Although polyamide is widely used for the production of multilayer films, still some prejudices are persistent. This presentation tries to explain the character of these prejudices to end with the conclusion that polyamide is a versatile polymer with good properties for multilayer films.

1. Prejudices about
Polyamide in multilayer films
Ted Brink 17 June 2015

2. Page  2 Polyamide in multilayer film - PPS 2015
Contents
• polyamide structure
• processing
• polyamide in barrier applications
• conclusions

3. Page  3
Prejudices

4. Page  4 Polyamide in multilayer film - PPS 2015
Prejudices about polyamide
• moisture is difficult to control
• processing temperature is too high
• PA6 not suitable for blown film
• a PE-layer is required for good oxygen barrier

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Structure

6. Page  6
The amide group

7. Page  7
Most common polyamides for extrusion
PA66
And PA6.66 copolyamide
PA6

8. Page  8 Polyamide in multilayer film - PPS 2015
Melting points of PA6.66, PA6 and PA66
190
220
255
PA6.66 PA6 PA66
meltingpoint[°C]

9. Page  9 Polyamide in multilayer film - PPS 2015
Influence of PA6/PA66 ratio on the melting point
150
175
200
225
250
275
0 25 50 75 100
meltingpoint[°C]
PA66 [%]
100 % PA6
100 % PA66PA6.66
(85/15 %)

10. Page  10 Polyamide in multilayer film - PPS 2015
Polyamide comparison
0
1
2
3
melting
point
crystallinity barrier clarity puncture
resistance
price
PA66
PA6
PA6.66
lowest
highest
medium
relative comparison

11. Page  11 Polyamide in multilayer film - PPS 2015
Moisture absorption of PA6.66, PA6 and PA66
0
2
4
6
8
10
12
PA6.66 PA6 PA66
H2Ocontent[%m/m]
50 % RH
in water
at 23 °C

12. Page  12 Polyamide in multilayer film - PPS 2015
Thermal properties of PA6
0
50
100
150
200
250
300
processing range
crystal growth
melting point
glass transition temperature
temperature[°C]

13. Page  13 Polyamide in multilayer film - PPS 2015
Crystallization of polyamide
• at fast cooling rates: no crystallization
• at low cooling rates: large crystals
• presence of nucleant: small crystals
postcrystallization when Tg
below ambient conditions

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Why use polyamide?

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Main reasons to use polyamide
O2
mechanical strength oxygen barrier

16. Page  16 Polyamide in multilayer film - PPS 2015
Oxygen versus moisture barrier
0.01
0.1
1
10
100
1000
10000
0.01 0.1 1 10 100
oxygenpermeability
(ml•cm/m²•day•bar)x100
water permeation at 23 °C and 85 % RH
[g/m²•day]
LDPE
EVOH 32 %
EVOH 38 %
EVOH 44 %
PA6
PVDC
BOPET
BOPP
film thickness 100 µm
measured at 23 °C

17. Page  17 Polyamide in multilayer film - PPS 2015
O2 permeability of PA6 related to humidity and
temperature
0
25
50
75
100
0 25 50 75 100
oxygenpermeability
(ml•cm/m2•day•bar)x100
relative humidity [% RH]
5 °C
23 °C
40 °C

18. Page  18 Polyamide in multilayer film - PPS 2015
Moisture sensitivity of PA6
Permeability:
• dry: 20 cm3/(m2dbar)
• at 85 % RH: 31 cm3/(m2dbar)
values for 50 µm film thickness

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Consequences for packaging
moisture inside
packaging
PE
PA
PE = 100 µm
PA = 20 µm
PA = outside
OTR = 16 ml/(m2day) OTR = 35 ml/(m2day)
moisture outside
packaging

20. Page  20
Processing

21. Page  21

22. Page  22

23. Page  23
Double trouble?

24. Page  24 Polyamide in multilayer film - PPS 2015
Melt stability
• polyamide is a condensation polymer
• when dry → polymerization
• when wet → hydrolysis

25. Page  25 Polyamide in multilayer film - PPS 2015
Melt stability
• reactivity depends on:
- moisture content
- residence time
- temperature
- end groups

26. Page  26 Polyamide in multilayer film - PPS 2015
Extrusion of PA6 – dry (<0.02 % H2O)
molecularweight
residence time
PA6 = high
viscous polymer

27. Page  27 Polyamide in multilayer film - PPS 2015
Extrusion of PA6 - wet (> 0.1 % H2O)
molecularweight
residence time
PA6 = high
viscous polymer

28. Page  28 Polyamide in multilayer film - PPS 2015
Influence processing temperature of dry PA6
molecularweight
residence time
low
normal
high PA6 = high
viscous polymer

29. Page  29 Polyamide in multilayer film - PPS 2015
Moisture during film processing
Too much moisture results in:
• bubbles in the film
• bubble breaks
• hydrolitic degradation
• feeding problems

30. Page  30 Polyamide in multilayer film - PPS 2015
How to deal with moisture
• resin is supplied dry and ready-to-use
• avoid moisture absorption
• maximum allowable moisture content 0.1 %

31. Page  31
Bubble
instability

32. Page  32 Polyamide in multilayer film - PPS 2015
Bubble instability during processing
Possible causes (PA-related):
• viscosity too low
- wrong grade selection
- too high temperature
- too high moisture content

33. Page  33 Polyamide in multilayer film - PPS 2015
Process temperature
Polyamides have a sharp crystalline melting point
Recommendations:
• melt temperature:
- PA6.66 ~ 225 °C
- PA6 ~ 240 °C
- PA66 ~ 270 °C
• apply a flat temperature or reversed temperature profile
• avoid adiabatic extrusion

34. Page  34 Polyamide in multilayer film - PPS 2015
Example temperature control for PA6
230
250
270
290
1 2 3 4 Tpol
temperature[°C]
barrel zone
set actual
230
250
270
290
1 2 3 4 5
temperature[°C]
barrel zone
set actual
flat temperature profile reversed temperature profile

35. Page  35 Polyamide in multilayer film - PPS 2015
Polyamide film properties
• films are hardly oriented
• films are transparent
• influence of moisture:
- when dry:
 high oxygen barrier
 high modulus
- when conditioned
 good oxygen barrier
 flexible
 postcrystallization possible

36. Page  36
Applications

37. Page  37 Polyamide in multilayer film - PPS 2015
Applications with polyamide - food
• meat
• cheese
• fish
• milk
• vegetables & fruits
• coffee

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Applications with polyamide – non food
• agricultural
• medical
• industrial

39. Page  39 Polyamide in multilayer film - PPS 2015
Conclusions
• polyamide is a versatile polymer
• polyamide is easy to process
• polyamide has excellent mechanical properties
• polyamide has good oxygen barrier properties

40. Page  40
Email: ted.brink@extrusionist.com
Tel.: +31 651109899
Internet: www.extrusionist.com
Thank you for
your attention