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Polymers for food packaging

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Polymers for food packaging An overview Polymers What are polymers? Types of polymer Polymerisation Polymer properties What are polymers Polymers are macromolecules ... – PowerPoint PPT presentation

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Title: Polymers for food packaging


1
Polymers for food packaging
An overview
2
Polymers
  • What are polymers?
  • Types of polymer
  • Polymerisation
  • Polymer properties

3
What are polymers
  • Polymers are macromolecules
  • They are based on a repeating unit derived from a
    small molecule
  • They may be natural - e.g. polysaccharides - or
    synthetic
  • They possess a variety of properties useful to
    food packaging

4
Examples of polymers
  • Polyethylene
  • LDPE
  • HDPE
  • Polypropylene
  • Polystyrene
  • Polyvinyl chloride (PVC)
  • Polyethylene terephthallate (PET)
  • Polycarbonate
  • Polyamide (Nylon)
  • Cellulose
  • Cellulose acetate
  • Cellophane

5
Classification of polymers
  • By properties
  • Thermoplastic melts on heating
  • Thermosetting decomposes on heating
  • By Polymerisation process
  • Addition
  • Condensation

6
Addition polymerisation
  • E.g. polyethylene

7
Condensation polymerisation
  • E.g. polyester

Teraphthallic acid ethylene glycol --gt PET
8
Mechanical Properties
  • Stress and Strain
  • Stress Force/Area
  • Strain change in length/original length

9
Mechanical Properties (2)
  • Yield strength
  • Ultimate tensile strength
  • Elongation at break
  • Burst Strength
  • Tear strength
  • Stiffness
  • Crease or flex resistance
  • Coefficient of friction

10
Other properties
  • Permeability
  • Gases can permeate through polymers

Gas diffused/Area Permeability/thickness x
pressure difference
11
Polymer degradation
  • Polymers can be degraded by
  • Oxygen
  • Heat
  • Light
  • uv
  • These tend to embrittle and weaken the polymer.

12
Polymer processing
  • Extrusion
  • Blow Moulding
  • Injection Moulding
  • Thermoforming
  • Polymer foams

13
Extrusion
  • Molten Polymer is forced through a die by means
    of a screw ram.

14
Injection Moulding
  • Molten polymer is forced into a mould

15
Vacuum forming
  • Polymer sheet is heated using ir heaters
  • A vacuum is applied below the sheet, drawing the
    sheet into the mould
  • Related processes are pressure forming and mould
    forming

16
Other processes
  • Film extrusion
  • polymer is extruded into a thin, cylindrical film
    which is wound up as film
  • Blow moulding
  • extruded polymer is fed into a mould where it is
    blown into shape. This is used to make bottles.

17
Polymer foams
  • Polymer is injection moulded with the addition of
    foaming agents so that a foam is formed in the
    mould.
  • Typically used for soft drink cups, using
    polystyrene where the thermal insulation property
    is useful.

18
Other polymer products
  • These include various film products
  • Laminated films where a number of polymers or
    polymer and paper products are layered together
  • Shrink wrap
  • Cling film

19
In conclusion
  • An understanding of the relation between the
    chemical structure and the physical properties
    enables the creation of designer polymers.
  • As a result the range of polymer products is very
    large and growing rapidly
  • This session is therefore only a very brief look
    at polymers.

20
The End
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