prejudices about polyamide for multilayer films

Prejudices about

Polyamide in multilayer filmsTed Brink 17 June 2015

Polyamide in multilayer film - PPS 2015

Contents

• polyamide structure

• processing

• polyamide in barrier applications

• conclusions

Prejudices


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

Structure

The amide group

Most common polyamides for extrusion

PA66

And PA6.66 copolyamide

PA6


Melting points of PA6.66, PA6 and PA66

PA6.66 PA6 PA66

190

220

255

melt

ing

po

int

[°C

]


Influence of PA6/PA66 ratio on the melting point

0 25 50 75 100150

175

200

225

250

275

PA66 [%]

melt

ing

po

int

[°C

]

100 % PA6

100 % PA66PA6.66(85/15 %)


Polyamide comparison

melting point

crys-tallinity

barrier clarity puncture resis-tance

price0

1

2

3

PA66PA6PA6.66lowest

highest

medium

relative comparison


Moisture absorption of PA6.66, PA6 and PA66

PA6.66 PA6 PA660

2

4

6

8

10

12

50 % RHin water

H2

O c

on

ten

t [%

m

/m] at 23 °C


Thermal properties of PA6

0

50

100

150

200

250

300

processing range

crystal growth

melting point

glass transition temperaturetem

pera

ture

[°C

]


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

Why use polyamide?

Main reasons to use polyamide

O2

mechanical strength oxygen barrier


Oxygen versus moisture barrier

0.01 0.1 1 10 1000.01

0.1

1

10

100

1000

10000

water permeation at 23 °C and 85 % RH [g/m²•day]

oxyg

en

perm

eab

ilit

y

(ml•

cm

/m

²•d

ay•b

ar)

x1

00 LDPE

EVOH 32 %EVOH 38 %

EVOH 44 %

PA6

PVDC

BOPET

BOPP

film thickness 100 µmmeasured at 23 °C


O2 permeability of PA6 related to humidity and temperature

0 25 50 75 1000

25

50

75

100

5 °C

23 °C

40 °C

relative humidity [% RH]

oxyg

en

perm

eab

il-

ity (

ml•

cm

/m

2•d

ay•b

ar)

x1

00


Moisture sensitivity of PA6

Permeability:

• dry: 20 cm3/(m2dbar)

• at 85 % RH: 31 cm3/(m2dbar)

values for 50 µm film thickness

Consequences for packaging

moisture insidepackaging

PEPA

PE = 100 µmPA = 20 µm

PA = outside

OTR = 16 ml/(m2day) OTR = 35 ml/(m2day)

moisture outsidepackaging

Processing

Moisture

Temperature

Double trouble?


Melt stability

• polyamide is a condensation polymer

• when dry → polymerization• when wet → hydrolysis


Melt stability

• reactivity depends on:- moisture content

- residence time

- temperature

- end groups


Extrusion of PA6 – dry (<0.02 % H2O)

residence time

mo

lecu

lar

weig

ht

PA6 = high viscous polymer


Extrusion of PA6 - wet (> 0.1 % H2O)

residence timemo

lecu

lar

weig

ht



Influence processing temperature of dry PA6

lownormal

residence timemo

lecu

lar

weig

ht



Moisture during film processing

Too much moisture results in:

• bubbles in the film

• bubble breaks

• hydrolitic degradation

• feeding problems


How to deal with moisture

• resin is supplied dry and ready-to-use

• avoid moisture absorption

• maximum allowable moisture content 0.1

%

Bubble instability


Bubble instability during processing

Possible causes (PA-related):

• viscosity too low- wrong grade selection- too high temperature- too high moisture content


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


Example temperature control for PA6

1 2 3 4 Tpol230

250

270

290set actual

barrel zone

tem

pera

ture

[°C

]

1 2 3 4230

250

270

290set actual

barrel zone

tem

pera

ture

[°C

]

flat temperature profile reversed temperature profile


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

Applications


Applications with polyamide - food

• meat• cheese• fish• milk• vegetables &

fruits• coffee


Applications with polyamide – non food

• agricultural• medical• industrial


Conclusions

• polyamide is a versatile polymer

• polyamide is easy to process

• polyamide has excellent mechanical

properties

• polyamide has good oxygen barrier

properties

Email: [email protected]

Tel.: +31 651109899

Internet: www.extrusionist.com

Thank you foryour attention

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