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MM361POLYMER ENGINEERING

Dr Yasir Joya

Lec-01Syllabus Introduction to polymeric materials; classification, structure, co-polymers,

Isomerism, types of polymerization reactions, molecular weights, Step

growth and chain polymerization, processing and forming of polymers,

characterization by DSC, FTIR and NMR, molecular structure and property

relationships, Kinetics, Mechanical properties of polymers, viscoelasticity,

special polymers: conducting polymers, engineering polymers, graft

polymers, and bio polymers.

Pre-requisite(s): MM102Text Book

Essentials of Polymer Science and Engineering, by

P Painter and M Coleman, 2009

References:

Principles of Polymer Engineering, N. G. McCrum,

C. P. Buckley and C. B. Bucknall, 1996

Material Science and Engineering: An Introduction, WD Callister, 8th Ed. 2010

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Related Lab Experiments

(MM344)

Injection Moulding of Polymers

Identification of Polymers

Tensile testing of Polymers

Effect of the strain rate on tensile properties of

Polymers

Determination of glass transition temperature (Tg) of

Polymers

Grading Policy

Assignments = 5%

Quizzes (surprise) = 15%

Midterm Exams = 30 %

Final Exams = 40%

Semester Project = 10%

Dr Yasir F Joya / Office:FMSE-G12, Off. Ext. 2327Email: yasir.joya@giki.edu.pk

Office Hours: From 8am-5pm weekdays,

Visiting hours: after 4 pm

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Course Objectives

To develop an understanding of the fundamental

composition-structure-properties relationships in polymers

and to apply this to the processing/manufacturing of

various polymers

Apply scientific and engineering knowledge to the

selection of plastics/elastomers for certain engineering or

technological applications

Prediction/interpretation of the behaviour and properties

of plastics, and the evaluation of new technologicaldevelopments in advanced polymers.

Course Learning Outcomes (CLO)

The course is designed for students to actively engage in the learning process

and analyse and synthesise the content in a real world environment.

It is expected that, in addition to attending classes, students will read, write,

discuss, and engage in analysing the course content.

The course content is designed to incorporate both theoretical and practical

concepts applicable to real-world situations.

Students are challenged by the course content and to challenge their own

knowledge, and understanding by questioning information, and

concepts/ideas during class and study.

Coursework, assignments, laboratories, examinations, and other forms of

learning and assessment are intended to provide students with the

opportunity to relate these activities in a meaningful way with their own

experience and knowledge. Induce critical thinking.

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Things to remember

80% min. attendance to sit in exams

For preparation of quiz/exams, make notes from

lectures as well as consult the corresponding chapters

of the prescribed text book.

If you are to miss a lecture/quiz/exam etc. you must

provide the reason in your application in advance.

For the lecture slides, keep in touch with your TA/GA

Any problem, make an appointment and discuss.

Lec-02Importance of Polymers

Natural Polymers such as Wood, Silk, rubber, cotton, wool, leather have

been used for centuries.

Other examples are hairs, proteins, enzyms, DNA

By using modern tools it has been possible to discover the structural

characteristic of the natural polymers, which lead to the synthesis and

design of new polymers.

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What is Polymer?

Poly many Mer units or parts M-M-M-M-M-M-M or -(M)n-

A large molecule made up of smaller building blocks or monomer (M).

These building blocks are mostly composed of hydrocarbons i.e. covalently

bonded H and C along with other elements.

First example that will come into your mind is probably plastics which is a

material. Polymer is a type of molecule (but a large one).

PE Bags

(shoppers)

Polymers

PET bottles

Nylon is another well known example from our daily life. For example, you

might have heard nylon shoes. Nylon is a polymer C, H, O and N.

Similarly polyester in textiles which is a polymer of C, H, and O.

The building elements for most of the polymers are one way or other

similar, mostly C, H and O. Its their structure which determine their

properties and suitability for certain application.

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Polymer Characteristics

Polymers have high MW, from 500 over to 10,000 or even 10^7 gm/mole

Consists of carbon, hydrogen as the major constituents, PE, PP, Polystyrene

Have low MP and BP, e.g. PE melts max. at 180C

Have covalent bonding between atoms

Chain like structure of repeating molecules/units

Polymers can be very resistant to chemicals (plastic bottles carry acids)

Polymers can be both thermal and electrical insulators, (electrical wireinsulations, foam core of refrigerators and freezers, insulated cups, coolers)

Generally, polymers are very light in weight with significant degrees ofstrength

Polymers can be easily processed in various ways, extrusion, injection mouldingand various other methods.

Composites made with polymers have superior strength to weight ratiocompared to metals/alloys. PMC find numerous applications in aerospace,automobile and many other industries.

