Class 8 Science Plastics Notes and Important Points

  

Plastics

Any Synthetic material which can be easily moulded into any desired shape on heating is called plastic.Plastic is also a polymer like the synthetic fibres.There are two types of arrangement in plastics linear and cross linked.


Plastics can be reused,recycled, coloured, melted, and rolled into sheets and drawn into wires.This is the reason that it finds such a variety of use in our life

Properties of Plastics:
1.They are cheap,light and available in different colours.
2.They are strong,durable and resistant to corrosion
3.They can be moulded to any shape when hot.
4.They are sensitive towards heat and melt quickly on heating.
5.They are bad conductors of heat and electricity.
6.They may be transparent,translucent or opaue.
7.They are non reactive can be used to store super acids like hydrofluro etc.
8.Plastics are non biodegrable

Types of Plastics:

1.Thermo Plastics

2.Thermosetting plastics

Thermoplastics
A plastic substance which can be melted repeatedly by heating and can be moulded again and again into different shapes is called a thermoplastic polymer.Polythene,PVC, and polystrene are common examples of thermoplastics.

Thermosetting Plastics
A plastic substance which does not soften much on heating once it is set i.e can be moulded  once is called a thermosetting plastic.Thus softening and moulding are irreversible. Bakelite and melamine are common examples of thermosetting plastics


Some common thermoplastics and their uses

Polythene (or Polyethylene)
Polythene is obtained by the polymerisation of ethylene monomers.It is unreakable,tough and flexible, it is resistant to chemical actions by acids,alkalis and other organic solvents.It is an insulator

Uses:
1.It is used as waterproofing material
2.It is used for making containers and pipes for storing and transporting water
3.It is used for making carry bags

PVC(polyvinyl chloride)
It is obtained by the polymerisation of vinyl chloride.It is tougher than polythene.

Uses:
1.It is used as insulating cover for electrical wiring.
2.It is rolled between rollers to produce pvc sheets
3.It is used for making hand bags,rain coats, and floor covering materials and suitcases
4.It is used to cover motoro car seats and furniture.
5.It is used for making gramophone records and refrigerator linings.
6.It is also used for making shoes and shoe soles.

Polystyrene
It is obtained by the polymerisation of styrene monomers.It is one of the cheapest plastics and is lighter than polythene.It is hard and brittle, it can be blown up into very large foam containing air bubbles.In this form, it is called styrofoam or thermocole.

Uses:
1.It is used as packing material for expensive items such as refrigerators,TVs, cellphones and other fragile objects

Perspex
Perspex is a substitute for glass.It is transparent and unreakable.
Uses:
1.It is used for making the windscreens of cars and windows in aircrafts
2.It is also used in street light fittings and telephones.

Teflon or Polytetrafluoroethylene
It is a thermoplastic and is polymer of tetrafluroethylene.It is one of the best plastic.It has much higher melting point,very low friction(non-stick) and is quite inert(non reactive)

USES:
1.It is used for making non-stick cookwares
2.It is used as lubricants in ball-bearings,chains,brakes etc.
3.IT is also uses as lens coating.
4.It is used for coating industrial parts og increase their durability.


Some Common Uses of Thermosetting Plastics

Bakelite
It is made by reacting phenol with formaldehyde in the presence of a catalyst.It is hard,stiff and a bad conductor of heat and electricity
Uses
1.It is used for making plugs,switches,telephone cases and other electrical fittings.
2.It is used for making radio and television casings.
3.IT is used for making handles of teat kettles,sauce pans, and pressure cookers.
4.It is used for making artificial leather.

Melamine
It is hard, it resists fire and can tolerate heat better than other plastics
Uses
1.IT is used for making unbreakable dinner ware and decoration pieces
2.IT is used for making floor tiles.
3.IT is used for making fire proof fabrics

Use of Plastics in various industries

 Plastics find extensive use in the health-care 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 affectthe plastic vessel.
Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cookwares.

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

Harmful Effects of Plastics

Plastics are non biodegrable and take several years to decomposes,, it is not environment friendly and causes environment pollution.

1.It's burning process is slow and it does not get burnt completely, and releases lots of poisonous fumes into the atmosphere causing air pollution.
2.Plastic materials when thrown out destory the natural beauty of the place and provide homes for many pathogens
3.Plastic bags choke the drains which results in overflowing of waste water.
4.Plastic bags sometimes eaten by stray animals along with leftover food chokes the respiratory system of these animals, or forms a lining in their stomachs and can be the cause of their death.
5.Use of recycled plastic bags to keep food items is harmful for health
6.IT reduces the percolation of water into the soil and prevents replenishment of ground water.
7.Dumping of plastic goods in waterbodies poses a threat to aquatic life.
8.It causes soil pollution.

Measures to Tackle Plastic Pollution
The environmental problem caused by plastic has become so alarming that p eople are advised to use following methods to prevent health hazards.

1.Reduce your dependence on plastic bags and other items made of plastics.
2.Carry your own cloth bag or jute bag for shopping.
3.Never burn plastic bags and other plastic items in the open.
4.Don't throw plastic articles here and there after use.
5.Say 'No' to plastics to save the future generation
6.Keep plastic bags clean and dry for reusing.
7.Keep separate garbage bins your home for biodegrable and non biodegrable waste
8.Avoid the use of plastic as far as possible.
9.Use biodegrable plastic instead of non biodegrable plastic.
10.Follow and practice the 4-r principle of reduce,reuse,recyle and recover to minimize environmental pollution.