24.1 Plastics as important materials in the modern world P. 1 / 4 Chapter 24 A ddition p olymers 24.1 Plastics as important materials in the modern world.

24.1 Plastics as important materials in the modern world

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Chapter 24 Addition polymers24.1 Plastics as important materials in the modern world

24.2 What are plastics?

24.3 Addition polymerization

24.4 Properties and uses of some addition polymers

24.5 Thermal properties and structures of thermoplastics

24.6 Plastics and economy

24.7 Environmental issues related to the use of plasticsKey terms

Check your progress

Experiment 24.1

Experiment 24.1 — Solution


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The plastic ageThe plastic age


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Where do plastics come from?Where do plastics come from?

Petroleum (raw materials)

Oil fractions (e.g. gas oil, fuel oil) alkenes

Plastics

fractional distillation

cracking

manufacture


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WHY ARE PLASTICS SO USEFUL?

Plastics have properties which make them very useful:

Usually strong but light

Inert:No reactions with air, water, acids, alkalis and most other chemicals


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Can be moulded easily into any shape

Good insulators of heat and electricity


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Can be dyed

Usually transparent


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Can be tailor-made to suit

special requirements

Usually flexible



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Defining plasticsDefining plasticsPlastics are polymers which are made up of very large molecules.

At some stage during processing, they can be turned into any desired shape by heating. moulding

monomermolecules

large polymer molecule

Polymerization A polymer


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Polymers and plasticsPolymers and plasticsAll plastics are polymers. On the other hand, not all polymers are plastics.

Wool

Polymeris

is not Plastic


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What is addition polymerization?What is addition polymerization?

Addition polymerization is a reaction in which monomer molecules join together repeatedly to form polymer molecules, without the elimination of small molecules (such a H2O or HCl).

The monomer molecules involved must contain carbon-carbon double bonds.


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In most cases, the monomers can be represented by a general formula:

where −X stands for an atom or a group of atoms such as −H, −CH3, , −Cl and so on.


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By breaking open the carbon-carbon double bond, a monomer molecule will have two ‘free electrons’ which can join to other molecules:

‘free electrons’ that can join to other molecules


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Each polymer chain consists of at least several hundred monomers joined together.

A section of a polymer chain


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Repeating unitRepeating unit

A repeating unit is the group of atoms inside a polymer chain coming from a monomer (or set of monomers), which repeats to give the whole polymer structure.


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The general equation for addition polymerization is:

n molecules of monomer

General formula to represent the polymer molecule (n usually varies from 1000 to 30 000)


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Fig. 24.4 A flexible paper-clip chain representing a polymer molecule. Each clip represents a monomer molecule.

Example 24.1Example 24.1

Example 24.2Example 24.2 Class practice 24.3Class practice 24.3


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Polyethene [polythene]Polyethene [polythene]

ethene polyethene or polythene


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General properties:

Low Density PE has a melting point of about 105°C. It softens in boiling water. It is flexible.

High Density PE has a melting point of about 135°C. It is quite rigid.


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Low-density polythene (straws) and high-density polythene (cup).


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Some polyethene products


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Toys made of low-density polyethene

Example 24.3Example 24.3


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Polypropene [polypropylene]Polypropene [polypropylene]

propene polypropene


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melting point: 165°C resistant to many chemical solvents,

alkalis and acids.

Properties:


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Some polypropene products

UsesUses


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Polyvinyl chloride (polychloroethene)Polyvinyl chloride (polychloroethene)

Polyvinyl chloride (PVC) is manufactured by heating chloroethene at about 60°C, in the presence of a catalyst (e.g. hydrogen peroxide H2O2).

IUPAC name: chloroethene polychloroethenecommon name: vinyl chloride polyvinyl chloride


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stiff brittle more flexible when mixed with a plasticis

er properties can be varied by the addition

of different amounts of plasticiser

Properties:


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PVC pipes

UsesUses


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Some PVC productsClass practice 24.4Class practice 24.4


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PolystyrenePolystyrene

Polystyrene is manufactured by heating styrene at about 100°C, in the presence of an organic peroxide as catalyst.

styrene or phenylethene

polystyrene or polyphenylethene


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Fig. 24.10 Styrene is a colourless liquid.


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white solid foam very light quite rigid excellent heat insulator good shock-absorbent non-toxic

Properties (Expanded polystyrene):

transparent hard brittle

Properties (Polystyrene):


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Some polystyrene products

UsesUses


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Foam cups and food boxes made of expanded polystyrene


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Perspex [Acrylic]Perspex [Acrylic]Perspex is made by heating methyl 2-methylpropenoate at about 60°C, in the presence of an organic peroxide.

methyl2-methylpropenoate

Perspex or polymethyl 2-methylpropenoate


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highly transparent tough, but does not break easily but quite easily scratched

Properties:


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This aquarium is made of Perspex

UsesUses


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Lenses of exterior lights of automobiles are made of Perspex

Activity 24.1Activity 24.1Class practice 24.5Class practice 24.5 Activity 24.2Activity 24.2

Do Question 22 on p. E56


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A thermoplastic is a plastic which can be softened by heating and hardened by cooling, the process being repeatable any number of times.

Thermoplastic and Thermoset

A thermoset is a plastic which once set hard cannot be softened by heating.


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the weak intermolecularforces are overcome byheat or external force

weak intermolecular forces

Class practice 24.6Class practice 24.6

warm or pull

Experiment 24.1Experiment 24.1



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Poisonous plastic articlesPoisonous plastic articles

E.g. PVC contains toxic substancesFire riskFire risk

Burning of plastics produces harmful fumes.

ProblemsProblems associated with the use Problems associated with the use of plasticsof plastics


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Problems

Disposal of plastic waste

Non-biodegradable Burning plastic waste in incinerators would lead to air pollution.

E.g. Burning PVC produces hydrogen chloride, chlorine gases, dioxins

Activity 24.4Activity 24.4 Activity 24.5Activity 24.5


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Solving plastic waste disposal Solving plastic waste disposal problemproblem1. Reduce the use of plastics

Fig. 24.19 Reducing use of plastic bags − Bring Your Own Bag (BYOB).


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2. Reuse plastic articles

Fig. 24.21 Many so-called ‘disposable’ plastic articles can in fact be used many times.


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3. Recycle plastic waste

Fig. 24.22 The international plastic coding system for recycling.


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4. Make biodegradable plastics


24.1 Plastics as important materials in the modern world P. 1 / 4 Chapter 24 A ddition p olymers 24.1 Plastics as important materials in the modern world.

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