What are the different types of plastic and how can they be separated?

It is best to avoid packaging waste altogether. If that is not possible, we should reduce, separate and recycle the waste as much as possible. To do this, we throw plastic packaging waste into specific garbage cans. During subsequent recycling, the different types must first be separated. But what types of plastic are there? And how does the separation process work?

Before you get started

If you are experimenting at home:
1. Let your parents know and discuss the experiments with them beforehand.
2. Do not eat or drink at your workspace.
3. Wash your hands thoroughly before and after the experiment.
4. Be careful and cautious with the materials.

Graphic figure boy pouring liquid in flask

assortment of plastic materials, salt and glass jar

You will need

A collection of empty plastic packaging
Small pieces of plastic made of PET, PE, PS and PVC materials
Drinking glass
Spoons
Table salt

Let’s get started!

close up of bottom of blue plastic bottle

1. Collect and identify plastic packaging

Collect some plastic packaging made of different types of plastic. Look for the recycling symbols and the abbreviations for plastic types on the plastic packaging. The abbreviation for the type of plastic is always under a recycling symbol. Write down the different abbreviations you find.

2. Cut plastic packaging into pieces

Search for the plastic types "PET", "HDPE or "PE", "PP", "PS" and "PVC". Then take a piece of each type and cut a few small pieces from it.

close up of beaker with water and plastic floating plastic pieces

3. Does it float or sink?

Plastic floats on water, right? Investigate the floating behavior of the different types of plastic that you have found.
Fill a glass with water. Immerse the first piece of plastic completely in the water and let it go. Observe what happens: Does it float or sink to the bottom? Test each type and write down whether it floats or sinks.

spoon with salt above glas with floating plastic pieces

4. Separate

You’ve learned which type of plastic sinks in pure tap water and which floats on top of the water. What happens if you change the properties of the water by gradually adding salt? Fill a glass with water and add pieces of PET, PE, PS and PVC plastic. Now add a small spoonful of table salt and stir everything briefly. Wait a little while until the water has settled. Repeat this four more times so that you have added a total of five spoonfuls of salt. What has happened?

Why do some pieces of plastic float on the water, and why do some sink?

Answer:

This is due to the different densities of the substances: The greater the density, the less space ‏(volume) a certain amount ‏(mass) of the substance requires. A 100-g bar of chocolate is quite small. In contrast, 100 g of cotton candy is quite a big pile. If a plastic has a smaller density than water, it floats on the water. If a plastic has a greater density than water, it sinks. Here, we change the density of the water by adding salt. The more salt added, the greater the density of the saltwater. When the saltwater reaches a greater density than one of the sunk pieces of plastic, the piece will start to float.