BK50A2700 Selection Criteria of Structural Materials

BK50A2700 Selection Criteria of Structural Materials

Lesson 52014

Selection of polymers

Lesson 52014

The goal of this lesson

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.

Outline

Selection of

Polymers

Special material

properties

Temperature related selection criteria

Tools for systematic selection

Viewpoints of

Chemistry

Special material properties

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

Fibrilsin polymer chains

Microvoids

Fibrilsin polymer chains

Microvoids

Strain

Strain

Relative elongation [%]

Stress [MPa]

Linear or non-linear plastic deformation

Reduction of the cross-section area

Plastic deformation

Ultimate tensile strength

Yeld strength

Viscoelasticity:Viscoelastic behavior is determined by rate of strain: elastic for rapidly applied stress, viscous for slowly applied stress!

Viewpoints of Chemistry

POLYMERS

POLYMERIZATION CHARACTERISTICS OF POLYMERS (TYPES)

THERMOPLASTIC

CONDENSATION POLYMERIZATION

THERMOSEPTIC

TYPES OF POLYMERCHAINS

ADDITION POLYMERIZATION

ELASTOMERS

CARBON-HYDROGEN POLYMERS (PE)

CARBON-CHAIN POLYMERS (PTFE)

HETEROCHAIN POLYMERS (PA)

POLYMER CONSTRUCTIONS WITH THE AROMATIC RINGS IN THE CHAIN (Kevlar)

AMIDI-GROUP

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

Stereo isometric forms

Double bonded (c=c)

Number of monomers

Construction of the polymer chain

Single bonded (c-c)

Co-polymers

LINEAR

CROSS-LINKED

Aromatic ringsIsotactic

Syndiotactic

Eutactic

TACTICITY

Heterotactic

Atactic

BRANCHED

DENSITY

Low-density LD

High-density HD

Medium-density MD

Linear low-density LDD

Ultra high- molecular weight (UHMW)

Homo-polymers

Bonding between

the atoms

Bonding energykJ/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

AFFECTS OF BONDING BETWEEN MERS

N

NO

O

H

Hn

H

OH

CHEMICAL STRUCTURE OF KEVLAR

AROMATIC RING

CH3 CH3 CH3 CH3 CH3 CH3 METHYLENE GROUPS

HIGH STRENGTH OF THE STRUCTURE

CH3 CH3 CH3 HIGH STIFFNESS AND RIGIDITY OF THE STRUCTURE

CH3 CH3 CH3

METHYLENE GROUPS

METHYLENE GROUPS

AFFECTS OF STEREOISOMETRIC FORMS (TACTICITY)

Density classification

Property LDPE LLDPE HDPE

Mass (g/cm³) 0,92-0,93

0,922-0,926

0,95-0,96

Tensile strenght (GPa) 6,2-17,3 12,4-20,0 20,0-37,3

Elongnation to rupture % 550-600 600-800 20-120

AFFECTS OF DENSITY

HDPE

LDPE

LLDPE

STRENGHT INCREASES

Amorfic polymers

Semicrystalline polymers

Elastomers

General polymers

Engineering polymers

High-performancepolymers

Ultra high-performancepolymers

PVC, PS

PEI, PSU

PC, ABS, PMMA

PIPEI

PP ,PE

PET, POM ,PA

PTFE, PPAPPS, PFA

PEEKPAI

NBR

EPR, EVA

FKM

PFPE

75 ºC

140 ºC

240 ºC

340 ºC

Temperature related selection criteria

ASPECTS AFFECTING

THE CRITICAL TEMPERATURE OF POLYMERS

Creeping strength at the specific temperature

Decomposition temperature of the polymer chain

Melting point

Required temperature during the manufacturing process

Fatigue strength at the specific temperature

Maximum operating temperature

Heat deflection temperature (load is

specified)

Glass transition temperature

Viscoelastic behavior related to temperature and impact forces

Brittleness temperature

Polymer degradation due to overheating

Minimum operating temperature

E(Modulus of elasticity)

Tglass transition Tmelting T (Temperature)

Glassy state

Leathery state

Rubbery flow

Liquid flow

Modulus of elasticity of polymers depending on temperature

Rigid state

Viscoelasticity : - glass at low temperatures- rubber at intermediate

temperatures- viscous liquid at high

temperatures.Viscoelastic behavior is determined by rate of strain(elastic for rapidly applied stress, viscous for slowlyapplied stress)

Examples of glass transition temperatures for some polymers

STRESS[MPa)

TIME NEEDED TO FRACTURE

[h]

TEMPERATURE

23ºC

70ºC

100ºC

1 100 10000

GREEPING STRENGTH

Many polymers susceptible to time-dependentdeformation under constant load – viscoelastic creepCreep may be significant even at room temperatureand under moderately low stresses (below yieldstrength).

PolymerHeat deflection temperature °C

(under 1.8 MPa loading)

Polyethylene (UHDPE) 40

Polypropylene (PP) 60

Polyamide (PA6,6 + nylon) 90

Polyamide-imide (PAI) 280

Tools for systematic selection

IMPACT STRENGTH

ULTIMATE TENSILE STRENGTH

MAX. OPERATING

TEMPERATURE

PI

PI

MIN. OPERATING

TEMPERATURE

PC

PC

PC+ glass-fiber

UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION

PC+ glass-fiber

Rejectedarea

RESISTANCE AGAINST ALCALINE AGENTS

RESISTANCE AGAINST ACID AGENTS

RESISTANCE AGAINST ORGANIC

SOLVENTS

1

WATER ABSORBTION

PTFE

PTFE

PTFE

PTFE

PIPI

PI

PI

UTILIZATION OF FOUR-FIELD ANALYSIS FOR POLYMERS’ SELECTION

Requiredarea

UTILIZATION OFCOBWEB-ANALYSIS FOR POLYMERS’ SELECTION

WEAR RESISTANCE

COMPRESSIONSTRENGTH

1B

1A

3C 3A

2A

2B

Required wear resistance

Required strength

Accepted area

Polymer

Max. / Min. operating

temperature

[ °C] / [ °C]

Glass deformatio

n temperatur

e[ °C]

Heat deflection

temperature

[ °C]

Brittleness temperatur

e

[ °C]

Creeping strength at

X °C[MPa]

Processing temperatur

e

[ °C]

Option 1Required range: [ °C] / [ °C]

Material property: [ °C] / [ °C]

Affecting load: [ MPa / °C]

Material property: [ MPa] / °C]

Energy costs:[€]

Option 2Required range: [ °C] / [ °C]

Material property: [ °C] / [ °C]

Affecting load: [ MPa / °C]

Material property: [ MPa] / °C]

Energy costs:[€]

Option 3Required range: [ °C] / [ °C]

Material property: [ °C] / [ °C]

Affecting load: [ MPa / °C]

Material property: [ MPa] / °C]

Energy costs:[€]

Option 4Required range: [ °C] / [ °C]

Material property: [ °C] / [ °C]

Affecting load: [ MPa / °C]

Material property: [ MPa] / °C]

Energy costs:[€]

COMPARISON TABLE TO FIT THE MATERIAL PROBERTIES WITH REQUIREMENTS

PA Polyamide (Nylon) - Minlon® PA

- Zytel® PA

PA 11 Polyamide 11

PA 12 Polyamide 12

PA 46 Polyamide 46

PA 6 Polyamide 6 - Minlon® PA

- Zytel® PA

PA 6 / 12 Polyamide 6 / Polyamide 12

PA 6 / 66 Polyamide 6 / Polyamide 66 -Zytel® PA

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

Amidegroup

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!

PolymerShrinkage during extrusion into mold %