Identification of Plastics

Introduction

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.
• See if it floats in water.
• Burn some of the sample.

These tests will give you a fair idea of what the basic polymer is.

Note: The tests given here are not necessarily definitive and the presence of certain additives (for instance flame retardants) can significantly change the behaviour of a product.

Testing

Stage 1: Look at the sample

This will give you a lot of information. The colour of the plastic will give you some information. Some polymers have restricted colour ranges, particularly the thermosetting types. Others tend to be more glossy in colour (polypropylene), whereas some are both glossy and glassy (the acrylics).

Stage 2: Feel the sample

After you have carried out the tests in the is series a few times you will start to get the feel for various plastics. The polyolefins have a very distinctive feel and you can generally tell if it is one of them. The presence of glass fibre or other reinforcement materials can alter the feel and stiffness of the sample but you can sometimes tell by the feel if there is a reinforcement present.

Stage 3: Cut a thin sliver from the edge of the sample. Follow the links to the appropriate page.

The first test is to cut a small sliver off the sample. This tells you a lot about the type of plastic you are trying to identify

Powdery chips formed - Generally thermosetting material.

Smooth sliver of plastic formed - Generally thermoplastic material.

The links will take you to the appropriate page and possibly identify the plastic you have.

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Results

The testing carried out should have given a possible result for your sample. Naturally we cannot always identify the given material from a series of such simple tests but with experience you ought to be able to get about 95% of the plastics identified.

We hope you found this simple guide useful.

Please contact Tangram Technology Ltd. if you need any additional information.

E-mail us now at info@tangram.co.uk

 

Last edited: 16/08/04

 © Tangram Technology Ltd. 1998

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