Amorphous vs Crystalline Saunders 10_06

Injection Molding

Amorphous vs Crystalline Resins

Dan SaundersSr. Technical Consultant

October 12,

2006

Copyright Copyright ©© 2006 E. I. du Pont de Nemours and Company. All rights reserve2006 E. I. du Pont de Nemours and Company. All rights reserved. DuPont Engineering Polymers.d. DuPont Engineering Polymers.

The information and suggestions provided in this presentation are based on data believed to be reliable, but the DuPont Company makes no warranties express or implied as to their accuracy and assumes no responsibility or liability arising out of its use by others. Further, the information and suggestions are not intended to substitute for any testing you may need to conduct to determine for yourself the suitability of a particular material for a particular purpose. DuPont makes no guarantee of results and assumes no obligation or liability in connection with the use of the information or suggestions provided in this seminar.

10/12/2006 DUPONT CONFIDENTIAL

2

Crystalline vs Amorphous Polymers

Similarities

• Broad range of commercial

formulation

• Multiple processing techniques

• Environmental sensitivities

What are the broad similarities and differences betweenWhat are the broad similarities and differences between

crystalline and amorphous polymers?crystalline and amorphous polymers?

Differences

• Molecular interactions of the

polymer chains

• Response to temperature

changes

• Solvent resistance

Amorphous - ABS, PC, PS, PMMA, etcCrystalline - PA, PE, PP, PET, PBT, etc

Injection molding, blow molding, extrusions

Upper and lower use temperatures, weathering, mechanical and electrical properties, etc

Amorphous – low order in solid phase

Crystalline – high order in solid phase

Amorphous – Tg onlyCrystalline – Tg and Tm

Crystalline polymers are generally better


3

Crystalline and Amorphous Plastic Properties

Crystalline resin strengths

solvent resistance, fatigue resistance, property enhancement

by fillers and reinforcing agents, creep, cycle time, flow

Amorphous resin strengths

clarity, low warpage, acceptance of plasticizers, density,

thermoforming

Amorphous resins are defined by their chemistry and Tg.Tg is the upper use limit

Crystalline resins are defined by their chemistry, Tg and Tm.Tm is upper use limit


4

Modulus vs. TemperatureCrystalline and Amorphous Polymers

TemperatureTemperature

ModulusModulus

High Crystallinity

Low CrystallinityAmorphousAmorphous

RigidRigid

Tg

C

Tg

A

Tm

C

The specific chemistry of the polymer (monomers) controls the actual values of Tg and Tm.


5

� "Rigid"

� Low fatigue resistance

� High creep resistance

� Brittle

� Good fatigue resistance

� Lower creep resistance

� Ductile

Below Tg

Above Tg� "Elastomeric“ – no

mechanical properties

� "Rigid"

� Moderate fatigue resistance

� High creep resistance

� Brittle

Amorphous Crystalline

0°C-100°C 100°C

PTFE PE

POM PCPS

PA 6/6

DAM

PVC

Nylon 11PA 6/6

Sat

PP

Tg

HTN

ABS

PMMA

Polymer Glass Transition Temperatures

The above are generalizations, exceptions due exist.

POM


6

Unique Features that differentiate polymer types

Feature Crystalline Amorphous

� Solvent resistance + 0

� Optical properties 0 +

� Endurance + 0

� Filler enhancement + 0

� Dimensional stability 0 +

Unique Features that differentiate polymer typesUnique Features that differentiate polymer types

FeatureFeature CrystallineCrystalline AmorphousAmorphous

�� Solvent resistanceSolvent resistance ++ 00

�� Optical propertiesOptical properties 00 ++

�� EnduranceEndurance ++ 00

�� Filler enhancementFiller enhancement ++ 00

�� Dimensional stabilityDimensional stability 00 ++

Property Summary Crystalline and Amorphous Polymers

Common Features – both amorphous and crystalline resins can be found that meet these requirements

� Mechanical – strength– toughness

� Electrical

� Flammability

� Useful temperature range


7

Property Summary Crystalline and Amorphous Polymers

• There are many parts that can be made using either an amorphous or a crystalline resin.

• Polymer modification is a broad and evolving process.

• Polymer suppliers are constantly adding new grades that aim to correct deficiencies and improve strengths.

