SYNTHETIC FIBRES AND PLASTICS Chapter 3 Class VIII (C.B.S.E.)

SYNTHETIC FIBRES AND PLASTICS Chapter 3 Class VIII (C.B.S.E.)

Key Learning Points- Introduction, Synthetic fibres, Polymers, Characteristics of Synthetic fibres, Types of synthetic fibres and their uses, Plastic, Types of plastics- thermoplastics and thermosetting plastics, Characteristics of synthetic fibres or plastic, Plastic and environment.

Plastics Articles

INTRODUCTION-The thin thread which is made up of natural or synthetic substance is called fibre. The natural fibres are obtained from plants and animals. e.g. Silk, cotton, wool, Jute etc. Natural fibres are limited in production as well as costly. Synthetic fibres are prepared in factories as an alternative of natural fibres and other reasons. They are durable i.e. last longer, cost-effective, and comparatively better in quality than natural fibres. e.g.- Rayon, Nylon, Acrylic, polyester, P.E.T., Terylene etc.

SYNTHETIC FIBRES- Those fibres which are made by chemical process using chemical substances are called synthetic or artificial or man-made materials. The synthetic fibres are prepared from petrochemicals. Synthetic fibres are made up of polymers. Polymers (Gr. Poly= many + mer =part/unit) are long chains of monomers. The synthetic fibres are made up of numerous polymers. Monomers are like units that combine together to form a polymer.

POLYMERS (Gr. Poly= many + mer =part/unit)-Polymers are long chain of repeating units called monomers. Numerous polymer chains form any particular substances. The monomers are changed into polymers by polymerization process. If we take the example of a necklace, the beads represent the monomers and the necklace represents the polymer. e.g.-‘Ester’ monomers form the ‘Polyester’ fibers. The cotton fibres are made up of ‘cellulose’ polymer. Cellulose polymer is made up of ‘glucose’ monomers.

Polymers are- light in weight, strong, durable, can be moulded into different shapes and cost-effective.

TYPES OF SYNTHETIC FIBRES-The main examples of synthetic fibres are-

1.  RAYON (or ARTIFICIAL SILK)- Natural silk is very costly and difficult to produce from cocoons. Towards the end of nineteenth century, a synthetic fibre was prepared from ‘wood pulp’. It was called ‘viscose’ and in 1924 named ‘rayon’. The wood is made up of cellulose (a complex carbohydrate). The rayon is prepared from cellulose units by decomposition and regeneration. So, the rayon is a regenerated fibre.

It is cheaper than natural silk, absorbs moisture and sweat and therefore is comfortable to wear clothes made up of rayon. Rayon shines like silk and can be dyed in different colours.

Uses of Rayon-

1. Rayon can be easily woven like silk fibres. Different coloured clothes can be made.

2. Rayon is used to make suit, sarees, blouse, tie, jacket etc.

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

4. Rayon is mixed with wool to make carpets.                  

2. NYLON- Nylon is the first fully synthetic material made in 1931. It was prepared from coal, water and air. None of the material used in its preparation was of plants or animal origin. The name ‘NYLON’ was coined based on the name of two cities NEW YORK (NY) AND LONDON (LON).

Nylon fibres are strong, elastic and light in weight. It has luster and can be easily washed. It is stronger than silk, wool, cotton and steel wire. These properties make nylon especial to make different articles. Nylon ropes are so strong and light weight that they are used in rock climbing.

Uses of Nylon-

1. Nylon is used to make clothes like socks, sportswear, hosiery garments, curtains etc.

2. Nylon is used to prepare ropes, toothbrush, tents, sleeping bags, car seat belts etc.

3. Nylon is used to make parachutes.  

                                                                    

                                                                   

3. POLYERTSER-This synthetic fibre is made up of ‘ester’ monomers. Esters have sweet smell like fruits. It is a very fine material for preparing clothes because it does not wrinkle, easy to wash and dries quickly. Terylene, Tyrolean, Dacron and P.E.T. are well known polyester. It can be mixed with cotton fibres to form polycot, mixed with wool to form polywool; terylene is mixed with cotton to form terrycot etc.

