Selection of polymers

Report
Lesson 5
2014
Lesson 5
2014
 Our goal is, that after this lesson, students
are able to recognize the key criteria for
selecting polymers and are able to use
different tools to support the systematic
material selection process for proper
selection of polymers.
Special
material
properties
Viewpoints
of
Chemistry
Selection
of
Polymers
Tools for
systematic
selection
Temperature
related
selection
criteria
Special materials properties affecting to proper
selection of polymers:
•
•
•
•
1. Glass transition temperature
2. Shape of the stress-strain curve
3. Viscoelastic behavior
4. Creeping strength and heat deflection
temperature
• 5. Fatigue strength and grazing
• 6. Impact strength and brittleness
temperature
• 7. Ageing
-sunlight, chemicals
• 8 .Stress cracking
- residual stresses due to manufacturing
- environmental reasons (e.g. some chemicals)
Fracture mechanisms of polymers
Both ductile and brittle fracture are possible.
Brittle fracture is favored at lower temperatures,
higher strain rates, and at stress concentrators
Brittle to ductile transition often occurs with
increasing temperature
The third “fracture mechanism is called “crazing “…
Crazing occurs when localized regions yield, forming microvoids inside
polymer chain structure.
Fibrillar bridges or fibrils are formed around and between voids.
Crazing absorbs fracture energy and increases fracture toughness
Strain
Strain
Microvoids
Fibrils
in polymer
chains
Microvoids
Fibrils
in polymer
chains
Stress
[MPa]
Viscoelasticity:
Viscoelastic behavior is determined by
rate of strain: elastic for rapidly applied
stress, viscous for slowly applied stress!
Ultimate
tensile strength
Yeld strength
Relative
elongation [%]
Linear or nonlinear plastic
deformation
Reduction of
the crosssection area
Plastic
deformation
POLYMERS
POLYMERIZATION
ADDITION
POLYMERIZATION
CHARACTERISTICS OF
POLYMERS (TYPES)
THERMOPLASTIC
THERMOSEPTIC
CONDENSATION
POLYMERIZATION
ELASTOMERS
TYPES OF
POLYMERCHAINS
CARBONHYDROGEN
POLYMERS (PE)
CARBON-CHAIN
POLYMERS (PTFE)
HETEROCHAIN
POLYMERS (PA)
AMIDI-GROUP
POLYMER
CONSTRUCTIONS
WITH THE
AROMATIC RINGS
IN THE CHAIN
(Kevlar)
Polymerization
• 1. Addition is a chain-reaction, where
monomer units are attached one at a time. E.g.
PVC.
• 2. Condensation is a step reaction, which
produce the mer units. Usually there is small
by-product that is later eliminated. E.g. PA.
• Note: Polymers manufactured with
condensation polymerization absorb easily
water, which can damage their structure
relatively soon!
Effects of the chemical structure on the polymers` properties
Structure and
bonding of mers
Molecular structure
Single bonded
(c-c)
Stereo isometric
forms
Construction of the polymer
chain
LINEAR
BRANCHED
Double
bonded (c=c)
Aromatic
rings
TACTICITY
Isotactic
Syndiotactic
Heterotactic
Atactic
Eutactic
CROSSLINKED
DENSITY
Lowdensity
LD
Highdensity
HD
Mediumdensity
MD
Linear
lowdensity
LDD
Ultra highmolecular
weight
(UHMW)
Number of
monomers
Copolymers
Homopolymers
AFFECTS OF BONDING BETWEEN MERS
Bonding
between
the atoms
Bonding energy
kJ/mol
C-C
350
C-H
410
C-F
440
C-Cl
330
C-O
350
C-S
260
C-N
290
N-N
160
N-H
390
O-H
460
C=C
810
C=O
715
C=N
615
O
OH
H
N
AROMATIC
RING
H
N
O
H
CHEMICAL STRUCTURE OF KEVLAR
n
AFFECTS OF STEREOISOMETRIC FORMS (TACTICITY)
METHYLENE GROUPS
CH3 CH3 CH3 CH3 CH3 CH3
HIGH STRENGTH OF
THE STRUCTURE
METHYLENE GROUPS
CH3
CH3
CH3
HIGH STIFFNESS AND
RIGIDITY OF THE
STRUCTURE
METHYLENE GROUPS
CH3
CH3
CH3
AFFECTS OF DENSITY
Density classification
Property
LDPE
LLDPE
HDPE
Mass (g/cm³)
0,920,93
0,9220,926
0,950,96
Tensile strenght (GPa)
6,2-17,3 12,4-20,0
Elongnation to rupture % 550-600
600-800
20,037,3
20-120
HDPE
LDPE
LLDPE
STRENGHT
INCREASES
Ultra high-performance
polymers
High-performance
polymers
Engineering
polymers
PEEK
PAI
PTFE, PPA
PPS, PFA
General
polymers
PET, POM ,PA
PP ,PE
Semicrystalline polymers
Maximum operating
temperature
Minimum operating
temperature
Required temperature during
the manufacturing process
Melting point
Decomposition temperature of
the polymer chain
Polymer degradation
due to overheating
Glass transition
temperature
ASPECTS
AFFECTING
THE CRITICAL
TEMPERATURE
OF POLYMERS
Viscoelastic behavior related to
temperature and impact forces
Brittleness temperature