• Resin selection for a specific application needs to be an iterative process that compares the application requirements with various polymer attributes.

• Processing characteristics are important.

• Environmental factors are important.


8

Due to their different thermal characteristics, amorphous – Tg and

crystalline – Tg and Tm, different molding rules are used for amorphous

and crystalline polymers

Unique Features Crystalline Amorphous

� Shrinkage High Low

� Flow High Low

� Sharp melting range Yes No

Unique FeaturesUnique Features CrystallineCrystalline AmorphousAmorphous

�� ShrinkageShrinkage HighHigh LowLow

�� FlowFlow HighHigh LowLow

�� Sharp melting rangeSharp melting range YesYes NoNo

Processing Crystalline and Amorphous Polymers

Common Features

� Multiple processing techniques

� Controlled heating and cooling

� Moisture sensitive


9

Plastic Processing

The density (volume) of amorphous and crystalline polymers

change at a different rate under the influence of changing

temperatures and pressures.

Mold Fill and Pack Parameters

Resin viscosity at processing temperatures and pressures

Mold Fill

The effect of resin modulus vs. temperature are different

Ejectability

Why are different processing conditions needed to injection Why are different processing conditions needed to injection

mold crystalline and amorphous polymers?mold crystalline and amorphous polymers?


10

�� Specific Volume is 1 / DensitySpecific Volume is 1 / Density

Density vs. Temperature at Atmospheric Pressure

Tg

C

Tg

A

Tm

C

Den

sity

, g

/cc

Amorphous

Crystalline

Temperature


11

Density vs. Specific Volume

Inverse Relationship

Density = 1 / Specific Volume

Specific Volume = 1 / Density

Density important to part weight

Specific volume important to molding conditions

Use PVT diagrams to highlight difference


12

PVT Diagrams

Plot of specific volume vs. temperature at different pressures

Easy to find

• Tg – Glass transition temperature

• Tm – Melting point

Easy to see how

• Volume increases with increasing temperature

• Volume decreases with increasing pressure

• Crystalline polymers undergo a rapid volume change at Tm which is missing in amorphous polymers

• Volume changes between RT and processing temperatures are:10–15% amorphous polymers20–25% crystalline polymers

• This difference in volume change is the primary reason for differences in shrinkage and warpage


13

PVT Data on Nylon 66 and PC

100100 200200 300300 400400 500500 600600 70070000

Temperature, Temperature, °°FF

1.101.10

1.051.05

1.001.00

0.950.95

0.900.90

0.850.85

0.800.80

Sp

ecif

ic V

olu

me,

cc

/ g

Sp

ecif

ic V

olu

me,

cc

/ g

Nylon 66

PC

Tm

Tg


14

PVT Data on Nylon 66 and PC

100100 200200 300300 400400 500500 600600 70070000

Temperature, Temperature, °°FF

1.101.10

1.051.05

1.001.00

0.950.95

0.900.90

0.850.85

0.800.80

Nylon 66

PC

P = 0

P = 15,000 psi

P = 0

P = 15,000 psi

Sp

ecif

ic V

olu

me,

cc

/ g

Sp

ecif

ic V

olu

me,

cc

/ g


15

Amorphous PVT Diagram

SpecificSpecific

VolumeVolume


P = 0P = 0

P = 14,500 psiP = 14,500 psi

CompressionCompression

Thermal ExpansionThermal Expansion

InjectionInjection

SofteningSoftening


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Amorphous PVT DiagramCooling

1.1. Decrease pressureDecrease pressure

�� expansionexpansion

2.2. Decrease temperatureDecrease temperature

due to coolingdue to cooling

�� shrinkageshrinkage

3.3. Best resultBest result

constant volumeconstant volume

SpecificSpecific

VolumeVolume


33

1122

00


17

Amorphous PVT DiagramEffects on Molding Rules

�� No movement through gateNo movement through gate

�� Injection pressure led by Injection pressure led by

cavity pressure (via cavity pressure (via

transducer)transducer)

Means:Means:

PressurePressure

TransducerTransducer

TimeTime

Inje

ctio

n P

ress

ure

Inje

ctio

n P

ress

ure

Constant volumeConstant volume

After filling time:After filling time:


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Amorphous PolymerPost-Molding Deformation

Internal stressesInternal stresses

From over packingFrom over packing

DeformationDeformation or stress crackingor stress cracking

Molecular orientation during molding may also cause these phenomena.


