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CBSE CLASS 8 - Fibers and plastics - Chapter notes
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Fiber
Fibers are thin, long, and flexible and hair or thread-like structures.
Fabrics are made up of fiber.
There are two types of fiber:-
1. Natural, 2. Man-made or synthetic
1. Natural Fibers
The fibers which are obtained from natural sources such as plants or animals are known as natural fibers.
Example:- Cotton, wool, silk, etc.
Cotton
• Cotton fibers are natural fibers.
• They are soft, cool, known as breathable fibers .
• Cotton fibers can hold water 24–27 times their own weight.
• They are strong, dye absorbent and can stand up against abrasion wear and high temperature.
Wool
• Wool is a natural fiber.
• Wool is a completely renewable fiber resource.
• Natural fibers, such as wool, are totally biodegradable.
Silk
• Silk is a natural fiber obtained from silkworms (developed by China)
• The process was first obtained in China.
• It is very expensive and has good texture and used to make sarees etc.
2. Man-made fibers or synthetic fiber
The fibers which are manufactured in factories by humans are known as man-made or Synthetic fibers.
Example:- Nylon, Rayon, acrylic, etc.
Did you know?
• Nylon is the first synthetic fiber. Which was developed as a replacement for silk around the time of World War II.
A synthetic fiber, as well as plastic, is made up of a chain of small units ( is a chemical substance called monomers) which combine to form polymers.
The chemical reaction of converting monomers into polymers is called Polymerization.
Monomers: A monomer is a single molecule that can bond with other identical molecules to form polymers through a process called Polymerization.
Polymers: Polymer is a Greek word in which 'poly' means 'many' and 'mer' means units. Hence, polymers are large molecule made up of several molecules (or monomers) linked together.
Example of Polymers:
• All synthetic fibers, such as Rayon and Nylon, are polymers.
• Polymers are also found in Nature. ‘Cotton’ is a polymer called ‘Cellulose’. ‘Cellulose’ is made up of a number of single units (or monomers) called ‘Glucose’.
Rayon
• First synthetic fiber.
• It is called artificial silk.
• Source of Rayon is wood pulp yet it man made fiber.
• It is cheaper than silk and can be woven like silk.
• Rayon can mixed with cotton for bed sheet making purpose and wool for carpet making purpose
Nylon
• It is developed in 1931.
• It was developed from coal water and air without using any natural raw material obtained from plant and animals.
• It was first fully synthetic fiber.
• Nylon fiber are strong elastic and light.
• It is lustrous and easy to wash.
• It is used for rope, shocks, tent, sleep bag , curtains, car covers etc.
• Nylon rope is stronger than steel rope.
• It is also used for making parachute and rope for rock climbing.
Facts to know
Synthetic fiber melt on heating and catches fire easily. We should avoid to use of synthetic fiber while working with fire because it melt on fire and stick to body .
All the synthetic fiber are prepared by a number of process using raw materials from petroleum origin called petrochemical.
Characteristics of synthetic fiber:-
• Synthetic fibers are cheaper than natural fiber.
• Synthetic fibers are stronger than natural fiber.
• Synthetic fibers are more durable than natural fiber.
• Synthetic fabrics are dried up in less time.
• Synthetic fibers are easy to maintain and wash.
Polyester
• Polyester is made up of repeating unit of chemical substance called ester .
• Easter is a organic chemical substance which gives fruit like smell.
• It is used to make cheep synthetic fiber.
• Polyester is Thermoplastics polymer.
• It is stronger and softer than nylon fiber.
• Natural fibers are mixed with polyester to obtain blended fabrics. Examples are polycot, polywool.
• PET Polyethylene terephthalates is a kind of polyester used for making drinking water bottle.
Acrylic
• Acrylic is a synthetic fiber.
• It is light in weight ,soft and warm like wool
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