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About crystallization of polyamide
Ted Brink
Page 2
Contents
• H-bonds in polyamide
• Thermal properties
• Crystallization
• Influence of moisture
• Crystal structures
• Conclusions
Page 3
Hydrogen bonds and interaction with water
water
Page 4
Consequences of H-bonds in polyamide
H-bonds influence:
• stiffness
• flexibility
• crystallinity
• glass transition point
• gas permeability
Page 5
Thermal properties of PA6
10
50
100
150
200
250
3001
processing range
crystal growth
melting point
glass transition temperaturetem
pera
ture
[°C
]
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Crystallization of polyamide
• fast cooling prevents crystallization
• low cooling rate results in large crystals
• presence of nucleant results in small crystalls
• moisture uptake results in decrease of Tg
- when Tg below ambient conditions → crystallization
Page 7
Influence crystallinity on the density of PA6
crystalline
amorphous
1 1.1 1.2 1.3
1.23
1.084
density [kg/m3]
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Influence moisture on Tg of PA6
0 2 4 6 8 10-20
0
20
40
60
moisture content [%]
Tg [
°C]
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Influence temperature on modulus of PA6
0 50 100 150 200 2500
1000
2000
3000
temperature [°C]
E-m
odulu
s [M
Pa]
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Moisture induced crystallization
Tg of PA6• dry ~ 55 °C• wet ~ -10 °C
Effects of moisture on PA6 film
• lower stiffness
• increased flexibility
• improved stretchability
• easier thermoforming
• lower O2 barrier at high RH
When Tg drops below ambient conditions, crystallization will occur
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Polyamide crystal structures
Structure α phase β phase γ phase
Crystal structure
Monoclinic Pseudo hexagonal
Monoclinic
Melting point
220 °C 214 °C
How created Slow cooling Quenching Specific nucleants
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Tensile behaviour crystal PA6 structures
0 1 2 3 4 50
20
40
60
80
AlphaBetaGamma
Extension ratio
Nom
inal
str
ess
[Mp
a]
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13
Transformations of the pure crystal phases
α β γ
αT αT γT
αλ αλαλ
Influence of temperature & stretching on the 3 crystal structures of PA6
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Conclusions
• PA6 crystallizes:
- from the melt at moderate cooling rate
- when Tg > ambient temperature
• α-phase is most stable
• β-phase is a mesomorphous state
• γ-phase is optimal for stretching
Page 15
Contact
Ted BrinkEmail: [email protected]
Internet: www.extrusionist.com
Tel.: +31 651109899
