Introduction to Polymer Materials - ETH Z · Thursday, February 23, 2017 Institute of Mechanical Systems - Structure Technology 34 Molecular weight -1-Molecular weight: mass of a

23.02.2017 Manufacturing of Polymer

Composites - Constitutent

1

Joanna Wong

23 February 2017

15:00 – 16:00

Introduction to Polymer Materials

Spring Semester 2017

151-0548-00L Manufacturing of Polymer Composites

Thursday, February 23, 2017 2Institute of Mechanical Systems - Structure Technology

Table of contents

General features of polymeric materials

Thermo-mechanical behaviour

Mr McGuire: I just want to say one word to you.

Just one word.

Benjamin: Yes, sir.

Mr McGuire: Are you listening?

Benjamin: Yes, I am.

Mr McGuire: Plastics.

Career advice to Dustin Hoffman's character in

the movie “The Graduate” (1967)

Quelle: Mayorga, G.D.: “Quality Assurance and Quality Control“ in International Encyclopedia of Composites, Ed. S. M. Lee, VCH Publishers, New York 1991

3


World Consumption of Polymers

Year Consumption

(kilotonnes)

2006 240,947

2016 402,022

Accenture, “Trends in manufacturing polymers: Achieving high performance in a multi-polar world” (2008).

Thursday, February 23, 2017 5Institute of Mechanical Systems - Structure TechnologyDonnerstag, 23. Februar 2017 5Centre of Structure Technologies

Acoustic

Insulation

Packaging

Lightweight

Structures

Thermal Insulation

Toys Furniture

Sandwich Cores

Floatation

Disposable Containers

Clothing

Electrical

Insulation

SealantsInsulating

Containers

Decor Filters


Why are polymers interesting materials?

Source: http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/basic.html

http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/basic.html


But we are here to learn about Composites



So how much carbon is

in my carbon

composite material?

Less than 50%

The majority is polymer!


When we speak of polymers, what exactly are we

talking about?

The word polymer means “many” (poly) “parts” (mer), compare with monomer,

and oligomer

Polymers consist of several ordered monomer repeat units

molecules whose molecular weight (or size) is in the range of several thousand or

more.

Synonyms: Plastic, macromolecules, synthetics

Polypropylene

monomerpolymer


Homopolymers & Copolymers

When a polymer is made by linking only one type of small molecule, or

monomer, together, it is called a homopolymer.

When two different types of monomers A and B are joined in the same polymer

chain, the polymer is called a copolymer.

Source: http://pslc.ws/mactest/copoly.htm

Homopolymer

http://pslc.ws/mactest/copoly.htm


Small Molecules, eg. water

Oligomers, several repeating unit, eg. Some oils

Polymers, many repeating units, e.g. PET, polycarbonate


Polymers = plastics

There would be no FRP composites without polymers.

What makes polymers different from small molecules?

Chain entanglement

Summation of intermolecular forces

Time scale of motion

Thermoplastic versus thermosetting polymers.

Take Away Points



Why size matters?


• Higher likelihood for entanglement

• Higher intermolecular forces

• Longer time scales for motion

Entanglement



Intermolecular forces



Longer Time Scales


Longer time scales: Pitch drop experiment


Longer time scale: Thermal Motion


Particles – Brownian Motion Polymer – Reptation

Equation for Diffusivity:

𝐷 =𝑥2

2𝑡= 𝜇𝑚𝑘𝑏T =

𝜇𝑅𝑇

𝑁=

𝑅𝑇

6𝜋𝜂𝑟𝑁

Time for diffusion:

𝑡 =𝑙2𝑛3𝜇𝑓

𝑛𝑒𝑘𝑏𝑇

D: diffusivity

x: displacement

t: time

μm: mobility

kb: Boltzmann constant

T: temperature

N: Avogadro’s number

R: Ideal gas constant

η: viscosity

r: particle radius

l: Kuhn length

n: number of Kuhn lengths in chain

μf: coefficient of friction

ne: number of lengths in blob model

𝑡 =6𝜋𝜂𝑟𝑁𝑥2

2𝑅𝑇


||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures

Viscoelastic deformation behavior

For small deformation and at low temperatures mechanical behavior

of polymers can be considered as elastic.

Depending on the temperature, polymers combine both viscous

liquid and elastic characteristics when undergoing deformation.

