Canning and Fish Packaging Technology

Unit 9 - Plastics for Packaging

9.3.6.Polyester or Polyethylene terephthatate (PET)
This was first developed as a textile fibre by I.C.I Ltd., Later it was developed to form film and for bottle by stretch below moulding. The important properties of PET are given below.

• High tensile strength and therefore withstands carbon dioxide pressure in bottles.
• High softening point i.e. 245-270^oC, but the jars/bottles suffer from distortion on hot filling.
• It has good sparkle and optical clarity.
• Good gas barrier, better than PVC and polyolefins (PE&PP). Hence used in Modified Atmosphere Packaging (MAP), Gas Packaging and Vacuum packaging.
• Fairly low water vapor permeability.
• Excellent oil and grease resistance.
• Chemical resistance to dilute acids and alkalies but attacked by concentrated areas.
• Excellent Printing Surface: PET bottles upto 3L capacity are widely used for carbonated drinks where its gas barrier properties and strengths are valuable. As a film difficult to heat seal (high M.P) and thus coated with PVDC or laminated to polyethylene. Such laminates are used in vacuum packaging of cooked meat products, and for boil in bag packs. More recent use for PET is in the manufacture of ovenable boards for heating in microwave or conventional hot air ovens. By laminating with other plastics it is also used in the manufacture of retortable pouches and pouches for MAP products.