cbb4423_chapter7

8/2/2019 CBB4423_Chapter7

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CBB 4423

Polymer Process Engineering

Cont`..

MRB


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WeekWeek DateDate Topics of LectureTopics of Lecture AssesmentAssesment

11Introductory Concepts and Definition

Some Definitions , Polymerisation and Functionality

Overview of Polymeric Materials

Why are Synthetic Polymers Useful?

Molecular Architecture,

Classification, Thermoplastics , Thermosets and Elastomer,

Polymer Nomenclature

Introductory Concepts and Definition

Some Definitions , Polymerisation and Functionality

Overview of Polymeric Materials

Why are Synthetic Polymers Useful?

Molecular Architecture,

Classification, Thermoplastics , Thermosets and Elastomer,

Polymer Nomenclature

22Polymerisation

NG/LPG/naphta to monomers,

Polymerisation and catalyst systems

Addition and Condensation

Control of MW and product quality, grade control

Basic Principles of Polymer Molecular Weight- Importance of MW control

- Number average, Mn,Weight average, M

w


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WeekWeek DateDate Topics of LectureTopics of Lecture AssesmentAssesment

33 Project 1Project 1

44

55

Lab Start

Mechanical/Physical Properties

Stiffness , Stress Analysis

Yielding and Crazing, Linear Fracture Mechanics ,

Elastic- plast ic Fracture, Britt le Fracture,

Toughening


Stiffness , Stress Analysis

Yielding and Crazing, Linear Fracture Mechanics,

Elastic- plast ic Fracture, Britt le Fracture,

Toughening

Structure of Polymer Solids

- Crystalline and Amorphous Polymer

- Thermal Transition, Tm- The Glass Transition Temperature, T

g

Effect of Polymer Structure on Tg


Tensile, Impact, etc

Plyethylene Polymerisation ,

Rector control and Grade change in gas phase PEreactor, Handling of polymer powder and pellets ( +

additives)

Case study


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6

7

8

9

10

Viscoelasticity

Creep, Stress relaxation, Viscoelastic

Model, Dynamic properties,

SEMESTER BREAK

RheologyOverview

Newtonian and Non-Newtonian Fluids

Effect of MW, Temperature, and

Pressure on Viscosity

Rheology

Torque Rheometry

Melt flow tester (MFI),

Test 1

Revision, Project 1 and

Assignment 1-4

Polymer processing/fabrication

Using injection, extrusion etc.


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11

12 (Submission of

P2)

13 Test 2

14

15

Thermoset/Cross-linked Polymers

The Sol-Gel Transition

Cross-links, Gels and Gelation,

reaction kinetics

Polymer Composites

-

Filler and Fiber reinforcement

Product performance and economic

evaluation-

New Development /Application

Fire retardant, Intumescent Polymer,Nanocomposite Material.

Biopolymer

Alloys and Blend

Compatibility , Thermodynamic of mixing,

Miscibility and Phase separation.

STUDY WEEK


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Polymer Composites/nano-compositesIntroduction, properties

Composite Applications and Discontinuous

(short) fibers (calculations)

Polymer/Composites processing and properties

Polymer/composites degradation and stabilityThermo- and photo-degradation

Mechanisms of polymer stabilization

Rheology: FundamentalsWhat is rheology?

Applications of rheology to problem solving


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What is Composites?

Combination of 2 or more materials

Each of the materials must exist more than

5% Presence of interphase

The properties shown by the compositematerials are differed from the initialmaterials

Can be produced by various processingtechniques


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Two or more chemically distinct materials which when

combined have improved properties over the individual

materials. Composites could be natural or synthetic.

Wood is a good example of a natural composite,combination of cellulose fiber and lignin. The cellulose

fiber provides strength and the lignin is the "glue" that

bonds and stabilizes the fiber.

Wood is a good example of a natural composite, combination of

cellulose fiber and lignin. The cellulose fiber provides strength and th

lignin is the "glue" that bonds and stabilizes the fiber.

What is Composites?


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Constituents of composite

materials1. Matrix phaseContinuous phase, the primary phase.It holds the dispersed phase and shares a load with it.

