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EBB 427. Technology and Application of Engineering Polymers. EBB 427. Course Synopsis : This course covers topics on technology and applications of various polymers in engineering applications.

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ebb 427

EBB 427

Technology and Application of Engineering Polymers

ebb 4271
EBB 427
  • 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 4272
EBB 427

Contribution of Assessment :

Final Examination : 70%

Coursework : 30%

references
References
  • 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
Revision

What is the difference between

polymers, plastics and resins???

revision1
Revision
  • Molecular Arrangement of Polymers

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.
revision2
Revision
  • 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.
slide12
Classification of Polymer

Linear chain molecules - Thermoplastics

Branched chain molecules - Thermoplastics

Weakly cross-linked chain molecules - Elastomers

Highly cross-linked molecules - 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.

revision3
Revision

Characteristics of plastics when compared to Metals and Ceramics

  • Applications of Plastics;
  • Packaging
  • Medical
  • Recreational
  • Textiles
  • Furniture & Housewares
  • Transportation
  • Construction, etc.
some important terminology
Some Important Terminology
  • Polymer
  • Plastics
  • Resin
  • Synthetic polymer
  • Natural polymer
slide16
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 terminology1
Some Important Terminology
  • Backbone atom
  • Branching
  • Copolymer
  • Homopolymer
  • Monomer
slide18
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 terminology2
Some Important Terminology
  • Crosslink
  • Curing
  • Thermoplastic
  • Thermoset
  • Catalyst
slide20
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 terminology3
Some Important Terminology
  • Amorphous
  • Crystallinity
  • Degree of crystallinity
  • Melting point (Tm)
  • Steric effect
slide22
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 terminology4
Some Important Terminology
  • Glass transition temperature (Tg)
  • Virgin material
  • Aging
  • Degradation
  • decomposition
slide24
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
Flow properties of polymer melts
  • 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
slide26
Traditional materials; 2 categories
    • 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
Viscosity
  • 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)
viscosity1
Viscosity
  • Consider 2 plates (A= area of the plate),
  • separated by distance, D
  • The space between them is occupied by
  • the liquid
  • One plate moves relatively to the other
  • with velocity U
  • The movement is resisted by the viscous
  • reaction in the fluid
  • Since the movement is in shear, the
  • Reaction is the shear viscosity

F

S

A

θ

D

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

viscosity2
Viscosity
  • The unit of viscositiy was poise, P, or centipoise, cP.

1 mPa·s = 1 cP.

  • ηrapidly 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 sheardeformation

Rheogram for Newtonian liquids.

A - high viscosity, B - low viscosity.

newtonian liquid
Newtonian Liquid
  • Newtonian liquid, where shear stress is proportional to shear rate, with the proportionality constant being the viscosity
  • 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.
  • If the liquid is not Newtonian, a plot of shear vs. the rate of shear is not a straight line but a curve
dilatant
Dilatant
  • 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
Pseudoplastic
  • Pseudoplastic, or shear-thinning fluids have a lower apparent viscosity at higher shear rates.

Pseudo-plastic substance

with yield value

Pseudo-plastic substance.

viscosity3
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)???
  • Dilatant behavior can cause processing
  • difficulties

Newtonian and non-Newtonian bahavior

Variation of apparent viscosity with shear rate

viscosity4
Viscosity
  • Thixotropy
  • Thixotropy is the property of some non-newtonianpseudoplastic 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.

viscosity5
Viscosity
  • When the curve is nonlinear, the viscosity
  • May be defined in two ways;
  • Calculating apparent viscosity, ηa
  • Calculating consistency viscosity, 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

ηc – the slope of the line at the

chosen value of Rate of shear

ηo

ηa

The ηa is greater than ηc

viscometers
Viscometers
  • are employed to measure viscosity.
    • Capillary viscometer
    • Rotational rheometer
    • Simple shear viscometer
    • Cone & plate rheometer
    • Parallel plate viscometer
    • Tensile & extensional viscometer

Schematic diagram of a cone and plate viscometer.

Schematic diagram of a rotational viscometer

melt flow index mfi
Melt Flow Index (MFI)
  • The Melt Flow Index is a measure of the ease of flow of the melt of a thermoplasticpolymer 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
MFI Apparatus
  • 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

How to relate MFI with molecular

weight???

melting of thermoplastic
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

latent heat
Latent heat
  • 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:
    • 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
Specific heat capacity
  • The typical unit for specific heat capacity is the kilojoule per kilogramkelvin, kJ·kg-1·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
Freezing of Melts
  • 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,