                         Polyester + Cotton = Polycot

                         Polyester + Wool = Polywool

                         Terylene + Cotton = Terrycot

P.E.T. (Polyethene Tetraphthalate) is prepared by polymerization of ethane tetraphthalate. It is used to make, shirts, magnetic tapes for audio and video cassette recorders and bottles for drinking water, cold drinks, oils etc.

Uses of Polyester-

1. Shirts, pants and other dressing materials are prepared from polyester particularly by mixing with cotton and wool.

2. Polyester is used to prepare insulating materials, upholstery paddings, cushions, bed sheets, conveyor belts etc.

3. P.E.T. is used to make utensils, bottles, films, wires etc.

4. ACRYLIC- This synthetic fibre is prepared by polymerization of acrylonitrite molecules. It is very soft and light as like wool. It hardly weathers.

Uses of Acrylic-

1. Acrylic is used to make sweaters and shawls.

2. Acrylic is used to make very light and warm woolen blankets.

5. PLASTIC-Plastics are synthetic polymers which can be drawn into fibre and moulded into different shapes. Plastic are normally non-expandable. Plastics are used in various ways because of property of being remoulded. There is hardly any field where plastic is not used. E.g. Polythene, PVC (Polyvinyl Chloride), Melamine, Bakelite etc.

There are two types of plastics- (a) Thermoplastics

                                                   (b) Thermosetting plastics

(a) Thermoplastics- Those plastics which get deformed easily on heating and can be bent easily are called thermoplastics. e.g. Polythene, PVC (Polyvinyl Chloride), Polystyrene, Polypropylene, Teflon etc. Teflon is used to make nonstick cook wares. They can be recycled. They become soft on heating and hard on cooling, therefore, can be remolded again.

Polypropylene (PP) containers

PET Containers

Polythene and PVC are used in making of toys, combs, wires and different types of containers.

HDPE Containers

(b) Thermosetting Plastics- Those plastics which when moulded once, cannot be softened and remoulded by heating easily. e. g. Melamine, Bakelite etc. They cannot be recycled. They often break on applying force. They are good insulators of heat and current. The articles made up of thermoplastics maintain their shape on very high temperatures.

Bakelite is used to prepare electric switches, handles of different utensils etc. Melamine resists fire and comparatively better in heat tolerance. It is used to prepare kitchen wares (crockery), microwave oven suitable containers, fire resistant clothes, floor tiles etc.

 Switch of Bakelite

Melamine Utensils

CHARACTERISTICS OF SYNTHETIC FIBRES OR PLASTIC-Synthetic fibre are light in weight, cost-effective, available in different colours, easy to handle and clean, do not react  with chemicals and acids, last longer, poor conductors of heat and electricity and free from bacterial actions.

The disadvantage of synthetic fibres is that they melt on heating. Synthetic clothes catch fire easily, melts and stick to the body of person wearing it. Therefore, utmost precautions must be taken while wearing synthetic clothes in the kitchen and laboratory.

PLASTIC AND ENVIRONMENT- Plastics are extensively used in packing industry. There excessive use also generates lots of plastic garbage. There is a challenge in disposal of plastic wastes. Plastics are not eco-friendly. Many plastics release carcinogenic chemicals in hot food kept in them. Medical wastes contain a number of plastic products. They are usually thrown in open or burnt in incinerators that cause air pollution. They choke the drainage pipes.

Those materials which decompose naturally by bacteria and fungi are called biodegradable materials. e.g. food waste, peels of fruits, paper, wood, cotton clothes, woolen clothes etc. Those materials which do not decompose naturally are called non-biodegradable materials. e. g.-Plastic wastes, metals objects etc. plastic products take several years to decompose. Burning of plastic wastes cause air pollution. Therefore, we should use biodegradable things as much as can be.  The use of cotton and jute bags is one such major as both are biodegradable.   Thermoplastics can be recycled but thermosetting plastics cause major problem of disposal. As a responsible citizen we should follow the principles of 4R- reduce, reuse, Recycle and Recover.

CHECK YOUR PROGRESS          TIME- 40 MINUTES           MARKS- 4 x 5=20

Q.1 What is synthetic fibre? Write characteristics of synthetic fibres.

