Pla

stic Fanta

stic

One major group of designer materials that have had phenomenal success andaltered our lifestyle are plastics. Plastics are everywhere. From an early age you weresurrounded by plastics—plastic toys, plastic containers, plastic bags, even non-stickcoatings on pans, chewing gum and Lycra in clothes are made from plastics.Although it may be difficult to believe, the development of plastics has occurredonly in the last 70 years or so. In fact they have been used on a massive scale onlyover the last 50 years. At this moment you are probably using a number of differentmaterials 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. Yourpen is made mainly of plastic, your calculator has a plastic case and so does yourmobile phone and computer. All the CDs and DVDs you play are made of plasticand so are their containers. Your sports shoes alone probably consist of six or moredifferent kinds of plastic, including the sole, the padding, the upper, the laces andeven the lace tips.Plastics are amazing materials. They come in every shape, size and colour andwith every material property you could think of—strong, flexible, elastic, hard,ductile, transparent, slippery, brittle to name a few. As chemists developed newplastics, the variety of properties and uses expanded dramatically.

The term plastic is applied to a wide range of materials with a wide range ofproperties and applications. Technically, ‘plastic’ means ‘deforms permanently whensubjected to a force’, but as a general term it has come to be used for a range ofsynthetic substances more appropriately known as polymers. Polymers are largemolecules made up of many repeating units. Poly is from the Greek for ‘many’ andmeros 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 alsoproduced 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 havecopied 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

ACTIVITY 7.1a 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 theiruse. 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 needto devise tests for these properties, being sure to control as many variables aspossible.Warning: Burning polymers give off toxic fumes so do not expose your sampledirectly to a flame unless this is done in a fume cabinet. To determine ease ofmelting you could use hot water, or a nail heated in a Bunsen burner, or placethe 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 totheir use.

Friday 7th?

By the 1990s the volume of plastics on the world market exceeded the total volumeof 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 forevery person. Packaging is the largest market for plastics, accounting for overa third of the consumption of raw plastic materials—Australians in 2004 used50 000 tonnes of soft-drink bottles, 30 000 tonnes of milk bottles and 6 billionplastic bags during the year .Although plastic packaging provides excellent protectionfor the product and is lightweight compared to metal or cardboard, it is proving to be a major environmentalproblem. In the past more than one-third of the plastic consumed in Australia was destined for landfi ll, but todaymany local councils have recycling facilities for plastic materials.

Six polymeric materials account for 66% of all plasticsused, but currently not all of these can be recycled. Sincemost plastics are incompatible when mixed together, thedifferent types of plastics need to be separated before they arerecycled. To help identify plastics, manufacturers use a plasticsidentifi cation code, which is normally stamped on all products.It is represented by a triangle with a number inside it. Peopleoften get this code confused with the recycling symbol, whichis a triangle made up of three arrows with no number inside.The plastics identifi cation code does not mean the plasticcontainer can be recycled—it gives the type of plastic theproduct is made from.

phone.wav

In 1862 Alexander Parkes produced the first plastic—cellulose nitrate—whichcould then be converted to various products. He made the cellulose nitrate fromwood or cotton and camphor. At the same time an American, John Hyatt, was alsoexperimenting with cellulose nitrate in an attempt to find a synthetic substitute thatcould replace the ivory originally used to make billiard balls, and win a US$10 000prize. 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, brushhandles, photographic film and table-tennis balls. It had the major disadvantageof being highly flammable. Its use boomed until the mid-1920s when other lessflammable materials were synthesised.

The first true synthetic polymer, called Bakelite, was developed by Dr LeoBaekeland in 1907. While celluloid was a natural polymer modifi ed by humans,Bakelite was produced from manufactured chemicals and was unlike anythingproduced in nature. It is still used to make electrical fi ttings such as socketsand plugs. Bakelite is a thermosetting plastic (goes hard when heated); all of thepolymers discussed in this chapter are thermoplastic (soften when heated).Baekeland’s discovery started a scientific and industrial revolution usingmanufactured chemicals to produce new materials, but it was not until the 1950sthat 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 arrayof 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 hydrocarbonsCurrently the petrochemical industry consumes about 3–5% of the total oil

usedin the world today. In fact about 95% of all synthetic carbon compounds are derivedfrom compounds produced from petroleum and natural gas.Research has shown that many of the compounds distilled from crude oilare not ideally suited for the desired applications. The most useful fractions arethe lighter ones and so there is a great demand for these. Over half the fractionsobtained from crude oil, however, are the heavier, less useful ones.Oil refi neries have developed methods in which fractions containing hydrocarbonsof 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 itis more commonly called, ethylene. (The historical name for ethene is ethylene andthis 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 thedeliberate decomposition or cracking of some of the higher boiling point fractions

http://goes.flexinet.com.au/page/chem12.html