Mathematical Analysis of the Process
Equation (1) was used for the calculation of the flow rate (Q) using the geometry and extruder operating conditions given in Table 4. We have considered a standard PET extrusion process with an initial intrinsic viscosity of 0.6, a mass flow in the feed of 99 g/minute, L/D extruder ratio of 30 and an extruder diameter of 0.033 m. Figure 2 shows the behavior of the flow along the extruder length. The changes of density or flow rate were produced by the temperature and the geometry of the extruder. Note that these changes were more significant in the first two sections at the same speed of change even though these sections showed differences in the geometry and temperature. On the other hand, the pressure along the screw was affected mainly by its geometry in the last extrusion zone. For the case of the extrusion process of recycled PET (Figure 3), this increasing pressure was mainly caused by the total fusion of the material and the geometry in the last 0.34 m of the extruder. If an increment of 10 % of mass flow variation in the feed is considered, the pressure does not present a considerable