2. Dispersed (reinforcing) phaseThe second phase (or phases) is imbedded in the matrix in acontinuous/discontinuous form.Dispersed phase is usually stronger than the matrix, therefore it is sometimescalled reinforcing phase.

3. InterfaceZone across which matrix and reinforcing phases interact (chemical, physical,mechanical)


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Typically, reinforcing materials are strong with low

densities while the matrix is usually a ductile or tough

material. If the composite is designed and fabricated

correctly, it combines the strength of the reinforcement

with the toughness of the matrix to achieve acombination of desirable properties not available in any

single conventional material.

Matrix materials

Polymers

Metals

Ceramics

Interface

Bonding

surface

Components of composite materials:

Reinforcement: fibers

Glass

Carbon

Organic

Boron

Ceramic

Metallic

Constituents of composite

materials


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Matrix: Function

however the distribution of loads depends on the interfacial bondingshowever the distribution of loads depends on the interfacial bondings


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however the distribution of loads depends on the interfacial bondingshowever the distribution of loads depends on the interfacial bondings

SEM micrographs

CNT/ PEEK composite


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Reinforcement can be in the form

of: Continuous fiber

Organic fiber- i.e. Kevlar, polyethylene

Inorganic fiber- i.e. glass, alumina, carbon Natural fiber- i.e. asbestos, jute, silk

Short fiber

whiskers Particle

Wire


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Interface: Function

To transfer the stress from matrix to

reinforcement

Sometimes surface treatment is carried outto achieve the required bonding to the

matrix

The essence of the concept of composites is that the load is

applied over a large surface area of the matrix. Matrix then

transfers the load to the reinforcement, which being stiffer,

increases the strength of the composite. It is important to note

that there are many matrix materials and even more fiber types,

which can be combined in countless ways to produce just the

desired properties.


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a) Concentration (b) size (c) shape (d) distribution

(e) orientation

Characteristics of dispersed phase that might influence

the properties of composites


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Types of composites


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Examples of composites

a) Particulate & randomb) Discontinuous fibers & unidirectionalc) Discontinuous fibers & randomd) Continuous fibers & unidirectional


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Classification based on Matrices

Compositematerials

Matrices

Polymer MatrixComposites (PMC)

Metal MatrixComposites MMC)

Ceramic MatrixComposites (CMC)

Thermoset Thermoplastic Rubber


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What is Hybrid composites?

What are the advantages of

hybrid composites?


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Widely used- ease of processing & lightweight


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Properties of composites depend

on

Amount of phase

- Amount/proportion (can be expressed in

weight fraction (Wf) or volume fraction(Vf))of phases strongly influence theproperties of composite materials.

Xc

= Xf

Vf

+ Xm

(1 - Vf

) - Rule of Mixture

Xc = Properties of composites

Xf= Properties of fiber

Xm= Properties of matrix


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Voids

Free volume

Gas emission leads to voids in thefinal product

In composites- Voids exist in thematrix, interface and in between fiber& fiber

Voids create stress concentrationpoints- influence the properties of thecomposites


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Geometry of dispersed phase

(particle size, distribution,

orientation)

Shape of dispersed phase (particle- spherical orirregular, flaky, whiskers, etc)

Particle/fiber size ( fiber- short, long,continuous); particle (nano or micron size)

Orientation of fiber/particle (unidirection, bi-directions, many directions)- influence isotropic

and anisotropic properties Distribution of dispersed phase

(homogenus/uniform, inhomogenus)


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Glass FiberThe types of glass used are as follows:

E

-Glass the most popular and inexpensive glass fibers. Thedesignation letter E means electrical (E-Glass is excellentinsulator). The composition of E-glass ranges from 52-56%SiO2, 12-16% A1203, 16-25% CaO, and 8-13% B203

S-Glass stronger than E-Glass fibers (the letter S meansstrength). High-strength glass is generally known as S-typeglass in the United States, R-glass in Europe and T-glass in

Japan. S-Glass is used in military applications and inaerospace. S-Glass consists ofsilica (SiO2), magnesia (MgO),alumina (Al2O3).

