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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.
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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?
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
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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.
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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
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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?
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�� 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
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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
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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
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
(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.