4. Making Polymers [Compatibility Mode]

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1 of 43 Boardworks Ltd 2006


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A world of plastic

How many different uses of plastic can you spot?


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The word polymer comes from the Greek words

poly(meaning many) and meros(meaning parts).

Polymers are very large molecules made when hundreds ofmonomersjoin together to form long chains.

Plastics are synthetic polymers that

can be shaped by heat or pressure.

What are polymers?


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Natural and synthetic polymers


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The monomers in a polymer are joined together by covalentbonds between atoms.

In a covalent bond, each atom shares one or more electrons

with another atom. The bonds are sometimes shown as sticks.

covalent

bond

What keeps the chain together?


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Many polymers are formed from alkenes, which are a familyof hydrocarbon molecules with the general formula CnH2n.

Alkenes contain at least one double covalent bond between

carbon atoms. The double bond makes them very reactive.

What are polymers made from?

The simplest alkene is

ethene (C2H4).

The second simplestalkene is propene (C3H6).

doublecovalent

bond


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How are monomers turned into polymers?

Making polymers


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Addition polymerization

Polyethene (sometimes called polythene) is a polymer madefrom ethene.

The process by which polyethene and other polymers is

made is called addition polymerization. This is becausemany monomers (ethene molecules) are added together.

addition polymerizationmonomers

polymer


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How is polyethene made?


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Drawing polymers shorthand formulae

Polymers contain thousands of molecules, so how can theirstructures be easily drawn?

Part of the polymer molecule can be drawn:

A better way is to show a shorthand formula:

The n means that the polymercontains a very large number of the

repeating unit shown in the brackets.


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Whats the monomer?

What is the monomer ofpolyvinylchloride (PVC)?

1. Draw two C atoms joined with a

double covalent bond.

2. Add the atoms attached to eachC atom.

3. Draw the brackets and n.

The equation forthe reaction canbe drawn as:


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What are the properties of plastics?

Plastics are all different, but they show a few generalproperties:

they do not conduct electricity and are poor

conductors of heat

they are unreactive most are not affected by water or

air, and many are not affected by chemicals.

Why is the unreactivity of plastics both useful and

problematic?

Their unreactivity makes plastics durable and able to safelycontain and protect many substances. However, it alsomeans that they persist in the environment for a long time.


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lined-up chainsmake plastics

dense, rigid andharder to melt(e.g. high-density

polyethene).

The properties of a plastics depend greatly on how thepolymer chains are arranged:

branching chains

make plasticslight, soft andeasy to melt(e.g. low-density

polyethene)

What makes plastics different?


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What factors might determine the properties of a plastics?

Temperature, pressure and catalystsaffect the length and branching of thepolymer chain.

The type of monomer used affects the

type of forces between polymer chains.

Additives can lubricate polymer

chains, join them together with cross-links, or preserve them from decay.

reactionconditions

monomer

additives

Factor Effect

Changing the properties of plastics


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Cooked spaghetti is solid when cold, but soft when warm.The strands can slide past each other. It is the same with

many polymers.weakintermolecular

forces these let thechains slide past

each other

What do polymer chains and spaghetti have in common?

What are thermosoftening plastics?

Plastics made of these polymers are stretchy and have a

low melting point. They are called thermosoftening plastics.


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Thermosoftening plastics (also called thermoplastics) do notcontain cross-links.

Uses of thermosoftening plastics

This means they are flexible, stretchy and have a low melting

point. It also means they can be moulded and shaped afterthey have been made, many times.

What are some examples of thermoplastics?

polyethene natural rubber


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Plastics made of these polymers cannot be stretched, arerigid and have a high melting point. They are called

thermosetting plastics (or thermosets).

strong

intermolecularforces(cross-links) these hold the

chains firmly inplace

Some polymer chains cannot slide past each other.

What are thermosetting plastics?