Q.2 Write short notes on – Rayon and Nylon.

Q.3 What is plastic? Differentiate between thermoplastic and thermosetting plastic.

Q.4 Why plastics are favored for storing the food items like pickle?

GROUP PROJECT- 

Collect different kinds of plastics and prepare a detail of each type of plastic.

                                         SOLVED EXERCISE QUESTIONS

Q.1 Explain why some fibres are called synthetic.

Ans- There are some fibres which are not found naturally. They are prepared by humans by chemical processes. That is why they are called synthetic or man- made fibres. e.g. – Nylon, Polyester, Acrylic, Plastic, etc.

Q.2 Mark the correct answer:

Rayon is different from synthetic fibres because

(a) it has a silk like appearance

(b) it is obtained from wood pulp

(c) its fibres can also be woven like those of natural fibres.

Ans- (b)

Q.3 Fill in the blanks with appropriate words:

(a) Synthetic fibres are also called ……………… or ……………… fibres.

(b) Synthetic fibres are synthesized from raw material called …………………….

(c) Like synthetic fibres, plastic is also a ………………..

Ans-(a) artificial , man-made    (b) petrochemicals   (c) polymers

Q.4 Give two examples which indicate that nylon fibres are very strong.

Ans-Nylon is very strong synthetic fibres. They are used in preparing climbing ropes, parachutes, tents, tooth brush etc. These examples show the toughness of nylon because of which they last longer.

Q.5 Explain why plastic containers are favoured for storing food.

Ans- Plastic containers are light in weight, durable, cost-effective, easy to handle and clean. Plastic containers do not have the effect of chemicals, food items kept in them and bacterial action is negligible. These features make plastic a favoured choice for storing food items.

Q.6 Explain the difference between the thermoplastic and thermosetting plastics. Ans-

S.N.	Thermoplastic Plastics	Thermosetting Plastics
1	They get softened and deformed on heating.	They do not become soft and retain the shape on heating.
2	They become soft on heating and hard on cooling.	They maintain the shape on heating.
3	They can be remoulded and recycled	On break on applying force and cannot be recycled.

 

Q.7 Explain why the following are made of thermosetting plastics:

      (a) Saucepan handles     (b) Electric plugs/ switches/ plug boards

Ans-(a) Saucepan handles are made up of thermosetting plastics because on heating their shape does not change. Thermosetting plastics are also poor conductors of heat.

(b) Electric plugs/ switches/ plug boards are made up of thermosetting plastics like Bakelite and melamine because they are poor conductors (or insulators) of heat.

 

 Q.8 Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’:

Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on electric wires, plastic chairs, electric switches

Ans-

Can be recycled	Cannot be recycled
Plastic toys	Telephone instruments
Carry bags	Cooker handles
Ball point pens	Electric switches
Plastic bowls
Plastic covering on electric wires
Plastic chairs

 

Q.9 Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic materials? Advise Rana, giving your reason.

Ans- Cotton clothes are good absorbent of sweat coming out of body. The absorbed sweat is exposed on outer layers of cotton clothes and start evaporating. So, the cooling is caused. This is the reason Rana should buy the cotton shirts for summer.

Q.10 Give examples to show that plastics are non-corrosive in nature.

Ans- Plastics hardly react with any chemical substance; therefore, they do not corrode easily. e. g.- Teflon is a plastic which is used to prepare non-stick coating on cooking pans and other utensils. e. g- Plastic containers are used to store many chemicals in laboratories.

Q.11 Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.

Ans- No, handle of toothbrush should be hard and flexible to withstand the stress applied by the person. Whereas, the bristles of the toothbrush should be made of soft, flexible and long-lasting synthetic fibres so that the gums and teeth do not get damaged as well as last longer.

 Q.12 ‘Avoid plastics as far as possible’. Comment on this advice.

Ans- Plastic is a non-biodegradable material. The used plastic products get accumulated in environment and cause several environment problems. Their disposal is a big challenge. On burning they produce harmful smokes and therefore cause air pollution.

When food items thrown in plastic carry bags are often eaten by stray animals and birds. Thus many health hazards are caused due to plastic in such animals. The polythene bags clog the drainage systems and cause many problems. These are some reasons due to which we should avoid plastic as far as possible.

