Science Chapter 3 Synthetic Fibres And Plastics

Some fibres are called synthetic because they do not occur naturally and are made by man using petrochemicals.

B.

it is obtained from wood pulp

man-made

artificial fibres

petrochemicals

polymer

Nylon fibres are very strong, thus they are used to prepare ropes for mountaineering. They are also used to prepare parachutes.

Advantages of storing foods in plastic containers are :

(a) The plastics do not react with the food stored in them.

(b)The plastics are light weight and are strong.

(c) They are easy to handle and safe.

(d) They are lower in price.

Plastics which when moulded once, cannot be softened by heating. These are called thermosetting plastics.

a) Saucepan handles are made of thermosetting plastics because it resist fire and tolerate heat better than other plastics. Example of this kind of thermosetting is Melamine.

b) Thermosetting plastics such as bakelite are poor conductor of heat and electricity. Therefore, they are used for making electric, plug switches, plug board, etc.

Can be Recycled : Toys, carry bags, plastic bowls, ball point pens, plastic chairs, plastic covering on electrical wires.

Cannot be Recycled : Cooker handles, electrical switches, telephone instruments.

1) Cotton clothes are preferred to synthetic clothes in summers because cotton allows better air circulation, which helps in absorbing and removing body moisture caused by sweat. It therefore minimizes fungal breeding by keeping your body dry and cool.

2) Cotton is light in weight and in colour unless it is dyed. being light coloured will help the light to pass through instead of being absorbed and hence we will not feel the heat as much.

Following examples show that plastics are non-corrosive in nature :

(i) They are used to store chemicals. For example cleansing chemical are very reacticve and store in plastic bottle.

(ii) They are used to store all types of food, as it does not react to materials stored in it.

(iii) It does not even react with air and water.

No, the handle and bristles of a tooth brush should not be made of the same material because the bristles should be soft and the handle should be hard. So the bristles should be made up of soft material so that it does not harm the gums. The handles should be made up of hard material so that it can give firm grip. 

Plastics are harmful for our environment. Plastics are non- biodegradable. It add pollution to the environment. They cannot be burnt because, when they burnt they release poisonous gases. Some of the plastics cannot be recycled, so they cannot be used again and thus cannot be finally disposed off. They thus, should be avoided as far as possible.

Manufacturing synthetic fibres is actually helping conservation of forests because raw material for natural fibers are mainly derived from plants and this means cutting a lots of trees. This leads to deforestation. But raw material of synthetic material are mainly petrochemicals.Therefore it does not require cutting plants to get the natural fibres.

We will design a circuit to see that thermosetting are poor conductors of electricity. We need a bulbs, some wires, and a batterys, a piece of metal, and plastic pipe. Set up the circuit first with the metal and then with the plastic pipes as (shown in figure). After you switch on the current, you will observe that the bulb glows in the former case. In the latter case, the bulb does not glow. Hence, a plastic pipe (which is a thermoplastic) is shown to be a poor conductor of electricity.

The fibres obtained from plants or animals are called natural fibres. 

Two example of natural fibres are:

(i) Cotton

(ii) Jute

The fibres made by human beings are called synthetic fibres.

Two synthetic fibres are:

(i) Nylon

(ii) Rayon

When a large number of small units combine to form a single large unit, then the large unit is called polymer. For example polythene is polymer made of small units ethene.

Cellulose is a natural polymer.

Polythene is a polymer and its monomer is ethene.

Rayon have similar properties of silk.

Rayon was obtained by chemical treatment of wood pulp.

Nylon is used to make fishing nets and parachute ropes.

Parachutes, ropes for rock climbing and fishing net. 

Nylon fibre shrinks on burning forming beads and giving a smell of burning hair.

Ethene is monomer of polythene.

Natural silk and wool are natural amide polymer.

Nylon is synthetic amide polymer.

Terylene (or Dacron)

The polymer made up of the repeating units of ester is called polyster. Terylene is a popular polyester.
 

Acrylic is synthetic fibre which works like wool.

Plastic synthetic material made of many oraginc polymer such as polyethene, nylon etc., that can be moudlded into shape while soft, and then set into a rigid or slightly elastic form.

There are two types of arrangement of units in plastics.

(i) Linear linking

(ii) Cross linking.

Two example of Thermoplastics are:
Polythene and PVC.

Thermosetting plastics are:
Bakelite and Melamine.

