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Class 8th-Science: Chapter 3-Synthatic Fibers and Plastics

Fibers

Fabrics: Fabrics are the materials made by using yarns, which in turn are made from fibers obtained from natural or artificial sources.

From Example: Cotton fabric, Silk fabric.

Yarn: Yarn is long, twisted and continuous strand composed of interlocked fibers. It is used for weaving or knitting fabrics.

For Example: Cotton yarn, Silk yarn.

Fibers: When a yarn is untwisted to loosen it, we see that it is made up of multiple thin hair-like strands called fibres.

For Example: Cotton fiber, silk fiber.

Types of Fibers

1.  Natural Fibers:

The fibers which are obtained from plants or animals are called natural fibers.

For Example: Cotton, Jute(obtained from plants),  Wool, silk(obtained from animals)

2.  Synthetic Fibers:

The fibers which are made by human beings are called synthetic fibers or man-made fibers or artificial fibers.

For Example:  Rayon, nylon, polyester, acrylic, etc.

Types of Synthetic Fibers

Depending upon the types of chemicals used for manufacturing synthetic fibers, they are classified into four major groups.

Synthetic Fibers

1. Rayon

2. Nylon

3. Polyester

4. Acrylic

1. Rayon:

 Silk fiber obtained from silkworm was discovered in china and was kept as a closely guarded secret for a long time.

Fabric obtained from silk fiber was very costly. But its beautiful texture fascinated everybody.

Attempts were made to make silk artificially. Towards the end of the nineteenth century, scientists were successful in obtaining a fiber having properties similar to that of silk.

Such a fiber was obtained by chemical treatment of wood pulp. This fiber was called rayon or artificial silk.

1. Rayon has properties similar to that of silk.

2. It is obtained treatment of wood pulp.

3. Rayon is different from other synthetic fibers because it is obtained from a natural source wood pulp (which is obtained from plants). Thats why it is called semi-synthetic.

4. It is cheaper than silk and can be woven like silk fibers.

5. It can also be dyed in a wide variety of colours. 

6. Rayon is mixed with cotton to make bed sheets.

7. It is mixed with wool to make carpets.

2. Nylon:

1. It 1931, it was made without using any natural raw material(from plant or animal).

2. It was prepared from coal, water and air.

3. It is the first fully synthetic fiber.

4. Nylon fiber is strong, elastic and light. It is lustrous and easy to wash. so, it is very popular for making clothes.

5. We use many articles made from nylon such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains etc.

6. A nylon thread is stronger than a steel wire.

7. It is used for making parachutes and ropes for rock climbing.

3. Polyester:

1. Fabric made from polyester does not get wrinkled easily. it remains crisp and is easy to wash. so, it is quite suitable for making dress material.

2. Terylene is a popular polyester. It can be drawn into very fine fibers that can be woven like any other yarn.

3. PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

4. Fabrics are sold by names like names like polycot, polywool, terrycot etc. As the name suggests, these are made by mixing two types of fibers.

Polycot = Polyester + Cotton, Polywool = Polyester + Wool, Terrycot = Terylene + Cotton

4. Acrylic

We wear sweaters and use shawls or blankets in the winter. Many of these are actually not made from natural wool, though they appear to resemble wool.

These are prepared from another type of synthetic fiber called acrylic.

The wool obtained natural sources is quite expensive, whereas clothes made from acrylic are relatively cheap.

1. Acrylic resembles wool.

2. It is used to make sweaters, shawls, blankets etc.

3. Clothes made from acrylic are cheaper than that made from wool.

4. They are available in a variety of colours.

Characteristics of Synthetic Fibers

1. Advantages of Synthetic Fibers

2. Disadvantages of Synthetic Fibers

Advantages of Synthetic Fibers

Synthetic fibers possess unique characteristics which make them popular dress materials.

1. They are easy to wash and maintain.

2 They dry up quickly.

3. They are durable.

4. They are less expensive.

5. They are readily available.

Because of these properties of synthetic fibers, they are more popular than natural fibers.

Q. Do synthetic fabrics soak less/more water than the natural fabrics? Do they take less/more time to dry?

Ans. Yes, synthetic fabrics soak less water than the natural fabrics and they take less time to dry.

Q. What does this activity tell you about the characteristics of the synthetic fabrics?

Ans. Synthetic fabrics soak less water and take less time to dry as compared to the natural fabrics.

Q. Find out from your parents about the durability, cost and maintenance of synthetic fabrics, compared with natural fabrics.

Ans. Synthetic fabrics are more durable, cheaper and need less maintenance than natural fabrics.

Disadvantages of Synthetic Fibers

When we burn synthetic fibers, their behaviour is different from that of the natural fibers.

1. Synthetic fibers cannot absorb moisture, hence synthetic clothes are not good for summers, when we sweat more.

2. Synthetic fibers catch fire easily.

3. They melt on heating.

4. Synthetic clothes are difficult to iron as they can melt because of heat.

Q. Why should we not wear synthetic clothes while working in the kitchen or in a laboratory?

Ans. Synthetic fibers melt on heating. This is actually a disadvantage of synthetic fibers. If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. Therefore, we should not wear synthetic clothes while working in the kitchen or in a laboratory.

All the Synthetic fibers are prepared by chemical processing of petrochemicals.

Petrochemicals:

The raw materials of petroleum origin are called petrochemicals.

Plastics

We use many plastic articles everyday like chair, bucket, mug, toys, combs, electrical switches, handles of frying pans, handles of screw drivers and many more.

All natural fibres, synthetic fibres and plastics are made of very large units called polymers.

Polymer:

Polymer is a chemical substance which is made up of many smaller units (called repeating unit or monomers). Each small unit (or repeating unit or monomer) is actually a chemical substance.

many ethenes

Polythene (Poly + ethene) is an example of a plastic. It is used for making commonly used polythene bags.

Q. What is the repeating unit in polythene?

Ans. Ethene

Q. What is the monomer of polythene?

Ans. Ethene

many esters

Polyester (Poly + ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell.

Q. What is the repeating unit in polyester?

Ans. Ester

Q. What is the monomer of polyester?

Ans. Ester

Chapter 3 Ncert Exercise Question Answers 

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