When you use polyethene to make some plastic in a pneumaticraft plastic mixer, you use up 50 mB of PE for one plastic.
You can also melt any plastic to make 400mB of oil. The oil can be distilled into Ethene and made into PE again, yielding more PE than it costs (not including other oil products).
I'm pretty sure this way of making raw oil straight from plastic is not intended at all and should be removed