– Newton‘s fluid:

– Hooke‘s law:

s =hdg

dt with h =h0 ×exp

EA

RT

æ

èç

ö

ø÷

G

23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 26


Creep and stress relaxation are well-suited to

investigate the long term material behavior

0

t

0

t 0

0

Creep compliance coefficient J(t)

Slope: 1

h

t

0

0

0 0

t 0

Relaxation module G(t)

Creep tests:

Stress relaxation tests:



Maxwell Modell

Newtonian damper and

Hookean elastic spring are

connected in series.

Addition of the deformations:

dt

d

Gdt

d

1

s =s 0 exp -t

t

æ

èç

ö

ø÷

with the relaxation time t =h

G

Kriech- und Wiederherstellungsverhalten

= const. = 0

d/dt = const. d/dt = 0

Relaxation

Kriechen



Voigt-Kelvin-Modell

Newtonian damper and Hookean

elastic spring are connected in

parallel.

Addition of the shear stress

components

G

t

G

Gdt

d

where

exp1 = const. = 0

Kriechen

d/dt = const. d/dt = 0

Relaxation



Dynamic Loading



Dynamic loading tests are well suited to

analyze the short time behavior

Harmonic shear strain

The stress and strain are shifted by the phase angle d:

Shear stress can be written as:

g t( ) =g0 sin wt( ) and therefore dg

dt=wg0 cos wt( )

t 0 sin t

(t) 0 sin t d GD 0 sin t d



Dynamic loading

Storage Modulus G‘ is in Phase with

Loss Modulus G‘‘ is in Phase with d/dt. In purely viscous materials,

strain and stress are shifted by a 90 degree phase lag

Mechanical loss factor d:

d tand G

G

Komplexer Modul im Zeiger-Diagramm

G* G i G

GD G* G 2 G 2



How do we measure polymer size?


Molecular weight -1-

Molecular weight: mass of a mole of chains.

Low M

High M

• Polymers can have various lengths depending on the number of repeat units.

• During the polymerization process not all chains in a polymer grow to the same

length, so there is a distribution of molecular weights.

• The molecular weight distribution in a polymer describes the relation between the

number of moles of each polymer species and the molar mass of that species.

Sources: Introduction to polymers, Second Edition, R.J. Young and P.A. Lovell

www.csun.edu/~bavarian/Courses/MSE%20227/Lectures_Exam1/Ch4-Polymers.ppt

http://www.csun.edu/~bavarian/Courses/MSE 227/Lectures_Exam1/Ch4-Polymers.ppt



iiw

iin

MwM

MxM

xi = number fraction of chains in size range i

wi = weight fraction of chains in size range i

Mi = mean (middle) molecular weight of size range i

Mn = the number average molecular weight

Mw = the weight average molecular weight

__

__

Source: www.csun.edu/~bavarian/Courses/MSE%20227/Lectures_Exam1/Ch4-Polymers.ppt



Molecular weight Example

Imagine a MW distribution as described below:

MW

(g/mol) n

n x MW

(g/mol) ni

ni x MW

(g/mol) wi

wix MW

(g/mol)

10000 1 10000 0.091 909 0.009 94

50000 3 150000 0.273 13636 0.142 7075

100000 5 500000 0.455 45455 0.472 47170

200000 2 400000 0.182 36364 0.377 75472

11 1060000 1.000 96364 1.000 129811



The molecular weight affects the thermo-mechanical properties

of polymers

Source: http://chem.chem.rochester.edu/~chem421/propsmw.htm

http://chem.chem.rochester.edu/~chem421/propsmw.htm


Polymer topology and chain interactions

Sources: http://www.chm.bris.ac.uk/webprojects2002/edwards/chemistryc_files/image004.gif

www.csun.edu/~bavarian/Courses/MSE%20227/Lectures_Exam1/Ch4-Polymers.ppt

http://pslc.ws/macrog/eposyn.htm

Branched Cross-Linked NetworkLinear

secondarybonding

The chains attached to

the backbone are

comparable in length

to the backbone itself

Kevlar EpoxyElastomers

http://www.chm.bris.ac.uk/webprojects2002/edwards/chemistryc_files/image004.gif


http://pslc.ws/macrog/eposyn.htm


Linear vs cross-linked polymers

Stretch

Linear Polymer

The chains can be stretched, which causes them to flow past each other. When released, the polymer will not return to its original form.

Source: bama.ua.edu/~kshaughn/poly-lecture.ppt

Stretch

Cross-Linked Polymer

The cross-links hold the chains together. When released, the polymer will return to it's original form.

