One gets natural and artificial polymers. Proteins, which any living body needs to grow, are an example of a natural polymer. Synthetic polymers were first invented about 100 years ago. They were very scarce and expensive then. Synthetic polymers can be divided into two groups: fibres and plastic. We are going to look mainly at plastic.

Synthetic Polymer: Plastic

Plastic can be clear or coloured and can be made into any shape.

How is plastic made?

Oil is found deep under the ground in certain places. People drill into the ground and pump the oil to the surface. This oil is thick and is called crude oil.

Look at the map below and identify the countries where oil is found. You can do this in your group.

Figure 1

Let’s do a simple experiment to see what processes crude oil goes through to make plastic.

When crude oil is heated more or less the same happens. The crude oil is taken to a refinery where it is heated to a very high temperature. The crude oil divides into darker and lighter oils. The light-coloured oil is used to manufacture plastic and some other substances.

Use of plastic

Certain plastics are hard and are used to make tables, chairs, and parts for motorcars that used to be made from steel. Plastic can be much harder than steel.

Other plastics are soft and flexible. These plastics are used to make things like shopping bags, shower curtains and raincoats.

Figure 2

Plastic is used to make containers for storing food. Many items on the shelves in supermarkets are stored in plastic containers.

Name some foods sold in plastic containers.

What role does plastic play in housing?

In informal settlements plastic is an important material used in the construction of shacks. Have you seen how plastic is used and do you know why plastic is such and important material? How can plastic protect the shack from various weather conditions?

How is plastic recycled and how is it used again? Look for information and give feedback.

Remember: Plastic can and should be recycled.

Interesting facts:

Plastic can be ten times harder than steel and can withstand high temperatures.

Credit cards are made of plastic and used instead of cash.

Surgeons use plastic to replace various body parts, e.g. heart valves, arteries, etc.

Advantages of plastic:

The use of plastic has created many jobs for people in South Africa.

Nature cannot produce enough cotton, wool wood, etc., so we have to use other materials such as plastic.

Disadvantages of plastic:

We throw away heaps of plastic every day. Animals and plants decompose, but not plastic.

Plastic causes the death of many animals, especially fish, which are strangled by plastic ropes.

Let's look at some other synthetic polymers. (This section is just for information)

FIBRE

Fibre is a term used to describe a long, thin thread of material. There are many sources for fibres. Some are from plants like cotton, paper and coir. Others come from animals, e.g. wool. Nylon and rayon are manmade fibres.

The human body contains a number of fibres, e.g. hair and nails. Each hair is actually a string of proteins called keratin. The hair is in the form of spirals. This makes the hair strong and elastic. Wet hair stretches but goes back to its original length when it dries.

SILK

Silk is a natural fibre. Many animals make silk. The most common one is a spider, but silk worms are farmed for their silk.

The caterpillar of the silkworm moth makes silk.

GLASS

There are many kinds of glass. The most common is the kind used for windows.

Properties of glass

How is glass made?

Glass is a stable substance and has important properties that make it very versatile – it can be used for many different things.

Glass does not weather.

Glass will not dissolve in water or most chemicals.

Glass can be used as containers for most foods and drinks.

Glass is transparent. Light can shine right through it.

Glass has a smooth hard surface that is hygienic and is easily cleaned for storing foodstuffs.

Glass can break easily but is also flexible if stretched into long fibres. These fibres are very strong and can be used to make many things, e.g. a canoe or a surfboard.

Figure 3

Layers of glass fibre can be put between the ceiling and the roof of a house to serve as insulation. What does this mean?

Figure 4

On a warm day it keeps out heat and so the house is cooler. On a cold day it keeps the heat in and the house is warmer.

Changing the composition of the mixture can change the properties of glass.

Special types of glass can be made, e.g. safety glass is used for car windows. When this glass breaks it crumbles into pieces that is held together by plastic (see sketch).

Figure 5

This is how a car window is made.

Glass Plastic Glass

Does the windscreen stay in one piece even if it has broken?

Why is this important?

Can you think of other places where glass plays an important role?

Interesting facts:

Nowadays we use windows in our houses. Before people knew about glass there were just holes in walls to let the light in. Houses were very dark inside. The Romans were the first to use glass for windows, but it was only in the 19^th century that most people could afford to have glass in their windows.

Modern houses have larger windows and even glass doors to give homes a warmer feeling.