Transcript EBB 427 - USM :: Universiti Sains Malaysia

EBB 427
Technology and Application of
Engineering Polymers
EBB 427
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Course Synopsis :
This course covers topics on technology and
applications of various polymers in engineering
applications.
The course covers the properties and the processing
techniques for three types of polymeric materials
such as thermoset, thermoplastics and elastomer.
It also covers the examples of new polymeric
materials and commercially available polymeric
materials, for instance thermoplastic and thermoset
for general and engineering applications
EBB 427
Contribution of Assessment :
Final Examination : 70%
Coursework : 30%
Assessment Methods:
%
Test
10
Quiz
5
Assignment and Report Writing
(PBL)
15
Final Examination
70
Total
100
Teaching Plans / Syllabus
No
Topic Contents
Teaching Weeks
1
The physical basis of polymer processing
 Viscosity and polymer processing
 Melt Flow Index
 Melting of Polymers
 Freezer of Polymer Melts
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2
Mixing process
 Polymers and additives (Modifying and Protective Additives)
 Types of mixing process (Blending and Compounding)
 Some processes and machines (Blending and Compounding)
 Forces in Mixing
 Routes for Mixing
2
Teaching Plans / Syllabus
3
Thermoplastic Materials (Commodity Plastics)
 Introduction
 Polyethylene (PE)
 Polypropylene (PP)
 Polystyrene (PS)
 Polyvinyl Chloride (PVC)
 Alloys and Blends
Thermoplastic Materials (Engineering Plastics)
 Introduction
 Polyamides or Nylon (PA)
 Thermoplastic Polyesters (PET/PBT)
 Polycarbonate (PC)
 Acrylics (PMMA, PAN)
 Fluoropolymers (PTFE, PFA)
 High Performance Thermoplastics
3
Teaching Plans / Syllabus
4
Processing and Applications of Thermoplastic Materials
 Introduction to the thermoplastic processing
 Extrusion
 Blow molding
 Injection molding
 Compression
 Transfer molding, etc
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5
New Thermoplastic Materials for Specific Applications
 Polylactic Acid; biodegradable resin for biomaterials
applications
 Polyether ether ketone; engineering applications
 Polyphenylene- Sulfide (PPS); engineering applications
 Polyimides (PI) & Polyether-Imide (PEI); engineering
applications
 Polytetrafluoroethylene; engineering applications
Environmental Aspect of plastics
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Recycling of plastics
5
Teaching Plans / Syllabus
6
Types of Elastomers
 Natural rubber and modified natural rubber,
 Synthetic rubbers:
 SBR, EPDM, IR, BR, CR, NBR, CSM etc
Basic principles of rubber chemistry and processing
 Basic Principles of rubber chemistry
 Basic terms, Macromolecules, polymers and monomers.
 Plastomers, elastomers, thermoplastics elastomers and
thermosets.
 Elastomer/Rubber processing flow chart
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7
Fundamentals of rubber compounding
 General compounding principles
 Rubber compounding ingredients: fillers, plasticizers, age
resistors, vulcanizing ingredients, special purpose ingredients,
 General elastomeric formulations and mixing equipments and
procedures
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References
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R J Young and P A Lovell, Introduction to Polymers, Chapman &
Hall, 1992.
R J Crawford, Plastics Engineering, Pergamon Press, 1990.
D H Morton-Jones, Polymer Processing, Chapman & Hall, 1989.
N G McCrum, C P Buckley, C B Bucknall, Principles of Polymer
Engineering, Oxford/ University Press, 1988.
An Introduction to Rubber Technology, Andrew Ciesielski, Rapra
Technology Ltd,1999.
Rubber Technology Handbook, Werner Hofmann, Hanser
Publisher, 1989.
Revision
What is the difference between
polymers, plastics and resins???
Revision
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Molecular Arrangement of Polymers
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Think of how spaghetti noodles look on a plate - Amorphous
organization.
An Amorphous polymers are generally transparent.
This is an important characteristic for many applications such as
food wrap, plastic windows, headlights and contact lenses.
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Revision
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Molecular Arrangement of Polymers
The translucent and opaque polymers crystalline arrangement.
By definition a crystalline arrangement has
atoms, ions, or in this case, molecules in a
distinct pattern.
You generally think of crystalline structures
in salt and gemstones, but not in plastics.
Just as quenching can produce amorphous
arrangements, processing can control the
degree of crystallinity. The higher the
degree of crystallinity, the less light can
pass through the polymer.
Therefore, the degree of translucence or
opaqueness of the polymer is directly
affected by its crystallinity.