A class of polymers can be recycled i.e. thermoplastics

Polymers and Oligomers

As a rule of thumb, molecules with MW say below 500 g/mol, are

regarded as low molecular weight materials. Polymers on the other hand,

are classed as high MW materials or Macromolecules exceeding 10, 000

g/mol and even up to 10^7 g/mol.

Between low MW and high MW extremes there is a region of moderately

high MW materials called oligomers.

Similarly dimer, trimers, stand for polymers with two and three monomer

molecules.

Polystyrene chain, with x

upto 5x10^6 g/molA carboxylic acid dimer

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Oligomers

If a polymer contains methylene groups joined together in linear chain,

considering the total weight of the oligomer is 500,000 g/mol. Calculate

the number of methylene groups in this oligomer.

3. Raw Materials of Polymers:Hydorcarbons Family

Paraffins, Olefins and Acetylenes

Hydrocarbon groups

Methyl, ethyl, phenyl etc.

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Polymers Classification

As the chain length increases of the linear

hydrocarbons, they tend to become viscous and

transform from liquid to semi-solid such as wax.

Even higher chain lengths typically exceeding

30,000 we have hard solid PE.

Natural and synthetic polymers obey the same

physical laws. Cellulose is a natural polymer found

cotton and other plants/trees. It consists of C, H

and O. Polyester and PET are synthetic polymers

also contains these elements. Its just the

arrangement or structure that differs.

Natural and synthetic Polymers

The first synthetic plastic was introduced in beginning of 20th century

invented by Leo Baekeland, is named after him as Bakelite (a cross-linked

polymer).

Charles Goodyear discovered how to cure natural rubber and make it

useful.

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Natural and synthetic Polymers

Cellulose is the most abundant polymer with a linear and

regular chain. This together with strong molecular hydrogen

bonding, results in tightly packed highly crystalline

polymeric material.

Cellulose is insoluble in nearly all solvents, and has high MP

and degrades before melting therefore cant be processed

in the melt. But it can be chemically modified to impart

softening and moldability which is possible due to polymer

science.

Polyisoprene which is natural rubber is another example of

widely used polymer (surgical gloves).cellulose

Homopolymer, Copolymer andFunctionality

When all of the repeating units along a chain are of the same type, the

resulting polymer is called a homopolymer. For example Polyethylene, PTFE

etc.

Chains may be composed of two or more different repeat units, in what are

termed copolymers. For example PVDF, PVC, Polypropylene etc.

The monomers have an active bond that may react to form two covalentbonds with other monomers forming a two-dimensional chainlike molecular

structure, as indicated earlier for ethylene. Such a monomer is termed

bifunctional.

In general, the functionality is the number of bonds that a given monomer

can form. For example, monomers such as phenolformaldehyde are

trifunctional; they have three active bonds, from which a three-dimensional

molecular network structure results.

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Monomer functionality

Trifunctional Phenol-formaldehyde

(Bakelite)

Bifunctional PET

(a polyester)

Polymers and the Environment:Waste disposal

Polystyrene/foam for food packaging, PE

But its structure protects it from degradation in landfill. Similarly papers are

not degradable in landfill. New biodegradable polymers are being

explored but its not that simple to synthesize such materials. Apart from

material properties, the soil bacteria, humidity, oxygen, pressure and

temperature have a role in decomposition reactions.

Compostable garbage bags have been recently invented for this purpose

and in vogue in San Francisco since 2007. They are biodegradable.

Incineration of plastic waste

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Biodegradable Polymers

The word biodegradable is distinct in meaning from compostable*.While biodegradable simply means an object is capable of beingdecomposed by bacteria or other living organisms, "compostable"is able to decompose in aerobic environments that are maintainedunder specific controlled temperature and humidity conditions.

Compostable polymers are capable of undergoing biologicaldecomposition in a compost site such that the material is notvisually distinguishable and breaks down into carbon dioxide,water, inorganic compounds and biomass at a rate consistent withknown compostable materials.

Plastic bags can be made oxo-biodegradable by beingmanufactured from a normal plastic polymer (i.e. polyethylene) or

polypropylene incorporating an additive which causesdegradation and then biodegradation of the polymer(polyethylene) due to oxidation.

*http://en.wikipedia.org/wiki/Biodegradable_bag

Lec-04Polymers Classification

When all monomers in a polymer molecule are of same type/unit, theresulting polymer is called Homopolymer. Examples: PE, PTFE,

If monomers are composed of two or more different units, the resultingpolymer is called Copolymer. Examples: PET, PP, PVC

http://en.wikipedia.org/wiki/Biodegradable_baghttp://en.wikipedia.org/wiki/Biodegradable_bag

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Types of Copolymers

Compolymers are useful, e.g. if two monomers each produce a

homopolymer with a desirable property, a copolymer can be produced

which combines the properties of different monomers.

The properties of the copolymer depend on the monomers and their

configuration; these may be divided into four categories: alternating,

random, block and graft copolymers.