19

Molding Amorphous Polymers

Overpacking is a major concern

• Parts stick in mold

• Parts crack during ejection

• Residual internal stress

Optimum molding conditions

• Inject using high pressure

• Pack pressure should decreasewith time – constant volume

• High mold temperatures reduceinternal stress


20

Crystalline PVT DiagramMelting – Injection – Crystallization

Sp

ecif

ic V

olu

me

Sp

ecif

ic V

olu

me


00

11,60011,600

psipsi

�� During meltingDuring melting

processprocess

(solid (solid �� liquid)liquid)

volume x 16%volume x 16%

�� Shrinkage by ~14%;Shrinkage by ~14%;

Voids created haveVoids created have

to be filled with liquidto be filled with liquid

polymerpolymer

�� Crystallization underCrystallization under

constant pressureconstant pressure

CrystallizationCrystallization

MeltingMelting


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Crystalline PolymerPost-Molding Deformation

Cold moldCold mold Poor crystal structurePoor crystal structure

Post shrinkage Post shrinkage --

recrystallization withrecrystallization with

time and temperaturetime and temperature

DeformationDeformation


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Controlling Crystallization During Molding

Mold Temperature

• The higher the mold temperature,

the higher the crystallinity

Pressure

• Low pressure increases rate of crystallinity

Stress During Crystallization

• Can produce orientation


23

Typical Melt Viscosity Amorphous Crystalline

Many resins are available in multiple flow ranges

A typical crystalline polymer will have a

lower melt viscosity

at its standard

processing

conditions vs typical amorphous

polymers.

This translate into

lower pressure to fill

the part.

Note - axis have different scales


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VentingVent depths are a function of resin viscosity and the time it takes the resin to form a rigid skin.

High viscosity Deep Vents

Low viscosity Shallow Vents

Typically vent for crystalline resins are more shallow than for amorphous resins.

Amorphous

ABS 0.0010 – 0.0015 inchPMMA 0.0015 – 0.0020 inch

PC 0.0015 – 0.0025 inch

Crystalline

PA 6,6 0.0003 – 0.0005 inch

PBT 0.0005 – 0.0007 inchPOM 0.0005 – 0.0010 inchPP 0.0005 – 0.0012 inch


25

Modulus vs. TemperatureCrystalline and Amorphous Polymers


ModulusModulus

High Crystallinity

Low Crystallinity

AmorphousRigidRigid

Tg

C

Tg

A

Tm

C

Delta between Tm and

processing temperature (crystalline)

less than between Tg and

processing temperature (amorphous)

Amorphous resins need to cool more prior to ejection from the mold

Processing window


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Estimated Maximum Ejection TemperatureCrystalline and Amorphous Polymers

Amorphous resins need to cool more prior to ejection

from the mold. An approximate maximum ejection

temperature is 0.45MPa deflection temperature – 15ºC.

ABS PC PS

6,6 nylonPBTPOMPP

CrystallineAmorphous

80C120C65C

160C165C150C

80C


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Injection Molding CyclesAmorphous / Crystalline Plastics

Calculated Cooling Time vs Wall Thickness - Median

Melt and Mold Temperatures

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

0 1 2 3 4

Wall Thickness (mm)

Co

olin

g T

ime

(s

ec

) 6,6 nylon

abs

pc

pp

pbt

ps

pom

pe


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COOLING COOLING

TIMETIME

Fill timeFill time

DosingDosing

ScrewScrew

stationstation--

aryary

OpenOpen

CloseClose

EjectEject

HoldHold

pressurepressure

timetime

MATERIALMATERIAL

UNDERUNDER

PRESSUREPRESSUREMATERIALMATERIAL

UNDERUNDER

PRESSUREPRESSURE

COOLING COOLING

TIMETIME

Fill timeFill time

HoldHold

pressurepressure

timetime

DosingDosing

OpenOpen

CloseCloseEjectEject

SafetySafety

timetime

Injection Molding CycleAmorphous Crystalline

• Actual times are dependent on specific resin, mold design and processing conditions.• Crystalline resins can usually be ejected right after gate freeze occurs. • Cooling time is only needed to recover screw. • Faster cycle times are frequently possible.


