2/7: Polymerization and curing or baking

There are so many “big words” that get thrown around in science that it can get overwhelming. If you’re like me, you just sort of hop over them when reading a sentence and just toss it into a category of “big sciency words” in your vocabulary. (I do the same with English Literature, so there you go.)

Polymerization is one of those words, I suppose. Polymerization is a biochemical reaction.

monomer + monomer —> polymerization process —> = polymer

Polymerization connects subunits into a chain via a biochemical reaction. Imagine a bunch of pop beads being put together to make a child’s necklace.

Our bodies do this naturally when we make DNA from nucleic acids. Plants do this when they make starch or cellulose from glucose. And in manufacturing, plastics are formed by polymerizing their respective subunits. All plastics are polymers, created by connecting monomers into a chain. That’s why you’ll often see “poly” in the names of many plastics. Polypropylene. Polyethylene. Polystyrene. Polyvinyl chloride. They’re all polymers that were polymerized.

Now back to vinyl. As I mentioned in the previous article, vinyl is made from polyvinyl chloride (aka PVC, which is a white powder). We can’t make PVC at home. It has to be purchased from chemical suppliers who manufacture it in an industrial facility. And yes, as you can guess, polyvinyl chloride is a polymer of vinyl chloride. That means that polyvinyl chloride is already polymerized. PVC is already a polymer. It was polymerized in the factory.

By the way, the PVC powder is finely ground particles of plastic. They’re really tiny. About 1 micron or smaller. (That’s about the size of a bacteria.) Each particle is made of plastic. And the plastic itself is made of really, really tiny molecule-sized polymer chains. But here’s the thing. Contrary to what polymer clayers repeat to each other, PVC is already polymerized and the chains don’t get “aligned” or rearranged or anything like that when we work with our polymer clay. (Yes, I’ll get there….stay with me. Conditioning is important!)

So what happens when vinyl is cured/baked to make a solid? Remember the plasticizer? All those tiny PVC plastic (powder) particles soak up the plasticizer and soften a bit. Then when the whole thing is heated, the particles melt and fuse. All that’s happening when vinyl is heated to cure is that the particles fuse together to form a solid mass. There is no polymerization reaction happening when polymer clay cures. (It’s not even a chemical reaction, technically.)

And there you have it. We bake/cure polymer clay to cause the PVC particles to fuse into a solid mass. And of course, it needs to be hot enough and you need to cure long enough for this to happen. This is why underbaked polymer clay is brittle and breaks when you flex it. It’s not yet fused, so any pressure and it snaps or crumbles. And this is also the reason that baking longer makes a stronger result. There’s more time for more fusion.

In the next article, I’ll talk about plastisols and plastigels and how they relate to polymer clay.

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