Plastics take several years to decompose, so it is not eco-friendly.

Plastic like thermosetting is a poor conductor of electricity and heat. Hence, it used to cover electric wires.

It is so because these are poor conductors of heat. They hardly allow to flow heat form them.

Thermosetting plastic is used for making handle of a  pressure cooker. 

The two main problems are:

(i) Soil pollution.

(ii) Blockage of drains and sewer lines.

Lightness, strength, durability, non-reactiveness and easily availble in market at lower cost.

Ethylene glycol and Terephthalic acid are monomer of decron.

Thermoplastic is better material for making of PVC pipes.

Synthetic fibres have so popular because of their much superior properties as compared to natural fibres like cotton, silk and wool. For example :

(i) Synthetic fibres absorb very little water. So, the clothes made of synthetic fibres dry quickly after washing.

(ii) Synthetic fibres are very strong. So the clothes made of synthetic fibres last for a long time. It is also used for making parachutes and ropes for rock climbing.

Advantage : They last longer as compared the fabrics made from natural fibres.

Disadvantage : Synthetic fibres are nonbiodegradable. Therefore, they cause soil pollution and sometimes they can also cause skin problems.

Properties of polyvinyl chloride :

(i) It is tougher than polythene.

(ii) It gets deformed easily on heating and can be bent.

Uses of polyvinyl chloride :

(i) It is used for making shoe-soles and shoes.

(ii) It is used for making rain coats and floor and ceiling fans.

Raw materials used in the preparation of bakelite are :-
phenol and formaldehyde.

Uses of Bakelite :

(i) It is used for making electrical switches and plugs.

(ii) It is used for making gear wheels and table top laminates.

Cloths made of synthetic fibres melt on heating and catches fire, it can very disatrous. The fabrics melts and sticks to the body of the person wearing it. Therefore, it is advised to not wear synthetic clothes while working in a laboratory or working near the fire in the kitchen.

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. This is because they are widely used in industries and household articles.

4R stands for 

(i) Reduce : The use of nonbiodegradable materials.

(ii) Reuse : We should use the materials again and again.

(iii) Recycle : We should use the materials which can be recycled.

(iv) Recover : Recover the lacking substances.

Melamine.

Teflon

Bakelite

PVC (Poly-Vinyl Chloride)

Bakelite

Polythene

Fibre B

Fibre C

Fibre A

Cellulose

Fibre C (Rayon)

Fibre B (Terylene)

Polythene carry bags are thrown here and there after using them. Stray cattle consume them. Since it is not digested by animal and it can choke the respiratory system and damage their stomach. It can even cause their death.

Those plastics which can melt on heating and which can be reshaped on moulding again and again are called thermoplastics. P.V.C., Polythene are examples of thermoplastics. Toys, containers, car grills, combs etc. are made with thermoplastics.

Thermosetting plastics are those plastics, which can be only moulded for once. They cannot be reshaped or reused because they do not get softened on heating. Bakelite, melamine etc. are examples of thermosetting plastics.

Bakelite is a thermosetting plastic. It is a bad conductor of heat. It does not allow heat to pass through it easily. So, it is used to make the handles of the utensils so that it does not get heated and it becomes easy to handle the cookware while cooking.

Plastics are poor conductor of electricity and resistant to heat, so they do not allow the electric current to pass through them making them safe to handle. So they are used to make electric switches and plugs.

Terylene, PET are polyesters.

Nylon

Acrylic

PET

Biodegradable substances are those substances which can be decomposed by bacteria and other natural processes. For example leaf, wood, silk etc.

Those substances which cannot be decomposed are called non-biodegradable substances. Plastics are non-biodegradable. For example polythene, nylon, plastics, etc.

Plastics are considered as threats to the environment because they are not easily decomposed. Being non-biodegradable its disposal is the major problem, which can pollute the environment.

Biodegradable materials : A material which gets decomposed through natural process, such as action by microorganisms is called biodegradable. For example, paper, leaves, vegetables, fruits etc.

Non-biodegradable materials : A material which is not easily decomposed by natural processes, such as action of microorganisms are called non-biodegradable materials. For example : Glass, copper, plastics, synthetic fibres etc.

Uses of Polyvinyl Chloride :

(i) It is used for the manufacture of raincoats, hand bags, plastic dolls, bathroom curtains etc.

(ii) It is used for manufacturing flooring and floor/ceiling tiles.

