Rearward devolatilization

Rearward devolatilization is used on melt fed extruders. In rearward devolatilization, the volatiles are extracted upstream of the feed opening of the extruder. This is shown schematically in Fig. 8.44. 

This machine is used in meit fed extrusion. The vent port is generaiiy iocated at ieast 1 D from the feed opening to avoid poiymer meit getting to the vent port. To improve the devoiatiiization capabiiity, the meit is often forced into the extruder through numerous smaii hoies exampies of this feature are shown in Figs. 8.45 and 8.48. 

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This system incorporates rearward venting, stranding of the meit at the iniet to increase surface area, variabie gap before the section vent port by axiai screw adjustment, water injection, and bypass venting at the finai vent port. Such a system can reduce the monomer ievei from 15% down to as low as 0.1% in one operation. Such devolatilization performance is quite comparable to that of twin screw devolatilization systems. 

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