Food Toxicology 2(2+0)

Lesson 27 : Food packaging material – potential contaminants from food packaging material

Summary of the main different types of flexible plastic films

A summary of the main different types of flexible plastic films is as follows:

1. Cellulose
   Plain cellulose is a glossy transparent film that is odourless, tasteless and biodegradable (within approximately 100 days).It is tough and puncture resistant, although it tears easily.It has dead-folding properties that make it suitable for twist-wrapping (e.g. sugar confectionery).

2. Polyethylene (or polythene)
   Low-density polyethylene (LDPE) is heat sealable, inert, odour free and shrinks when heated.It is a good moisture barrier but is relatively permeable to oxygen and is a poor odour barrier. LDPE is also used for shrink- or stretch-wrapping High-density polyethylene (HDPE) is stronger, thicker, less flexible and more brittle than LDPE and a better barrier to gases and moisture. Sacks made from HDPE have high tear and puncture resistance and have good seal strength.They are waterproof and chemically resistant and are increasingly used instead of paper or sisal sacks.

3. Polypropylene
   Polypropylene is a clear glossy film with a high strength and puncture resistance.It has a moderate barrier to moisture, gases and odours, which is not affected by changes in humidity. It is widely used to pack biscuits, snackfoods and dried foods.

4. Other films
   Polyvinylidene chloride is very strong and is therefore used in thin films.It has a high barrier to gas and water vapour and is heat shrinkable and heat sealable. They are used with other polymers to make them heat sealable at lower temperatures and to improve the barrier properties, and are used to pack meats and cheeses.

5. Coated films
   They are used for packaging meats before smoking and cooking. A thin coating of aluminium (termed ‘metallisation’) produces a very good barrier to oils, gases, moisture, odours and light.