PET
Film Extrusion with Degassing
Walter Michaeli, Torsten
Schmitz
Pontstraße 49, 52062
Abstract
At present, when polyethylene terephthalate (PET) is processed on a single screw extruder, the raw material has to be predried, because hydrolytic degradation will otherwise occur in the extruder if water absorbed during storage is still present. But predrying involves not only high investment and energy costs, it also restricts flexibility in product changeovers because of the long residence times that are needed, and it also affects process reliability due to the additional upstream processing step. For this reason, research is currently being carried out in a pilot plant into the venting technology on a single screw extruder. The aim is to get by without predrying altogether through the use of a vented hopper system in combination with a melt-degassing unit. With the aid of the intrinsic viscosity of the specimens and the pressure losses measured during the process, it is shown that such a solution is basically possible with the existing extrusion line.