EBB 220/3 ENGINEERING POLYMER

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EBB 220/3ENGINEERING POLYMER

• DR AZURA A.RASHID
• Room 2.19
• School of Materials And Mineral Resources
  Engineering,
• Universiti Sains Malaysia, 14300 Nibong Tebal, P.
  Pinang
• Malaysia

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COURSE CONTENT

1. Introduction
2. Principle of viscoelasticity
3. Polymer failure (short term long term)
4. Polymer Rheology
5. Polymer types additives
6. Polymer processing methods
7. Elastomer (rubber)
8. Advanced Polymeric materials
9. Polymer Composites

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REFERENCES

1. R J Young and P A Lovell, Introduction to
   Polymers, Chapman Hall, 1992.
2. R J Crawford, Plastics Engineering, Pergamon
   Press, 1990.
3. D H Morton-Jones, Polymer Processing, Chapman
   Hall, 1989.
4. N G McCrum, C P Buckley, C B Bucknall, Principles
   of Polymer Engineering, Oxford/ University Press,
   1988.
5. R Moore, D E Kline, Properties and Processing of
   Polymers for Engineers, Prentice-Hall, 1984.
6. P C Powell, Engineering with Polymers, Chapman
   and Hall, 1983.

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MARKING SCHEME

• Final Exams 70
• Test Assignment 30
• Contribution
• Dr Azlan 15
• Dr Azura 15
• Final Exams 7 Question ? answer 5

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SOME THOUGHT

• What you understand about polymer?
• Why it is important?

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EBB 220/3INTRODUCTION

• DR AZURA A.RASHID
• Room 2.19
• School of Materials And Mineral Resources
  Engineering,
• Universiti Sains Malaysia, 14300 Nibong Tebal, P.
  Pinang
• Malaysia

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WHAT IS POLYMER??

• Polymers are made up of many many molecules all
  strung together to form really long chains
• This is a polymer. It is a large molecule

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• Poly- means "many" and -mer means "part" or
  "segment". Mono means "one". So, monomers are
  those molecules that can join together to make a
  long polymer chain.
• Many many many MONOmers make a POLYmer! usually a
  single polymer molecule is made out of hundreds
  of thousands (or even millions!) of monomers!
• Sometimes polymers are called "macromolecules" -
  "macro" means "large" ? polymers must be very
  large molecules
• The chemical reactions which monomers joined
  together to form polymer are called
  polymerization reactions

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DIFFERENCES BETWEEN MOLECULE MONOMER
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POLYMER SYNTHESIS
2 types of Polymerization
Addition polymerization
Condesation polymerization
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ADDITION POLYMERIZATION
Involves a simple addition of monomer molecules
to each other without the loss of any atoms from
the original molecule
NOTES It is possible to produce a saturated
long chain polymer from unsaturated monomer
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CONDENSATION POLYMERIZATION
Involves a reaction between bifunctional
reactants in which a small molecule is eliminated
during each step of the polymer building reaction
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MOLECULAR WEIGHT OF POLYMERS

• The molecular weight of one single macromolecule
  is equal to the molecular weight of the repeating
  unit multiplied by number of repeating unit (n)
  in the molecule.
• The molecular weight of Polyethylene (PE) ? can
  be calculated from the formula (C2H4)n 28. If n
  1000 ? the molecular weight of PE will be 2800.
• The molecular weight of PE can be vary from below
  2000 to above one million according to
  polymerization reaction conditions.
• Some polymers consists of macromolecules with
  different molecular weight ? average molecular
  weight will be used to describe their molecular
  weight.

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Homopolymer
Polymer consisting of multiples of the same
repeating units as Polyethylene
Copolymer
Resulted products from two different monomers
(e,g A and B) polymerized together
Terpolymers
Polymers obtained from three different monomers
(e.g. A, B and C)
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TYPES OF COPOLYMER
Random copolymer
Graft Copolymer
-A-B-B-A-A-B-A-B-
-A-A-A-A-A-A B B B
Alternating copolymer
-A-B-A-B-A-B-A-B-
Block copolymer
-A-A-A-B-B-B-A-A-A-B-B-B
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CONFIGURATIONS OF MACROMOLECULES

• The polymer chain may be linear, Branched or
  crosslinked.
• The properties of polymer depend mainly on
• the length and configuration of the
  macromolecules,
• the extent of interaction among them and
• the presence or absence of functional group.

