Crystal structures of polyamide

1. About crystallization of polyamide
Ted Brink

2. Page  2
Contents
• H-bonds in polyamide
• Thermal properties
• Crystallization
• Influence of moisture
• Crystal structures
• Conclusions

3. Page  3
Hydrogen bonds and interaction with water
water

4. Page  4
Consequences of H-bonds in polyamide
H-bonds influence:
• stiffness
• flexibility
• crystallinity
• glass transition point
• gas permeability

5. Page  5
Thermal properties of PA6
1
0
50
100
150
200
250
300
1 2 3
processing range
crystal growth
melting point
glass transition temperature
temperature[°C]

6. Page  6
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

7. Page  7
Influence crystallinity on the density of PA6
1.23
1.084
1 1.1 1.2 1.3
crystalline
amorphous
density [kg/m3]

8. Page  8
Influence moisture on Tg of PA6
-20
0
20
40
60
0 2 4 6 8 10
Tg[°C]
moisture content [%]

9. Page  9
Influence temperature on modulus of PA6
0
1000
2000
3000
0 50 100 150 200 250
E-modulus[MPa]
temperature [°C]

10. Page  10
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

11. Page  11
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

12. Page  12
Tensile behaviour crystal PA6 structures
0
20
40
60
80
0 1 2 3 4 5
Nominalstress[Mpa]
Extension ratio
Alpha
Beta
Gamma

13. Page  13 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

14. Page  14
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

15. Page  15
Contact
Ted Brink
Email: ted.brink@extrusionist.com
Internet: www.extrusionist.com
Tel.: +31 651109899