Wednesday 26 January 2022

Synthetic Fibres and Plastics (सिंथेटिक फाइबर और प्लास्टिक) Full Chapter Class 8 Science | NCERT Science Class 8 Chapter 3


There are two types of fibres:

फाइबर दो प्रकार के होते हैं:

Natural Fiber is fibre which is obtained by plants and animals, like cotton, wool, silk, etc.

Synthetic fiber is man- made fiber. It’s  a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer like rayon, nylon and polymer.

Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

Types of Synthetic Fibres:

    सिंथेटिक फाइबर के प्रकार:

Ryonrayon or artificial silk is man-made copy fibre of silk, it is made by chemical treatment of wood pulp. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. 

It is cheaper than silk and can be woven like silk fibres. It can also be dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.

Nylon: it is the first fiber which is 100% man-made without taking any component from animals and plants. It was invented in 1931 and made by mixing coal, water and air. 

Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. So, it became very popular for making clothes. It is used to make -socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains,  parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

Polyester and Acrylic:

पॉलिएस्टर और एक्रिलिक:

Polyester: Polyester is another synthetic fibre. Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material.Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yarn.

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

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. Fabrics are sold by names like polycot, polywool, terrycot, etc. As the name suggests, these are made by mixing two types of fibres. Polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and wool.

Acrylic: it is basically artificial woolen and warm like wool. Clothes made from acrylic are relatively cheap. They are available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres. 

Characteristics of Synthetic Fibres

Some benefits of synthetic fibers are:

Dry up quickly


Less expensive

Readily available

Easy to maintain

If there are many benefits of synthetic fibers but there is one big disadvantage is melting 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.



Plastic is also a polymer like the synthetic fibre. Plastic articles are available in all possible shapes and sizes as you can see. Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires. 

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

We have seen there is one plastic which can be bent and another which can’t be bent and gets broken. Lets understand these two types plastics:

Thermoplastics- it is a form of plastic with a very low melting point, this plastic gets deformed easily on heating and can be bent easily. Polythene and PVC are some of the examples of thermoplastics. These are used for manufacturing toys, combs and various types of containers.

Thermosetting plastics- these plastics, when moulded once, can not be softened by heating. It means its melting point is high. Two examples are bakelite and melamine. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics.

Plastics as Materials of Choice

 Nowadays plastic is everywhere from kitchen to operation theater. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metals, plastics are used in cars, aircrafts and spacecrafts, too. List is never ending. 

Here we why plastic is extensively used:

  • Plastic is Non-reactive- plastic doesn't react and erodes in the open. Unlike metals, it reacts in the open like if iron is kept in the open it gets eroded.

  • Plastic is Light, Strong and Durable - Plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals. They are widely used in industry and for household articles.

  • Plastics are Poor Conductors - plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screwdrivers, handles of frying pans are also made of plastic.

  • Plastics find extensive use in the healthcare industry. Some examples of their use are the packaging of tablets, threads used for stitching wounds, syringes, doctors’ gloves and a number of medical instruments.

  • Special plastic cookware is used in microwave ovens for cooking food. In microwave ovens, the heat cooks the food but does not affect the plastic vessel. 

  • Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating on cookware.

  • Fire-proof plastics: Although synthetic fibre catches fire easily, it is interesting to know that the uniforms of firemen have a coating of melamine plastic to make them flame resistant. 


Plastics and the Environment 

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 non-biodegradable.

Therefore, according to definition plastic is non-biodegradable and doesn't go with the environment. plastic takes several years to decompose, it is not environment friendly. It causes environmental pollution.

It also doesn't get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution.

How can we limit the use of plastic?

  • Avoid the use of plastics as much as possible. Make use of bags made of cotton or jute when you go shopping.

  • The biodegradable and nonbiodegradable wastes should be collected separately and disposed off separately.

  • It is better to recycle plastic waste. Most of the thermoplastics can be recycled.

  • Use the 5 R principle. Reduce, Reuse, Recycle, Recover and Refuse. Develop habits which are environment friendly. 

  •  Do not throw plastic bags in the water bodies or on the road. 

  • Try to minimise the use of plastic materials e.g., use a steel lunch box instead of a plastic one. 

हम प्लास्टिक के उपयोग को कैसे सीमित कर सकते हैं?

  • जितना हो सके प्लास्टिक के इस्तेमाल से बचें। खरीदारी के लिए जाते समय रुई या जूट के बैग का प्रयोग करें।

  • बायोडिग्रेडेबल और नॉनबायोडिग्रेडेबल कचरे को अलग-अलग एकत्र किया जाना चाहिए और अलग-अलग निपटाया जाना चाहिए।

  • प्लास्टिक कचरे को रिसाइकिल करना बेहतर है। अधिकांश थर्माप्लास्टिक को पुनर्नवीनीकरण किया जा सकता है।

  • 5 आर सिद्धांत का प्रयोग करें। कम करें, पुन: उपयोग करें, रीसायकल करें, पुनर्प्राप्त करें और मना करें। ऐसी आदतें विकसित करें जो पर्यावरण के अनुकूल हों।

  •  प्लास्टिक की थैलियों को जलाशयों में या सड़क पर न फेंके।

  • प्लास्टिक सामग्री के उपयोग को कम से कम करने का प्रयास करें, उदाहरण के लिए, प्लास्टिक के बजाय स्टील लंच बॉक्स का उपयोग करें।

Summary Ends.

सारांश समाप्त।


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