Q.13 Match the terms of column I correctly with the phrases given in column II.

Ans-      Column I                                                         Column II

         (i) Polyester                                  (a) Prepared by using wood pulp

         (ii) Teflon                                      (b) Used for making parachutes and stockings

         (iii) Rayon                                     (c) Used to make non-stick cookwares

         (iv) Nylon                                      (d) Fabrics do not wrinkle easily

Ans- (i) –d      (ii)-c   (iii)-a     (iv)- b

Q.14 ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.

Answer- Natural fibres are obtained from plants and animals. In a forest, plants and animals are interdependent upon each other. The natural fibres are generally obtained by cutting the plants and killing of animals. On the other hand synthetic fibres are prepared from petrochemicals. Therefore, manufacturing of synthetic fibres is in fact helps in conservation of forests.

Q.15 Describe an activity to show that thermoplastic is a poor conductor of electricity.

Ans- In this simple electric circuit, the metal wire is replaced by a small piece of plastic. When switch is on the bulb does not glows. This proves that presence of plastic is not allowing the current to pass and thermoplastic is a poor conductor (or insulator) of current. 

Plastic as an insulator

COMPONENTS OF FOOD Chapter 2 Class 6 (C.B.S.E.)

Understanding Concepts- Food, Functions of Food, Components of Food and their functions, Obesity, Balanced Diet, Deficiency Diseases

COMPONENTS OF FOOD   Chapter   2 Class 6 (C.B.S.E.)

Introduction-Food is the basic requirement of all living organisms. We eat different kinds of food. Some foods provide us energy, some food provide us energy to work, some food help in development and maintenance of body while some others  keep us healthy and strong. Food provides different kinds of nutrients. By eating different varieties of food, we get different kinds of nutrients. The food on which daily energy and nutrients requirements of a person / organism depends is called diet.

Functions of Food-Following are the functions of food-

1.       Food give us energy to do various activities

2.       Food helps us for the growth and development of our body.

3.       Food provides various nutrients for maintenance of body.

4.       Food helps in repair of injury and cut, replacing dead tissue and healing of wounds.

5.       Food helps to fight against germ (pathogens) and protect us from diseases.

6.       A balanced and healthy food makes us healthy and strong.

Components of Food-In different parts of the world different kinds of food are eaten. The main food eaten in any region is called staple food. e.g.- Rice, wheat flour (Atta), pearl millet (bajra), potato and pulses are the staple foods of India. The climatic conditions and prevailing food habits decide the type of crops cultivated in any region.

The dish (prepared food) contains one or more ingredients. The essential things called nutrients are found in the food. The nutrients are of two types-

(a)    Micro-nutrients-

(b)   Macro-nutrients-

Micro-nutrients are required in fewer amounts while macro-nutrients are required in more amounts. These nutrients belong to seven categories- carbohydrate, protein, fats (lipids), vitamins, minerals, dietary fibers and water.

1.   Carbohydrate- They give energy by undergoing digestion and then by oxidation inside the cells. Glucose, a carbohydrate is formed during photosynthesis in plants. Glucose changes to starch (a complex carbohydrate) in plants.  Carbohydrates are sweet in taste. The carbohydrate is found in potato, rice, wheat, sugar, sweet fruits etc. Carbohydrate turns bluish- black in colour on testing with iodine.
                              

2.    Protein- Proteins are body building components of food. They help in formation of new cells. They help in repair of injured cells, growth and development of body.  Proteins are of different types. On adding 10 drops of sodium hydroxide and 2 drops of Copper (II) sulphate the sample of protein changes to bluish- violet colour. This is called Biurette test of protein.  Protein is found in – milk, eggs, fish, meat, soya bean, grams, peas, lentils, beans, etc. Milk is called complete food. It gives carbohydrate, protein, fat, calcium and phosphorus like minerals.

                                   

 

Functions-Protein helps in growth and development of the body. Protein is helpful for nails, hairs, skin and muscles. Proteins help in repair of injured cells. In Red blood cells protein is found.