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Thermosetting plastics contain cross-links. This means thatthey:

Uses of thermosetting plastics

What type of objects might you make from thermosetting

plastics?

are rigid

will break when bent

have a high melting point (they char rather than melt)

must be moulded into shape when they are being made,


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uPVC is perfect for windowframes as it is strong, lightand durable.

uPVC chains

chains packedtightly together

The u stands for

unplasticized, and meansthe polymer is rigid.


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Adding a plasticizer lets the chains slide.

Oiling the chains?

plasticizer

How will the plasticizer change the polymers properties?

The polymer will be flexible, not rigid.


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Matching polymers to their uses


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P-P-Polymers, plastics and properties


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Waste reduction facts and figures


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In the UK, 3.5 million tonnes of plastic packaging is thrownaway each year!

There are three ways to dispose of waste plastics:

Each method of disposal hasits own advantages and

disadvantages.

landfill

incineration (burning)

recycling

Why has the issue of dealing with waste plastic in a cheap

and environmentally-friendly way become more important?

How much waste plastic?


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Disposing of plastics

Wh h l i i l dfill i ?


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Plastic bags are a major source ofwaste at landfill. British shoppers useover 8 billion of them a year!

Landfill is a convenient method of wastedisposal but it is only designed to buryrubbish, not to break it down.

Most plastics are made up of tightly

bonded molecules that cannot bedecomposed by micro-organisms.

These will remain buried at landfill sitesfor thousands of years without rotting.

The UK has 4,000 landfill sites and it ispredicted that the largest of these will

become full in less than 5 years.

What happens to plastics in landfill sites?

L dfill d


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Landfill pros and cons

H l ti id tifi d f li ?


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Most plastic products carrya symbol that shows whichtype of polymer they are

made from.

Many plastic items look and/or feel similar to each other butthey are actually made from different materials, e.g.margarine tubs (polystyrene) and plant pots (polypropene).

Usually, the only types ofplastic to be recycled are

PET, PVC and HDPE.

If different polymers are mixed together during recycling, itcan reduce the quality and value of the final recycled plastic.

How are plastics identified for recycling?

R li b l f l ti


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Recycling symbols for plastics

What is the effect of recycling plastics?


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Recycling plastic uses less water and energy resources thanin producing new plastics, and produces fewer greenhousegases.

This is because the polymer chains become damaged or

contaminated with food or other types of plastic.

What is the effect of recycling plastics?

One problem withrecycling, however,is that is reduces

the strength andversatility of theplastic over time.

Recycling pros and cons


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Recycling pros and cons

What are biodegradable plastics?


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Biodegradable plastics areincreasingly being used incarrier bags, bin bags and

food packaging.

One of the problems with traditional plastics is that they donot break down when thrown away.

Biodegradable plastics areplastics that can be brokendown. They are converted into

carbon dioxide, water andminerals by micro-organisms.

Biodegradable plastics, such as polylactide, are plant-basedpolymers. They are often made from starch that has beenmodified to become more stable.

What are biodegradable plastics?

How is biodegradable plastic made?


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How is biodegradable plastic made?

Dealing with waste


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what can businessesand individuals do to

reduce the amount ofwaste they produce?

Dealing with waste isimportant, but there aremany issues involved:

if more products are made of biodegradable plastics, howwill the management of landfill sites change?

Dealing with waste

how many products could be made from biodegradable

plastic?

what will happen to closed landfill sites in future?


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Glossary


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Glossary

biodegradable A substance that can be naturally brokendown by micro-organisms.

cross-link A chemical bond that joins one polymer chainto another.

monomer A molecule that is the building block of apolymer.

polymer A long chain molecule formed from many

monomers joined together. polymerization The reaction used to convert monomers

into a polymer.

thermosetting A type of plastic that is hard, rigid and hasa high melting point.

thermosoftening A type of plastic that is flexible,stretchy and has a low melting point.

Anagrams


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Anagrams

Multiple-choice quiz


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Multiple choice quiz

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4. Making Polymers [Compatibility Mode]

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