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Home > Reprocessing & End Products > Identifying Plastics > Polymer Identification Tests

Polymer Identification Tests

In the UK there is no legal requirement for manufacturers to label the material type. There are however  a number of simple tests that you can carry out to get an idea of the plastic used for the manufacture of any given product. These tests are straightforward, requiring no special equipment and are described under the following pages polymer identification tests.

Step-by-step polymer identification. Working through this section, a series of questions will be asked, the answers to which depend on the polymer identification test results. By selecting answers to the questions, initial identification of a sample can be achieved.

The tests described here are simple to carry out and require no special equipment. It should be noted however that some of the tests can be dangerous if performed improperly.

Before embarking on these tests, why not try some samples of known plastic from your household, which should belong to one of the six main polymer types? This will facilitate comparisons to be made when trying to identify unknown polymers. For example, milk bottles are HDPE, water/fizzy drinks bottles are PET, most sauce bottles are PP; be sure to check for an identification code on the bottom to assist you.

These tests are designed to give you a first guess only and are not definitive. There are also some more complicated tests that can be carried out, but these require some standard laboratory equipment. There are many other less common types of plastics not included in this identification system and ultimately there is no substitute for a full analysis of the plastic; most reprocessors will request a sample for analysis prior to accepting material.

Samples of rigid/flexible material to be tested should be cut or sawn to a manageable size.

Materials Needed

  • Plastic samples of a  suitable size (matchstick size, or slightly bigger will suffice)
  • Small bowl
  • Water
  • Washing up liquid
  • Vegetable oil
  • Copper wire
  • Wire cutters
  • Pliers (to hold wire)
  • Lighter/matches
  • Candle
  • Acetone (commonly used in nail polish remover and paint stripper)

Safety Precautions

The copper wire will get hot when heated in a flame. One end of the wire should held with tongs or pliers to avoid burns.

When undertaking the copper wire test DO NOT INHALE THE FUMES, these can be highly toxic. Work in a well ventilated area. It is advisable to wear protective goggles when undertaking this test.

Acetone is flammable and the vapours are considered toxic. Keep the top on the bottle when you are not using it and work in a well ventilated area. Avoid flames.

Sliver Test (rigid / flexible plastics)

Cut a small sliver from the sample:

  • If powdery chips are formed the material is likely to be a thermoset
  • If a smooth sliver results the material is likely to be a thermoplastic

*Thermosets tend not to be recycled, as they cannot be remelted.*

Float Test (Water) (rigid / flexible plastics)

Fill a small bowl with water, adding a little washing-up liquid (if the washing-up liquid is not added, surface tension will prevent the sample from behaving as it should). Place the sample in the bowl, gently pushing it down. Release it and wait a couple of minutes to see whether it floats or sinks.

Float Test (Mazola Corn Oil) (rigid / flexible plastics)

This test should be used on the samples that floated in the water. Fill a small bowl with Mazola corn oil* (found in most supermarkets). Place the sample in the bowl, gently pushing it down. Release it and wait a couple of minutes to see whether it floats or sinks.

* The reason a specific brand has been suggested here is that not all corn and vegetable oils have the necessary density and the test may therefore not work using other brands

Copper Wire (Flame) Test (rigid / flexible plastics, plastic films & foams)

This test should be used on the samples that sank in the water and can also be used to identify plastic films and foams. You will need a piece of copper wire about 5cm in length. Hold one end of the wire with a pair of tongs or pliers, so you are not touching the wire directly while it is heated.

Set out a candle on a clear work surface and light it. With the plastic sample to hand, place the free end of the wire into the flame until it is hot and the flame no longer has a green colour.

Remove the wire from the flame and touch the hot wire to the plastic sample. A small amount of the plastic should melt onto the wire. If the wire sticks to the plastic use a pair of tongs to remove it. (You should not burn a large piece of plastic due to the toxicity of the fumes.)

Place the end of the wire, with the small amount of plastic on it, into the flame. The flame should burn green, yellow/orange, or blue depending on the type of plastic.

Acetone Test (rigid / flexible plastics)

This test should be used on the samples that produced a yellow/orange flame. Ensure that you are working in a well ventilated area.

Place the plastic sample in the bottom of a small bowl and pour in sufficient acetone to just cover it. Leave the sample in the acetone for 30 seconds.

Using tongs, remove the sample and press firmly between your fingers. A positive reaction has occurred if the plastic sample is soft and sticky. Scrape the sample with your fingernail to see if the outer layer has softened. If the sample is unchanged, this means that no reaction has taken place.

Flexibility Test (rigid / flexible plastics)

Bend the sample to determine whether it is flexible, semi-rigid, or rigid.

  • Flexible: sample will bend repeatedly without breaking
  • Semi-rigid: sample will break after repeated bending
  • Rigid: sample will break almost immediately

Surface Test (rigid / flexible plastics)

Feel the sample to determine whether it has a hard glass-like surface, a soft waxy feel that scratches easily, or a dull unpolished surface.

Stretch & Strength Tests (plastic films)

Comparing the stretch and strength characteristics of plastic film can be used to distinguish between the different polyethylene films. This is difficult to do without some experience however, and is not usually necessary, as a majority of reprocessors will accept mixed PE film.

Co Reg: 2435729 | VAT Reg No: 546 5837 10 | Reg Charity No: 1072029

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