3.  Fats (Lipids)-They are richest source of energy as compared to carbohydrates. Excess fat is stored in our body and gives energy as per requirement. Polar bears, walrus and whale especially store fats in their body. Fats in liquid state are called lipids. Fats add flavor to food along with spices. When the fatty or oily substance like poori, pakauri, chips etc.  is taken in the white paper, some greasy spots can be seen.

Functions- Fats give highest energy on oxidation in the cells. Fats keep the body warm by making a thermal insulator layer below the skin. So, the loss of heat of the body is negligible. The deposition of fat as a layer below the skin protect from jerks.

4.  Vitamins-Vitamins are essential for the protection of body from diseases. They are required in trace amount. Deficiency diseases are caused due to lack of vitamins. e. g-Anemia, Rickets, Scurvy etc. Vitamins are mainly found in fruits and vegetables. Vitamins are also found in cereals, milk, honey, egg, fish, meat, pulses and sprouts. Vitamins are taken from outside our body but in the sunlight our body can prepare vitamin D.

On the basis of their solubility, there are two types of vitamins-

                                              

 (i) Fat soluble vitamins- They are easily absorbed by the body fats. E.g.- Vitamin- A, D, E, and K.

(ii) Water soluble vitamins- They dissolve in water. Excess amount of these kinds of vitamins are removed from the body through urine. e.g.- Vitamin B Complex and Vitamin C. 

Functions-

 (A). Vitamin A helps in keeping eyes and skin healthy, normal growth, and prevent from infections.

(B). Vitamin B-Complex (B₁, B₂, B₃, B₅, B₆ and B₁₂) help in normal digestion of carbohydrate, protein and fats. They help in normal growth and nervous tissue functions.  Vitamin B₁₂ prevents from anemia.

(C). Vitamin C-It, chemical name is ascorbic acid. It is useful for skin, teeth, gums, bones, immunity development and formation of red blood cells. Indian gooseberry (Amla) (Phyllanthus emblica or Emblica officinalis) is the richest source of vitamin C. Citrus fruits like –lemon, orange, turmeric, tomato, oranges, melons vegetables etc are good sources of vitamin C.

(D). Vitamin D- It’s chemical name is calciferol. It helps in absorption of calcium to teeth and bones. Sunlight helps in formation of Vitamin D in our body.

        (E). Vitamin E- It’s deficiency causes infertility. It helps in protecting eyesight, glowing skin, boosting immunity, reduces chance of heart problems and cancer. It is found in vegetables, fruits, sprouts and edible oils.

        (K). Vitamin K- It helps in blood clotting during injury. It is found in cereals, groundnuts, potatoes, meat, fish and chicken.

5.  Mineral-salts- Mineral salts are essentially required in trace amount. About 20 types of mineral-salts are required by our body. Mineral-salts help in proper growth, development and maintenance of the body. E.g.-Calcium-it is essential for bones teeth and blood clotting. It is found in milk, milk products, vegetables, fruits, meat etc.

       e.g.-Iodine- is necessary for normal growth of mind and body. It is necessary for thyroxin hormone formation by thyroid gland. Iodine is found in iodized salt, ocean fish, water, eggs, pineapple, tomato, spinaches, papaya etc.
         

 

    e.g.-Iron- It is an essential part of hemoglobin found in red blood  cells that help in carrying oxygen in our body. Iron is found in apple, papaya, sugarcane juice, jaggery, vegetables, spinach, meat, chicken, fish etc.

  Other important minerals are phosphorus, manganese, sodium, potassium etc.

                6.  Dietary fibres (Roughages)-They are fibres present in the food.                          They do not provide any energy but help in cleaning the                                       alimentary canal of the body. Plant based foods like vegetables,                            fruits, cereals, pulses, potatoes etc provide dietary fibres. Dietary                        fibres helps in digestion   by bowel movement, do not cause                                  constipation, control blood sugar level, reduce cholesterol level 

                    and retain water in the body.

                                    

          7. Water- About 70 % of our body is made up of water. Water is  necessary for metabolic activities and fulfills mineral-salts requirements. Water regulates the body temperature. The excess salts, urine and waste materials are removed from the body due to water. It dilutes the blood and help in transportation of nutrients.

