Polymers

Polymers

1. Polymers in Commercial Packaging

   • Thermoplastic polymers are widely used in commercial packaging.
   • A thermoplastic is a material that, once heated, can be formed into a variety of interesting shapes using different forming techniques such as blow moulding. When cooled, the shape remains permanent.
   • Thermoplastics can be reheated, softened, shaped and cooled many times over. So they can be recovered and recycled easily.
   • Polymers used in packaging can be identified by an internationally recognised coding system moulded into the base of each product/ package/ printed on the label, this system enable them to be easily recycled.
   • Each polymer has its own useful properties that make it suitable for use in different areas of the packaging industry.
   • Advantages
     • Easily printed on
     • Inexpensive
     • Recyclable
     • Rigid
     • Versatile
     • Tough
     • Strong
     • Durable
     • Water resistant
     • Easily formed and moulded
     • Impact resistant
     • Lightweight

2. Styrofoam for block modelling

   • Styrofoam is extruded polystyrene foam manufactured for the construction industry for insulating buildings. However it makes an excellent modelling material, especially for block modelling purposes.
   • Available in a range of thicknesses and can be glued together with polyvinyl acetate (PVA) to create larger block sizes and also can be painted with acrylic paints to give a good quality finish.
   • Advantages
     • High compressive strength
     • Can be sanded to a high surface finish
     • Easily cut and shaped with hand tools
     • Great Rigidity
   • Disadvantages
     • Can become dinted when using a file or ripped when sanding if care isn’t taken
     • The surfaces break away quite easily, therefore unsuitable for models that require great detail
     • Weak

3. Polyethylene Terephthalate (PET)

   • Properties
     • Sparkling ‘crystal clear’ appearance
     • Very tough
     • Lightweight – low density
     • Does not flavour the contents
     • Prevents gas from escaping package
     • Excellent barrier against atmospheric gases
   • Uses
     • Carbonated (fizzy drinks) bottles
     • Packaging for highly flavoured foods
     • Microwavable food trays

4. High Density Polyethylene (HDPE)

   • Properties
     • Highly resistant to chemicals
     • Tough and hard wearing
     • Lightweight and floats on water
     • Good barrier to water
     • Decorative when coloured
     • Rigid
   • Uses
     • Unbreakable bottles (for washing up liquid, detergents, cosmetics, toiletries)
     • Very thin packaging sheets

5. Polyvinyl chloride (PVC)

   • Properties
     • Weather resistant – does not rot
     • Chemical resistant – does not corrode
     • Protects products from moisture and gases while holding-in preserving gases
     • Can be manufactured either rigid or flexible
     • Good abrasive resistance and tough
     • Strong
   • Uses
     • Water and fruit juices
     • Pharmaceutical products
     • Food and confectionary
     • Packaging for toiletries

6. Low density Polyethylene (LDPE)

   • Properties
     • Decorative when coloured
     • Very light and floats on water
     • Very flexible
     • Tough and hard wearing
     • Good barrier to water, but not gases
     • Good resistance to chemicals
   • Uses
     • Stretch wrapping (cling film)
     • Milk carton coatings

7. Polypropylene (PP)

   • Properties
     • Rigid
     • Lightwieght
     • Excellent chemical resistance
     • Versatile – can be stiffer than polyethylene or very flexible
     • Low moisture absorption
     • Good impact resistance
   • Uses
     • Food packaging – yoghurt and margarine pots, sweet and snack wrappers
     • Used for laminating paper and board

8. Polystyrene (PS)

   • Rigid Polystyrene
     • Properties
       • Rigid
       • Lightweight
       • Low water absorption
       • Transparent
     • Uses
       • Food packaging – yoghurt pots
       • CD jewel cases
       • Audio cassette cases
   • Expanded polystyrene
     • Properties
       • Very good heat insulation
       • Durable
       • Low water absorption
       • Lightweight
       • Excellent impact resistance
     • Uses
       • Egg cartons
       • Cups
       • Packing for electrical and fragile products
       • Fruit, vegetable and meat trays

9. Acrylic

   • Acrylic usually is cast into sheets but is also available in rods and tubes.
   • Acrylic is self finishing and doesn’t need an applied surface finish.
   • Uses
     • Signage and point of sale displays
   • Advantages
     • Able to withstand extreme weather conditions
     • Low cost
     • Can be clear or frosted
     • Easy to fabricate
     • Lightweight
     • Chemical resistant
     • Excellent aesthetic properties
     • Durable and able to resist long term stresses
   • Disadvantages
     • Cracks are easily formed and spread through the acrylic
     • Low scratch resistance
     • Brittleness

10. Environmental concerns

    • Recycling certain types of polymers can also be unprofitable, i.e. polystyrene is rarely recycled becauseit is usually not cost effective.
    • Although different schemes have been put into place, it is difficult to separate products, i.e. drinksbottles, as the bottle and closures are made of different polymers.
    • Recycling may be the answer to this problem, as thermoplastics can be moulded into different things,although the main problems are sorting and collection.
    • Then there’s the problem with disposal, polymers are durable and degrade very slowly, which is a problem for landfill sites. Incineration may not be the answer either, as in some cases burning polymers can release toxic fumes.
    • Oil is the raw material of synthetic polymers, and is not an infinite resource but consumes a lot of energy in the production process and produces pollution. The manufacture of blow moulding for example, also uses a lot of energy.
    • There is ongoing environmental concerns of how sustainable polymers are.