Transcript EBB 220/3 ENGINEERING POLYMER

EBB 220/3
ENGINEERING POLYMER
DR AZURA A.RASHID
Room 2.19
School of Materials And Mineral Resources Engineering,
Universiti Sains Malaysia, 14300 Nibong Tebal, P. Pinang
Malaysia
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
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.
MARKING SCHEME
Final Exams : 70%
Test & Assignment : 30%
Contribution:
 Dr Azlan 15%
 Dr Azura 15%
Final Exams : 7 Question  answer 5
SOME THOUGHT

What you understand about
polymer?

Why it is important?
EBB 220/3
INTRODUCTION
DR AZURA A.RASHID
Room 2.19
School of Materials And Mineral Resources Engineering,
Universiti Sains Malaysia, 14300 Nibong Tebal, P. Pinang
Malaysia
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

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
DIFFERENCES BETWEEN
MOLECULE & MONOMER
POLYMER SYNTHESIS
2 types of Polymerization
Addition polymerization
Condesation polymerization
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
CONDENSATION POLYMERIZATION
Involves a reaction between bifunctional reactants
in which a small molecule is eliminated during each
step of the polymer building reaction
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.
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)
TYPES OF COPOLYMER
Random copolymer
-A-B-B-A-A-B-A-B-
Graft Copolymer
-A-A-A-A-A-A
|
Alternating copolymer
-A-B-A-B-A-B-A-BBlock copolymer
-A-A-A-B-B-B-A-A-A-B-B-B
B
|
B
|
B
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.
CONFIGURATIONS OF
MACROMOLECULES
Linear
•
Branched
Crosslinked
Polymer can be divided into 4 groups according
to their deformation properties in the solid
state:
Plastomers
(thermoplastic)
Thermoset
(Duromers)
POLYMER
Elastomer
(vulcanized rubbers)
Thermoplastic
Elastomer
(TPe)
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.

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.
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.

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.

During vulcanization  the chain molecules of
the crude rubber are joined by widely spaced
crosslinks.

After having been crosslinks  the soft plasticlike 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.
Thermoplastic Elastomer (TPe)

Block copolymer that possess elastic
properties within a certain range of
temperature e.g from room temperature 70°C.

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.

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.
Thermosets (duromers)
TERMOSET
(Duromer)

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
crosslinked than those of elastomer.

After been crosslinked  there are infusible
and insoluble and the scrap or reject parts
cannot be reprocessed.
tightly
CONFIGURATIONS OF POLYMER
TYPES
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

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.
Crystalline
region
Amorphous
region
EBB 220/3
POLYMER 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
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
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:
1.
Corrosion resistance: adequate resistance to
water, petrol, oil & salt
2.
Insulation: thick walled tyres tend to get warm
especially if under inflated
3.
Fatigue resistance : excellent
4.
Toughness: Adequate resists crack growth
provided the rubber is protected from oxidative
degradation
5.
Flexibility: Modulus ~1 MPa, grips road and seals
to wheel rim
6.
Energy absorption: a smooth, quiet ride over
rough surfaces (part of the suspension system)
7.
Lubrication: Water is a superb lubricant for
rubber; road holding relies on efficient thread
design to squeeze water out of the way.
8.
Orientation of plies: Selected to confer desired
road
holding,
suspension
and
steering
characteristics.
9.
Low density: light weight construction
10.
Complicated shape: achieved with repeatable
precision
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:
1.
Low density: easy to transport and install.
2.
Corrosion resistance: minimal maintenance,
negligible build-up of scale and able to resist
aggressive media (by suitable choice of plastic).
3.
Insulation: low thermal conductivity or build in
lagging, low electrical conductivity – possible
hazard in pumping non-conducting powders
4.
Easy to make: by extrusion of polymer melt
through die
5.
Colour coded: some plastic are transparent too.
6.
Expansion: thermal expansion must be allowed for in
design of the pipe system.
7.
Flammability: the hydrocarbon nature of polymers
ensures that all polymers will burn, some more readily
than others.
8.
Temperature: the service range is from -5°C. Most
plastics can cope with 50°C, relatively few with 100°C
under prolonged pressure, one or two survive 200°C.
9.
Stiffness: modulus of the order of few GPa or less
10.
Strength: yield stress usually less than 20 MPa
11.
Toughness: in the range 1-3 MPa, less under cyclic or
prolonged load, able to withstand normal use.
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
5.
Dimensional stability: A few polymers can absorb
some liquids, causing swelling or even dissolution,
accompanied by changes in physical properties.


6.
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..
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.
Some special features of plastics
1.
Modulus: About 109 (N/m2)Pa or less
2.
Range of toughness: Some plastic are
tough e,g low density polyethylene, some
fragile e.g general purpose polystyrene.
3.
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.
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:
1. Amorphous Plastic can be very transparent,
2. Partially crystalline ones can be translucent
or opaque
3. Colour plastics with dyes or pigments