Nylon
Nylon is a synthetic fibre obtained from coal, water and air.
The first fully synthetic fibre obtained was nylon.
The characteristic properties are that it is light, strong, and elastic.
Nylon finds application in the manufacturing of socks, ropes, tents, car seat belts, sleeping bags, curtains etc.
Pushy – Pull Polyesters
Polyester
Polyester is made of repeating units of a chemical called an ester.
It is a crease free synthetic fibre.
It is best suited for the making of dress materials as it is crisp and is easy to wash.
A popular polyester is Terylene.
Fake Sheep – Acrylic
Acrylic Fibre
Acrylic is a synthetic fibre that resembles wool.
The wool obtained from natural sources is quite expensive, whereas clothes made from acrylic are relatively cheap.
Synthetic fibres are more durable and affordable which makes them more popular than natural fibres.
Plastic Attack Alert
Plastic
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.
Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires. That is why it finds such a variety of uses.
Thermoplastics
Plastic, which gets deformed easily on heating and can be bent easily are known as thermoplastics. Eg: polythene and PVC
Thermosetting Plastics
Plastics, which when moulded once, can not be softened by heating. Eg: bakelite and melamine.
Characteristics of Plastics
– Plastic is non-reactive
– Plastic is light, strong and durable
– Plastic is a poor conductor
Biodegradable and Non-Biodegradable Materials
A material that decomposes through natural process is biodegradable and materials that are not easily decomposed by natural processes is termed as non-biodegradable.
Eg: Biodegradable – fruits, paper
Non Biodegradable – plastic, tin
Environmental Effects on Plastic
Plastic takes several years to decompose, it is not environmental friendly.
It causes pollution.
The burning process in the synthetic material is quite slow and it does not get completely burnt easily.
It releases lots of poisonous fumes into the atmosphere causing air pollution in the process.
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