What is plasticsWhat is plastics
Are materials which can be shapedAre materials which can be shaped
or moulded under appropriateor moulded under appropriate
conditions of temperature andconditions of temperature and
pressure, and then hold theirpressure, and then hold their
Plastic has become increasingly important in ourPlastic has become increasingly important in our
every day lives.every day lives.
For the most part, plastics are organic highFor the most part, plastics are organic high
polymers, which means they are made of largepolymers, which means they are made of large
chain that contain carbon.chain that contain carbon.
These polymers are changed into a plastic stateThese polymers are changed into a plastic state
either as they transition from a small-moleculeeither as they transition from a small-molecule
chemical to a solid.chemical to a solid.
i. Thermoplastici. Thermoplastic
Become soft when heated and harden whenBecome soft when heated and harden when
cool and the process can be repeated iscool and the process can be repeated is
calledcalled thermo-softening plasticthermo-softening plastic or simplyor simply
Is like waxIs like wax
Thermoplastics are linear with no crosslinksThermoplastics are linear with no crosslinks
between the polymeric chains.between the polymeric chains.
Can be recycling because can be melted andCan be recycling because can be melted and
Conc… thermoplasticConc… thermoplastic
The bonds holding the polymer chains togetherThe bonds holding the polymer chains together
are usually the weak Van der Waals force.are usually the weak Van der Waals force.
When heated, the distance between the chainWhen heated, the distance between the chain
increases and the polymer becomes soft.increases and the polymer becomes soft.
Allow the polymer chains to slide past oneAllow the polymer chains to slide past one
On cooling, the chains come closer and theOn cooling, the chains come closer and the
polymer becomes hard.polymer becomes hard.
ii. Thermosetting Plasticsii. Thermosetting Plastics
Is like concrete.Is like concrete.
Highly cross-linked chains and hence usuallyHighly cross-linked chains and hence usually
are rigid and brittle.are rigid and brittle.
They must be given their shape before theirThey must be given their shape before their
final chemical structure is produced.final chemical structure is produced.
Structure ofStructure of
thermosetting plasticsthermosetting plastics
1. More tougher 2. More elastic
3. More heat resistant 4. High Melting point
5. Less soluble in organic solvent
6. 6. More chemical innert
Conc…thermosetting plasticsConc…thermosetting plastics
They cannot be molten, but will decompose atThey cannot be molten, but will decompose at
high temperatures.high temperatures.
They are entirely insoluble and will not swellThey are entirely insoluble and will not swell
when treated with solvents.when treated with solvents.
They do not lend themselves to recycling.They do not lend themselves to recycling.
( like with eggs, once hard boiled, they cannot( like with eggs, once hard boiled, they cannot
be softened ).be softened ).
Processing of thermosettingProcessing of thermosetting
Compression molding forms thermosetting plasticCompression molding forms thermosetting plastic
objects in a steel mold.objects in a steel mold.
When heat and pressure are applied, the softenedWhen heat and pressure are applied, the softened
plastic squeezes into all parts of the mold to form theplastic squeezes into all parts of the mold to form the
desired shape.desired shape.
Laminating binds layers of materials together in a plasticLaminating binds layers of materials together in a plastic
The layers are fused when heated plates melt the plasticThe layers are fused when heated plates melt the plastic
and squeeze the material together.and squeeze the material together.
Processing of ThermoplasticsProcessing of Thermoplastics
Calendering process, continuous plastic sheets are formed byCalendering process, continuous plastic sheets are formed by
forcing hot plastic between successive sets of heated rollers.forcing hot plastic between successive sets of heated rollers.
Injection molding uses a screw to push plastic through aInjection molding uses a screw to push plastic through a
heated tube into a mold.heated tube into a mold.
Extrusion is a continuous process that heats plastic pellets inExtrusion is a continuous process that heats plastic pellets in
a long barrel. A screw pushes the heated plastic through a diea long barrel. A screw pushes the heated plastic through a die
opening to form objects such as garden hose and piping.opening to form objects such as garden hose and piping.
In thermoforming a hot plastic sheet is draped over a moldIn thermoforming a hot plastic sheet is draped over a mold
and a vacuum draws the plastic down into the mold.and a vacuum draws the plastic down into the mold.
Blow molding forms containers from soft, hollow plastic tubesBlow molding forms containers from soft, hollow plastic tubes
that have a mold fitted around the outside. The tube is heated,that have a mold fitted around the outside. The tube is heated,
and air injected into the heated tube expands the plasticand air injected into the heated tube expands the plastic
against the walls of the mold.against the walls of the mold.
AdditivesAdditives are used in both forms ofare used in both forms of
These can include:These can include:
StabilisersStabilisers to prevent degradation due to moisture or UV light.to prevent degradation due to moisture or UV light.
LubricantsLubricants such as sulphides and waxes to make the polymer easier tosuch as sulphides and waxes to make the polymer easier to
form and self lubricating in use.form and self lubricating in use.
PigmentsPigments - often referred to as 'master batch' adding colours to the plastic.- often referred to as 'master batch' adding colours to the plastic.
PlasticisersPlasticisers - added to make the plastic les hard or brittle.- added to make the plastic les hard or brittle.
FillersFillers - these can be added to enhance properties such as- these can be added to enhance properties such as
wear/strength/toughness/durability and talc and clay may be used to bulkwear/strength/toughness/durability and talc and clay may be used to bulk
out the plastic reducing costs.out the plastic reducing costs.
Flame retardantsFlame retardants - to prevent combustion in materials such as domestic- to prevent combustion in materials such as domestic
Blowing agentsBlowing agents - to permit foams to be blown.- to permit foams to be blown.
Anti-static agentsAnti-static agents - used to prevent the build up of electrical charge.- used to prevent the build up of electrical charge.
Common properties of plasticsCommon properties of plastics
TransparentTransparent (most of them)(most of them)
Resistant to stainResistant to stain
Non- biodegradableNon- biodegradable
Resistant to chemicalsResistant to chemicals
Resistant to oxidation agentResistant to oxidation agent