Identification of Plastics
When working with plastics there is often a need to identify which particular plastic material has been used for a given product. This is essential to get an idea of the cost and likely properties of the product. The identification of plastics is generally very difficult due to:
The wide range of basic polymers that are available for use. The wide range of additives that can be used to modify the properties of the basic polymer. The wide range of mixtures or compounds of polymers that can be manufactured to get the required properties. Despite this there are some simple tests that can be carried out to get a basic idea of the possible base polymer used for the manufacture of any given product. These tests are simple to carry out for most people and require no special equipment. These tests are a first guess only at the material type and should always be confirmed if definite answers are needed.
Note: The tests given here can be dangerous if performed improperly. Carry all testing out with care, particularly when burning or smelling plastics fume, some fumes are dangerous! Be careful when using burning tests and carry out the tests under supervision only.
There are also some more complicated tests that can be carried out but these require some standard laboratory equipment, details of these are given in "Simple Methods for Identification of Plastics" by Dietrich Braun (Hanser Verlag ISBN 0-02-949260-2 for English text) but there is no substitute for a full analysis of the plastic. Details of the these methods can be obtained direct form Tangram Technology Ltd.
The difference between a polymer and a plastic
A polymer is the basic long chain molecule and is the pure molecule. Polymers are rarely useful in themselves and are most often modified or compounded with additives (including colours) to form useful materials. The compounded product is generally termed a plastic. Most people have little contact with "polymers" because most articles that they come across are actually modified and coloured and therefore are actually plastics.
Thermoplastics materials and thermosetting materials The basic division of polymer based materials is between "thermoplastic materials" and "thermosetting materials". Thermoplastic materials can be melted many times and will harden on cooling to return to their normal state. Applying heat will soften them again.
Thermosetting materials can be shaped and hardened once only. Applying heat will not soften the material but will burn or char it . The basic tests
The basic tests to apply are:
Look at the sample. Feel the sample. Cut the sample.
…. Hold the sample away from your nose (about 20 - 30 cm) and sniff just enough to get the smell. Do not inhale deeply. Take care of any dripping polymer - it will be very hot and can burn.
Glossy surface, does not scratch, burns with the smell of paraffin wax - Polypropylene Glossy surface, slight scratching, burns and drips like wax - Polyethylene (High Density)
Not very glossy surface…
… just enough to get the smell. Do not inhale deeply. Take care of any dripping polymer - it will be very hot and can burn.
Burns but is self-extinguishing. Carbolic smell present. The sample is usually black or brown - Phenol formaldehyde resin.
Burns but is self-extinguishing. Sharp acrid odour. The sample is light in colour - Phenol formaldehyde epoxide resin.
Burns with a fishy smell. The…
… away from your nose (about 20 - 30 cm) and sniff just enough to get the smell. Do not inhale deeply. Take care of any dripping polymer - it will be very hot and can burn.
Characteristic smell of polystyrene - Polystyrene Characteristic smell of polystyrene + a bitter smell - Styrene-acrylonitrile Characteristic smell of polystyrene + smell of rubber - Acrylonitrile-butadiene-styrene copolymer…
Non-styrene based polymers
Place the sample in a small bowl of water that has had some detergent added to it . Note: you must have the detergent or surface tension will prevent the sample from behaving as it should. For foam samples this test obviously does not work !
Sample floats - generally a polyolefin.
Sample sinks - not generally a polyolefin.
Polyolefin type polymers
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