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Classification of Polymer
Linear chain molecules
Branched chain molecules
Weakly cross-linked chain molecules
Highly cross-linked molecules
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Thermoplastics
Thermoplastics
Elastomers
Thermosets
Thermoplastic - meaning that once the polymer is formed it can be
heated and reformed over and over again (facilitates recycling)
. Thermosets & Elastomers - can not be remelted.
Revision
Characteristics of plastics when compared to Metals and Ceramics
Applications of Plastics;
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Packaging
Medical
Recreational
Textiles
Furniture & Housewares
Transportation
Construction, etc.
Some Important Terminology
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Polymer
Plastics
Resin
Synthetic polymer
Natural polymer
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Polymer- long molecules made up of smaller
molecules-joined together by chemical bonds
Plastics- Large molecules (synthetically made
or naturally occuring), are highly modified
Resin- Polymer that has not been formed into
its final useful shape
Synthetic polymer- polymer that do not occur
naturally, they are manufactured
Natural polymer- polymer that occur in nature
Some Important Terminology
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Backbone atom
Branching
Copolymer
Homopolymer
Monomer
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Backbone atom- atom along the main chain of a
polymer
Branching- side chain of a polymer main chain
Copolymer- a polymer formed from more than the
minimum number of monomer, i.e. ABS
Homopolymer- polymer made from the minimum
number of monomer type
Monomer- a single unit that can be combined with
others to form a polymer
Some Important Terminology
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Crosslink
Curing
Thermoplastic
Thermoset
Catalyst
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Crosslink- covalent bond between polymer chain
Curing- process of hardening a polymer by the
formation of crosslink
Thermoplastic- a polymer solid at room temp, that
can be melted and cooled to solidify in the desired
shape
Thermoset- a polymer that may be either liquid or
solid at room temp., when heated it will harden and
cure
Catalyst- a molecule or material that facilitates a
chemical reaction, but does not become part of the
reaction
Some Important Terminology
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Amorphous
Crystallinity
Degree of crystallinity
Melting point (Tm)
Steric effect
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Amorphous- no regular structural pattern occur in a
area of polymer
Crystallinity- area within a polymer in which a
polymer molecules fold into a tight, regular structure
Degree of crystallinity- the amount of structure that
is crystalline as opposed to the amount that is
amorphous
Melting point (Tm)- the temperature at which
material changes from solid to liquid (vice versa)
Steric effect- The influence of molecule shapes on the
properties of a material
Some Important Terminology
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Glass transition temperature (Tg)
Virgin material
Aging
Degradation
decomposition
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Glass transition temperature (Tg)Virgin material- Resin that has not been
previously processed
Aging- long term, low temperature
degradation
Degradation- the decomposition of a material
Decomposition- the breaking of primary bond
in a molecule
Flow properties of polymer melts
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Rheology- science of the deformation and flow of
bodies
Rheometry- the technology of measuring the flow
behavior
In plastic processing, the materials to be processed
must be in flowable condition- through increase in
temperature caused melting, dissolving the materials
in solvent, etc.
During such processing, the viscosity is important
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Traditional materials; 2 categories
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Elastic solid (iron, concrete, copper, etc)materials completely recover their shape &
restore energy
Viscous fluid (water, oil, etc)- materials that
flow when exposed to an imposed shear
force, do not return to original shape
Polymer- do not follow the trend of
traditional materials….Why???
Viscosity
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Viscosity is a measure of the resistance of a
fluid to deform under shear stress
Viscosity describes a fluid's internal resistance
to flow and may be thought of as a measure
of fluid friction (water is "thin", having a
lower viscosity, while vegetable oil is "thick"
having a higher viscosity)
During flow process in plastic processing
machinery, the melt is subjected to shear
This can be illustrated by 2 plate model (next
slide)
Viscosity
S
A
F
θ
D
1. Consider 2 plates (A= area of the plate),
separated by distance, D
1. The space between them is occupied by
the liquid
3. One plate moves relatively to the other
with velocity U
4. The movement is resisted by the viscous
reaction in the fluid
5. Since the movement is in shear, the
Reaction is the shear viscosity
Shear stress, ζ = Shear force/Area of the shear face
= F/A Nm-2
Shear strain,γ = Amount of shear displacement, S/Distance between shearing surfaces (D)
= Tan θ
Viscosity, η = Shear stress/Rate of shear strain
= ζ / (d γ/dt) = ζ / γ
Viscosity
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The unit of viscositiy was poise, P, or centipoise, cP.
1 mPa·s = 1 cP.
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η
rapidly decreases as temperature increases.
