Overview of materials and technologies used for the production of sausage casings

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