This document provides guidelines for processing polyamide extrusion. It discusses how to properly handle moisture in polyamide resins to avoid issues in extrusion like foaming and breakdown. The appropriate screw design parameters and temperature settings for polyamide extrusion are covered. Post-treatment options for polyamide films are discussed, though they provide little additional benefit due to polyamide's inherently good properties. Common applications for polyamide films include food packaging and agricultural films.

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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