Using plastics



Plastics can made with many different properties. Each property is designed to make the plastic useful in a particular way.
The special property of plastics is that they are made up of tiny particles that can be joined in many different ways. This is what allows scientists to make so many kinds of plastic.

The squeegee is used for cleaning windows. It gives a good example of how varied plastics can be. The squeegee is made from three plastics. The handle is made from hard rigid, shiny plastic which allows it to be gripped firmly. The blade is made of flexible elastic plastic which can be rubbed across the glass to remove dirt. The sponge is elastic and absorbent. It is used to rub soapy water onto the glass.
Without a squeegee you would need to put the soapy water on with a cloth, put the cloth down pick up a wash leather to wipe the window dry.
How were plastics discovered?
Plastics were invented not discovered. They are substances which are made by mixing different chemicals together. They are manufactured materials.
The first plastic was invented in 1862 by Alexander Parkes. He made it from cellulose and other chemicals when he was trying out some experiments. Parkes could not think of a use for his plastic. In 1869 another scientist called John Hyatt improved its properties so it could be used to make billiard balls instead of the ivory ones which were being used at that time. Hyatt called his plastic celluloid. It was soon used for baby's rattles, stiff shirt collars and the film that goes in cameras. As more plastics were invented, so the uses for plastics grew.
Why are plastics known as 'designer' materials?
Because they are designed to solve problems. As plastics can be made cheaply they are designed to replace a more expensive material. For example, up until the 1930's parachutes had been made of silk which is an expensive material. In 1931 Wallace Carothers invented a plastic that became known as nylon to replace silk. But then it was found that the same material was such a hard-wearing plastic that it could also be used to make gears in machines and even curtain fittings.
Can plastics be invented by accident?
Yes. For example in 1909 Leo Baekeland invented a plastic he called bakelite. He was originally trying to invent a material to replace an expensive material called shellac. This substance is produced by certain insects and is used to make a kind of >varnish. Instead of inventing a plastic for this purpose Baekeland found he had invented a tough plastic which could be moulded into almost any shape. It did not replace shellac, but it came to replace wood in the making of objects such as radio cabinets.


Why do plastics have such odd names?
Plastics belong to a group of chemicals called polymers. 'Poly' means 'many' and 'mer' means 'part'. This tells us that a polymer has many parts.
Plastics are made from chemicals which have long strange sounding names. Sometimes these names are used in the plastic's name but they may be made shorter because the name is easier to say. For example polythene is the name for a plastic which has many parts made from a chemical called ethene. Polyethene is difficult to say, so many people use the name polythene instead.
Sometimes a plastic is known by a number of letters. This is done when the name is long and complicated. For example one plastic is called PVC. This name is used instead of the plastic's real name which is polyvinyl chloride.


Is there a raw materials for plastics?

Yes. It is oil which is found in the ground. Plastics can also be made from coal, natural gas and wood. Each of these natural materials contains many chemicals. Some of these chemicals are used to make plastic. They are separated from the oil, coal etc., by heating.


What are the most common plastics?
Polythene is made in the largest amounts. There are two kinds of polythene. In one kind the chemicals that make the polythene are packed together tightly. They make a stiff material that is used to make plastic bottles with strong, non-flexible sides.
In the second kind of polythene the chemicals are not packed so tightly and they make a more flexible material. This kind of polythene is used for making bottles with flexible sides such as those used for washing up liquids. It is also used for making polythene bags.
PVC is the second most widely used plastic. It is made with a range of hardness and flexibility and is made into floor coverings, guttering, drainpipes, washing up bowls and shower curtains.
Polystyrene is the third most widely used plastic. It is used to make cups in vending machines, toys and covers for cassettes and CDs.
Do plastics have any similar properties
Yes they do. They are all light in weight and many are strong. Most of them do not conduct electricity and many melt if they get hot. Some also give off dangerous fumes when they burn.
Some plastics seem very light in weight. How are they made?
When these plastics are made, some chemicals in the plastic give off a gas such as carbon dioxide. The gas is used to make bubbles in the plastic. The result is a foam. The foam used in cushions has bubbles in it. Ceiling tiles and some packing materials are made from closely-packed beads of foamed plastic.

How are plastic cups made?
Plastic cups are made by placing a sheet of plastic over a mould. The sheet is then warmed and air is sucked out of the mould. This draws in the molten plastic sheet until it covers the inside of the mould. The plastic cools and sets and a cup is formed.
How is a plastic bowl made?
Plastic chips are pushed into a space under a heater. The chips melt and the liquid plastic is pushed through a hole into the mould. The plastic sets and the bowl is removed from the mould. If you look on the bottom of a plastic bowl you may see a small bump in the centre. This is the last piece of plastic to enter the mould. The size of the bump shows you the size of the hole through which the plastic passed to enter the mould.