eli5: simple explanation on how a bunch of natural materials that decay make up plastic; a material that virtually lasts forever
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The chemical reactions, for the temperatures we have on this planet, are usually happening between molecules.
Each molecule can react with another molecule. Some are more prone to reaction than others. There are happy molecules that are happy to stay what they are, and angry molecules that want to react with other angry molecules, in order to become happy molecules.
For example, iron oxide is pretty happy to stay iron oxide. Oxygen molecule, O2, instead is a angry molecule that tries to oxide whatever it finds in range, for example, react with pure iron to make the iron oxide.
In the case of plastic, some relatively angry molecules are merged into a single very long molecule, and quite happy as a molecule. This molecule does not want to react much. This is the main reason for its very slow decay. Altho, being so big, there are things that can hit that molecule and split it. Example sunlight, or extreme temperatures. So plastic is chemically stable but can be broken with relative ease. That’s why it still can decay. Altho, very slowly.
It’s also a very long molecule, big molecule. Meaning that a kg of plastic is made of way fewer molecules than a kg of oxygen. Having fewer molecules per kg means you have fewer chances for a reaction. Now, this is a second order reason for it to be long lasting. For example, it’s easier to burn hydrogen than petrol, but the fact that petrol is a long molecule doesn’t spare it from reacting, it just takes slightly longer than a small molecule with a similar “anger”.
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