Relax

Thermosetting polymers are provided as uncured resins, or monomers

(oligomers) that undergo a chemical reaction to form a polymer network

Thermosetting plastics when heated, will chemically decompose, so they can

not be recycled. Yet, once a thermoset is cured it tends to be stronger than a

thermoplastic.

The networked structures are thermosets.


Thermosetting polymers


Menges, G.: Werkstoffkunde der Kunststoffe, 2. Auflage; Carl Hanser Verlag, München, Wien 1984

Domininghaus, H.: Die Kunststoffe und ihre Eigenschaften; 4. Auflage, VDI-Verlag, Düsseldorf 1992

Thermosets Elastomer



Thermoplastics polymers

A thermoplastic is a polymer that turns to a liquid when heated above Tm and

freezes to a very glassy state when cooled below Tg.

Most thermoplastics are high-molecular-weight polymers whose chains

associate through weak Van der Waals forces (polyethylene); stronger

dipole-dipole interactions and hydrogen bonding (nylon).

Typically, linear polymers with minor branched structures (and flexible

chains) are thermoplastics.


Principali classi di materiali polimerici, Universita’ di Salerno.

amorphous Semicrystalline

Thermoplastics



Polymer crystallinity

Polymers are rarely 100% crystalline

Difficult for all regions of all chains to

become aligned;

A crystalline polymer has two components:

the crystalline and the amorphous portion.

crystalline region

amorphousregion




Thermosets versus Thermoplastics

Spaghetti Fishing net


Glass transition and melting

Glass Transition Temperature (Tg): The temperature (actually a range of

temperatures) at which chains in amorphous (i.e., disordered) regions of the

polymer gain enough thermal energy to begin sliding past one another at a

noticeable rate. Polymers with no order are hard and brittle below a certain

temperature and soft and pliable above it.

Melting Temperature (Tm): The temperature (actually a range of temperatures)

at which the ordered regions of a crystalline polymer melt, similar to a small

molecule. Crystallization is essential for many high-performance polymers

because it greatly increases the strength of the material.

Melting is something that happens to a crystalline polymer, while the glass

transition happens only to polymers in the amorphous state.

Source: http://chem.chem.rochester.edu/~chem421/propsmw.htm

http://chem.chem.rochester.edu/~chem421/propsmw.htm


Glass transition and melting

This is another big difference between melting and glass transition.

Heat capacity: The amount of heat required to raise the temperature of one

degree Celsius of one gram of the polymer.

Source: http://pslc.ws/mactest/tg.htm

http://pslc.ws/mactest/tg.htm


Wrap-up thermomechanical behaviour

Me is a critical molecular weight.

Below this value, the molecules are

too short for interacting among them.

Source: Polymere Werkstoffe & Werkstoffcharakterisierung, composite technologien 2008


Thermomechanical behaviour of different polymers

Domininghaus, H.: Die Kunststoffe und ihre Eigenschaften; 4. Auflage, VDI-Verlag, Düsseldorf 1992

Dyn

am

ic M

od

ule

Lo

ss f

acto

r

Temperature

Dyn

am

ic M

od

ule

Lo

ss f

acto

r

Temperature

Thermosets

Semi-crystalline Thermoplastics

Dyn

am

ic M

od

ule

Lo

ss f

acto

r

Temperature

Amorphous Thermoplastics



Behaviour in Hot/Wet Environments

Water absorption is descirbed by

the Fick's first law:

F is the diffusion flux [mol/m2.s]

– D [m2/s] is the diffusion

coefficient, which depends on the

temperature

– c is the concentration

The variation of the water

concentration is described by the

Fick's second law:

x

cD

2

2

x

cD

t

c

Arendts, F.J., Aktuelle Entwicklungen in der Strukturtechnik, Z. Flugwiss.

Weltraumforschung, 16 (1992) 231-246




Deutsche Zentrum für Luft- und Raumfahrt

Water absorbtion in the matrix is

affecting mechanical properties

Reduction of matrix stiffness and

strength

accentuate viscoelastic

deformation

Reduction of the glass transition

temperature Tg

Reduction of the interlaminar shear

stiffness




P. Ermanni, Die kombinierte Nasswickel- und Prepregbauweise: Ein Verfahren zur wirtschaftlichen Herstellung von CFK-

Flugzeugrumpfstrukturen, Dissertation ETH Nr. 9339, Zürich 1990.


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Introduction to Polymer Materials - ETH Z · Thursday, February 23, 2017 Institute of Mechanical Systems - Structure Technology 34 Molecular weight -1-Molecular weight: mass of a