One major group of designer materials that have had phenomenal success and altered our lifestyle are plastics. Plastics are everywhere. From an early age you were surrounded by plastics —plastic toys, plastic containers, plastic bags, even non-stick coatings on pans, chewing gum and Lycra in clothes are made from plastics.

Although it may be difficult to believe, the development of plastics has occurred only in the last 70 years or so. In fact they have been used on a massive scale only over the last 50 years. At this moment you are probably using a number of different materials that did not exist even 10 years ago, particularly in electronics technology.

It is likely that at least some of your clothing contains synthetic fi bres. Your pen is made mainly of plastic, your calculator has a plastic case and so does your mobile phone and computer. All the CDs and DVDs you play are made of plastic and so are their containers. Your sports shoes alone probably consist of six or more different kinds of plastic, including the sole, the padding, the upper, the laces and even the lace tips.

Plastics are amazing materials. They come in every shape, size and colour and with every material property you could think of —strong, flexible, elastic, hard, ductile, transparent, slippery, brittle to name a few. As chemists developed new plastics, the variety of properties and uses expanded dramatically.

The term

plastic

is applied to a wide range of materials with a wide range of properties and applications. Technically, ‘plastic’ means ‘deforms permanently when subjected to a force ’, but as a general term it has come to be used for a range of synthetic substances more appropriately known as polymers.

Polymers

are large molecules made up of many repeating units.

Poly

is from the Greek for ‘many’ and m

eros

is the Greek for ‘part’. Common names or brands for these polymers include; rayon, nylon, Lycra, polyurethane, Teflon, Styrofoam and PVC.

All plastics are polymers, but not all polymers are plastics. Polymers are also produced in profusion by nature. Some of the many natural polymers are cellulose, cotton and rubber (found in plants), wool, skin and hair (proteins from animals).

The DNA found in all living things is another natural polymer. Chemists have copied many of these natural polymers, often making small changes to them.

Many synthetic polymers were originally created as substitutes for expensive, naturally occurring materials or to improve on natural polymers.

teflon

Friday 7th?

ACTIVITY 7.1

a

Collect a variety of plastic items from your home —plastic bags, soft drink bottles, milk bottles, takeaway food containers and whatever happens to be on hand.

The plastics used to make the items will have different properties related to their use. You are to test and compare some of the properties of these plastics.

b Decide on some properties to investigate, such as colour, fl exibility, elasticity, hardness, water absorbency, ease of melting and heat shrinkage. You will need to devise tests for these properties, being sure to control as many variables as possible.

W

arning

: Burning polymers give off toxic fumes so do not expose your sample directly to a flame unless this is done in a fume cabinet. To determine ease of melting you could use hot water, or a nail heated in a Bunsen burner, or place the sample in an oven.

c Draw up a table to record your results.

d Use your test results to identify items that are made from the same material.

e Compare the properties of the different plastics and relate their properties to their use.

By the 1990s the volume of plastics on the world market exceeded the total volume of metals. Plastics production worldwide now exceeds 80 million tonnes a year.

Australia contributes almost 1.3 million tonnes to that total —more that 71 kg for every person. Packaging is the largest market for plastics, accounting for over a third of the consumption of raw plastic materials —Australians in 2004 used 50 000 tonnes of soft-drink bottles, 30 000 tonnes of milk bottles and 6 billion plastic bags during the year .Although plastic packaging provides excellent protection for the product and is lightweight compared to metal or cardboard, it is proving to be a major environmental problem. In the past more than one-third of the plastic consumed in Australia was destined for landfi ll, but today many local councils have recycling facilities for plastic materials.

Six polymeric materials account for 66% of all plastics used, but currently not all of these can be recycled. Since most plastics are incompatible when mixed together, the different types of plastics need to be separated before they are recycled. To help identify plastics, manufacturers use a plastics identifi cation code, which is normally stamped on all products.

It is represented by a triangle with a number inside it. People often get this code confused with the recycling symbol, which is a triangle made up of three arrows with

no

number inside.

The plastics identifi cation code does not mean the plastic container can be recycled —it gives the type of plastic the product is made from.

phone.wav

In 1862 Alexander Parkes produced the first plastic —cellulose nitrate—which could then be converted to various products. He made the cellulose nitrate from wood or cotton and camphor. At the same time an American, John Hyatt, was also experimenting with cellulose nitrate in an attempt to find a synthetic substitute that could replace the ivory originally used to make billiard balls, and win a US$10 000 prize. He produced a material that he called celluloid and patented it in 1869.

Although it was unsuitable for billiard balls it was used to make combs, brush handles, photographic film and table-tennis balls. It had the major disadvantage of being highly flammable. Its use boomed until the mid-1920s when other less flammable materials were synthesised.

The first true synthetic polymer, called Bakelite, was developed by Dr Leo Baekeland in 1907. While celluloid was a natural polymer modifi ed by humans, Bakelite was produced from manufactured chemicals and was unlike anything produced in nature. It is still used to make electrical fi ttings such as sockets and plugs. Bakelite is a

thermosetting

plastic (goes hard when heated); all of the polymers discussed in this chapter are

thermoplastic

(soften when heated).

Baekeland ’s discovery started a scientific and industrial revolution using manufactured chemicals to produce new materials, but it was not until the 1950s that the most common polymers (nylon, polyethylene, polystyrene and PVC) were manufactured in significant quantities for the general public ’s use.

The refining of crude oil by fractional distillation produces an impressive array of products. As you also learnt in the transport context, crude oil contains a range of hydrocarbons that vary in size and structure, including straight and branched alkanes, alkenes and cyclic hydrocarbons Currently the

petrochemical industry

consumes about 3 –5% of the total oil used in the world today. In fact about 95% of all synthetic carbon compounds are derived from compounds produced from petroleum and natural gas.

Research has shown that many of the compounds distilled from crude oil are not ideally suited for the desired applications. The most useful fractions are the lighter ones and so there is a great demand for these. Over half the fractions obtained from crude oil, however, are the heavier, less useful ones.

Oil refi neries have developed methods in which fractions containing hydrocarbons of higher molecular mass can be converted into the lower molecular mass hydrocarbons, which are more in demand. The process used is called

catalytic cracking

.

The most widely used starting substance for making polymers is ethene or, as it is more commonly called, ethylene. (The historical name for ethene is ethylene and this historical name tends to be the preferred name and so is more commonly used.) Ethylene is obtained from crude oil, either as a by-product of petrol refi ning or by the deliberate decomposition or cracking of some of the higher boiling point fractions