ABSTRACT
The falling-strand devolatilizer (FSD) operates via vapor flashing from a polymer melt at a temperature such that the pressure maintained in the devolatilizer is below the saturation pressure of the volatiles in the melt. If FSD chamber pressure is not changed when additives are used, the partial pressure of the higher boiling volatile vapor will be lowered by the presence of the inert vapor. This will lower the equilibrium concentration of the volatile in the melt and thereby increase the devolatilization driving force. For many applications, including polystyrene and rubber-modified polystyrene, carbon steel has frequently been a satisfactory FSD material. With some polymers, stainless steel and sometimes aluminum have been preferred to prevent black specks, product discoloration, or other corrosion-related problems. The importance of preheater design and operation to improved FSD performance cannot be overstated. Indeed, patents related to the FSD have to a considerable extent focused on the preheater.
