jiha, I finally managed to make recycling sheets with a good surface on both sides which are easy to remove from the mold. So weighing the material in andvance helps to get a good fillfactor. I just multiplied the mold volume with the density of the material and added 10% safety. Worked out well. 

Got a big Flake-hill on my mold with the 5-8mm flakes. Smaller ones should work better.