Obesity- Overeating and not doing exercise, enough work causes obesity. Persons suffering from obesity are called obese. Obesity   makes the person unhealthy and unfit to do work efficiently. Food calories should be taken in required amount and must be burnt to reduce over weight.

Balanced Diet-A diet that contains carbohydrate, protein, fats, vitamins, minerals and dietary fibres (roughages) in required proportion is called a balanced diet.

Balanced diet is necessary for growth, development and maintenance of good health. The energy present in the food is measured in calories. Every kind of food has some calories. We should take calories as per our age and nature of work we do.

Deficiency Diseases- Those diseases which are caused due to lack of taking of essential nutrients, vitamins, minerals in the food for long time are called deficiency diseases. Deficiency diseases can be lethal. Taking of balanced diet prevents deficiency diseases. e.g.- Kwashiorkor, Marasmus, Anemia, Rickets, Scurvy, Night blindness, Goiter , Beriberi etc. 

Vitamin/ Mineral	Deficiency disease/disorder	Symptom
Vitamin A	Loss of vision	Loss of vision, Less vision, night blindness
Vitamin B1	Beriberi	Less energy, Weak muscles
Vitamin C	Scurvy	Less healing of wound, bleeding gum
Vitamin D	Rickets	Soft bones and bending
Calcium	Bone and Tooth Decay	Weak bones ,Tooth decay
Iodine	Goiter	Mental weakness, Swollen neck
Iron	Anemia	Fatigue, Breathlessness

              PROJECT WORKS--

1. Prepare a group project on healthy eating habits.

2. Prepare a diet chart for- a baby, an adolescent boy, an adolescent girl, an adult person and an old person.

3. Explain deficiency diseases with a suitable table of characteristics of deficiency diseases.

4. Prepare a detailed report on excess eating of fats, protein and vitamins.

5. What should be the diet for a milch and a drought animal? Describe.

CHECK YOUR PROGRESS  Time =40 Minutes   Total Marks= 5 x 4 = 20

1. What is food? Write all its components.

2. Write one function each of- Carbohydrate, proteins, fats, Vitamins, minerals and dietary fibres.

3. What is balanced diet? Write its advantage.

4. What are deficiency diseases? Cite three examples of such diseases.

                                    SOLVED EXERCISE QUESTIONS

Q.1 Name the major nutrients in our food.

Ans- The major nutrients in our food are- carbohydrate, protein, fats (lipids), vitamins and minerals. Dietary fibres and water are minor nutrients.

Q.2 Name the following:

   (a) The nutrients which mainly give energy to our body.

   (b) The nutrients that are needed for the growth and maintenance of             our body.

   (c) A vitamin required for maintaining good eyesight.

   (d) A mineral that is required for keeping our bones healthy.

Ans- (a) Carbohydrate and fats (lipids)            (b) Protein  

         (c) Vitamin A                                              (d) calcium

Q.3 Name two foods rich in:

    (a) Fats      (b) starch     (c) Dietary fibres     (d) Protein

Ans- (a) Fats- Cooking oil, Butter                      (b) Starch- Rice, Potato

         (c) Dietary fibres- Vegetables, Fruits        (d) Protein- Milk, Eggs

Q.4 Tick (√) the statements that are correct.

    (a) By eating rice alone, we can fulfill nutritional requirement of                   our body. ( )

   (b) Deficiency diseases can be prevented by eating a balanced diet. ( )

   (c) Balanced diet for the body should contain a variety of food items( )

   (d) Meal alone is sufficient to provide all nutrients to the body. ( )

Ans- (a) Incorrect (x)                                    (b) Correct (√)

         (c) Correct (√)                                       (d)Incorrect(x)                                            

Q.5 Fill in the blanks.

   (a) …………is caused by deficiency of Vitamin D.

   (b) Deficiency of …………causes  a disease known as beri-beri.

   (c) Deficiency of Vitamin C causes a disease known as …………

   (d) Night blindness is caused due to deficiency of ……..in our food.

Ans- (a) Rickets                                               (b) Vitamin B₁

          (c) Scurvy                                               (d) Vitamin A