Synthetic fibres and plastics

 FIBRES

•     Long strands of molecules interwoven to form a linear, string-like structure are known as fibres.

•      Fibres can be natural as well as synthetic depending on the source of the raw material.

•     Fibres are made up of molecules called polymers.

POLYMERS

 Polymers are huge molecules- usually consisting of long chains made from thousands of similar molecules called monomers.

·    Polymers are huge molecules- usually consisting of long chains made from thousands of similar molecules called monomers.

·   The structure of a monomers can be compared to that of a beaded necklace- with the beads being the monomers.

·  The process by which monomers are linked together to form polymers is called polymerization.

·   Polymers can be linear or cross-linked in structure.

There are two types of fibres. They are

1.  Natural Fibres: - Natural fibres may be made from Plants or Animals.

    Cotton. Jute and Coconut are Plant fibres where as Silk and Wool are Animal fibre.

2.  Synthetic Fibres: - Synthetic fibres are man-made fibres. They are made from bye- products of petroleum known as the petrochemicals.

Examples:-Rayon, Nylon, Polyester, Acrylic  

Polymers:-  Poly = Many Meres= Units

Polymers are long chain molecules formed by the combination of many smaller units known as monomers (mono=single,  mere=units

The process of formation of long chain compounds polymers by the combination of monomers is called polymerisation reaction.

Rayon

Rayon is a man made fibre obtained from wood pulp(cellulose) on chemical treatment with NaOH,Carbon disulphide and Sulphuric acid .

he properties of rayon is similar to silk and it shrink like silk.So it is commonly called Artificial Silk

Properties of rayon :-

·  Rayon is soft, durable and strong fibre.

·  It can be dyed into various colours.

 Uses of rayon :-

·  Used for making fabrics

·   For making bed sheets and carpets 

·   Used to make surgical products like bandages.

Nylon:-

·   Nylon is the first fully synthetic fibre made in 1931.

·  Its name is derived from the cities of New York and London, where it was first marketed.

·   It was prepared from coal, water and air.

·   Nylon is made by the polymerisation of a dicarboxylic acid with a diamine.

 Properties of nylon :-

·   Very strong (stronger than steel wire)

·  Elastic and Light

·     Wrinkle and Wear resistant

·  Easy to wash

·  Absorbs very little water

·   Lustrous in appearaance

 Uses of nylon :-

·  Used for making fishing nets.

      · Various fabrics are made from nylon. 

·   Ropes are made from nylon

·   Tooth brush, tents, car seats etc are made.

·   Parachutes are made using nylon.

·  Curtains, bags, socks, etc are made.

Polyester:-

·  Polyesters are polymers of alcohols and carboxylic acids.

·   Terylene is popular polyester formed from terepthallic acid and glycol.

·  PET - Poly Ethylene Terepthallate is familiar form of polyester used for making bottles, films, wires, vessels, etc.

·   With cotton it makes Polycot and with wool it makes Poly-wool.

Properties of polyester- 

·  Very strong

·    Elastic

·   Light

·  Crease-resistant

·  Water-resistant

Uses of polyester-

·  It is used to make clothes such as trousers, shirts

·  Being water resistant it is used to make jackets and garments used in wet or damp environments

· PET is a form of polyester used to make bottes, films, utensils, wires, etc

Acrylic :- 

· It is a type of synthetic fibre that resembles  wool       in it’s properties.

· Clothes made from acrylic are cheaper than wool.

Properties of acrylic 

·  Acrylic are very cheap or affordable

·  Light weight

·   Soft and Warm

·  Wrinkle-resistant

·   Resists shrinkage

· Can be dyed in various  colours

Acrylic Uses:

·  Acrylic Fabrics-It is used to make sweaters, tracksuits etc. as it is soft and warm like wool.

·   Paints

· Utensils

Characteristics of Synthetic Fibres :-

· Synthetic fibres are less expensive or affordable to all.

  · They are durable.

· Readily available.

·   Easy to maintain.

      · Synthetic clothes dry quickly.

      ·   Light weight

       · Chemically inert.

