Clear plastic wrap. Tupperware containers. Scotch tape. Swimsuits. Are all of these things plastic in different forms? What is the unifying chemical structure common to all these different things that makes them all plastic?
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They are made up of small repeating hydrocarbon units, usually extracted from crude oil.
For instance, PVC (polyvinylchloride) is 2 carbons, 3 hydrogens, and a chlorine per unit, and that unit (called a polymer) can be repeated any number of times, linked end to end by the carbons.
The unifying chemical structure, then, is a hydrocarbon chain, with something else attached to the side of it at regular intervals, ie, a chain of polymers.
As for what counts as plastic… yes, most modern clothing, tape, etc, but also tyre rubber, hair styling gum, some types of glue, faux leather, and so many other things.
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Other people are explaining what carbon based polymers are, which is brilliant, but miss one important bit:
Why are some things plastics, some rubbers (elastomers), and some gel or liquid, despite all being carbon based polymers.
And the difference is… Well, exactly what it seems. The consistency. Polymers can exist in most of these states depending on temperature. Rubbers become rigid and crack when cooled. Plastics soften and stretchy when heated. Polymers that aren’t crosslinked (like vulcanised rubber is) can melt.
The only difference really is what properties the specific polymers have in the “human” temperature range, or the one they’re meant to otherwise operate in. Plastics are hard and stiff in “our” temperatures, that’s honestly the only definition (Of course it can get complicated real fast with some edge cases). Rule of thumb, jf it’s a polymer but is isn’t stretchy or runny at room temperature, it’s a plastic.
In technical terms, there’s a thing called “glass-rubber transition temperature”, most polymers have one. Rubber is obviously rubber, “glass” is what we commonly call plastic. It’s called that because it’s solid, stiff and brittle but not a crystal, so the technical definition of “glass”. So we divide things into “rubbers” and “plastics” roughly based on whether the glass transition temperature is above or below about 0-30C.
Generally plastics consist of long chained molecules (called poymers). Think spaghetti. These chains can wriggle around at room temperature, which makes the material flexible or even rubbery. However some plastics dont wriggle at room temperature (e.g. perspex) so the material is hard. However if you heat them above the “glass transistion” temperature then chains can start wriggling and the material becomes soft or even flowable.
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