This was a kind of odd project, but I think it’ll fit. Back when I was researching ways to reuse plastic from 3d-printers, I ran across a thread discussing HDPE, turning plastic bags (if you can find only filmed HDPE ones) into printer filament through something like a filastruder, and that got me thinking about milk jugs. HDPE is a very strong plastic, is readily available, and can tolerate being re-melted better than many others. When melted and formed into shapes, it’s hard, and glossy/smooth.
My experimental design was simple, a little owl figure (like a squishmallow) to make into a necklace for my spouse.
I carved a simple wooden mold, and set up outside with an old toaster oven (the fumes can be dangerous, it’s important not to heat it anywhere near 400 degrees Fahrenheit – I found 250 to be more than sufficient). I cut part of a milk jug into thin strips and piled them on a piece of sheet tin and let them soften in the oven. Once they were soft and sticky, I used a pair of pliers to wad them into a ball and pressed them into the mold.
It took a little clean up (trimming the flat disk of extra plastic which forms between the two sides of such a crude mold and adding the faint little face) but it worked alright. After a few tries, the soft pine of the mold started to compress a little, the softer wood around the dark grain receding slightly so the grain marked the plastic.
It was an interesting one-off with some potential, but probably better done by people who know more than I do. I don’t generally like plastic projects like this because of the scrap which isn’t going to get accepted by a recycling center (if they actually recycle it at all) but I like the potential for local reuse of material and I could always melt it again. I thought about making a beta fish mold, so the disk of extra would form its fins, but never got around to it and let the project drop. As materials go, it actually feels pretty nice to touch and to carve, and I could see perhaps using it to make tool handles or something similar, if for some reason I wanted plastic rather than wood, which generally works best for me.
Yeah I think there's definitely some room for clever uses of the material (even artistically, as milk bottle caps are also HDPE, melt the same, and come in a variety of colors). The molded parts really are quite nice; they're very hard, and smooth and glossy, milky white with a bit of a swirled texture from being melted. They're easy to work with a sharp knife, and the tool marks are similary smooth and glossy.
For me for the moment it's a bit of a solution in search of a problem - but if I had to make a bunch of things of similar dimensions, and needed them to be hard plastic rather than wood or metal, it'd be a good place to start. Maybe replacement plastic parts for machines, or something that needed to hold up through outdoor use?