C-Glass corrosion and chemical resistant glass fibers. Toprotect against water erosion, a moisture-resistant coating suchas a silane compound is coated onto the fibers duringmanufacturing. Adding resin during composite formationprovides additional protection. C-Glass fibers are used formanufacturing storage tanks, pipes and other chemicalresistant equipment.


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F

iberglasses (Glass fibers reinforced polymer matrixcomposites) are characterized by the followingproperties:

High strength-to-weight ratio;

High modulus of elasticity-to-weight ratio;

Good corrosion resistance; Good insulating properties;

Low thermal resistance (as compared to metals andceramics).

Fiberglass materials are used for manufacturing:

boat hulls and marine structures, automobile andtruck body panels, pressure vessels, aircraft wingsand fuselage sections, housings for radar systems,swimming pools, welding helmets, roofs, pipes.

Glass Fiber


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Carbon Fiber The types of carbon fibers are as

follows: UHM (ultra high modulus). Modulus of

elasticity > 65400 ksi (450GPa).

HM (high modulus). Modulus ofelasticity is in the range 51000-65400

ksi (350-450GPa). IM (intermediate modulus). Modulus of

elasticity is in the range 29000-51000ksi (200-350GPa).

HT (high tensile, low modulus). Tensilestrength > 436 ksi (3 GPa), modulus ofelasticity < 14500 ksi (100 GPa).

SHT (super high tensile). Tensilestrength > 650 ksi (4.5GPa).


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C

arbonF

iberR

einforced Polymers (CFR

P) are ch

aracterizedby the following properties:

Light weight;

High strength-to-weight ratio;

Very High modulus elasticity-to-weight ratio;

High Fatigue strength;

Good corrosion resistance; Very low coefficient of thermal expansion;

Low impact resistance;

High electric conductivity;

High cost.

Carbon Fiber Reinforced Polymers (CFRP) are used formanufacturing: automotive marine and aerospace parts, sportgoods (golf clubs, skis, tennis racquets, fishing rods), bicycleframes.

Carbon Fiber


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Kevlar Fiber

Kevlaris the trade name (registered by DuPont Co.)of aramid (poly-para-phenylene terephthalamide)fibers.

Kevlar fibers were originally developed as areplacement of steel in automotive tires.

Kevlar filaments are produced by extrusion of theprecursor through a spinnert. Extrusion impartsanisotropy (increased strength in the lengthwisedirection) to the filaments.

Kevlar may protect carbon fibers and improve theirproperties: hybrid fabric (Kevlar + Carbon fibers)combines very high tensile strength with high impactand abrasion resistance.


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Kevlar fibers possess the following properties:

High tensile strength (five times stronger perweight unite than steel);

High modulus of elasticity;

Very low elongation up to breaking point;

Low weight; High chemical inertness;

Very low coefficient of thermal expansion;

High Fracture Toughness (impact resistance);

High cut resistance;

Textile processibility; Flame resistance.

The disadvantages of Kevlar are: ability to absorbmoisture, difficulties in cutting, low compressivestrength.

Kevlar Fiber


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There are several modifications of Kevlar,developed for various applications:

Kevlar 29 high strength (520000 psi/3600 MPa),low density (90 lb/ft/1440 kg/m) fibers used formanufacturing bullet-proof vests, composite armorreinforcement, helmets, ropes, cables, asbestos

replacing parts. Kevlar 49 high modulus (19000 ksi/131 GPa),

high strength (550000 psi/3800 MPa), low density(90 lb/ft/1440 kg/m) fibers used in aerospace,automotive and marine applications.

Kevlar 149 ultra high modulus (27000 ksi/186GPa), high strength (490000 psi/3400 MPa), lowdensity (92 lb/ft/1470 kg/m) highly crystallinefibers used as reinforcing dispersed phase forcomposite aircraft components.

Kevlar Fiber


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Composites Polymer/Fibers


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Properties of Reinforced Plastics

The mechanical properties of reinforced plastics vary with the kind,

shape, relative volume, and orientation of the reinforcing material, andthe length of the fibers.