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CONFIGURATIONS OF MACROMOLECULES
Linear
Branched

Crosslinked
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Polymer can be divided into 4 groups according to
their deformation properties in the solid state
Plastomers (thermoplastic)
Thermoset (Duromers)
ThermoplasticElastomer (TPe)
Elastomer (vulcanized rubbers)
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Plastomer (Thermoplastics)

• Polyethylene (PE), Polystyrene (PS) and PVC
  consist of entangled or branched macromolecules
  held together by intermolecular forces
• In the solid state they deform permanently and do
  not recover after complete release of the force
  producing the deformation.
• This is because their macromolecules are loose
  and can slip past each other on the application
  of pressure.

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• Plastomer are usually supplied in granular or
  pelleted form can be repeatedly softened by
  heating and hardened by cooling within a
  temperature range characteristic of each plastic.
• In the softened state ? can be shaped into
  articles by moulding or extrusion.
• The change upon heating is substantially
  physical ? scrap or reject parts can be
  reprocessed.
• Plastomer can be dissolved in suitable solvents
  regain their properties when the solvent is
  evaporated.

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Elastomer (vulcanized rubbers)

• Elastic materials that recover to almost their
  original shape after complete release of the
  applied force.
• They are insoluable and infusible ? can be swell
  only in solvents such as benzene and methyl ethyl
  ketone and decompose when heated far beyond the
  maximum service temperature.
• The unique properties because the macromolecules
  are crosslinked by chemical bonds.

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• The crosslinks prevent the long chain molecules
  from slipping past each other on the application
  of force from dissolving in solvents or melting
  by heating.
• The number of crosslinks can be increased until a
  rigid network results as in the case of hard
  rubber (ebonit).
• Elastomer are produced from crude rubbers ? in
  which a variety of compounding ingredients are
  incorporated.
• The obtained rubber mixtures are usually tacky,
  thermoplastic and soluble in strong solvents.

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• During vulcanization ? the chain molecules of the
  crude rubber are joined by widely spaced
  crosslinks.
• After having been crosslinks ? the soft
  plastic-like material exhibits a high degree of
  elastic recovery, losses its tackiness, becomes
  insoluble in solvents infusible when heated and
  more resistant to deterioration caused by aging
  factors.
• Scrap or reject parts cannot be processed unless
  the crosslinks have been destroyed by chemical or
  mechanical processes.

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Thermoplastic Elastomer (TPe)

• Block copolymer that possess elastic properties
  within a certain range of temperature e.g from
  room temperature -70C.
• The elastic properties are due to physical
  crosslinks resulting from secondary
  intermolecules forces such as hydrogen bonding.
• These crosslinks disappear when heated above
  certain temperature and reform immediately on
  cooling to develop elastic properties.

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• Thermoplastic elastomers fill the gap between non
  crosslinked plastomers and the chemically
  crosslinked elastomer.
• They can be processed even reprocessed in the
  manner of thermoplastic materials without
  vulcanization.
• Some thermoplastic elastomers can be dissolved in
  common solvents regain their properties when
  the solvent is evaporated.

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TERMOSET (Duromer)
Thermosets (duromers)

• Phenolic resins, urea melamine plastics ? are
  rigid materials that are produced from certain
  reactants.
• By heating, they undergo a chemical change in
  which space network molecules are formed similar
  to vulcanization of rubber mixtures.
• The macromolecules are much tightly crosslinked
  than those of elastomer.
• After been crosslinked ? there are infusible and
  insoluble and the scrap or reject parts cannot be
  reprocessed.

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CONFIGURATIONS OF POLYMER TYPES
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Crystalline Amorphous structure of polymers

• Some polymers are almost completely amorphous
  under normal condition but may become crystalline
  when stretched or when conditioned in certain low
  temperatures ranges.
• The term crystalline ? to describe a polymer
  processing both crystalline and amorphous
  regions.
• Those regions are not mechanically separable
  phases ? the same macromolecules may at the same
  region ? semicrystalline

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• Some elastomer particularly crosslinked natural
  rubbers ? have an ability to undergo this kind of
  crystallization when stretched.
• Under the extension force ? the chain molecules
  are oriented in the direction of pull.
• Many properties of polymers such as hardness,
  modulus, tensile strength and solubility ? are
  affected by the degree of crystallinity in the
  polymer.
• Those polymers which do not have the ability to
  crystallize on stretching exhibit inferior
  tensile strength.

