Yesterday we had a brief introduction to plastics in terms of their role in marine pollution at the Science Underground Academy. Here I’ll list some of the points I made and some further reading for follow-up. This is part of a larger work looking at marine pollution in general.
Introduction to plastics and biodegradability
- Plastics are a group of materials with a wide range of properties, traditionally made from petroleum.
- Their chemical structure – long chains or strings of of carbon atoms, which have groups of atoms coming off them. The arrangement of the atoms in these materials changes their properties.
- Most plastics are not biodegradable. Their long, strong chains and strong bonds between chains mean they cannot be broken down by most bacteria and fungi.
- There are new plastics where the long chains that make them up are derived from plant materials such as starch, and these can be broken down by bacteria and fungi.
- There have recently been discovered one fungus and one bacteria that can eat traditional plastics.
- Pestalotiopsis microspora has been found to devour polyurathane and has been used in this fantastic project Fungi Mutarium by LIVIN Studios
- Ideonella sakaiensis has been found to devour PET – researchers discovered this by analysing microbes that were found on plastic debris – who knows what other microbes are out there making use of our waste?
- It’s important to remember that toxic chemicals are often used in plastic production, for instance PCBs are frequently used in extrusion of PVC. These chemicals are either used as part of the plastic production process or as additives to change the properties of the plastic. Even if the plastics are broken down, these toxic chemicals can still persist, either in the environment or in the creatures that are decomposing the plastics.
Identification of plastics
- The first thing to check when identifying plastics is whether it is labelled. Many plastics have a symbol like this:
The number inside the triangle denotes what kind of plastic it is, and is used to help sorting in recycling centres. Recycling means melting the plastic and turning it into another shape. If different types of plastic are mixed together, this process can fail, creating more plastic waste.
- Makezine has a great introduction to plastic identification. In short, you can identify plastics using:
- The burn test – this differentiates between the 2 classes of plastic: thermoset and thermoplastics. Thermosets burn, thermoplastics melt. More information can be found here: http://www.boedeker.com/burntest.htm
- Plastics have different densities. You can identify them by using density columns with different reference liquids http://www.nclark.net/Density_Column.pdf
- The copper wire burn test or Beilstein test is used to detect if there are halides in your plastic. Halides are Fluorine, Chlorine, Bromine, Iodine. Some of these halides are found in plastics such as poly vinyl chloride (PVC). Here’s a step-wise explanation of the test: https://sha.org/assets/documents/Beilstein.pdf