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Other Processing Considerations

Shrinkage

• Typically molds cut for amorphous resins need to be re-cut for crystalline resins and vice versa.

Gating

• Gates for crystalline resins are larger than for amorphous resins

Surface appearance

• Surface appearance differs due to crystalline resins being opaque and amorphous resins being clear.

Tool wear

• Little definitive data comparing wear. Generally believed that tool wear is similar for both types of resins. Typically dominated by additive and fillers

General trends are seen for both amorphous and crystalline resins, however, specific differences are grade dependent.


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Typical Range (flow and cross flow) of Shrinkage Crystalline and Amorphous Polymers

•Higher shrinkage of crystalline resins makes them more prone to

warping. •The difference in shrinkage between flow and cross flow directions

becomes more important as absolute shrinkage increases.

•The presence of glass fiber reinforcement can increase the difference

between flow and cross flow shrinkage.

ABS 0.5-0.7%PC 0.5-0.7%PS 0.2-0.8%

6,6 nylon 1.0-2.5%PBT 1.0-2.0%POM 2.0-3.5%PP 1.0-3.0%

CrystallineAmorphous


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0.05 Sec0.05 Sec

3.00 Sec3.00 Sec1.50 Sec1.50 Sec

0.09 Sec0.09 Sec

Gating, Filling of the Mold, Hold Pressure

t = 01.5s

t = 0.05s t = 0.09s

t = 03.0s

Crystalline Style

Crystalline Style

Crystalline Style

Crystalline Style

Amorphous Style Amorphous Style

Amorphous StyleAmorphous Style

Molding crystalline resins using amorphous style gates can cause problems

with shrinkage, warp, mechanical properties and appearance


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Hold Pressure – Packing

8.00 Sec8.00 Sec

24.0 Sec24.0 Sec18.0 Sec18.0 Sec

9.00 Sec9.00 Sec

t = 08.0s t = 09.0s

t = 18.0s t = 24.0s

Crystalline Style Amorphous Style Amorphous Style

Amorphous StyleAmorphous StyleCrystalline Style Crystalline Style

Crystalline Style

Molding crystalline resins using amorphous style gates can cause problems

with shrinkage, warp, mechanical properties and appearance


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Typical Tool Steels

Steel TypeSteel Type DD--22 AA--22 AA--66 LL--66 HH--1313 PP--2020 SS--77 420S.S.420S.S.

Analysis Analysis -- %%

CC 1.51.5 1.001.00 0.700.70 0.700.70 0.350.35 0.350.35 0.500.50 0.150.15

MnMn 0.500.50 0.80.8 2.02.0 0.350.35 0.350.35 –– –– 1.01.0

NiNi –– –– –– 1.751.75 –– –– –– ––

CrCr 12.012.0 5.05.0 1.01.0 1.01.0 5.05.0 1.251.25 3.253.25 13.513.5

MoMo 1.01.0 1.01.0 1.01.0 –– 1.51.5 0.400.40 1.51.5 0.50.5

SiSi 0.30.3 0.30.3 0.30.3 0.250.25 1.01.0 –– –– 1.01.0

VV 0.90.9 0.20.2 –– –– 1.01.0 –– –– ––

ToughnessToughness LowLow MedMed MedMed HighHigh HighHigh HighHigh XX--HighHigh MedMed

Wear ResistanceWear Resistance HighHigh MedMed MedMed FairFair FairFair PoorPoor MedMed FairFair

Usual WorkingUsual Working 5858 5959 5858 5858 5050 3030 5858 4848

RRCC 6161 6262 6060 6262 5454 3636 6060 5454

ResinsResins Filled resinsFilled resins UnUn--filledfilled CorrosionCorrosion

(recommendations for cavities)(recommendations for cavities) long working lifelong working life ResistanceResistance

A.I.S.I. TypeA.I.S.I. Type


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Crystalline vs Amorphous Polymers

Some broad similarities and differences between amorphous and crystalline resins have been reviewed.

The differences seen in properties and processing are based on fundamental differences in the structure of the polymers and intermolecular forces that hold the molecules together.

Some differences can be overcome by part design or optimization of processing conditions while other differences can not.


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Amorphous vs Crystalline Saunders 10_06