Ideal fluids are called Newtonian. The viscosity is independent
of the rate of shear
Shear rate is a measure of the rate
of shear deformation
Rheogram for Newtonian liquids.
A - high viscosity, B - low viscosity.
Newtonian Liquid
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Newtonian liquid, where shear stress is proportional to shear
rate, with the proportionality constant being the viscosity
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A Newtonian fluid (named for Isaac Newton) is a fluid that
flows like water
For example, water is Newtonian, because it continues to
exemplify fluid properties no matter how fast it is stirred or
mixed.
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If the liquid is not Newtonian, a plot of shear vs. the rate of
shear is not a straight line but a curve
Dilatant
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A dilatant material is one in which viscosity increases with the
rate of shear (also termed shear thickening).
The dilatant effect can be seen more readily with a mixture of
corn starch and water
Pseudoplastic
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Pseudoplastic, or shear-thinning fluids
have a lower apparent viscosity at
higher shear rates.
Pseudo-plastic substance.
Pseudo-plastic substance
with yield value
Viscosity
- Most polymer melts & rubber compound
behave in pseudoplastic.
How can we relate the pseudoplastic
behavior to the morphology of the polymer
(long chain & coiled in complex structure)???
Newtonian and non-Newtonian bahavior -Dilatant behavior can cause processing
difficulties
Variation of apparent viscosity with shear rate
Viscosity
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Thixotropy
Thixotropy is the property of some non-newtonian pseudoplastic
fluids to show a time-dependent change in viscosity .
Viscosity decreases as the material is stirred until some minimum value
is reached. It increases again when the substance is no longer
agitated.
Many gels and colloids are thixotropic materials, exhibiting a stable
form at rest but becoming fluid when agitated
Thixotropic substance at different shear rates.
Viscosity
When the curve is nonlinear, the viscosity
May be defined in two ways;
1. Calculating apparent viscosity, ηa
2. Calculating consistency viscosity, ηc
ηc
ηo – viscosity at a very low shear
Rate, which behave like
Newtonian behavior
ηa – is the slope of the secant line
from the origin to the shear stress
at the given value of shear rate
ηc – the slope of the line at the
chosen value of Rate of shear
ηo
ηa
The ηa is greater than ηc
Viscometers
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are employed to measure viscosity.
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Capillary viscometer
Rotational rheometer
Simple shear viscometer
Cone & plate rheometer
Parallel plate viscometer
Tensile & extensional viscometer
Schematic diagram of a rotational viscometer
Schematic diagram of a cone and plate viscometer.
Melt Flow Index (MFI)
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The Melt Flow Index is a measure of the ease of
flow of the melt of a thermoplastic polymer or a
measure of the ability of the material's melt to flow
under pressure.
It is defined as the weight of polymer in grams
flowing in 10 minutes through a capillary of specific
diameter and length by a pressure applied via
prescribed alternative gravimetric weights for
alternative prescribed temperatures.
The melt flow rate is an indirect measure of
molecular weight, high melt flow rate corresponding
to low molecular weight
The melt flow rate is inversely proportional to the
viscosity of the melt at the conditions of the test
MFI Apparatus
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How to relate MFI with molecular
weight???
Comprises a cylinder
containing polymer melt which
loaded from above by a piston
carrying a weight.
There is a capillary die at the
bottom of the cylinder
The procedure is to measure
the output by cutting off
sections of extrudate at known
time intervals and weighing
them
Melting of Thermoplastic
Originally solid, must be heated to
above its melting or softening point
 The heat comes from 2 sources;
1. The external heat supplied-i.e. by
heater on the barrel of extruder, etc
2. Heat generated when a highly viscous
fluid being sheared at high shear rate
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Latent heat
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the amount of energy in the form of heat that is
required for a material to undergo a change of phase
(also known as "change of state").
Two latent heats are typically described. One is the
latent heat of fusion (melting), and the other is the
latent heat of vaporization (evaporation).
They are so named as to describe the direction of
heat flow from one phase to the next:
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solid → liquid → gas.
The energy change is endothermic when going from
solid to liquid to gas, but exothermic when going in
the opposite direction.
Specific heat capacity
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The typical unit for specific heat capacity is
the kilojoule per kilogram kelvin, kJ·kg1·C-1
the amount of energy required to raise the
temperature of one kilogram of the substance
by one Celcius. Heat capacity can be
measured by using calorimetry. The SI unit
would be joule per kilogram celsius
Freezing of Melts
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The reverse of the melting process
The molding must be removed from a
mould without danger of its distortion.
To estimate cooling rate, need to find
thermal diffusivity,