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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
Thursday, February 23, 2017 4Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 6Institute of Mechanical Systems - Structure Technology
Why are polymers interesting materials?
Source: http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/basic.html
Thursday, February 23, 2017 7Institute of Mechanical Systems - Structure Technology
But we are here to learn about Composites
Thursday, February 23, 2017 9Institute of Mechanical Systems - Structure Technology
So how much carbon is
in my carbon
composite material?
Less than 50%
The majority is polymer!
Thursday, February 23, 2017 10Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 11Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 12Institute of Mechanical Systems - Structure Technology
Small Molecules, eg. water
Oligomers, several repeating unit, eg. Some oils
Polymers, many repeating units, e.g. PET, polycarbonate
Thursday, February 23, 2017 13Institute of Mechanical Systems - Structure Technology
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?
Thursday, February 23, 2017 16Institute of Mechanical Systems - Structure Technology
• Higher likelihood for entanglement
• Higher intermolecular forces
• Longer time scales for motion
Intermolecular forces
Thursday, February 23, 2017 19Institute of Mechanical Systems - Structure Technology
Longer Time Scales
Thursday, February 23, 2017 21Institute of Mechanical Systems - Structure Technology
Longer time scales: Pitch drop experiment
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Longer time scale: Thermal Motion
Thursday, February 23, 2017 23Institute of Mechanical Systems - Structure Technology
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
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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:
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 27
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 28
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 29
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
Dynamic Loading
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 30
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 31
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 32
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How do we measure polymer size?
Thursday, February 23, 2017 34Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 35Institute of Mechanical Systems - Structure Technology
Molecular weight -2-
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
Thursday, February 23, 2017 36Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 37Institute of Mechanical Systems - Structure Technology
Molecular weight -3-
The molecular weight affects the thermo-mechanical properties
of polymers
Source: http://chem.chem.rochester.edu/~chem421/propsmw.htm
Thursday, February 23, 2017 38Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 39Institute of Mechanical Systems - Structure Technology
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.
Thursday, February 23, 2017 40Institute of Mechanical Systems - Structure Technology
Thermosetting polymers
Source: www.csun.edu/~bavarian/Courses/MSE%20227/Lectures_Exam1/Ch4-Polymers.ppt
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
Thursday, February 23, 2017 41Institute of Mechanical Systems - Structure Technology
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.
Source: www.csun.edu/~bavarian/Courses/MSE%20227/Lectures_Exam1/Ch4-Polymers.ppt
Principali classi di materiali polimerici, Universita’ di Salerno.
amorphous Semicrystalline
Thermoplastics
Thursday, February 23, 2017 42Institute of Mechanical Systems - Structure Technology
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
Source: www.csun.edu/~bavarian/Courses/MSE%20227/Lectures_Exam1/Ch4-Polymers.ppt
Thursday, February 23, 2017 43Institute of Mechanical Systems - Structure Technology
Thermosets versus Thermoplastics
Spaghetti Fishing net
Thursday, February 23, 2017 44Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 45Institute of Mechanical Systems - Structure Technology
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
Thursday, February 23, 2017 46Institute of Mechanical Systems - Structure Technology
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
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 47
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 48
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
Behaviour in Hot/Wet Environments
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
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 49
||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures
Behaviour in Hot/Wet Environments
P. Ermanni, Die kombinierte Nasswickel- und Prepregbauweise: Ein Verfahren zur wirtschaftlichen Herstellung von CFK-
Flugzeugrumpfstrukturen, Dissertation ETH Nr. 9339, Zürich 1990.
23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 50
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