Effect of type, length, % volume, and orientation of fibers in a fiber

reinforced plastic (nylon)


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Reasons for the use of polymeric

materials as matrices in composites

The mechanical properties of polymers are

inadequate for structural purposes, hence

benefits are gained by reinforcing thepolymers

Processing of PMCs need not involve high

pressure and high temperature The equipment required for PMCs are much

simpler


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Disadvantages of PPMC

Low maximum working

temperature

High coefficient of thermal

expansion- dimensional

instability

Sensitivity to radiation andmoisture

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Classification of Polymer

Matrices(Recall? )

1. Thermoset

2. Thermoplastic- crystalline &

amorphous

3. Rubber


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Thermoset

Thermoset materials are usually liquid ormalleable prior to curing,and designed to be molded into their final form

has the property of undergoing a chemical reaction by the actionof heat, catalyst, ultraviolet light, etc., to become a relativelyinsoluble and infusible substance.

They develop a well-bonded three-dimensional structure uponcuring. Once hardened or cross-linked, they will decompose ratherthan melt.

A thermoset material cannot be melted and re-shaped after it iscured.

Thermoset materials are generally stronger than thermoplasticmaterials due to this 3-D network of bonds, and are also bettersuited to high-temperature applications up to the decomposition

temperature of the material.


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Thermoplastic is a plastic that melts to a liquid when heated and

freezes to a brittle, very glassy state when cooledsufficiently.

Most thermoplastics are high molecular weight

polymers whose chains associate through weak van

der Waals forces (polyethylene); strongerdipole-

dipole interactions and hydrogen bonding (nylon); or

even stacking ofaromatic rings (polystyrene).

The bondings are easily broken by the cobined actionof thermal activation and applied stress, thats why

thermoplastics flow at elevated temperature

unlike thermosetting polymers, thermoplastic can be

remelted and remolded.


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Thermoplastics can go throughmelting/freezing cycles repeatedly and the

fact that they can be reshaped uponreheating gives them their name

Some thermoplastics normally do notcrystallize: they are termed "amorphous"

plastics and are useful at temperaturesbelow the Tg. They are frequently used inapplications where clarity is important.Some typical examples of amorphousthermoplastics are PMMA, PS and PC.

Generally, amorphous thermoplastics areless chemically resistant


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Depends on the structure of thethermoplastics, some of the polymeric structure

can be folded to form crystalline regions, willcrystallize to a certain extent and are called"semi-crystalline" for this reason.

Typical semi-crystalline thermoplastics are PE,

PP, PBT and PET. Semi-crystalline thermoplastics are more

resistant to solvents and other chemicals. If thecrystallites are larger than the wavelength of

light, the thermoplastic is hazy or opaque. Why HDPE exhibits higher cystallinity thanLDPE?


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Comparison of typical ranges of

property values for thermoset and

thermoplastics

Properties t/set t/plastic

Youngs Modulus (GPa)1.3-6.0 1.0-4.8

Tensile strength(MPa) 20-180 40-190

Max service temp.(C) 50-450 25-230

Fracture toughness,KIc 0.5-1.0 1.5-6.0

(MPa1/2)


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Thermoplastics are expected to

receive attention compared to

thermoset due to:

Ease of processing

Can be recycled

No specific storage

Good fracture modulus


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Rubber

Common characteristics;

Large elastic elongation (i.e. 200%)

Can be stretched and then immediately return totheir original length when the load was released

Elastomers are sometimes called rubber or rubberymaterials

The term elastomeris often used interchangeably withthe term rubber

Natural rubber is obtained from latex from Hevea

Brasiliensis tree which consists of 98% poliisoprena Synthetic rubber is commonly produced frombutadiene, spt styrene-butadiene (SBR) dan nitrile-butadiene (NBR)


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To achieve properties suitable for

structural purposed, most rubbershave to be vulcanized; the long

chain rubber have to be crosslinked

The crosslinking agent in

vulcanization is commonly sulphur,

and the stiffness and strength

increases with the number of

crosslinks


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