I flaired as “other,” but I suspect this involves both chemistry due to state of matter changes and physics due to the involvement of thermodynamics. I don’t know. If you want to tell me with your answer which flair would’ve been more appropriate, I’d appreciate it.
I’ve tried looking up injection molding, since I assume it’s similar (although it seems the processes I’m reading about require a more solid resin than the “Goop” you used in these toy molds). Even though the Goop isn’t quite solid, I’m assuming the process is still that it melts down even more and then becomes more solid during the cooling process.
I’m just not understanding why. I might understand if it had started solid, since then cooling it just returns it to its natural state after heating. That would just be like making fudge. But this stuff was gooey, and it came out firmer (although still pretty wobbly) after you cooked and cooled it. How would you explain the science of how this works in child-friendly terms? How does reducing a goo into liquid and then cooling it make it firmer?
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Nothing much chemical would happen when you heated the goop and injected it. It’s just that it would be heated to it’s melting point you could squish it into the mold and then it cools and solidifies at room temperature. Kind of like how you can melt/cast/melt/cast beeswax into different shapes
Certain polymers, the type of thing that plastics and goops are, can be of a certain type called thermosetting polymers. This gives them a neat property, that instead of getting more gooey/liquid-like when they heat, it instead solidifies them. It does this because as it heats it gets energy to fuel a chemical reaction called crosslinking. The polymer has little bits on it that either stick off, sometimes with the aid of something else, can latch on with some other ones chemically. Which now makes the liquid bind together to make a solid, when it cools down it still stays bonded together.
Imagine you’re on a crowded trampoline with a lot of friends. If you all have a lot of energy (heat) And you start bouncing you’re going to be moving around a lot (liquid) And if you keep bouncing with such high excitement, some of you might fall off (turn to gas). If you get tired (cool down), You’re going to move less and maybe even get the people who fell off back on. (Turn solid again).
What if instead all of you wore Velcro suits? (Thermosetting polymers with the bits) . If you started bouncing (heating up) instead of moving around a lot And maybe falling off you’d all just stick to each other and no one would go anywhere (become a solid). Even when you stop trying to bounce, you’re still stuck to each other until someone comes and pulls you off (breaks the plastic.)
So, chemistry is a complicated thing. Sometimes two compounds react when they touch each other. This can result in all kinds of chemical reactions. Sometimes they make air. Sometimes they make heat. Sometimes they get harder. Sometimes they get softer. Sometimes they attach what they’re touching when they harden.
The main ingredient in creepy crawler goop was PVC, or a kind of plastic. Lots of plastic that looks and acts different is also PVC, so PVC can be a wide range of things. Lots of plastic gets harder when you heat it up — that was the first way we started making shapes out of plastic. That’s why a lot of cheaper plastic things have a seam on the sides of them! That means they were once a liquid, poured into a mold into the shape of the thing someone wanted, and then heated up. Once it cools, it stays solid! More expensive things can also be made this way — they just try to file or treat the seam so it isn’t as obvious.
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