But an article about recycling HDPE (high density polythene) into blocks for machining purposes really piqued my interest, as I am always on the lookout for plastic scraps to use for machining stuff.
The great thing about HPDE and PP (Polypropylene) is that they are both quite durable plastics; not too brittle like melamine and perspex (acrylic) can be . They both also melt at low temperatures and don't give off any toxic fumes while doing so.
A bit of experimentation in the oven found that HDPE melts at round 180 C, PP at 200; though these can vary a bit according to the exact sample. The HDPE (recycle code 2) comes from plastic milk bottles and the PP (code 5) from ice-cream containers! When I say melt, it is doughy rather than fluid, but quite workable.
Once out of the oven, it hardens quickly so you have to work fast. I made up some 5mm spacers out of ally tube so I could squish the blob between two boards, and the spacers would maintain the resulting sheet at a consistent thickness.
As you can see due to insufficient care I ended up with a crease or two where the material was under that thickness, but apart from that it was bang on, so I decided to press (!) on; It was for a boomerang, so I could carve the thickness down a little to remove the variations. Incidentally PP remelts fine, so if you stuff-up, just re-do the process. HDPE seems a little more difficult to re-melt; I haven't yet established how much higher in temperature I need to go for success.
I had laid out the material to be melted on the oven tray in the rough shape I needed, to avoid waste, and it was easily cut out from that.
I'm really excited about all this; at last I don't have to make do with materials and thicknesses that aren't suitable, as I can control that; and all I have to do to get them is eat a lot of ice-cream! win-win, as they say.
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