Sunday, 28 September 2014

Recycling HDPE and PP Plastic

I've been playing around with my old lathe a lot lately (its a pre-WW2 Myford ML1 museum piece, slop everywhere, but its surprisingly useful for working in soft metals and plastic), and browsing Youtube to that end.

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.

No comments:

Post a Comment