Generally, the processing of WPC samples was a two-stage process. In the first processing step, the raw materials were com- pounded in a heating mixer (TSHK 100, Loedige) followed by cooling in a plough-blade mixer (FM 130 DS, Loedige). Compounds were extruded into a tape profile with the dimensions of 4 mm × 40 mm using a conical, counter rotating twin-screw extruder with 54 mm screw diameter (Battenfeld Minibex 2-54C). Tapes were cut into small segments and ground using a laboratory mill to obtain homogeneous samples for analysis.