Mathematical Analysis
Mathematical equations for the process design analysis were adapted to the extruder and raw materials used in the present communication. These equations were based on the PET degradation during reprocessing and the results reported in [25]. Specifically, the total flow equation (Q) inside the extruder was obtained by solving the moment, heat and mass balances. This problem was considered as a fluid movement between two surfaces, in which one of them is movable (screw) and using a rectangular coordinate in z direction (channel of the screw). Then, the total flow is given by