Basic guidelines to facilitate extrusion of polyamide

1. Polyamide extrusion
Processing guidelines Ted Brink

2. Page  2

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Moisture

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How to deal with moisture
• reliable resin manufacturers supply nylon
dry and ready-to-use
• avoid moisture absorption
• use packaging size according to consumption
• shield hopper from atmosphere
• maximum allowable moisture content 0.1 %

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Too high moisture
• too high moisture content results in:
• bubbles/foaming of the melt
• holes in the film
• bubble collapses
• hydrolytic breakdown

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Screws for polyamide extrusion
General Purpose screws can be used, provided:
• the barrel is not grooved (unless .....)
• the heating capacity is sufficient
• the compression ratio is < 4.0
• the L/D ratio is > 24
• barrier screws suitable

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Mixing or dispersing elements
• mixing sections on standard 3-zone screws may be
needed
• dispersing antiblock agent
• pigments
• not needed for standard additives
• mixing elements:
• pineapple (distributive mixing)
• pin (distributive mixing)
• Maddock (dispersive mixing)

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Screen pack
Function:
• build-up pressure
• filtration

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Extruder output PA6 extrusion
0
200
400
600
800
30 60 90 120 150 180
output[kg/hr]
screw diameter [mm]
• single screw
• 3-zone
• Tcil 250 C

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Thermal properties of PA6
0
50
100
150
200
250
300
processing range
crystal growth
melting point
glass transition temperature
temperature[°C]

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Communicate with the machine
• listen to what the machine is telling you
• watch energy demand of band heaters
– shows where energy is needed
– shows where no energy is needed
• avoid adiabatic extrusion
– the machine is in control, not you!
– Tpol will show large variations

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Temperature settings
• too low settings may result in too high polymer
temperature
• nylons with higher crystallinity require different
approach

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Melt stability
• polyamide is a condensation polymer
• consequence for extrusion:
• when dry: polymerization occurs
• when wet: depolymerization occurs
• reactivity depends on:
• moisture content
• residence time
• temperature
• end groups

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Miscelleneous
Blown film:
• BUR 1:1 – 1:3
• lay flat when film is stil warm to prevent wrinkles
General:
• die gap 1 – 1.2 mm
Cast film:
Chill roll temperature:
• 20 – 40 C for optimum thermoforming behavior
• 80 – 130 C for optimum dimensional stability
• chill roll as close to the die to avoid neck-in

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Film post treatment
• Corona treatment
• Plasma treatment
• Flame surface treatment
• Purpose of these treatments:
• increase surface energy so that inks “wet-out”
• improve adhesion during lamination
However, polyamide has intrinsically
good printing and lamination performance
and thus no real need for Corona treatment
untreated film
treated film

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Polyamide film properties
• films are (near to) isotropic
• films are transparent
• high puncture resistance

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Influence of moisture on film properties
• when dry:
• very high oxygen barrier
• high modulus
• when conditioned
• high oxygen barrier
• increased flexibility
• postcrystallization possible
• dimensional fluctuations

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Coextrusion
• polyamide mostly used in multilayer structures
• polyamide function:
• mechanical protection
• barrier properties
• tie resin required for adhesion to nonpolar polymers
like PE and PP
• coectruded polymers should rheologically match

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Applications
Food packaging
• cheese
• meat
• fish
Non food
• agricultural films
• medical films
• release films for smc

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