(iii) It is used to manfacture pipes.

Uses of Bakelite :

(i) It is used for making electrical switches and plugs.

(ii) It is used for making gear wheels and table top laminates.

Following are the main artificial fibres with their uses:

(i) Rayon : Rayon called the artificial silk as it has great lustre and is light in weight. It is obtained by the chemical treatment of wood pulp. It can be woven like silk and dyed in different colours. It is used as dress material. Mixed with cotton, it is used to make curtains, bedsheets etc. It is mixed with wool to make beautiful carpets.

(ii) Nylon : It is the strongest fibre. It is made by coal, water and air. It is elastic in nature and light in weight. It is lustrous and thus ideal for making dresses. It is also used to make stockings, seat belts, ropes, tents, toothbrushes, sleeping bags, curtains and parachutes etc.

(iii) Polyester : It is made up of multiple units of ‘esters’. The clothings made of this fibre do not get wrinkled easily. It is always crisp and easily washable. PET is also derived from polyester which in turn is used to make containers, utensils, films, wires etc.

(iv) Acrylic : Acrylic is just like wool and is used to make sweaters and suit lengths.

A polyester fibre is prepared by reacting a dicarboxylic acid with a dihydric alcohol. The reaction between acid groups and alcohol jumps of these two compounds leads to the formation of a long-chain polymer called polyester. A typical polyester fibre is terylene.

Polyester fibres absorb very little water due to which polyester clothes dry quickly after washing. On the other hand, cotton fibres absorb a lot of water due to which cotton clothes do not dry quickly after washing.

Uses :

(i) Polyester fibres are used in the manufacture of textiles like sarees, dress materials and curtains.

(ii) Polyester fibres are used for making sails of sail boats and water hoses for fire fighting operations.

Plastic is a wonder material. Following characteristic features make it a common and popular choice :

(i) Plastics are light in weight so they are easy to handle and manage.

(ii) Plastics are strong and durable so they are used to make buckets, mugs, ropes etc.

(iii) Plastics are non-reactive as they do not get corroded when they come in contact with other materials or substances. This property make them perfect for storing food items and chemicals.

(iv) Plastics are poor conductors of electricity. They do not allow the electric current to pass through them easily. They are, therefore, used to make coverings of electric wires and other electric appliances.

v) plastics are cheaper. Therefore everyone can afford it.

Synthetic fibres are made from chemical substances. Their qualities are quite different from those of natural fibres. Following are the characteristic features of the synthetic fibres :

1. Raw material : All synthetic fibres are made from chemicals. They are prepared by a number of processes using raw materials of petroleum family called petrochemicals.

2. Strength : Synthetic fibres are quite strong. Nylon is the strongest known fibre.

3. Durability : Synthetic fibres are quite durable. They do not wither easily. They are so strong and durable that ropes and parachutes etc. are made by using synthetic fibres.

4. Soak less water : Synthetic fibres absorb small quantities of water and loose it quick, so they dry up very soon.

5. Availability and cost : Synthetic fibres are less expensive and readily available. That makes it a popular dress material.

Procedure :
1. Take a 15-20 cm long loose strand of cotton fibre. Break it into two parts of nearly equal size. Twist one part of it to make a thread. Let the other piece be as such.

2. Hold the untwisted part and apply a pull on its both the ends till it breaks.

3. Repeat the same with the twisted part till it breaks.

4. Compare the pull required to break the twisted and the untwisted thread.

Observation :
Greater force (or pull) is required to break the twisted thread than the untwisted thread.

Inference :
Twisting of fibres into yarn (or thread) increases the strength of the fibres.

The articles are parachute and ropes for rock climbing.

The substance used in making these articles is Nylon.

Nylon is actually stronger and lighter than any other substance. Therefore, it is used to make these kind of article.  

a) Linear arrangment:



b) Cross linked arrangment:

The articles are as follows :

(a) Chair (Thremosetting)

(b) Bucket(Thremoplastics)

(c) Glass (Thremoplastics)

(d) Toy Scooter (Thremoplastics)

Cellulose

man-made

polythene

remoulded

plants

ethene

Bakelite

Thermosetting

silk

Melamine

resistant

C.

rayon

D.

rayon

B.

thermoplastics

C.

rayon

B.

fibre

C.

bakelite

C.

bakelite

A.

rayon

B.

nylon

B.

polyester