identifying different types of plastics and polymers

Different plastics are made from different types of polymers. The different types of polymer give the plastics different characteristics and make them good for different applications, for example fizzy pop bottles are made from PET (Polyethylene Terephthalate); milk, juice and detergent bottles are made from HDPE (High Density Polyethylene); a few bottles are still made from PVC (Polyvinyl Chloride)

Most plastic products carry a symbol that shows what they are made of. Sometimes they have letters on them, some have letters and a triangle, while some only have a triangle with a number in it. This is because different polymers have their own names and numbers.

Here are a couple of quick tricks to help you to find out which type of plastic your bottle is made from:

If your bottle is clear, it is likely to be made from PET. PET bottles can also be slightly tinted, such as mineral water bottles, but the colour is never usually strong. Check that there is a small dimple on the bottom of the bottle and, in the case of fizzy drink bottles, a flower-shaped base. This flower shape helps the PET bottle to cope with the pressure put on it by fizzy drinks. The dimple is caused when the bottle is blow-moulded upside down - the dimple is where the plastic was forced into a mould and then cut off. PET bottles carry a number '1'.

If the bottle is an opaque milk or juice bottle, it is made from HDPE natural. If your bottle is coloured or white (not opaque), it is HDPE coloured. HDPE bottles cannot cope with pressure so they are used for liquids like milk and fabric softeners. They have a line running all around the edge of the bottle where the two moulded halves have been stuck together. HDPE bottles carry a number '2'.

Very few plastic bottles are made from PVC, although some of the larger squash bottles with handles are still manufactured from PVC. PVC bottles are clear in colour and have a kind of smile on the bottom. Just like the PET bottles, this line is part of the manufacturing process and gives PVC bottles a distinctive marking. PVC bottles also have a seam around the edge. They carry a number '3'.

Of course there are lots of other plastics being used all the time in many different applications. Yogurt pots, for instance, are made from polystyrene. Other plastics, like polypropylene, are used in many products.

So why do we only talk about recycling plastic bottles? There are many types of plastic being used, but many of them are blends of different polymer types, not all food tubs are made from the same polymers and if different polymer types are recycled together, they lose their special qualities. For example, if a load of PET was to be recycled with a load of HDPE to create a new blended plastic, it is unlikely that the new material will have the pressure bearing properties of the original PET.