How to Deal with the Devolatilization Problem of Twin Screw Extruder

The main screw speed, feeding rate and barrel set temperature are the main factors affecting the devolatilization process in the twin screw extruder. The changes of these factors will affect the material temperature, screw groove fullness, residence time and effective full length, thus affecting devolatilization in many ways. For a specific process, there is an optimal working point, and the highest devolatilization efficiency can be obtained under stable working conditions.

Increasing the screw speed is conducive to the formation, growth and rupture of bubbles, reducing the filling length of the material in the groove, enhancing the renewal effect of the material quality transfer surface, and improving the devolatilization efficiency. However, an excessively high speed will cause the material to be degassed. The residence time of the volatilization section decreases sharply, and the devolatilization efficiency drops instead.

Appropriately reducing the feed rate can reduce the full rate of the venting section and improve the devolatilization efficiency. However, a too low feed rate not only reduces the extrusion rate and produces fluctuations, but also because the full rate is too low to form a molten pool. Consequently, the efficiency of foaming and devolatilization is reduced, so the feeding amount must be moderate.

Increasing the melt temperature will increase the diffusion coefficient and Henry's constant and decrease the melt viscosity, which is beneficial to the devolatilization process.

Increasing the residence time of the material in the devolatilization section and increasing the length of the devolatilization section can improve the devolatilization efficiency. For this reason, the length of the venting section and the use of multi-stage venting can be considered in the design of the screw structure.