FET PHASE OXFORD SUCCESSFUL
PHYSICAL SCIENCES OUP SA
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Physical Sciences CORE CLASSROOM COURSE
Oxford Successful Physical Sciences Grade 12 Learner’s Book Secondary Catalogue 55
FET PHASE
UNIT 11 New words
synthetic: man-made, formed through chemical processes
macromolecule: very large molecule consisting of many smaller identical structural sub-units linked together
polymer: compound consisting of large molecules made up of a linked series of repeated simple monomers
monomer: molecule that is the basic unit for polymers
inert: unreactive
Polymers
When you look around you, you will notice how many things are made from some type of plastic. Our everyday life is filled with plastic products, like paints, containers, clothes, carpets and packaging. Plastics are made from very large synthetic organic molecules, called macromolecules. Organic macromolecules are common in nature. They make up many components in our bodies like our DNA, fats, proteins and enzymes. Naturally occurring macromolecules can also be found in plants such as cotton. Polymers form when many small molecules join together and form a structure that repeats itself over and over again. The small repeating units are called monomers. Monomers bond to other monomers to form a repeating chain molecule. Figure 1 shows how single units (monomers) link together in a repeating pattern to form a large polymer.
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Figure 1 Diagrammatic representation of repeating units of monomers that link together to form a polymer.
Plastics are synthetic polymers
Plastics are synthetic polymers. Most plastics are made from chemicals found in the naphtha fraction of crude oil.
Did you know?
The word “plastic” is a Greek term that means something that can be molded into shape without breaking. This is true for all plastics while they are being made.
Crude oil is a mixture of organic compounds. Naphtha (an inflammable liquid distilled from petroleum) makes up about 10%–15% of the mixture.
Physical properties of plastics
Plastics have many useful properties. They are: insulators and do not conduct heat or electricity. inert; they do not react with air, water, acids or other chemicals so they are usually safe for storing things, including food
Figure 2 Plastic products have many different uses.
not brittle and do not break easily when dropped
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light in weight; this makes them easy to handle and move. It also saves on transport costs
relatively robust (strong); it takes a large amount of force to tear or pull them apart.
Plastics also do not catch fire easily. Some types of plastics soften and melt when heated, while others char (go black).
lt on
126 Module 2 Matter and materials (Part 1) 2015/02/05 9:36
MODULE 2
Changing the properties of plastics
When we choose specific monomers and reaction conditions carefully, we can control the properties of the plastics that we produce. For example, we control the conditions when making the polymer polyethene so that it can be used for plastic bags or for rigid containers such as milk bottles.
Activity 1 Build a polymer
In this activity you will build a linear and a branched polymer. Each paperclip represents a monomer. When these are linked together they form a polymer chain.
METHOD Step 1 Make a linear polymer by connecting paperclips in a straight line. Step 2 Make a branched polymer by attaching paper clips to either the top or bottom of the paperclip chain.
Step 3 Make a cross-linked polymers by connecting at least two linear polymer chains. Use the branches to connect the polymers to each other.
Figure 3 High density polyethene (HDPE) is used to make rigid containers.
MATERIALS paper clips
Figure 4 Linear polymers have a tight arrangement that leads to a sturdy and rigid polymer.
Figure 5 Branched polymers are softer and more flexible than linear polymers because they have a looser structure.
Figure 6 Cross-linked polymers are not easily broken apart from each other. The more cross-links between polymers, the more rigid they become.
Plastic recycling
Each type of plastic is made from a different polymer. A milk jug is made from a different type of plastic to a yoghurt container. These have different properties, so to recycle plastics we first need to separate the plastics into the different types.
The plastics industry has developed a system to identify different types of plastic. This system divides plastic into seven categories using a number code, called the Resin Identification Code. The code is printed on containers.
Why recycle plastic?
In South Africa we throw away thousands of tonnes of plastic bottles every year. Many of these end up in landfills. Plastics can be light but very bulky, so they take up a large amount of space.
Website
www.plastics-elearning.com/
Unit 11 Polymers 127
9780199048250_OS_PS_12_LB.indb 127
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