This document discusses synthetic sausage casings. It describes the different types of materials that can be used including polymers like polyethylene, polyamides, and ethylene vinyl alcohol. Synthetic casings are often produced through blown film extrusion as mono- or multi-layer films. Multilayer casings typically have 5 layers and may include combinations of polymers and adhesive tie layers. The document outlines the requirements for synthetic casings including barrier properties, mechanics, and adhesion to meat. It provides details on production processes and common materials used to make casings that meet industry standards.

1. Synthetic sausage casings
Ted Brink

2. Page  2
Contents
• types of casings
• synthetic casings
- materials
- production process
- mono and multilayer
- requirements

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Types of sausage casings
• animal casings
- for traditional casings, edible
• collagen casings
- made from gelatinous substances of bones, cartilage and connective
tissue of mammals, edible
• cellulose casings
- made from solubilized cotton
• fibrous casings
- from paper and viscose
• polymer casings
- polyolefins and polyamides

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Types of sausage casings
natural animal
polymer cellulose
collagen

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Why plastic casings?
• price
• barrier properties
• mechanical strength

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Production of plastic casings
• always blown film
• can be stretched biaxial (double/triple bubble process)
• monolayer
• multilayer

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Requirements of synthetic casings
• barrier properties
• oxygen
• moisture
• flavour
• microbiological
• mechanical properties
• puncture resistance
• tear strength
• defined shrinkability
• retortability
• meat (protein) adhesion
• printability
• food contact approved

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Monolayer synthetic casings
Materials used:
• polythylenes
• polyamides
- PA6
- PA66
- PA6.66
- PA11
- PA12

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Polyethylene in sausage casings
• no adhesion with meat
• applied mainly for frozen minced meat
• high layer thickness: between 100 and 250 μm

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Multilayer casings - materials
• polyethylenes
• polypropylenes
• polyamides
- PA6
- PA6.66
- amorphous
• EVOH
• PVDC
• ionomers

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Multilayer casings
• process: double bubble stretched casings
• typical 5 layers
• blends are common
Example
12 μm PA6/PA6.66
3 μm tie resin
10 μm LDPE
3 μm tie resin
25 μm PA6/AmPA

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Coextrusion
• requires rheology match of individual polymers
- viscosity
- elasticity
• mismatch of rheology may result in:
- optical defects
• rheology match in practice often trial-and-error
- MFI used for polyolefins
- RSV or VN used for engineering plastics

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The double bubble process
Heat setting
determines
shrinkage %
Main machine producers:
• Kuhne
• Plamex

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Casings production plant

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Effects of orientation of PA-based casings
property not oriented oriented
tear strength ++ +
tensile strength + +++
modulus + +++
oxygen barrier + ++
cooking of sausages in molds in hanging position

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Post treatment
• printing
• shirring

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Polymer properties
property unit PE PP EVOH PET PA6
melting
point
°C 100-140 150-165 176 260 220
tensile
strength
MPa 25-35 30-40 25
100
180 *)
85
250 *)
E-modulus GPa 100-300 1500-3000 1000-2000
2000
4500 *)
1500
3000 *)
strain at
break
% 500-800 250-600 150 250-600 300-500
H2O g/m2 d 0.5-5 1-5 50 15 40
O2 ml/m2 d bar 4000 2500 3-10 160 80
*) oriented

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Polyamide in sausage casings
Strong points of polyamide:
• strength
• stiffness
• oxygen barrier
• thermal resistance
• protein adhesion
• stretchability
• easy to process

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Moisture absorption of polyamides
0
2
4
6
8
10
12
moistureabsorption[%]
23 °C/50 % RH
23 °C in water

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Polymer blends are common
• PA6 with ionomer
- improvement of water barrier
- fine-tuning of meat adhesion
• PA6 with amorphous polyamide
- improvement of transparency
- improvement of oxygen barrier
- improvement of UV barrier
• PA6 with Arnitel
- improvement of smoke permeation

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Additives
• pigments and colourants
• nucleating agents (unoriented casings)
• heat stabilizers
• UV-absorbers
• antimicrobial agents
Multitude of colours used for casings

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Structures of commercially available casings
0 10 20 30 40 50 60 70
G
F
E
D
C
B
A
outer layer inner layer
PA
PA
PA
PA
PA
PA
PA
tie tiePE PA
PE + tie PA
IO
IO
+ PA
EVOH tie PP PA
PP + tie PA
thickness in micron
PA polyamide
tie adhesive
PP polypropylene
IO ionomer
EVOH ethylene vinyl
alcohol
PE polyethylene

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Handling of casings
shirred casings

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Bon appetit

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