Cascade devolatilization

The venting takes place between the first and second extruder. The system shown in Fig, 8,47 is often used for devolatilization of PVC, The devolatilization effectiveness can be improved by stranding the polymer melt as it enters the second extruder. This is shown in Fig. 8.48, 

The distance of the strand die to the second extruder is made reasonably long to improve devolatilization. The distance is limited by the fact that the strands cannot cool below the point where the intake of the second extruder is affected. 

The major advantage of the cascade devolatilizing system is that the control of the output of the first stage to the pressure generating capability of the second stage is much better than in a single extruder devolatilization system. Obviously, the cost will be higher, and the decision for one system or the other must be based on the importance of improved flexibility and controllability. 

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Figure 8.47 Cascade devolatilization with a planetary gear extruder feeding a single screw...

TSE s have been used to prepare new families of engineering materials of high performance, polymers and their blends. Polycondensation, free radical, anionic and cationic polymerizations were conducted to obtain, e.g., PA, PEST, POM, styrenic or acrylic resins. When the reaction is conducted in a low molecular weight liquid (e.g., solution or emulsion polymerization), usually devolatilization and compounding are carried out in a cascade second extruder. Functionalization and chemical modifications have been performed in TSE on virtually all polymers. 

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