Bubble growth controlled devolatilization in twin‐screw extruders

Abstract

AbstractAn experimental study of polymer soluticn devolatilization in a counterrotating twin‐screw extruder has been undertaken. In an effort to ultimately predict mass transfer rates in such a process, this work analyzes the experimental results to determine the controlling mechanisms in the separation of volatile components from the polymer. The devolatilization process at hand encompasses the heavily foaming and nonfoaming regimes. Historically, the literature has centered primarily around the highly concentrated, bubble‐free diffusion‐controlled devolatilization regime. The analysis presented in this paper centers on the performance of the heavily foaming stages of the process. Recent and previously reported (1) data on the polystyrene/ethylbenzene (PS/EB) system, as well as newly collected data on the poly(methyl methacrylate)/methyl methacrylate (PMMA/MMA) system, are analyzed. In the foaming stages of the process, two regimes have been found. These regimes are differentiated by the availability of volume into which the foam can grow. Deformation and mixing effects appear to be secondary. Furthermore, temperature changes across the range of realistic operating conditions appear to affect mainly the thermodynamic driving force. It is only at extremely high temperatures that these effects are truly controlling.