       Advantagesof synthetic fibres-

       ·     Crease-resistant

       ·    Elastic

· Moth proof

·  Easy to wash

·    Last for along time

Disadvantages of synthetic fibres

·   Do not absorb sweat

·   Stick to the body in hot and humid weather

·  Catches fire very rapidly

·    Melt on heating and stick to the body and can cause severe burn injuries

                       Plastics

A material is said to be plastic if it can be moulded or formed into different shapes. They are made of polymers.

Sources of plastics

The main source of these plastics is crude oil.

Properties of plastics with their linked uses

·  INSOLUBLE IN WATER -They are waterproof and insoluble in water and so are used to make raincoats, water bottles, buckets etc.

· LOW THERMAL CONDUCTIVITY-They are poor conductors of heat and that is why they are used to make handles of cooking utensils and as insulating wool in refrigerators.

· POOR CONDUCTOR OF ELECTRICITY-They are poor conductors of electricity and so electric wires, cords of electrical appliances and cables have a plastic coating.

· NON-REACTIVE-They have no reaction with water and air. They do not corrode easily. They are therefore used to store chemicals such as acids.

· INFLAMMABLE

     They are inflammable i.e. burns easily and so can be melted, moulded and recycled into different products.

Types of plastics

Plastics can be categorized into two different groups depending on their reaction to heat. These are:

1.     Thermoplastics

2.     Thermosetting plastics

Difference between Thermoplastics and thermosetting plastics

THERMOPLASTICS	THERMOSETTING PLASTICS
In these plastics, the process of softening by heating and hardening on cooling can be repeated again and again to soften the plastic to get different shapes.	These plastics can be softened by heating only once. Once they are put into a mould and allowed to harden on cooling, they cannot be softened again on heating.
They cannot maintain their shape and size at very high temperature. Ex. – Polythene	They can maintain their shape and size even at very high temperature. Ex. – Bakelite

Some common plastics and their uses

MAN-MADE  PLASTIC	TYPE OF  PLASTIC	PROPERTY	USES
Polythene	Thermoplastic	Strong but flexible, can be rolled into sheets or moulded into any shape, water resistant	Sheets of polythene are used to pack liquids such as milk, polythene pipes are used to transport liquids such as oil or water, polythene containers are used to store liquids
Polyvinyl chloride (PVC)	Thermoplastic	Tougher than polythene, insulator	Used as covering for electric wires, used to make shoes, handbags, furniture, upholstery, floor coverings, raincoats and bottles
Polystyrene	Thermoplastic	Easily moulded	Used as a packaging material for delicate objects like electronic items and to make thermocol, used to insulate the hollow walls of refrigerators
Perspex	Thermoplastic	Transparent like glass, but much stronger	Used as a substitute for glass, for making windows in aeroplanes and windscreens of cars
Teflon or PTFE (polytetra -fluoroethylene)	Thermoplastic	Slippery, not affected by heat and does not react chemically with other substances	Used as a non-stick coating on pans and other cooking utensils
Bakelite	Thermosetting	Harder than other plastics and a good electrical insulator	Used for making buttons, plugs, switches and other electrical fittings
Formica and Melamine	Thermosetting	Hard and smooth surface	Used as table-tops, and for making crockery

Problems with plastics

Though plastics are very useful, there is a concern today about their increasing use because of the following reasons:

· They are non-biodegradable, i.e. they cannot be decomposed by the microorganisms in the soil.

·  Careless disposal of them chokes drains, chokes the soil and hinders the absorption of water by the soil.

·   If eaten by animals, they may be killed.

· Plastic bags can also contaminate foodstuffs because of poisonous dyes getting absorbed into food.

·  If burnt, they release poisonous fumes and pollute the air.

Saving environment by reducing plastic pollution

 To reduce the problem of plastic pollution we need to do the following –

· Always remember and follow the 4R principle – Reduce, Reuse, Recycle, Recover

· Buy products with less plastic packaging.

·  Practice and promote proper disposal of plastics in your home.

·  Use your own cloth or paper bags for shopping.

·   Support recycling schemes and promote support for one in your local area.