Creeping strength at the
specific temperature
Heat deflection
temperature (load is
specified)
Fatigue strength at the
specific temperature
Modulus of elasticity of polymers depending on temperature
E
(Modulus of elasticity)
Viscoelasticity :
- glass at low temperatures
- rubber at intermediate temperatures
- viscous liquid at high temperatures.
Rigid state
Glassy state
Viscoelastic behavior is determined by rate
of strain
(elastic for rapidly applied stress, viscous for
slowly
applied stress)
Leathery state
Rubbery flow
Liquid flow
Tglass transition
Tmelting
T (Temperature)
Examples of glass transition temperatures for some polymers
GREEPING STRENGTH
Many polymers susceptible to time-dependent
deformation under constant load – viscoelastic creep
Creep may be significant even at room temperature
and under moderately low stresses (below yield
strength).
STRESS
[MPa)
TEMPERATURE
23ºC
70ºC
100ºC
1
100
10000
TIME
NEEDED TO
FRACTURE
[h]
Polymer
Heat deflection
temperature °C
(under 1.8 MPa loading)
Polyethylene (UHDPE)
40
Polypropylene (PP)
60
Polyamide (PA6,6 + nylon)
90
Polyamide-imide (PAI)
280
UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION
ULTIMATE TENSILE STRENGTH
PC+ glass-fiber
PI
Rejected
area
PC
MAX.
OPERATING
TEMPERATURE
MIN.
OPERATING
TEMPERATURE
PI
PC+ glass-fiber
PC
IMPACT STRENGTH
UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION
RESISTANCE AGAINST ACID AGENTS
PTFE
PTFE
PI
PI
Required
area
1
WATER
ABSORBTION
PI
RESISTANCE
AGAINST
ORGANIC
SOLVENTS
PI
PTFE
PTFE
RESISTANCE AGAINST
ALCALINE AGENTS
UTILIZATION OFCOBWEB-ANALYSIS FOR POLYMERS’ SELECTION
WEAR
RESISTANCE
1A
Accepted area
3A
3C
Required wear resistance
2B
2A
1B
COMPRESSION
STRENGTH
Required strength
COMPARISON TABLE TO FIT THE MATERIAL PROBERTIES WITH REQUIREMENTS
Polymer
Option 1
Option 2
Option 3
Option 4
Max. / Min.
operating
temperature
[ °C] / [ °C]
Glass
deformation
temperature
[ °C]
Heat
deflection
temperature
[ °C]
Brittleness
temperature
[ °C]
Creeping
strength at
X °C
[MPa]
Required range:
[ °C] / [ °C]
Affecting load:
[ MPa / °C]
Material
property:
[ °C] / [ °C]
Material
property:
[ MPa] / °C]
Required range:
[ °C] / [ °C]
Affecting load:
[ MPa / °C]
Material
property:
[ °C] / [ °C]
Material
property:
[ MPa] / °C]
Required range:
[ °C] / [ °C]
Affecting load:
[ MPa / °C]
Material
property:
[ °C] / [ °C]
Material
property:
[ MPa] / °C]
Required range:
[ °C] / [ °C]
Affecting load:
[ MPa / °C]
Material
property:
[ °C] / [ °C]
Material
property:
[ MPa] / °C]
Processing
temperature
[ °C]
Energy costs:
[€]
Energy costs:
[€]
Energy costs:
[€]
Energy costs:
[€]
Amide
group
PA
Polyamide (Nylon)
- Minlon®
PA
- Zytel® PA
PA 11
Polyamide 11
PA 12
Polyamide 12
PA 46
Polyamide 46
PA 6
Polyamide 6
PA 6 / 12
Polyamide 6 / Polyamide 12
PA 6 / 66
Polyamide 6 / Polyamide 66
PA 6 / 69
Polyamide 6 / Polyamide 69
PA 6 / 6T
Polyamide 6 / Polyamide 6t
PA 610
Polyamide 610
PA 612
Polyamide 612
PA 6-3-T
Polytrimethylene Hexamethylene
Terephthalamide
PA 66
Polyamide 66
- Minlon®
PA
- Zytel® PA
PA 66 / 6
Polyamide 66 / Polyamide 6
- Zytel® PA
PA 66 /
610
Polyamide 66 / Polyamide 610
PA 68
Polyamide 68
- Minlon®
PA
- Zytel® PA
-Zytel® PA
HDPE
High Density Polyethylene
- Rigidex®
Polyethylene
- Eraclene® LDPE
- TIPELIN® HDPE
LDPE
Low Density Polyethylene
- INEOS LDPE
- Riblene® LDPE
- Borstar Polyolefin
- Ipethene® LDPE
- TIPOLEN® LDPE
LLDPE
Linear Low Density Polyethylene
PEHD
High-Density Polyethylene
- Eraclene® HDPE
- ExxonMobil™ HDPE
- Rigidex®
Polyethylene
- TIPELIN® HDPE
UHMWPE
Ultrahigh Molecular Weight
Polyethylene
ULDPE
Ultra Low Density Polyethylene
-Clearflex® LLDPE
Applications from mechanical engineerig:
 Polymer gears:
 High Performance Polymers (PEEK,PES,PI)

Harsh loading conditions
 Polyasetal POM

Good fatigue strength
 Polyamide PA

Good adhesive wear resistance
 Phenol polymers, e.g. PF

Cost-effectiveness
 Sliding bearings:
 Polyamide PA, Polyethylene PE, Teflon (small friction
coefficient with adjacent steel components)
 The properties of polymers can be
improved by reinforcing the matrix
(carbon, aramid or other fibers) or by
surface treatments (e.g. MoS2)
Remember the manufacturability aspects!
Polymer
Shrinkage during
extrusion into mold %

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