How to Identify Different Types of Plastic

Plastic types are distinguished and separated based on the chemical makeup and codes allocated by international agreement.Here is the recognised guideline on the recycling codes assigned to plastic products for recycling:

The huge floating island of plastic in the Pacific ocean comprises only the plastics that float. What about all those that sink? Where are they?

The easiest way to identify between broad groups of plastic is by establishing whether they float or sink. While there are exceptions, the polyolefins generally float in water and the rest, generally sink. The polyolefins include numbers 2, 4 and 5 above - High Density Polyethylene (2), Low Density Polyethylene (4) and Polypropylene (5). So as a rule of thumb, if a piece of the plastic floats, it will be one of these and otherwise, it will something else.

This sounds astonishing, but try this and you will see. Chop a manageable piece (possibly thumbnail-sized) off a milk bottle (HDPE) and it will float; conversely, a piece from a cool drink bottle (PET) will sink!

The frightening part of this, is that the massive floating island of plastic in the ocean, comprises primarily plastics that float and, as you can see from those the sink vs those that float, there are many types of plastic that sink and that we must presume are all lying on the bottom of our oceans.

There are many misconceptions about the floating "island of garbage" and the reality is very different from the public image of a giant pile of trash floating in the ocean. The plastic pieces are generally very small and an interesting article on the subject can be found here, although this does not form the subject matter of this hub.

Flame

Blue with a yellow tip would be indicative of the polyolefins and nylon. You might think, well how would you separate these two if their flame is the same? Remember from above, the polyolefins would float and nylon (PA) would sink.

A yellow flame with a green tip on contact shows PVC (Polyvinyl Choride), yellow with dark smoke could be PET or Polycarbonate and yellow with sooty, dark, smoke could be polystyrene or ABS (the plastic housing of your computer monitor).

Burn

The polyolefins ignite quite readily - be very careful if you are testing this type of plastic because molten plastic can drip and will leave an ugly burn if you make contact with it.

PVC (many garden hosepipes and certain piping for household plumbing, but it is becoming an unpopular plastic in modern times) and ABS will only ignite with moderate enthusiasm and will soften, but not release dripping "firebombs" of plastic; while PET also ignites moderately, but bubbles as it melts.

Smell

After you have applied a flame to the plastic piece to test it, and carefully observed the smoke and ignition potential, you can carefully waft some of the smoke towards your nose. WARNING: if you have already identified the plastic from other methods and particularly in where you suspect the plastic is PVC, do not smell the smoke.

If you must, and we advise against it where possible, a small whiff of the smoke will give you further clues as to the plastic identification code under which your suspect can be classified.

PET smells similar to burnt sugar (the odour reminds the author of eating candy-floss or sugar-candy in his childhood); PVC has an acrid smell like chlorine - stay away from the smoke and gas given off by PVC; LDPE and HDPE smell like candle wax, while Polypropylene smells similar to candle wax, but with an element of paraffin to it; ABS and polystyrene both smell like styrene, but the ABS also has a faint rubbery smell to it.

Touch and Sound

The polyolefins are a rather tricky bunch of characters. They generally all float, have the same flame and dripping "firebomb" effect and even smell the same! This makes them rather tricky to tell apart, particularly when they are in the form of film - in other words, when they are packaging like packets or film wrapping.

Plastic packets can be made from LDPE, HDPE or PP. Now your senses of touch and hearing are drafted into play.

LDPE feels soft and smooth, like the bag Mom packs your sandwich into. Additionally, if you rub it together, it will make a soft swishing sound, as opposed to a crinkling, harsher sound.

HDPE feels harder and essentially, more crinkly. Many plastic shopping bags are manufactured from HDPE and the easiest way to distinguish them from LDPE bags, is from the sound the make when you crinkle them in your hands. If the sound is soft and swishing (think of green leaves blowing in the trees), then you have identified LDPE; if the sound is crisper and crinkly (think of dry leaves being squished together), then you have HDPE. The two sounds are quite distinct.

Our final campaigner in this section is PP, also known as polyprop or polypropylene. Packets made of this plastic sound similar to HDPE and are crinkly. PP is generally used for packaging food, such as chocolate and chips wrappers, or the clear packets you might buy a gentleman's shirt in. It feels much firmer and stiffer, but the most important trick here, is that it does not stretch. It simply rips and tears without stretching at all first.