Multi-vent devolatilization

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. 

A more conventional three-stage extruder screw is shown in Fig. 8.46. 

This system has two vent ports and is used in applications where a single vent port cannot remove a sufficient amount of volatiles. It is used, for instance, in ABS extrusion as described by Brozenick and Kruder [18] and with acrylic, polycarbonate, polypropylene, etc., as described by Nichols, Kruder, and Ridenour [19]. This system can remove moisture levels as high as 5 to 7%. 

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