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Crystalline region
Amorphous region
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EBB 220/3POLYMER IN ENGINEERING

• DR AZURA A.RASHID
• Room 2.19
• School of Materials And Mineral Resources
  Engineering,
• Universiti Sains Malaysia, 14300 Nibong Tebal, P.
  Pinang
• Malaysia

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WHY POLYMERS

• Within polymers, there are various subgroups
  which within each subgroup there are many
  individual polymers each having its own
  individual portfolio of properties.
• Pure polymers are hardly used on their own to
  make articles or product because polymers have a
  number of limiting features.
• Commonly to use compounds made from polymers and
  ingredients (additives) selected to confer
  desirable characteristics.
• Plastic referring ? plastic polymer additives
• Rubber referring ? elastomer additives

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Radial tyres for car wheels

• Vehicle tyres account for more than half the
  total use of rubber (combination of SBR and
  natural rubber)
• The rubber in tyre has the following general
  characteristics
• Corrosion resistance adequate resistance to
  water, petrol, oil salt
• Insulation thick walled tyres tend to get warm
  especially if under inflated
• Fatigue resistance excellent
• Toughness Adequate resists crack growth provided
  the rubber is protected from oxidative
  degradation

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1. Flexibility Modulus 1 MPa, grips road and seals
   to wheel rim
2. Energy absorption a smooth, quiet ride over
   rough surfaces (part of the suspension system)
3. Lubrication Water is a superb lubricant for
   rubber road holding relies on efficient thread
   design to squeeze water out of the way.
4. Orientation of plies Selected to confer desired
   road holding, suspension and steering
   characteristics.
5. Low density light weight construction
6. Complicated shape achieved with repeatable
   precision

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Plastics pipes fitting

• About 10 of all pipes and fitting are made from
  plastics mainly thermoplastics pipe.
• Thermoplastics used in pipes have the following
  general characteristics
• Low density easy to transport and install.
• Corrosion resistance minimal maintenance,
  negligible build-up of scale and able to resist
  aggressive media (by suitable choice of plastic).
• Insulation low thermal conductivity or build in
  lagging, low electrical conductivity possible
  hazard in pumping non-conducting powders
• Easy to make by extrusion of polymer melt
  through die

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• Colour coded some plastic are transparent too.
• Expansion thermal expansion must be allowed for
  in design of the pipe system.
• Flammability the hydrocarbon nature of polymers
  ensures that all polymers will burn, some more
  readily than others.
• Temperature the service range is from -5C. Most
  plastics can cope with 50C, relatively few with
  100C under prolonged pressure, one or two
  survive 200C.
• Stiffness modulus of the order of few GPa or
  less
• Strength yield stress usually less than 20 MPa
• Toughness in the range 1-3 MPa, less under
  cyclic or prolonged load, able to withstand
  normal use.

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General properties of polymers

1. Density Typically 800-1500 kg/m3 for uniform
   polymers, foamed or cellular polymers down to 10
   kg/m3, heavily filled polymers to about 300 kg/m3
   
2. Insulation Outstanding insulation, exploited in
   wire covering and capacitor dielectrics.
3. Expansion coefficient At about room temperature,
   linear expansion coefficient in the approximate
   range 60-200x10-6 K-1
4. Burning All polymers can be destroyed by flame
   or excessive heat. The rate of destruction
   depends on the type of polymer, the surface to
   volume ratio, the temperature, and the duration
   of exposure to heat

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• Dimensional stability A few polymers can absorb
  some liquids, causing swelling or even
  dissolution, accompanied by changes in physical
  properties.
• Natural rubber readily absorbs large quantities
  of hydrocarbons liquids
• Nylon absorbs moisture in small quantities,
• Chemical resistance Can be very good but must be
  depend on the chemical nature of the polymers.
• Example polymer hydrocarbon such as
  polyethylene are not compatible with hydrocarbon
  oils.
• Some polymers are not oil resistant..

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Some special features of rubber

1. Reversible high extensibility For example up to
   several hundred percent in gum natural rubber
   vulcanizates stretched above Tg
2. Modulus typically about 106 N/m2
3. Energy absorption There is massive area under
   the stress-strain curve, even though the modulus
   is low, which provides a large capacity for
   strain energy.
4. Fatigue resistance For example tyre behaviour.
5. Toughness Good resistance to crack growth under
   cyclic loading if the rubber is protected from
   oxidative degradation.

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Some special features of plastics

• Modulus About 109 (N/m2)Pa or less
• Range of toughness Some plastic are tough e,g
  low density polyethylene, some fragile e.g
  general purpose polystyrene.
• Friction coefficient Unlubricated, some polymers
  have coefficients of about 0.3-0.5
• PTFE rubbing on itself about 0.2
• Some soft plastics just adhere.

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• 4. Temperature range
• Amorphous Plastic are not used above Tg.
• Partially crystalline used mainly between Tg and
  fairly well below Tm and some are used a little
  below Tg.
• 5. Appearance
• Amorphous Plastic can be very transparent,
• Partially crystalline ones can be translucent or
  opaque
• Colour plastics with dyes or pigments

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