Example are

Polymer Microstructure:Linear vs Branched Polymers

Unlike in metals and ceramic, the microstructure in polymer related to the

molecular arrangement along the polymer chain. Minor change in chain

structure can have considerable effect on the macroscopic properties

(hardness, density, strength) and ability of the material to crystallize.

Crystallinity in polymers is related to the regular, repeating, ordered chain

molecules 3-D array in space. Polymers due to their large size and

complexity, are often partially crystalline or semicrystalline. Any chain

disorder or misalignment will result in an amorphous region.

Which among linear and branched chain would crystallize more easily?

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Polymers Microstructures

Linear Polymers

Units are joined together end to end in a single

Chain. There may be van der Wassls bonding

between chains. Examples are PE, PVC, PS, PMMA,

Nylon etc.

Branched Polymers

Have side groups/chains connected to the main

chain or carbon backbone. Packing efficiency is

Reduced due to side branches resulting in lowerdensity. Examples, high-density polyethylene (HDPE)

is primarily a linear polymer, whereas low-density

polyethylene (LDPE) contains short chain branches.

Can you draw their structure?

Cross-linking in Polymers

Polymeric network can be made by taking linear polymer chains and linking

them by using covalent bonds. For example, natural rubber or polyisoprene

is reacted with sulphur to form cross-links. This process is called

vulcanization. The sulphur interconnects the chains by reacting with double

bonds.

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Network Formation

Multifunctional monomer forming three or more active covalent bonds make

3-D networks and are termed network polymers. A highly cross-linked

polymer may also be classified as a network polymer. Examples, epoxies,

polyurethanes and phenol formaldehyde.

Network Formation in synthesis ofBakelite

The hydrogen in the ortho and para position to the OH groups can react

with formaldehyde to form oligomers initially. As the reaction proceeds

molecules like this continue to react building and interconnected network.

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Linear vs Branched Polymers

It is easier for linear chains to branch regularly, by folding over each other

in an ordered manner.

Polymers crystallinity

Which among the Linear (more crystalline) polymer

OR branched (less crystalline) one would be more

dense?

High density polyethylene (HDPE)

Low density polyethylene (LDPE)

Chain that are highly branched and can notcrystalline they look like cooked spaghetti, Resulting

in random coils, hence there would be fewer

chains/unit volume and the density would be less.

Density variations in amorphous and crystalline

Regions also effect their optical properties, as the light

Is scattered that makes the material look opaque.

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Polymer Crystallinity

Polymers never crystallize completely and have regions of order and

disorder with different properties.

Polymer Microstructure:

Polymers may be up to 95% crystalline. Crystalline polymer are more

dense compared to the amorphous of the same material and molecular

weight.

The degree of crystallinity by weight may be determined from accurate

density measurements as follows;

Where is the density of perfectly crystalline polymer, is the density

of totally amorphous polymer and is the density of specimen under

consideration.

100)(

)(%

acs

ascityCrystallin

c

a

s

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Polymer Configuration

For polymers having more than one side atom or group of atoms bonded tothe main chain, the regularity and symmetry of the side group arrangementcan significantly influence the properties.

Head to Tail configuration

Head to Head configuration

In most polymers, the head-to-tail configuration predominates; often a polar

repulsion occurs between R groups for the head-to-head configuration.

H to HH to T

HT

Isomerism in Polymers

Polymers with same composition may have different atomic configuration.

The phenomenon is termed isomerism. For example there are two isomers

for butane, i.e. normal butane (n-butane) and iso-butane and hence both of

these possess different physical and chemical properties.

Isomerism

Sequenceisomerism

Stereo-isomerism

Structuralisomerism

Iso-butane, BP= -12 C

n-butane, BP= 0 C

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1. Sequence Isomerism

Consider a polymer chain during polymerization where an active site at the

end of chain exists where the next unit will add. For example, vinyl polymer

with the formula.

CH2=CXY + R* R-CH2-CXY* or R-CXY-CH2*

Therefore the reactive radical R can attach to the vinyl polymer either

through TH or HT configuration.

For example, Polystyrene, addition

may occur mostly through HT fashion due to

steric repulsion of benzene ring in HH.Both are sequence monomers.

H TT H

2. Stereo Isomerism

Stereoisomerism denotes the situation in which atoms are linked together

in the same order (head-to-tail) but differ in their spatial arrangement.

For one stereoisomer, all of the R groups are situated on the same side of

the chain as shown. This is called an isotactic configuration

Solid wedges represent bond position which are out of the plane of this

slide, and dashed one represent into the slide plane.

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Lec-05

Stereo Isomerism

In a syndiotactic configuration, the R

groups alternate sides of the chain while

for random positioning, the term atactic

configuration is used.

Syndiotactic configuration

Atactic configuration